Method for detecting coffee sugar content by using CuAu alloy composite carbon nanospheres

Abstract

The invention provides a method for detecting the sugar content of coffee by using CuAu alloy composite carbon nanospheres as an electrochemical sensing material. The CuAu alloy composite carbon nanospheres used in the method are prepared through a one-step method, high-pressure conditions and gas protection are not needed in the process, and the method has industrial production potential. The spherical symmetrical structure can effectively inhibit the reduction of the specific surface area caused by the aggregation of nano-particles. Compared with detection means such as chromatography and the like needing expensive equipment, the electrochemical method adopted by the invention is simple and convenient to operate, and does not need enzyme to participate in complex pretreatment. In addition, the sensing material provided by the invention only has excellent anti-interference capability on carbohydrates in coffee, and can effectively ensure the test accuracy.

Description

Technical Field

[0001] The present invention relates to the field of nanomaterial applications, and in particular to a method for detecting the sugar content of coffee using CuAu alloy composite carbon nanospheres. Background Art

[0002] Coffee is a common beverage for young people. While coffee itself contains very little sugar, its flavor is often enhanced by added sugars. However, excessive sugar intake can lead to health risks such as obesity and diabetes. Currently, many milk tea and coffee shops do not provide clear information about their product ingredients. Therefore, accurately measuring the sugar content in coffee is crucial for health management.

[0003] There are many methods for determining sugar in food, which can be roughly divided into chemical analysis (Fehling's reagent method, anthrone colorimetry, phenol-sulfuric acid method), chromatography, spectroscopic analysis (near-infrared spectroscopy, ultraviolet-visible spectrophotometry), and enzyme analysis (glucose oxidase method, sucrase-glucose oxidase combined method).

[0004] Chemical analysis methods are susceptible to interference from other reducing substances, enzymatic analysis methods require strict control of reaction temperature and time, and chromatographic analysis methods have complex pre-treatment processes, require derivatization steps, and have long testing cycles. In contrast, non-enzymatic electrochemical methods utilize the functional relationship between the current generated by the catalytic oxidation of glucose at the working electrode and the concentration of sugars such as glucose. This allows for rapid detection of sugar content in liquids, is portable, and does not require complex pre-treatment.

[0005] However, the method of using non-enzymatic electrochemical methods to determine the sugar content in solutions is mainly limited to the detection of low-concentration samples such as blood glucose. To date, there have been no reports on the use of non-enzymatic electrochemical methods to determine sugars in coffee. The reason for this phenomenon is that the concentration of sugars in most coffees is relatively high, and the working electrodes of traditional electrochemical tests are difficult to detect high concentrations of glucose. Therefore, it is of great significance to develop an electrocatalytic material (electrode material) that can detect high concentrations of sugars. In addition, at the commercial level, effective cost control of electrode materials is a key prerequisite for promoting the application of electrochemical detection technology for sugar content in coffee. However, most of the electrode materials (electrocatalysts) for electrochemical detection of sugars currently on the market are expensive, making it difficult to balance high sensitivity and cost control. Summary of the Invention

[0006] The present invention addresses the challenges presented by the prior art and provides a method for detecting the sugar content of coffee using CuAu alloy-composite carbon nanospheres. The CuAu alloy-composite carbon nanospheres exhibit excellent catalytic oxidation properties for high-concentration sugars, effectively promoting the adsorption / desorption and oxidation reactions of reactants, enabling the detection of high-concentration sugars such as glucose. Furthermore, research has shown that the CuAu alloy-composite carbon nanospheres exhibit high specificity for sugars such as glucose, and their detection signal is not susceptible to interference from substances such as caffeine in coffee, enabling rapid and accurate detection of the sugar content in coffee.

[0007] The specific steps of the method for detecting the sugar content of coffee using CuAu alloy composite carbon nanospheres are as follows:

[0008] (1) Add KOH powder to the coffee solution to be tested, reduce it by half and adjust the pH of the solution to 14.0;

[0009] (2) Using a three-electrode system, a certain amount of CuAu alloy composite carbon nanospheres and perfluorosulfonic acid ion exchange resin mixed solution was deposited on a glassy carbon electrode. After the liquid evaporated, the modified electrode was used as the working electrode, Hg / HgO was used as the reference electrode, and a Pt wire electrode was used as the counter electrode, and connected to an electrochemical workstation;

[0010] (3) Set the working potential to 1.26 vs Hg / HgO, use a 1 mol / L KOH solution to dilute coffee with a known sugar content of C (mg / mL), continuously measure the chrono-response current curves at different concentrations, and fit a linear equation based on the functional relationship between the response current density and the coffee concentration to establish a calibration curve Y (uA / cm 2 )=KX(%)+B;

[0011] (4) Measure the response current Y1 of any coffee concentration to be tested, and use the calibration curve Y (uA / cm 2 )=KX(%)+B, thereby calculating X1 and obtaining the sugar content in coffee X1*C / 100 (mg / mL).

[0012] The CuAu alloy composite carbon nanospheres are prepared as follows: first, ascorbic acid is hydrothermally decomposed to form a carbon nanosphere template, followed by in-situ deposition of the CuAu alloy on the template surface. Hydrothermal carbon nanosphere formation effectively prevents the reduction in specific surface area caused by nanoparticle agglomeration, thereby improving electrochemical sensing sensitivity while fully utilizing the precious metal and significantly reducing the cost of the sensing material. The entire preparation process can be completed at ambient pressure, providing a direct, one-step method to obtain the desired product, making it suitable for large-scale production.

[0013] The steps of the proposed method for preparing CuAu alloy composite carbon nanospheres are as follows:

[0014] (1) Mixing a 4 mmol / L ascorbic acid solution and a certain concentration of hydrochloric acid solution at room temperature in proportion to obtain a mixed solution 1;

[0015] (2) adding polyvinyl pyrrolidone powder to the mixed solution 1, placing the mixture in a water bath at 95 to 98 degrees Celsius, and heating and stirring for 8 hours to obtain a reaction solution 1;

[0016] (3) Using deionized water as the solvent, the reaction solution 1 was diluted to 2.5 times of its original volume, potassium chloride powder was added in proportion, and ultrasonic treatment was performed to uniformly disperse the precipitate in the solution to obtain a mixed solution 2;

[0017] (4) Add equal volumes of 400 mmol / L copper chloride and 40 mmol / L chloroauric acid solution to the mixed solution 2 in proportion and stir evenly to obtain a mixed solution 3;

[0018] (5) Add 0.5 mol / L ascorbic acid to the mixed solution 3 in proportion, and continue stirring and reacting at 80 to 90 degrees Celsius for 4 to 6 hours to obtain a reaction solution 2;

[0019] (6) Filtering the reaction solution 2, and washing the resulting precipitate with deionized water and ethanol 1 to 2 times respectively. The washed precipitate is dried to obtain a powder, namely, CuAu alloy composite carbon nanospheres;

[0020] In step (1), the concentration of the hydrochloric acid solution is 1 to 3 mol / L, and the volume ratio of the ascorbic acid solution to the hydrochloric acid is 43:10;

[0021] In step (2), the mass of polyvinyl pyrrolidone powder added per milliliter of mixed solution 1 is 0.9 to 1.1 mg;

[0022] In step (3), the mass of potassium chloride powder added per milliliter of reaction solution 1 is in the range of 9.0 to 10.0 mg;

[0023] In step (4), the volume ratio of the mixed solution 2 to the added copper chloride is in the range of 7:1 to 9:1;

[0024] In step (5), the volume ratio of the mixed solution 3 to the ascorbic acid solution with a concentration of 0.5 mol / L is in the range of 4:1 to 5:1.

[0025] In the above process, the low concentration ascorbic acid (4 mmol / L) used in step (1) is decomposed into small-sized carbon hydrothermal carbon nanosphere carriers at 95 to 98 degrees Celsius, and the high concentration hydrochloric acid solution helps to lower the decomposition temperature of ascorbic acid.

[0026] The copper chloride and chloroauric acid used in step (4) are used as precursors and are reduced by ascorbic acid in step (5) to form a CuAu alloy, which is in situ deposited on the surface of the supporting carbon nanospheres, thereby reducing the usage rate of precious metals.

[0027] The following positive effects can be achieved by using the method of the present invention to detect the sugar content of coffee.

[0028] (1) The sensing material is easy to obtain, the preparation process does not require high pressure conditions and gas protection, and uses environmentally friendly reagents, which has the potential for industrial production.

[0029] The sensor material (CuAu alloy composite carbon nanospheres) provided by this invention is prepared in a single step, eliminating the tedious steps of intermediate product separation, washing, and drying. The maximum reaction temperature does not exceed 98°C, and the entire process does not require special equipment such as a high-pressure hydrothermal reactor or inert gas protection, making it fully suitable for industrial production.

[0030] (2) CuAu alloy composite carbon nanospheres fully exert the size effect of nanomaterials, which is beneficial to the improvement of sensitivity.

[0031] The spherically symmetrical structure of the CuAu alloy composite carbon nanospheres provides them with greater mechanical strength, reduces particle aggregation at high temperatures or under reactive conditions, and effectively suppresses the resulting decrease in specific surface area. Their nano-confinement effect not only enhances the sensitivity of electrochemical sensing but also maximizes the utilization of precious metals, significantly reducing the cost of sensing materials.

[0032] (3) The electrochemical method is easy to implement, has a fast response speed, and does not require complex pretreatment of the test solution.

[0033] Compared to methods such as chromatography that require expensive equipment, the electrochemical workstation equipment used in the electrochemical method provided by the present invention is highly popular and easy to operate. No enzyme test is required to ensure that the test results are not affected by temperature. Before the test, the sample to be tested only needs to add KOH powder to adjust the pH of the test solution (to improve the detection sensitivity). The detection process does not require complex pre-treatment operations such as precipitation, filtration or hydrolysis of the sample. The response is fast and a stable signal can be obtained within 5 seconds, making it particularly suitable for rapid on-site detection.

[0034] (4) The constructed sensor has strong specificity and is not easily interfered by other soluble substances in coffee.

[0035] The sensing material provided by the present invention only responds to changes in the sugar content in coffee. Compared with latte coffee with a higher sugar content, the sensor's response signal to sugar-free or low-sugar coffee is significantly weakened or disappears, indicating that the sensor has obvious specificity for sugar substances in coffee, effectively ensuring the accurate detection of the sugar content in the coffee solution. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 is the X-ray diffraction pattern of the product obtained in Example 1.

[0037] Figure 2 This is a scanning electron micrograph of the CuAu alloy composite carbon nanospheres obtained in Example 1.

[0038] Figure 3 This is the current density of the CuAu alloy composite carbon nanospheres in Application Example 1 in response to different concentrations of Nescafe Latte coffee solutions.

[0039] Figure 4 is the fitted linear equation for the functional relationship between the response current density and the concentration of Nescafe Latte coffee in Application Example 1.

[0040] Figure 5 is the response current density of different concentrations of Nestle American coffee in Example 1.

[0041] Figure 6 This is a comparison chart of the current density values ​​of CuAu alloy composite carbon nanospheres in response to the same concentration of Nestle Latte coffee solution and Nestle American coffee. DETAILED DESCRIPTION

[0042] In order to make the objectives, technical solutions and advantages of the present invention more clear, the present invention will be described in further detail below with reference to the accompanying drawings.

[0043] Example 1: Preparation of CuAu alloy composite carbon nanospheres

[0044] (1) Mix 43 mL of 4 mmol / L ascorbic acid solution and 10 mL of 3 mol / L hydrochloric acid solution at room temperature to obtain a mixed solution 1;

[0045] (2) Add 53 mg of polyvinyl pyrrolidone powder to the mixed solution 1, place the mixture in a 95°C water bath, and heat with stirring for 8 hours to obtain a reaction solution 1;

[0046] (3) Add 79.5 mL of deionized water to dilute the reaction solution 1 to 2.5 times its original volume, add 1.27 g of potassium chloride powder in proportion, and sonicate for 10 minutes to uniformly disperse the precipitate in the solution to obtain a mixed solution 2;

[0047] (4) 17.6 mL of 400 mmol / L copper chloride and 17.6 mL of 40 mmol / L chloroauric acid solution were added to the mixed solution 2, and stirred evenly to obtain a mixed solution 3;

[0048] (5) Add 35.3 mL of 0.5 mol / L ascorbic acid solution to the mixed solution 3 in proportion, and continue stirring and reacting at 80°C for 4 hours to obtain reaction solution 2;

[0049] (6) The reaction solution 2 was filtered, and the resulting precipitate was washed once with deionized water and once with ethanol. The washed precipitate was dried in a forced air drying oven at 60 degrees Celsius, and the resulting powder was CuAu alloy composite carbon nanospheres.

[0050] In order to explore the composition of the obtained material, we conducted XRD test on the sample. Figure 1 As shown, the product diffraction peaks are located at 2θ = 38.2°, 44.4°, 64.6°, 77.8°, 81.7° for Au (JCPDS card 040784) and 2θ = 43.2°, 50.4°, 74.2°, 89.9° for Cu (JCPDS card 040836). Based on this, it can be determined that the product contains a CuAu alloy, and the shift of its diffraction peaks compared to the metallic Au is due to the interfacial lattice strain during the CuAu alloying process.

[0051] This lattice strain effect also promotes the adsorption / desorption behavior of sugar molecules such as glucose on the electrode surface, making it more sensitive as a sensing material.

[0052] In the process of preparing CuAu alloy composite carbon nanospheres, ascorbic acid decomposes under 95℃ hydrothermal conditions to generate amorphous carbon, and its X-ray diffraction spectrum does not show obvious diffraction peaks, so no impurity peaks are detected. In order to obtain the morphology of the CuAu alloy nanocrystals obtained in Example 1, we conducted field emission scanning electron microscopy tests on the obtained samples. Figure 2 The solid particles obtained in Example 1 are CuAu alloy, and the light gray spherical parts are hydrothermal carbon nanospheres decomposed from ascorbic acid molecules. The carbon nanospheres are used as supporting materials to improve the dispersibility of the CuAu alloy.

[0053] In summary, the product obtained in Example 1 of the present invention is CuAu alloy composite carbon nanospheres.

[0054] Application Example 1: Detection of Sugar Content in Coffee

[0055] (1) Take 10 mL of Nescafe Latte coffee stock solution, add KOH powder to the coffee solution to be tested, stir evenly, and adjust the solution pH to 14.0;

[0056] (2) Using a three-electrode system, a certain amount of CuAu alloy composite carbon nanospheres and perfluorosulfonic acid ion exchange resin mixed solution was deposited on a glassy carbon electrode. After the liquid evaporated, the modified electrode was used as the working electrode, Hg / HgO was used as the reference electrode, and a Pt wire electrode was used as the counter electrode, and connected to an electrochemical workstation;

[0057] (3) The working potential was set to 1.26 V vs Hg / HgO. A Nescafe latte coffee with a known sugar content of 50 mg / mL was diluted with a 1 mol / L KOH solution. The chrono-response current curves at different concentrations were continuously measured. Based on the functional relationship between the response current density and the coffee concentration, a linear equation was fitted to establish a calibration curve Y (uA / cm 2 )=KX(%)+B;

[0058] (4) Measure the response current Y1 of any coffee concentration to be tested, and use the calibration curve Y (uA / cm 2 )=KX(%)+B, thereby calculating X1 and obtaining the sugar content in coffee X1*C / 100 (mg / mL).

[0059] In Application Example 1, step (1) is to increase the sensitivity (K value) to the analyte by increasing the alkalinity of the solution.

[0060] In step (2) of Application Example 1, the CuAu alloy composite carbon nanospheres are used as the sensing material to trigger the electrocatalytic oxidation reaction of sugars in the coffee, generating a response current. As shown in Figure 3, as the coffee solution gradually dilutes, the concentration of sugars in the solution decreases, and the amount of charge involved in the reaction decreases accordingly, resulting in a linear downward trend in the response current.

[0061] Instructions attached Figure 4 The linear function relationship between the response current density and the concentration of the coffee solution is given, and the fitting equation is: 103.64X (%) + 2190.4 = Y (uA / cm 2 The linear fit is 0.991. The slope is 103.64. This demonstrates the high sensitivity of the coffee sugar detection method provided by this patent. This higher sensitivity stems from the high specific surface area of ​​the CuAu alloy nanocomposite carbon nanospheres.

[0062] Using the above equation, we can calculate the coffee content (X1-axis coordinate value) based on the response current (Y1-axis coordinate value) of any coffee. Based on the sugar concentration of 50 (mg / mL) in the original coffee, the sugar content in the coffee to be tested can be calculated as X1*0.5 (mg / mL).

[0063] Comparative Example 1: Detection of Low-Sugar Nestle Coffee (Selective Verification)

[0064] The method for detecting sugar in coffee provided by this invention has good selectivity. To verify that the change in the response current at the working potential is due to changes in the sugar content in the coffee (rather than other substances), the following comparative example was conducted. The specific steps are as follows:

[0065] (1) Take 10 mL of Nestle American coffee stock solution, add KOH powder to the coffee solution to be tested, stir evenly, and adjust the solution pH to 14.0;

[0066] (2) Using a three-electrode system, a certain amount of CuAu alloy composite carbon nanospheres and perfluorosulfonic acid ion exchange resin mixed solution was deposited on a glassy carbon electrode. After the liquid evaporated, the modified electrode became the working electrode, Hg / HgO was used as the reference electrode, and a Pt wire electrode was used as the counter electrode, which was connected to an electrochemical workstation.

[0067] (3) The working potential was set to 1.26 V vs Hg / HgO, and the Nestle American coffee concentrate was diluted with a 1 mol / L KOH solution. The chrono-response current curves at different coffee concentrations were continuously measured.

[0068] Compared with Application Example 1, Comparative Example 1 replaces the "Nescafe Latte Coffee Stock Solution" with the "Nescafe American Coffee Stock Solution" with lower sugar content. Figure 5 As shown in the figure, the response current does not change significantly as the American coffee stock solution is diluted. This indicates that the change in the response current observed when the present invention detects coffee is due to the change in sugar content and has nothing to do with other substances in the coffee stock solution (such as caffeine, etc.). Figure 6 As shown, the current generated by 25% American coffee (1717.31μA / cm 2 ) only occupies 25% of the response current density of the latte (4724.74μA / cm 2 The above results prove that the detection method provided by the present invention has excellent selectivity (anti-interference) and can effectively ensure the accuracy of the test.

[0069] Example 2: Preparation of CuAu alloy composite carbon nanospheres

[0070] (1) Mix 43 mL of 4 mmol / L ascorbic acid solution and 10 mL of 3 mol / L hydrochloric acid solution at room temperature to obtain a mixed solution 1;

[0071] (2) Add 53 mg of polyvinyl pyrrolidone powder to the mixed solution 1, place the mixture in a 95°C water bath, and heat with stirring for 8 hours to obtain a reaction solution 1;

[0072] (3) Add 79.5 mL of deionized water to dilute the reaction solution 1 to 2.5 times its original volume, add 1.27 g of potassium chloride powder in proportion, and sonicate for 10 minutes to uniformly disperse the precipitate in the solution to obtain a mixed solution 2;

[0073] (4) 17.6 mL of 400 mmol / L copper chloride and 17.6 mL of 40 mmol / L chloroauric acid solution were added to the mixed solution 2, and stirred evenly to obtain a mixed solution 3;

[0074] (5) Add 35.3 mL of 0.5 mol / L ascorbic acid solution to the mixed solution 3 in proportion, and continue stirring at 90°C for 6 hours to obtain reaction solution 2;

[0075] (6) The reaction solution 2 was filtered, and the resulting precipitate was washed once with deionized water and once with ethanol. The washed precipitate was dried in a forced air drying oven at 60 degrees Celsius, and the resulting powder was CuAu alloy composite carbon nanospheres.

[0076] In summary, the present invention proposes a method for detecting the sugar content of coffee using CuAu alloy composite carbon nanospheres, and verifies its excellent anti-interference performance. It should be noted that the above is a preferred embodiment of the invention. Those skilled in the art will readily appreciate that improvements and modifications can be made without departing from the principles of the present invention, and such improvements and modifications are considered within the scope of protection of the present invention.

Claims

1. A method for detecting the sugar content of coffee using CuAu alloy composite carbon nanospheres, characterized in that: The specific steps for testing the sugar content of coffee are as follows: (1) Add KOH powder to the coffee solution to be tested, reduce it by half and adjust the pH of the solution to 14.0; (2) Using a three-electrode system, a certain amount of CuAu alloy composite carbon nanospheres and perfluorosulfonic acid ion exchange resin mixed solution was deposited on a glassy carbon electrode. After the liquid evaporated, the modified electrode was used as the working electrode, Hg / HgO was used as the reference electrode, and a Pt wire electrode was used as the counter electrode, and connected to an electrochemical workstation; (3) The working potential was set to 1.26 V vs Hg / HgO. Coffee with a known sugar content of C (mg / mL) was serially diluted using a 1 mol / L KOH solution. The chrono-response current curves at different coffee concentrations were measured. Based on the functional relationship between the response current density and the coffee concentration, a linear equation was fitted to establish a calibration curve Y (uA / cm 2 )=KX(%)+B; (4) Measure the response current Y1 of any coffee concentration to be tested, and use the calibration curve Y (uA / cm 2 )=KX(%)+B, thereby calculating X1 and obtaining the sugar content in coffee X1*C / 100 (mg / mL).

2. A method for detecting the sugar content of coffee using CuAu alloy composite carbon nanospheres, characterized in that: The method for preparing the CuAu alloy composite carbon nanospheres used in claim 1 comprises the following steps: (1) Mixing a 4 mmol / L ascorbic acid solution and a certain concentration of hydrochloric acid solution at room temperature in proportion to obtain a mixed solution 1; (2) adding polyvinyl pyrrolidone powder to the mixed solution 1, placing the mixture in a water bath at 95 to 98 degrees Celsius, and heating and stirring for 8 hours to obtain a reaction solution 1; (3) Using deionized water as the solvent, the reaction solution 1 was diluted to 2.5 times of its original volume, potassium chloride powder was added in proportion, and ultrasonic treatment was performed to uniformly disperse the precipitate in the solution to obtain a mixed solution 2; (4) Add equal volumes of 400 mmol / L copper chloride and 40 mmol / L chloroauric acid solution to the mixed solution 2 in proportion, and stir evenly to obtain a mixed solution 3; (5) Add 0.5 mol / L ascorbic acid to the mixed solution 3 in proportion, and continue stirring and reacting at 80 to 90 degrees Celsius for 4 to 6 hours to obtain a reaction solution 2; (6) Filtering the reaction solution 2, and washing the resulting precipitate with deionized water and ethanol 1 to 2 times respectively. The washed precipitate is dried to obtain a powder, namely, CuAu alloy composite carbon nanospheres; In step (1), the concentration of the hydrochloric acid solution is 1 to 3 mol / L, and the volume ratio of the ascorbic acid solution to the hydrochloric acid is 43:10; In step (2), the mass of polyvinyl pyrrolidone powder added per milliliter of mixed solution 1 is 0.9 to 1.1 mg; In step (3), the mass of potassium chloride powder added per milliliter of reaction solution 1 is in the range of 9.0 to 10.0 mg; In step (4), the volume ratio of the mixed solution 2 to the added copper chloride is in the range of 7:1 to 9:1; In step (5), the volume ratio of the mixed solution 3 to the ascorbic acid solution with a concentration of 0.5 mol / L is in the range of 4:1 to 5:1.

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