A gas sensor based on multi-channel tunneling effect and preparation and application thereof

Abstract

This invention provides a gas sensor based on the multi-channel tunneling effect, its fabrication, and its application for gas identification and sensing. It involves fabricating a discontinuous metal thin film with a multi-channel tunneling effect, and then modifying each tunnel junction of the discontinuous metal thin film with a monolayer self-assembled olfactory receptor via dielectrophoresis, thus functionalizing the device. When the device is exposed to a target gas, the olfactory receptor layer captures target gas molecules, forming molecular bridges across the tunnel junctions. Gas capture lowers the potential barrier for electron tunneling at the notch edge region and establishes an additional conductive path for charge transport between the gold electrodes, resulting in increased transient conductivity. This achieves high sensitivity and cycling stability to the target gas, as well as ultra-low operating power, demonstrating the feasibility of its olfactory sensing capabilities.

Description

Technical Field

[0001] This invention relates to the field of gas sensing technology, specifically to an ultra-low power quantum gas sensor based on the multi-path tunneling effect, which is particularly suitable for low-power, high-sensitivity identification and sensing of gases such as ammonia in complex environments. Background Technology

[0002] Gas sensors have wide applications in environmental monitoring, industrial safety, and life and health monitoring. For example, they can detect harmful gases such as ammonia to ensure crop growth and personnel safety. Traditional gas sensors (such as electrochemical metal oxide sensors) not only have limitations in core performance, such as poor selectivity, slow response recovery, and poor sensitivity, but their high power consumption and cost also constitute a bottleneck for large-scale deployment. Especially for field applications in complex gas environments, sensors need to have ultra-low power consumption, high sensitivity, stability, and portability.

[0003] In existing technologies, the fabrication of traditional microneedle-type tunneling electrodes typically relies on multi-step wet etching and metal deposition processes, which are prone to introducing interfacial contamination. The structural design usually only constructs a single electron tunneling pathway, severely limiting the large-scale production and application expansion of these devices. Furthermore, some traditional methods, such as fracture junction or electromigration techniques, struggle to achieve large-area, uniform nano-gap arrays, and the functionalization modification steps are cumbersome, resulting in low device yields and high costs. These functional limitations make it difficult for these devices to meet the application requirements of gas molecule sensing, interfacial catalytic reaction kinetics, and spatially resolved spectral monitoring.

[0004] Our research team previously developed a discontinuous metallic thin film (CN120249913B) with tunneling effect, which is a miniaturized integrated high-density electron tunneling pathway array capable of accurate detection and response to multi-path tunneling effects. Building on this, to bridge the gaps currently faced by gas sensors, the team further investigated the self-assembly method of gas-sensitive molecules at the tunnel junction gap interface, demonstrating its application potential in gas sensing.

[0005] Quantum tunneling refers to the quantum behavior of electrons traversing the potential barrier of nanometer gaps. Based on this principle, multi-channel tunneling gas sensors exhibit highly sensitive tunneling currents to extremely small changes in the gap distance. The adsorption of gas molecules can directly modulate the current, thereby achieving ultra-high sensitivity detection.

[0006] Therefore, the present invention develops a gas sensor that integrates a high-density tunnel junction array, is low-power, and is easy to functionalize, which is of great significance for meeting the real-time, stability, and economic requirements of complex gas monitoring. Summary of the Invention

[0007] To address the problems of existing technologies, this invention provides an ultra-low-power olfactory chip based on multi-path tunneling effect, its fabrication, and its application for gas identification and sensing. A large-area, uniform, ultra-thin gold film is grown in situ on a glass substrate using magnetron sputtering deposition, constructing an on-chip multi-channel metal-insulator-metal tunneling junction with a sub-10 nm structure. Subsequently, a monolayer of self-assembled olfactory receptors (thiol molecules) is modified within each tunneling junction via dielectrophoresis to functionalize the device. The olfactory chip prepared by this method exhibits controllable quality, high yield, and low cost. When the device is exposed to a target gas (ammonia), the olfactory receptor layer captures the target gas molecules, forming molecular bridges across the tunneling junctions. Gas capture lowers the potential barrier for electron tunneling at the notch edge region and establishes an additional conductive path for charge transport between the gold electrodes, resulting in increased transient conductivity. This achieves high sensitivity and cycling stability to ammonia, as well as ultra-low operating power, demonstrating the feasibility of its olfactory sensing capabilities.

[0008] On one hand, the present invention provides a gas sensor based on the multi-path quantum tunneling effect, comprising a discontinuous metal thin film and an olfactory receptor layer; the discontinuous metal thin film comprises a substrate and a nano-gap film disposed on the substrate; the nano-gap film comprises randomly distributed nano-islands, with a nano-gap formed between any two adjacent nano-islands; the olfactory receptor layer is modified on the nano-gap film.

[0009] The gas sensor based on the multi-path quantum tunneling effect described in this invention refers to a gas sensor containing at least two or more tunneling gaps, generally referring to a chip made of an array of metal nanoparticles with a large number of tunneling paths.

[0010] Existing tunneling gas sensors only use a single tunneling junction structure, where gas molecules can only interact with a tiny gap region. This results in a low molecule capture probability, slow response speed, and limited stability and sensitivity of the detection results.

[0011] Based on the previously prepared discontinuous metal thin film with multi-path tunneling effect (CN120249913B), this invention permeates the olfactory receptor layer onto the discontinuous metal thin film, achieving precise modification of the olfactory receptor layer at the nanoscale. This successfully constructs an ultra-low-power olfactory chip with a permeated metal nanoparticle array. The chip has a large-scale, high-density, and uniform tunneling junction array, in which gas molecules can diffuse in three dimensions, greatly increasing the contact area and collision probability between gas molecules and the receptor layer. It has strong signal, low noise, and high reproducibility, cleverly solving the fundamental bottlenecks of traditional single tunneling sensors in terms of practicality, stability, and manufacturability.

[0012] The gas sensor based on the quantum tunneling effect provided by this invention can also be an olfactory computing chip with a miniaturized size and is an ultra-low power olfactory computing chip.

[0013] The ultra-low power olfactory computing chip refers to a chip whose electrodes operate at a current in the pA range and are subjected to a voltage of 1V, thereby greatly reducing operating power.

[0014] Meanwhile, the ultra-low power also refers to the ability to sense at room temperature, compared to traditional metal-semiconductor-oxide gas sensors which require an activation temperature of 200-400 °C. The gas sensor provided by this invention overcomes the bottleneck of room temperature detection in traditional gas sensors to a certain extent, and is therefore more suitable for on-site detection in real-world scenarios.

[0015] Furthermore, the olfactory receptor layer is modified on both sides, both ends, edges, tips, or nano-gap locations of the nano-gap film using dielectrophoresis.

[0016] The main function of the olfactory receptor layer in a gas sensor is to selectively capture target gas molecules (such as ammonia NH3) into the tunneling gap for detection through the functional groups (such as carboxyl-COOH) or molecular structure at its ends, while other gas molecules do not respond or only adsorb weakly.

[0017] Therefore, the olfactory receptor layer needs to be precisely modified on the sidewalls of both sides of the nanogap to capture the target gas into the nanogap. In other words, the modification of the nanogap film provided by this invention is a precise operation at the nanoscale. It cannot be modified on the surface of the nanoislands, but must be done near the nanogap. The precision requirements are extremely high. Moreover, there are a large number of nanogaps in the nanogap film, and all nanogaps need to be modified simultaneously and efficiently to produce this gas sensor.

[0018] The modification is applied near the nano-gap, or at the sides, ends, edges, tips, or the nano-gap itself, so that the molecular structure of the olfactory receptor layer extends precisely within the nano-gap. Its terminal functional groups (such as -COOH, -OH, -B(OH)2, etc.) can capture the target gas (such as ammonia) into the nano-gap through different forces (covalent bonds, coordination bonds, hydrogen bonds, etc.), thereby achieving a specific or non-specific response to the target gas.

[0019] Studies have shown that dielectrophoresis can precisely modify olfactory receptor layers near nano-interstic gaps, and simultaneously and precisely modify both sides of all nano-interstic gaps in the chip. The core mechanism of dielectrophoretic force driving small molecules is that by applying an AC voltage across the nano-interstic gaps in the gold film, a highly concentrated non-uniform electric field is generated, with its gradient being greatest at the gap edges and pore openings. For thiols and most organic solvents, the molecular polarizability is usually higher than that of the solvent, and therefore they are subjected to positive dielectrophoretic force, being pulled towards the region with the strongest electric field strength—that is, the edges of the gold electrodes and the interior of the nano-interstic gaps / pores. Dielectrophoresis achieves this goal by actively driving, enriching, and "assembling" thiols to the target location using the force generated by the non-uniform electric field, rather than relying on a passive diffusion process.

[0020] Furthermore, the distance of the nano-gap is sub-10 nm; the olfactory receptor layer is a monolayer self-assembled membrane, including any one or more of thiol molecules, metal oxide semiconductors, polymers, metal-organic frameworks, and carbon nanomaterials.

[0021] It is understandable that modifying any olfactory receptor layer on a discontinuous metal thin film, such as thiol molecules, metal oxide semiconductors, polymers, metal-organic frameworks, carbon nanomaterials, etc., can play a role in capturing gases. Therefore, any olfactory receptor layer can be used to prepare gas sensors with tunneling nanogap arrays. However, gas sensors prepared using different olfactory receptor layers will have differences in detection performance, and the yield of gas sensors based on multi-path quantum tunneling effect will also vary. The yield mentioned here refers to the electrode chip with sensitive gas-sensing characteristics.

[0022] Furthermore, the olfactory receptor layer is composed of thiol molecules, including any one or more of the following: 11-mercaptoundecanoic acid, 4-mercaptobenzoic acid (for detecting alkaline gases such as NH3), cystamine (for detecting acidic gases such as NO2), 1-octanethiol (for detecting nonpolar organic vapors), 4-methylbenzylthiophenol (for detecting aromatic VOCs), porphyrin thiol derivatives (for highly selective detection of formaldehyde, NO, etc.), 4-mercaptophenylboronic acid, 1-hexadecylthiol, and 6-mercapto-1-hexanol.

[0023] Studies have demonstrated that thiol molecules possess significant advantages over metal oxide semiconductors, polymers, metal-organic frameworks, and carbon nanomaterials. First, the thiol group (-SH) of the thiol molecule (R-SH) can form stable sulfur-gold covalent bonds with the gold surface (when gold is chosen as the material for the nano-gap film), spontaneously forming a dense, ordered self-assembled monolayer. The modification process is simple and controllable. Second, by selecting different molecular weights, the length of the molecular bridge can be controlled to adapt to tunneling gaps below 10 nm, optimizing sensing performance. Third, the sulfur-gold bond exhibits high chemical stability and is not easily detached, ensuring the long-term stability of the sensing layer during repeated gas exposure and recovery processes. Furthermore, different functional groups can be modified at the ends of the thiol molecule, enabling selective recognition of different gases.

[0024] It should also be noted that thiol molecules can migrate directionally in an electric field, making them particularly suitable for efficient and uniform modification using dielectrophoresis. They exhibit good self-assembly, stable bonding, adjustable length, and ease of modification, making them especially suitable for large-area array fabrication.

[0025] In some approaches, 4-mercaptobenzoic acid is preferred as the olfactory receptor layer. The length of the thiol molecule (approximately 1-2 nm) is well-suited to the sub-10 nm gaps in the gold film, achieving an optimal balance between sensitivity and stability. The molecular chain length effectively bridges the nanoscale gaps, reduces the tunneling barrier, enhances gas capture efficiency, and improves sensitivity. The sulfur-gold covalent bonds formed after annealing further enhance mechanical and chemical stability (RSD < 3% after 100 cycles).

[0026] In some embodiments, the substrate of the discontinuous metal thin film is selected from one or more of silicon dioxide, glass, silicon, silicon nitride, and sapphire; and / or, the nano-gap film of the discontinuous metal thin film is selected from one or more of gold, silver, aluminum, and copper.

[0027] Understandably, silicon dioxide, glass, silicon, silicon nitride, and sapphire can all be used to prepare substrates, while gold, silver, aluminum, and copper can all be used to prepare nano-gap films, thus allowing for arbitrary combinations to create discontinuous metal films.

[0028] In some embodiments, the substrate is preferably made of glass. This is because glass has high light transmittance, with excellent transmittance in the visible light range (typically >90%), which does not interfere with the optical properties of the metal film; moreover, it has high surface flatness and smoothness, and good chemical stability, thermal stability, and mechanical strength.

[0029] In some embodiments, the nano-gap thin film material is selected from gold. When the material is gold, due to its chemical inertness, high reduction potential, and stable electronic structure, the discontinuous metal film formed by it can maintain structural stability and oxidation resistance for a long time at room temperature.

[0030] In some methods, the discontinuous metal film is obtained by depositing a nano-gap film on the substrate surface using a magnetron sputtering method.

[0031] On the other hand, the present invention provides a method for fabricating a gas sensor based on the multi-path tunneling effect, wherein an olfactory receptor layer is modified on the surface of a discontinuous metal thin film; the discontinuous metal thin film includes a substrate and a nano-gap film disposed on the substrate; the nano-gap film includes randomly distributed nano-islands, and a nano-gap is formed between any two adjacent nano-islands; the olfactory receptor layer is modified on the nano-gap film.

[0032] Furthermore, it includes the following steps: (1) Preparation of discontinuous metal thin films; (2) An olfactory receptor layer was modified on the surface of a nano-gap film of a discontinuous metal film using dielectrophoresis.

[0033] Traditional gas sensors based on interdigital electrodes typically modify the olfactory receptor layer by immersion or physical coating. The modification precision is generally on the micrometer scale. The modification process relies on active diffusion, and the uniformity and repeatability of the modified devices are inconsistent, making it difficult to mass-produce them.

[0034] This invention requires driving near-monomer solution molecules into nanoscale gaps, which is equivalent to a method of nano-interface assembly. Moreover, it is aimed at the simultaneous modification of large-scale, high-density sub-10 nm gaps, which faces challenges with traditional modification methods, while dielectrophoretic modification provides unique advantages.

[0035] The method for modifying olfactory receptor layers using dielectrophoresis provided by this invention does not rely passively on concentration diffusion or physical adsorption (which easily leads to the formation of non-uniform films at the micrometer scale), but actively uses electric field force to drive molecules to enter and modify the sub-10 nm nanometer gaps in a directional and orderly manner, achieving true "nanoscale precise functionalization". The devices prepared have highly consistent performance and high yield, making them suitable as standardized sensor products.

[0036] Further, the dielectrophoresis technique in step (2) includes: placing a substrate with a deposited permeated metal nanofilm in a solution containing acceptor molecules, applying an electric field with an intensity of 1~10 V / μm for 1~10 minutes to drive the acceptor molecules to orientedly assemble to both sides of the nano gap.

[0037] Specific electric field strengths (1~10 V / μm) and times (1~10 min) are key windows for achieving high-quality, monolayer, and directional modification through dielectrophoresis, and are based on a fine balance of molecular dynamics, electric field forces, and diffusion processes.

[0038] Studies have shown that when the electric field strength is <1 V / μm, the electric field force is too weak to overcome the molecular thermal motion (Brownian motion) and diffusion energy barrier, resulting in random molecular adsorption, inability to oriented assembly, and slow and uneven modification. When the electric field strength is >10 V / μm, the excessively strong electric field force may cause molecules to accumulate too quickly, forming multilayers, potentially leading to solution electrolysis, and even damaging the gold film or substrate, causing problems such as film inhomogeneity, structural damage, and device failure. Only when the electric field strength is between 1 and 10 V / μm is the electric field force sufficient to drive the oriented migration of molecules to the electrode gap and align the molecules along the electric field direction, promoting precise modification of molecules in the nano-gap, resulting in high modification efficiency and good consistency.

[0039] Meanwhile, controlling the assembly of molecules under an electric field through dielectrophoresis is actually a dynamic equilibrium process of "migration-adsorption-alignment." A suitable time window (1-10 min) must be selected to allow molecules sufficient time to migrate to all nano-interstic spaces and to complete their orientation alignment, forming an ordered olfactory receptor layer. Too short or too long a time will lead to membrane degradation.

[0040] It is evident that 1~10V / μm and 1~10 min are the "golden windows" optimized through experiments, which can ensure the formation of a dense, ordered, and stable monolayer acceptor membrane in the sub-10 nm nanometer gap. This is a condition for achieving high yield in the fabrication of gas sensors and a key process guarantee for realizing high-sensitivity and high-stability quantum tunneling sensors.

[0041] Furthermore, it also includes step (3): an annealing process to enhance the bonding stability between the acceptor layer and the metal film.

[0042] To enhance the stability of the acceptor layer, thermal annealing is required after modification. Annealing promotes the formation of stable sulfur-gold covalent bonds between thiol molecules and the gold film surface, thereby activating the gas-sensing properties; moreover, annealing improves the color uniformity and enhances the oxidation resistance of the device. Therefore, annealing is a crucial activation step that determines the long-term stability and performance of the sensor.

[0043] In some methods, the annealing parameters are as follows: the chip is placed in a 60 °C oven and annealed in air for 15 min at a heating rate of 5 °C / min, and then naturally cooled to room temperature.

[0044] Furthermore, the present invention provides a gas detection method, wherein the method uses the gas sensor described above for detection, and includes the following steps: (a) Place the gas sensor in the vacuum test chamber; (b) The gas flow rate is programmed for gas intake, and the electrical conductivity signal is collected by an electrical signal device.

[0045] In some methods, step (b) involves detecting the change in its conductivity or its it curve.

[0046] Furthermore, the present invention provides applications of the gas sensor described above or the gas sensor prepared by the preparation method described above in any one or more of the following: In the field of agricultural and food gas monitoring, this includes the detection of any one or more of ammonia, ethylene, sulfur dioxide, hydrogen sulfide, and methane. The field of ambient air quality monitoring includes urban and regional ambient air quality monitoring (such as PM2.5, ozone, nitrogen oxides, sulfur dioxide, carbon monoxide, formaldehyde, volatile organic compounds, etc.). In the field of industrial process control and safety monitoring, this includes early warning of leaks of flammable and toxic gases (such as hydrogen, methane, n-butane, benzene, ethylene, etc.) in scenarios such as hazardous chemical storage and transportation, and fire emergency rescue. In the fields of medical health and life sciences, it is used for disease screening and health monitoring (such as biomarkers in human exhaled breath: acetone, benzaldehyde, nitric oxide, ammonia, hydrogen sulfide, etc.).

[0047] The present invention has the following beneficial effects: 1) This invention proposes a novel quantum olfactory gas sensing mechanism based on multi-channel tunneling effect. A high-density tunneling junction array is constructed by permeating metal nanofilms, and gas molecule detection is achieved through multi-channel quantum tunneling effect.

[0048] 2) To simulate the human olfactory system, a novel method for small molecule modification at the sub-10 nm gap scale is proposed. The olfactory receptor layer is efficiently modified by dielectrophoresis, which significantly improves selectivity and response speed and increases device yield.

[0049] 3) Select appropriate small molecules to prepare the olfactory receptor layer to improve the modification effect and the capture effect of the target gas; 4) The device achieves ultra-low power (1~100 pW) and high sensitivity (detection limit LOD of 30 ppm) through its excellent characteristics such as low initial voltage (1 V), low initial current 1 nA and room temperature operating temperature, making it suitable for long-term detection in complex gas environments and in-situ detection at room temperature.

[0050] 5) The prepared quantum gas sensor can operate for a long time at room temperature and has a cycle stability of more than 100 times (more than 10,000 s), which confirms the feasibility of its olfactory sensing.

[0051] 6) The device has a simple structure and low manufacturing cost, which is conducive to miniaturization and mass production, and is suitable for large-scale real-world applications.

[0052] 7) This invention is not limited to gas sensing, but has important application value in fields such as electronic devices (e.g., photodetectors, single-electron transistors), nanotechnology (e.g., surface-enhanced Raman scattering substrates) and biomarker analysis (e.g., protein detection); its high-density tunneling junction array design supports multi-functional integration, such as achieving multi-gas selective detection by modifying different receptor layers, providing modular solutions for environmental monitoring, medical diagnosis and industrial safety. Attached Figure Description

[0053] Figure 1 This is a physical image of the quantum gas sensor based on the multi-channel tunneling effect in Example 1; Figure 2 This is a schematic diagram of the quantum olfactory mechanism of gas sensing in Example 2; Figure 3 The graph shows the response speed detection results of the quantum gas sensor based on the multi-channel tunneling effect in Example 2. Figure 4 The image shows the 100-cycle stability curve of the quantum gas sensor based on the multi-channel tunneling effect in Example 2. Figure 5 This is a graph showing the gas-sensing response of the quantum gas sensor in Example 2 in 100~1000 ppm ammonia gas; Figure 6 This is a bar chart showing the specific response of the quantum gas sensor in Example 2. Detailed Implementation

[0054] To describe the present invention more specifically, the technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. These descriptions are merely illustrative of how the present invention is implemented and do not limit the specific scope of the present invention. The scope of the present invention is defined in the claims.

[0055] Example 1: Fabrication of a quantum gas sensor based on multi-channel tunneling effect The fabrication of the quantum gas sensor based on the multi-channel tunneling effect provided in this embodiment requires first preparing a discontinuous metal thin film, and then modifying it with an olfactory receptor layer. The fabrication method is as follows: I. Preparation of discontinuous metal thin films; The preparation method of discontinuous metal thin films with multi-channel tunneling effect is described in CN120249913B.

[0056] 1) A Cr (chromium) layer of approximately 1 nm thickness is deposited on the substrate surface as an adhesion layer using a magnetron sputtering deposition device. The specific operation steps are as follows; Sample loading: Place the Cr target (purity of 99.999%) into the corresponding cavity of the magnetron sputtering equipment, fix the substrate to the turntable with tape, and hang it vertically on the electron gun in the center of the cavity with the front side facing down.

[0057] Vacuum pump: Click PC Pump to evacuate the chamber and bring the pressure inside the chamber to 1.6E-6MPa.

[0058] Parameter settings: Select the corresponding working end, click Switch to switch, and open the working end cover of the Cr target. The initial power is 50W, the deposition time is set to 5 s, and the rotary table speed is set to 20 rmp.

[0059] Sputter deposition: Clicking the Substrate Shutter initiates dust generation. A high-voltage electric field is applied to ionize the inert gas (argon), producing high-energy ions. These ions bombard the target material, causing Cr target atoms to be sputtered and deposited on the substrate surface, forming a uniform thin film. The atmospheric conditions are: nitrogen pressure = 0.07 mPa, argon pressure = 0.05 mPa, and air pressure = 0.55 mPa.

[0060] Post-processing: After deposition is completed, the substrate with the deposited adhesive layer is removed from the cavity and subjected to subsequent processing or fabrication.

[0061] The substrate is a glass slide, which has undergone pretreatment, namely, applying acetone and isopropanol to the glass slide (15 cm²) respectively. The surface of the sample was ultrasonically cleaned for 5 minutes (15 cm) to remove impurities adsorbed on it, then rinsed with deionized water and dried with nitrogen.

[0062] 2) A nano-gap thin film was deposited in situ on the adhesion layer using a magnetron sputtering deposition device. The specific operation steps are as follows: Sample loading: Place the Au target in the corresponding cavity, and fix the substrate after the adhesion layer is deposited in step 1) on the turntable with tape, and hang it vertically on the electron gun in the center of the cavity with the front side facing down.

[0063] Vacuum: Click PC Pump to evacuate the chamber, bringing the pressure inside the chamber to 1.6E-6MPa.

[0064] Parameter settings: Select the corresponding working end, click Switch to switch, and open the working end cover of the Au target. The initial power is 50 W, the deposition time is set to 20 s, and the rotary table speed is set to 20 rmp.

[0065] Sputter deposition: Clicking the Substrate Shutter initiates the dust generation process. A high-voltage electric field is applied to ionize the inert gas (argon), producing high-energy ions. These ions bombard the target material, causing Au target atoms to be sputtered and deposited on the surface of the adhesion layer, forming a nano-gap film. This nano-gap film contains randomly distributed nano-islands. Adjacent nano-islands and the nano-gap between them form a tunneling junction, resulting in a discontinuous film with a tunneling effect. The atmospheric conditions are: nitrogen pressure = 0.07 mPa, argon pressure = 0.05 mPa, and air pressure = 0.55 mPa.

[0066] Post-processing: After deposition is complete, the substrate with the deposited nano-gap film is removed from the cavity to obtain a discontinuous metal film.

[0067] The obtained discontinuous thin film was photographed and scanned by electron microscopy, which proved that the discontinuous thin film is composed of several randomly distributed, independent nanoislands with clear boundaries. There are channels (nano gaps) between the nanoislands and adjacent nanoislands. Two adjacent nanoislands and the nano gap between them form a tunnel junction.

[0068] The width of the nano-gap between two adjacent nano-island structures in the SEM image was analyzed using Nano Measurer software, and the average nano-gap was 5 nm. The coverage of the nano-gap was analyzed and calculated using ImageJ software, which is the area of ​​the nano-gap divided by the area of ​​the substrate. The coverage of the nano-gap was calculated to be 21.69%.

[0069] 3) Mask: The size of the mask is 5. The sample is 8 mm in diameter and contains 35 interdigitated slits spaced 30 µm apart. The non-perforated areas in the mask act as a barrier, preventing the formation of a conductive layer on the discontinuous metal film surface in that area. The mask is then attached to the discontinuous metal film surface with tape, and the sample is placed in the sputtering chamber.

[0070] 4) Sputtering deposition: Subsequently, a continuous gold film of approximately 10 nm thickness is deposited on the mask surface for 120 s as a conductive layer, and electrode pairs are formed at both ends. After sputtering is completed, the mask is removed.

[0071] 5) Laser cutting: Cutting is performed using a laser cutting system.

[0072] 6) Wire bonding: A 30 µm aluminum wire is bonded to both ends of the electrode pair using a wire bonding machine. The other end of the aluminum wire is connected to the PCB pad, and the working electrode and reference / counter electrode of the microcurrent instrument are connected through pin headers and DuPont wires to obtain a sensor chip with deposited metal nanofilm.

[0073] II. Modification of the olfactory receptor layer An olfactory receptor layer was modified on the surface of a discontinuous metal thin film through nano-gap electrophoresis. The specific steps are as follows: 1) Preprocessing The sensor chip with deposited permeated metal nanofilm was lightly rinsed with ethanol and dried with nitrogen to remove surface adsorbates. The chip was then treated with oxygen plasma (100 W, 2 min) to improve surface hydrophilicity.

[0074] 2) Solution preparation The solution required for functionalization modification is a thiol molecular solution, used to form a self-assembled monolayer acceptor. The preparation process requires strict control of concentration and solvent purity to ensure uniform adsorption of molecules within the nanoscale gaps.

[0075] This embodiment uses 4-mercaptobenzoic acid (4-MBA) as a typical olfactory receptor molecule. Its molecular chain length can effectively bridge nanoscale gaps, enhancing gas capture efficiency and achieving an optimal balance between sensitivity and stability. Concentration preparation: Accurately weigh 4-MBA powder and dissolve it in ethanol / water to prepare a concentration of 100 nM. Sonicate until completely dissolved. The solution should be stored in the dark at 4 °C to prevent thiol oxidation and degradation. Allow the solution to reach room temperature before use.

[0076] 3) Dielectrophoresis equipment and parameter settings Dielectrophoretic modification relies on an electric field to drive the directional assembly of molecules, and parameter settings directly affect the coverage and stability of the acceptor layer. The equipment adopts a standard dielectrophoresis system, including electrode plates, power supply, and temperature control unit. The power supply is a programmable DC / AC power supply, supporting a voltage range of 0-100 V and a frequency range of 0-10 MHz (using AC mode).

[0077] The chip was fixed in place and injected with freshly prepared 100 nM 4-MBA ethanol / water solution (approximately 100 µL, completely covering the chip). A voltage was then applied (5 V for 3 min) to induce directional molecular migration, followed by incubation for 5 min to form interfacial assembly through the covalent interaction of thiol groups with gold.

[0078] Key parameters are shown in Table 1.

[0079] Table 1. Key parameters of dielectrophoresis 4) Washing and drying After dielectrophoresis, the chip was removed and rinsed three times with water (1 minute each time) to remove unbound thiol molecules. After drying with nitrogen, a dense monolayer acceptor membrane was formed on the chip surface, and the chip exhibited a uniform matte finish.

[0080] 5) Activation To enhance the stability of the acceptor layer, thermal annealing was performed after modification: annealing promotes the formation of stable sulfur-gold covalent bonds between thiol molecules and the gold film surface, thereby activating the gas-sensitive properties. After annealing, the device exhibits improved color uniformity and enhanced oxidation resistance.

[0081] Annealing parameters: Place the chip in a 60 ℃ oven and anneal in air for 15 min. Heating rate: 5 ℃ / min. Allow to cool naturally to room temperature.

[0082] A quantum gas sensor based on the multi-channel tunneling effect was fabricated, and its structural schematic diagram is shown below. Figure 1 As shown.

[0083] Example 2: Study on the gas-sensing performance of a quantum gas sensor This embodiment studies the performance of the quantum gas sensor based on the multi-channel tunneling effect prepared in Example 1. A schematic diagram of its quantum olfactory mechanism for gas sensing is shown below. Figure 2 As shown, by modifying functionalized molecules within each tunnel junction, target gas molecules are captured by these functionalized molecules, forming molecular bridges across the tunnel junctions. This gas capture lowers the potential barrier for electron tunneling in the notch edge region and establishes an additional conductive path for charge transport between the gold electrodes, resulting in improved transient conductivity and achieving high sensitivity and cycling stability for ammonia.

[0084] 1. Response time Ammonia gas at a concentration of 100 ppm was used as the target gas, and tests were conducted at room temperature (25 °C) and in dry air (relative humidity <5%). The sensor was placed in a 100 mL sealed vacuum chamber, and dry nitrogen gas was introduced at a constant flow rate (500 sccm) as the baseline carrier gas. After the initial current baseline stabilized, the system was quickly switched to dry ammonia gas containing 100 ppm, and the exposure was sustained for 30 s, during which the current change over time was recorded. Subsequently, the system was switched back to pure dry nitrogen gas, and the process of the current recovering to the baseline was recorded.

[0085] The response speed is defined as the time difference from the start of intake to 90% of the current response, denoted by T. The formula for the response speed is (I-I0). 90% / T, response speed test results are shown below. Figure 3 .

[0086] like Figure 3 As shown, the current rises rapidly upon contact with ammonia vapor. Test results indicate that the average response time T of the sensor is 24 ± 3 s. This rapid response is attributed to the uniform and dense acceptor interface formed by the 4-MBA self-assembled monolayer, and the rapid diffusion of gas molecules within the nanoporous film structure.

[0087] 2. Response Sensitivity The study evaluated the sensor's sensitivity by testing its response to different concentrations of ammonia.

[0088] Test method: Under the same test conditions, ammonia gas with concentration gradients of 100 ppm, 200 ppm, 400 ppm, 800 ppm, and 1000 ppm was sequentially introduced. After each test, the sensor was thoroughly purged with compressed nitrogen until the resistance completely returned to the baseline. The steady-state conductivity change and conductivity response value of the sensor were recorded at each concentration point.

[0089] The change in conductivity ΔG is defined as follows: ΔG = 1 / ΔR = 1 / (Rg - R0); The conductivity response value Rsponse is defined as follows: Response = ΔR / R0 × 100% = (Rg - R0) / R0 × 100%; Where Rg is the steady-state resistance when exposed to gas, and R0 is the baseline resistance.

[0090] Test results are as follows Figure 4 As shown, the sensor's response value monotonically increases with increasing ammonia concentration. Within the 100-1000 ppm range, a good linear relationship exists between the response value and the gas concentration, with a linear fit (R²) greater than 0.995. Its limit of detection (LOD) (i.e., 3S0 / K, where 3S0 is the standard deviation of the blank sample and K is the slope of the standard curve) is approximately 30 ppm. Notably, even at low concentrations (100 ppm), the sensor still produces a significant and distinguishable signal response, with a signal-to-noise ratio (SNR) greater than 5, indicating excellent detection capability for low-concentration gases. This high sensitivity stems from the unique "tunneling effect" of the metal film near the percolation threshold; even weak adsorption of gas molecules can cause a dramatic reconstruction of the conductive pathway network, leading to a significant change in resistance.

[0091] 3. Cyclic stability study Cyclic stability is an important parameter for evaluating the lifespan and reliability of sensors. This study conducted multiple repetitive gas exposure-recovery cycle tests on the same sensor. 100 consecutive cycles were performed under 1000 ppm ammonia conditions. Each cycle included 1 minute of gas exposure followed by 1 minute of clean air recovery. The response amplitude for each cycle was recorded, and the results are as follows: Figure 5 As shown.

[0092] like Figure 5As shown, after 100 cycles of testing, the sensor's response amplitude RSD is less than 6%, demonstrating high cycling stability. This excellent stability is mainly attributed to the thermal annealing process used in Example 1, which effectively promotes the formation of strong sulfur-gold covalent bonds between thiol molecules and the gold film surface, enhancing the mechanical and chemical stability of the self-assembled monolayer under continuous gas-solid interactions.

[0093] 4. Specificity assessment In practical applications, the sensor's ability to distinguish a target gas from other interfering gases is crucial. This study evaluates the sensor's specificity by testing its cross-response to a variety of common volatile organic compounds. Under the same conditions (all concentrations of 100 ppm), the sensor's responses to ammonia, nitrogen, argon, oxygen, and air were tested separately.

[0094] The results are as follows Figure 6 As shown in the bar chart, the sensor's response to ammonia is significantly higher than that to other interfering gases. Its selectivity coefficient (response ratio, ammonia response value / nitrogen response value) is approximately 4.8, and its selectivity coefficient (ammonia response value / argon response value) is approximately 6.4.

[0095] This excellent specificity stems from the differences in interactions between the 4-MBA acceptor layer and different gas molecules. Ammonia has a strong covalent bond with the carboxyl group of the thiol chain, while its interactions with other straight-chain molecules or small polar molecules are weaker, thus enabling selective recognition of ammonia.

[0096] Example 3: Comparison of sensing performance differences using traditional metal oxide-based gas sensors This embodiment uses the quantum gas sensor based on the multi-channel tunneling effect prepared in Example 1 and compares it with a traditional metal oxide-based gas sensor (purchased from Guangzhou Ruiboyi Electronic Technology Co., Ltd., model MQ137). The gas sensing performance of the two gas sensors is examined according to the method provided in Example 2, and the results are shown in Table 2.

[0097] Table 2. Comparison of sensing performance with traditional gas sensors As can be seen from Table 2, compared with traditional gas sensors, the quantum gas sensor based on multi-channel tunneling effect provided by this invention has significant advantages in response time, sensitivity, cycle stability, operating temperature and power consumption.

[0098] Example 4: Comparison of different modification methods This embodiment uses the quantum gas sensor based on the multi-channel tunneling effect prepared in Example 1. The modification methods employed are: 1. Dielectrophoresis (Example 1); 2. Solution immersion (specifically, the chip electrode is placed in a petri dish, and a modification solution (100 mM 4-MBA solution) is added to the electrode surface to completely cover it. After standing for 6 h, the electrode is removed, and unbound thiol molecules are slowly rinsed with deionized water, followed by nitrogen drying); 3. Physical coating (specifically, 10 mg of gas-sensitive molecules are placed in a 1.5 mL centrifuge tube, 2-3 drops of deionized water are added to prepare a viscous slurry, which is then coated onto the electrode surface using a wolf-hair brush and dried at 60 ℃). The time, cost, yield, and performance of the three sets of gas sensors were investigated. The yield was determined by: (a) using electrochemical CHI to test the cv curve, which showed typical nonlinearity with a conductivity range of 1-1000 nS; (b) testing 100... Under ppm ammonia conditions, the IT gas-sensitive response curve is shown (a peak change in the response curve indicates a good product, while no response is indicated by a flat straight line). The performance testing method is as shown in Example 2, and the results are shown in Table 3.

[0099] Table 3. Effects of different modification methods As shown in Table 3, the use of dielectrophoresis for modification results in higher modification efficiency and a higher yield of the prepared gas sensors. This is because dielectrophoresis can rapidly modify large-scale nano-gap structures. This is achieved by utilizing the force generated by a non-uniform electric field to actively drive, enrich, and "assemble" thiol molecules to the target sites, rather than relying on a passive diffusion process. Therefore, it offers higher controllability and more stable quality.

[0100] Example 5: Screening of materials for modifying olfactory molecular layers This embodiment uses the quantum gas sensor based on the multi-channel tunneling effect prepared in Example 1. The following materials were used as modifiers for the olfactory molecular layer: 1. Thiol molecules (4-MBA); 2. Metal oxide semiconductor (zinc oxide ZnO); 3. Polymer (polyaniline PANI); 4. Metal-organic framework (UIO-66); 5. Carbon nanomaterials (carbon nanotubes CNTs). Under the same conditions, the operability, yield, and performance of the five quantum gas sensors were examined. The yield was tested using the following methods: (a) Electrochemical CHI test showed a typical nonlinear cv curve with a conductivity range of 1-1000 nS; (b) Testing the it gas-sensitive response curve under 100 ppm ammonia conditions (a peak change in the response curve indicates a good product, while no response is indicated by a flat straight line). The performance testing method is as shown in Example 2, and the results are shown in Table 4.

[0101] Table 4. Influence of different olfactory molecular layer materials As shown in Table 4, using 4-MBA as the modifying material results in higher modification efficiency, stronger binding strength, better specificity, lower cost, higher sensitivity, and a higher yield and more stable quality of the prepared quantum gas sensor. The reasons for this are: 1) Dielectrophoretic maneuverability: Good. Although 4-MBA is a small molecule with low polarizability, it is easily driven in optimized high-frequency electric fields (e.g., 1-10 MHz) and low-conductivity solvents. Its small molecular size allows it to easily penetrate and modify deep into nano-interstic gaps.

[0102] 2) Bonding strength: strongest. It spontaneously forms an ordered and dense self-assembled monolayer through Au-S covalent bonds, exhibiting strong bonding and high stability.

[0103] 3) Specificity: The selectivity is enhanced mainly through the specific interaction between the terminal functional group (-COOH) and the gas.

[0104] Example 6: Effects of different thiol molecules This embodiment uses the quantum gas sensor based on the multi-channel tunneling effect prepared in Example 1. In the selection of thiol molecules, the following were used as modification materials: 1, 1-hexadecylthiol; 2, 11-mercaptoundecanoic acid; 3, 6-mercapto-1-hexanol; 4, 4-mercaptobenzoic acid (4-MBA). Under the condition that other conditions remain the same, the performance of the three sets of quantum gas sensors was examined. The performance detection method is as shown in Example 2, and the results are shown in Table 5.

[0105] Table 5. Effects of different thiol molecules As can be seen from Table 5: 1) Dielectrophoretic controllability is positively correlated with polarity: the higher the molecular polarity / polarizability (such as 4-MBA, 11-mercaptoundecanoic acid), the better the dielectrophoretic controllability, and the easier it is to achieve precise and rapid enrichment of nano-gap through electric field parameters (frequency, voltage).

[0106] 2) The long-term stability of the modified layer is strongly correlated with the alkyl chain length: long-chain alkyl thiols (such as 1-hexadecyl thiols) have the best stability and are suitable for long-term monitoring; short-chain or rigid structure thiols (such as 4-MBA) are more suitable for short-term or high-performance demand scenarios.

[0107] 3) Functional group and gas-sensitivity specificity dependence: There are many types of thiols with complete functional groups such as amino, carboxyl, hydroxyl, methoxy, carbonyl, etc. Different thiols can be adapted to different types of gases to achieve specific detection.

[0108] Therefore, the optimal solution can be matched according to the molecular polarity, chain length and functional group type, depending on the different test scenarios and target gases.

[0109] In addition, when used for ammonia response, both 11-mercaptoundecanoic acid and 4-MBA are applicable, but when 4-MBA is used as a modifying material, the response sensitivity to ammonia is higher (30 ppm, while 11-mercaptoundecanoic acid is 45 ppm), the response time is shorter (24 s, while 11-mercaptoundecanoic acid is 39 s), and the yield is also higher (30%, while 11-mercaptoundecanoic acid is 28%). This may be because 4-MBA can effectively bridge the nano-gap, enhance the gas capture efficiency, and achieve the best balance between sensitivity, specificity and stability.

[0110] While the present invention has been disclosed above, it is not limited thereto. Any person skilled in the art can make various modifications and alterations without departing from the spirit and scope of the invention; therefore, the scope of protection of the present invention should be determined by the scope defined in the claims.

Claims

1. A method for preparing a gas sensor based on the multi-channel quantum tunneling effect, characterized by, An olfactory receptor layer is modified on the surface of a discontinuous metal film; the discontinuous metal film comprises a substrate and a nano-gap film disposed on the substrate; the nano-gap film comprises randomly distributed nano-islands, with nano-gap formations between any two adjacent nano-islands; the olfactory receptor layer is modified onto the nano-gap film; the modification includes the following steps: (1) Preparation of discontinuous metal thin films; (2) An olfactory receptor layer is directionally modified on the surface of a nano-gap film of a discontinuous metal film using dielectrophoresis; the olfactory receptor layer is composed of thiol molecules.

2. The production method according to claim 1, wherein Step (2) The dielectric electrophoresis technique includes: placing a substrate with a deposited permeated metal nanofilm in a solution containing acceptor molecules, applying a voltage of 1~10 V for 1~10 min, and driving the acceptor molecules to orientedly assemble to both sides of the nano gap.

3. The production method according to claim 2, wherein It also includes step (3): annealing process to enhance the bonding stability between the acceptor layer and the metal film.

4. A gas sensor based on the multi-channel quantum tunnelling effect, characterised in that, The invention comprises a discontinuous metal film and an olfactory receptor layer; the discontinuous metal film includes a substrate and a nano-gap film disposed on the substrate; the nano-gap film includes randomly distributed nano-islands, with nano-gap formed between any two adjacent nano-islands; the olfactory receptor layer is modified onto the nano-gap film; the olfactory receptor layer is monolayer oriented and modified onto the nano-gap of the nano-gap film by dielectrophoresis; the olfactory receptor layer is composed of thiol molecules.

5. The gas sensor of claim 4, wherein The distance of the nano-gap is sub-10 nm.

6. The gas sensor of claim 5, wherein The olfactory receptor layer is composed of thiol molecules, including any one or more of 11-mercaptoundecanoic acid, 4-mercaptobenzoic acid, 1-octanethiol, 4-methylthiophenol, 1-hexadecylthiol, L-cysteine, 6-mercapto-1-hexanol, and porphyrin thiol derivatives.

7. A gas detection method characterized by, Detection using a gas sensor as described in any one of claims 4 to 6 includes the following steps: (a) Place the gas sensor in the vacuum test chamber; (b) Set the programmed gas intake through a gas flow meter and collect the conductivity signal through an electrical signal device; The method described is not intended for the diagnosis and treatment of diseases.

8. The application of the gas sensor according to any one of claims 4 to 6 or the gas sensor prepared by the preparation method according to any one of claims 1 to 3 in any one or more of the following: In the field of agricultural and food gas monitoring, this includes the detection of any one or more of ammonia, ethylene, sulfur dioxide, hydrogen sulfide, and methane. The field of ambient air quality monitoring, including urban and regional ambient air quality monitoring; In the field of industrial process control and safety monitoring, this includes early warning of leaks of flammable, toxic and harmful gases in hazardous chemical storage and transportation, and fire emergency rescue scenarios; In the fields of healthcare and life sciences, not for the diagnosis and treatment of diseases.

Images