Electrode for detecting volatile ammonia in meat and meat products and preparation method thereof

Abstract

The invention provides an electrode for detecting volatile ammonia in meat and meat products and a preparation method thereof, the electrode is a polyaniline-hydroxylated carbon nanotube electrode synthesized by an electrochemical one-step method, and polyaniline is polymerized in situ on an interdigital electrode by cyclic voltammetry. The ammonia gas detection electrode prepared by the method does not have a polyaniline coating step, the quality and thickness of the sensitive film can be controlled more easily, and polyaniline doped with hydroxylated carbon nanotubes has a larger specific surface area, so that the sensitivity and response speed of the electrode are improved. The electrode has strong selective response capability to volatile ammonia in meat and meat products, can stably detect the deterioration degree of meat, and has important application in meat food deterioration detection.

Description

Technical Field

[0001] The present invention relates to the technical field of gas-sensitive materials, and in particular to an electrode for detecting volatile ammonia in meat and meat products and a preparation method thereof. Background Art

[0002] Meat spoilage, a dish ingredient, refers to the deterioration of meat quality, loss of nutrients, and release of harmful substances during storage, processing, or transportation due to microbial growth, enzymatic reactions, and chemical changes. This spoilage not only affects the sensory quality of the food but can also lead to food safety issues, health hazards, and environmental pollution. In the early stages of meat spoilage, the main manifestation is a change in quality. Protein breakdown reduces the nutritional value of the meat, making it loose and inelastic, and imparting a sour and bitter taste. Fat oxidation produces a rancid odor and harmful oxidation products. Further breakdown of fat and protein during the spoilage process releases heterocyclic compounds such as amines, sulfides, and aldehydes, seriously impacting food safety. Ingestion of volatilized amine gases (TVB-N, such as cadaverine, putrescine, and histamine) can lead to hypertension, allergic reactions, and neurotoxicity.

[0003] The freshness of meat used in dishes is a complex parameter encompassing diverse microbiological, physicochemical, and biochemical properties. Numerous methods exist for evaluating the freshness of meat used in dishes. Traditional evaluation methods include sensory evaluation (such as ISO sensory analysis), physical methods (such as machine vision, texture analysis, and gas chromatography-mass spectrometry (GC-MS)), chemical and biochemical methods (electronic tongue, volatile basic nitrogen (TVB-N), capillary electrochromatography), and microbiological methods (total bacterial count). A more specialized testing method uses the volatile basic nitrogen (TVBN) content generated during the deterioration of meat as an evaluation indicator, providing an approximate assessment of the freshness of a meat sample.

[0004] Volatile basic nitrogen (TVB-N) refers to the collective term for alkaline, nitrogenous volatiles produced by protein breakdown during food spoilage. These primarily include volatile ammonia (NH3), trimethylamine (TMA), dimethylamine (DMA), methylamine (MA), and amine compounds such as cadaverine and putrescine. Ammonia is produced by the deamination of amino acids, while trimethylamine is a product of the microbial reduction of choline and trimethylamine oxide in aquatic products (the primary source of fishy odor). Cadaverine and putrescine, among others, originate from the decarboxylation of amino acids. The complex composition of TVB-N makes it difficult to measure its specific volatility using a single sensitive material. Measuring these signature gases can aid in the selection of sensitive materials and their targeted improvement. Furthermore, among the various volatile gases, volatile ammonia is the most volatile due to its inherent influence on its content, boiling point, and saturated vapor pressure. Therefore, it serves as a representative volatile gas produced by the deterioration of meat and meat products. Therefore, quantitative measurement of ammonia content can be used to establish a relationship with the volatile basic nitrogen content to characterize the freshness of meat and meat products.

[0005] In the widespread application of polyaniline, the primary synthesis method is chemical in situ oxidative polymerization. However, due to its dependence on oxidant concentration, temperature, pH, and other factors during the synthesis process, control precision is low. Consequently, the resulting polyaniline chains are disordered, with a higher likelihood of branching or cross-linking. This also results in polyaniline's insensitive response to gases, making it unable to meet the standards for meat freshness testing. Electrochemical polymerization of polyaniline, on the other hand, allows for precise control of polymerization rate and thickness by controlling the potential / current, resulting in higher precision. Summary of the Invention

[0006] The present invention provides an electrode for detecting volatile ammonia in meat and meat products and a preparation method thereof, so as to overcome the defects in the prior art of difficult-to-control thickness of electrode sensitive membrane and insufficient sensitivity, realize the process-controlled and stable synthesis of polyaniline (PANI)-hydroxylated carbon nanotubes (CNTs) electrode, and improve the sensitivity and response speed of the electrode.

[0007] In a first aspect, the present invention provides an electrode for ammonia detection, the electrode comprising: interdigitated electrodes; A polyaniline-hydroxylated carbon nanotube sensitive layer, wherein the polyaniline-hydroxylated carbon nanotube sensitive layer is located on the surface of the interdigitated electrode; The polyaniline-hydroxylated carbon nanotube sensitive layer is in-situ synthesized on the surface of the interdigital electrode by an electropolymerization method.

[0008] The above-mentioned electrode is prepared by an electropolymerization method, and a polyaniline-hydroxylated carbon nanotube sensitive layer can be synthesized in situ in a one-step method on the interdigitated electrode, without the need to first synthesize the sensitive material and then coat it. The process is simpler and more controllable. The synthesized polyaniline-hydroxylated carbon nanotube sensitive layer has a larger specific surface area and has higher sensitivity and response speed in ammonia detection.

[0009] Preferably, the thickness of the polyaniline-hydroxylated carbon nanotube sensitive layer in the above-mentioned electrode is 100-300 nm.

[0010] Preferably, the interdigital electrode material in the above-mentioned electrode is Cu / Ni alloy, Au, Pt, etc., among which Au, Pt and other metals are relatively precious and do not conform to the experimental material selection principle, so Cu / Ni alloy is preferably used.

[0011] In a second aspect, the present invention provides a method for preparing the above-mentioned electrode, comprising the following steps: (1) sulfuric acid, aniline, and hydroxylated carbon nanotubes are sequentially added to water and uniformly dispersed to obtain an aniline solution; (2) Add the above aniline solution dropwise onto the electrode and cover the entire electrode surface; (3) Cyclic voltammetry is used to treat the aniline solution so that it polymerizes into a polyaniline-hydroxylated carbon nanotube sensitive layer on the electrode surface. The residual solution after the reaction is rinsed with deionized water and dried.

[0012] The researchers discovered that during electropolymerization, CNTs, with their high electrical conductivity, act as a preferential conductive path, inducing polyaniline to grow along the hydroxylated carbon nanotubes, thereby forming a long fibrous structure. Compared to nanoparticle-like polyaniline, this fibrous structure has a larger specific surface area, offering the potential for further improving gas sensing performance.

[0013] From an overall structural perspective, the high surface area of ​​hydroxylated carbon nanotubes provides more nucleation sites for the growth of polyaniline, promoting the formation of a more uniform and dispersed polyaniline structure. Furthermore, the high conductivity and unique surface chemistry of CNTs further optimize the growth of polyaniline, resulting in a more porous three-dimensional network. This porous structure not only increases the diffusion rate of gas molecules but also enhances the interaction between polyaniline and gas molecules, thereby improving the sensitivity and response speed of the sensor.

[0014] Preferably, in the above preparation method, the aniline concentration in the solution in step (1) is 0.15-0.25 mol / L, the sulfuric acid concentration is 0.4-0.6 mol / L, and the mass ratio of hydroxylated carbon nanotubes is 10-14 wt.%; Preferably, the aniline concentration in the solution is 0.18-0.22 mol / L, the sulfuric acid concentration is 0.45-0.55 mol / L, and the mass ratio of the hydroxylated carbon nanotubes is 11-13 wt.%.

[0015] Preferably, stirring, ultrasound or the like can be used to better disperse the aniline and hydroxylated carbon nanotubes in the solution.

[0016] Preferably, before the aniline solution is added dropwise, the interdigitated electrode can be cleaned by ultrasonic washing in ethanol and deionized water and air-drying to improve the sensitivity of the electrode.

[0017] Preferably, the amount of the aniline solution added in step (2) of the above preparation method is 18-22 μl.

[0018] Preferably, the cyclic voltammetry parameters in step (3) of the above preparation method are: scanning voltage 0.5-2 V, scanning speed set to 50 mV / s, and number of cycles set to 15-25 cycles.

[0019] The above solution ratio and cyclic voltammetry parameters can achieve the best polymerization effect, make the thickness of the sensitive layer moderate and the process more stable.

[0020] In a third aspect, the present invention provides application of the above-mentioned electrode or the above-mentioned preparation method in ammonia detection.

[0021] In a fourth aspect, the present invention provides a method for detecting ammonia gas, specifically, the above-mentioned electrode is placed in a detection environment and energized, and the NH3 concentration is determined by the change in resistance. The greater the resistance, the greater the NH3 concentration.

[0022] The polyaniline-hydroxylated carbon nanotube electrode provided by the present invention has a detection limit for NH3 as low as 50 ppb and has a relatively fast response time. Its reaction time for NH3 is 33.3s and its desorption time is 50.2s. It can accurately and efficiently detect ammonia in the environment.

[0023] In a fifth aspect, the present invention provides an application of the above-mentioned electrode or the above-mentioned detection method in detecting the degree of meat deterioration.

[0024] The polyaniline-hydroxylated carbon nanotube electrode provided by the present invention, through improvements to the polyaniline-hydroxylated carbon nanotube polymerization process, produces a sensitive layer with a larger specific surface area, making it more susceptible to gas adsorption and more selectively adsorbing volatile ammonia produced during meat spoilage. Its responsiveness to cadaverine, putrescine, dimethylamine, trimethylamine, triethylamine, alcohols such as ethanol, and lipids such as ethyl acetate, produced during the spoilage process, is much lower than that of volatile ammonia. While the levels of these biogenic amines, alcohols, and lipids vary significantly depending on the type and part of the meat, as well as the type of bacteria contaminated, the selective response to volatile ammonia significantly reduces this variability, thus broadening the application range of the polyaniline-hydroxylated carbon nanotube electrode provided by the present invention.

[0025] The present invention provides an electrode for detecting volatile ammonia in meat and meat products, and its preparation method. By improving the electrode material and the polyaniline-hydroxylated carbon nanotube polymerization process, a volatile ammonia detection electrode can be synthesized in a one-step process. The electrode production process is simple and highly controllable. The prepared electrode's sensitive layer has a larger specific surface area, and the polyaniline thereon exhibits a porous structure, which not only increases the diffusion rate of gas molecules but also enhances the interaction between the polyaniline and gas molecules, thereby improving the sensor's sensitivity and response speed. The detection limit for NH3 can be as low as 50 ppb, and the electrode exhibits a fast response time, with a reaction time of 33.3 seconds and a desorption time of 50.2 seconds. Compared to various biogenic amines, alcohols, and lipids, the electrode exhibits a highly selective response to NH3, with a response intensity over four times that of the next highest molecule, cadaverine. The detection results are less susceptible to interference, making it suitable for detecting the degree of meat spoilage. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the technical solutions in the present invention or the prior art, a brief introduction is given below to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0027] Figure 1 It is a schematic flow chart of the synthesis method of the PANI / SWCNT-OH electrode provided by the present invention.

[0028] Figure 2 Schematic diagram of the appearance of the interdigitated electrode before and after preparation provided by the present invention, wherein (A) is before preparation and (B) is after preparation.

[0029] Figure 3 This is the CV curve during the synthesis process of the PANI / SWCNT-OH electrode provided by the present invention.

[0030] Figure 4 This is the CV curve during the synthesis process of the PANI electrode provided by the present invention.

[0031] Figure 5 These are the electron microscopy characterizations of the PANI and PANI / SWCNT-OH electrode sensitive layers provided by the present invention, wherein (A) and (B) are SEM characterizations of the PANI material at 1 μm and 100 nm, (C) is the TEM characterization of the PANI material at 200 nm, (D) and (E) are SEM characterizations of the PANI / SWCNT-OH material at 1 μm and 100 nm, and (F) is the TEM characterization of the PANI / SWCNT-OH material at 200 nm.

[0032] Figure 6 It is a linear fitting curve of the gas response of the PANI and PANI / SWCNT-OH electrodes provided by the present invention to different concentrations of NH3.

[0033] Figure 7 This is the response curve of the PANI / SWCNT-OH electrode provided by the present invention to 50ppmNH3.

[0034] Figure 8 This is the response curve of the PANI / SWCNT-OH electrode provided by the present invention under a larger concentration range of NH3.

[0035] Figure 9 This is the corresponding intensity fitting curve of the PANI / SWCNT-OH electrode provided by the present invention under a larger concentration range of NH3.

[0036] Figure 10 This is a graph showing the response speed of the PANI and PANI / SWCNT-OH electrodes provided by the present invention to NH3.

[0037] Figure 11 This is a test result diagram of the repeatability and stability of the PANI / SWCNT-OH electrode provided by the present invention.

[0038] Figure 12 This is a diagram showing the selectivity results of the PANI / SWCNT-OH electrode provided by the present invention. DETAILED DESCRIPTION

[0039] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts shall fall within the scope of protection of the present invention.

[0040] Example 1 This embodiment provides a method for synthesizing a PANI / SWCNT-OH electrode. The schematic diagram of the synthesis method is shown in FIG. Figure 1 shown.

[0041] Preparation of aniline solution: Take 273 μL of sulfuric acid and add it to 5 mL of deionized water. Stir continuously with a glass rod, then add 182 μL of aniline solution and make the volume to 10 mL. Ultrasonicate for 0.5 h to dissolve all the generated white precipitate. Weigh 22 mg of hydroxylated carbon nanotubes and add them to the solution system. Stir magnetically for 0.5 h and then ultrasonicate for 1 h to evenly disperse the hydroxylated carbon nanotubes. At this time, the aniline concentration is 0.2 M / L, the sulfuric acid concentration is 0.5 M / L, and the mass ratio of hydroxylated carbon nanotubes is 12 wt.%.

[0042] Preparation of interdigitated electrodes: The substrate of the interdigitated electrodes is PET, and the interdigitated electrodes are composed of ten pairs of 5*10 mm interdigitated fingers made of Cu / Ni alloy with a spacing of 100 μm. The electrodes are placed in an ethanol solution and ultrasonically treated for 0.5 h. After being removed, they are rinsed several times with deionized water. Then, they are immersed in deionized water and ultrasonicated for 0.5 h. After being removed, they are placed in a clean culture dish and air-dried in a ventilated place. The air-dried electrodes are as follows: Figure 2 As shown in (A).

[0043] Electropolymerization by cyclic voltammetry: Use a pipette to measure 20 μL of aniline solution and drop it onto the surface of the interdigitated electrode, covering the entire surface of the electrode with the droplets. Polyaniline was polymerized by cyclic voltammetry. The scanning voltage was set to 0.5-2 V, the scanning speed was set to 50 mV / s, and the number of cycles was set to 20. The reference electrode and the counter electrode were short-circuited, and then the working electrode and the counter electrode were clamped to the two pins of the interdigitated electrode to start electropolymerization. Deionized water was used to rinse off the unreacted sulfuric acid and aniline on the surface, and the electrode was placed in a ventilated place to dry naturally. The prepared electrode is as follows: Figure 2 As shown in (B).

[0044] The CV curves of the PANI / SWCNT-OH electrode during preparation are shown in Figure 2. Figure 3 As shown, the oxidation peak is located around 1.6 V. The potential of the oxidation peak reflects the oxidative polymerization process of the aniline monomer, and its position is generally affected by the electronic structure, conductivity, and interfacial charge transfer of the material. Hydroxylated carbon nanotubes have excellent conductivity and electron transport capabilities, acting as an electron transport bridge and reducing the charge transfer impedance of the entire system. Furthermore, since electrons can be transferred to the working electrode more quickly, the excitation energy required for the oxidation process is reduced, resulting in a shift of the oxidation peak to a lower potential (1.6 V).

[0045] Comparative Example 1 This comparative example provides a method for synthesizing a PANI electrode.

[0046] Preparation of aniline solution: Add 273 μL of sulfuric acid to 5 mL of deionized water and stir continuously with a glass rod. Then add 182 μL of aniline solution and adjust the volume to 10 mL. Ultrasonicate for 0.5 h to completely dissolve the generated white precipitate. At this time, the aniline concentration is 0.2 M / L and the sulfuric acid concentration is 0.5 M / L.

[0047] Preparation of interdigitated electrodes: The substrate of the interdigitated electrodes is PET, and they consist of ten pairs of 5×10 mm interdigitated fingers made of Cu / Ni alloy with a spacing of 100 μm. The electrodes were placed in an ethanol solution and ultrasonically treated for 0.5 h. After being removed, they were rinsed several times with deionized water. Then, they were immersed in deionized water and ultrasonicated for 0.5 h. After being removed, they were placed in a clean culture dish and air-dried in a ventilated place. The air-dried electrodes were as follows: Figure 2 As shown in (A).

[0048] Electropolymerization by cyclic voltammetry: Use a pipette to measure 20 μL of aniline solution and add it dropwise to the surface of the interdigitated electrode until the droplets cover the entire surface of the electrode. Polyaniline is polymerized by cyclic voltammetry. Set the scanning voltage to 0.5-2 V, the scanning speed to 50 mV / s, and the number of cycles to 20 cycles. Short-circuit the reference electrode and the counter electrode, and then clamp the working electrode and the counter electrode to the two pins of the interdigitated electrode to start electropolymerization. After the end, use deionized water to rinse off the unreacted sulfuric acid and aniline on the surface, and place it in a ventilated place to dry naturally.

[0049] The only difference between this comparative example and Example 1 is that no hydroxylated carbon nanotubes were added.

[0050] The CV curves during the preparation of PANI electrodes are shown in Figure 2. Figure 4 As shown in the figure, the oxidation peak of PANI during the synthesis process is located at around 1.8 V. In the PANI system, electron transport mainly depends on the conjugated structure formed during the polymerization process. However, due to the low conductivity and large charge transfer resistance of PANI in the initial polymerization stage, a higher potential (1.8 V) is required to drive the oxidative polymerization reaction.

[0051] Example 2 In this example, the PANI / SWCNT-OH electrode and the PANI electrode sensitive layer structure morphology synthesized in Example 1 and Comparative Example 1 were characterized by TEM and SEM. The results are as follows: Figure 5 shown.

[0052] Depend on Figure 5As shown in Figures (A) and (B), in the absence of hydroxylated carbon nanotubes, the electropolymerization of polyaniline is primarily influenced by the small-molecule acidic dopant, sulfuric acid (H₂SO₄), which tends to induce the formation of nanogranular structures. These PANI particles are approximately 140 nm in diameter, small in size, and short in length. Throughout the electropolymerization process, the resulting polyaniline sensitive layer is densely packed, resulting in a relatively uniform overall morphology and minimal porosity. While this dense structure enhances the material's stability, it may affect gas diffusion efficiency, thus limiting its gas-sensing performance.

[0053] Depend on Figure 5 As shown in (D) and (E), the morphology of polyaniline has changed significantly, exhibiting a fibrous structure with a diameter of approximately 70 nm, which is significantly different from the nanogranular structure when undoped with CNTs. This morphological change may be due to the high conductivity of CNTs during the electropolymerization process, which can serve as a preferential conductive path, inducing the growth of polyaniline along the hydroxylated carbon nanotubes, thus forming a long fibrous structure. Compared with nanogranular polyaniline, this fibrous structure has a larger specific surface area, which provides the possibility of further improving gas sensing performance.

[0054] The high surface area of ​​hydroxylated carbon nanotubes provides more nucleation sites for the growth of polyaniline, promoting the formation of a more uniform and dispersed polyaniline structure. In addition, the high conductivity and unique surface chemical properties of CNTs further optimize the growth of polyaniline, allowing it to form a more porous three-dimensional network structure.

[0055] Depend on Figure 5 As shown in (C), the morphology and size of single polyaniline are basically consistent with the SEM results, indicating that doping CNTs has a direct effect on the growth morphology of PANI. Figure 5 In (F), it can be observed that the CNT-doped polyaniline fibers are tightly wrapped around the surface of the hydroxylated carbon nanotubes, further demonstrating that the morphology of polyaniline changes during the electropolymerization process due to the influence of the hydroxylated carbon nanotubes. This phenomenon suggests that the hydroxylated carbon nanotubes may act as a template or guide during the growth of polyaniline. This role, influenced by the difference in conductivity between the two materials, promotes the directional growth of polyaniline on the surface, forming a continuous, interconnected nanofiber network.

[0056] In summary, the SEM and TEM results demonstrate that the doping of hydroxylated carbon nanotubes not only improves the morphology of polyaniline but also optimizes the material's microstructure. This change gives the doped polyaniline a higher specific surface area, a better pore structure, and more efficient electron transport, significantly improving its sensing performance and promising potential for application in gas detection.

[0057] Example 3 This example provides the gas responses of PANI and PANI / SWCNT-OH electrodes to different concentrations of NH3.

[0058] The above gas response ∆R% is defined by the relative change in resistance as shown below: Where R0 is the resistance when exposed to air, R is the resistance when exposed to the gas to be tested, and all resistances are calculated from the IT curve of the electrochemical analyzer. PANI and PANI / SWCNT-OH were exposed to 20 ppm, 25 ppm, 30 ppm, 35 ppm, and 40 ppm NH3 environments, and the resistance change curves were measured. The results are shown in Figure 2. Figure 6 shown.

[0059] Depend on Figure 6 It can be clearly seen that the material has a good response to NH3 before and after doping, and both show good linearity. The expression of the multi-concentration fitting curve of the PANI electrode is y=0.9828x-14.5173, R 2 =0.99, while the fitting curve expression of PANI / SWCNT-OH electrode is y=2.178x-27.25446, R 2 =0.99. Compared with the state before doping, the response after doping with hydroxylated carbon nanotubes is significantly higher, with the maximum value being about 298% of the state before doping. The theoretical LOD of the PANI / SWCNT-OH electrode is 26.6 ppb according to the detection limit calculation formula.

[0060] However, in the actual experiment, due to the limited configuration conditions, the minimum NH3 concentration was 50 ppb. Figure 7 The sensor still responded to 50 ppb NH3 concentration, demonstrating that PANI / SWCNT-OH has good sensitivity and detection limit.

[0061] This example further tests the PANI / SWCNT-OH electrode in a wider range of NH3 concentrations. Figure 8 As shown in the figure, it can be seen that the material still has a good response effect in a larger measurement range, and the current response results show a certain linearity.

[0062] The results of the current response are fitted, and the results are as follows Figure 9 As shown in the figure, it is found that in a larger range, the response of the material is closer to nonlinear, and the sensitivity decreases in a lower concentration environment. The fitting expression is y=6.4369×exp(x / 15.92843)-6.25458, R 2=0.99, which proves that the PANI / SWCNT-OH electrode has the ability to detect trace amounts of NH3 volatilized from raw meat.

[0063] Example 4 This example provides a response time test of PANI and PANI / SWCNT-OH electrodes to NH 3 and a stability test of the PANI / SWCNT-OH electrode.

[0064] Response time is one of the important performance indicators of gas sensors. It usually refers to the time (T90) required for the resistance or current signal of the gas sensor to reach 90% of the stable value when detecting the target gas.

[0065] The reaction time and desorption time of the two electrodes were tested using 15ppm NH3. The results are as follows: Figure 10 shown.

[0066] Depend on Figure 10 From (A), we can see that the reaction time of the pure PANI electrode is 121.3 s and the desorption time is 360+ s (desorption is not completed after the measurement).

[0067] Depend on Figure 10 As shown in (B), the PANI / SWCNT-OH electrode has a reaction time of 33.3 s and a desorption time of 50.2 s, significantly outperforming the pure PANI before doping, with a 2.64-fold reduction in reaction time. The fibrous structure of the hydroxylated carbon nanotubes acts as a supporting framework, inhibiting the aggregation of polyaniline chains and forming an open, porous network. This structure facilitates the rapid diffusion of reactants (such as gas molecules or ions). The high surface area (100–300 m² / g) of the nanostructure significantly increases the effective active surface area of ​​the composite, providing more adsorption sites and promoting rapid molecular detachment during desorption. This increased detection speed is of great significance in the rapid testing of meat samples, enabling faster detection and ensuring accurate and timely testing.

[0068] This example further tests the repeatability and stability of the PANI / SWCNT-OH electrode. Prepare three pieces of sensitive materials from the same batch and place them in a gas sampling bag at the same time. Fill the bag with 50 ppm ammonia directly. After the reaction, the gas in the sampling bag is evacuated to a vacuum. Wait for the resistance to recover. After recovery, continue to fill the bag with ammonia. Repeat this cycle five times. The resistance change trend is shown in the figure below. Figure 11 As shown in the figure, after multiple cycles of short-term testing, the RSD is 3.84%, and the sensor has good repeatability.

[0069] Example 5 In this example, the selectivity of the PANI / SWCNT-OH electrode was tested.

[0070] The selectivity of materials is a crucial parameter in freshness detection. Since meat products emit a wide variety of amine gases when they spoil, if the material selectivity is not strong, the final measurement results will be easily affected by interfering gases. Therefore, cadaverine (CAD), putrescine (PUT), dimethylamine (DMA), trimethylamine (TMA), triethylamine (TEA), alcohols such as ethanol (EtOH), and lipids such as ethyl acetate (EtOAc) were selected to test the sensor response and compared with NH3. Except for ethanol and ethyl acetate, the concentrations of the other substances were all 5ppm. The results are as follows: Figure 12 shown.

[0071] Depend on Figure 12 As can be seen, under the same conditions, the PANI / SWCNT-OH electrode's response to NH₃ is far superior to other amines, alcohols, and lipids, exceeding the second-highest response of CAD by more than four times. This is primarily due to the small size and strong polarity of NH₃ molecules, while electrochemically polymerized polyaniline becomes more ordered under the action of an electric field, exposing more active sites. However, the material is less susceptible to reactions with large volatile amines such as cadaverine and putrescine. While dimethylamine and trimethylamine, while structurally similar to volatile ammonia, are less susceptible to acidic doping with the prepared material. This demonstrates the material's strong response to volatile ammonia and excellent selectivity, enabling targeted detection of volatile ammonia in meat and meat products.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An electrode for ammonia detection, characterized in that: The electrode comprises: interdigitated electrodes; A polyaniline-hydroxylated carbon nanotube sensitive layer, wherein the polyaniline-hydroxylated carbon nanotube sensitive layer is located on the surface of the interdigitated electrode; The polyaniline-hydroxylated carbon nanotube sensitive layer is in-situ synthesized on the surface of the interdigital electrode by an electropolymerization method.

2. The electrode according to claim 1, characterized in that The thickness of the polyaniline-hydroxylated carbon nanotube sensitive layer is 100-300 nm.

3. The electrode according to claim 1 or 2, characterized in that The interdigital electrode material is Cu / Ni alloy, Au, or Pt, preferably Cu / Ni alloy.

4. The method for preparing the electrode according to any one of claims 1 to 3, characterized in that: The following steps are involved: (1) sulfuric acid, aniline, and hydroxylated carbon nanotubes are sequentially added to water and uniformly dispersed to obtain an aniline solution; (2) Add the above aniline solution dropwise onto the electrode and cover the entire electrode surface; (3) The polyaniline-hydroxylated carbon nanotube sensitive layer is polymerized on the electrode surface by cyclic voltammetry, and the residual solution after the reaction is rinsed with deionized water and dried.

5. The preparation method according to claim 3, characterized in that In the solution of step (1), the concentration of aniline is 0.15-0.25 mol / L, the concentration of sulfuric acid is 0.4-0.6 mol / L, and the mass ratio of hydroxylated carbon nanotubes is 10-14 wt.%; Preferably, the aniline concentration in the solution is 0.18-0.22 mol / L, the sulfuric acid concentration is 0.45-0.55 mol / L, and the mass ratio of the hydroxylated carbon nanotubes is 11-13 wt.%.

6. The preparation method according to claim 3 or 4, characterized in that The amount of the aniline solution added in step (2) is 18-22 μl.

7. The preparation method according to any one of claims 3 to 5, characterized in that The cyclic voltammetry parameters in step (3) are: scanning voltage 0.5~2 V, scanning speed set to 50 mV / s, and number of cycles set to 15~25 cycles.

8. Use of the electrode according to any one of claims 1 to 3 or the preparation method according to any one of claims 4 to 7 in ammonia detection.

9. A method for detecting ammonia, characterized in that: The electrode according to any one of claims 1 to 3 is placed in a detection environment and energized, and the ammonia concentration is determined by the change in resistance. The greater the resistance, the greater the ammonia concentration.

10. Use of the electrode according to any one of claims 1 to 3 or the detection method according to claim 9 in detecting the degree of meat deterioration.

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