Preparation method of high-conductivity multivalent nanowire and application of enzyme-free glucose sensor

Abstract

The invention discloses a preparation method of a high-conductivity multivalent nanowire and application of the high-conductivity multivalent nanowire to a non-enzyme glucose sensor. The copper nanowire with a high length-diameter ratio is prepared, a certain amount of thiourea is directly added into an ethanol solution of the copper nanowire, and conversion from the copper nanowire to the high-conductivity multivalent nanowire can be achieved under the condition of a specific reaction temperature. In the conversion process, the surface of the nanowire is synchronously induced to form a coarse structure, non-single valence copper sulfide active sites are constructed, and the formed synergistic effect can remarkably increase the number of the active sites, reduce an electrocatalytic oxidation reaction energy barrier and strengthen the specific adsorption capacity of glucose molecules, so that the non-enzyme glucose sensor is manufactured. The sensor shows ultrahigh detection sensitivity, ultralow response speed and excellent anti-interference performance, the preparation process is extremely simple, the cost is low, and the sensor has remarkable technical advantages and wide application prospects in the field of quantitative detection of glucose.

Description

Preparation method of highly conductive multivalent nanowires and application of enzyme-free glucose sensor Technical Field

[0001] This invention relates to the technical field of functional materials and sensors, and in particular to a method for preparing highly conductive multivalent nanowires and their application as an enzyme-free glucose sensor. Background Technology

[0002] Electrochemical biosensor technology provides a highly efficient analytical tool for monitoring glucose levels in physiological systems. Among various electrochemical sensors, enzyme-based glucose sensors have attracted widespread attention due to their high catalytic efficiency; however, they still face many challenges in practical applications, such as the complexity of enzyme catalysis, susceptibility to denaturation and inactivation, and high manufacturing costs. To overcome these limitations, non-enzymatic electrochemical glucose sensing technologies have gradually developed, becoming a promising alternative strategy due to their high stability, good reproducibility, and cost-effectiveness.

[0003] Metal nanoparticles, metal oxide nanostructures, and metal-based nanocomposites such as Au, Fe, Ni, Pt, Cu, and Zn have attracted widespread interest due to their ability to directly catalyze the oxidation of glucose molecules. To overcome the limitations of enzyme sensors, non-enzymatic electrochemical glucose sensing technology has gradually developed, utilizing metals, metal oxides, or other nanomaterials to directly catalyze glucose oxidation. However, existing non-enzymatic sensors still have significant shortcomings in material design and fabrication. Many metal or metal oxide nanomaterials (such as copper oxide) have inherently low electrical conductivity, resulting in high charge transfer impedance and limiting electron transfer rates. Furthermore, their complex fabrication processes and structural control pose challenges to performance optimization, leading to limitations in the prepared materials' active surface area and insufficient accessibility of catalytic sites, thus affecting the sensor's sensitivity, detection limit, and anti-interference capabilities. Summary of the Invention

[0004] To address the shortcomings of traditional enzyme sensors, such as poor stability and high cost, as well as the problems of existing enzyme-free sensors that rely on multi-step synthesis and complex structural regulation, this invention provides a method for preparing highly conductive multivalent nanowire materials. The prepared nanowires themselves possess excellent conductivity, overcoming the disadvantage of low conductivity leading to high charge transfer impedance in traditional copper oxide materials. Furthermore, the high specific surface area of ​​the rough porous network morphology and the strong catalytic activity of the multivalent components form a triple synergistic effect, effectively improving the detection performance of glucose.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing highly conductive multivalent nanowires, comprising:

[0007] Step 1) Using copper salt, nickel acetylacetone, and oleylamine as raw materials, copper nanowires are grown by liquid phase method in a nitrogen or inert gas atmosphere. The copper nanowires are dispersed in ethanol solution after centrifugation; the aspect ratio of the copper nanowires is greater than 1000.

[0008] Step 2) Thiourea is added to the ethanol solution of the copper nanowires, and the temperature is raised to 70-80 °C and maintained for 1-3 h in a nitrogen or inert gas atmosphere to sulfide the copper nanowires. After centrifugation of the reaction product, the precipitate is dried to obtain highly conductive multivalent nanowires.

[0009] Optionally, in step 2), the molar ratio of the added thiourea to the copper salt is 0.05-0.2 g: 0.8 mmol.

[0010] Optionally, in the highly conductive multivalent nanowires, sulfur may include S. 2- S2 2- and SO4 2- Multiple chemical states coexist.

[0011] Optionally, the diameter of the copper nanowire is 10~40 nm; the diameter of the sulfided highly conductive multivalent nanowire is 50~150 nm, and it has a rough and porous surface.

[0012] Optionally, in step 2), after the sulfidation reaction is completed, excess thiourea is removed by multiple centrifugations with ethanol solution, and finally the lower precipitate is dried in air to obtain the highly conductive multivalent Cu. x S nanowires.

[0013] Optionally, in step 1), the liquid-phase growth of copper nanowires involves mixing copper salt, nickel acetylacetonate, and oleylamine in a ratio of 0.8 mmol : 0.3-0.5 mmol : 10-15 mL, first heating to 80-90 °C and holding for 10-20 min, then raising the temperature to 180-190 °C and holding for 4-6 h; after the reaction is complete, the mixture is purified by repeated sonication and centrifugation; the copper salt is one of copper chloride dihydrate, copper acetylacetonate, copper acetate, and copper nitrate. Further, the dispersion solvent used for centrifugation purification is one of isopropanol and n-hexane.

[0014] An enzyme-free glucose sensor includes a working electrode, a counter electrode, and a reference electrode. The working electrode is one of a glassy carbon electrode, a graphite electrode, and a gold electrode, and is modified with highly conductive multivalent nanowires prepared by the above-mentioned method for preparing highly conductive multivalent nanowires. The counter electrode is one of a platinum electrode, a graphite electrode, and a gold electrode. The reference electrode is one of an Ag / AgCl electrode and a Hg / HgO electrode.

[0015] Optionally, the modification method is as follows: the highly conductive multivalent nanowires, ethanol and Nafion solution are mixed and ultrasonically formed into a suspension, the suspension is dropped onto the surface of the working electrode and air-dried naturally.

[0016] Optionally, the ratio of the highly conductive multivalent nanowires, ethanol, and Nafion solution is 50 mg: 800-1000 µL: 50-200 µL.

[0017] Optionally, the modification amount of the highly conductive multivalent nanowires on the working electrode is 3.0-4.2 mg / cm. 2 .

[0018] The beneficial effects of this invention are as follows:

[0019] The technical process of this invention is simple, low-cost, and requires no multi-step synthesis or complex structural control.

[0020] The highly conductive multivalent nanowire material of this invention is a one-dimensional nanowire network structure with advantages of high electron transport efficiency and ultra-large specific surface area. Its abundant valence states provide a synergistic catalytic effect for glucose oxidation, and it exhibits excellent conductivity without the need for conductive treatment. Its superior electron transfer capability is positively correlated with the response current of glucose oxidation. The prepared sensing electrode demonstrates ultra-high sensitivity and low detection limit in the electrochemical detection of glucose, providing a solid material foundation for the development of low-cost, high-stability, and high-sensitivity enzyme-free glucose sensors. Attached Figure Description

[0021] Figure 1 shows the highly conductive multivalent Cu in Embodiment 1 of the present invention. x Schematic diagram of the fabrication process of S nanowire materials;

[0022] Figure 2 shows the Cu nanowire material (left) and highly conductive multivalent Cu from Example 1 of this invention. x SEM image of S nanowire material (right);

[0023] Figure 3 shows the highly conductive multivalent Cu in Embodiment 1 of the present invention. x XPS spectra of S nanowire materials;

[0024] Figure 4 shows the highly conductive multivalent Cu in Embodiment 1 of the present invention. x S 2p orbital diagram of S nanowire material;

[0025] Figure 5 shows the highly conductive multivalent Cu in Embodiment 1 of the present invention. x Raman spectrum of S nanowire material;

[0026] Figure 6 shows the highly conductive multivalent Cu in Embodiment 1 of the present invention. xThin film resistance test diagram of S nanowire material;

[0027] Figure 7 shows the highly conductive multivalent Cu in Embodiment 1 (left) of the present invention. x SEM images of S nanowires and nanowire materials of Comparative Example 1 (middle) and Comparative Example 2 (right);

[0028] Figure 8 shows the highly conductive multivalent Cu in Embodiment 2 of the present invention. x Cyclic voltammetry curves of S nanowire sensing electrodes at different voltage scan rates;

[0029] Figure 9 shows the highly conductive multivalent Cu in Embodiment 2 of the present invention. x Glucose concentration gradient measurement using S nanowire sensing electrode;

[0030] Figure 10 shows the highly conductive multivalent Cu in Embodiment 2 of the present invention. x Selectivity test diagram of glucose by S nanowire sensing electrode. Detailed Implementation

[0031] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0032] Example 1

[0033] Referring to Figure 1, the highly conductive multivalent Cu x A schematic diagram of the preparation process of S nanowire materials. First, copper nanowires are grown using the liquid phase method. 0.1364 g of copper chloride dihydrate powder, 0.1024 g of nickel acetylacetonate and 10 ml of oleylamine are weighed using a balance and placed in a three-necked flask for mixing. The three-necked flask is then placed on a constant-temperature heating magnetic stirrer. Under the protection of nitrogen gas, the reaction apparatus is first heated to 85 °C and held for 15 min for pre-reaction. At this time, copper ions are reduced to copper atoms to form seed crystals. Then, the temperature is raised to 185 °C and held for 4 h. During this process, oleylamine acts as a structure directing agent and nickel acts as a catalyst. A large number of copper atoms extend along the (111) crystal plane of the copper seed crystal and along the

[110] direction to form a nanowire network. After the reaction is completed, the copper nanowires purified by repeated sonication and centrifugation with n-hexane are placed in 40 ml of ethanol solution for later use.

[0034] 50 mg of thiourea was measured and added to a three-necked flask along with 40 ml of copper nanowire ethanol solution. The flask was placed on a magnetic stirrer under constant temperature heating. Under nitrogen protection, the temperature was raised to 75 °C and maintained for 1 h to sulfidate the copper nanowires. After completion, excess thiourea was removed by repeated centrifugation with ethanol solution. Finally, the precipitate was collected and dried in air, revealing highly conductive multivalent Cu. x S nanowires.

[0035] Figure 2 shows the initial copper nanowires and the synthesized Cu.x SEM image of the S nanowires. The aspect ratio of the prepared copper nanowires is approximately 1500–1800. Compared to the smooth surface of the original copper nanowires, the surface of the sulfided nanowires becomes rough, and the diameter increases from about 16 nm to about 100 nm, forming a rough and porous surface morphology with a large specific surface area.

[0036] The XPS spectrum in Figure 3 shows the presence of elements such as Cu and S on the surface of the nanowire sample, confirming the presence of Cu from an elemental perspective. x Synthesis of S nanowires.

[0037] Figure 4 shows the 2p orbital spectrum of the S element. Due to spin-orbit coupling, the S 2p orbital splits into S 2p orbitals. 3 / 2 and S2p 1 / 2 The two peaks, at 161.3 and 162.8 eV, belong to S. 2− and S2 2− It can be found in all copper sulfides. Another splitting peak is visible at 167.9 eV, which is due to the presence of some sulfate on the nanowire surface (possibly from the decomposition of thiourea), indicating that sulfur in the sample coexists in multiple chemical states, which is a manifestation of multivalent states.

[0038] Figure 5 shows the synthesis of Cu. x The Raman spectrum of the S nanowires shows a strong peak at 473 cm⁻¹ due to the vibration of the SS bond, while the weaker peak at 264 cm⁻¹ is attributed to the vibration of the Cu-S bond. The absence of a peak corresponding to the copper oxidation state further confirms the composition of the nanowires.

[0039] Figure 6 shows the synthesized Cu x S nanowires were transferred to a 1*1 cm⁻¹ mass via filtration imprinting. 2 The sheet resistance test pattern of a thin film on a silicon substrate, measured using a four-probe electrical testing platform, is calculated using the following formula: , It is a thin-film sheet resistance, in which It is the measured pressure drop. It is the size of the applied current source. This is the correction factor for sheet resistance, calculated to be 60.162 Ω, Cu. x S-nanowire network films exhibit excellent conductivity. Notably, copper nanowires grown in traditional oleylamine liquid-phase growth systems require conductivity-enhancing treatment to achieve conductivity due to the presence of oleylamine ligands on their surface. However, this method achieves conductivity without deliberate conductivity enhancement. During the sulfidation process, the oleylamine ligands gradually decompose at high temperatures, and the Cu... xThe mixed valence states of copper ions and the abundance of copper vacancies in Si nanowires create a natural "self-doping" effect, providing extremely high carrier concentrations and enabling them to exhibit metal-like or degenerate semiconductor conductivity. Further, in the field of glucose sensing, the core of enzyme-free glucose sensing lies in the electrochemical reaction on the surface of the catalytic material: glucose is oxidized on the material surface (releasing electrons), and these electrons must be transported through the material itself to the electrode, ultimately forming a detectable response current. If the material has good conductivity, electrons can be transported quickly and with low loss, resulting in a stronger response current (corresponding to higher signal sensitivity). This is also why Cu... x The advantage of S nanowire materials compared to traditional copper oxide materials lies in the fact that traditional copper oxide materials have high charge transfer impedance due to low conductivity, which limits the transmission of response current.

[0040] Comparative Example 1

[0041] Except for the vulcanization temperature of 45 °C, all other conditions were the same as in Example 1.

[0042] Comparative Example 2

[0043] Except for the vulcanization temperature being room temperature (15 °C), all other conditions were the same as in Example 1.

[0044] As can be seen from the morphology of the nanowires synthesized at different temperatures in Figure 7, the decrease in sulfidation temperature leads to incomplete reaction of a large amount of precursors, which remain on the surface of the nanowires. The nanowires synthesized in Comparative Examples 1 and 2 do not possess the high conductivity of the multivalent Cu in Example 1. x The morphology of S nanowires also lacks their properties. At higher temperatures of 70-80 °C, copper nanowires can be transformed into highly conductive multivalent Cu nanowires. x The conversion of S nanowires simultaneously induces the formation of a rough, porous structure on the nanowire surface, constructs non-single-valence copper sulfide active sites, and exhibits excellent electron transport properties. Higher temperatures will lead to excessive ethanol volatilization, thus affecting the sulfidation reaction.

[0045] Example 2

[0046] In terms of structure, one-dimensional Cu x Si nanowire networks possess advantages such as high electron transport efficiency and ultra-large specific surface area, which can significantly improve the sensitivity to glucose response. In terms of valence states, the rich variety of valence states provides a synergistic catalytic effect for glucose oxidation. This synergistic effect can significantly increase the number of active sites, lower the energy barrier of electrocatalytic oxidation reaction, and enhance the specific adsorption capacity of glucose molecules, thereby enabling the fabrication of enzyme-free glucose sensors.

[0047] Measure 50 mg of Cu from Example 1 xS nanowire powder, 900 µL ethanol, and 100 µL 0.5% Nafion solution were mixed and sonicated for 10 min to form a suspension. 5 µL of this suspension was then pipetted onto the surface of a glassy carbon electrode (3 mm in diameter) and allowed to air dry to complete the Cu process. x Fabrication of S nanowire sensing electrodes.

[0048] Furthermore, Cu was tested using an electrochemical workstation. x S nanowires respond to glucose; a three-electrode system is used, with the working electrode being the aforementioned Cu. x The S nanowire / glassy carbon sensing electrode has a platinum sheet electrode as the counter electrode, an Ag / AgCl electrode as the reference electrode, and a 0.1 M NaOH solution as the test substrate.

[0049] Figure 8 shows the Cu under different voltage scan rates. x Cyclic voltammetry curves of Cu nanowires against 2 mM glucose show that the anodic and cathode peak currents are linearly related to the square root of the scan rate. This indicates that Cu... x The electrochemical kinetics of S nanowires in glucose sensing are driven by a typical diffusion-controlled process, which ensures the amperometric current measurement of glucose.

[0050] Figure 9 shows Cu x The glucose concentration gradient test plot of the S nanowire sensing electrode, and the sensitivity obtained by linearly fitting the corresponding glucose concentration and response current is 3971 µA mM. -1 cm -2 It has a detection range of 1-3526 µM and a detection limit of 0.59 µM (calculated based on a signal-to-noise ratio (S / N) = 3), exhibiting excellent sensitivity.

[0051] Figure 10 shows Cu x The selectivity of Cu nanowire sensing electrodes for glucose was tested, and common interfering substances (sucrose, fructose, lactose, uric acid, ascorbic acid) were selected to verify the selectivity of Cu nanowire sensing electrodes. x The S nanowire sensing electrode only responds to glucose with a corresponding current.

[0052] The examples demonstrate how a simple preparation process can effectively and successfully achieve highly conductive multivalent Cu. x The preparation of S nanowire materials fully leverages the unique advantages of low-dimensional nanowire structures and the high conductivity of multivalent Cu. x S's excellent electrocatalytic activity makes it suitable for developing low-cost, high-stability, and high-sensitivity enzyme-free glucose sensors.

[0053] The above embodiments are only used to further illustrate the preparation method of a highly conductive multivalent nanowire and its application as an enzyme-free glucose sensor according to the present invention. However, the present invention is not limited to the embodiments. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing highly conductive multivalent nanowires, characterized in that, include: Step 1) Using copper salt, nickel acetylacetone, and oleylamine as raw materials, copper nanowires are grown by liquid phase method in a nitrogen or inert gas atmosphere. The copper nanowires are dispersed in an ethanol solution after centrifugation. The aspect ratio of the copper nanowires is greater than 1000. Step 2) Thiourea is added to the ethanol solution of the copper nanowires. The temperature is raised to 70-80 ℃ and maintained for 1-3 h in a nitrogen or inert gas atmosphere to sulfide the copper nanowires. After centrifugation, the reaction product is precipitated and dried to obtain highly conductive multivalent nanowires.

2. The method for preparing highly conductive multivalent nanowires according to claim 1, characterized in that: In step 2), the molar ratio of the added thiourea to the copper salt is 0.05-0.2 g: 0.8 mmol.

3. The method for preparing highly conductive multivalent nanowires according to claim 1, characterized in that: In the highly conductive multivalent nanowires, sulfur can include S 2- S2 2- and SO4 2- Multiple chemical states coexist.

4. The method for preparing highly conductive multivalent nanowires according to claim 1, characterized in that: The copper nanowires have a diameter of 10-40 nm; the highly conductive multivalent nanowires after sulfidation have a diameter of 50-150 nm and a rough, porous surface.

5. The method for preparing highly conductive multivalent nanowires according to claim 1, characterized in that: In step 2), after the sulfidation reaction is completed, excess thiourea is removed by multiple centrifugations with ethanol solution. Finally, the lower layer of precipitate is removed and dried in air to obtain the highly conductive multivalent nanowires.

6. The method for preparing highly conductive multivalent nanowires according to claim 1, characterized in that: In step 1), the liquid-phase growth of copper nanowires involves mixing copper salt, nickel acetylacetonate, and oleylamine in a ratio of 0.8 mmol : 0.3-0.5 mmol : 10-15 mL, first heating to 80-90 °C and holding for 10-20 min, then raising the temperature to 180-190 °C and holding for 4-6 h; after the reaction is complete, the mixture is purified by multiple sonications and centrifugation; the copper salt is one of copper chloride dihydrate, copper acetylacetonate, copper acetate, and copper nitrate.

7. An enzyme-free glucose sensor, characterized in that: The device includes a working electrode, a counter electrode, and a reference electrode. The working electrode is one of a glassy carbon electrode, a graphite electrode, and a gold electrode, and is modified with highly conductive multivalent nanowires prepared by the method for preparing highly conductive multivalent nanowires according to any one of claims 1 to 6. The counter electrode is one of a platinum electrode, a graphite electrode, and a gold electrode, and the reference electrode is one of an Ag / AgCl electrode and a Hg / HgO electrode.

8. The enzyme-free glucose sensor according to claim 7, characterized in that: The modification method is as follows: the highly conductive multivalent nanowires, ethanol and Nafion solution are mixed and ultrasonically formed into a suspension, the suspension is dropped onto the surface of the working electrode and air-dried naturally.

9. The enzyme-free glucose sensor according to claim 8, characterized in that: The ratio of the highly conductive multivalent nanowires, ethanol, and Nafion solution is 50 mg: 800-1000 µL: 50-200 µL.

10. The enzyme-free glucose sensor according to claim 7, characterized in that: The modification amount of the highly conductive multivalent nanowires on the working electrode is 3.0-4.2 mg / cm. 2 .

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