An ultra-trace heavy metal ion detection chip based on quantum capacitance density fingerprint and a detection method thereof

Abstract

The application discloses a kind of based on quantum capacitance state density fingerprint trace heavy metal ion detection chip and its detection method, the trace heavy metal ion detection chip includes: surface insulation substrate;Two-dimensional material working layer is distributed on the surface of substrate;Part of the edge of two-dimensional material working layer is compounded and extends to the edge of substrate Metal electrode and lead wire;Covered on substrate and has micron level rectangular hole in the center position of two-dimensional material working layer Insulating dielectric layer;Micro well with through hole;Reference electrode and counter electrode, inserted into electrolyte in micro well, with metal electrode constitutes three electrode system.The detection chip of the application can directly read out the change of local electronic state density near fermi level caused by heavy metal ion adsorption, obtain DOS fingerprint such as defect peak in band gap, band edge slope, effective band gap, multi-signal cooperative verification greatly improves anti-interference ability and quantitative accuracy, breaks through detection sensitivity bottleneck.

Description

Technical Field

[0001] This invention belongs to the field of material testing or analysis through capacitance testing, specifically relating to an ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprint and its detection method. Background Technology

[0002] Heavy metal ions, such as chromium ions, are used extensively in industrial production processes such as electroplating, mining, and dyeing. Their long-term accumulation and migration in the aquatic environment can cause significant harm to ecosystems and human health. Therefore, accurate detection of their concentration is of great importance. Existing analytical methods, such as atomic absorption spectrometry and inductively coupled plasma mass spectrometry, can achieve low detection limits, but they rely on large-scale experimental equipment, are costly, and have complex operating procedures, making it difficult to meet the needs of rapid on-site detection and long-term online monitoring.

[0003] In recent years, electrochemical and optical sensors based on microfabricated chips have attracted widespread attention. By constructing functionalized interfaces on the chip, the adsorption of target ions can be converted into changes in channel current, interface potential, or optical signals. However, the signals of such single scalar readout methods are often affected by multiple factors, such as carrier transport processes, interfacial reaction kinetics, electrolyte conductivity, and background noise. Under complex environments and extremely low concentration conditions, the weak electronic state changes caused by adsorption are easily submerged, making it difficult to simultaneously achieve optimal detection limit, linear stability, and anti-interference capability.

[0004] Density of states (DOS) describes the number of quantum states that an electron can occupy within a unit energy range. Theoretically, it is possible to directly capture the fingerprint information of material changes at the electronic structure level based on the material's DOS, thus opening up new possibilities for achieving ultra-high sensitivity and strong anti-interference selectivity concentration monitoring in the field. However, there is currently a lack of mature solutions for chip-level, energy-resolved metal ion detection. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art by providing an ultra-trace heavy metal ion detection chip and its detection method based on quantum capacitance density of state fingerprint. The heavy metal ion detection chip has a simple structure and can directly read the DOS near the Fermi level in a conductive electrolyte, and use the difference in DOS before and after adsorption as an electronic density of state fingerprint for ultra-trace metal ion detection.

[0006] The first aspect of this invention provides an ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprinting, the ultra-trace heavy metal ion detection chip comprising: At least a surface-insulated substrate; A two-dimensional material working layer distributed on the surface of the substrate and located in the middle of the substrate; Metal electrodes and leads that are partially composited with the edge of the two-dimensional material working layer and extend to the edge of the substrate; An insulating dielectric layer covering the substrate and having a micron-sized rectangular hole at the center of the two-dimensional material working layer; A microwell with through holes, one end of which is bonded to an insulating dielectric layer and surrounded by a micron-sized rectangular hole, is used to hold electrolyte. The reference electrode and the counter electrode are inserted into the electrolyte in the microwell, forming a three-electrode system with the metal electrode for quantum capacitance testing.

[0007] According to the above scheme, the substrate is a silicon wafer, glass substrate, ceramic substrate, or flexible polymer film with an insulating dielectric layer, used to support subsequent device structures. Preferably, the substrate is a silicon wafer with a silicon dioxide layer, the thickness of which is 50~500nm, to ensure compatibility with conventional microscopy characterization and reduce parasitic capacitance.

[0008] According to the above scheme, the two-dimensional material working layer is a two-dimensional semiconductor material layer or a two-dimensional conductive material layer with tunable Fermi level, selected from one or more of MoS2, WS2, MoSe2, WSe2, InSe, GaSe, black phosphorus, graphene, and MXene.

[0009] According to the above scheme, the insulating dielectric layer with micron-sized rectangular holes is selected from one or more of polyimide, parylene, SiO2, Al2O3, HfO2, SiNx, polymethyl methacrylate (PMMA), and photoresist SU-8, with a thickness of 0.5~100μm, and the length and width of the micron-sized rectangular holes are 2~1000μm.

[0010] According to the above scheme, the microwell material is selected from one of the following: silicone rubber, thermoplastic elastomers based on total polystyrene (TPS), thermoplastic elastomers based on total polyolefin (TPO), thermoplastic elastomers based on total polyurethane (TPU), thermoplastic elastomers based on total polyamide (TPAE), PDMS (polydimethylsiloxane), PMMA, PC, and PI. The microwell is bonded to an insulating dielectric layer to form a micro-electrolytic cell. Its inner diameter and height are designed to accommodate the electrolyte and insert the reference electrode and counter electrode.

[0011] According to the above scheme, the electrolyte is an ion-conducting electrolyte that can form an electrical double layer and maintain electrochemical stability within -3~3V (a predetermined bias voltage scanning range). It is selected from one or a combination of several of the following: aqueous electrolytes (e.g., deionized water or aqueous solutions containing supporting electrolytes), acid / alkali solutions (e.g., sulfuric acid solutions), metal ion salt solutions, buffer solutions, polymer electrolytes, ionic liquids, gel electrolytes, molten salts, and liquid metal-based conductive media.

[0012] Preferably, the electrolyte is an ionic liquid selected from 1-ethyl-3-methylimidazolium tetrafluoroborate, 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, 1-ethyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide, N-butylpyridine bis(trifluoromethanesulfonyl)imide, 1-octyl One or more of the following: 3-methylimidazolium tetrafluoroborate, 1-octyl-3-methylimidazolium hexafluorophosphate, 1-decyl-3-methylimidazolium tetrafluoroborate, N-butylpyridine tetrafluoroborate, N-butylpyridine hexafluorophosphate, N-methyl-N-butylpyrrolidine bis(trifluoromethyl)sulfonylimide, N-methyl-N-butylpiperidine bis(trifluoromethyl)sulfonylimide, tetraethylammonium tetrafluoroborate, and tetraethylammonium bis(trifluoromethyl)sulfonylimide.

[0013] According to the above scheme, the reference electrode is selected from one of a saturated calomel electrode, a silver / silver ion electrode, a silver / silver chloride electrode, or a platinum / gold quasi-reference electrode; the counter electrode is one of a platinum, gold, carbon rod, graphite, glassy carbon, or carbon cloth electrode.

[0014] A second aspect of this invention provides a method for fabricating the aforementioned ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprinting, comprising the following steps: 1) The substrate is ultrasonically cleaned in acetone, isopropanol and deionized water in sequence for 1 to 30 minutes each time. After cleaning, the surface is dried with nitrogen and then baked to remove surface moisture, resulting in a clean and dry substrate. 2) Preparation of two-dimensional material working layer: Two-dimensional material layer is prepared by mechanical exfoliation, chemical vapor deposition, molecular beam epitaxy, solution method or combination thereof, and the two-dimensional material layer is set on the substrate surface by dry transfer, wet transfer or direct growth method to obtain two-dimensional material working layer; 3) Fabrication of metal electrodes and leads: Metal electrode and lead patterns are formed on the substrate using photolithography and metal deposition-lift technology. The electrode and lead patterns partially cover the two-dimensional material working layer, and the remaining part extends outside the two-dimensional material working layer area (for external electrical connection). An adhesion layer and a conductive layer are sequentially deposited on the substrate where the electrode and lead patterns are formed. Then, the conductive layer in the non-electrode and lead pattern area is removed using a photolithographic lift-off process to obtain metal electrodes and leads that are electrically connected to the two-dimensional material working layer. 4) Forming an insulating dielectric layer and openings: Spin-coating, depositing or laminating an insulating dielectric layer material on the substrate surface after the metal electrode and lead fabrication are completed in step 3), and forming micron-sized openings at predetermined positions of the corresponding two-dimensional material working layer by photolithography, etching, laser processing or a combination thereof, to obtain an insulating dielectric layer with openings; 5) Fabrication of ultra-trace heavy metal ion detection chip: When quantum capacitance testing is required, micro-wells with through holes are bonded on the insulating dielectric layer. The micro-wells surround the micron-sized rectangular holes to hold the electrolyte and limit the electrolyte volume and reaction area. A reference electrode and a counter electrode are inserted into the electrolyte to form a three-electrode system with the metal electrode for quantum capacitance testing.

[0015] A third aspect of this invention provides a method for detecting heavy metal ions using the aforementioned ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprinting, the specific steps of which are as follows: S1. First, prepare a series of heavy metal ion solutions of different concentrations and set up a blank control group (deionized water without heavy metal ions). Sequentially contact the micron-sized rectangular holes of the ultra-trace heavy metal ion detection chip with the heavy metal ion solutions of different concentrations, allowing the heavy metal ions to be adsorbed on the surface of the two-dimensional material working layer. Each heavy metal ion solution is adsorbed for the same time, with the adsorption time set to 5-120 minutes. After adsorption, rinse the surface of the ultra-trace heavy metal ion detection chip with deionized water (to remove unadsorbed ions), then dry the surface to remove residual moisture. Next, install a microwell for quantum capacitance testing, injecting electrolyte into the microwell. Through three... The electrode system is connected to an external electrochemical workstation to apply a scanning DC bias voltage to the ultra-trace heavy metal ion detection chip and superimpose a small signal AC excitation. The impedance is measured to calculate the quantum capacitance and plot the quantum capacitance-potential spectrum. The abscissa of the quantum capacitance-potential spectrum is converted from the electrochemical potential to the energy coordinate relative to the vacuum energy level to obtain the quantum capacitance-energy spectrum. DOS fingerprint feature parameters are extracted from it. After each test, the surface of the detection chip is cleaned and the electrolyte is replaced. The DOS fingerprint feature parameters measured by heavy metal ion solutions of different concentrations are correlated with the metal ion concentration to obtain the concentration-DOS fingerprint feature parameter standard curve. S2. The micron-sized rectangular hole of the ultra-trace heavy metal ion detection chip is brought into contact with the aqueous solution containing heavy metal ions. The DOS fingerprint feature parameters are tested using the same method as in S1, and compared with the concentration-DOS fingerprint feature parameter standard curve obtained in step S1 to obtain the concentration of heavy metal ions in the aqueous solution.

[0016] According to the above scheme, the heavy metal ion mentioned in step S1 is Cr 3+ Hg 2+ Cd 2+ Pb 2+ Cu 2+ Zn 2+ Ni 2+ Mn 2+ Co 2+ As 3+ As 5+ 、Tl + 、Tl3+ Sn² + Mo 4+ V³ + Ta 5+ 、Nb 5+ Zr 4+ Ga³ + In³ + One or more of the heavy metal ions, with a solution concentration of 10. -21 ~10 -5 mol / L.

[0017] According to the above scheme, the DC bias scanning range in step S1 is -3~3V, and it is located within the electrochemical stability window of the electrolyte. The small-signal AC excitation is a sinusoidal voltage with an amplitude of 1~200mV, and the test frequency is single-frequency or multi-frequency (e.g., 0.1~10). 4 Hz).

[0018] According to the above scheme, the DOS fingerprint feature parameters in step S1 include one or more of the following: peak value of defect peaks within the bandgap (such as IG1, IG2, CB1), peak position of defect peaks within the bandgap, slope of valence band edge / conduction band edge (such as VB edge, CB edge slope), and effective bandgap width (or width of low density of states region). Optionally, auxiliary parameters such as peak area, peak width, and peak number can also be extracted, and each feature parameter can be fitted with ion concentration (preferably the logarithm of concentration) to construct a concentration-DOS fingerprint standard curve, realizing multi-parameter joint quantitative detection. The error risk caused by single feature drift / noise is reduced through multi-parameter joint calibration.

[0019] Two-dimensional semiconductor materials, especially monolayer molybdenum disulfide, possess atomic-level thickness and tunable band structures. The adsorption of even a small number of ions on their surface can cause significant changes in local electronic state density. Since quantum capacitance is directly related to state density, this invention designs a chip with a simple structure to accurately reflect the changes in local electronic states caused by the adsorption of a small number of metal ions on the surface of monolayer molybdenum disulfide. This is achieved by testing the changes in multi-signal DOS fingerprint characteristic parameters, including peaks within the band gap, band edge slope, and effective band gap. This reduces the detection limit to 10-1. -21 At mol / L, a single quantum capacitance test can obtain multiple independent and mutually corroborating DOS fingerprint feature parameters. Within the test range, each parameter is strongly linearly correlated with the logarithm of the ion concentration. Compared with a single current or potential signal, multi-signal collaborative verification significantly improves anti-interference capability and quantitative accuracy. The quantitative results are more accurate, have better linearity, and are more resistant to background interference, solving the problem of signals being easily submerged at low concentrations.

[0020] The beneficial effects of this invention are as follows: 1. The ultra-trace heavy metal ion detection chip based on quantum capacitance density of states fingerprint provided by this invention achieves energy-resolved readout of interface density of states in an electrolyte environment, constructs a multi-signal DOS fingerprint, and realizes ultra-trace, high-sensitivity detection of metal ion concentration and valence state. Compared with a single scalar signal, it has higher redundancy and cross-verification capability, overcomes the shortcomings of existing technologies such as errors caused by drift / noise of a single scalar signal and poor integration, and also has the advantages of simple structure, small size, and integration with other microsystems (such as microfluidics), making it suitable for mass production and having the application potential for developing portable detection devices. The monitoring chip based on DOS fingerprint feature parameters has good scalability in material selection and ion type, providing a foundation for constructing multi-ion and multi-fingerprint two-dimensional material electronic state maps. 2. The detection method of this invention is carried out in two steps. First, metal ions are adsorbed in an aqueous solution, and then quantum capacitance testing is performed in an electrolyte. The adsorption process and electrochemical readout process can be designed and optimized separately, while avoiding multi-signal interference when performing fine impedance testing directly in the metal ion solution, thus improving the test stability. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the ultra-trace heavy metal ion detection chip of Embodiment 1 of the present invention. Reference numerals: 1-substrate; 2-insulating layer; 3-metal electrode; 4-monolayer molybdenum disulfide working layer; 5-insulating dielectric layer; 6-electrolyte; 7-counter electrode; 8-reference electrode; 9-elastic microwell. Figure 2 This is a schematic diagram of the fabrication process of the ultra-trace heavy metal ion detection chip in Example 1; Figure 3 This is a schematic diagram showing the charge distribution and quantum capacitance changes of a single layer of molybdenum disulfide before and after metal ion adsorption in the ultra-trace heavy metal ion detection chip of Example 1. Figure 4 For different concentrations of Cr in Example 1 3+ Quantum capacitance-energy spectrum obtained from solution testing; Figure 5 The peak values ​​of defects within the bandgap (IG1, IG2, CB1), valence band slope, conduction band slope, and effective bandgap width in the quantum capacitance-energy spectrum of Example 1 are related to Cr. 3+ Concentration standard curve. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solution of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0023] Example 1 A schematic diagram of an ultra-trace heavy metal ion detection chip based on quantum capacitance density fingerprinting is shown below. Figure 1 As shown, the detection chip mainly includes: a substrate 1 with an insulating layer 2, a single-layer molybdenum disulfide working layer 4, a metal electrode 3, an insulating dielectric layer 5, an elastic microwell 9, a reference electrode 8, and a counter electrode 7.

[0024] A monolayer molybdenum disulfide working layer 4 is disposed on the substrate surface and located in the middle of the substrate, serving as the working interface in electrochemical testing. The metal electrode 3 is partially composited with the monolayer molybdenum disulfide working layer 4 to form an ohmic contact, and extends to the outside of the chip via leads as a working electrode.

[0025] The insulating dielectric layer 5 almost completely covers the substrate 1, with only micron-sized rectangular pores (4μm × 6μm) on the pre-designed monolayer molybdenum disulfide working layer 4. The insulating dielectric layer 5 defines the effective area for electrochemical reactions and metal ion adsorption. One end of an elastic microwell 9 with through holes is attached to the insulating dielectric layer 5 and surrounds the micron-sized rectangular pores. It is used to hold the electrolyte 6 to construct a micro-electrolytic cell. The reference electrode 8 and the counter electrode 7 are inserted into the electrolyte in the elastic microwell 9, forming a three-electrode system with the metal electrode 3 for quantum capacitance testing.

[0026] The fabrication method of the ultra-trace heavy metal ion detection chip based on quantum capacitance density fingerprinting in this embodiment includes the following steps, and the fabrication process is illustrated in the schematic diagram below. Figure 2 As shown: (1) Substrate preparation: A silicon wafer with a silicon dioxide layer on the surface (SiO2 / Si substrate, 2cm×2cm) was selected as the substrate. The SiO2 thickness was 300nm to be compatible with conventional microscopic characterization and reduce parasitic capacitance. The SiO2 / Si substrate was ultrasonically cleaned in acetone, isopropanol and deionized water in sequence for 5min each time. After being dried with nitrogen, it was baked on a hot plate at 100℃ for 5min to remove surface moisture and obtain a clean and dry substrate. (2) Preparation of a single layer of molybdenum disulfide working layer: Multiple layers of MoS2 (single or few layers) are peeled off from the blocky natural molybdenum disulfide crystal using adhesive tape. A silicon wafer is used to imprint the tape with the layers of MoS2. A silicon wafer with a single layer of MoS2 is selected. Then, under a microscope, a PC film (made by dissolving 1 part by mass of polycarbonate in 2 parts by mass of dichloromethane and then pressing and scraping the film with two glass slides) is used to adhere the single layer of MoS2 on the silicon wafer. The film is aligned with the SiO2 / Si substrate surface and bonded at 170°C (to dissolve the PC film). After standing for 4 hours, the single layer of MoS2 is dry-transferred to the substrate. Then, it is cleaned with dichloromethane, acetone and isopropanol in sequence to remove residual polymers, and a single layer of MoS2 with a complete morphology in the central region of the substrate is obtained as the reaction area of ​​the subsequent device. (3) Preparation of metal electrodes and leads: Positive photoresist LOR 3A was spin-coated onto a substrate with a monolayer molybdenum disulfide working layer. The spin-coating was first performed at 500 rpm for 20 s, followed by 2000 rpm for 50 s, with a spin-coating thickness of 0.8~2.2 μm. After spin-coating, the substrate was placed on a hot plate at 160℃ for 5 min to evaporate the solvent. Then, positive photoresist S1813 was spin-coated, first at 500 rpm for 20 s, followed by 2000 rpm for 50 s, to obtain a photoresist layer with a thickness of about 2-8 μm. The substrate was then placed on a hot plate at 100℃ for 1 min to evaporate the solvent. The substrate was then exposed using a photolithography exposure device. Through the development step, a pattern opening for external metal electrodes and leads was formed on one side of the monolayer MoS2 (see the shape). Figure 2 In the "photolithography and development" step, one end of the pattern covers the monolayer MoS2 region, and the other end extends into the bare SiO2 region to facilitate subsequent probe contact. An adhesion layer and a conductive layer are sequentially deposited on the substrate forming the pattern opening. The adhesion layer is Ti with a thickness of 15 nm, and the conductive layer is Au with a thickness of 50 nm. After metal deposition, the substrate is immersed in acetone for 1 hour and then gently sonicated to complete the photoresist stripping, removing the metal from the non-patterned areas, retaining only the Au electrode and external leads in contact with MoS2. Figure 2 In the steps of "preparing the external electrode" and "removing the adhesive with acetone", a working electrode with a well-defined structure is obtained: a monolayer of MoS2 as the channel and Au as the external electrode connection port; (4) Spin-coating the insulating dielectric layer and opening a micron-sized rectangular hole at the center of the monolayer molybdenum disulfide working layer: Spin-coating epoxy-based negative photoresist SU-8 onto the substrate surface after the metal electrode and lead fabrication in step (3), the spin-coating speed is 1000 rpm, corresponding to a thickness of about 2 μm after curing, heating at 95℃ for 2.5 min to pre-cur SU-8, transferring the mask pattern to the SU-8 surface through photolithography alignment, exposure and development processes, and opening a 4 μm × 6 μm micron-sized rectangular hole at the center of the corresponding monolayer molybdenum disulfide working layer ( Figure 2 The "photolithography windowing" step exposes the target area of ​​the monolayer molybdenum disulfide working layer. Then, it is heated at 95°C for 1-5 minutes to completely solidify SU-8 to form an insulating dielectric layer. The substrate surface, except for the micron-sized rectangular holes, is covered by the insulating dielectric layer to limit the electrochemical reaction area and reduce parasitic capacitance and leakage channels. (5) PMMA microwell and three-electrode configuration: When quantum capacitance testing is required, a PMMA microwell with through holes (6 mm inner diameter and 5 mm height) is pasted on the insulating dielectric layer to further limit the electrolyte volume and reaction area. A silver / silver ion electrode is inserted into the electrolyte as a reference electrode, and a carbon rod electrode is inserted as a counter electrode.

[0027] Figure 3This illustration demonstrates the multi-signal state density fingerprint sensing mechanism of the ultra-trace heavy metal ion detection chip based on monolayer MoS2 quantum capacitance in this embodiment. (a) is a schematic diagram of the intrinsic monolayer MoS2 crystal structure, exhibiting an S-Mo-S three-atom-layer sandwich configuration and a regular hexagonal lattice, where no coordination adsorption occurs on the surface; (b) shows the adsorption of Cr... 3+ Schematic diagram of charge reconstruction after Cr 3+ Located at the central site of the six-membered ring of MoS2, it forms coordination with surrounding atoms. The yellow isosurface in the figure represents the charge accumulation region, and the cyan isosurface represents the charge depletion region, indicating that electrons undergo significant rearrangement between Cr-S-Mo, thereby introducing new impurity energy levels within the band gap and perturbing the band edge state density; (c) is the quantum capacitance spectrum without adsorbed metal ions. By scanning the DC bias voltage and superimposing a small AC excitation in the three-electrode system, the quantum capacitance-potential spectrum is obtained. At this time, the quantum capacitance value within the band gap is low, and it only rises smoothly near the top of the valence band and the bottom of the conduction band; (d) is the adsorbed metal ion Cr 3+ The quantum capacitance spectrum shows new characteristic peaks within the band gap and the band edge rises steeper. Therefore, multiple DOS fingerprint feature parameters, such as the peak value, peak position, band edge slope, and effective band gap width, can be extracted simultaneously in the same device. The feature parameters are then calibrated with the metal ion concentration to achieve multi-signal, high-sensitivity density of states fingerprint detection of trace metal ions.

[0028] The specific steps of the heavy metal ion detection method using the aforementioned quantum capacitance state density fingerprint-based ultra-trace heavy metal ion detection chip are as follows: S1. First, dissolve chromium chloride in deionized water to prepare a series of Cr solutions with different concentrations. 3+ Solution (10) -20 mol / L, 10 -19 mol / L, 10 -18 mol / L, 10 -17 mol / L, 10 -16 mol / L, 10 -15 mol / L), and set up a blank control group (deionized water without heavy metal ions). The micron-sized rectangular holes of the ultra-trace heavy metal ion detection chip were sequentially exposed to different concentrations of Cr. 3+ Solution contact causes Cr 3+ Adsorption of various Cr compounds on the surface of a single-layer molybdenum disulfide working layer 3+The solution adsorption time was the same (the adsorption completion criterion was that the quantum capacitance characteristic signal tended to be stable). The adsorption time was set to 10 min. After the adsorption was completed, the surface of the ultra-trace heavy metal ion detection chip was rinsed with deionized water (to remove unadsorbed ions). Then the surface was dried to remove residual moisture. Then PMMA microwells were installed for quantum capacitance testing. Ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt) was injected into the elastic microwell as electrolyte. Silver / silver ion electrodes and carbon rod electrodes were inserted into the electrolyte to form a three-electrode system. An external electrochemical workstation was connected to apply a scanning DC bias voltage (DC bias scanning range was -1.5~2V, and it was within the electrochemical stability window of the ionic liquid) to the ultra-trace heavy metal ion detection chip. A small signal AC excitation (sine wave voltage with an amplitude of 20mV and a test frequency of 5Hz) was superimposed. The interfacial impedance between the monolayer molybdenum disulfide working layer and the ionic liquid was measured. The total interfacial capacitance was calculated according to the following formula (1): C T = 1 / (2πf Z′′)(1) C T Let f be the total interface capacitance, where f is the test frequency and Z′′ is the imaginary part of the impedance.

[0029] Quantum Capacitor C Q and double-layer capacitance C DL Series capacitance equals the total interfacial capacitance. Within the bandgap and low density of states region of a single-layer molybdenum disulfide layer, the double-layer capacitance is typically much larger than the quantum capacitance. In C... Q C DL Under approximate conditions, the total interfacial capacitance can approximately characterize the quantum capacitance, thereby plotting a quantum capacitance-potential spectrum. To facilitate comparison between the experimentally obtained quantum capacitance-potential spectrum and the theoretically calculated density of states (DOS), the abscissa of the quantum capacitance-potential spectrum can be converted from the electrochemical potential V to the electron energy coordinate E (eV) relative to the vacuum level. Based on this, the electrochemical potential V (vs. Ag / Ag) is calculated. + The energy can be converted into electronic energy coordinates E for characterization, resulting in a quantum capacitance-energy spectrum. The energy offset required for the conversion can be determined by referring to a table in the literature (The absolute electrode potential: an explanatory note (Recommendations 1986) [J]. Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1986, 209(2): 417–28.) or by pre-calibrating using an internal standard redox pair.

[0030] The DOS fingerprint characteristic parameters were extracted from the obtained quantum capacitance-energy spectrum: peak value of defects in the band gap (IG1, IG2, CB1), valence band slope, conduction band slope, and effective band gap width. After each test, the surface of the detection chip was cleaned (first rinsed with isopropanol 2-3 times, then rinsed with deionized water 2-3 times to remove residual electrolyte and unstable adsorbed ions), the surface was dried and the electrolyte was replaced. The above DOS fingerprint characteristic parameters measured by heavy metal ion solutions of different concentrations were correlated with the metal ion concentration to obtain the concentration-DOS fingerprint characteristic parameter standard curve. S2, Connect the micron-sized rectangular aperture of the ultra-trace heavy metal ion detection chip to a Cr-containing... 3+ The solution to be tested is brought into contact with the DOS fingerprint characteristic parameters using the same method as in step S1, and compared with the concentration-DOS fingerprint characteristic parameter standard curve obtained in step S1 to obtain the concentration of heavy metal ions in the solution to be tested.

[0031] like Figure 4 The figure shows different concentrations of Cr in this embodiment. 3+ The quantum capacitance-energy spectrum of the solution was obtained using the same testing method described above. Figure 4 The upper part gives different Cr 3+ The quantum capacitance spectrum at a certain concentration shows that the quantum capacitance increases slightly in the valence band region, and the characteristic peaks gradually appear and intensify in the band gap region, with a steeper rise near the conduction band edge. Figure 4 The lower part illustrates the corresponding band structure, showing the valence band, conduction band, and band structure formed by Cr. 3+ The defect energy levels within the band gap introduced by adsorption are also indicated. With Cr 3 + With increased concentration, the quantum capacitance peak shape corresponding to the defect energy levels within the bandgap significantly enhances, the low-density-state region shrinks, and the density of states near the band edge increases. By selecting parameters such as the peak value of defects within the bandgap (IG1, IG2, CB1), the valence band slope, the conduction band slope, and the effective bandgap width, and comparing them with Cr... 3+ Calibration relationships were established for each concentration to obtain the relationship between each parameter and Cr. 3+ The standard curve of concentration, the results are as follows Figure 5 As shown, the results demonstrate that the energy-resolved density of states fingerprint obtained using quantum capacitance can transform the ion adsorption process into a set of concentration-dependent quantum capacitance signals, enabling the detection of ultra-trace amounts of Cr. 3+ Multi-parameter quantitative detection significantly improves detection sensitivity and reliability.

[0032] Besides Cr 3+In addition, the ultra-trace heavy metal ion detection chip provided in this embodiment of the invention can be extended to detect other heavy metal ions. Different ions produce different numbers of defect states, energy level positions, and enhancement degrees of band-edge state density within the band gap, resulting in different sets of characteristic peaks on the energy axis. Therefore, under the same chip structure and testing conditions, only the metal ion to be tested needs to be changed to obtain the DOS fingerprint characteristic parameters of that ion, which can then be used to distinguish different types of metal ions and construct a multi-ion detection method.

[0033] The above are merely exemplary embodiments of this disclosure and should not be construed as limiting the scope of this disclosure. Any equivalent changes and modifications made in accordance with the teachings of this disclosure shall still fall within the scope of this disclosure. Other embodiments of this disclosure will be readily apparent to those skilled in the art upon consideration of the specification and practice of the disclosure herein. This application is intended to cover any variations, uses, or adaptations of this disclosure that follow the general principles of this disclosure and include common knowledge or customary techniques in the art not described herein.

Claims

1. A chip for detecting ultra-trace heavy metal ions based on quantum capacitance density of state fingerprinting, characterized in that, The ultra-trace heavy metal ion detection chip includes: At least a surface-insulated substrate; A two-dimensional material working layer distributed on the surface of the substrate and located in the middle of the substrate; Metal electrodes and leads that are partially composited with the edge of the two-dimensional material working layer and extend to the edge of the substrate; An insulating dielectric layer covering the substrate and having a micron-sized rectangular hole at the center of the two-dimensional material working layer; A microwell with through holes, one end of which is bonded to an insulating dielectric layer and surrounded by a micron-sized rectangular hole, is used to hold electrolyte. The reference electrode and the counter electrode are inserted into the electrolyte in the microwell, forming a three-electrode system with the metal electrode for quantum capacitance testing.

2. The ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprinting according to claim 1, characterized in that, The substrate is a silicon wafer, glass substrate, ceramic substrate, or flexible polymer film with an insulating dielectric layer, used to support subsequent device structures.

3. The ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprinting according to claim 1, characterized in that, The two-dimensional material working layer is a two-dimensional semiconductor material layer or a two-dimensional conductive material layer with an adjustable Fermi level, selected from one or more of MoS2, WS2, MoSe2, WSe2, InSe, GaSe, black phosphorus, graphene, and MXene.

4. The ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprinting according to claim 1, characterized in that, The insulating dielectric layer with micron-sized rectangular holes is selected from one or more of polyimide, parylene, SiO2, Al2O3, HfO2, SiNx, polymethyl methacrylate, and photoresist SU-8, with a thickness of 0.5~100μm and a length and width of 2~1000μm for the micron-sized rectangular holes; the microwell material is selected from PDMS, silicone rubber, styrene-based thermoplastic elastomers, polyolefin-based thermoplastic elastomers, polyurethane-based thermoplastic elastomers, polyamide-based thermoplastic elastomers, PMMA, PC, and PI.

5. The ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprinting according to claim 1, characterized in that, The electrolyte is an ion-conducting electrolyte that can form an electrical double layer and maintain electrochemical stability within a range of -3 to 3V. It is selected from one or a combination of several of the following: aqueous electrolyte, acid / alkali solution, metal ion salt solution, buffer solution, polymer electrolyte, ionic liquid, gel electrolyte, molten salt, and liquid metal-based conductive medium.

6. The ultra-trace heavy metal ion detection chip based on quantum capacitance state density fingerprinting according to claim 1, characterized in that, The reference electrode is selected from one of a saturated calomel electrode, a silver / silver ion electrode, a silver / silver chloride electrode, or a platinum / gold quasi-reference electrode; the counter electrode is one of a platinum, gold, carbon rod, graphite, glassy carbon, or carbon cloth electrode.

7. A method for fabricating an ultra-trace heavy metal ion detection chip based on quantum capacitance density fingerprinting as described in any one of claims 1-6, characterized in that, Includes the following steps: 1) The substrate is ultrasonically cleaned in acetone, isopropanol and deionized water in sequence for 1 to 30 minutes each time. After cleaning, the surface is dried with nitrogen and then baked to remove surface moisture, resulting in a clean and dry substrate. 2) Preparation of two-dimensional material working layer: Two-dimensional material layer is prepared by mechanical exfoliation, chemical vapor deposition, molecular beam epitaxy, solution method or combination thereof, and the two-dimensional material layer is set on the substrate surface by dry transfer, wet transfer or direct growth method to obtain two-dimensional material working layer; 3) Fabrication of metal electrodes and leads: Metal electrode and lead patterns are formed on the substrate using photolithography and metal deposition-lifting technology. The electrode and lead patterns partially cover the two-dimensional material working layer, and the remaining part extends outside the two-dimensional material working layer area. An adhesion layer and a conductive layer are sequentially deposited on the substrate where the electrode and lead patterns are formed. Then, the conductive layer in the non-electrode and lead pattern area is removed using a photolithography lift-off process to obtain metal electrodes and leads that are electrically connected to the two-dimensional material working layer. 4) Forming an insulating dielectric layer and openings: Spin-coating, depositing or laminating an insulating dielectric layer material on the substrate surface after the metal electrode and lead fabrication are completed in step 3), and forming micron-sized openings at predetermined positions of the corresponding two-dimensional material working layer by photolithography, etching, laser processing or a combination thereof, to obtain an insulating dielectric layer with openings; 5) Fabrication of ultra-trace heavy metal ion detection chip: When quantum capacitance testing is required, micro-wells with through holes are bonded on the insulating dielectric layer. The micro-wells surround the micron-sized rectangular holes to hold the electrolyte and limit the electrolyte volume and reaction area. A reference electrode and a counter electrode are inserted into the electrolyte to form a three-electrode system with the metal electrode for quantum capacitance testing.

8. A method for detecting heavy metal ions using the quantum capacitance state density fingerprint-based ultra-trace heavy metal ion detection chip according to any one of claims 1-6, characterized in that, The specific steps are as follows: S1. First, prepare a series of heavy metal ion solutions of different concentrations and set up a blank control group. Sequentially contact the micron-sized rectangular holes of the ultra-trace heavy metal ion detection chip with the heavy metal ion solutions of different concentrations, allowing the heavy metal ions to be adsorbed on the surface of the two-dimensional material working layer. Each heavy metal ion solution is adsorbed for the same time, with the adsorption time set between 5 and 120 minutes. After adsorption, rinse the surface of the ultra-trace heavy metal ion detection chip with deionized water, then blow dry the surface to remove residual moisture. Next, install an elastic microwell for quantum capacitance testing. Inject electrolyte into the elastic microwell and connect it to an external electrode through a three-electrode system. A chemical workstation applies a scanning DC bias voltage to the ultra-trace heavy metal ion detection chip and superimposes a small-signal AC excitation. The impedance is measured to calculate the quantum capacitance and a quantum capacitance-potential spectrum is plotted. The abscissa of the quantum capacitance-potential spectrum is converted from electrochemical potential to energy coordinates relative to the vacuum energy level to obtain the quantum capacitance-energy spectrum. DOS fingerprint feature parameters are extracted from it. After each test, the surface of the detection chip is cleaned and the electrolyte is replaced. The DOS fingerprint feature parameters measured by heavy metal ion solutions of different concentrations are correlated with the metal ion concentration to obtain a concentration-DOS fingerprint feature parameter standard curve. S2. The micron-sized rectangular hole of the ultra-trace heavy metal ion detection chip is brought into contact with the aqueous solution containing heavy metal ions. The DOS fingerprint feature parameters are tested using the same method as in S1, and compared with the concentration-DOS fingerprint feature parameter standard curve obtained in step S1 to obtain the concentration of heavy metal ions in the aqueous solution.

9. The method for detecting heavy metal ions according to claim 8, characterized in that, The heavy metal ion mentioned in step S1 is Cr 3+ Hg 2+ Cd 2+ Pb 2+ Cu 2+ Zn 2+ Ni 2+ Mn 2+ Co 2+ As 3+ As 5+ 、Tl + 、Tl 3+ Sn² + Mo 4+ V³ + Ta 5+ 、Nb 5+ Zr 4+ Ga³ + In³ + One or more of the heavy metal ions, with a solution concentration of 10. -21 ~10 -5 mol / L.

10. The method for detecting heavy metal ions according to claim 8, characterized in that, The DC bias scanning range in step S1 is -3~3V, and is within the electrochemical stability window of the electrolyte. The small-signal AC excitation is a sinusoidal voltage with an amplitude of 1~200mV, and the test frequency is single frequency or multiple frequency. The DOS fingerprint feature parameters in step S1 include one or more of the following: peak value of defects in the bandgap, peak position of defects in the bandgap, valence band slope, conduction band slope, and effective bandgap width.

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