Chemical sensor with metal nanoparticles, method of making same, and method of using same to sense a target substance

Abstract

A chemical sensor including: (a) a first electrode; (b) a second electrode spatially separated from the first electrode by an electrode gap; (c) metal nanoparticles disposed within the electrode gap between the first electrode and the second electrode, the metal nanoparticles separated from each other by nanoparticle gaps; and (d) a semiconductor material disposed within the electrode gap and the nanoparticle gaps. Additionally disclosed is a method of making the chemical sensor including a metal layer forming step, which can include a dewetting step that forms the metal nanoparticles from the metal layer formed during the metal layer forming step. Further disclosed is method for sensing a target substance with the chemical sensor.

Description

CHEMICAL SENSOR WITH METAL NANOPARTICLES, METHOD OF MAKING SAME, AND METHOD OF USING SAME TO SENSE A TARGET SUBSTANCECROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 63 / 656673 filed on June 6, 2024, the content of which is relied upon and incorporated herein by reference in its entirety.TECHNICAL FIELD

[0002] The present disclosure pertains to a chemical sensor to detect a target substance, and more particularly to a chemical sensor that includes metal nanoparticles, as well as methods of making and using the same.BACKGROUND

[0003] Early detection and diagnosis of various health conditions can be beneficial. Human breath contains markers for many such health conditions. For example, concentration of ammonia in the breath can be correlated with various liver impairments. As another example, specific volatile organic compounds present in the breath might be correlated with one or more types of cancer. In short, a health condition can generate unique metabolic byproducts that are exhaled as a person breathes.

[0004] With breath containing such markers, there is a need for sensors that can detect the presence of at least one of the markers. A common example is a breathalyzer, which detects and measures the level of alcohol within the breath of a person. Another common example is a detector that detects the level of acetone within the breath of a person, which can indicate that the person is in a state of metabolic ketosis. Further, sensors to detect the presence of the SARS-CoV-2 spike protein from the breath of the person have been developed and utilized.

[0005] Prior chemical sensors have been suboptimal in various respects, including in terms of complication, cost, and performance. Therefore, there is a need in the art for improved chemical sensors, methods of making, and methods of use. The present disclosure is directed towards these, as well as other, ends.SUMMARY

[0006] In some aspects, the present disclosure provides a chemical sensor that includes metal nanoparticles and a semiconductor material disposed between two electrodes, and a method of making the chemical sensor that, in some aspects, includes forming the metal nanoparticles through a dewetting step that dewets a metal layer to form the metal nanoparticles. In some aspects, the methods described herein to make the chemical sensor are less complicated and less expensive to perform than the prior efforts. In some aspects, use of metal nanoparticles as disclosed herein obviates any need to generate porosity. Further, the methods disclosed herein are scalable.

[0007] In some aspects, disclosed is a chemical sensor comprising: a first electrode; a second electrode spatially separated from the first electrode by an electrode gap; metal nanoparticles disposed within the electrode gap between the first electrode and the second electrode, the metal nanoparticles separated from each other by nanoparticle gaps; and a semiconductor material disposed within the electrode gap and the nanoparticle gaps.

[0008] In some aspects, disclosed is a method of making a chemical sensor comprising: an electrodes forming step comprising forming a first electrode and a second electrode on a primary surface of a substrate, the first electrode and the second electrode spatially separated by an electrode gap; a metal layer forming step comprising forming a metal layer at least partially within the electrode gap; and a dewetting step comprising heating the metal layer to a dewetting temperature resulting in the formation of metal nanoparticles within the electrode gap, the metal nanoparticles separated from each other by nanoparticle gaps.

[0009] In some aspects, disclosed is a method for detecting a target substance in a fluid, the method comprising: subjecting the fluid to a chemical sensor disclosed herein, and determining whether a change in an electrical parameter of the chemical sensor is present that is characteristic of the target substance.

[0010] Additional features and advantages will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the aspects as described herein, including the detailed description which follows, the claims, as well as the appended drawings.

[0011] It is to be understood that both the foregoing general description and the following detailed description are merely exemplary and are intended to provide an overview or framework to understanding the nature and character of the claims. The accompanying drawings are included to provide a further understanding and are incorporated in and constitutea part of this specification. The drawings illustrate one or more aspects, and together with the description explain principles and operation of the various aspects.BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In the Drawings:

[0013] FIG. 1 is a cross-sectional elevation view of aspects of a chemical sensor of the present disclosure, illustrating metal nanoparticles and semiconductor material disposed between a first electrode and a second electrode;

[0014] FIG. 2 is an overhead plan view of aspects of a chemical sensor of the disclosure, illustrating a target substance interacting with the semiconductor material, which can alter current flowing between the first electrode and the second electrode;

[0015] FIG. 3 is a schematic illustration of aspects of a method of making a chemical sensor, illustrating, among other steps, an electrodes forming step during which the first electrode and the second electrode are formed, a metal layer forming step during which a metal layer is formed at least between the first electrode and the second electrode, and a dewetting step during which the metal layer physically transforms into the metal nanoparticles;

[0016] FIGs. 4A-4C, pertaining to Example 1 , are scanning electron microscope (SEM) images of metal nanoparticles formed on a silicon wafer substrate after the dewetting step of metal layers having variable thicknesses, illustrating an average characteristic largest dimension of the metal nanoparticles decreases as a function of a thickness of the metal layer decreasing; and

[0017] FIGs. 5A-5C, pertaining to Example 2, are scanning electron microscope (SEM) images of metal nanoparticles formed on a glass substrate after the dewetting step of metal layers having variable thicknesses, illustrating an average characteristic largest dimension of the metal nanoparticles decreases as a function of a thickness of the metal layer decreasing and the metal nanoparticles having a more spherical shape compared to Example 1.DETAILED DESCRIPTION

[0018] Reference will now be made in detail to the present preferred aspects, examples of which are illustrated in the accompanying drawings. Whenever possible, the same reference numerals will be used throughout the drawings to refer to the same or like parts.

[0019] Referring initially to FIG. 1, a chemical sensor 10 is herein described. The chemical sensor 10 includes a first electrode 12, a second electrode 14, metal nanoparticles 16, and a semiconductor material 18. An electrode gap 20 spatially separates the first electrode 12 fromthe second electrode 14. The metal nanoparticles 16 are disposed within the electrode gap 20. Further, nanoparticle gaps 22 separate adjacent metal nanoparticles 16. The semiconductor material 18 is disposed within the electrode gap 20 and the nanoparticle gaps 22.

[0020] In aspects, such as the aspect illustrated, the chemical sensor 10 further includes a substrate 24. The substrate 24 includes a primary surface 26. The first electrode 12 and the second electrode 14 are disposed on the primary surface 26 of the substrate 24. At least a portion of the metal nanoparticles 16 and at least a portion of the semiconductor material 18 are disposed on the primary surface 26 of the substrate 24. The primary surface 26 can be planar or approximately planar (e.g., planar within manufacturing constraints) but need not be, such that, for example, the primary surface 26 may additionally or alternatively be curved, have depressions, and / or have channels.

[0021] In aspects, such as the aspect illustrated, the first electrode 12 and the second electrode 14 are sandwiched between the substrate 24 and the semiconductor material 18. The metal nanoparticles 16 can be sandwiched between the substrate 24 and the semiconductor material 18 as well. However, in some instances, the semiconductor material 18 can be disposed over the primary surface 26 of the substrate 24 while not covering a portion (not illustrated) of at least some of the metal nanoparticles 16.

[0022] In aspects, the primary surface 26 of the substrate 24 is inert, non-conductive, or both inert and non-conductive. “Inert” for purposes of this disclosure means that the primary surface 26 of the substrate 24 is not intended to interact with a target molecule, as further discussed herein. “Non-conductive” for purposes of this disclosure means an electrical conductivity of 100 Siemens per meter (S / m) or less (e.g., an electrical resistivity of 0.01 fTm or more). Electrical conductivity is measured at 20 °C, and in accordance with ASTM 1004-17.

[0023] In aspects, the substrate 24 includes, or is made of, silicon, a glass, a glass-ceramic, a ceramic, a polymer, or any combination thereof. Suitable glass compositions include a soda lime glass, a borosilicate glass, an alkali aluminosilicate glass, an alkali aluminoborosilicate glass, an alkaline earth boro-aluminosilicate glass (e.g., Willow® glass, Coming, Inc.) among other options. Suitable ceramic compositions include AI2O3, S13N4, ZrCh / AECh, AIN, or any combination thereof. Suitable polymer materials include polydimethylsiloxane (PDMS), polyethylene terephthalate (PET), polypropylene) (PP), poly(ethylene naphthalate) (PEN), poly(ether ketone) (PEEK), poly(tetrafluoroethylene) (PTFE), or any combination thereof.

[0024] In aspects, one or both of the first electrode 12 and the second electrode 14 include a metal layer 32. The metal layer 32 can include, or be made of, gold, silver, platinum, palladium,copper, nickel, any alloy thereof, or any combination thereof. That list is not meant to be exhaustive, and other metals are envisioned, such as aluminum and / or stainless steel.

[0025] The metal nanoparticles 16 include, or are made of, a metal. The metal can be silver, gold, copper, aluminum, chromium, any alloy thereof, or any combination thereof. That list is not meant to be exhaustive, and other metals are envisioned.

[0026] In aspects, in a plane 34 parallel to the primary surface 26 of the substrate 24, the metal nanoparticles 16 have an average characteristic largest dimension 36 that is less than 2 pm. For example, the average characteristic largest dimension 36 of the metal nanoparticles 16 can be less than 100 nm, or less than 50 nm. In aspects, the average characteristic largest dimension 36 is less than 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, or 2000 nm (2 pm), or within any range bound by any two of those values (e.g., from 500 nm to 1800 nm, from 1200 nm to 1400 nm, and so on).

[0027] The average characteristic largest dimension 36 is the average cross-sectional linear dimension of the largest metal nanoparticles 16 within a viewing field parallel to the plane 34. A scanning electron microscope (SEM) can typically be used to measure dimensions of the metal nanoparticles 16. The viewing field is proportional to the largest metal nanoparticles 16, and typically has an area of approximately 30(average largest dimension)x30(average largest dimension). If, for example, the average largest dimension is approximately 10 micrometers, then the viewing field from which the twenty largest metal nanoparticles 16 are selected is approximately 300 pm x 300 pm. Slight changes in the size of the viewing field do not significantly affect the average largest dimension. The standard deviation of the twenty largest features that are used to determine the average cross-sectional linear dimension should generally be less than about 40% of the average value, i.e., major outliers should be ignored since these are not considered “characteristic” features.

[0028] Referring additionally to FIG. 2, the chemical sensor 10 and metal nanoparticles 16 exist in three dimensions. While FIG. 1 illustrates the chemical sensor 10 and metal nanoparticles 16 having a depth 40 dimension, FIG. 2 illustrates the chemical sensor 10 and metal nanoparticles 16 extending in what can be referred to as width 42 and length 44 dimensions. For example, the features such as metal nanoparticles 16 exhibit a surface area and a volume. Because of the process by which the metal nanoparticles 16 can be formed, which is discussed below, the metal nanoparticles 16 can have an approximately spherical shape. Consequently, the metal nanoparticles 16 exhibits a ratio of surface area to volume thatincreases as the dimensions of the metal nanoparticles 16 decreases drastically. The metal nanoparticles 16 occupy relatively little volume but provide relatively high surface area. That is beneficial for the purposes for which the metal nanoparticles 16 are used herein. In aspects, the metal nanoparticles 16 are at least approximately spherical and the average characteristic largest dimension can be thought of as twice the radius of the metal nanoparticles 16.

[0029] At least a portion of, if not all, the nanoparticle gaps 22 separating the metal nanoparticles 16 have a dimension 38 within a range of from 4 nm to 2 pm. The SEM can also be utilized to determine the dimension of the nanoparticle gaps 22. The dimension 38 is determined parallel to the plane 34. In aspects, the dimension 38 is 4 nm, 10 nm, 50 nm, 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, 1100 nm, 1200 nm, 1300 nm, 1400 nm, 1500 nm, 1600 nm, 1700 nm, 1800 nm, 1900 nm, 2000 nm (2 pm), or within any range bound by any two of those values (e.g., from 10 nm to 700 nm, from 1000 nm to 1900 nm, and so on).

[0030] In aspects, the first electrode 12 and the second electrode 14 each comprise fingers 46. “Fingers,” for purposes of this disclosure, means that a length 48 of a portion of the electrode 12, 14 is much greater than (e.g., at least 3 times) a width 50 (FIG. 1) of the electrode. In aspects, at least some, if not all, of the fingers 46 of the first electrode 12 are interdigitated with some of the fingers 46 of the second electrode 14. At least a portion of the fingers 46 that are adjacent to each other (e.g., the finger 46a and the finger 46b) are separated by a distance 54 that is within a range of from 100 nm to 500 pm. For example, the distance 54 can be 100 nm, 200 nm, 500 nm, 1 pm, 10 pm, 50 pm, 100 pm, 200 pm, 300 pm, 400 pm, 500 pm, or within any range bound by any two of those values (e.g., from 200 nm to 300 pm, from 100 pm to 400 pm, and so on). The distance 54 can be measured parallel to the plane 34 with the standard calibrated optical light microscope, SEM, or any other suitable method known in the art.

[0031] As mentioned, each of the fingers 46 has the length 48 and the width 50. In aspects, a ratio of the length 48 to the width 50 of at least a portion, if not all, of the fingers 46 is within a range of from 5 to 100. For example, the ratio can be 5, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, or within any range bound by any two of those values (e.g., from 20 to 60, from 10 to 80, and so on).

[0032] As mentioned, the chemical sensor 10 includes the semiconductor material 18. The semiconductor material 18 is not particularly limited in composition. In some instances, the semiconductor material 18 is an inorganic semiconductor. Examples of suitable inorganic semiconductor materials 18 include silicon, ZnO, ZnS, ZnSe, ZnTe, CdO, CdS, CdSe, CdTe, HgO, HgS, HgSe, HgTe, AIN, A1P, AlAs, AlSb, GaN, GaP, GaAs, GaSb, GaSe, InN, InP,InAs, InSb, TIN, TIP, TlAs, TISb, PbO, PbS, PbSe, PbTe, alloys thereof, mixtures thereof, or any combination thereof. In other instances, the semiconductor material 18 is an organic semiconductor. Examples of suitable organic semiconductors include heterocyclic organic compounds, such as fused thiophene compounds. More particular examples include the organic semiconductor polymers described in International Patent Application Publication No. W02020112394A1, which is incorporated herein by reference, such as:Other more particular examples include the organic semiconductor polymers described in International Patent Application Publication No. WO2020117556A1, which is incorporated herein by reference, such as:or a combination thereof. Still other more particular examples include the organic semiconductor polymers described in International Patent Application Publication No. W02020076882A1, which is incorporated herein by reference, such as:where n is at least 4, x is at least 1, and y is at least 1. Still other more particular examples include the organic semiconductor polymers described in United States Patent Application Publication No. US20220031228A1, which is incorporated herein by reference, such as:

[0033] In aspects, the metal chosen for the metal nanoparticles 16 exhibits a work function compatible with the energy level of the highest unoccupied molecular orbital of the semiconductor material 18. Such compatibility facilitates efficient charge injection, which can facilitate low voltage operation of the chemical sensor 10.

[0034] The composition of the semiconductor material 18 is selected to interact with at least one target substance 56. Examples of the at least one target substance 56 include ammonia, acetone, chloroform, ethanol, NO2, H2S, CO, or any combination thereof. The universe of suitable target substances 56 expands as research discovers new markers indicative of certain health conditions. The provided list is thus not meant to be exclusive but only exemplary. “Interact” for purposes of this disclosure means any form of interaction that causes a measurable change in one or more electrical conditions (e.g., voltage, current, and so on). The interaction may be adherence of the target substance 56 to the semiconductor material 18, for example, by any covalent or non-covalent bonding mechanism.

[0035] Referring now to FIG. 3, the present disclosure now describes a method 100 of making the chemical sensor 10. The method 100 includes an electrodes forming step 102 and a metal nanoparticle deposition step 103. In aspects, however, the method 100 begins with a substrate presentation step 110. During the substrate presentation step 110, the substrate 24 is presentedwith the primary surface 26 thereof that is configured to accept deposition of the first electrode 12 and the second electrode 14.

[0036] In some aspects, the electrodes forming step 102 includes forming the first electrode 12 and the second electrode 14 on the primary surface 26 of the substrate 24. The electrode gap 20 spatially separates the first electrode 12 from the second electrode 14. To form the first electrode 12 and the second electrode 14, a pattern (such as to provide for the interdigitation) can be defined on the primary surface 26 through a suitable lithography technique. The conductive material of the first electrode 12 and the second electrode 14 is then deposited on the primary surface 26, as patterned, such as via physical vapor deposition. A thickness 112 (see FIG. 1) of the deposited conductive material can be within a range of from 10 nm to 1 pm. For example, the thickness 112 can be 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm (1 pm), or within any range bound by any two of those values (e.g., from 50 nm to 800 nm, from 100 nm to 450 nm, and so on).

[0037] The metal nanoparticle deposition step 103 includes forming or depositing the metal nanoparticles 16 within the electrode gap 20, with the metal nanoparticles 16 separated from each other by the nanoparticle gaps 22. In some aspects, the metal nanoparticles 16 can be prepared by any known methods in the art, such as top-down and / or bottom-up approaches, and then added to the chemical sensor 10 by any known technique, such as by spraying or otherwise coating a carrier containing the nanoparticles onto the substrate 24 (e.g., containing the electrodes 12, 14 and / or the semiconductor material 18). In some aspects, the coating can be performed using the Langmuir-Blodgett technique known in the art.

[0038] In some aspects, the metal nanoparticle deposition step 103 (and thus the method 100 generally) includes a metal layer forming step 104 and a dewetting step 106. In some aspects, the metal layer forming step 104 includes forming a metal layer 114 at least partially within the electrode gap 20 between the first electrode 12 and the second electrode 14. In some aspects, the metal layer 114 can be formed as a continuous layer over the primary surface 26 so that the first electrode 12 and the second electrode 14 are sandwiched between the substrate 24 and the metal layer 32. In other aspects, metal layer 114 is not necessarily continuous but may be deposited as noncontinuous islands of material. Like the conductive material forming the first electrode 12 and the second electrode 14, the metal layer 114 can be formed via physical vapor deposition, chemical vapor deposition, sputtering, and / or other known techniques. The metal layer 114 as deposited has a thickness (orthogonal to the plane 34, inthe illustration of FIG. 3). In aspects, the thickness is within a range of from 3 nm to 100 nm. For example, the thickness can be 3 nm, 5 nm, 10 nm, 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, or within any range bound by any two of those values (e.g., from 20 nm to 50 nm, from 30 nm to 60 nm, and so on). The metal layer 32 can be silver, gold, copper, aluminum, chromium, any alloy thereof, or any combination thereof.

[0039] In some aspects, the dewetting step 106 includes heating the metal layer 114 to a dewetting temperature. Heating the metal layer 114 to the dewetting temperature causes the metal layer 114 to physically separate into discrete droplets or islands on the primary surface 26 of the substrate 24. Those discrete droplets or islands are referred to herein as the metal nanoparticles 16. The dewetting process generates the metal nanoparticles 16 with relatively large values for the surface area per unit volume, as highlighted elsewhere herein. At least a portion of the metal nanoparticles 16 form within the electrode gap 20 from the metal layer 32. Some of the metal nanoparticles 16 may form upon the first electrode 12 and the second electrode 14, as well. The metal nanoparticles 16 are separated from each other by the nanoparticle gaps 22. In aspects, the dewetting temperature is within a range of from 200 °C to 400 °C. For example, the dewetting temperature can be 200 °C, 210 °C, 220 °C, 230 °C, 240 °C, 250 °C, 260 °C, 270 °C, 280 °C, 290 °C, 300 °C, 310 °C, 320 °C, 330 °C, 340 °C, 350 °C, 360 °C, 370 °C, 380 °C, 390 °C, 400 °C, or within any range bound by any two of those values (e.g., from 230 °C to 330 °C, from 220 °C to 250 °C, and so on).

[0040] The dimensions (e.g., average characteristic largest dimension 36) of the metal nanoparticles 16 are a function of at least the thickness of the metal layer 32. The dimensions of the metal nanoparticles 16 can additionally be a function of one or more of the identity of the metal layer (e.g., silver, gold, etc.), the dewetting temperature, a dewetting time period, a composition of an atmosphere to which the metal layer 32 is exposed during the dewetting step 106, and a pressure of the atmosphere. In aspects, the dewetting time period is less than 1 hour, such as less than 10 minutes, such as less than or equal to 30 seconds, or any range formed from any two of these values, such as 30 seconds to 1 hour, 30 seconds to 10 minutes, or 10 minutes to 1 hour. The composition of the atmosphere can be air. In other instances, the composition of the atmosphere can be a gas other than air, such as O2, N2, or Ar, among other options. Flowing N2 or Ar for example can help reduce oxidation of the metal layer 32 during the dewetting step 106. The pressure of the atmosphere to which the metal layer 32 is exposed can be atmospheric pressure. In other instances, the pressure is less than atmospheric pressure, such as close to vacuum conditions. In some aspects, the atmosphere can have ambient relativehumidity, added humidity relative to ambient, or be dried so as to have a lower humidity than ambient (such as being substantially free of humidity).

[0041] However, in some aspects as mentioned, the metal layer forming step 104 and dewetting step 106 are not performed because the metal nanoparticles 16 can be prepared and deposited by other techniques known in the art.

[0042] In aspects, the method 100 further includes a semiconductor material forming step 108. In some aspects, the semiconductor material forming step 108 includes forming the semiconductor material 18. The semiconductor material 18 is formed at least within the electrode gap 20 and the nanoparticle gaps 22. The semiconductor material 18 can be applied over the primary surface 26 of the substrate 24 such that the first electrode 12, the second electrode 14, and the metal nanoparticles 16 are sandwiched between the substrate 24 and the semiconductor material 18. In some aspects, how the semiconductor material 18 is applied depends on the composition of the semiconductor material 18. The semiconductor material 18 with an inorganic composition may be formed through vapor deposition techniques. The semiconductor material 18 with an organic semiconductor composition can be deposited using, for example, solution-based methods, such as spin coating, dipping, spraying, and so forth, or any combination thereof.

[0043] In some aspects, the method 100 further includes a wire connecting step 116. During the wire connection step 116, a pair of wires 118 can be connected to the first electrode 12 and the second electrode 14, respectively, to form an electrical circuit. Any wire bonding technique can be utilized.

[0044] Although a certain order of steps is depicted in FIG. 3, it is contemplated that any order of steps may be employed. For example, in some aspects, the semiconductor material forming step 108 may take place before the metal layer forming step 104 and dewetting step 106. In some aspects, the electrodes forming step 102 may take place as the last step. All other possible variations of order of the steps 102, 103, 104, 106, 108, 110, 116 of the method 100 are contemplated.

[0045] Now made, the chemical sensor 10 can be utilized to perform a method for detecting the target substance 56 in a fluid. In particular, the method 100 includes subjecting the fluid to the chemical sensor 10. In aspects, the fluid originates from a fluid from a mammal or animal. The fluid can be primarily a liquid such as blood or saliva, or primarily a gas such as breath. The mammal can be a human, a pet (e.g., dog, cat), a farm animal (e.g., horse, cow, goat, pig, chicken), or zoo animal (e.g., gorilla, monkey, zebra, lion, tiger, bear, rhinoceros). The fluid can be made to interact with the chemical sensor 10, such as by disposing the chemical sensor10 in a housing with one or more fluid flow channels in communication with the chemical sensor 10. The fluid can be introduced into the one or more fluid flow channels to flow to the chemical sensor 10.

[0046] The method for detecting the target substance 56 further includes determining whether a change in an electrical parameter of the chemical sensor is present that is characteristic of the target substance 56. The electrical parameter can be associated with the electrical circuit. The electrical parameter can be current, among other options. The change, in present, is a function of the presence of the target substance 56 interacting with the semiconductor material 18 of the chemical sensor 10. For example, a stable current can be applied between the first electrode 12 and the second electrode 14. The fluid containing, or not containing, the target substance 56 can then be caused to flow over the semiconductor material 18. If the target substance 56 is present within the fluid, the target substance 56 interacts with the semiconductor material 18. The interaction with the semiconductor material 18 causes the current flowing through the semiconductor material 18 between the first electrode 12 and the second electrode 14 to drop. The drop is detectable and is associated with the presence of the target substance 56. Further, the magnitude of the drop can be associated with the concentration of the target substance 56 within the fluid, because the greater the number of molecules of the target substance 56 that interact with the semiconductor material 18, the greater the change in the electrical parameter (e.g., the greater the drop in the current). The presence of the metal nanoparticles 16 is believed to enable large changes in current as a function of the presence of the target substance 56. The metal nanoparticles 16 alter the charge transfer of the semiconductor material 18, improving sensitivity of the chemical sensor 10.

[0047] In some aspects, the method 100 forms the chemical sensor 10 without any isolated layers, etching processes, or both. In some aspects, the method 100 is inexpensive to perform, and scaling up of the method 100 is contemplated.

[0048] According to Aspect 1 of the present disclosure, a chemical sensor comprises (a) a first electrode; (b) a second electrode spatially separated from the first electrode by an electrode gap; (c) metal nanoparticles disposed within the electrode gap between the first electrode and the second electrode, the metal nanoparticles separated from each other by nanoparticle gaps; and (d) a semiconductor material disposed within the electrode gap and the nanoparticle gaps.

[0049] According to Aspect 2 of the present disclosure, the chemical sensor of Aspect 1 further comprises a substrate comprising a primary surface, wherein, the first electrode, the second electrode, and at least a portion of the metal nanoparticles are disposed on the primary surface of the substrate.

[0050] According to Aspect 3 of the present disclosure, the chemical sensor of Aspect 2, or any preceding Aspect, is presented, wherein the first electrode, the second electrode, and the metal nanoparticles are sandwiched between the substrate and the semiconductor material.

[0051] According to Aspect 4 of the present disclosure, the chemical sensor of any one of Aspects 2-3, or any preceding Aspect, is presented, wherein the primary surface of the substrate is inert and non-conductive.

[0052] According to Aspect 5 of the present disclosure, the chemical sensor of any one of Aspects 2-4, or any preceding Aspect, is presented, wherein the substrate comprises silicon, a glass, a glass-ceramic, a ceramic, a polymer, or any combination thereof.

[0053] According to Aspect 6 of the present disclosure, the chemical sensor of any one of Aspects 2-5, or any preceding Aspect, is presented, wherein in a plane parallel to the primary surface of the substrate, the metal nanoparticles have an average largest characteristic dimension that is less than 2 pm.

[0054] According to Aspect 7 of the present disclosure, the chemical sensor of Aspect 6, or any preceding Aspect, is presented, wherein the average characteristic largest dimension of the metal nanoparticles is less than 100 nm.

[0055] According to Aspect 8 of the present disclosure, the chemical sensor of Aspect 6, or any preceding Aspect, is presented, wherein the average characteristic largest dimension of the metal nanoparticles is less than 50 nm.

[0056] According to Aspect 9 of the present disclosure, the chemical sensor of any one of Aspects 1-8, or any preceding Aspect, is presented, wherein the first electrode and the second electrode each comprise a metal layer.

[0057] According to Aspect 10 of the present disclosure, the chemical sensor of Aspect 9, or any preceding Aspect, is presented, wherein the metal layer comprises gold, silver, platinum, palladium, copper, nickel, any alloy thereof, or any combination thereof.

[0058] According to Aspect 11 of the present disclosure, the chemical sensor of any one of Aspects 1-10, or any preceding Aspect, is presented, wherein the metal nanoparticles comprise a metal.

[0059] According to Aspect 12 of the present disclosure, the chemical sensor of any one of Aspects 1-11, or any preceding Aspect, is presented, wherein the metal nanoparticles comprise silver, gold, copper, aluminum, chromium, any alloy thereof, or any combination thereof.

[0060] According to Aspect 13 of the present disclosure, the chemical sensor of any one of Aspects 1-12, or any preceding Aspect, is presented, wherein at least a portion of the nanoparticle gaps have a dimension within a range of from 4 nm to 2 pm.

[0061] According to Aspect 14 of the present disclosure, the chemical sensor of any one of Aspects 1-13, or any preceding Aspect, is presented, wherein (i) the first electrode and the second electrode each comprise fingers, and (ii) at least some the fingers of the first electrode are interdigitated with at least some of the fingers of the second electrode.

[0062] According to Aspect 15 of the present disclosure, the chemical sensor of Aspect 14, or any preceding Aspect, is presented, wherein at least a portion of adjacent fingers are separated from each other by a distance that is within a range of from 100 nm to 500 pm.

[0063] According to Aspect 16 of the present disclosure, the chemical sensor of any one of Aspects 14-15, or any preceding Aspect, is presented, wherein (i) each of the fingers comprises a length and a width, and (ii) a ratio of the length to the width of at least a portion of the fingers is within a range of from 5 to 100.

[0064] According to Aspect 17 of the present disclosure, the chemical sensor of any one of Aspects 1-16, or any preceding Aspect, is presented, wherein the semiconductor material comprises an inorganic semiconductor.

[0065] According to Aspect 18 of the present disclosure, the chemical sensor of any one of Aspects 1-16, or any preceding Aspect, is presented, wherein the semiconductor material comprises an organic semiconductor.

[0066] According to Aspect 19 of the present disclosure, the chemical sensor of any one of Aspects 1-18, or any preceding Aspect, is presented, wherein a composition of the semiconductor material is selected to interact with at least one target substance.

[0067] According to Aspect 20 of the present disclosure, the chemical sensor of Aspect 19, or any preceding Aspect, is presented, wherein the target substance is ammonia, acetone, chloroform, ethanol, NO2, H2S, CO, or any combination thereof.

[0068] According to Aspect 21 of the present disclosure, a method of making a chemical sensor comprises: (a) an electrodes forming step comprising forming a first electrode and a second electrode on a primary surface of a substrate, the first electrode and the second electrode spatially separated by an electrode gap; and (b) a metal nanoparticle deposition step comprising forming or depositing metal nanoparticles within the electrode gap, the metal nanoparticles separated from each other by nanoparticle gaps.

[0069] According to Aspect 22 of the present disclosure, the method of Aspect 21, or any preceding Aspect, is presented, wherein the metal nanoparticle deposition step comprises: (i) a metal layer forming step comprising forming a metal layer at least partially within the electrode gap; and (ii) a dewetting step comprising heating the metal layer to a dewetting temperature resulting in the formation of the metal nanoparticles within the electrode gap.

[0070] According to Aspect 23 of the present disclosure, the method of Aspect 22, or any preceding Aspect, is presented, wherein the dewetting temperature to which the metal layer is heated during the dewetting step is within a range of from 200 °C to 400 °C.

[0071] According Aspect 24 of the present disclosure, the method of any one of Aspects 22-23, or any preceding Aspect, is presented, wherein the metal layer formed during the metal layer forming step comprises a thickness within a range of from 3 nm to 100 nm.

[0072] According to Aspect 25 of the present disclosure, the method of any one of Aspects 21-24, or any preceding Aspect, further comprises a semiconductor material forming step comprising forming a semiconductor material within the electrode gap and the nanoparticle gaps.

[0073] According to Aspect 26 of the present disclosure, a method for detecting a target substance in a fluid, the method comprises: (a) subjecting the fluid to the chemical sensor of any one of first through twentieth aspects, and (b) determining whether a change in an electrical parameter of the chemical sensor is present that is characteristic of the target substance.

[0074] According to Aspect 27 of the present disclosure, the method of Aspect 26, or any preceding Aspect, is presented, wherein the change, if present, is a function of presence of the target substance interacting with the semiconductor material of the chemical sensor.

[0075] According to Aspect 28 of the present disclosure, the method of any one of Aspects 25- 26, or any preceding Aspect, is presented, wherein the fluid originates from a mammal or animal.

[0076] EXAMPLES

[0077] Example 1 - For Example 1, the metal layer forming step and the dewetting step of the method of the present disclosure were performed on three substrates, all of which silicon wafers, thus resulting in three samples (Samples 1A-1C). The composition of the metal (particularly Ag) for the metal layer forming step was identical for the three samples. The dewetting step for all three samples was performed at ambient pressure, at a dewetting temperature of 300 °C, which was obtained at a ramp rate of 10 C / min, and for a dewetting time at the dewetting temperature of 30 minutes. However, the thickness of the metal layer applied during the metal layer forming step was sequentially decreased. For Sample 1 A, the thickness of the metal layer was 14 nm. For Sample IB, the thickness of the metal layer was 8 nm. For Sample 1C, the thickness of the metal layer was 4 nm. SEM images were then captured for each of the Samples 1 A-1C after the dewetting step, each image having the same magnification. The images are reproduced at FIGs. 4A-4C. The images reveal that the average characteristic largest dimension of the metal nanoparticles generated from the dewetting stepdecreases as the thickness of the metal layer generated during the metal layer forming step decreases. Consequently, the thickness of the metal layer affects the density of the metal nanoparticles, which in turn affects the sensitivity of the chemical sensor.

[0078] Example 2 - For Example 2, the metal layer forming step and the dewetting step of the method of the present disclosure were performed on three glass substrates, all of which had the same alkaline earth boro-aluminosilicate composition (EagleXG®), thus resulting in three samples (Samples 2A-2C). The composition of the metal (again Ag) for the metal layer forming step was identical for the three samples. The dewetting step for all three samples was performed at ambient pressure, at a dewetting temperature of 300 °C, which was obtained at a ramp rate of 10 C / min, and for a dewetting time at the dewetting temperature of 30 minutes. However, the thickness of the metal layer applied during the metal layer forming step was sequentially decreased. For Sample 2A, the thickness of the metal layer was 15 nm. For Sample 2B, the thickness of the metal layer was 10 nm. For Sample 2C, the thickness of the metal layer was 5 nm. SEM images were then captured for each of the Samples 2A-12 after the dewetting step, each image having the same magnification. The SEM images are reproduced at FIGs. 5A-5C. The images reveal that the average characteristic largest dimension of the metal nanoparticles generated from the dewetting step decreases as the thickness of the metal layer generated during the metal layer forming step decreases. Consequently, the thickness of the metal layer affects the density of the metal nanoparticles, which in turn affects the sensitivity of the chemical sensor. In addition, the images reveal, when compared to the images of FIGs. 4A-4C, that the composition of the substrate affects the shape of the metal nanoparticles formed by the dewetting step, with the glass composition of Example 2 resulting in a more spherical shape. As discussed herein, as the shape of the metal nanoparticles approaches a spherical shape, the surface area to volume ratio increases, which increases the sensitivity of the chemical sensor employing the metal nanoparticles.

[0079] It will be apparent to those skilled in the art that various modifications and variations can be made without departing from the spirit or scope of the claims.

Claims

CLAIM(S)What is claimed is:

1. A chemical sensor comprising: a first electrode; a second electrode spatially separated from the first electrode by an electrode gap; metal nanoparticles disposed within the electrode gap between the first electrode and the second electrode, the metal nanoparticles separated from each other by nanoparticle gaps; and a semiconductor material disposed within the electrode gap and the nanoparticle gaps.

2. The chemical sensor of claim 1 further comprising: a substrate comprising a primary surface, wherein, the first electrode, the second electrode, and at least a portion of the metal nanoparticles are disposed on the primary surface of the substrate.

3. The chemical sensor of claim 2, wherein the first electrode, the second electrode, and the metal nanoparticles are sandwiched between the substrate and the semiconductor material.

4. The chemical sensor of any one of claims 2-3, wherein the primary surface of the substrate is inert and non-conductive.

5. The chemical sensor of any one of claims 2-4, wherein the substrate comprises silicon, a glass, a glass-ceramic, a ceramic, a polymer, or any combination thereof.

6. The chemical sensor of any one of claims 2-5, wherein in a plane parallel to the primary surface of the substrate, the metal nanoparticles have an average largest characteristic dimension that is less than 2 pm.

7. The chemical sensor of claim 6, wherein the average characteristic largest dimension of the metal nanoparticles is less than 100 nm.

8. The chemical sensor of claim 6, wherein the average characteristic largest dimension of the metal nanoparticles is less than 50 nm.

9. The chemical sensor of any one of claims 1-8, wherein the first electrode and the second electrode each comprise a metal layer.

10. The chemical sensor of claim 9, wherein the metal layer comprises gold, silver, platinum, palladium, copper, nickel, any alloy thereof, or any combination thereof.

11. The chemical sensor of any one of claims 1-10, wherein the metal nanoparticles comprise a metal.

12. The chemical sensor of any one of claims 1-11, wherein the metal nanoparticles comprise silver, gold, copper, aluminum, chromium, any alloy thereof, or any combination thereof.

13. The chemical sensor of any one of claims 1-12, wherein at least a portion of the nanoparticle gaps have a dimension within a range of from 4 nm to 2 pm.

14. The chemical sensor of any one of claims 1-13, wherein the first electrode and the second electrode each comprise fingers, and at least some the fingers of the first electrode are interdigitated with at least some of the fingers of the second electrode.

15. The chemical sensor of claim 14, wherein at least a portion of adjacent fingers are separated from each other by a distance that is within a range of from 100 nm to 500 pm.

16. The chemical sensor of any one of claims 14-15, wherein each of the fingers comprises a length and a width, anda ratio of the length to the width of at least a portion of the fingers is within a range of from 5 to 100.

17. The chemical sensor of any one of claims 1-16, wherein the semiconductor material comprises an inorganic semiconductor.

18. The chemical sensor of any one of claims 1-16, wherein the semiconductor material comprises an organic semiconductor.

19. The chemical sensor of any one of claims 1-18, wherein a composition of the semiconductor material is selected to interact with at least one target substance.

20. The chemical sensor of claim 19, wherein the target substance is ammonia, acetone, chloroform, ethanol, NO2, H2S, CO, or any combination thereof.

21. A method of making a chemical sensor comprising: an electrodes forming step comprising forming a first electrode and a second electrode on a primary surface of a substrate, the first electrode and the second electrode spatially separated by an electrode gap; and a metal nanoparticle deposition step comprising forming or depositing metal nanoparticles within the electrode gap, the metal nanoparticles separated from each other by nanoparticle gaps.

22. The method of claim 21, wherein the metal nanoparticle deposition step comprises: a metal layer forming step comprising forming a metal layer at least partially within the electrode gap; and a dewetting step comprising heating the metal layer to a dewetting temperature resulting in the formation of the metal nanoparticles within the electrode gap.

23. The method of claim 22, wherein the dewetting temperature to which the metal layer is heated during the dewetting step is within a range of from 200 °C to 400 °C.

24. The method of any one of claims 22-23, wherein the metal layer formed during the metal layer forming step comprises a thickness within a range of from 3 nm to 100 nm.

25. The method of any one of claims 21-24 further comprising: a semiconductor material forming step comprising forming a semiconductor material within the electrode gap and the nanoparticle gaps.

26. A method for detecting a target substance in a fluid, the method comprising: subjecting the fluid to the chemical sensor of any one of claims 1-20, and determining whether a change in an electrical parameter of the chemical sensor is present that is characteristic of the target substance.

27. The method of claim 26, wherein the change, if present, is a function of presence of the target substance interacting with the semiconductor material of the chemical sensor.

28. The method of any one of claims 26-27, wherein the fluid originates from a mammal or animal.

Images