Functionalized asphaltene nanoparticles, methods for their preparation and their use

Abstract

Embodiments of the present invention are directed to a method of synthesizing a nanoparticle, e.g., asphaltene quantum dots ("AQD") and / or asphaltene carbon dots ("ACD"), the method comprising: contacting a source of asphaltene with an organic solvent to form an asphaltene and organic solvent mixture; removing; contacting the asphaltene and organic solvent mixture with an acid to form an acidic mixture; heating the acidic mixture to form an unpurified AQD and / or ACD; removing the acid; and adjusting the pH to form the AQD and / or ACD.

Description

COMPOSITION FOR AND METHOD OF MAKING A NANOPARTICLECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to and the benefit of the filing of U.S. Provisional Patent Application No. 63 / 472,995, entitled "COMPOSITION FOR AND METHOD OF MAKING RATIOMETRIC SENSING NANOPARTICLE", filed on June 14, 2023, and the specification thereof is incorporated herein by reference.BACKGROUND OF THE INVENTIONField of the Invention (Technical Field):

[0002] The present invention relates to a composition for and method of making an asphaltene-derived nanoparticle.Background:

[0003] Asphaltenes are present in crude oil, coal extracts, bitumen, refining bottoms, oil shale extracts, shale oils, and numerous naturally occurring asphaltites, asphalts, asphaltoids, and oilsands deposits in Canada, Venezuela, Iran, and Saudi Arabia. Precipitation and subsequent deposition of petroleum asphaltenes in the pipelines significantly reduce the productivity of oilfields. In Canada, for instance, oil production from oilsands has garnered increasing environmental concerns at various stages of mining, extraction of the oilsands, transportation of oilsands products, and conversion of asphaltenes in the oilsands to tar pitch waste. Converting asphaltenes to tar pitch waste is expensive and large stockpiles of tar pitches exist today in Alberta Canada with attendant environmental hazards. It is therefore important to develop technologies that utilize asphaltenes as feedstock to generate high-value materials for practical applications. However, progress is hindered by the structural complexity of asphaltenes. While carbon fibers have been investigated extensively as potential value-added products, quantum dots have not. The structural comparability of asphaltenes with graphene could be leveraged todesign a facile synthesis route to generate asphaltenes-derived quantum dots (“AQD”) and provide an easy tailoring of the applications of AQD.

[0004] Quantum dots are semiconductor nanoparticles around the size of 15 nanometers (“nm”) and below, with inherent electronic quantum confinement leading to fascinating photoluminescence. These and other interesting properties of quantum dots including tunable size, bandgap, light emission, low cytoxicity, and easy surface modification are responsible for their suitability in a wide range of applications. Specifically, both inorganic and organic quantum dots have been applied in metal-ion sensing, cancer phototherapy, optical bioimaging, pharmaceuticals, drug delivery, electronics, and energy conversion. Available methods for generating AQD and nitrogen-doped AQD include microwave-assisted and acid-based chemical oxidation of asphaltenes. However, these methods operate at high synthesis temperatures and generate unwanted by-products that necessitate post-synthesis filtration, resulting in low mass yield of recovered AQD and poor dispersibility in water. A strategy to generate super hydrophilic AQD from asphaltenes at improved mass yield and low synthesis temperature is needed to improve their market readiness and enable utilization of AQD in new applications, such as ratiometric analyte sensing and biomedicine.

[0005] Ratiometric sensing involves quantification of analytes by leveraging complementary information from fluorescence signal and light scattering responses to surmount analyte-independent interferences such as environmental change, same background signal, and measurement instrument fluctuations. Light scattering can coexist with fluorescence signal when the Stokes shift is small, and this scattered light signal detected at double the excitation wavelength is the second-order scattering (“SOS”). Ratiometric sensors have been developed and are applied widely in chemical and biological sciences. Most of such sensors are organic dyes, carbon dots, inorganic-based quantum dots, graphene quantum dots, and graphene oxide quantum dots. Whereas organic dyes exhibit photobleaching upon prolonged exposure to light that jeopardize sensitivity to analytes, carbon dots, inorganic-based quantum dots and graphene and / or graphene oxide quantum dots are usually functionalized to achieve meaningful sensitivity to analytes. There is limited information regarding unfunctionalized inorganic and graphene / graphene oxide quantum dots and other pristine nanomaterials for ratiometric sensing.

[0006] Detection of iron, vanadium, and lead is important for both water quality evaluation and maintaining adequate human body function. Iron plays an important role in heme groups, iron sulfur clusters, electron transport in respiratory chain, and enzymatic reactions. It is also a regular component of wastewater. Iron deficiency can cause anemia, and its excess can disrupt biological systems as it catalyzes reactive oxygen species production. Vanadium, an inhibitor of enzyme Na+ / K+-ATPase is essential for cell growth in trace amounts but exhibits cytotoxicity at high concentrations. It is also a key component of industrial effluents as it participates in the manufacturing of special steels, glass, paints, and pigments, and used in combination with non-ferrous metals in atomic energy production, space technology, and aircraft manufacturing. Vanadium detection could benefit strategies for its on-site extraction and recovery after industrial use. Excessive lead exposure, a common water contaminant, has been linked to kidney and brain damage, weakness, anemia, and neurological disorder in developing fetuses. Therefore, adequate detection of these metals in real water and biological fluid is important. What is needed is a low-cost and efficient bioparticle for ratiometric sensing.

[0007] Oxidative stress in the human body is balanced by two major antioxidants, ascorbic acid (“AA”) and glutathione (“GSH”), the excess or deficiency of which can cause cellular disfunction in a human body. The levels of biomarkers such as AA or GSH determine their antioxidant efficacy. Designing a facile, robust, and sensitive platform for sensing biomarkers such as AA or GSH is thus important. Available analytical techniques such as atomic absorption spectroscopy, plasmonic atomic emission spectroscopy, and anodic stripping voltammetry for the detection of metal ions and the biomarkers are expensive, time-consuming, and require laborious sample treatment. Modern methods such as electrochemical and electronic analyses suffer from complicated on-site sampling, low sensitivity, and instability. The fluorescence spectrophotometric detection method is promising as it offers easy sample handling and quick data collection, but the high cost of commercial organic dyes still presents a challenge.

[0008] Friction and wear represent key factors that account for major losses in energy consumption in various systems. Water-based lubrication has therefore emerged as an effective lubrication strategy to bolster energy consumption in such aspects including industrial machinery, automobiles, aircraft, and contact interfaces at large. However, theuncertain tribological behavior of water-based lubricants coupled with their poor viscosity necessitates the use of additives.

[0009] Lubricants are important for the operation of automobiles, aviation machinery, industrial equipment, helicopter transmissions, etc., due to their involvement in the critical functions of friction reduction, wear particles removal, efficiency enhancement, and reduction of energy loss. A large portion of non-renewable energy resources (e.g., petroleum) is devoted to overcoming friction in mechanical systems. Moreover, a substantial fraction of the fuel utilized for energy generation turns into CO2, which is one of the core greenhouse gases responsible for global warming and climate change. Waterbased lubrication has therefore gained attention in recent years due to increasing resource scarcity deterioration and environmental concerns. They are already in use as alternatives to petroleum-based lubricants in various applications such as hydraulic fluids, cooling fluids for the cutting of metals, and stern tube bearings in ship propeller shafts.

[0010] Using water as a lubricant offers advantages such as low cost, abundance, environmental friendliness, effective cooling, easy cleaning, and enhanced thermal conductivity. The major drawback is that water provides poor lubrication in steel and allied materials which are widely deployed in sliding, rolling, or contact interfaces in industrial machinery as well as natural and biological systems. This is coupled by the uncertain tribological performance of water-based lubricants, where additives are added to water to improve its performance as a lubricant. Nanomaterial-based additives such as nano-TiC>2, carbon dots, nano-PEG, and graphene-based nanomaterials, dominate the landscape of currently researched additives for improving friction and wear in water-based lubricants.

[0011] Among the various nanomaterial-based additives of nanofluids for waterbased lubrication, silica nanoparticles, graphene-based nanoparticles including graphene oxide; reduced graphene oxide; and graphene quantum dots are the most extensively investigated. The high yield strength, appreciable dispersibility in polar lubricants, high thermal conductivity, and low shear strength have been implicated as peculiar properties of graphene-based nanoparticles that account for their wide application as water-based lubricant additives. However, the high cost and difficulty in large-scale production of graphene-based nanoparticles are bottlenecks to be overcome for their commercial application as nanofluid components for water-based lubrication. It is therefore important to develop cheap, scalable, and super hydrophilic nanomaterials of high-performancefriction-reduction property to ultimately bolster energy consumption. The structural similarities of graphene and asphaltenes could be leveraged to synthesize AQD whose friction-reduction performances could be comparable to those of graphene quantum dots analogues.

[0012] Near infrared (“NIR”) irradiation-induced cancer photothermal therapy (“PTT”) has gained the interest of researchers as an efficacious therapeutic strategy. This treatment strategy takes advantage of the transparency of biological tissues in the NIR region, enabling photothermal agents to effectively convert optical energy to heat energy with minimal invasiveness. Materials such as polymer nanoparticles (“NPs”), gold (“Au”) and covellite (CuS) NPs, carbon nanomaterials, and organic dyes, have been explored as photothermal agents because of their high light absorption in the tissue transparent NIR region. Unfortunately, the inorganic-based agents have been linked to potential long-term toxicity, which arise from their low extent of degradation in the body. The most extensively used and studied inorganic photothermal agents (Au NPs) exhibit low photostability, as the integrity of their NIR absorption peaks and morphology are not retained after a long laser exposure period, due to the well-known melting effect specific to metals.

[0013] It is therefore imperative to shift research direction to organic and biocompatible therapeutic agents with appreciable photothermal conversion capabilities. In this regard, polypyrrole and the FDA-approved indocyanine green (“ICG”) are two of the numerous organic-based photothermal agents that have been continuously studied as potential alternatives to the inorganic analogues. Polypyrrole, a conducting polymer, has wide application in biomedicine and electronics due to its intriguing conductivity, NIR absorbance, biocompatibility, facile self-polymerization, cost efficacy, and stability. Clinical translation of polypyrrole-based photothermal therapeutic systems is currently hindered by the low photoconversion efficiency of conducting polymers, which necessitates utilization of NIR lasers at high power densities (1.5 Watts / cm2) to irradiate such systems, which is unsafe for body tissues. The organic dye ICG has also been applied in the clinic for both cancer PTT and fluorescence imaging. However, it still suffers from low photostability due to the well-documented photodegradation of organic dyes upon prolonged irradiation.What is needed is a photothermal particle that is biocompatible, cost-effective, and stable while maintaining a high photoconversion efficiency.BRIEF SUMMARY OF THE INVENTION

[0014] Embodiments of the present invention relate to a method for synthesizing a nanoparticle, the method comprising: contacting a source of asphaltene with an organic solvent; removing the organic solvent to form an asphaltene; contacting the asphaltene with an acid; and removing the acid. In another embodiment, the organic solvent comprises toluene. In another embodiment, the acid is a mixture of acids.

[0015] In another embodiment, the acid comprises HNO3. In another embodiment, the acid comprises H2SO4. In another embodiment, the method further comprises oxidizing the asphaltene. In another embodiment, method further comprising attaching a functional groups to the surface of the asphaltene. In another embodiment, the functional group comprises oxygen. In another embodiment, the functional group comprises nitrogen.

[0016] Embodiments of the present invention also relate to a method of killing a tumor cell, the method comprising: disposing a nanoparticle comprising asphaltene into or in proximity to a tumor cell; applying photons to the nanoparticle comprising asphaltene; heating the nanoparticle comprising asphaltene. In another embodiment, the nanoparticle comprises an asphaltene quantum dot. In another embodiment, the nanoparticle comprises an asphaltene carbon dot. In another embodiment, the photons are applied by a laser. In another embodiment, the method further comprising imaging the nanoparticle. In another embodiment, the imaging is photothermal imaging.

[0017] Embodiments of the present invention also relates to a nanoparticle composition, the composition comprising: an oxidized asphaltene; and a functional group attached to a surface of said asphaltene. In another embodiment, the functional group comprises oxygen. In another embodiment, the functional group comprises nitrogen. In another embodiment, the functional group comprises a hydroxyl group. In another embodiment, the functional group comprises an amino group.

[0018] Further scope of applicability of the present invention will be set forth in part in the detailed description to follow, taken in conjunction with the accompanying drawings, and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention. The objects and advantages ofthe invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0019] The accompanying drawings, which are incorporated into and form a part of the specification, illustrate one or more embodiments of the present invention and, together with the description, serve to explain the principles of the invention. The drawings are only for the purpose of illustrating one or more embodiments of the invention and are not to be construed as limiting the invention. In the drawings:

[0020] Fig. 1 is a diagram showing the structure of an AQD and the photoluminescence (“PL”) intensity vs. wavelength for metal ions and antioxidants, according to an embodiment of the present invention;

[0021] Fig. 2 is a diagram showing the synthesis of AQD from asphaltene and its application as a ratiometric nanobiosensor to detect metal ions and antioxidants in various media, according to an embodiment of the present invention;

[0022] Figs. 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H, and 3I are a series of diagrams and graphs showing transmission electron microscope (“TEM”) and scanning transmission electron microscope (“STEM”) images of the AQD, AQD dispersion in water, a 3D confocal microscopic image of AQD, a Fourier transform infrared (“FT-IR”) asphaltene spectra, and an X-ray photoelectrons spectroscopy (“XPS”) survey of AQD, according to an embodiment of the present invention;

[0023] Figs. 4A, 4B, 4C, 4D, 4E, and 4F are a series of graphs showing the ultraviolet-visible (“UV-vis”) spectrum of AQD, a fluorescence spectra of AQD, excitation wavelengths using AQD, X-ray diffraction (“XRD”) patterns of pristine asphaltenes and AQD, a Raman spectrum of the AQD, and thermogravimetric profiles of asphaltenes and AQD, according to an embodiment of the present invention;

[0024] Figs. 5A, 5B, 5C, 5D, 5E, 5F, 5G, and 5H is a series of diagrams and graphs showing AQD dispersion in water, a fluorescence spectra of AQD dispersion inwater, a fluorescence spectra of AQD with Fe3+in water, and a fluorescence spectra of AQD with V4+in water, according to an embodiment of the present invention;

[0025] Figs. 6A, 6B, 6C and 6D are a series of diagrams and graphs showing Stern-Volmer plots for the variations of PL intensity of the AQD with Fe3+and V4+concentrations, according to an embodiment of the present invention;

[0026] Fig. 7 is a table showing a comparison of probes for sensing metal ions and antioxidants in water samples, according to an embodiment of the present invention;

[0027] Figs. 8A, 8B, 8C, 8D, 8E, 8F, 8G, 8H, and 81 are a series of diagrams and graphs showing variations of PL intensity of the AQD and corresponding Stern-Volmer plots after adding various concentrations of AA and GSH in DI water and biological fluid, according to an embodiment of the present invention;

[0028] Fig. 9 is a table showing a comparison of probes for sensing metal ions and antioxidant in biological fluids, according to an embodiment of the present invention;

[0029] Fig. 10 is a diagram showing the mechanism of ratiometric sensing of metal ions and antioxidants using the AQD, according to an embodiment of the present invention;

[0030] Figs. 11 A, 11 B, 11C, and 11 D are a series of graphs showing a schematic illustration of the tribology set up for friction reduction evaluation of the AQD nanofluid and water in steel / steel contact interface, according to an embodiment of the present invention;

[0031] Figs. 12A, 12B, and 12C are a series of diagrams and a graph showing scanning electron microscope (“SEM”) images of wear scars formed on the steel plates after friction and wear tests using water and the AQD nanofluids, according to an embodiment of the present invention;

[0032] Fig. 13 is a series of diagrams showing laser scanning confocal microscopic images of AQD nanofluid, according to an embodiment of the present invention;

[0033] Fig. 14 is a graph showing viscosity of the AQD nanofluid, according to an embodiment of the present invention;

[0034] Fig. 15 is a series of images showing NIR photothermal images of water and different concentrations of AQD, according to an embodiment of the present invention;

[0035] Fig. 16 is a graph showing temperature elevations of water and different concentrations of AQD, according to an embodiment of the present invention;

[0036] Fig. 17 is a graph showing temperature variations of AQD over ten on / off cycles of laser exposure, according to an embodiment of the present invention;

[0037] Figs. 18A, 18, and 18C are a series of graphs showing FT-IR, UV-vis, and Raman spectra of AQD synthesized from a different source of asphaltene, according to an embodiment of the present invention;

[0038] Fig. 19 is a series of diagrams and graphs of the temperature optimization of the synthesis route to AQD, according to an embodiment of the present invention;

[0039] Fig. 20 is a table showing elemental analysis of pristine asphaltene and AQD, according to an embodiment of the present invention;

[0040] Fig. 21 is a series of graphical images showing dispersibility of the AQD in common solvents, according to an embodiment of the present invention;

[0041] Fig. 22 is a graph showing the effect of pH on the fluorescence and SOS signals of the AQD, according to an embodiment of the present invention;

[0042] Figs. 23A, 23B, 23C, and 23D are a series of graphs showing fluorescence spectra of fluorescein isothiocyanate dye and AQD, and the UV-vis spectra of fluorescein isothiocyanate dye and AQD, according to an embodiment of the present invention;

[0043] Figs. 24A, 24B, and 24C are a series of graphs showing PL intensities of the AQD dispersion in water at different pH levels, according to an embodiment of the present invention;

[0044] Fig. 25 is a graph showing PL intensity of the AQD at excitation and emission slit widths of 10 and 20 nm, respectively, according to an embodiment of the present invention;

[0045] Figs. 26A, 26B, and 26C are a series of graphical images and graphs showing fluorescence spectra and Stern-Volmer plots of the AQD in water with Pb2+and Bi3+, according to an embodiment of the present invention;

[0046] Fig. 27 is a table showing elemental compositions of river and produced water, according to an embodiment of the present invention;

[0047] Fig. 28 is a graph showing Stern-Volmer plots for the SOS signal variations of the AQD in water with Fe3+, Pb2+, Bi3+, and V4+, according to an embodiment of the present invention;

[0048] Fig. 29 is a table showing a comparison of probes for sensing Pb2+and Bi3+in water, according to an embodiment of the present invention;

[0049] Figs. 30A, 30B, and 30C are a series of graphical images and graphs showing fluorescence spectra and Stern-Volmer plots of AQD in PBS with AA and GSH, according to an embodiment of the present invention;

[0050] Figs. 31 A, 31 B, 31C, 31 D, and 31 E are a series of graphical images, diagrams, and graphs showing a schematic illustration of the synthesis of hydrophobic AQD, dispersion of hydrophobic AQD in organic solvents and water, and the size distribution of the hydrophobic AQD, according to an embodiment of the present invention;

[0051] Fig. 32 is a diagram showing the synthesis of asphaltene carbon dots (“ACD”) from asphaltene, according to an embodiment of the present invention;

[0052] Figs. 33A, 33B, 33C, 33D, 33E, 33F, 33G, 33H, and 33I are a series of graphical images, diagrams, and graphs showing the physicochemical characterization of ACD, according to an embodiment of the present invention;

[0053] Figs. 34A, 34B, 34C, 34D, 34E, 34F, 34G, and 34H are a series of diagrams and graphs showing the friction-reducing performance of lubricant ACD nanofluids, according to an embodiment of the present invention;

[0054] Figs. 35A, 35B, and 35C are a series of graphical images and graphs showing scanning electron microscope (“SEM”) analysis of wear scars formed after continuous shearing, according to an embodiment of the present invention;

[0055] Figs. 36A, 36B, 36C, 36D, and 36E are a series of graphs showing steel plate surface roughness, according to an embodiment of the present invention;

[0056] Figs. 37A, 37B, 37C, 37D, and 37E are a series of graphs showing rheology of lubricant nanofluids before and after continuous shearing, according to an embodiment of the present invention;

[0057] Figs. 38A, 38B and 38C are a series of diagrams showing tribofilm formation by ACD and silica nanoparticles on a steel ball and plates, according to an embodiment of the present invention;

[0058] Fig. 39 is a diagram showing ACD synthesis from asphaltenes precursor and subsequent application in cancer photothermal imaging and therapy, according to an embodiment of the present invention;

[0059] Figs. 40A, 40B, 40C, 40D, 40E, and 40F are a series of graphical images and graphs showing physicochemical characterization of ACD, according to an embodiment of the present invention;

[0060] Figs. 41 A, 41 B, 41C, 41 D, and 41 E are a series of graphs and diagrams showing temperature variations of ACD, according to an embodiment of the present invention;

[0061] Figs. 42A, 42B, 42C, and 42D are a series of graphs and diagrams showing non-radiative transitions, light scattering, and heat generation for ACD, according to an embodiment of the present invention;

[0062] Figs. 43A, 43B, 43C, and 43D are a series of graphs and graphical images in vitro cytotoxicity of ACD, according to an embodiment of the present invention;

[0063] Fig. 44 is a series of graphical images showing laser confocal fluorescence images of 4T 1 cells co-incubated with ACD, according to an embodiment of the present invention; and

[0064] Figs. 45A, 45B, 45C, 45D, 45E, 45F, and 45G are a series of graphical images, diagrams, and graphs showing cancer photothermal imaging and therapy with ACD, according to an embodiment of the present invention.DETAILED DESCRIPTION OF THE INVENTION

[0065] Embodiments of the present invention are directed to a method of synthesizing a nanoparticle, e.g., asphaltene quantum dots (“AQD”) and / or asphaltene carbon dots (“ACD”), the method comprising: contacting a source of asphaltene with an organic solvent to form an asphaltene and organic solvent mixture; removing, e.g., evaporating the organic solvent to form an asphaltene; contacting the asphaltene and organic solvent mixture with an acid to form an acidic mixture; heating the acidic mixture to form an unpurified AQD and / or ACD; removing the acid; and adjusting the pH to form the AQD and / or ACD. The acid may comprise HNO3, H2SO4, or a combination thereof. The residue may be contacted with HNO3and H2SO4 in a 1 :1 volume ratio. The mixture may be heated to 80 °C. The mixture may be centrifuged to remove the acid components. The unpurified AQD and / or ACD may be dispersed in water and brought to a neutral pH base. The base may comprise NaOH. The unpurified AQD and / or ACD may be purified by dialysis or other filtration method. The AQD and / or ACD may comprise functional groups attached to the surface of the AQD and / or ACD. Contacting the asphaltene and organic solvent mixture with an acid may oxidize the asphaltene. The nanoparticle may be a ratiometric nanoparticle.

[0066] The method may also comprise synthesizing a hydrophobic AQD and / or ACD, the method comprising: contacting a source of asphaltene with an organic solvent; contacting the source of asphaltene with a caustic to form a mixture; and heating the mixture. The caustic may comprise NaOH.

[0067] Embodiments of the present invention are also directed a method for treating a cell. The method may comprise a least partially disposing a nanoparticle into, orin proximity to a cell; applying a photon to the nanoparticle; heating the nanoparticle; and killing the cell. The cell may be a tumor and / or cancerous cell. The cell may be an infected cell. The nanoparticle may comprise an asphaltene. The nanoparticle comprise an AQD and / or ACD. The photon may be applied by a laser. The wavelength of the laser may be about 808 nm. The cell may be killed by the heat emitted from the nanoparticle. The nanoparticle may be fluorescent. The method may further comprise imaging the nanoparticle. The imagine may be photoimaging.

[0068] Embodiments of the present invention are also directed to a nanoparticle composition. The nanoparticle may comprise an asphaltene. The asphaltene may be oxidized. The nanoparticle may comprise a functional group attached to the asphaltene. The functional group may comprise a nitrogen atom, oxygen atom, a lone electron pair, or a combination thereof.

[0069] The term “target” as used herein means a metal ion or an antioxidant.

[0070] The term “metal ion” as used herein means a metal atom with a valence charge.

[0071] The terms “source of asphaltene”, “sources of asphaltene” as used herein include, but are not limited to, asphaltenes powder, an asphaltene precursor, crude oil, coal extract, bitumen, refining bottoms, asphaltene, oil shale extract, shale oil, asphaltites, asphalts, asphaltoids, oilsands, or a combination thereof.

[0072] This method may allow scalable and consistent synthesis of the AQD and / or ACD from one or more sources of asphaltenes, which evades the well-known drawbacks in asphaltenes technological development arising from source-dependent asphaltenes structural variation. AQD and / or ACD may be synthesized at low temperatures and with easily tuned surface charge. The AQD and / or ACD exhibit varying degrees of dispersibility, ranging from super hydrophilic to hydrophobic. AQD and / or ACD may exhibit dual-modal fluorescence emission that offers complementary avenues to quantify their detection capability to different analytes in biological fluid and various real waters. AQD and / or ACD may be re-dispersible in an aqueous solution after drying.

[0073] Rapid and sensitive detection of important clinical biomarkers and metal ions with inexpensive nanobiosensors is of great importance for applications in health and environment sectors. Asphaltenes may provide a cost-effective precursor to engineer value-added materials for practical applications. AQD and / or ACD may be used as a ratiometric nanobiosensor. AQD and / or ACD may be used as an analyte in any sensing application, including but not limited to, metal ions and antioxidants. Optimized oxidation may be used to convert asphaltenes to quantum confined nanoparticles having high hydrophilicity. AQD and / or ACD may be at temperatures up to 80 °C, which is a lower temperature than conventional for most quantum and / or carbon dot synthesis. AQD and / or ACD may exhibit structural behaviors analogous to graphene quantum dots. AQD and / or ACD may be sensitive to Fe3+, Pb2+, Bi3+, and V4+and allow for rapid ratiometric sensing (< 3 seconds (“s”)) in deionized water, industrial wastewater, and / or river water. The limits of detections (“LOD”) of Fe3+, Pb2+, Bi3+and V4+in water may be 0.12 pM, 0.04 pM, 0.03 pM, and 0.79 pM, respectively. The intriguing dual fluorescence emission of the AQD and / or ACD may exhibit dual fluorescence emission, which may be used for ratiometric sensing of prime antioxidants including, but not limited to, ascorbic acid and glutathione, and Fe3+and Pb2+in biological fluid. AQD and / or ACD may be a cost-effective nanoplatform for instantaneous real-time ratiometric detection of metal ions (Fe3+, Pb2+, Bi3+, and V4+) and salient antioxidants such as AA and GSH, in complex systems.

[0074] AQD and / or ACD may have an appreciable mass yield and may comprise a hydrophilicity that outperforms those of most commercially available hydrophilic nanomaterials. The synthesis may comprise top-down nanomaterials synthesis steps using inorganic acids to generate the AQD and / or ACD from asphaltenes at lower temperature. The as-synthesized label-free AQD may show an additional SOS fluorescence emission peak that provides an enabling platform for efficacious rapid and sensitive ratiometric detection of various metal ions (Fe3+, Pb2+, Bi3+, and V4+) in real waters such as river and produced waters.

[0075] AQD and / or ACD may be used as a nano-based water-lubricant additive that provides friction and wear reduction in water to reduce energy consumption in industrial machinery, automobiles, aircraft, and contact interfaces. The additive may be synthesized by oxidation of asphaltenes to generate asphaltenes-derived quantum dots (average size 5 nm) at appreciable mass yield and lower temperature compared to otherAQD and / or ACD synthesis methods. Oxidation of the asphaltenes may allow AQD and / or ACD to be more hydrophilic compared to other nanomaterials and may enable dispersion of high amounts of the AQD in water without a conventional external impetus. Low concentrations of the AQD and / or ACD (0.2 wt.% - 1.0 wt.%) may be used to reduce the coefficient of friction of water with corresponding wear reduction in steel plates. AQD and / or ACD may show typical Newtonian fluid behavior, thus reducing friction in waterbased systems without the formation of extended networks.

[0076] The AQD and / or ACD and / or an asphaltene-based material may comprise photothermal properties that allow AQD and / or ACD to generate heat in response to exposure to light. The AQD and / or ACD may be resistant to degradation by repeated cycles of light exposure and may be biocompatible. The AQD and / or ACD may exhibit low cytotoxicity relative to other materials used in cancer PPT.

[0077] Turning now to the figures, Fig. 1 shows the structure of an AQD and the photoluminescence intensity vs. wavelength for metal ions and antioxidants. Asphaltenes powder pre-treatment protocol is deployed as a blueprint to improve susceptibility of the asphaltenes to acid-mediated oxidation. The asphaltenes are dispersed in toluene first, followed by solvent removal to improve their susceptibility to acid oxidation. This protocol ensures oxidation of the asphaltenes which sidesteps the conventional post-synthesis filtration step which has been responsible for low mass yield of AQD and their graphene- derived analogues. Consequently, an appreciable recovery (> 57%) of super hydrophilic AQD of uniform size distribution is achieved. This method may avoid solvent evaporation by allowing an arrest of the product at a fixed time during synthesis. This may allow for recovery by conventional centrifugation at low speed (3000 rpm), which may be a more amenable approach to large-scale synthesis. This method may also reduce reagent demand in the acid ratio required for synthesis and base compound for neutralizing the acids in bulk mixture, without prejudice to the structural and thermal integrity of the product. This method of AQD synthesis does not rely on a specific asphaltenes source and / or a specific asphaltenes structural variation.

[0078] Fig. 2 shows the synthesis of AQD from asphaltene and its application as a ratiometric nanobiosensor to detect metal ions and antioxidants in various media.

[0079] Figs. 3A, 3B, 3C, 3D, 3E, 3F, 3G, 3H, and 31 shows transmission electron microscope (“TEM”) and scanning transmission electron microscope (“STEM”) images of the AQD, AQD dispersion in water, a 3D confocal microscopic image of AQD, a Fourier transform infrared (“FT-IR”) asphaltene spectra, and an X-ray photoelectrons spectroscopy (“XPS”) survey of AQD, respectively. Fig. 3A shows TEM and Fig. 3B shows STEM images of the AQD. Fig. 3C shows the hydrodynamic size of the AQD dispersion in water as determined by dynamic light scattering (“DLS”). Inset shows the zeta potential of the AQD dispersion in water. Fig. 3D shows confocal microscopic image of 275 mg ml_'1AQD dispersion in water. Fig. 3E shows FT-IR spectra of pristine asphaltene and the AQD. Fig. 3F shows an XPS full survey of the AQD. Figs. 3G, 3H, and 3I show XPS scans of AQD show O1s, C1s, and N1s, respectively. The morphology of the AQD is evaluated by TEM as shown. The particles are oval with uniform size distribution and no obvious aggregation. The particles are stable on scanning transmission electron microscope (“STEM”) beam and possess nanographitic structure with lattice distance of 0.23 nm. This lattice distance is similar to the graphitic in-plane lattice spacing of 0.17 nm - 0.25 nm. Size uniformity of the AQD is also confirmed by the DLS. The hydrodynamic size of the AQD as measured by DLS is 8 ± 0.31 nm which is typical of quantum dots synthesized from either graphene or asphaltene compounds. In addition, the average size measured by DLS, and the observed sharp peak indicates a uniform size distribution which corresponds to the size and uniform distribution of the AQD in the TEM images. The zeta potential of the AQD shows a negative surface charge of -38.1 ± 0.27 mV, which may be due to the extensive oxidation of the asphaltenes resulting in the introduction of various oxygen-comprising functional groups (e.g., hydroxyl, epoxy, carbonyl) to the AQD. The oxygen-comprising functional groups may be responsible for the high negative zeta potential of the AQD and may contribute to the AQD hydrophilicity. This AQD hydrophilicity is shown with a uniform field of view of fluorescence (absence of aggregates) in 3D confocal image of the AQD dispersion at concentration of 275 mg mL'1.

[0080] XPS full survey of the AQD, shows oxidation with an oxygen content of 47.2%. Carbon and nitrogen content are 50.6% and 2.24%, respectively. Such a high atomic percentage for oxygen in comparison to carbon may be attributed to the oxidation of the asphaltenes aided by the effective solvent-exchange pretreatment strategy that adequately exposed the asphaltene molecules to acid-oxidation. The amount of nitrogen (2.2%) in the AQD is typical of materials without nitrogen-doping. Individual scans forcarbon, oxygen, and nitrogen show the specific functional groups in the AQD. From the oxygen scan, three oxygen-comprising functional groups are present in the AQD: (i) hydroxyl group C-OH (atomic percentage 77%) at 528.6 eV, (ii) carboxyl group C(O)-OH (17%) at 529.9 eV, and (iii) ether functional group C-O-C (6%) at 533.3 eV. These values indicate that abundance of hydroxyl groups on the AQD surfaces in synergy with the carboxylic acid and ether groups generate the-superhydrophilicity of the AQD. It is important to note that the oxygen-comprising functional groups could serve as favorable sites for surface modification of the AQD for tailored applications. Hydroxyl and carboxyl anions on the surfaces of the AQD may be used as ligand sites for potential complexation with metal ions and reduction sites for antioxidants to afford complexation- and reduction- induced ratiometric sensing, respectively.

[0081] The carbon scan reveals five types of carbon viz: (i) sp2carbon C=C (atomic percentage 37%) at 281.9 eV for the inherent aromatic alkenes which are the bedrock of the polycyclic aromatic carbon of AQD; (ii) sp3carbon C-C / C-H (32%) at 282.4 eV for the alkane moieties; (iii) nitrogen-bonded carbon C-N (12%) at 283.8 eV for the nitro, pyridinic and pyrrolic nitrogen groups; (iv) oxygen-bonded carbon C-0 (15%) at 285.4 eV for hydroxyl and ether groups; (v) and carbonyl carbon C=O (4%) at 286.2 eV for the carboxyl functional group. Even though the amount of the sp2carbons (C=C; 37%) dominates those of other carbon types, a combination of the oxygen- and nitrogen-comprising carbons amounts to 31%, showing that more than half of the entire polycyclic aromatic carbon of AQD are coupled with oxygen and nitrogen groups after the synthesis process. In addition, the total amount of oxygen-comprising carbons is more than 1.5-fold higher than nitrogencomprising carbons. The nitrogen scan of the AQD shows three kinds of nitrogencomprising functional groups including nitro group, pyrrolic and pyridinic nitrogen are present at 403.7, 397.2, and 396.1 eV with atomic percentages of 40%, 55%, and 5%, respectively. The presence of the nitro group up to 40% of the entire nitrogen-comprising functional groups points to the effective oxidation of the asphaltenes by the nitric acid component of the mixed acids used for synthesizing the AQD. The nitro group, pyrrolic (secondary amine) and pyridinic (tertiary amine) nitrogen may be electron rich nitrogenbased groups that may provide additional sites for an array of reactions to modify the surfaces of the AQD.

[0082] The basic functional groups in the AQD were determined by FT-IR spectroscopy. The acid-mediated oxidation of the asphaltenes may introduce various oxygen- and nitrogen-comprising functional groups (e.g., hydroxyl, epoxy, carbonyl, nitro) to the synthesized AQD. The FT-IR spectrum of the AQD contains broad band for the hydroxyl and amino groups in the AQD is seen at 3309 cm-1confirming that the oxidation process used in this method introduced hydroxyl groups to the AQD. The amino groups may be inherited from the intrinsic pyrrolic and pyridinic nitrogen of asphaltenes. Corresponding -OH bending vibration occurs at 1372 cm-1. The two bands at 1580 and 1356 cm-1correspond to N-0 for nitro groups introduced in the AQD by the oxidation process. The band at 1580 cm'1overlaps with the C=C stretching vibration of the aromatic rings in the AQD, which occurs at 1580 cm'1in asphaltenes. The strong band at 1097 cm'1is ascribed to C-O-C stretching vibration of ether groups, which is quite weak in asphaltenes. The doublet at 2914 and 2853 cm'1in the asphaltenes spectrum represent the aromatic C-H stretching vibrations with analogous C-H rocking vibrations in the triplet between 855 and 745 cm'1. The C-H rocking vibrations are also inherited by the AQD as a bump at 774 cm'1. The alkanes in asphaltenes may be used as oxidation sites for conversion to oxygen-comprising functional groups. Prominent C-N stretching vibrations in the asphaltenes spectrum at 2106 and 1904 cm'1are also present in exactly the same intensity in the AQD spectrum at 2108 and 1916 cm'1, respectively. In addition, C=O stretching vibration of the carbonyl groups in AQD presents at 1711 cm'1.

[0083] Fig. 4A shows UV-vis spectrum of the AQD. Figs. 4B and 4C show fluorescence spectra at different concentrations of AQD and excitation wavelengths using 0.02 mg*mL'1AQD in water, respectively. Fig. 4D shows XRD patterns of pristine asphaltenes and AQD. Fig. 4E shows the Raman spectrum of the AQD. Fig. 4F shows thermogravimetric analysis profiles of pristine asphaltenes and the AQD.

[0084] The optical properties of the AQD are investigated by UV-vis and fluorescence spectroscopies. A broad UV-vis absorption range between 280 and 800 nm may be ascribed to complex band structure and random energy levels in the AQD. The most prominent peak at 305 nm could be attributed to n-n* transition due to C-0 conjugate carbon domains (e.g., carboxyl, hydroxyl) that are introduced in the AQD by the oxidation process. The peak at 286 nm corresponds to TT-TT* transition of the inherent sp2carbons in the asphaltene precursor that forms the bedrock of the AQD. Upon exposure to a UV lamp operated at 365 nm in the dark, greenish yellow luminescence is observed.

[0085] The photoluminescence (PL) spectra of various concentrations of the AQD show maximum emission at 507 nm with 0.02 mg mL'1AQD dispersion in water. The wavelength of maximum PL emission redshifts as concentration increases. The redshift may be due to re-absorption of emitted light by individual particles in very close proximity at higher concentration, with accompanying emission of light at longer wavelength. Intensity of the emitted light increases as concentration increases up to 0.02 mg mL'1where a threshold is attained. AQD synthesized by this method may possess a broad full width at half maximum (“FWHM”) of -200 nm which may be used for various sensing applications and tumor biomedical imaging. Additionally, the AQD exhibit SOS signal at 644 nm whose intensity decreases as the concentration of AQD dispersion increases. At 1.00 mg mL'1, the SOS signal in the AQD is no longer visible. The presence of SOS signal in the AQD may complement the fluorescence signal at 507 nm in ratiometric sensing of analytes.

[0086] Fig. 5A shows digital images of AQD dispersion in water before and after adding various metal ions and observed under a UV lamp operated at 365 nm in the dark. Fig. 5B shows fluorescence spectra of the AQD dispersion in deionized (“DI”) water (pH 7) after adding different metal ions. Fig. 5C, 5D, and 5E show fluorescence spectra of the AQD with various Fe3+concentrations in DI water, river water, and produced water, respectively. Figs. 5F, 5G, and 5H show fluorescence spectra of the AQD with various V4+concentrations in DI water, river water, and produced water, respectively. Insets show digital images of the AQD dispersion observed under UV lamp (365 nm) in the dark.

[0087] Li+, Ni+, Fe3+, Cd+, Zn2+, Co2+, Cu+, Ca2+, Mg+, Pb2+, Mn2+, K+, Bi3+, Al3+, Ba+, and Na+are added to AQD dispersion in DI water at pH 7 and PL changes in few seconds (< 3 s) post-addition of metal ions under UV lamp in the dark are observed.

[0088] The variations in fluorescence and SOS signals of the AQD at pH 7 are shown. PL measurements are taken at excitation and emission slit widths of 5 nm each to enable visualization of the SOS peaks.

[0089] The linearity and sensitivity of the AQD in ratiometric sensing of Fe3+, Pb2+, and Bi3+is shown. The variations of both fluorescence and SOS signals of the AQD dispersion in DI water after adding various concentrations of Fe3+are indicated in Fig. 5. The fluorescence intensity (J max = 507 nm) decreases linearly, and SOS signal (J max = 644 nm) generally increases as Fe3+concentration increases.

[0090] AQD ratiometrically detected Fe3+and V4+in the real water samples (DI water and Bow River). Both real water samples are not diluted prior to the metal-ion detection tests. The fluorescence signal originally at 507 nm in DI water is blue shifted to 460 and 403 nm in river water and produced water, respectively. However, the SOS signal at 644 nm in DI water maintains the same position in both river water and produced water. Whereas fluorescence signal intensity decreases in river water and produced water as metal-ion concentration increases, SOS signal intensity increases in river water but decreases in produced water. The decrease in fluorescence signal could be attributed to metal ion-induced PL quenching by possible binding of the metal-ions to the surfaces of the AQD.

[0091] PL spectra of 0.02 mg mL'1AQD dispersion in water excited at different wavelengths (280 nm - 540 nm) are shown. The AQD generally exhibit an excitationdependent PL emission with maximum emission intensity recorded at excitation wavelength of 320 nm. AQD synthesized according to this method show red shifting of the PL emission is generally consistent on moving from 280 to 540 nm excitation wavelengths. The PL intensity of the AQD synthesized according to this method steadily decreases at excitation wavelengths between 320 and 400 nm, followed by a sharp increase at 420 nm, and a near-steady intensity decrease thereafter up to 540 nm. AQD may maintain a considerable broad-range fluorescence emission in the green-yellow region which may be responsible for the observed greenish yellow luminescence of the AQD dispersion under UV lamp.

[0092] The Raman spectrum of the AQD shows two bands for defect (“D”) and graphene-like (“G”) that are commonly used to probe graphite and graphene materials. The G and D bands at 1583 cm-1and 1356 cm-1, respectively, are not perfect doublets but broadened bands, suggesting the AQD are majorly like nanocrystalline graphite. The high intensity of the G band nearing the reference value of 1600 cm'1and the high defect ratio ( / D / / G = 1 14) suggest the presence of appreciable sp3carbons in the AQD structure. The significantly higher intensity of the D band to the G band confirms the earlier indication that the AQD are defect-rich nanographitic materials. Moreover, the presence of these defect states evidenced by the introduced oxygen- and nitrogen-comprising functional groups on the AQD via the synthesis process, could be highly beneficial for surface modification.

[0093] Thermal stability of the AQD in comparison with their asphaltenes precursor is assessed by thermogravimetry. Marked degradation of asphaltenes at 390 °C may be due to destruction of intermolecular association and weak chemical bonds between the polycyclic aromatic hydrocarbon sheets in asphaltenes structure. Side aliphatic chains and heteroatom components are also lost at this stage, in line with earlier reports on thermal stability profile of pristine asphaltenes. Conversely, the profile for AQD does not exhibit multiple weight drops as they rather exhibit a near-steady degradation up to 800 °C. This indicates a gradual loss of weak chemical bonds and intermolecular associations inherited from the parent asphaltenes, alongside gradual degradation of acquired oxygen- and nitrogen-comprising functional groups in the AQD from the oxidation process. The slight weight loss in the AQD at 200 °C may be attributed to loss of hydroxyl and ether functional groups, similar to that of graphene oxide. Carboxylic acid groups (highly oxidative) are less prone to temperature degradation than hydroxyl and ether groups and have been reported to positively impact the thermal stability of graphene oxide. The carboxyl groups in the AQD are degraded at 450 °C, while the nitro groups are lost during soothing above 750 °C. The carboxylic acid and nitro groups in the AQD, detected by both FT-IR and XPS analyses, may allow the AQD with the near-steady degradation profile. Moreover, results from elemental analysis of asphaltenes and AQD have already shown removal of substantial amounts of the heteroatoms in AQD which ultimately contributes to the observed near-steady degradation of AQD. It is interesting that 55.7% of the initial weight of the AQD remains after heat exposure up to 600 °C, contrary to the total weight loss of graphene oxide at the same temperature. Synthesized AQD may maintain thermal stability and may be used in material platforms and / or systems that are applied at appreciably high temperatures.

[0094] Crystal property and defects in the AQD are evaluated by XRD spectroscopy. The broad peak centered at 26.1°C and the medium peak at 41.9°C represent the (002) and (100) diffraction planes in the nanographitic structure of the AQD. The diffraction planes in the AQD are believed to be inherited from the parent asphaltenes whose XRD pattern show a less broad peak centered at 25.8°C and weak peak at 43.7°C for the (002) and (100) diffraction planes, respectively. The (002) diffraction planes in asphaltenes and AQD could be compared to the peak at 26° in the XRD pattern for neat graphite, pointing to structural similarity of the trio. This suggests a few layers of graphene sheets are stacked in the nanographitic structure of the AQD by a 0.23 nm interlayerspacing. Also, broadening of the peak in the AQD could be ascribed to (i) expansion of the interlayer distance via chemical defects introduced by oxygen- and nitrogen-comprising functional groups introduced on the AQD from the oxidation synthesis route, and (ii) the nanographitic sheets size in the AQD that can decrease the strength of interlayer attraction. The edge carbons of the nanographitic sheets may contribute more than inner sheets carbons to the defects in the AQD caused by the oxidation synthesis process. The position of the edge carbons may predispose them to reaction with the oxidizing agents during synthesis. The description of the AQD as defect-rich nanographite material by XRD may be pinpointed by Raman spectroscopy.

[0095] Figs. 6A, 6B, and 6C show Stern-Volmer plots for the variations of PL intensity of the AQD with Fe3+and V4+concentrations in DI water, river water, and produced water, respectively. Fig. 6D shows the effect of AQD concentration on Fe3+- induced PL quenching is shown by diagram.

[0096] The linearity of the signal intensity variation with metal-ion concentration could be modelled with the Stern-Volmer plot using either the fluorescence or SOS signal variations separately, to determine the limits of detection (“LOD”) for each metal ion. In the Stern-Volmer plots, / 0and I represent the fluorescence or SOS intensity of AQD without metal ions, and intensity at any given metal-ion concentration, respectively. Linear relationships between intensity and metal-ion concentration from both fluorescence and SOS signal variations in the Stern-Volmer plot are relatively same, but R2values from the fluorescence variations are generally higher than those of SOS signal variations. Fluorescence intensity variation is consequently selected for modelling with the Stern- Volmer plot in DI water, river water (shown as Bow River) and produced water. The LODs for Fe3+, Pb2+, Bi3+and V4+are 0.12 pM, 0.04 pM, 0.03 pM, and 0.79 pM, respectively, in DI water. The LODs may be compared to the drinking water standards of 5.37 pM, 0.07 pM, and 4.52 pM for Fe3+, Pb2+, and V4+according to the US Environmental Protection Agency, and the World Health Organization standard of 0.05 pM for Bi3+. LODs of 1.13 pM and 5.51 pM in river water, and 5.19 pM and 12.82 pM in produced water are determined for Fe3+and V4+, respectively. AQD may be less sensitive to V4+than Fe3+in the various water samples. The difference in sensitivity is most pronounced in river water, which could be attributed to two factors: (i) According to the ICP data for Bow River water, chloride ions are the most prominent and may interact with the V4+to possibly form vanadium tetrachloride (VCI4); and (ii) vanadium-chlorine (V-CI) bond strength is higher than that ofiron-chlorine (Fe-CI), indicating that some of the spiked V4+ions during the detection studies are more tightly held by the chloride ions than in the case for Fe3+detection. These two factors may account for the less availability of V4+than Fe3+that could interact with the AQD in river water to quench luminescence. AQD detected V4+in the presence of ionic interference-mediated low sensitivity. AQD may exhibit appreciable sensitivity towards Fe3+in comparison to Pb2+, Bi3+and V4+and may be used as a ratiometric nanoprobe for Fe3+in various media.

[0097] The effect of AQD concentration on ratiometric sensing using Fe3+as a representative metal is shown. AQD may be sensitive to low concentrations of metal ions, which is a highly valued quality for ratiometric sensors.

[0098] Fig. 7 shows comparison of various probes for sensing metal ions and antioxidants in various water samples. The LODs for Fe3+and V4+are 0.12 pM and 0.79 pM in DI water (shown in Fig. 7 as water), respectively. The LODs for Fe3+and V4+are 1.13 pM and 5.51 pM in river water, respectively. The LODs for AA and GSH are 1.13 pM and 5.51 pM in DI water (shown in Fig. 7 as water), respectively.

[0099] The LODs of the metal ions (Fe3+and V4+) and antioxidants in various water samples as achieved with AQD are compared to the LODs of other probes in Table 1 . Bismuth is used as a precursor or dopant in synthesizing quantum and carbon dots. LOD of V4+is therefore compared to those of V5+that are available in literature for carbon and quantum dots. Table 1 shows that the LODs for the metal ions in DI water recorded are generally lower compared to other quantum and / or carbon dots without element-doping.

[0100] Figs. 8A, 8B, 8C, 8D, 8E, 8F, 8G, and 8H shows variations of PL intensity of the AQD and corresponding Stern-Volmer plots after adding various concentrations of AA and GSH in DI water (Figs. 8A, 8B, and 8C), and biological fluid, e.g., human urine (Figs. 8D, 8E, and 8E). Fig. 8G and 8H show the variations of PL intensity of the AQD in biological fluid (human urine) with concentrations of Fe3+, Pb2+, respectively. Fig. 8I shows the corresponding Stern-Volmer plot.

[0101] After rapid ( < 3 s) PL quenching in the UV lamp, quantification of the ratiometric sensing shows that both AA and GSH induce a decrease in fluorescence intensity and increase in SOS signals of the AQD in DI water. In DI water, color change ofthe AQD from greenish yellow to green and blue occurs under UV lamp as the concentration of AA increases. Fluorescence spectroscopy also reveals blue shifting of the AQD emission wavelength to 447 nm. The color changes indicate a reaction between AQD and AA, that may be leveraged to tune the surface properties and luminescence of the AQD. AA is an antioxidant and may induce a reduction reaction with the AQD.

[0102] Using the Stern-Volmer plot, LODs of 0.81 pM and 9.26 pM for AA and GSH, respectively, are obtained in DI water. There is an appreciable interaction of AA and GSH with the AQD. Consequently, AQD dispersion in human urine is shown and is spiked with various concentrations of AA and GSH to ratiometrically detect both biomarkers by monitoring the variations in the fluorescence and SOS signals of the AQD. There is blue shifting of the original AQD emission wavelength from 507 nm to 450 nm which could be attributed to inherent variable organic compounds in the urine sample. As the concentration of GSH increases, fluorescence signal of the AQD decreases with attendant increase in SOS signal intensity. Contrary to this trend which is also observed with metal ions in various water samples, increasing the concentration of AA decreases both the fluorescence and SOS signals of the AQD. Such a rare sensing pattern for AA which is contrary to the general reports in the literature where AA has always been used to recover or enhance fluorescence of fluorophores, has also been observed by few researchers. Deploying the Stern-Volmer plot once more to model the fluorescence variations of the AQD with concentrations of AA and GSH in human urine, LODs of 3.63 x 10'3mM and 0.03 mM are obtained for AA and GSH, respectively. The LODs are far below the human body allowable levels of 0.28 mM and 10 mM for AA and GSH, respectively. The low sensitivity of the AQD to GSH in comparison with AA could be attributed to the competition of GSH with other aminothiols of similar structure such as cysteine, homocysteine, and cysteinyl glycine that are inherent in human urine.

[0103] AQD may also be used as a nanoprobe to ratiometrically sense metal ions in such a complex medium. This is shown by the human urine dispersion of the AQD spiked with different concentrations of Fe3+and Pb2+. Fe3+is a biomarker that plays an important role in the human body to catalyze reactive oxygen species production, electron transport in respiratory chain, and participates in enzymatic reactions. Using AQD to detect Pb2+may be beneficial to quantitatively determine Pb levels in the human body for cases of Pb poisoning. PL quenching of the AQD in human urine is also observed in a UVlamp ( < 3 s) post-addition of the metal ions, indicating that AQD are not only sensitive to metal ions in water, but may also offer rapid sensing of metal ions in biological fluid. This is a highly valued quality of nanobiosensors for clinical application. As is the case in DI water, river water (shown as Bow River), and produced water, fluorescence intensity decreases and SOS signal increases as Fe3+and Pb2+concentrations increase in the urine samples. Using the Stern-Volmer plot for modelling, the fluorescence signal variations with Fe3+and Pb2+concentrations give LODs of 2.06 pM and 3.87 pM, respectively, in human urine. The LODs may be compared to the normal values of 62.4 pM and 1.5 pM for Fe3+, and Pb2+in healthy human urine. AQD may detect divalent Pb2+even though with low sensitivity compared to the trivalent Fe3+. This may be attributed to the superiority of trivalent ions to the divalent analogues in effective interaction with the AQD that leads to PL quenching.

[0104] Fig. 9 shows a comparison of various probes for sensing metal ions and antioxidants in biological fluids. The LODs for Fe3+and Pb2+in human urine are 2.06 pM and 3.87 pM, respectively. The LODs for AA and GSH in human urine are 3.63 pM and 30.00 pM, respectively. The LODs for AA and GSH in PBS are 6.18 pM and 3.63 pM, respectively.

[0105] The LODs achieved for the sensing of Fe3+, Pb2+and the antioxidants (AA and GSH) are compared to those of other reports in Table 2. Such low LODs are obtained with pristine AQD, especially for AA and Fe3+, are rarely obtained for un-modified carbon or quantum dots, indicating that AQD may be highly sensitive to metal ions and antioxidants in biological fluid.

[0106] Fig. 10 shows the mechanism of ratiometric sensing of metal ions Fe3+, Pb2+, Bi3+and V4+50, and antioxidants AA and GSH 52 using AQD. The scale bars are equal to 20 pm. Whereas the metal ions induce complexation, the antioxidants reduce the AQD to cause PL intensity to decrease in both cases.

[0107] Complexation occurs in the ground state, typical of static fluorogenic PL quenching mechanism, resulting in aggregation of the AQD. Upon aggregation, AQD become relatively compact particles where any emitted light from excited electrons in one particle of the AQD is re-absorbed by neighboring AQD particles, ultimately resulting in net- zero emission of light. Non-radiative electron-hole recombination also occurs in the AQD-metal ion aggregated state, which may be attributable to ligand-metal charge transfer in chromogenic sensing mechanism, where excited electrons from the AQD transfer to the partially filled d-orbitals of Fe3+(4s23d5) and V4+(4s23d3), or p-orbitals of Pb2+(5d106p2) and Bi3+(6s26p3). Without being limited by a particular theory, the foregoing mechanism propositions may account for the capability of the AQD to effectively detect Fe3+amidst high interference from different species in real water samples such as river water.

[0108] Biomarkers (AA and GSH) that possess reducing-agent properties, may induce reduction of the oxygen- and nitrogen-comprising functional groups on the surfaces of the AQD, which follows reductive photoinduced electron transfer PL quenching mechanism. Electron transfer may occur from the highest occupied molecular orbitals of AA and GSH (acting as electron donors) to the lowest unoccupied molecular orbitals of the AQD, leading to decrease in PL. This assertion may be supported by the reduction of hydroxyl and carbonyl groups in the AQD by the antioxidants to their corresponding alkanes and hydroxyl groups, respectively, while the nitro and pyrrolic groups in AQD may be reduced to primary amines. Additionally, the etheric and pyridinic groups in AQD may be reduced by the antioxidants to alkenes and secondary amines, respectively. Reduction process may change the surface properties of the AQD in solution, leading to a decrease in luminescence. The antioxidants (AA and GSH) may act as electron donors to reduce the AQD in the presence of UV irradiation in a typical reductive photoinduced electron transfer mechanism for fluorogenic PL quenching. AQD synthesized according to this method may be used as a ratiometric nanosensor to detect metal ions in real water and / or a biological fluid, alongside effective biomarker detection in a biological fluid.

[0109] Fig. 11A shows a diagram of the tribology set up comprising steel ball 54 and steel plates 56 and 58 for friction reduction evaluation of the AQD nanofluid and water in steel / steel contact interface. Fig. 11 B shows the Stribeck curve of the friction reduction performance of water and the AQD nanofluids. Fig. 11C shows friction reduction performance of water and the AQD nanofluids upon constant shearing for 1 hour at the mixed region from the Stribeck curve. Fig. 11 D shows a comparison of the friction reduction performance of the AQD nanofluids and commercial silica nanoparticles at similar concentrations (0.2 wt.%, 1.0 wt.%, 4.0 wt.%, and 8.0 wt.%).

[0110] Tribology tests are shown with various concentrations of the AQD(0.2, 0.5, 1.0, 2.0, 4.0, 6.0, and 8.0 wt.%) to determine their capability of reducing friction in water.For the tests, steel balls on steel plates were deployed and water was used as control. The Stribeck curve reveals all the concentrations of the AQD reduce the coefficient of friction of water. This points to the friction-reduction property of the AQD. The coefficient of friction reduces up to 4.0 wt.% and increases thereafter. This indicates that the nanoparticle percolation threshold for the AQD may be 4.0 wt.%. As a comparison, a similar graph is shown with commercial nanoparticles (silver nanoparticles) to understand the behavior of the AQD in comparison to other nanomaterials. Silver nanoparticles provide minimal reduction in the coefficient of friction. AQD show superior friction reduction performance compared to commercial silver nanoparticles. Accordingly, AQD may be used as a cheap nano additive for preparing nanofluids for water-based lubrication in contact interfaces.

[0111] Figs. 12A and 12B show SEM graphical images of wear scars formed on the steel plates after friction and wear tests using water and the AQD nanofluids. Fig. 12C shows wear diameter in steel plates after friction and wear reduction tests using water and the AQD nanofluids.

[0112] Results from steel plates used for the steel and steel tribology test are shown by scanning electron microscopy (“SEM”) after one hour of constant shearing at a particular point. Wear diameter of 517 pm on the steel plates with water as friction reduction fluid is shown. The wear diameter on the steel plates generally reduces using the AQD nanofluid. The least wear reduction to 464 pm is recorded with 1.0 wt.% AQD. Significant wear damages are elicited on the steel plates using water as lubricant, while such damages are minimal with the AQD nanofluid.

[0113] Fig. 13 shows a laser scanning confocal microscopic images of AQD nanofluid before and after one hour of constant shearing. AQD aggregates appear when the AQD wt.% is 4.0% or greater.

[0114] Consequently, the AQD nanofluid are observed using laser scanning confocal microscopy at 405 nm excitation wavelength. Aggregation of the AQD(obvious black spots) at concentrations higher than 4.0 wt.% is shown. The aggregation of the AQD disrupts dispersibility and leads to low lubrication performance.

[0115] Fig. 14 shows viscosity of the AQD nanofluid before and after constant shearing for one hour. The 8 wt.% AQD solution shows the greatest decrease in viscosity after one hour of constant shearing.

[0116] AQD in nanofluid exhibit typical Newtonian fluid behavior. There is no obvious change in the viscosity profiles of the AQD nanofluids before and after one hour shearing. This shows that AQD may reduce friction without the formation of extended networks. In general, viscosity of the nanofluids increases after 1 h shearing. This increase in viscosity is more pronounced at high concentrations (4.0 wt.% and above).

[0117] Fig. 15 shows NIR photothermal images of water and different concentrations of AQD on an 808 nm laser irradiation at 1 W / cm2for 5 minutes. The 100 pg / mL AQD solution shows the greatest increase in temperature. AQD synthesized according to the present method may convert NIR light to heat (a photothermal property) and may be deployed in cancer PTT. AQD irradiated with an 808 nm laser operated at 1 W / cm2show temperature elevations at various concentrations of the AQD after being recorded for 5 min using an NIR photothermal camera.

[0118] Fig. 16 shows temperature elevations of water and different concentrations of AQD on an 808 nm laser irradiation at 1 W / cm2for 5 minutes. The 100 pg / mL AQD solution shows the greatest increase in temperature.

[0119] AQD may offer a temperature elevation that outperforms polypyrrole and ICG based photothermal agents, and which is comparable to Au NPs. 100 pg / mL AQD provide about 20 °C temperature elevation in 5 min upon laser irradiation at 1 W / cm2, which may be achieved with a 10-fold higher concentration (1000 pg / mL) of polypyrrole NPs. A study on Au NPs for cancer PTT achieves about 23 °C temperature elevation in 5 min also using 1000 pg / mL Au NPs which was irradiated at higher laser power density of 1.13 W / cm2.

[0120] Fig. 17 shows temperature variations of 100 pg / mL AQD solutions over ten on and off cycles upon 808 nm laser exposure (1 W / cm2). Inset images represent NIR photothermal images at various points when the laser was turned ‘on’ and ‘off’. The 100 pg / mL AQD solution shows photothermal stability during the ten on and off cycles.

[0121] Photostability is a crucial parameter for cancer photothermal agents intended for in vivo application. AQD are photostable up to at least ten laser “on / off” cycles. Comparatively, ICG specifically loses half of its temperature elevation in the third on / off cycle and does not survive beyond five cycles, and the photostability of unmodified Au nanorods (NRs) show diminished photostability before the fifth on / off cycle. AQD show near-steady photostability up to at least the tenth on / off cycle. AQD that show appreciable photoconversion property and photostability may be used for cancer PTT. AQD may be encapsulated in biocompatible polymers such as polyethylene glycol and chitosan to ameliorate cytotoxicity and improve AQD biocompatibility.

[0122] Figs. 18A, 18B, and 18C show FT-IR, UV-vis, and Raman spectra, respectively, of AQD synthesized from a different source of asphaltene. This indicates that AQD may be obtained from various sources of asphaltenes.

[0123] Fig. 19 shows temperature optimization of the synthesis route to AQD. Obtained particles sizes at and below 70 °C are above 30 nm. Insets show water dispersions of the obtained particles. An acid ratio at or above 1 :1 (HNOs^SO^ shows improved generation of the AQD, while temperatures at or above 80°C ensure sufficient oxidation conditions to achieve the quantum-size range product. At temperatures below 80°C, super hydrophilic nanoparticles are also recovered, but with particle sizes above 30 nm. Consequently, acid ratio of 1 :1 may be used for synthesizing the super hydrophilic AQD at 80°C.

[0124] Fig. 20 shows elemental analysis of pristine asphaltene and AQD. AQD comprise more sulfur compared to pristine asphaltene and less of the other elements shown. Elemental analysis of pristine asphaltenes and the AQD also show the capability of the acids utilized in this work to substantially reduce the concentrations of trace elements in the asphaltenes precursor.

[0125] Fig. 21 shows dispersibility of the AQD in common solvents. The suspension is obtained by merely shaking the AQD by hand in a vial without the need for water bath sonication. To further illustrate the high affinity of the AQD to water, various common solvents are shown for the dispersion of the AQD. Upon the addition of one drop of water to each solvent-comprising vial, the dispersibility of AQD is immediately improved in some solvents.

[0126] Fig. 22 shows the effect of pH on the fluorescence and SOS signals of the AQD. The intensities of both the fluorescence and SOS signals are also affected by pH of the dispersion medium. Whereas the fluorescence intensity increases as pH increases up to pH 7 and declines in basic medium, the SOS signal exhibits no consistent change across the pH range but is remarkably high at pH 1. At low pH, there is possible protonation of the oxygen- and nitrogen-comprising functional groups on the AQD, which are responsible for water dispersibility, resulting in low dispersibility, aggregation and subsequent precipitation of the AQD with attendant loss of luminescence.

[0127] Figs. 23A and 23B show fluorescence spectra of the fluorescein isothiocyanate dye and AQD, respectively. Figs. 23C and 23D show the UV-vis spectra of fluorescein isothiocyanate dye and AQD, respectively, used to calculate quantum yield of the AQD. Quantum yield of the AQD is calculated using fluorescein isothiocyanate reference from their fluorescence and UV-vis spectra. The calculated value of 2.04% for the AQD is comparable to those of quantum dots derived from coal (1.8%), coal tar pitch (2.37%), orange pericarp (2.88%), lignocellulosic residue (2.77%), and boron nitride quantum dots (2.5%), and to commercial organic dyes such as indocyanine green (2.5% in water), methylene blue (2% in water), and Cy3 (4% in PBS).

[0128] Figs. 24A, 24B, and 24C show PL intensity of the AQD at excitation and emission slit widths of 10 nm and 20 nm. Higher intensity of the AQD may readily be obtained by adjusting the excitation and emission slit widths of the spectrofluorometer. The complexation sweep is used in determining the selectivity of the AQD to Fe3+, Pb2+, and Bi3+, as they caused the most significant PL quenching at neutral and slightly acidic pH values corresponding to typical pH of wastewater. Metals with oxidation numbers of two and above may be effectively detected by the AQD.

[0129] Fig. 25 shows fluorescence spectra of the AQD dispersion in DI water with various concentrations of Pb2+and Bi3+. Stern-Volmer plots for the fluorescence variations of the AQD in DI water with concentrations of Pb2+and Bi3+. Ratiometric sensing of Pb2+and Bi3+using the AQD is shown. The sensitivity of the AQD towards multivalent metals (Fe3+, Pb2+, and Bi3+) indicates strong binding affinity of the AQD with metal ions of two or more valence states. Accordingly, AQD may be used to ratiometrically detect a metal with higher valency, such as V4+.

[0130] Figs. 26A, 26B, and 26C show elemental compositions of river water and produced water. Produced water shows a greater elemental concentration than river water, shown here as Bow River water. AQD are used for the ratiometric detection of metal ions in real water samples (Bow River and produced water), where there are possible interferences from various inorganic and organic species. Different concentrations of Fe3+and V4+are added to AQD dispersion in Bow River and produced water. The various inorganic species present in the Bow River and produced water is shown by inductively coupled mass spectrometry (“I CP- MS”). The produced water contains 469.86 mg L'1total organic carbon which accounts for its organic composition including saturated hydrocarbons, benzene, toluene, ethylbenzene, xylene, polycyclic aromatic hydrocarbons, steranes, and ketone compounds.

[0131] Fig. 27 shows Stern-Volmer plots for the SOS signal variations of the AQD in DI water with concentrations of Fe3+, Pb2+, Bi3+, and V4+.

[0132] Fig. 28 shows a comparison of various probes for sensing Pb2+and Bi3+in water. The LODs for Pb2+and Bi3+were 0.04 pM and 0.03 pM, respectively. Comparison of LODs for Pb2+and Bi3+in water with literature reports is presented.

[0133] Fig. 29 shows a comparison of probes for sensing Pb2+and Bi3+in water, according to an embodiment of the present invention.

[0134] Figs. 30A and 30B show fluorescence spectra of the AQD dispersion in PBS with various concentrations of AA and GSH, respectively. Fig. 30C shows Stern-Volmer plots for the fluorescence show variations of the AQD in PBS with concentrations of AA and GSH. The color change is also visualized upon adding different concentrations of AA in PBS dispersions of the AQD \, where GSH also exhibits considerable interaction with the AQD.

[0135] Fig. 31 A shows a schematic of the synthesis of hydrophobic AQD and the non-selectivity for water phase. Fig. 31 B shows the dispersion of hydrophobic AQD in various organic solvents and water. Fig. 31 C shows the size distribution of the hydrophobic AQD measured by dynamic light scattering. The inset shows the zeta potential value. Fig. 31 D shows the UV-vis spectra of pristine asphaltenes andhydrophobic AQD. Fig. 31 E shows the FT-IR spectra of pristine asphaltenes, hydrophobic and hydrophilic AQD.

[0136] Fig. 32 shows the synthesis of ACD from asphaltene and their application as a water-based lubricant for friction reduction in steel-steel tribological interface. An organic solvent pre-treatment, e.g. contact with toluene, enhances the susceptibility, e.g. the extent and efficiency, of acid-mediated oxidation of asphaltenes precursor. The enhanced susceptibility causes the asphaltenes precursor to exhibit improved water re-dispersibility after drying compared to asphaltenes precursor that is not pre-treated with an organic solvent. The pre-treatment comprises: dissolving an asphaltene in toluene to form an asphaltene and toluene mixture; and contacting the asphaltene with acids (HNO3 / H2SO4). Without being limited to a particular theory, the pre-treatment exposes the active sites in asphaltenes to acid-mediated oxidation. Exposing the active sites allows extensive oxidation of the asphaltenes and the contacting of oxygen and nitrogen-comprising functional groups with the ACD. Oxidation of the asphaltenes may allow re-dispersibility after drying the ACD.

[0137] Figs. 33A, 33B, 33C, 33D, 33E, 33F, 33G, 33H, and 33I show the physicochemical characterization of ACD. Figs. 33A and 33B show TEM and STEM graphical images of ACD, respectively. Figs. 33C and 33D show the size and zeta potentials, respectively of the ACD, and 5 and 20 nm silica nanoparticles dispersion in water. Fig. 33E shows the 3D confocal microscopic diagram of 275 mg ml_'1ACD dispersion in water. Figs. 33F and 33G show the FT-IR spectra and contact angles, respectively, of the ACD, and 5 and 20 nm silica nanoparticles. Figs. 33H shows the XPS full survey of the ACD. Fig. 33I shows the O1s XPS scans of the ACD.

[0138] The morphology of the ACD is evaluated by TEM as shown in Fig. 33A. The particles exhibit no visible aggregation and are generally nanodiscs as shown on the scanning TEM (S / TEM) (Fig. 33B). Fig. 33C shows the hydrodynamic size of the ACD measured by DLS is 5 nm which indicates appreciable dispersion (negligible aggregation) of the particles in water. DLS analysis of commercial 5 nm and 20 nm silica nanoparticles show that their hydrodynamic sizes are 11 and 25 nm, respectively, indicating some form of aggregation in 5 nm silica nanoparticles. Fig. 33D shows the zeta potentials of the ACD, 5 nm and 20 nm silica nanoparticles which indicate negative surface charges of -58.8 mV, -35.5 mV, and -18.9 mV, respectively. The higher negative charge of the ACD may beattributed to the extensive oxidation of the asphaltenes leading to the introduction of oxygen-comprising functional groups (e.g., hydroxyl, epoxy, carbonyl) to the ACD. The oxygen-comprising functional groups may be coupled with a nitro and / or amino groups introduced, e.g., bound to the asphaltene and / or asphaltene precursor, by the oxidation process. The oxygen-comprising functional groups coupled with a nitro and / or amino groups may bind to the asphaltene and / or asphaltene precursor and cause the ACD to be hydrophilic or promote hydrophilicity of the ACD. ACD hydrophilicity is shown by the uniform fluorescence field (absence of aggregates) in the 3D confocal image of 275 mg mL1ACD suspension in water, as shown in Fig. 33E.

[0139] Fourier-transform infrared (“FT-IR”) spectroscopy is used to determine the basic functional groups in the ACD and 5 and 20 nm silica nanoparticles. Without being limited to a particular theory, oxidation of the asphaltenes for forming the ACD may introduce oxygen- and / or nitrogen-comprising functional groups including, but not limited to, hydroxyl, epoxy, carbonyl, and nitro groups, or a combination thereof, to the ACD. The FT-IR spectrum of the ACD shows a broad band at 3380 cm'1, confirming the presence of hydroxyl and amino groups which result from the oxidation process, as shown in Fig. 33F. The amino groups in the ACD may result from the pyrrolic and pyridinic nitrogen of the asphaltenes precursor. The presence of N-0 stretching vibration for nitro groups introduced in the ACD by the oxidation process is evidenced by the two bands at 1580 cm'1and 1356 cm'1. The C=C stretching vibration for the aromatic rings in the ACD at 1580 erm1overlaps with the N-0 stretching vibration. The band at 1097 cm'1and 1711 cm'1are attributed to C-O-C and C=O stretching vibrations of ether and carbonyl groups in the ACD, respectively. Both 5 and 20 nm silica nanoparticles also show the characteristic Si- O-Si and Si-OH stretching vibrations at 1043 cm'1and 782 cm'1, respectively, indicating that they are mainly composed of SiO2. The FT-IR spectrum of the ACD also show the hydroxyl stretching vibration at around 3380 cm'1. The peaks at 2870 cm'1and 1453 cm'1in the 5 nm silica nanoparticles spectrum correspond to the C-H and C=C stretching vibrations in the aromatic rings of fluorescein isothiocyanate (“FITC”), respectively. The ACD comprise more hydroxyl groups than either 5 nm or 20 nm silica nanoparticles as the intensity of the hydroxyl stretching bands is much lower than in ACD.

[0140] The hydroxyl groups, carboxyl, ether, nitro, and amino groups in the ACD may facilitate hydrogen bonding with water molecules and may produce lower contactangle of 29.33° for the ACD in comparison with 37.14° and 39.66° for 5 nm and 20 nm silica nanoparticles, respectively, a show in Fig. 33G. Room temperature water uptake is 26.7%, 14.5% and 13.4% for the ACD, 5 and 20 nm silica nanoparticles, respectively, at 95% relative humidity (graph not shown).

[0141] The oxidation of the asphaltenes precursor is confirmed from the XPS full survey of the ACD, which shows oxygen, carbon, and nitrogen contents of 40.2%, 51.9% and 7.9%, respectively, as shown by Fig. 33H. The oxygen scan in Figure 33I shows three oxygen-comprising functional groups in the ACD, specifically, (i) hydroxyl group C-OH (atomic percentage 65%, binding energy 528.4 eV); (ii) carboxyl group C(O)-OH (10%, 529.3 eV); and (iii) ether functional group C-O-C (25%, 533.0 eV). Without being limited to a particular theory, the hydroxyl groups on the ACD surfaces in synergy with the carboxylic acid and ether groups constitute the highly hydrophilic nature of the ACD.

[0142] Figs. 34A, 34B, 34C, 34D, 34E, 34F, 34G, and 34H show the frictionreducing performance of lubricant ACD nanofluids. Fig. 34A shows a schematic illustration of the facile preparation of ACD nanofluids with different ACD loadings (0.2 wt.%, 0.5 wt.%, 1.0 wt.%, 2.0 wt.%, 4.0 wt.%, 6.0 wt.%, and 8.0 wt.%). Fig. 34B shows laser scanning confocal microscope (“LSCM”) images of representative ACD and 5 nm silica nanofluids (scale bars = 20 pm). Fig. 34C, 34D, and 34E show Stribeck curves showing the friction reduction performance of water and different loadings of ACD and silica nanofluids (0.2 wt.%, 1.0 wt.%, 4.0 wt.%, and 8.0 wt.%). Figs. 34F, 34G, and 34H show time-dependent friction during constant shearing of water, ACD, and silica nanofluids.

[0143] Fig. 34A shows the facile process of preparing the ACD nanofluids for lubrication assessments. Fig. 34B shows the uniform fluorescence of the ACD. The uniform dispersion of the ACD and 5 nm silica nanofluids indicate the hydrophilicity of the nanoparticles. The friction-reduction performance of water (control), ACD, and silica (5 and 20 nm) nanofluids at various sliding speeds are shown in the Stribeck curves, as shown in Figs. 34C, 34D, and 34E. At low speeds (boundary regime), the surfaces compress nanoparticles between contacting asperities, and there is no fluid film present. As the speed increases, the entraining fluid increases the normal pressure, causing the surfaces to separate and transition into the mixed lubrication regime. At higher sliding speeds, the primary friction mechanism becomes hydrodynamic lubrication from a fully formed fluid film.

[0144] All ACD loadings reduce the friction factor of water in the boundary regime (surface contact dominated), indicating their use as a nano-additive for water-based lubricants. Using 4 wt.% of ACD, 8 wt.% of 5 nm silica, and 1 wt.% of 20 nm silica, demonstrating the most effective friction-reduction formulation within each nanofluid group, the high boundary friction factor of pure water (-0.65) decreases to 0.26, 0.36, and 0.45, respectively. For the ACD, the friction factor decreases with loading until 4.0 wt.%, after which it increases for the 6.0 wt.% and 8.0 wt.% loadings.

[0145] Compared to water, both the ACD and silica nanofluids exhibit a delayed transition to the mixed and hydrodynamic lubrication regimes, as shown in Figs. 34C, 34D, and 34E. The steep drop observed in the mixed regime for water, which indicates a substantial lubricant effect between the steel surfaces, is also reduced with the ACD and silica (5 nm and 20 nm) nanofluids. In the hydrodynamic regime, low loadings of 5 nm silica and ACD (0.2 wt.% to 2.0 wt.%) closely follow the trend of water. Conversely, high loadings (4.0 wt.% and above) do not follow this trend, indicating that the multiple-body contacts between nanoparticles present in the tribological contact may be involved in the lubrication mechanism. In addition to having the highest boundary friction levels, all loadings of 20 nm silica exhibit a similar behavior in the hydrodynamic regime like water. There is no transition to the mixed and hydrodynamic regimes above 4 wt.% of the ACD and with 8 wt.% of 5 nm silica nanoparticles.

[0146] The hydrophilic ACD may form a structured hydration shell resistant to shear under load that reduces boundary friction and dissipates heat more effectively. The formation of a structured hydration shell is indicated by the lower contact angle and superior water uptake of the ACD compared to 5 nm and 20 nm silica nanoparticles. The hydration shell may be formed by water molecules enveloping charges that are resistant to removal under compression but which display pronounced fluidity upon shearing. Compared to ACD, the water layers between silica nanoparticles are more easily displaced, which leads to inferior lubrication. At higher sliding speeds, the ACD help to distribute the load more effectively by preventing direct steel-to-steel contact between the rubbing surfaces. This delays the transition from boundary to mixed lubrication, where a combination of surface-to-surface contact and fluid film lubrication begins to take placeconcurrently. This transition may also be delayed by ACD localizing within micro-pits to effectively reduce the direct contact area between steel surfaces.

[0147] Fig. 34F shows that, during continuous shearing for one hour, water maintains a friction factor of -0.69 throughout the entire evaluation period, while ACD nanofluids consistently show much lower values. At loadings above 4.0 wt.%, the ACD nanofluids exhibit higher friction factors, as also observed in the Stribeck curves, as shown in Fig. 34C. Low loadings of ACD (0.2 wt.% to 4.0 wt.%) nanofluid may substantially reduce the friction factor of water and offer long wear stability of over one hour. Use of low nano-additive loadings in water-based lubricants may create friction reductions.

[0148] The 4.0 wt.% ACD nanofluid record the lowest friction factor of -0.32, representing a 54% reduction compared to water and corroborating the reductions seen in the Stribeck curves (Fig. 34C). This friction-reduction extent outperforms the best values achieved by bare silica nanoparticles (30% to 45%), amine-functionalized silica nanoparticles (38%), as well as carbon-based nanofluids such as graphene quantum dots and graphene oxide (42% and 24%, respectively) (results not shown). Comparatively, other organic-based lubricants including triethylamine, 3-amino-1-propanol, and 1 ,4- butylene provided 30%, 12%, and 30% reductions in friction factor of water, respectively, at their optimum loadings (results not shown). Moreover, the friction-reduction extent outperforms those of undoped carbon dots, PEG, as well as copper-, magnesium- and iron-doped carbon dots loadings (results not shown).

[0149] Fig. 34G shows commercial silica nanoparticles (5 nm and 20 nm) subjected to tribology tests of constant shearing for one hour. All loadings of 20 nm silica nanoparticles did not achieve the least friction-reduction performance recorded with any of the ACD nanofluids. Fig. 34H shows that the ACD provided improved friction-reduction performance compared to the 5 nm silica nanofluids. Whereas ACD nanofluids exhibit near-steady friction reduction for prolonged periods (500 seconds to 3600 seconds), the profiles for all loadings of 5 nm silica nanoparticles are irregular, showing high (0 second to 1500 seconds) and low (1500 seconds to 3600 seconds) friction-factor regimes. Tribofilms formed by the ACD are held together by interparticle interactions caused by the oxygen- and nitrogen-comprising functional groups on the ACD surfaces. The oxygen- and nitrogen-comprising functional groups also provide different kinds of anions and lone pair ofelectrons for effective binding of ACD tribofilms to the positive steel surfaces. In contrast, interparticle interactions in silica nanoparticles and silica-steel binding is only with their silanol groups. The nanodisc nature of the ACD also allow the particles to easily stack on each other thereby improving inter-particle interactions and enhancing the durability of the tribofilms, unlike in silica nanoparticles whose spherical nature does not support stacking. Moreover, the ACD may re-disperse in water to evade aggregation upon stacking and display a near-steady friction reduction up to 3600 seconds. All nanofluids prepared with the ACD are stable for more than 12 months without phase separating. This stability may be attributed to the hydrophilicity and re-dispersibility of the ACD.

[0150] Figs. 35A, 35B, and 35C show scanning electron microscope (“SEM”) analysis of wear scars formed after one hour of continuous shearing. Fig. 35 shows SEM images of wear scars formed on the steel plates using water and 4.0 wt.% of the ACD and silica (5 nm and 20 nm) nanofluids. Figs. 35B and 35C show energy dispersive spectrometry (“EDS”) elemental mapping of regions of interest on the wear scars. Insets in Fig. 35C show regions of spot EDS elemental analysis on high magnification SEM images and tables of elemental composition quantification at the spots.

[0151] The wear protection capacity of the nanofluid lubricants is by SEM and EDS are shown in Figs. 35A, 35B, and 35C to examine the wear scars on steel plates used in the one hour constant shearing tribology tests. Fig. 35A shows representative wear scars on steel plates lubricated with water, and 4.0 wt.% ACD and silica (5 nm and 20 nm) nanofluids. Compared to water, the wear scar diameter decreases in the ACD nanofluids to 4.0 wt.% and increases at 6 wt.% and 8 wt.%. Accordingly, low loadings of the ACD (0.2 wt.% to 4.0 wt.%) may reduce contact-contact adhesion energy to protect the steel surfaces during relative motion. For the 20 nm silica nanofluids, the wear scar diameter initially reduces with nanoparticle loading and later increases after 4.0 wt.%. This trend does not hold for the 5 nm silica nanofluids as wear scar diameter generally increases with the nanoparticles loading and results in the largest diameters. Even though the wear scar in 4.0 wt.% 20 nm silica nanoparticles is smallest in comparison to ACD and 5 nm silica nanoparticles, large dark spots are shown on the scar. The dark spots indicate extensive abrasive wear of the steel surface which results the unstable friction factor trend for 20 nm silica nanoparticles.

[0152] SEM images of the wear scars at higher magnification and their corresponding EDS elemental maps clearly show the deposition of the ACD and silica (5 nm and 20 nm) nanoparticles in the wear grooves, as shown in Fig. 35B. The deposition of the ACD and nanoparticles in the wear grooves silica indicates that ACD and silica (5 nm and 20 nm) nanoparticles have the capability to form tribofilms at the contact interfaces to reduce friction and protect against wear. The EDS signals show that the most uniform dispersion of particles in the grooves is obtained with the ACD. This may be attributed to the shape of the ACD (nanodiscs compared to spheres for 5 nm and 20 nm silica nanoparticles) which allow for stacking of ACD tribofilm in the grooves and the functional groups attached to the to the surface of the ACD which include, but are not limited to, hydroxy, nitro, carboxy anions, and lone pair electrons in pyrrolic and pyridinic groups, or a combination thereof. The functional group on the ACD bind the particles to the steel surface unlike in silica nanoparticles where only silanol groups bind to the steel surfaces.

[0153] EDS elemental mapping of the wear scars from the ACD nanofluids shows signals for carbon, oxygen, and nickel. The ACD are carbon-based and comprise oxygencomprising functional groups, while nickel is present due to the asphaltenes precursor. In contrast, silica (5 nm and 20 nm) nanofluids show low carbon signal but with intense signals for silicon and oxygen which are the key elemental components of these nanoparticles. Iron, chromium, and sulfur are inherent elements of steel plates. Spot analysis of each wear scar pinpoints the elements present in each tribofilm, as shown in Fig. 35C. The ACD tribofilm exhibits prominent carbon, oxygen, and nickel peaks, while silicon and oxygen peaks dominated in the tribofilms of silica (5 nm and 20 nm) nanofluids. The results show that tribofilm formation by ACD and silica (5 nm and 20 nm) nanofluids protects the steel surfaces during friction.

[0154] Figs. 36A, 36B, 36C, 36D, and 36E show steel plate surface roughness. Figs. 36A, 36B, 36C, 36D, and 36E show the 3D morphologies of bare steel plates, plates lubricated with water, plates lubricated with ACD, plates lubricated with 5 nm silica, and plates lubricated with 20 nm silica nanoparticles, respectively. Wear depth and wear width on each plate are presented for the corresponding images.

[0155] The 3D morphologies of the wear scars show lower wear volume and roughness in ACD against water and silica nanofluids, shown in Figs. 36A, 36B, 36C, 36D, and 36E. The 20 nm silica nanoparticles induce irregular grooves on the plates but withless wear depth than the ACD. The reduced wear depth may be due to the lower contact points made on the plates by the 20 nm silica particles whose sizes are four times larger than the ACD. The silica nanoparticles may have greater hardness and form protective layers, mitigating wear despite higher friction factor, while ACD may exhibit more severe wear due to their softer nature but with lower friction factor.

[0156] Figs. 36A, 36B, 36C, 36D, and 36E show the viscosity of the ACD and silica (5 nm and 20 nm) nanofluids before and after one hour of constant shearing. Figs. 36A, 36B, 36C, and 36D show that all nanofluids exhibit a Newtonian behavior (shear-rate independent viscosity) within the experimentally accessible shearing range, both before and after one hour of continuous shearing. The viscosity of the fluids does not change significantly as temperature increases, indicating that the ACD provide comparable frictionreduction performance in systems that operate above room temperature, as shown in Fig. 36E. The stable viscosity with respect to temperature of the ACD indicates that the ACD and silica (5 nm and 20 nm) nanofluids reduce friction without the formation of extended nanoparticle networks that aid friction reduction in mixed and hydrodynamic lubrication modes. The viscosity of the nanofluids increases after one hour of shearing, with higher ACD loadings (above 4.0 wt.%) showing greater increases in viscosity. The difference between sheared and unsheared samples remains minimal for both 5 nm and 20 nm silica nanoparticle suspensions. This minimal differenced may be attributed to their surface charge disparities as the ACD have a surface charge of -58.8 mV (vide supra), whereas the 5 nm and 20 nm silica nanoparticles possess surface charges of -35.5 mV and -18.9 mV, respectively, as shown Fig. 36D. The strong negative surface charge of ACD shows that both the enhanced inter-particle repulsion and the potential to enhance affinity towards water molecules. During shear, the hydration shell can undergo two primary effects. First, it may deform and align in in the direction of the shear, and second, the shear forces can cause thinning of the hydration layer by disrupting the water molecule network at the surface of the particles. At higher ACD loadings, the increased viscosity indicates a rise in inter-particle friction, which may be due to deforming and / or thinning of the hydration shell. The deforming and / or thinning of the hydration shell may be due to the decreased proximity of the particles. With silica particles, the solvation shell effect is less pronounced, and silica particles are more prone to aggregation and breakage under shear. At loadings higher than 4.0 wt.%, friction reduction effect is decreased with ACD, while this is not the case with silica nanoparticles.

[0157] Figs. 37A, 37B, 37C, 37D, and 37E show the rheology of lubricant nanofluids before and after one hour of continuous shearing. Figs. 37A and 37B, show the viscosity of water and the ACD before and after shearing, respectively. Figs. 37C and 37D show the viscosity of 20 nm and 5 nm silica nanofluids before and after shearing, respectively. Fig. 37E shows the viscosity of water compared with 4.0 wt.% ACD and 5 and 20 nm silica nanofluids at different temperatures.

[0158] Figs. 38A, 38B and 38C show tribofilm formation by ACD and silica nanoparticles on a steel ball and plates. The ACD comprise oxygen- and nitrogencomprising functional groups that bind to the steel surfaces and form protective hydration shells to offer improved wear stability. The purple dotted lines represent interparticle linkages by hydrogen bonding and electrostatic interactions. The red dotted lines show the electrostatic linkages between the anions in ACD and silica nanoparticles with the positively charged steel surfaces.

[0159] The ACD comprising of hydroxyl, carboxyl, and ether groups (among others (as indicated by FT-IR and XPS data), may undergo intramolecular ether-ether, carboxycarboxy and hydroxy-hydroxy electrostatic, and / or non-stable hydrogen bond interactions. The hydrogen bond interactions may cause stacking of ACD nanodiscs into boundary filmlike structures, referred to as tribofilms, as shown in Fig. 38B. The flattened shape of the ACD (nanodiscs) allows stacking to form the tribofilms compared to 5 nm and 20 nm silica nanoparticles which cannot stack to their regular sphere shape. In addition, 5 nm and 20 nm silica nanoparticles depend only on their silanol groups in binding to the steel surfaces. The anions from the oxygen-comprising functional groups (e.g., carboxylate and hydroxyl groups) on the surfaces of the ACD, as well as the lone pair of electrons in their pyrrolic, pyridinic, and etheric groups collectively bind with the intrinsic positive charges on the steel surfaces by electrostatic interaction during the friction process. The oxygen- and nitrogencomprising functional groups on the ACD result in the higher negative zeta potential (-58.8 mV, -35.5 Mv, and -18.9 mV), lower contact angle (29.33°, 37.14°, and 39.66°), and higher water uptake (26.7%, 14.5%, and 13.4%) for the ACD, 5 nm and 20 nm silica nanoparticles, respectively. The interaction between the ACD and steel surfaces may confine the ACD-based tribofilm on the surface, which in combination with the hydration shell formation of the ACD may reduce friction and provide higher stability compared to 5 nm and 20 nm silica nanoparticles during prolonged shearing.

[0160] The lubricity of the ACD may also be promoted by their small size and corresponding large surface area for such small-size particles. The ACD size and surface area may result in packing of the particles in the tribofilm and tribofilm-steel surface electrostatic interactions. The packed particles may stack on each other, due to the nanodisc nature of the ACD, to further strengthen the tribofilm. Moreover, their small size may prevent stability degradation caused by micro-bulges of rubbing surfaces and may allow the ACD to penetrate the contact area of interfaces to form the tribofilm. The frictionreduction mechanisms of the ACD may be mending and polishing due to their nanodisc geometry.

[0161] Fig. 39 shows ACD synthesis from asphaltenes precursor and subsequent application in cancer photothermal imaging and therapy. A solvent pre-treatment process comprises contacting asphaltenes with toluene to dissolve the asphaltenes. Contact with toluene improves the susceptibility of asphaltenes to oxidation with mixed acids including, but not limited to, HNO3 and H2SO4. This pre-treatment process causes oxidation of the asphaltenes to ACD with oxygen- and nitrogen-based functional groups which allow for solvation of water molecules. The ACD are recovered at appreciably high mass yield (57%) and re-disperse in water even after oven drying.

[0162] Figs. 40A, 40B, 40C, 40D, 40E, and 40F show physicochemical characterization of ACD. Figs. 40A and 40B show transmission electron microscope (“TEM”) and scanning transmission electron microscope (“STEM”) images of the ACD. Figs. 40C shows the size and zeta potential of the ACD dispersion in water. Figs. 40D, 40E, and 40F show the FT-IR spectra, X-ray photoelectron spectroscopy (“XPS”) full survey, ultraviolet-visible (“UV-vis”) spectrum of the ACD, respectively. Inset represents absorbance of the ACD in the near infrared (“NIR”) region. Fig. 40G shows the fluorescence spectra of the ACD at various excitation wavelengths.

[0163] Figs. 40A and 40B show the TEM and scanning transmission electron microscope (“STEM”) images of the morphology of the ACD. The particles show dispersion without forming aggregates in water and may be described as nanodiscs in geometry. The dynamic light scattering (“DLS”) analysis shows a hydrodynamic size of 5 nm in line with the particle size observation from the TEM images and corroborating the considerable water dispersibility of the ACD, as shown in Fig. 40C. Surface charge of theACD is -58.8 mV which may be attributed to the presence of high oxygen- and nitrogenbased functional groups including, but not limited to, hydroxyl, epoxy, carbonyl, nitro, amino groups, or a combination thereof. The functional groups are introduced into the ACD by the oxidation process resulting from contact with mixed acids (e.g., HNO3 and H2SO4). The ACD are hydrophilic and generate uniform fluorescence (absence of aggregation) in the 3D confocal image obtained with 275 mg mL'1ACD in water (figure not shown).

[0164] The XPS full survey shows the abundance of the oxygen and nitrogencomprising functional groups in the ACD, as shown in Fig. 40D. The contents of oxygen (40.2%) and nitrogen (7.9%) show that most of the carbon atoms in the asphaltenes precursor are introduced with and / or converted to oxygen and nitrogen-comprising functional groups.

[0165] Fig. 40E shows the ACD possess a broad absorption range (200 nm to 900 nm) between the UV-vis and NIR region. The absorbance of the ACD in the NIR region (inset in Fig. 40E) is similar to those of graphene-based nanomaterials and carbon dots that have been used for cancer photothermal therapy at 808 nm laser irradiation. The ACD exhibit both TT-TT* and n-n* transitions corresponding to their sp2and C-0 conjugate carbon domains (e.g., carboxyl, hydroxyl), respectively. Fluorescence spectroscopy conducted on various concentrations of the ACD in water shows maximum emission wavelength of 472 nm, as shown in Fig. 40F. The light emission by the ACD is dependent on excitation wavelength, showing an initial blue shift from 200 nm to 320 nm, followed by a red shift as excitation wavelength increases up to 500 nm. Low emission is shown between excitation wavelengths of 700 nm and 808 nm, indicating that most of the absorbed light by the ACD in those excitation wavelengths is converted to heat via non-radiative transitions.

[0166] Figs. 41 A, 41 B, 41C, 41 D, and 41 E show temperature variations of ACD. Figs. 41 A and 41 B show concentrations using a laser optical power of 1.5 W cm-2and laser optical power densities using a fixed ACD concentration of 100 pg*mL'1, respectively. Laser wavelength is 808 nm and exposure time is 5 min. Fig. 41C shows NIR photothermal graphical images generated with different concentrations of the ACD with 1.0 W cm'2laser power densities in 5 min. The red arrow shows the direction of laser irradiation. Fig. 41 D shows photothermal graphical images of 100 pg*mL'1ACD exposed to 808 nm laser at various power densities (0.5 W*cnr2, 1.0 W*cnr2, 1.5 W*cnr2, and 2.0W*crrr2). Fig. 41 E shows temperature elevations of ACD dispersion (100 pg*mL'1) over 10 laser on / off cycles at 1 .5 W*cm'2.

[0167] To evaluate the capability of ACD to induce cancer cell death by photothermal therapy, the in vitro photothermal behavior of different ACD concentrations (20, 40, 60, 80, and 100 pg*mL'1) are shown on a digital NIR photothermal imaging system, as shown by Figs. 41 A, 41 B, 41 C, 41 D, and 41 E. The ACD exhibit a concentration- controlled temperature elevation profile upon exposure to an 808 nm NIR laser irradiation for 5 minutes, as shown in Fig. 41A. Temperature elevation with 1 mL of 100 pg*mL'1ACD dispersion reaches 48.7 °C in 5 minutes. Pure water serving as control shows marginal temperature elevation upon laser exposure (30.3 °C, 5 minutes). When the NIR laser optical power density is increased to 2.0 W cm'2, the temperature elevation may reach 56.4 °C in 5 minutes using 1 mL of 100 pg*mL'1ACD dispersion, as shown in Fig. 41 B.

[0168] Preliminary photothermal imaging capability of the ACD is established from the heat maps generated with different concentrations of ACD dispersions in water after 5- minute exposure to the 808 nm laser operated at 1.5 W cm'2, as shown in Fig. 41 C. Photothermal graphical images of 100 pg mL'1ACD exposed to the 808 nm laser at various power densities are shown in Fig. 41 D. The photostability of the ACD is determined via laser on / off cycles. The ACD exhibit near-steady photostability for 10 laser on / off cycles using 1.5 cm'2laser optical power density, as shown in Fig. 41 E. The ACD may maintain photostability above 10 laser on / off cycles. The ACD photostability may be used to generate prolonged heating of cancer cells in vivo to enhance cancer treatment efficacy.

[0169] Figs. 42A, 42B, 42C, and 42D show non-radiative transitions, light scattering, and heat generation for ACD. Figs. 42A and 42B show non-radiative transitions and possible light scattering by the ACD upon 808 nm laser irradiation, respectively. Fig. 42C shows heat generation by different concentrations of the ACD at 5 minutes upon 808 nm laser irradiation (1 .5 W*cm'2). Fig. 42D shows heat generation at 5 minutes using 100 pg*mL'1ACD exposed to different power densities of the 808 nm laser.

[0170] A mechanism for heat generation for cancer photothermal therapy with carbon-based nanoparticles is indicated by the stimulation of loosely bound TT electrons and subsequent relaxation of excited electrons. The majority of the energy absorbed by that nanomaterial at a particular wavelength is dissipated as heat rather than lightemission, for a nanomaterial to exhibit low quantum yield. ACD possess low quantum yield of 2.04% and show low light emission upon excitation at 808 nm. Almost all energy absorbed by the ACD at that wavelength is dissipated as heat via non-radiative transitions, as shown by Fig. 42A. The generated heat in the process consequently increases the local temperature of the immediate surrounding of the ACD particles which can be leveraged to induce cancer photothermal therapy. In some other nanomaterials, light scattering can enhance heat generation. Fig. 42B shows light scattering for ACD, which may enhance heat generation. The heat generated at 5 min by different concentrations of the ACD upon 808 nm irradiation (Fig. 42C) and those generated at different laser power densities using a specific ACD concentration (Fig. 42D) are linear. For light scattering to occur, an increase in ACD concentration may cause a deviation from linearity in terms of heat generation possibly due to the reduced interparticle distance. Non-radiative electron relaxation including internal conversion and vibrational relaxation may also cause heat generation by the ACD.

[0171] Figs. 43A, 43B, 43C, and 43D show in vitro cytotoxicity of ACD. Fig. 43A shows cell viability of 4T 1 cells co-incubated with various concentrations of ACD for 24 hours. Figs. 43B and 43C show cell viability of 4T 1 cells after 5 minutes of treatment with different concentrations of ACD under laser exposure at 1.5 W*cnr2and different laser optical power densities. Values are presented as mean ± standard deviation, respectively. Fig. 43D shows Hematoxylin and Eosin (“H&E”) staining micrographs of mice major organs excised at 14 days post-intravenous injection of phosphate buffered solution (“PBS”) as a control and ACD (200 pL, 2 mg*mL"1, scale bar = 50 pm).

[0172] Tissue tolerance is a critical parameter for materials intended for in vivo use. Moreover, considering the asphaltenes precursor of the ACD the biocompatibility of ACD is evaluated. The in vitro cytotoxicity of the ACD was therefore evaluated in accordance with the conventional MTT assay for biocompatibility assessment. After co-incubation of mice breast cancer (4T1) cells with the ACD for 24 hours, cell viability of the cells is >87% even at 100 mg mb1ACD, as shown in Fig. 43A. Elemental analysis of the ACD shows that the contents of noxious elements inherent in the asphaltenes precursor which may have jeopardized ACD biocompatibility were decreased after oxidation with the mixed acids. The ACD do not cause significant damage to cells and may be used as tissue-tolerant nanoparticles for in vivo cancer imaging and therapy.

[0173] The in vitro cancer photothermal therapeutic performance of the ACD is shown using 4T1 cancer cells alongside 808 nm laser irradiation by the MTT assay. Cancer cell death is caused by the ACD after 808 nm laser irradiation (1.5 W*cnr2) for 5 min with the effect intensifying as ACD concentration increases, as shown in Fig. 43B. Also, when a fixed concentration of the ACD is used (50 pg*mL1), cancer cell mortality increases as the laser optical power density increases from 0.5 W*cm_2to 2.0 W*cnr2, as shown in Fig. 43C. This indicates that the ACD are effective at absorbing NIR light to generate sufficient heat levels capable of eradicating cancer cells.

[0174] To use the ACD in vivo for cancer imaging and therapy, it is important to evaluate their in vivo cytotoxicity. Fig. 43D shows the results of 200 pL of 2 mg / mL ACD is injected into healthy mice and observed for 14 days. PBS serves as the control. H&E staining micrographs obtained from the main organs of mice (including the heart, kidney, lung, spleen, and liver) at 14 days post-injection show no noticeable damage or inflammations to the organs compared with the control (PBS) group. Nuclei chromatin and vacuole membranes distributions in the ACD and PBS groups are comparable. Also, mice in both ACD and PBS groups do not show abnormalities in their feeding, drinking, and movement habits.

[0175] Fig. 44 shows laser confocal fluorescence images of 4T 1 cells co-incubated with ACD for four hours. The cellular uptake of the ACD by 4T 1 cancer cells is shown to determine whether the ACD could be taken up by the cancer cells for imaging and therapeutic purposes. 4T 1 cells are then co-incubated with the ACD for 4 hour and the inherent fluorescence property of the ACD is leveraged to acquire images of the ACD in the cells. The ACD are successfully taken up by the 4T 1 cells via the enhanced permeability and retention (“EPR”) effect typical of passive cancer cells targeting. The ACD accumulate more in the cell nuclei and some of the particles accumulate in the cell membrane. The results show 4T 1 cellular uptake of the ACD for cancer theranostics and confirm the use of the ACD to track cancer cells by leveraging their pronounced accumulation in the cell membranes.

[0176] Figs. 45A, 45B, 45C, 45D, 45E, 45F, and 45G shows cancer photothermal imaging and therapy with ACD. Fig. 45A shows the timeline of mice PTT with the ACD. Fig. 45B shows the time-course NIR photothermal images of whole mice revealing the tumor region upon laser irradiation (800 nm; 1.5 W*crrr2) of the ACD. PBS serves ascontrol. Fig. 45C shows temperature elevations induced by the ACD and PBS (control) in mice tumor during laser irradiation. Fig. 45D and 45E show mice body weight and tumor volume changes, respectively, monitored for 15 days post-treatment with ACD and PBS. Data are expressed as mean ± standard deviation. Fig. 45F shows representative graphical images of the tumors excised from mice treated with ACD and PBS at 15 days post-treatment. Fig. 45G shows H&E staining micrographs of tumors excised at 15 days post-treatment with ACD and PBS control (scale bar = 50 pm).

[0177] Following inoculation of cancer cells in BALB / c mice, cancer photothermal imaging and therapy creates the pattern shown in Fig. 45A. One-time NIR irradiation is used to ensure protection of normal cells from hypothermia-induced cell damage. The timecourse NIR photothermal images of whole BALB / c mice after injection with the ACD enable imaging of the cancer region by the heat maps generated from the ACD in the cancer region (Fig. 45B). This shows the capability of ACD to serve as a cancer photothermal imaging agent.

[0178] Fig. 45C shows the local temperature elevations caused by the ACD and control (PBS) in the cancer region. The ACD provide up to 53°C rise in the local temperature of the tumor region which is sufficient to cause cancer cell death. Observation of the mice body weight over 15 days post-treatment shows no significant change, suggesting that the mice behavior is relatively stable, as shown in Fig. 45D. It also confirms that the ACD do not induce noticeable cytotoxicity to mice. The tumor volume shows continuous decrease in the ACD-treated mice group contrary to the PBS group, as shown in Fig. 45E. After the 15-day observation period, tumors in all the mice were excised to visualize the therapeutic efficacy. A Graphical image of the excised tumors shows substantial decrease in tumor volume in the ACD mice group is shown in Fig. 45F. In two of the mice in ACD group, the remaining tumors after treatment are too small to be excised, indicating photothermal therapeutic performance of the ACD. Additionally, H&E staining micrographs of excised tumors at 15 days post-treatment show pronounced tumor-cell apoptosis in ACD-treated mice compared with the PBS group, as shown in Fig. 45G.

[0179] The AQD and / or ACD may comprise an oxidized asphaltene. The AQD and / or ACD may comprise a nanodisc geometry.

[0180] The AQD and / or ACD may comprise functional groups attached to the surface of the AQD and / or ACD. The functional groups may comprise oxygen and / or nitrogen. The functional groups may include, but are not limited to, hydroxyl, epoxy, carbonyl, nitro, amino groups, hydroxy, carboxy anions, pyrrolic, and / or pyridinic functional groups, or a combination thereof.

[0181] Without being restricted to a single theory, the mechanism for ratiometric sensing of the metal ions and antioxidants may be due to an effective binding between Fe3+, Pb2+, Bi3+, V4+, and / or antioxidants and the AQD and / or ACD is more than mere physical interaction. There may be a chemical interaction between metal ions and AQD in sensing applications. Additionally, as monovalent metals are unable to substantially quench the PL of the AQD and / or ACD, complexation is therefore proposed as the mechanism for the PL quenching of the AQD by elements of higher valency. According to the information obtained from XPS and FT-IR analyses of the AQD and / or ACD, it may be established that there is an abundance of oxygen- and nitrogen-comprising functional groups on the surfaces of the AQD and / or ACD. The nitro and amino (pyrrolic and pyridinic nitrogen) groups and anions of the oxygen-comprising functional groups (e.g., hydroxyl and carboxylate anions) in solution could serve as ligand sites for complexation with the positively charged metal ions.

[0182] AQD and / or ACD ratiometric sensing of antioxidants may be conducted in an aqueous medium including but not limited to, deionized water, river water, produced water, or a combination thereof. The ions may include, but are not limited to Fe3+, Zn2+, Co2+, Ca2+, Pb2+, Mn2+, Bi3+, Al3+, V4+, any other metal ion with a valency greater or equal to 2+, or a combination thereof. The concentrations of the metal ion may be at least about 0.001 mM, about 0.001 mM to about 1 .5 mM, about 0.003 mM to about 1.25 mM, about 0.01 mM to about 1 mM, about 0.05 mM to about 0.5 mM, about 0.1 mM to about 0.25 mM, or about 1.5 mM. AQD and / or ACD dispersion in DI water may be used to determine the effect of metal-ion concentration on PL quenching. PL quenching of the AQD and / or ACD dispersion (e.g., sensing) may occur in less than about 5, about 5 to about 0.5, about 4.5 to about 1 , about 4.0 to about 1.5, about 3.5 to about 2, about 3 to about 2.5, or about 0.5 seconds post-addition of metal ions and antioxidants with a UV lamp operated at 365 nm in the dark.

[0183] AQD and / or ACD may be de-complexed from a target by contact with a reagent including, but not limited to, NaOH, L-cysteine, EDTA, or a combination thereof. Quantitative analysis of the sensing process may be conducted by fluorescence spectroscopy obtained after target contact with AQD and / or ACD. The limit of detection (“LOD”) may be calculated as 3o / , where o is the standard error of AQD and / or ACD dispersion without metal ion or biomarker and k is the Stern-Volmer constant.

[0184] AQD and / or ACD ratiometric sensing of antioxidants may be conducted in a physiological medium including but not limited to, urine, and phosphate buffer saline (“PBS”). AQD and / or ACD may detect concentrations of biomarkers in fluid. The antioxidants may be concentrations of less than about 0.1 mM, about 0.1 mM to about 0.001 mM, about 0.05 mM to about 0.003 mM, about 0.025 mM to about 0.006 mM, or about 0.001 mM. The concentration of the AQD and / or ACD may be less than about 0.1 mg*mL'1, about 0.1 mg*mL1to about 0.01 mg*mL1, about 0.09 mg*mL1to about 0.02 mg*mL'1, about 0.08 mg*mL'1to about 0.03 mg*mL'1, about 0.07 mg*mL'1to about 0.04 mg*mL'1, about 0.06 mg*mL'1to about 0.05 mg*mL'1, or about 0.01 mg*mL'1.

[0185] AQD and / or ACD dispersion in PBS and the mixtures may observed in a UV lamp after AA and GSH simultaneously sensed by fluorescence spectroscopy. Sensing may occur in less than about 5, about 5 to about 0.5, about 4.5 to about 1, about 4.0 to about 1.5, about 3.5 to about 2, about 3 to about 2.5, or about 0.5 seconds.

[0186] AQD and / or ACD may be used for ratiometric sensing of metal ions including, but not limited to Fe3+, Pb2+, Bi3+, and V4+, and biomarkers including, but not limited to, AA and GSH. AQD and / or ACD may possess intrinsic fluorescence and SOS signals that are key to ratiometric sensing. Metal ions and antioxidants may interact with AQD and / or ACD resulting in fluorescence and / or SOS signal variations of the AQD and / or ACD to afford ratiometric sensing of the analytes. Sensing may occur in less than about 5, about 5 to about 0.5, about 4.5 to about 1 , about 4.0 to about 1.5, about 3.5 to about 2, about 3 to about 2.5, or about 0.5 seconds.

[0187] AQD and / or ACD nanofluids may be used as a nano additive for friction reduction by water-based lubrication strategy. AQD and / or ACD may serve as a cheap nano additive to prepare water-based lubricants, benefiting from the low cost of the asphaltenes precursor for synthesizing the AQD and / or ACD coupled with the low reagentdemand, considerable mass yield, and short synthesis time. Low concentrations of AQD and / or ACD may provide friction and wear reduction. Friction and wear reduction may reduce material demand and economic cost of formulating water-based lubricants. AQD and / or ACD nanofluids may be Newtonian fluids whose viscosity is independent of shear rate. AQD and / or ACD nanofluid may not form extended networks during friction reduction. The friction and wear reduction performances of AQD and / or ACD nanofluid point to their potential usefulness as protective coatings for corrosion inhibition in steel-based surfaces.

[0188] AQD and / or ACD may be synthesized from cheap and abundant asphaltenes precursors. AQD and / or ACD may exhibit fluorescence properties and / or high hydrophilicity. AQD and / or ACD may absorb near infrared light and convert same to heat to ablate cancer cells in a typical cancer photothermal therapy. AQD and / or ACD may offer photoconversion performance comparable to gold nanoparticles and may outperform conducting polymers, such as polypyrrole, and indocyanine green dye for clinical use in photothermal therapy. AQD and / or ACD may advantageously be photothermally stable for at least about 1, about 1 to about 20, about 2 to about 18, about 4 to about 16, about 6 to about 14, about 8 to about 12, or about 20 on / off photoconversion cycles. AQD and / or ACD may simultaneously provide fluorescence imaging of cancer cells alongside photothermal therapy. The super hydrophilicity of AQD and / or ACD may allow them to be used as cancer therapeutic nanomaterials; water dispersibility and intravenous injection are key priorities.

[0189] The method may comprise contacting a source of asphaltene with an organic solvent. The organic solvent may include, but is not limited to, toluene. The method may comprise heating an acid and residue mixture to a temperature of at least about 40 °C, about 40 °C to about 100 °C, about 50 °C to about 90 °C, about 60 °C to about 80 °C, or about 100 °C.

[0190] The method of synthesizing a hydrophobic AQD and / or ACD may comprise heating the mixture at a temperature of at least about 75 °C to about 85 °C, about 76 °C to about 84 °C, about 77 °C to about 83 °C, about 78 °C to about 82 °C, about 79 °C to about 81 °C, or about 85 °C. The mixture may be heated for at least about 2.5 hours, about 2.5 hours to about 5.5 hours, about 3 hours to about 5 hours, about 3.5 to about 4.5 hours, or about 5.5 hours.

[0191] AQD and / or ACD may be dispered in organic solvents. The organic solvents may comprise toluene, tetrahydrofuran, cyclohexan, benzyle chloride, xylene, or a combination thereof. AQD and / or ACD may be hydrophobic (hydrophobic AQD and / or ACD) and may have a wavelength of maximum absorption of 350 nm as determined by US-vis spectroscopy. Hydrophobic AQDmay not show the broad band for hydroxyl groups in an FT-IR spectrum, and may show the prominent C-H vibrations at 2922 cm'1, 2840 cm'1and 1433 cm'1. The size of the hydrophobic AQDmay be at least about 4 nm, about 4 nm to about 5 nm, about 4.1 nm to about 4.9 nm, about 4.2 nm to about 4.8 nm, about 4.3 nm to about 4.7 nm, about 4.4 nm to about 4.6 nm, or about 5 nm. The surface charge of the hydrophobic AQDis at least about 0.5 mV, about 0.5 mV to about 1.5 mV, about 0.6 mV to about 1.4 mV, about 0.7 mV to about 1.3 mV, about 0.8 mV to about 1.2 mV, about 0.9 mV to about 1.1 mV, or about 1.5 mV.

[0192] Embodiments of the present invention provide a technology-based solution that overcomes existing problems with the current state of the art in a technical way to satisfy an existing problem for diagnostic, lubricant, and cancer therapy manufacturers. Embodiments of the present invention achieve important benefits over the current state of the art, such as decreased cost of manufacture, ratiometric sensing capabilities, dispersibility in aqueous solutions, and photothermal reactivity. Some of the unconventional steps of embodiments of the present invention include contacting asphaltenes in an organic solvent, evaporating the organic solvent, contacting asphaltenes with acid, heating the asphaltenes and acid mixture to form unpurified AQD ACD, removing the acid, and purifying the AQD ACD.Industrial Applicability:

[0193] The invention is further illustrated by the following non-limiting examples. For the experimental examples, the materials used included, but were not limited to, asphaltenes in powder form; HNO3, H2SO4, NaOH, and L-cysteine, and reduced L- glutathione (GSH); L-ascorbic acid (AA); ethylenediaminetetraacetic acid (“EDTA”); river water sourced from Bow River, Calgary, Canada; and produced water sample was obtained from an oilsands plant. All metal salts were of analytical grade. Deionized water(resistivity = 18.2 MQ) was used in all experiments. All chemicals were used as received without further purification.Example 1

[0194] AQD were synthesized. The synthesis of asphaltene-derived AQD proceeded by solvent exchange prior to oxidation. In a typical experiment, 1 g asphaltenes powder was first dispersed in toluene, followed by solvent evaporation. Thereafter, a 1:1 volume ratio of HNC and H2SO4 (70% and 98% aqueous solutions, respectively) were added to the residue. The mixture was stirred at 80 °C for four hours and allowed to cool to room temperature. Thereafter, the mixture was centrifuged at 3000 rpm for 10 minutes and this process was repeated three times to remove the acid components. The recovered product was dispersed in water and brought to neutral pH with a few drops of 0.1 M NaOH. The product was further purified by dialysis in a dialysis membrane (molecular weight cut off = 3500 Da) against DI water for 2 days with daily change of water. The super hydrophilic AQD were then obtained as fine black powder after vacuum drying for 48 hours at 40 °C and used for characterization, ratiometric sensing, lubrication, and cancer therapy without post-synthesis modification.Example 2

[0195] Tests were performed to characterize the AQD. The morphology of the AQD was investigated on a transmission electron microscope, which was operated at a 200 kV accelerating voltage. The microscope was equipped with a cold field-emission gun and a probe spherical aberration corrector. DLS and zeta potential distribution of the AQD were measured on a zetasizer device to determine the sizes and surface charges of the nanoparticles, respectively. The functional groups in pristine asphaltenes and AQD were determined by XPS using an XPS spectrometer, and FT-IR spectroscopy. Ultraviolet- visible spectroscopy was conducted on UV-vis spectrometer to measure the light absorption of the AQD. The crystalline structure of the AQD was determined by XRD using a diffractometer with Cu Ka (40 KV, 30 mA) in the step-scan mode. Thermal stability of pristine asphaltenes and AQD was determined by TGA in N2 flow and heating rate of 5 °C min-1using TGA and differential scanning calorimetry (“DSC”). PL of the AQD was measured on a fluorescence spectrophotometer. The dispersibility of the AQD was established by confocal microscopy at 405 nm excitation wavelength. The Ramanspectrum was recorded using a confocal Raman microscope with laser irradiation of 532 nm to study the defects on the AQD. Elemental analysis of pristine asphaltene and AQD was conducted on an inductively coupled plasma mass spectrometer.Example 3

[0196] Ratiometric sensing in DI and real waters was performed. The ratiometric sensing of metal ions was first conducted in DI water using a 0.04 mg*mL'1AQD dispersion. To achieve this, 1 mL of 0.1 mM Li+, Ni+, Fe3+, Cd+, Zn2+, Co2+, Cu+, Ca2+, Mg+, Pb2+, Mn2+, K+, Bi3+, Al3+, Ba+, and Na+was added to 3 mL of the AQD dispersion.Subsequently, various concentrations (0.001 mM, 0.003 mM, 0.006 mM, 0.013 mM, 0.025 mM, 0.05 mM, and 0.1 mM) of Fe3+, Pb2+, Bi3+, and V4+were added to the 0.04 mg mL'1AQD dispersion in DI water to determine the effect of metal-ion concentration on PL quenching. The same concentrations (0.001 mM, 0.003 mM, 0.006 mM, 0.013 mM, 0.025 mM, 0.05 mM, and 0.1 mM) of the antioxidants (AA and GSH) were also tested on 0.04 mg L'1AQD dispersion in DI water. In real water samples, the concentration of Fe3+was extended from 0.001 mM - 0.1 mM and 0.001 mM - 1.0 mM in river water and produced water, respectively. Tested V4+concentrations were 0.001 mM - 1.0 mM and 0.001 mM - 1.5 mM in river water and produced water, respectively. River water and produced water were used without dilution. PL quenching of the AQD dispersion was visually observed few seconds ( < 3 s) post-addition of metal ions and antioxidants with a UV lamp operated at 365 nm in the dark.Example 4

[0197] To explore the effect of AQD dispersion concentration, 1 mL solution of specific concentration of a representative metal ion (Fe3+; 0.1 mM) was added to 3 mL AQD dispersion of different concentrations (0.04 mg*mL'1, 0.08 mg*mL'1, 0.15 mg*mL'1, 0.3 mg*mL'1, 0.6 mg*mL'1, 1.25 mg*mL'1, and 2.5 mg*mL'1). The mechanism of PL quenching was deduced by decomplexation reaction in NaOH, L-cysteine, and EDTA. Quantitative analysis of the sensing process in each case was conducted by fluorescence spectroscopy obtained immediately after metal-ion addition, while monitoring the SOS signal at 644 nm in all cases and fluorescence signals at 507, 460, and 400 nm for DI water, river water, and produced water, respectively. The LOD was calculated as 3o / , where o is the standard error of AQD dispersion without metal ion or biomarker and k is the Stern-Volmer constant.Example 5

[0198] Tests were performed to evaluate the ratiometric sensing by AQD in biological fluids. Ratiometric sensing of AA and GSH was first conducted in a physiological medium (phosphate buffer saline, PBS) to determine the compatibility and sensing capability of the AQD in an improvised biological fluid prior to using human urine. Various concentrations (0.001 mM, 0.003 mM, 0.006 mM, 0.013 mM, 0.025 mM, 0.05 mM, and 0.1 mM) of 1 mL solution comprising the biomarkers (AA and GSH) were added to 3 mL of a 0.04 mg*mL1AQD dispersion in PBS and the mixtures were observed in a UV lamp immediately after AA and GSH addition (< 3 s) and simultaneously quantified by fluorescence spectroscopy. Fluorescence and SOS signals were monitored at 507 and 644 nm, respectively, while deploying the Stern-Volmer plot to determine LOD. Human urine was diluted 100 times and used as medium to prepare 0.04 mg mL-1AQD dispersion. Different concentrations (0.001 mM -0.1 mM) of the antioxidants (AA and GSH) and metal ions (Fe3+and Pb2+) were added to 3 mL of the AQD dispersion in human urine. Visual observation of possible PL quenching in < 3 s was also done with a UV lamp (365 nm) in the dark, while quantitative analysis of the ratiometric sensing was simultaneously carried out by fluorescence spectroscopy while monitoring the fluorescence and SOS signals at 450 and 644 nm, respectively. Stern-Volmer plot was also used to determine LCDs of the biomarkers and metal ions in the human urine.Example 6

[0199] Tribology tests were conducted with various concentrations of the AQD (0.2 wt.%, 0.5 wt.%, 1.0 wt.%, 2.0 wt.%, 4.0 wt.%, 6.0 wt.%, and 8.0 wt.%) to determine their capability of reducing coefficient of friction in water. For the tests, steel balls on steel plates were deployed and water was used as control. The Stribeck curve showed that all concentrations of AQD substantially reduced the coefficient of friction of water. This indicated that AQD possessed friction-reduction properties. The coefficient of friction reduced at AQD concentration of up to 4.0 wt.% and increased thereafter. As a comparison, a similar test was performed with commercial nanoparticles (silver nanoparticles) to understand the behavior of the AQD in comparison to other nanomaterials. Silver nanoparticles provided only a minimal reduction in the coefficient of friction. AQD showed superior friction reduction performance compared to commercial silver nanoparticles.

[0200] The preceding examples can be repeated with similar success by substituting the generically or specifically described reactants and / or operating conditions of this invention for those used in the preceding examples.

[0201] Note that in the specification and claims, “about” or “approximately” means within twenty percent (20%) of the numerical amount cited. The terms, “a”, “an”, “the”, and “said” mean “one or more” unless context explicitly dictates otherwise. All percentages are by weight unless otherwise stated.

[0202] Although the invention has been described in detail with particular reference to these embodiments, other embodiments can achieve the same results. Variations and modifications of the present invention will be obvious to those skilled in the art and it is intended to cover in the appended claims all such modifications and equivalents. The entire disclosures of all references, applications, patents, and publications cited above are hereby incorporated by reference

Claims

CLAIMSWhat is claimed is:

1. A method for synthesizing a nanoparticle, the method comprising: contacting a source of asphaltene with an organic solvent; removing the organic solvent to form an asphaltene; contacting the asphaltene with an acid; and removing the acid.

2. The method of claim 1 wherein the organic solvent comprises toluene.

3. The method of claim 1 wherein the acid is a mixture of acids.

4. The method of claim 1 wherein the acid comprises HNO3.

5. The method of claim 1 wherein the acid comprises H2SO46. The method of claim 1 further comprising oxidizing the asphaltene.

7. The method of claim 1 further comprising attaching a functional groups to the surface of the asphaltene.

8. The method of claim 7 wherein the functional group comprises oxygen.

9. The method of claim 7 wherein the functional group comprises nitrogen.

10. A method of killing a tumor cell, the method comprising: disposing a nanoparticle comprising asphaltene into or in proximity to a tumor cell; applying photons to the nanoparticle comprising asphaltene; heating the nanoparticle comprising asphaltene.

11. The method of claim 10 wherein the nanoparticle comprises an asphaltene quantum dot.

12. The method of claim 10 wherein the nanoparticle comprises an asphaltene carbon dot.

13. The method of claim 10 wherein the photons are applied by a laser.

14. The method of claim 10 further comprising imaging the nanoparticle.

15. The method of claim 14 wherein the imaging is photothermal imaging.

16. A nanoparticle composition, the composition comprising:an oxidized asphaltene; and a functional group attached to a surface of said asphaltene.

17. The composition of claim 16 wherein said functional group comprises oxygen.

18. The composition of claim 16 wherein said functional group comprises nitrogen.

19. The composition of claim 16 wherein said functional group comprises a hydroxyl group.

20. The composition of claim 16 wherein said functional group comprises an amino group.

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