Single-particle nano-catalyst detection system and method based on quantum tunneling effect

Abstract

The invention provides a single-particle nano-catalyst detection system based on a quantum tunneling effect, a detection method and application. A quantum tunneling electrode with sub-5nm gaps is constructed as a sensing core, the surface of the tunneling electrode is modified with a functional layer, and a gate potential is combined to regulate and control the catalytic reaction of a single-particle nano-catalyst, so that a'conductivity-electrochemical 'signal joint characterization strategy is formed, and in-situ capture and recognition of a single nano-particle can be realized at an extremely high signal-to-noise ratio; and physical attributes and dynamic catalytic reaction information are synchronously obtained, so that a brand new technical scheme is provided for accurate and comprehensive characterization of the nano-catalyst on a single molecule level.

Description

Technical Field

[0001] This invention relates to the field of single-particle nanocatalyst detection technology, and more specifically, to a single-particle nanocatalyst detection system and method based on the quantum tunneling effect. Background Technology

[0002] In the field of nanocatalysis, accurately characterizing the physical properties and catalytic activity of individual nanocatalysts is crucial for understanding their intrinsic performance and revealing the structure-activity relationship. Single-particle electrochemical characterization techniques have become an important research tool in this field due to their high sensitivity, real-time monitoring capabilities, and quantitative analysis potential.

[0003] Traditional characterization of nanocatalysts typically involves averaging measurements across a population of hundreds of millions of particles. This method masks the individual differences between particles. The performance of nanocatalysts is not uniform; these individual differences are crucial for understanding and optimizing their performance. Many factors contribute to these individual differences, such as variations in size, shape, surface condition, and the microenvironment in which they exist. Averaging measurements produce blurry and distorted images that fail to reveal the true structure-activity relationship.

[0004] By directly measuring the catalytic activity of individual, well-defined nanoparticles and simultaneously acquiring their size, morphology, surface chemistry, and other physical properties, a precise structure-performance correspondence can be established. For example, a 5nm icosahedral gold particle with cysteine ​​modified on its surface can directly provide the intrinsic transformation frequency of hydrogen peroxide decomposition at pH=7 through single-particle measurement, a feat impossible with group measurements. Based on real single-particle data, synthetic scientists can be guided to precisely control synthetic parameters, mass-produce catalysts with desired high-performance structures, and in the future, this can be developed into a catalyst screening chip at the single-particle level, greatly accelerating the development cycle of new catalytic materials and possessing disruptive potential.

[0005] Existing methods for detecting single-particle nanocatalysts typically employ collisional electrochemistry using micrometer-sized electrodes, relying on monitoring Faraday current steps induced by random particle collisions to obtain catalytic activity information. However, these methods suffer from extremely high background noise due to the use of macroscale electrodes, making the detection of weak signals (such as small-sized, low-activity particles) extremely difficult. They can only acquire statistical electrochemical signals, failing to simultaneously obtain the intrinsic physical properties of the same particle (such as size and dielectric properties). Furthermore, non-specific adsorption of particles on the electrode surface is difficult to avoid, resulting in insufficient analytical fidelity for single-particle events. The detection limit of this method is only about 5 nanometers, and in conventional collision experiments, nanoparticles may undergo non-specific adsorption or aggregation on the electrode surface, leading to simultaneous reactions of multiple particles or signal overlap. This makes it difficult to guarantee that the observed current step originates from a clear, isolated single-particle event, affecting the accuracy of kinetic data interpretation.

[0006] High-sensitivity detection of microscopic matter can be achieved by monitoring electrical signals such as quantum tunneling current using scanning tunneling microscopy or nanogap devices. However, these techniques are mostly focused on static conductivity measurements in ultra-high vacuum or atmospheric environments, making them difficult to directly apply to in-situ, dynamic monitoring of liquid-phase catalytic reactions. Meanwhile, the stable fabrication of sub-5 nm gaps suitable for electrochemical systems still faces significant technological challenges. To capture transient collision signals, micrometer-scale or tens of nanometer-scale electrodes are typically used. Larger electrode surface areas result in excessively large background capacitance currents generated by double-layer charging. The weak Faradaic current changes (typically in the pA range) generated by nanocatalyst reactions are easily drowned out by background noise and difficult to distinguish effectively, fundamentally limiting further improvements in signal-to-noise ratio and sensitivity. The current signal intensity is directly proportional to the number of electrons transferred in the catalytic reaction. For reactions with few reaction sites, extremely small sizes (<5 nm), or slow catalytic kinetics (electron transfer rate constant k), this is particularly problematic. 0 Small nanocatalysts generate weak current signals, and the detection capabilities of existing platforms are severely insufficient, resulting in blind spots in the performance research of such catalysts.

[0007] Therefore, there is an urgent need to find a method based on the quantum tunneling effect to detect single-particle nanocatalysts with higher precision. Summary of the Invention

[0008] To address the problems existing in the prior art, this invention provides a single-particle nanocatalyst detection system, detection method, and application based on the quantum tunneling effect. By constructing a quantum tunneling electrode with a sub-5 nm gap as the sensing core and modifying the surface of the tunneling electrode with a functionalized layer, and combining this with gate potential modulation of the catalytic reaction of the single-particle nanocatalyst, a joint characterization strategy of "conductivity-electrochemical" signals is formed. This strategy enables in-situ capture and identification of individual nanoparticles with an extremely high signal-to-noise ratio, simultaneously acquiring their physical properties and dynamic catalytic reaction information. Therefore, it provides a novel technical solution for the precise and comprehensive characterization of nanocatalysts at the single-molecule level.

[0009] On one hand, the present invention provides a detection system for single-particle nanocatalysts, the system including a tunneling electrode with a nano-gap of sub-5 nanometers; the single-particle nanocatalyst is bridged on the nano-gap of the tunneling electrode by diffusion, or diffuses into the nano-gap of the tunneling electrode.

[0010] This invention aims to provide a single-particle nanocatalyst detection platform based on the quantum tunneling effect, addressing core issues in existing characterization techniques such as high background noise, limited information dimensions, insufficient detection capability for weak-signal catalysts, and low fidelity of single-particle events. This platform achieves ultra-high sensitivity detection under extremely low background noise, ensuring the detection of clearly defined single-particle events, and stably and effectively tests nanocatalysts that are difficult to characterize using traditional collisional electrochemistry.

[0011] This invention changes the detection signal of a single-particle nanocatalyst from the macroscopic Faraday current on the surface of a micrometer electrode to the quantum tunneling current within the sub-nanometer gap. The tunneling current essentially flows only through atomic-scale channels, resulting in extremely low background capacitance current and a significantly improved signal-to-noise ratio.

[0012] The spacing of the quantum tunneling electrodes needs to be stably controlled within sub-5 nanometers, which is the physical hardware foundation for achieving ultra-high signal-to-noise ratio and extreme detection sensitivity of single-particle nanocatalysts. The noise of micrometer electrodes mainly comes from the large electrode / solution interface; the equivalent electrochemical area of ​​a sub-5 nanometer gap is approximately 10 times smaller than that of a micrometer electrode. 8 The background noise is reduced dramatically by a factor of two. For particles with extremely small size (e.g., < 3 nm) or very low catalytic activity, their ability to modulate the potential barrier or transfer electrons is extremely weak. Only by utilizing the exponential amplification effect of tunneling current can these weak perturbations be converted into measurable current changes. In larger gaps, such perturbations are drowned out by the background. Tunneling current has exponential sensitivity to small changes in the dielectric environment within the gap, enabling reliable detection and amplification of weak perturbations caused by the entry of individual nanoparticles or even molecules into the gap. This allows for single-particle characterization of small-sized (< 3 nm) and low-activity catalysts.

[0013] The tunneling electrode provided by this invention comprises a pair of metal electrodes with a stable spacing of 1-5 nanometers, forming a quantum tunneling junction. This gap is achieved through a controllable electrode fabrication process (such as mechanically controlled fracture or electrochemical deposition / etching), ensuring its mechanical and electrochemical stability in an electrolyte environment. The quantum tunneling electrode pair is integrated into a carbon-filled nanopipette tip, constituting the sensing region where the quantum tunneling effect occurs. The electrode tip is composed of a conductive material, such as common metals (gold, silver, platinum, etc.).

[0014] When the particle size of a single nanocatalyst is smaller than the nano-gap of the tunneling electrode, the single nanocatalyst can diffuse into the 1-3 nanometer quantum tunneling gap, and its tunneling current modulation signal has a high signal-to-noise ratio and distinguishability.

[0015] When the particle size of a single nanocatalyst is larger than the nano-gap of the tunneling electrode, it diffuses and bridges the nano-gap of the tunneling electrode (bridging is also an instantaneous and random event; the current at this instantaneous bridging is sufficient, without the need for long-term adhesion). In other words, the single nanocatalyst can act as a bridge across the nano-gap, connecting the two ends of the nano-gap and enabling the currents of the two electrodes to flow together. The single nanocatalyst can be detected with high sensitivity at the instant of connection.

[0016] Furthermore, the nano-gap of the tunneling electrode is 1-3 nanometers; the diameter of the single-particle nanocatalyst is 1-50 nanometers.

[0017] The gap between the quantum tunneling electrodes is preferably 1 to 3 nanometers, which is a key scale to ensure the purity, stability and exponential sensitivity of the quantum tunneling effect. At the same time, it reserves space for the anti-adsorption functionalized layer on the electrode surface, and is also the best balance between physical limits and engineering feasibility.

[0018] Traditional collisional electrochemistry can typically detect particles larger than 5 nanometers, but its sensitivity is insufficient for smaller particles. This technology advances the detection limit to 1 nanometer or even smaller through a tunneling mechanism, but the upper limit is still limited by the gap size and signaling mechanism. Therefore, setting it to 50 nanometers is a reasonable engineering and scientific compromise.

[0019] When the particle size of a single-particle nanocatalyst is 1–3 nanometers and smaller than the nano-gap of the tunneling electrode, the single-particle nanocatalyst can diffuse into the 1–3 nanometer quantum tunneling gap. However, when the particle size of a single-particle nanocatalyst is larger than 3 nanometers and larger than the nano-gap of the tunneling electrode, it diffuses and bridges the nano-gap of the tunneling electrode for detection. It is evident that the single-particle nanocatalyst cannot be too large; if it is too large, it may be unable to bridge the tunneling gap, making effective modulation of the tunneling current difficult.

[0020] Therefore, the preferred particle size of the single-particle nanocatalyst to be tested is 1 to 50 nanometers, and the preferred nano-gap of the tunneling electrode is 1 to 3 nanometers. This is the preferred combination, exhibiting the best matching relationship. When the particle size is comparable to the gap size (1-3 nanometers), the particle can modulate the tunneling barrier to the maximum extent, generating the strongest detection signal, suitable for the detection of extremely small objects. When the particle size is larger than the gap size but smaller than approximately 50 nanometers, the particle can still effectively contact the gap region through a bridge-like mechanism, generating a clearly distinguishable signal. Therefore, it is suitable for the detection of most highly active nanocatalysts, enabling a single-specification tunneling probe to be applicable to the characterization of nanocatalysts across a wide size range, ensuring ultra-high sensitivity while possessing broad applicability.

[0021] Furthermore, the surface of the tunneling electrode is modified with a functionalized layer, which includes an anti-adsorption functionalized layer and / or a trapping functionalized layer; the anti-adsorption functionalized layer is used to prevent single-particle nanocatalysts from adsorbing onto the surface of the tunneling electrode during diffusion; the trapping functionalized layer is used to trap single-particle nanocatalysts with microbubbles during the catalytic reaction.

[0022] When tunneling electrodes are used to detect the physical properties of single-particle nanocatalysts, their surfaces need to be modified with an anti-adsorption functionalized layer. This is because, during detection, single-particle nanocatalysts diffuse randomly into the tunneling gap region. If non-specific adsorption occurs on the electrode surface, a single nanocatalyst may be adsorbed near or within the nano-gap for an extended period, resulting in the detection of the same current signal. Alternatively, multiple single-particle nanocatalysts may be adsorbed near the nano-gap simultaneously, making it impossible to truly detect single-particle nanocatalysts. Therefore, the core function of modifying the surface of the nano-gap electrode pair with an anti-adsorption functionalized layer is to prevent non-specific adsorption of the nanocatalyst on the electrode surface, ensuring that the nanocatalyst in solution enters the tunneling gap region randomly and independently only through diffusion, thus guaranteeing that each current change signal corresponds to an isolated single-particle event.

[0023] By using an anti-adsorption functionalized layer on the electrode surface, the random adsorption and aggregation of nanoparticles on the electrode surface are physically blocked, ensuring that only individual particles diffused into the nano-gap region can be detected, fundamentally improving the fidelity of single particle detection and the reliability of data.

[0024] When single-particle nanocatalysts generate bubbles during catalytic reactions (for example, platinum and palladium particles act as catalysts, reducing specific molecules in the solution, such as hydrazine, to hydrogen gas on the nanoparticle surface, creating bubbles that encapsulate the particle surface), the surface of the tunneling electrode needs to be modified with a trapping functionalized layer. This layer traps the nanoparticles in the tunneling gaps through intermolecular forces, allowing the nanoparticles to continuously generate bubbles for the catalytic reaction, thus enabling longer-term detection of the catalytic reaction process. During the catalytic reaction, as the reaction proceeds, the size of the microbubbles generated on the surface of the single-particle nanocatalyst gradually increases, eventually forming nitrogen bubbles that encapsulate and isolate the single-particle nanocatalyst from the solution. These bubbles can carry the nanoparticles away from the tunneling gaps, making it difficult to detect the entire catalytic reaction process. To ensure that the process of gradually generating microbubbles until completely encapsulating and isolating them can be fully detected, the surface of the tunneling electrode needs to be modified with a trapping functionalized layer. This ensures that the single-particle nanocatalyst is always trapped within the nano-gap of the tunneling electrode, allowing for real-time monitoring and continuous recording of the transient signal changes in the tunneling current throughout the entire reaction process.

[0025] Further, the anti-adsorption functionalized layer includes any one or more of mercaptopropane, propyl disulfide, 6-mercapto-1-hexanol (MCH), 1-dodecanethiol, 1-octanethiol, 1-dodecanethiol, (3-aminopropyl)triethoxysilane, octadecyl phosphoric acid, polyethylene glycol, polyacrylic acid, and polystyrene sulfonic acid; the trapping functionalized layer includes any one or more of mercaptopropionic acid, cysteine, and aminopropyltriethoxysilane.

[0026] In some embodiments, the anti-adsorption functionalized layer comprises an organic compound having a thiol group.

[0027] The specific components of the anti-adsorption functionalized layer and the trapping functionalized layer need to be selected based on the specific composition of the single-particle nanocatalyst. Different single-particle nanocatalysts may require different anti-adsorption and trapping functionalized layers. For example, for a single-particle nanocatalyst, the anti-adsorption functionalized layer on the tunneling electrode must prevent long-term adsorption of single particles while ensuring that the single-particle nanocatalyst to be tested can be successfully bridged or enter the nano-interstitial spaces for successful detection. In other words, the anti-adsorption performance of the anti-adsorption functionalized layer cannot be too good, which would prevent the single-particle nanocatalyst to be tested from being successfully bridged or entering the nano-interstitial spaces, thus making it undetectable; nor can it be too bad, which would result in long-term adsorption of single particles, affecting the detection effect.

[0028] In some approaches, when the single-particle nanocatalyst is a gold nanoparticle, mercaptopropane is preferably used as the anti-adsorption functional layer and cysteine ​​as the capture functional layer.

[0029] Furthermore, when microbubbles are generated during the catalytic reaction of the single-particle nanocatalyst, the surface of the tunneling electrode is modified with a trapping functionalized layer; when microbubbles are not generated during the catalytic reaction of the single-particle nanocatalyst, the surface of the tunneling electrode is modified with an anti-adsorption functionalized layer.

[0030] When tunneling electrodes are used to detect the catalytic kinetics of single-particle nanocatalysts, two scenarios need to be considered. If bubbles are generated during the catalytic reaction of the single-particle nanocatalyst, the surface of the tunneling electrode needs to be modified with a trapping functionalized layer. If no bubbles are generated during the catalytic reaction of the single-particle nanocatalyst, the tunneling electrode modified with an anti-adsorption functionalized layer can continue to be used.

[0031] In other words, if a single-particle nanocatalyst can actively leave the surface through its own reaction (generating microbubbles), then a trapping functionalized layer is needed to anchor it to the electrode surface as much as possible. If a single-particle nanocatalyst does not have a similar effect, then a repulsive functionalized layer needs to be modified to allow each spike signal to be statistically analyzed as an independent event.

[0032] Furthermore, it also includes a weak current detection component and a gate potential control component; the weak current detection component is electrically connected to the tunneling electrode and is used to apply a bias voltage to the tunneling electrode and detect tunneling current changes in the picoampere to femtoampere range; the gate potential control component is used to control the gate potential of the tunneling electrode.

[0033] The weak current signal detection component consists of a high-sensitivity current amplifier (weak current detection device) and a signal acquisition unit, with its input terminal directly connected to the electrode lead at the tail end of the tunneling electrode. This component is responsible for applying a bias voltage (Vbias) between the tunneling electrodes to establish a measurable quantum tunneling current baseline and for real-time acquisition of the quantum tunneling current. Its detection sensitivity needs to reach the femtoampere (fA) to picoampere (pA) range, which is crucial for achieving high signal-to-noise ratio detection on this platform.

[0034] The gate potential control system includes an adjustable power supply and a precision sliding rheostat. One end of the adjustable power supply is connected to a reference electrode and placed in a solution tank, while the other end is connected to the precision sliding rheostat, which is connected to a weak current signal detection system. By changing the output of the power supply and the resistance value of the sliding rheostat, a corresponding potential can be applied to the surface of the quantum tunneling electrode, thereby controlling the surface potential (gate potential, Vgating) of the quantum tunneling electrode pair (working electrode).

[0035] The gate potential refers to the voltage applied to the individual gate electrodes (i.e., the overall offset of the two working electrode voltages relative to the reference electrode voltage), used to regulate the energy level structure of the system. The bias voltage refers to the voltage applied between the two working electrodes (tunneling electrodes) (i.e., the voltage applied across the single particle under test), used to drive electron tunneling. For example, the reference electrode voltage can be considered as 0, the potential of working electrode 1 is Vr, and the potential of working electrode 2 is Vr + Vb. Vr is called the gate voltage, which is the overall offset of the two working electrode voltages relative to the reference electrode voltage, and Vb is called the bias voltage between the two electrodes.

[0036] By employing a weak current detection component and a gate potential control component, the dynamic catalytic reaction process of single-particle nanocatalysts can be detected, which is also a form of dynamic detection. Dynamic detection refers to real-time adjustment of the gate potential during detection using a tunneling electrode; static detection refers to maintaining a constant gate potential and bias voltage during detection using a tunneling electrode. In static detection, no catalytic reaction occurs in the single-particle nanocatalyst, so only its physical properties are detected. In dynamic detection, as the gate potential changes and reaches the catalytic reaction energy level of the single-particle nanocatalyst, the catalytic activity of the nanocatalyst is activated, i.e., a catalytic reaction occurs. This allows for the detection of catalytic kinetic information of single-particle nanocatalysts, overcoming the limitations of passive observation in traditional single-particle nanocatalyst detection and enabling dynamic control and high-dimensional analysis of the conductivity of single-particle nanocatalysts.

[0037] The conductivity refers to the resistance value obtained by the single-particle nanocatalyst under specific current and voltage conditions.

[0038] In some approaches, a data acquisition and processing system is also included to simultaneously acquire and analyze the changes in tunneling current over time and potential.

[0039] The data acquisition and processing system consists of a high-speed data acquisition card and host computer software. It synchronously records the current signal from the current amplifier and performs real-time analysis and feature extraction on the current-time curve through built-in algorithms (such as identifying current spikes and calculating residence time), thereby converting the tunneling current signal into the conductivity information and catalytic reaction information of the nanocatalyst.

[0040] As can be seen, the detection system provided by this invention can realize multi-dimensional signal integration detection of single-particle nanocatalysts: in a single test, by monitoring the step change of steady-state tunneling current caused by particle entry, the size or presence of non-Faraday modes can be detected; by applying a reaction potential on the basis of the step and observing the further time-domain fluctuation of the current, the Faraday catalytic kinetic information of the single particle can be obtained simultaneously.

[0041] Furthermore, it also includes a reaction chamber containing an electrolyte, wherein the electrolyte comprises any one or more of the following: phosphate buffer, phosphate buffer, acetate buffer, sodium perchlorate, potassium nitrate, and potassium chloride solution.

[0042] In quantum tunneling detection, the electrolyte has multiple influences because it directly constitutes the "medium environment" in which tunneling occurs. It affects the diffusion, surface charge, and stability of single-particle nanocatalysts, and may even influence the catalytic reaction rate and the functionalized layer of the tunneling electrode. Therefore, selecting a suitable electrolyte (such as a 10-100 mM buffer salt) to balance electric field localization and solution effects, and to ensure the diffusion performance, surface charge, and stability of single-particle nanocatalysts, helps improve the detection performance of these nanocatalysts.

[0043] In some embodiments, when the single-particle nanocatalyst is a gold nanoparticle, the electrolyte is a phosphate buffer solution.

[0044] Furthermore, the present invention provides a method for detecting single-particle nanocatalysts, the method employing the detection system described above, and comprising the following steps:

[0045] (1) Contact the tunneling electrode with the sample solution containing the single-particle nanocatalyst to be tested;

[0046] (2) Capture the tunneling current signal generated by the diffusion bridging of single-particle nanocatalysts on the nano gaps of the tunneling electrode, or by the diffusion into the nano gaps of the tunneling electrode, to obtain the first type of characteristic signal of single-particle nanocatalysts.

[0047] Furthermore, the first type of feature signal includes physical property signal, and the physical property information includes any one or more of the core material, modification group, size, and solution environment of the single-particle nanocatalyst; step (1) requires first contacting the sample solution without the single-particle nanocatalyst to be tested through the tunneling electrode to obtain the background signal.

[0048] In some methods, step (1) includes:

[0049] S1: Provides a functionalized nano-gap tunneling electrode with a gap distance of sub-nanometer to 5 nanometers and an anti-adsorption functionalized layer on the electrode surface.

[0050] S2: The functionalized nano-gap tunneling electrode is immersed in an electrolyte containing the nanocatalyst to be tested, and a constant bias voltage is applied between the tunneling electrodes to establish a stable background quantum tunneling current.

[0051] Step (2) includes:

[0052] S3: Monitor the change of quantum tunneling current over time; when a single nanocatalyst particle diffuses into the nano gap region, the particle modulates the tunneling barrier within the gap, causing the quantum tunneling current to generate a first-type characteristic signal change.

[0053] Furthermore, it also includes step (3): changing the gate potential of the tunneling electrode to excite the single-particle nanocatalyst to undergo a catalytic reaction, capturing the tunneling current signal generated by the single-particle nanocatalyst to obtain the catalytic kinetic information (second type of characteristic signal) of the single-particle nanocatalyst.

[0054] During detection, the nanocatalyst in solution undergoes free diffusion. When a single catalyst particle randomly enters the tunneling region of the functionalized nano-interstic gap, it significantly modulates the electron tunneling barrier of the gap, causing a discrete step change in the baseline tunneling current. Subsequently, a specific electrochemical potential is applied through a potential control system to excite the catalytic reaction of the particle. During the reaction, the instantaneous changes in the electronic state (redox state) of the catalyst are reflected with high sensitivity and in real time as fluctuations or secondary step signals superimposed on the aforementioned current step. By analyzing this composite current signal, the catalytic characteristics of a single particle can be obtained.

[0055] During the dynamic adjustment of the gate potential, the catalytic reaction of a single-particle nanocatalyst typically involves the following three processes: 1. It is in a stable state; 2. As the gate potential increases, the catalytic reaction begins; 3. The gate potential continues to increase, and the single particle is continuously subjected to catalytic reactions. The gate potential required for the three processes of different single-particle nanocatalysts is different, and their tunneling current signal spectra are also completely different.

[0056] In some approaches, depending on the purpose of the test, a functionalized layer needs to be modified on the surface of the tunneling electrode. If the physicochemical information of a single-particle nanocatalyst is required, an anti-adsorption functionalized layer needs to be modified on the surface of the tunneling electrode before the test; if the catalytic kinetic information of a single particle is required, and the single-particle nanocatalyst generates bubbles during the catalytic process, a trapping functionalized layer needs to be modified on the electrode surface.

[0057] In some embodiments, the method includes the following steps:

[0058] Step 1: Test System Initialization and Background Baseline Establishment. A functionalized nanopipette probe (with an anti-adsorption functionalized layer modified on the surface of the tunneling electrode) is immersed in an electrolyte containing a reactive substrate (such as hydrazine or hydrogen peroxide). A predetermined tunneling bias V_Bias and a non-reactive surface potential (e.g., 0 mV vs. Ag / AgCl for hydrazine oxidation) are applied via a weak current detection component and a gate potential control component. In this steady-state state, the data acquisition system records the current for a period of time to obtain a low-noise background tunneling current baseline I1.

[0059] Step 2: Nanocatalyst conductivity acquisition. A nanocatalyst dispersion (i.e., a solution containing nanocatalysts, including nanocatalysts and a solvent, specifically a 20 mM phosphate buffer solution (pH=7.4)) is introduced into the electrolyte. The catalyst particles diffuse via Brownian motion. When a single nanocatalyst particle randomly enters the interstitial region, its physical presence significantly modulates the effective dielectric constant or electron tunneling barrier within the interstitial region, resulting in a discrete, step-like jump (I2) in the tunneling current. This signal is captured by the system and labeled as a "single-particle capture event." By statistically analyzing the I2 of a large number of such events, the characteristic conductivity distribution of the particle population can be obtained, which can be used to distinguish particle size, material, or surface modification.

[0060] Step S3: Excitation and Real-time Monitoring of the Catalytic Reaction by the Nanocatalyst. The anti-adsorption functionalized layer on the surface of the tunneling electrode is replaced with a trapping functionalized layer. Keeping the bias voltage V_Bias constant, the surface potential Vg of the tunneling electrode is switched to a preset catalytic reaction potential (e.g., +600 mV vs. Ag / AgCl for silver particle oxidation) using a gate potential control system. At this point, the trapped nanoparticles are activated, and a catalytic reaction occurs on their surface. The accompanying electron transfer changes the tunneling current state in real-time, rapidly, and with high gain, thus generating an additional signal amplification on top of the current I2. By monitoring and analyzing the amplitude, frequency, and other characteristics of these dynamic signals, the catalytic kinetics of the single particle can be determined.

[0061] Step S4: Data Analysis and Result Output. The system software automatically processes the current-time-location data collected throughout the process, extracts feature parameters from multiple dimensions, including single-particle characteristic conductivity, reaction current amplitude, and signal decay time, and generates corresponding statistical charts to complete the evaluation of the comprehensive performance of the nanocatalyst.

[0062] Furthermore, this invention provides a method for detecting the physical properties of single-particle nanocatalysts. The method employs the detection system described above and includes the following steps:

[0063] (1) Contact the tunneling electrode with the sample solution containing the single-particle nanocatalyst to be tested;

[0064] (2) Capture the tunneling current signal generated by the diffusion bridging of single-particle nanocatalysts on the nano gaps of the tunneling electrode, or by the diffusion into the nano gaps of the tunneling electrode, and obtain the physical property information of single-particle nanocatalysts.

[0065] Furthermore, this invention provides a method for detecting the catalytic kinetics information of single-particle nanocatalysts. The method employs the detection system described above and includes the following steps:

[0066] (1) Contact the tunneling electrode with the sample solution containing the single-particle nanocatalyst to be tested;

[0067] (2) Change the gate potential of the tunneling electrode to excite the single-particle nanocatalyst to undergo catalytic reaction, capture the tunneling current signal generated by the single-particle nanocatalyst to obtain the catalytic kinetic information of the single-particle nanocatalyst.

[0068] The beneficial effects of this invention are as follows:

[0069] 1. Limiting sensitivity and ultra-high signal-to-noise ratio: The quantum tunneling junction has an extremely small equivalent electrochemical surface area, and its background capacitance and thermal noise are several orders of magnitude lower than those of micrometer electrodes, making it possible to detect the weak catalytic current of a single nanoparticle (especially the low electron transfer process).

[0070] 2. Ensure the fidelity of single-particle detection: The unique anti-adsorption functional design of the electrode surface effectively prevents particle aggregation and non-specific adsorption, ensuring that each detection signal corresponds to a clear and isolated single-particle event, making the kinetic analysis more accurate and reliable.

[0071] 3. Expanding the detection limit: It can effectively characterize small-sized (<3 nm), low-activity, slow-kinetic nanocatalysts that cannot be reliably detected by traditional collision electrochemistry, filling the gap in existing technology.

[0072] 4. Provides multidimensional information: In a simple experiment, the physical existence signal of a single nanoparticle (modulated by tunneling current) and the intrinsic catalytic activity signal (excited by potential) can be obtained simultaneously, realizing a more comprehensive characterization of single-particle catalysts.

[0073] 5. Introduction of single-particle event guarantee mechanism: Through the anti-adsorption functionalized layer on the electrode surface, the random adsorption and aggregation of nanoparticles on the electrode surface are physically blocked, ensuring that only single particles diffuse into the nano gap region can be detected, which fundamentally improves the fidelity of single-particle detection and the reliability of data. Attached Figure Description

[0074] Figure 1 This is a schematic diagram of the overall structure of the quantum tunneling probe device (tunneling electrode) based on a double-hole glass pipette in the quantum tunneling probe detection device of Example 1.

[0075] Figure 2 This is a schematic diagram of the pyrolysis carbon deposition process in Example 1;

[0076] Figure 3 This is a typical tunneling probe tip morphology in Example 2;

[0077] Figure 4The equivalent circuit diagram of the weak current signal detection system in Example 2 is shown below.

[0078] Figure 5 This is the circuit diagram of the test system in Example 2;

[0079] Figure 6 This is a schematic diagram illustrating the detection principle of the single-particle nanocatalyst in Example 3;

[0080] Figure 7 This is an example diagram of the statistical method for the main characteristic current-time curve in Example 3;

[0081] Figures 8-10 The image shows the detection spectrum of L-cysteine-modified gold nanoparticles in Example 4. Figure 8 This represents the characteristic tunneling current signal of gold nanoparticles. Figure 9 Analysis of signal event width for different bias current boost values. Figure 10 The current enhancement value of gold nanoparticles, and the relationship between conductivity ratio and bias voltage;

[0082] Figures 11-12 The above is the detection spectrum of gold nanoparticles modified with mercaptopropionic acid and mercaptopropylamine in Example 4, wherein... Figure 11 The characteristic conductivity distribution of gold nanoparticles with different modification groups in PB solution is shown. Figure 12 To distinguish gold nanoparticles with different modified groups in a mixed phase by statistically analyzing their electrical conductivity characteristics;

[0083] Figures 13-14 The images show the detection spectra of nanocatalysts with different core materials in Example 4; whereby... Figure 13 The spectrum of nanocatalysts detected by silver nanoparticles; Figure 14 The spectrum of the nanocatalysts detected by the gold nanoparticles;

[0084] Figure 15 This is a current-time distribution diagram of gold nanoparticles with different protecting groups in Example 4 under different pH environments;

[0085] Figure 16 This is a distribution diagram of characteristic signals from non-redox potential to redox potential in Example 5, where the red circles represent the characteristic signals of silver particle oxidation;

[0086] Figure 17 This is a correlation diagram of the peak signal conductivity distribution vs. surface potential intensity of the 10nm silver particles in Example 5.

[0087] Figure 18 The figure shows the effect of particle size on electron transfer capability and catalytic response intensity in Example 6;

[0088] Figures 19-21This is a diagram showing the differences in tunneling characteristic signals of 10nm silver particles with different modified groups in Example 6 at a bias voltage of 100mV and a surface potential of 600mV; whereby... Figure 19 Modified with L-mercaptopropylamine group; Figure 20 Modified with L-cysteine ​​groups; Figure 21 Modified with L-mercaptopropionic acid group;

[0089] Figure 22 Ag in Example 6 44 The relationship between the conductivity ratio and surface potential of silver nanoclusters;

[0090] Figures 23-25 The diagram shows the structure and properties of the silver nanoclusters in Example 6. Figure 23 The specific structure of silver nanoclusters, Figure 24 Electron micrograph of silver nanoclusters. Figure 25 The image shows the UV-Vis absorption spectrum of silver nanoclusters.

[0091] Figures 26-29 The graphs show the detection results of different anti-adsorption functionalized layers used in Example 9; wherein... Figure 26 This refers to the case of an unmodified electrode; Figure 27 This refers to the case of propyl disulfide modification; Figure 28 For cases modified by MCH; Figure 29 The case is modified with 1-dodecylthiol;

[0092] Figures 30-31 This is the detection result spectrum of the cysteine-based trapping functionalized layer used in Example 10; wherein... Figure 30 This refers to the case of an unmodified electrode; Figure 31 This refers to the case of L-cysteine ​​modification. Detailed Implementation

[0093] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate understanding of the present invention and are not intended to limit it in any way. The reagents used in this embodiment are all known products and were obtained by purchasing commercially available products.

[0094] Example 1: Preparation of tunneling electrode

[0095] The quantum tunneling probe device (tunneling electrode) based on a two-hole glass pipette in the quantum tunneling probe detection device provided in this embodiment is as follows: Figure 1 As shown, ① is a nano-gap electrode pair, ② is a conductive material, ③ is a metal wire, and ④ is a dual-channel glass pipette. The preparation method is as follows:

[0096] Step 1: Draw the double-hole glass pipette into a probe with a single-sided tip.

[0097] The double-hole glass pipette, after being treated with a plasma cleaner, was placed in a P-2000 laser drawing instrument and drawn using a two-step method. The double-hole glass tube has an outer diameter of 1.2 mm, an inner diameter of 0.9 mm, and a length of 100 mm.

[0098] The two-step method is as follows: First, a laser beam is applied to heat the middle part of the thin glass tube while simultaneously pulling it. The pulling parameters are set as follows: Heat: 850, Filament: 4, Velocity: 30, Delay: 160, Pull: 100. Second, the parameters are set as follows: Heat: 860, Filament: 3, Velocity: 20, Delay: 140, Pull: 160. The pulling process ends, resulting in two identical double-hole glass probes with single-sided tips.

[0099] Step 2: Deposit pyrolytic carbon inside a double-hole glass tube with a single-sided tip.

[0100] The double-hole glass probe prepared in step one is placed in a single-hole quartz glass tube, and a constant flow rate of 0.2 m³ / s is passed through the single-hole glass tube from the tip of the double-hole glass tube to the tail end. 3 Argon gas is used as a protective gas at a pressure of 1 / min. A rubber hose is connected to the tail end of the double-hole glass probe, and the hose is connected to butane gas at 3 atmospheres. The butane flame preheats the front end of the quartz tube. The protective gas inside the tube carries the heat to the tip of the double-hole tube, which glows yellow. This glow is maintained for 10 seconds, during which time the butane inside the double-hole tube pyrolyzes into elemental carbon, which is deposited at the tip. The butane flame is then slowly moved towards the tail end of the double-hole tube until the pyrolyzed carbon is fully deposited about 1 cm from the tip. The carbon deposition process is as follows: Figure 2 As shown.

[0101] Step 3: Deposit gold electrode pairs with nano-interstic gaps at the tip of the double-hole glass tube using electrochemical deposition.

[0102] A metal wire was inserted into the tail end of a double-hole glass tube, ensuring full contact with the pyrolytic carbon. Hot melt adhesive was used to fix the wire to ensure device stability. The tip of the double-hole glass tube was then placed in the gold plating solution. The tail end of the metal wire was connected to an electrochemical workstation using a three-electrode configuration: the working electrode was connected to one side of the wire, and the counter and reference electrodes were connected to the other side. These electrodes were periodically swapped throughout the deposition process to achieve simultaneous gold plating at both ends. Electrochemical gold deposition was performed using a constant current mode, and the voltage between the two electrodes was monitored. When the voltage between the electrode pairs approached 0 volts, it indicated that the distance between the electrode pairs was on the nanometer scale, and electrochemical deposition was terminated. At this point, the tunneling probe was removed from the gold plating solution and stored in ultrapure water. The metal wire was a copper wire with an outer diameter of 0.2 mm. The gold plating solution was a self-prepared gold electroplating solution containing 4.4 mM NH4AuSO3 and 52 mM (NH4)2SO3. The ultrapure water had a resistivity of 18.2 MΩ·cm. The entire electrochemical deposition process is carried out in a Faraday cage. The nanogap is controlled by adjusting the deposition time, which ranges from 10 to 600 seconds, to obtain a tunneling electrode with a nanogap of sub-5 nanometers. In this embodiment, the nanogap of the tunneling electrode is 1 to 3 nanometers (deposition time is 120 to 240 seconds).

[0103] Example 2: Single-particle nanocatalyst detection system

[0104] The single-particle nanocatalyst detection system package provided in this embodiment is an integrated precision measurement system, which mainly consists of the following four core subsystems connected by specific electrical and mechanical links to form an organic whole: quantum tunneling electrode, weak current signal detection component, gate potential control component, and data acquisition and processing system.

[0105] 1. Quantum tunneling electrode

[0106] Its core component is a functionalized tunneling electrode. The quantum tunneling electrode is integrated into the tip of a carbon-filled nanopipette, forming the sensing region where the quantum tunneling effect occurs. The electrode tip is composed of a conductive material, such as common metals (gold, silver, platinum, etc.), and its morphology is as follows: Figure 3 As shown. This embodiment uses the tunneling electrode prepared in Example 1 and performs functional modifications on it.

[0107] When used for detecting the physical properties of single-particle nanocatalysts, they need to be modified with an anti-adsorption functional layer; when used for detecting catalytic kinetics information, they need to be modified with a trapping functional layer.

[0108] 2. Weak current signal detection component

[0109] Composed of a high-sensitivity current amplifier (weak current detection device) and a signal acquisition unit, its input is directly connected to the electrode leads at the tail end of the nanopipette. This subsystem is responsible for applying a bias voltage (Vbias) between the tunneling electrodes to establish a measurable quantum tunneling current baseline and for real-time acquisition of the quantum tunneling current. Its detection sensitivity needs to reach the femtoampere (fA) to picoampere (pA) range, which is crucial for achieving high signal-to-noise ratio detection on this platform. The equivalent circuit diagram of the weak current signal detection component is shown below. Figure 4 The working electrode in the diagram is the tunneling electrode. The reference electrode (silver / silver chloride electrode (Ag / AgCl)) is used to monitor and control the potential of the working electrode, and the counter electrode (platinum counter electrode) is used to close the current loop to ensure the reaction proceeds.

[0110] 3. Gate potential control component

[0111] It includes an adjustable power supply and a precision sliding rheostat. One end of the adjustable power supply is connected to the reference electrode (Ag / AgCl can also be used as both the reference and counter electrode) and placed in the solution cell. The other end of the adjustable power supply is connected to the precision sliding rheostat, which is connected to a weak current signal detection system. By changing the output of the power supply and the resistance of the sliding rheostat, the corresponding potential can be applied to the surface of the quantum tunneling electrode pair, thereby controlling the surface potential (Vgating) of the quantum tunneling electrode pair.

[0112] 4. Data Acquisition and Processing System

[0113] It consists of a high-speed data acquisition card and host computer software. It synchronously records the current signal from the current amplifier and performs real-time analysis and feature extraction on the current-time curve through built-in algorithms (such as identifying current spikes and calculating residence time), thereby converting the tunneling current signal into the conductivity information and catalytic reaction information of the nanocatalyst.

[0114] Example 3: Detection method for single-particle nanocatalysts

[0115] This embodiment uses the single-particle nanocatalyst detection system provided in Example 2 to detect single-particle nanocatalysts. The detection principle diagram is shown below. Figure 6 As shown, this includes physical property information detection and catalytic kinetic information detection, specifically including the following steps:

[0116] 1. Test system initialization and background baseline establishment

[0117] The tunneling electrode prepared in Example 1 was functionalized by using an organic compound with a mercapto group, such as mercaptopropane. Taking mercaptopropane as an example, the specific modification method was as follows: the tunneling electrode was immersed in an ethanol solution containing 1 μM mercaptopropane for 24 hours, and then the tunneling electrode was taken out of the modification solution and rinsed with anhydrous ethanol for 1 minute.

[0118] The functionalized tunneling electrode was immersed in an electrolyte (such as phosphate buffer, phosphate buffer, acetate buffer, etc.; in this embodiment, it was 20 mM PB buffer, pH=7.4). Since the nanocatalyst used in this embodiment is silver particles, the silver particles undergo their own oxidation reaction, which is independent of the reaction substrate in the environment, and therefore no reaction substrate is required. A set tunneling bias voltage V_Bias and a non-reactive surface potential (e.g., 0 mV vs. Ag / AgCl for hydrazine oxidation) were applied through a potential control subsystem. Under this steady-state condition, the data acquisition system recorded the current for a period of time to obtain a low-noise background tunneling current baseline I1.

[0119] 2. Detection of physical properties of single-particle nanocatalysts

[0120] A nanocatalyst dispersion (i.e., a solution containing nanocatalysts, comprising nanocatalysts and a solvent, specifically 20 mM PB buffer at pH 7.4) is introduced into the electrolyte, where the catalyst particles diffuse via Brownian motion. When a single nanocatalyst particle randomly enters the interstitial region, its physical presence significantly modulates the effective dielectric constant or electron tunneling barrier within the interstitial space, resulting in a discrete, step-like jump (I²) in the tunneling current. This signal is captured by the system and labeled as a "single-particle capture event." Statistical analysis of I² from a large number of such events yields the characteristic conductivity distribution of the particle population, which can be used to differentiate particle size, material, or surface modification.

[0121] 3. Detection of catalytic kinetics information of single-particle nanocatalysts

[0122] The anti-adsorption functionalized layer on the surface of the tunneling electrode is replaced with a trapping functionalized layer. Keeping the bias voltage V_Bias constant, the surface potential Vg of the tunneling electrode is switched to a preset catalytic reaction potential (e.g., +600 mV vs. Ag / AgCl for silver particle oxidation) using a gate potential control system. At this point, the trapped nanoparticles are activated, and a catalytic reaction occurs on their surface. The accompanying electron transfer changes the tunneling current state in real time, rapidly, and with high gain, thus generating an additional signal amplification on top of the current I2. By monitoring and analyzing the amplitude, frequency, and other characteristics of these dynamic signals, the catalytic kinetics of this single-particle nanocatalyst can be determined.

[0123] 4. Data Analysis and Results Output

[0124] The system software automatically processes the current-time-location data collected throughout the process, extracting feature parameters from multiple dimensions, including single-particle characteristic conductance, reaction current amplitude, and signal decay time, and generating corresponding statistical charts. Figure 7The statistical method for the main characteristic current-time curve I2 is shown, which completes the evaluation of the comprehensive performance of the nanocatalyst.

[0125] Example 4: Differentiating the intrinsic properties of nanocatalysts based on quantum tunneling current characteristics

[0126] This embodiment uses the single-particle nanocatalyst detection system provided in Example 2, and performs intrinsic characteristic (physical property information) detection of the single-particle nanocatalyst according to the method in Example 3. By analyzing the transient signal (spike) of the quantum tunneling current, the surface chemical modification, core material composition, and electrical properties of the nanocatalyst in different solution environments are distinguished and evaluated. The test system construction process is as follows:

[0127] 1. Establishment of background current baseline

[0128] The functionalized tunneling probe was prepared by adding 1 μM propyl disulfide and 1 mM TCEP to deionized water and sonicating for 30 minutes. Then, the tunneling probe was immersed in the modification solution at room temperature for 24 hours and rinsed with anhydrous ethanol for 1 minute to obtain the functionalized tunneling probe.

[0129] 20 mM phosphate buffer (PB, pH=7.4) was injected into the electrochemical chamber (1 mL volume) using a pipette. Functionalized tunneling probes (working electrodes WE1 and WE2) were immersed in the solution, forming a three-electrode system (Ag / AgCl serving as both reference and counter electrode) with the Ag / AgCl reference electrode (RE) and counter electrode (CE). The potential of the entire weak current testing system was set to 0 mV vs Ag / AgCl for WE by adjusting the sliding rheostat in the external circuit. Subsequently, the potential of tunneling probe WE1 was finely controlled to 0 mV vs Ag / AgCl, and the potential of WE2 to 100 mV vs Ag / AgCl using the weak current testing system. A stable, low-noise background tunneling current-time curve was recorded and denoted as I1.

[0130] 2. Detection and Characteristic Conductivity Extraction of Single-Particle Nanocatalysts: Add 1 μL of a 1 μM solution of L-cysteine-modified gold nanoparticles (10 nm diameter, 20 mM PB solvent (pH=7.4)) to the above chamber and let stand for 10 minutes to allow for sufficient particle diffusion. Then record the current-time curve I2, as shown below. Figures 8-10 As shown, where Figure 8 This represents the characteristic tunneling current signal of gold nanoparticles. Figure 9 Analysis of signal event width for different bias current boost values. Figure 10 The current enhancement value of gold nanoparticles represents the relationship between conductivity ratio and bias voltage.

[0131] When a single gold nanoparticle randomly diffuses and contacts the nanogap, it modulates the local tunneling barrier, generating a characteristic transient current spike on the I² curve. By statistically analyzing the peak amplitude and dwell time of a large number of such spike signals, the average characteristic conductivity of the batch of gold nanoparticles under the stated conditions can be calculated. This 10nm gold nanoparticle needs to be bridged across the tunneling electrode nanogap for detection, such as... Figure 6 This represents the state of bridging by gold nanoparticles.

[0132] 3. Differentiating Nanoparticles with Different Surface Modifications: After completing the above tests (in this embodiment, the same functional layer was used for modification), the chamber and nano-gap device were thoroughly rinsed with 20 mM PB buffer until the background current I3 measured after re-injection of fresh PB solution was on the same order of magnitude as the initial baseline I1 and remained stable. Subsequently, 1 μL of mercaptopropionic acid-modified gold nanoparticles (10 nm in diameter, 20 mM PB (pH=7.4)) with a concentration of 1 μM was added to the chamber, and the tests and data analysis in step 2 were repeated to obtain the statistical characteristics of its current peak. This cleaning and testing process was repeated to test L-mercaptopropylamine-modified gold nanoparticles (10 nm in diameter). Figures 11-12 As shown in the figure (amino groups refer to mercaptopropylamine-modified gold nanoparticles, carboxyl groups refer to mercaptopropionic acid-modified gold nanoparticles, amino acid groups refer to L-cysteine-modified gold nanoparticles, and the mixed phase refers to a mixture of mercaptopropionic acid and L-cysteine), it can be seen that gold nanoparticles of the same size but with different surface modifications exhibit statistically distinguishable characteristic conductivity distributions, thus achieving surface chemical differentiation based on electrical signals.

[0133] 4. Differentiating Nanocatalysts with Different Core Materials: After thoroughly washing the system with 20 mM PB buffer and establishing a new baseline I4 (I4 is on the same order of magnitude as the initial baseline I1 and is stable), add 1 μL of 1 μM mercaptopropionic acid-modified silver nanoparticles (10 nm in diameter, 20 mM PB solvent, pH 7.4) to the chamber. Repeat step 2, record the current curve IAG, and perform peak analysis. Similarly, test with 1 μM catalase solution after washing the system. Figure 13 and Figure 14 As shown, the current spikes generated by silver nanoparticles and gold nanoparticles (or enzyme molecules) show significant differences in amplitude, frequency, or waveform distribution, proving that the platform can distinguish between nanocatalysts of different materials.

[0134] 5. Evaluating the Influence of Solution Environment on the Electrical Properties of Nanoparticles: The system was thoroughly cleaned with ultrapure water. First, 10 mM NaCl solution was injected to establish the background current Ib. Mercaptopropionic acid-modified gold nanoparticles (1 μM, 10 nm, solvent: 20 mM PB, pH = 7.4) were added, and after collecting over 1000 current spike events, the system was cleaned. Subsequently, the chamber solution was successively changed to 10 mM HCl solution and then 10 mM NaOH solution, and the process of adding the same nanoparticles and collecting signals was repeated. The characteristics of the current spike signals collected in neutral, acidic, and alkaline environments (such as changes in average amplitude and frequency of occurrence) were compared and analyzed. Figure 15 As shown, this method can assess the effect of solution pH (i.e., the reaction environment) on the surface charge state and apparent conductivity of nanoparticles. This method is also applicable to evaluating particles with other surface modifications (such as mercaptopropylamine modification). (In the figure, amino groups refer to mercaptopropylamine-modified gold nanoparticles, carboxyl groups refer to mercaptopropionic acid-modified gold nanoparticles, and amino acid groups refer to L-cysteine-modified gold nanoparticles.) By combining differences in conductivity distribution with theoretical surface charge simulations, the property changes of nanocatalysts with different surface modifications in specific chemical environments can be correlated.

[0135] This embodiment fully demonstrates that the platform can not only detect single-particle events, but also achieve highly sensitive differentiation and characterization of multi-dimensional physical properties such as surface chemistry, core materials and environmental response of nanocatalysts through statistical analysis of quantum tunneling current transient signals, showing its outstanding application potential in the analysis of complex systems.

[0136] Example 5: Catalytic process of nanocatalyst based on quantum tunneling current characteristics

[0137] This embodiment demonstrates how to utilize the platform to distinguish intrinsic conductivity information from characteristic conductivity information during the reaction process by comparing and analyzing the quantum tunneling current response of nanoparticles at non-reaction potentials and catalytic oxidation potentials. The test system construction process is as follows:

[0138] 1. Establishing the background current baseline:

[0139] A functionalized tunneling probe with an anti-adsorption layer was prepared by adding 1 μM propyl disulfide and 1 mMTCEP to deionized water and sonicating for 30 minutes. The probe was then immersed in the modification solution at room temperature for 24 hours and rinsed with anhydrous ethanol for 1 minute to obtain the functionalized tunneling probe.

[0140] 20 mM phosphate buffer (PB) was injected into the electrochemical chamber (1 mL volume) using a pipette. Functionalized tunneling probes (working electrodes WE1 and WE2) were immersed in the solution, forming a three-electrode system with the Ag / AgCl reference electrode (RE) and the counter electrode (CE). The potential of the entire weak current testing system was set to WE = 0 mV vs. Ag / AgCl by adjusting the sliding rheostat in the external circuit. Subsequently, the potential of tunneling probe WE1 was precisely controlled to 0 mV vs. Ag / AgCl, and the potential of WE2 to 100 mV vs. Ag / AgCl using the weak current testing system. A stable, low-noise background tunneling current-time curve was recorded and denoted as I1.

[0141] 2. Acquisition of tunneling current signal under non-redox potential conditions: 1 μL of a 1 μM citric acid-modified silver nanoparticle solution (10 nm diameter, 20 mM PB solvent, pH 7.4) was added to the above chamber and allowed to stand for 10 minutes to allow for sufficient particle diffusion. Current-time curves were recorded while maintaining the surface potential of WE at 0 mV vs. Ag / AgCl (surface potential) and the bias voltage between WE1 and WE2 at 100 mV. At this time, the silver particles do not undergo oxidation. The observed transient current signal (spiking peak) indicates that the nanocatalyst has reached the quantum tunneling region through diffusion in the solution, changing the potential barrier height within the tunneling region and generating the first characteristic conductance signal.

[0142] 3. Signal Acquisition under Catalytic Oxidation Conditions: After acquiring the characteristic conductivity information of silver particles, the surface potential of the working electrode was switched to 600mV vs. Ag / AgCl (bias voltage maintained at 100mV) by adjusting the resistance value of the sliding rheostat, and the new current-time curve I2 was recorded. At this potential, when silver particles collide with the electrode surface, there is a probability of silver oxidation and electron transfer. The characteristic signal distribution diagram from non-redox potential to redox potential is shown in [reference needed]. Figure 16 The red circle indicates the characteristic signal of silver particle oxidation.

[0143] 4. Data Analysis and Impact Assessment: Statistical analysis was performed on the transient current signals I1 and I2 collected in steps 2 and 3, focusing on extracting and comparing characteristic parameters such as average current amplitude and event frequency. Gaussian distribution statistics were then applied, and the results are shown in [the table below]. Figure 17 The figure shows a 10nm silver particle, illustrating the correlation between peak signal conductance distribution and surface potential intensity. As the gate potential changes, the conductance also changes significantly.

[0144] The results show that the silver nanocatalyst exhibits distinguishable tunneling signal characteristics at both the non-reaction potential and the catalytic potential, namely, a "second weak current enhancement information" contributed by the oxidation reaction. This demonstrates that the platform can excite the catalytic activity of the nanocatalyst in the solution phase and monitor the electrical information of the catalyst during the catalytic process.

[0145] Example 6: Catalytic properties of nanocatalysts based on quantum tunneling current characteristics

[0146] This embodiment demonstrates how to utilize the aforementioned platform to systematically test and correlate the quantum tunneling electrical signals of nanocatalysts with their core structural parameters (such as size and surface ligand chemistry), thereby conducting an in-depth quantitative study of the influence of catalyst structural characteristics on their apparent catalytic behavior. The test system construction and implementation process is as follows:

[0147] 1. Background current baseline establishment and single-nanocatalyst event detection and characteristic conductivity extraction: 20 mM phosphate buffer (PB) was injected into the electrochemical chamber (1 mL volume) using a pipette. A tunneling probe with surface-modified propyl disulfide (1 μM propyl disulfide and 1 mM TCEP were added to deionized water and sonicated for 30 minutes. Subsequently, the tunneling probe was immersed in the modification solution at room temperature for 24 hours to obtain a functionalized tunneling probe) was rinsed with anhydrous ethanol for 1 minute and immersed in the test solution to form a three-electrode system. Through precise control, the working electrode (WE) potential was set to 0 mV vs. Ag / AgCl, and a bias voltage of 100 mV was applied to obtain a stable background tunneling current baseline I1. Subsequently, 1 μL of 1 μM citric acid-modified silver nanoparticles (10 nm in diameter, 20 mM PB (pH = 7.4)) was added to the chamber as a model sample, and after static diffusion, the current-time curve I2 was recorded. The system captures discrete current spikes caused by individual particles entering and exiting the tunneling region. By statistically analyzing the amplitude and residence time of a large number of spikes, the average characteristic conductivity of the batch of particles is calculated, and a standard single-particle detection and conductivity extraction process is established.

[0148] 2. Catalytic Conductivity Response Analysis of Silver Nanoparticles with Different Particle Sizes: Under the same test conditions (0 mV vs. Ag / AgCl, 100 mV bias), three different diameters (5 nm, 10 nm, 20 nm) of silver nanoparticles with the same surface modification (citric acid) were tested (1 μL, 1 μM concentration, 20 mM PB solvent (pH = 7.4)). The complete procedure of step 1 was independently repeated for each particle size sample to obtain its respective characteristic conductivity distribution. Statistical analysis showed that the average value and distribution width of the characteristic conductivity systematically changed with increasing particle size. Subsequently, the working electrode potential was switched to the catalytic oxidation potential (e.g., 600 mV vs. Ag / AgCl), and the "catalytic state" characteristic conductivity of each particle size under this condition was repeatedly measured and calculated. By comparing the trend and amplitude differences of characteristic conductivity with particle size under non-catalytic and catalytic conditions, the influence of particle size on its electron transfer ability and catalytic response intensity can be quantitatively evaluated. The results are as follows: Figure 18 As shown, it can be seen that the characteristic conductivity of silver particles of different sizes is significantly different under oxidation potential. As the diameter of the silver particles increases, the conductivity signal is significantly enhanced, indicating that the catalytic reaction process on the particles is enhanced with the increase of size.

[0149] 3. Effect of Different Protecting Groups on the Catalytic Process of Silver Nanoparticles: Silver nanoparticles with the same core size (10 nm diameter) were selected, but modified with three different ligand molecules—L-cysteine, L-mercaptopropionic acid, and L-mercaptopropylamine—as protecting groups, while keeping other conditions consistent. The three nanoparticles were tested at 0 mV using a sliding rheostat to obtain their intrinsic characteristic conductivity distribution, thus characterizing the differences in tunneling electrical information caused by the ligands. Subsequently, the three nanoparticles were retested at an adjusted catalytic oxidation potential (600 mV). The relative shift in the conductivity distribution of the silver nanoparticles with different ligands at the catalytic potential was observed. The results are as follows: Figures 19-21 As shown, the differences in tunneling characteristic signals of 10 nm silver particles with different modified groups at a bias voltage of 100 mV and a surface potential of 600 mV are presented. This indicates that different ligands not only affect the initial conductivity of the particles, but also significantly modulate their electrical response amplitude and stability at the catalytic potential, thus directly revealing the regulatory role of surface chemistry on the electron transport path of the catalytic process.

[0150] 4. Detection and analysis of catalytic conductivity signals of silver nanoclusters: The test objects were expanded to smaller sizes (1.44 nm) and well-defined structures (Ag... 44 The silver nanoclusters modified with 4-nitro-3-mercaptobenzoic acid (structure as shown) Figure 23 As shown, the electron microscope image is as follows: Figure 24 As shown, Figure 25(See its UV-Vis absorption spectrum). When tested on the same platform, when the surface potential of the tunneling electrode is set to a potential window that allows the silver nanoclusters to undergo oxidation, a current spike signal pattern similar to that of larger nanoparticles can be observed (see...). Figure 22 Meanwhile, at higher surface potentials (gate potentials), another discrete conductivity step can be observed. By analyzing the occurrence probability, amplitude distribution, and stability changes of characteristic conductivity signals of silver nanoclusters before and after the catalytic potential, it is possible to detect their unique catalytic active sites and reaction mechanisms originating from molecular energy level structures. This demonstrates the platform's excellent detection sensitivity for sub-nanoscale catalytic units (capable of detecting single-particle nanocatalysts with a diameter of 1.44 nm and a concentration of 1 pM). This embodiment systematically demonstrates that this platform can not only sensitively distinguish nanocatalysts with different structures, but also establish a quantitative relationship of "structure-electrical response-catalytic behavior" at the single-particle level by correlating their quantum tunneling conductivity characteristics with structural parameters (size, ligands), providing a powerful in-situ analytical tool for the rational design and optimization of nanocatalysts.

[0151] Example 7: Investigating the environmental catalytic induction process of nanocatalysts using tunneling probes

[0152] This embodiment demonstrates how to utilize the aforementioned platform to study the induction and regulation of electron transfer behavior and interfacial states in nanocatalysts during catalysis. The test system construction and implementation process is as follows:

[0153] 1. Background current baseline establishment and single-particle characteristic signal acquisition: A mixed solution containing 12 mM hydrazine and 50 mM phosphate buffer (PBS, pH 7.4) was injected into the electrochemical chamber (1 mL volume) using a pipette. A tunneling probe with a surface modified with propyl disulfide (modification method: the tunneling electrode was immersed in an ethanol solution containing propanethiol at room temperature for 1 hour, and then washed with an ethanol-deionized water mixture for 1 min to remove residual propanethiol, obtaining an anti-adsorption layer functionalized tunneling probe) was immersed in the solution to form a three-electrode system. The surface potential of the working electrode (WE) was set to 0 mV vs. Ag / AgCl, and the bias voltage was 100 mV, and a stable background tunneling current baseline I1 was recorded. 1 μL of 1 μM platinum nanoparticles (5 nm in diameter, in solvents of 12 mM hydrazine and 50 mM phosphate buffer (PBS, pH 7.4)) were added to the chamber, and after static diffusion, the current-time curve was recorded. The system captures discrete current spike signals and obtains the average characteristic conductivity of the batch of particles under the basic environment through statistical analysis.

[0154] 2. Real-time monitoring of electron transfer process at catalytic potential: Based on the stable detection of signals from citric acid-modified platinum nanoparticles, the gate potential of the tunneling electrode was adjusted to 2V vs Ag / AgCl for 30 seconds. At this time, the Au-S coordination bonds on the surface of the tunneling electrode undergo a breakage reaction at the high gate potential. The tunneling electrode was immersed in a 10 mM PBS solution containing 1 mM cysteine ​​for 1 hour. After rinsing with ethanol-deionized water for 1 minute to remove residual cysteine, the tunneling electrode was placed in the test solution containing nanoparticles and connected to a weak current detection device. The surface potential of the tunneling electrode was switched to +500mV vs Ag / AgCl, and the bias voltage between the tunneling electrodes was set to 100mV. The current was continuously monitored at this potential. A significant change in the frequency and amplitude distribution of current spikes was observed compared to 0mV. Dynamic parameters such as the rise time and full width at half maximum (FWHM) of the spike signal were analyzed through high-time-resolution recording. In addition to the characteristic electrical information of the platinum nanoparticles, another characteristic conductivity information can be observed in the spike signal. This characteristic conductivity information changes in real time with the change of surface potential, indicating that a redox reaction of hydrazine has occurred on the surface of a single platinum particle, and an electron transfer process that can be monitored by the tunneling current has taken place.

[0155] 3. Real-time observation and control of nanocatalyst surface activity: In the hydrazine catalysis process described in step 2, hydrazine reacts to generate nitrogen gas, which adheres to the surface of platinum particles in the solution phase and forms microbubbles. During the reaction, the size of the bubbles increases with the catalytic reaction on the platinum particles, eventually forming nitrogen bubbles that can encapsulate and isolate the nanocatalyst from the solution. In this state, as the bubbles grow larger, they can carry the nanoparticles away from the tunneling electrode surface, terminating the catalytic process on the nanoparticle surface, and a decay process in the signal frequency or amplitude of the tunneling current is observed. Based on this principle, by functionalizing the electrode interface with cysteine ​​and controlling the surface potential of the tunneling electrode to +500mV vsAg / AgCl, individual platinum nanoparticles are adsorbed onto the electrode surface through intermolecular forces to generate a continuous hydrazine catalytic process, and the changing trend of the transient signal of the tunneling current is recorded. Through statistical analysis of each set of transient signals, the reaction process on the surface of the platinum particles can be monitored in real time and in situ, and the differences in catalytic rates between different platinum particles can be compared. This enables the evaluation of the catalytic efficiency of the nanocatalyst at the nitrogen molecule level.

[0156] This embodiment demonstrates that the platform can achieve synchronous, real-time resolution and monitoring of intrinsic conductivity signals and Faraday process electron transfer signals of catalytic reactions at the single-particle level, and can correlate interfacial dynamic changes and deactivation processes caused by reaction byproducts (such as bubbles). Furthermore, it enables in-situ visualization of the relationship between nanoparticle interfacial changes and catalytic reaction rates, and real-time monitoring of the dynamic chemical state and stability of the catalyst / solution interface, providing a key tool for understanding catalytic behavior under complex real-world conditions.

[0157] Example 8: The Influence of the Nanogap Between the Tunneling Electrode on the Detection Results of Single-Particle Nanocatalysts

[0158] This embodiment uses the method provided in Example 6 to detect particles with a size of 1.44 nm and a well-defined structure (Ag). 44 The physical properties of silver nanoclusters modified with 4-nitro-3-mercaptobenzoic acid and silver nanoparticles with a size of 20 nm were investigated. The electrolyte was 20 mM PB (pH=7.4). Tunneling electrodes with different nano-gap sizes were used to detect the physical properties and catalytic reaction information. All other conditions were kept consistent. The detection sensitivity and signal-to-noise ratio were examined. The sensitivity was detected by gradually increasing the concentration from 1 fM until a peak signal appeared, at which point statistical analysis was performed. The signal-to-noise ratio was detected by the ratio of the peak signal to the baseline current. The detection results are shown in Table 1.

[0159] Table 1. Influence of nano-gap size on detection results

[0160]

[0161] As shown in Table 1, the sub-5 nm tunneling electrode can successfully detect single-particle nanocatalysts. Especially when the nanoparticle gap is 1–3 nm, it can achieve higher sensitivity detection of 1.44 nm silver nanoclusters and 20 nm silver nanoparticles, with a lower signal-to-noise ratio (SNR). Generally, a SNR higher than 0.1 indicates that the properties of the analyte can be accurately detected. However, when the SNR is lower than 0.005, the signal is submerged in the noise fluctuations of the baseline current and therefore cannot be recognized as a signal on the current-time curve. A higher SNR indicates better detection accuracy.

[0162] Example 9: The effect of the anti-adsorption functionalized layer

[0163] This embodiment uses the method provided in Example 6 to detect the physical properties of 10 nm silver nanoparticles (citric acid modified). The tunneling electrodes used are: 1. Unfunctionalized; 2. Anti-adsorption functionalized with propyl disulfide (the method involves immersing the tunneling electrode in an ethanol solution containing 1 μM propyl disulfide for 24 hours, then rinsing it with anhydrous ethanol for 1 minute after removal from the modification solution, and finally placing it in a sealed box for testing; 3. Anti-adsorption functionalized with 6-mercapto-1-hexanol (MCH) (method as above); 4. Anti-adsorption functionalized with 1-dodecylthiol. Other conditions remain the same. Detection spectra are collected, and the signal generation frequency and signal-to-noise ratio are examined. The signal generation frequency is detected by the acquisition probability of the test signal, and the signal-to-noise ratio is detected by the ratio of signal intensity to background current. The results are as follows: Figures 26-29 As shown in Table 2.

[0164] Table 2. Influence of the anti-adsorption functional layer on the detection results of physical property information

[0165]

[0166] As shown in Table 2, compared with the detection results without the anti-adsorption functionalized layer, although the signal-to-noise ratio is slightly reduced after modifying the tunneling electrode with the anti-adsorption functionalized layer, it can prevent adsorption and result in a multi-particle detection result (based on a large number of experimental statistics, the signal generation frequency is higher than 16.9s). -1 (For multi-particle systems), ensuring that only a single particle is detected, thus improving the detection accuracy of single-particle nanocatalysts.

[0167] Meanwhile, the detection results varied significantly when different anti-adsorption functionalized layers were used. This is because the anti-adsorption effects of different functionalized layers differ. Furthermore, achieving efficient detection of single-particle nanocatalysts requires a dynamic balance between single-particle detection and anti-adsorption in the anti-adsorption functionalized layer; excessively strong anti-adsorption may lead to detection difficulties. Therefore, it is essential to screen different anti-adsorption functionalized layers for different single-particle nanocatalysts. For example, for the citric acid-modified silver nanoclusters in this embodiment, screening propyl disulfide (Group 2) as the anti-adsorption functionalized layer significantly improved the signal-to-noise ratio and detection sensitivity.

[0168] Example 10: The impact of the capture layer functionalization layer

[0169] This embodiment uses the method provided in Example 7 to detect the catalytic reaction information of citric acid-modified platinum nanoparticles (5 nm in diameter, in a solvent of 12 mM hydrazine and 50 mM phosphate buffer (PBS, pH=7.4)). The tunneling electrodes used are: 1) unfunctionalized; 2) functionalized with L-cysteine ​​by immersing the tunneling electrode in a 10 mM PBS solution containing 1 μM cysteine ​​overnight for 24 hours; 3) functionalized with mercaptopropionic acid by immersing the tunneling electrode in a 10 mM PBS solution containing 1 μM mercaptopropionic acid at room temperature. Soak in PBS solution for 1 hour; keep other conditions consistent. Collect detection spectra and examine the distribution of the first-order tunneling current intensity (perform frequency distribution histogram statistics on the peak signal, and then derive the statistical signal from the mean parameter in the Gaussian distribution), and the frequency of the second-order signal. The second-order signal represents the diffusion of hydrazine molecules in the solution to the surface of the platinum nanoparticle and the occurrence of a redox reaction when the first-order signal is continuously monitored (this state indicates that the functionalized modification layer has captured a platinum nanoparticle in the tunneling region for a long time, and the material conductivity information of the platinum nanoparticle has been monitored). The electron transfer process of the reaction generates an additional spike signal on the first-order signal, which is considered the second-order signal. By analyzing the frequency and magnitude of the second-order signal, the catalytic kinetic information of the platinum particle can be resolved. The results are shown in Table 3, where the detection spectrum of cysteine ​​as the trapping functionalized layer is shown in Table 3. Figures 30-31 .

[0170] Table 3. Impact of the Capture Functionalized Layer on Detection Results

[0171]

[0172] As shown in Table 3, compared with the detection results without the modified trapping functionalized layer, modifying the tunneling electrode with the trapping functionalized layer significantly improves the dynamic detection time of the catalytic reaction of single-particle nanocatalysts, thereby improving detection accuracy. Meanwhile, the detection results also show significant differences when using different trapping functionalized layers, because different trapping functionalized layers have varying trapping effects on microbubbles. Therefore, it is necessary to screen different trapping functionalized layers for different single-particle nanocatalysts. For example, for the platinum nanoparticles in this embodiment, screening cysteine ​​as the trapping functionalized layer can significantly improve the accuracy of dynamic detection of the catalytic reaction.

[0173] Example 11: Effects of Different Electrolytes

[0174] This embodiment uses the method provided in Example 7 to detect the physical properties and catalytic reaction information of citric acid-modified platinum nanoparticles (5 nm in diameter, in solvents of 12 mM hydrazine and 50 mM phosphate buffer (PBS, pH 7.4)). The tunneling electrodes were prepared using four different electrolytes: 1. 20 mM PB (prepared from KH₂PO₄ / Na₂HPO₄, pH=7.4); 2. 20 mM acetate buffer (pH=5.0); 3. 20 mM phosphate buffer (PBS, containing 137 mM NaCl, pH=7.4); 4. 0.1 M potassium chloride solution (pH adjusted to 7.4 with KOH). The collected detection spectra were analyzed to examine the detection sensitivity and signal-to-noise ratio, and the results are shown in Tables 4 and 5.

[0175] Table 4. Effects of different electrolytes on the detection of physical property information

[0176]

[0177] Table 5. Effects of different electrolytes on the detection of catalytic reaction information

[0178]

[0179] As shown in Tables 4 and 5, different electrolytes affect the signal-to-noise ratio and detection sensitivity of platinum nanoparticles during the detection of their physical properties and catalytic reaction kinetics. Furthermore, different electrolytes also affect the detection accuracy of platinum nanoparticles during the dynamic detection of their catalytic reactions. This is mainly due to differences in the ionic strength, pH, and specific adsorption of the electrolytes themselves. The optimal electrolyte is 20 mM PB (pH=7.4), which ensures the diffusion performance, surface charge, and stability of platinum nanoparticles. It not only exhibits the highest first-order tunneling current intensity and the highest signal generation frequency, indicating that this electrolyte condition promotes the capture process of citric acid-modified platinum nanoparticles, but also the highest frequency of second-order signals, suggesting that this electrolyte condition promotes the catalytic process of citric acid-modified platinum nanoparticles and improves the detection performance of platinum nanoparticles.

[0180] All patents and publications mentioned in this specification represent publicly available technologies that can be used in this invention. It is understood that the embodiments described herein are preferred embodiments and features, and any modifications and variations can be made by those skilled in the art based on the spirit of the description, and such modifications and variations are also considered to fall within the scope of this invention and the limits defined by the independent and appended claims.

Claims

1. A detection system for single-particle nanocatalysts, characterized in that, It includes a tunneling electrode with a nano-gap of sub-5 nanometers; the single-particle nanocatalyst is bridged on the nano-gap of the tunneling electrode by diffusion, or diffuses into the nano-gap of the tunneling electrode.

2. The detection system as described in claim 1, characterized in that, The nano-gap of the tunneling electrode is 1-3 nanometers; the particle size of the single-particle nanocatalyst is 1-50 nanometers.

3. The detection system as described in claim 2, characterized in that, The surface of the tunneling electrode is modified with a functionalized layer, which includes an anti-adsorption functionalized layer and / or a trapping functionalized layer. The anti-adsorption functionalized layer is used to prevent single-particle nanocatalysts from adsorbing onto the surface of the tunneling electrode during diffusion. The trapping functionalized layer is used to trap single-particle nanocatalysts carrying bubbles during the catalytic reaction.

4. The detection system as described in claim 3, characterized in that, The anti-adsorption functionalized layer includes any one or more of mercaptopropane, propyl disulfide, 6-mercapto-1-hexanol (MCH), 1-dodecanethiol, 1-octanethiol, 1-dodecanethiol, (3-aminopropyl)triethoxysilane, octadecyl phosphoric acid, polyethylene glycol, polyacrylic acid, and polystyrene sulfonic acid; the capture functionalized layer includes any one or more of mercaptopropionic acid, cysteine, and aminopropyltriethoxysilane.

5. The detection system as described in claim 4, characterized in that, When the single-particle nanocatalyst generates bubbles during the catalytic reaction, the surface of the tunneling electrode is modified with a trapping functionalized layer; when the single-particle nanocatalyst does not generate bubbles during the catalytic reaction, the surface of the tunneling electrode is modified with an anti-adsorption functionalized layer.

6. The detection system as described in claim 2, characterized in that, It also includes a weak current detection component and a gate potential control component; the weak current detection component is electrically connected to the tunneling electrode and is used to apply a bias voltage to the tunneling electrode and detect tunneling current changes in the range of picoamperes to femtoamperes. The gate potential control component is used to control the gate potential of the tunneling electrode.

7. The detection system as described in claim 2, characterized in that, It also includes a reaction chamber containing an electrolyte, which includes any one or more of the following: phosphate buffer, phosphate buffer, acetate buffer, sodium perchlorate, potassium nitrate, and potassium chloride solution.

8. A method for detecting single-particle nanocatalysts, characterized in that, The detection is performed using the detection system described in any one of claims 1 to 7, comprising the following steps: (1) Contact the tunneling electrode with the sample solution containing the single-particle nanocatalyst to be tested; (2) Capture the tunneling current signal generated by the diffusion bridging of single-particle nanocatalysts on the nano gaps of the tunneling electrode, or by the diffusion into the nano gaps of the tunneling electrode, and obtain the physical property information of single-particle nanocatalysts.

9. The method as described in claim 8, characterized in that, The physical property information includes the core material, modification groups, size, and any one or more of the solution environment of the single-particle nanocatalyst; step (1) requires first contacting the sample solution without the single-particle nanocatalyst to be tested with the tunneling electrode to obtain the background signal.

10. The method as described in claim 8, characterized in that, It also includes step (3): changing the gate potential of the tunneling electrode to excite the single-particle nanocatalyst to undergo a catalytic reaction, capturing the tunneling current signal generated by the single-particle nanocatalyst to obtain the catalytic kinetic information of the single-particle nanocatalyst.

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