Iron / molybdenum-doped carbon dots nanoszyme, and preparation method and application thereof

Abstract

This application belongs to the field of materials science, specifically relating to an iron / molybdenum-doped carbon dot nanozyme, its preparation method, and its application. The preparation method of the iron / molybdenum-doped carbon dot nanozyme includes the following steps: S1. Mixing solid trivalent iron source, solid nitrogen source, solid carbon-sulfur source, and solid molybdenum source, and grinding them to perform solvent-free in-situ carbonization to obtain powder; S2. Dissolving the powder in water, ultrasonically treating it, and filtering it through a filter membrane to obtain the iron / molybdenum-doped carbon dot nanozyme.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to an iron / molybdenum doped carbon dot nanozyme, its preparation method, and its application. Background Technology

[0002] Hydroquinone (HQ) is an important industrial raw material widely used in cosmetics, photography, pharmaceuticals, and petrochemicals. However, hydroquinone exhibits significant cytotoxicity, persistent degradation, and bioaccumulation. It can enter the human body through skin contact or inhalation, causing dermatitis, eye damage, respiratory harm, and even liver and kidney dysfunction and organ failure. Its potential endocrine disruption and carcinogenic risks have also attracted widespread attention. Therefore, developing rapid, sensitive, and reliable methods for detecting hydroquinone is of great significance for environmental pollution control, cosmetic safety supervision, and public health protection. Currently, commonly used detection methods include chromatography and electrochemical methods. While these two methods possess high sensitivity, they typically require complex sample pretreatment procedures, are cumbersome, use expensive instruments, and demand highly skilled operators, making them unsuitable for rapid on-site detection and high-throughput screening.

[0003] In recent years, nanozymes (a class of nanomaterials with enzyme-like catalytic activity) have shown great promise in the field of biosensing due to their high stability, low cost, and tunable catalytic performance. Carbon dots (CDs), as emerging carbon-based nanomaterials, not only possess excellent biocompatibility, tunable fluorescence, and ease of functionalization, but also allow for effective regulation of their electronic structure and surface chemical properties through heteroatom doping, thereby significantly enhancing enzyme-like activity. Currently, most nanozyme sensing platforms still rely on a single signal output (usually colorimetric methods), which are easily affected by environmental background interference, instrument deviation, and operator subjectivity, thus limiting their accuracy and reliability in complex matrices. Summary of the Invention

[0004] In view of this, the present invention provides an iron / molybdenum doped carbon dot nanozyme, its preparation method and application.

[0005] To achieve the above solution, the technical solution of the present invention is as follows: This application provides a method for preparing iron / molybdenum doped carbon dot nanozymes, the method comprising the following steps: S1. Mix solid trivalent iron source, solid nitrogen source, solid carbon sulfur source and solid molybdenum source, grind them and perform solvent-free in-situ carbonization to obtain powder; S2. Dissolve the powder in water, sonicate it, and filter it through a filter membrane to obtain the iron / molybdenum doped carbon dot nanozyme.

[0006] Optionally, in step S1, the molar ratio of the solid trivalent iron source, solid nitrogen source, solid carbon-sulfur source and solid molybdenum source is 0.5-2.0: 4.0-6.0: 0.5-1.5: 0.3-0.4.

[0007] Optionally, in step S1, the solid trivalent iron source is selected from at least one of ferric chloride, ferric nitrate, and ferric sulfate.

[0008] Optionally, in step S1, the solid nitrogen source is selected from urea.

[0009] Optionally, in step S1, the solid carbon-sulfur source is selected from 2,2'-dithiodibenzoic acid (DTSA).

[0010] Optionally, in step S1, the solid molybdenum source is selected from ammonium molybdate tetrahydrate ((NH4)6Mo7O 24 ·4H2O).

[0011] Optionally, in step S2, the temperature of the solvent-free in-situ carbonization is 180-220℃, and the time of the solvent-free in-situ carbonization is 18-26h.

[0012] Optionally, in step S2, the duration of the ultrasonic treatment is 15-30 minutes.

[0013] This application also provides an iron / molybdenum doped carbon dot nanozyme prepared according to the method described above.

[0014] This application also provides the use of the iron / molybdenum doped carbon nanodot nanozyme as described above in the preparation of products for detecting the content of hydroquinone and / or ascorbic acid and / or hydrogen peroxide and / or glutathione.

[0015] The present invention has the following beneficial effects: Unlike existing nanozyme sensing platforms that generally rely on a single signal output (usually colorimetric), this application constructs a dual-mode sensing strategy based on iron / molybdenum-doped carbon nanozymes. This dual-mode sensing strategy integrates two signal outputs based on different principles (fluorescence and colorimetry) to achieve built-in self-verification and cross-calibration functions, significantly improving the accuracy and robustness of detection results. It has been successfully applied to the quantitative analysis of HQ in actual whitening and freckle-removing cream samples, providing a novel and reliable sensing strategy for monitoring harmful substances in environmental and health risks. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the preparation process of the iron / molybdenum doped carbon nanoparticle nanozyme of this application. Urea represents urea, Gridding represents grinding, Solvent-free carbonization represents solvent-free carbonization, Hydroquinone represents hydroquinone, Fluorescence represents fluorescence method, and Colorimetry represents colorimetry. Figure 2 High-resolution transmission electron microscopy (20 nm) image of Fe / Mo-CDs1 nanozyme. Figure 3 High-resolution transmission electron microscopy (5 nm) image of Fe / Mo-CDs1 nanozyme. Figure 4 The particle size distribution diagram of Fe / Mo-CDs1 nanozymes is shown. Size represents particle size, and frequency represents the percentage. Figure 5 The image shows the Fourier transform infrared (FT-IR) spectrum of the Fe / Mo-CDs1 nanozyme. Wavenumber represents the wave number, and intensity represents the intensity.

[0017] Figure 6 The image shows the X-ray photoelectron spectroscopy (XPS) results of Fe / Mo-CDs1 nanozymes. Binding Energy represents the binding energy, and Intensity represents the intensity. Figure 7 The fluorescence emission spectra of Fe / Mo-CDs1, Fe / Mo-CDs2, Fe / Mo-CDs3 and Mo-CDs are shown (λex = 315 nm), where Intensity represents intensity and Wavelength represents wavelength. Figure 8 A represents the UV-Vis absorption spectrum, fluorescence excitation spectrum, and fluorescence emission spectrum of Fe / Mo-CDs1, where Wavelength represents wavelength, FL.Intensity represents fluorescence intensity, and Absorbance represents absorbance. Figure 8 B is a digital photograph of Fe / Mo-CDs1 under 315 nm ultraviolet light, which emits bright blue fluorescence; Figure 9 The graph shows the time-dependent changes in absorbance catalyzed by different concentrations of Fe / Mo-CDs1. Absorbance represents absorbance, and Time represents time. Figure 10 The results show the effect of different temperatures on the catalytic activity of Fe / Mo-CDs1. Absorbance represents absorbance, and Temperature represents temperature. Figure 11The results show the effect of different pH values ​​on the catalytic activity of Fe / Mo-CDs1. Figure 12 The UV-Vis spectra of the Fe / Mo-CDs1+ H2O2 system before and after the addition of HQ when TMB is used as a substrate; Figure 13 The figure shows the results of the steady-state dynamic analysis; Figure 14 The image shows the ultraviolet-visible spectrum (A), the corresponding linear calibration curve (B), and the visual color gradient (C) in the colorimetric mode of the dual-signal sensing system. Figure 15 The fluorescence spectrum (A) and the corresponding linear calibration curve (B) of the dual-signal sensing system in fluorescence mode are shown. Detailed Implementation

[0018] The present invention will be further illustrated by specific examples below. However, it should be noted that the specific material ratios, process conditions and results described in the embodiments of the present invention are only for illustrating the present invention and cannot be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

[0019] The present invention will be described in detail below through specific examples and embodiments. It should also be understood that the following embodiments are only for specific illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0020] (I) Synthesis, characterization and performance testing of iron / molybdenum doped carbon dot nanozymes (i.e., Fe / Mo-CDs nanozymes) Fe / Mo doped carbon dots (Fe / Mo-CDs) with different iron doping ratios were synthesized in an autoclave using a solventless in-situ carbonization method. Specifically, three types of Fe / Mo-CDs with different iron doping ratios (labeled Fe / Mo-CDs1, Fe / Mo-CDs2, and Fe / Mo-CDs3) and a control sample Mo-CDs without iron doping were synthesized. The raw materials used are shown in Table 1.

[0021] Table 1. Raw materials used As shown in Table 1, the specific steps for preparing Fe / Mo-CDs1 nanozyme are as follows: 0.5 mmol ferric chloride hexahydrate, 0.33 mmol ammonium molybdate tetrahydrate, 5.0 mmol urea, and 1.0 mmol 2,2'-dithiodibenzoic acid (DTSA) are mixed evenly and ground in a mortar for 10 min to obtain a mixture; the mixture is transferred to a 30 mL polytetrafluoroethylene-lined stainless steel autoclave and carbonized in situ at 200 °C for 24 h; the resulting carbonized powder is dried for later use; then 50 mg of carbonized powder is weighed and dissolved in 50 mL of deionized water, and ultrasonically treated at room temperature for 20 min to ensure complete dissolution, and filtered through a 0.22 μm filter membrane to remove impurities and residual particles; the resulting filtrate (which is the Fe / Mo-CDs1 nanozyme) is collected in a sample bottle, sealed, and stored at 4 °C for subsequent use; Synthesis of Fe / Mo-CDs2 nanozyme: Except for adjusting the amount of ferric chloride hexahydrate to 1.0 mmol, the amounts of ammonium molybdate tetrahydrate, urea, and 2,2'-dithiodibenzoic acid were kept the same as those of Fe / Mo-CDs1, and the preparation method was the same. Synthesis of Fe / Mo-CDs3 nanozyme: Except for adjusting the amount of ferric chloride hexahydrate to 2.0 mmol, the amounts of ammonium molybdate tetrahydrate, urea, and 2,2'-dithiodibenzoic acid were kept the same as those of Fe / Mo-CDs1, and the preparation method was the same. Synthesis of undoped iron control carbon dots (i.e., Mo-CDs) nanozymes: Except for adjusting the amount of ferric chloride hexahydrate to 0 mmol, the amounts of ammonium molybdate tetrahydrate, urea, and 2,2'-dithiodibenzoic acid were kept the same as those of Fe / Mo-CDs1, and the preparation method was the same. Transmission electron microscopy was performed on the Fe / Mo-CDs1 nanozyme, and the results are as follows: Figure 2 As shown.

[0022] High-resolution transmission electron microscopy (HRTEM) scanning was performed on the Fe / Mo-CDs1 nanozyme, and the results are as follows: Figure 3 As shown.

[0023] Depend on Figure 2 It can be seen that the Fe / Mo-CDs1 nanozyme is spherical.

[0024] Depend on Figure 3 It can be seen that the Fe / Mo-CDs1 nanozyme lattice fringes are clear.

[0025] Depend on Figure 4It is known that the average particle size of Fe / Mo-CDs1 nanozyme is 2.3 nm.

[0026] Fourier transform infrared spectroscopy was used to characterize the Fe / Mo-CDs1 nanozyme, and the results are as follows: Figure 5 As shown.

[0027] X-ray photoelectron spectroscopy (XPS) analysis was performed on the Fe / Mo-CDs1 nanozyme, and the results are as follows: Figure 6 As shown.

[0028] Depend on Figure 5 It is known that Fe / Mo-CDs1 nanozymes are rich in hydrophilic functional groups such as hydroxyl, carboxyl and amino groups, which endows the material with good water solubility.

[0029] Figure 6 The results showed that the Fe / Mo-CDs1 nanozyme contained C, N, O, Fe, Mo, and S elements, with Fe and Mo occurring in the form of Fe³⁺ / Fe²⁺ and Mo⁻, respectively. 6 The ⁺ form was successfully doped.

[0030] The fluorescence intensity of Fe / Mo-CDs1, Fe / Mo-CDs2, Fe / Mo-CDs3, and Mo-CDs nanozymes was compared. The specific steps were as follows: 1 mg / mL solutions of each of the four nanozymes were prepared using deionized water, then added to NaAc buffer (0.2 M, pH adjusted to 4.0). The solutions were then compared and analyzed using a fluorescence spectrophotometer. The results are shown below. Figure 7 As shown.

[0031] Depend on Figure 7 As can be seen, the fluorescence intensity is related to the iron content, with Fe / Mo-CDs1 exhibiting the strongest emission. No Q-band redshift was observed after Fe doping, indicating that the basic electronic structure of the carbon core remains intact. Given its excellent fluorescence properties, Fe / Mo-CDs1 was selected as the material for all subsequent studies.

[0032] Further optical property tests were conducted on the Fe / Mo-CDs1 nanozyme. The specific steps were as follows: 1 mg / mL of Fe / Mo-CDs1 nanozyme was added to NaAc buffer (0.2 M, pH adjusted to 4.0), and after thorough mixing, the mixture was analyzed using both UV spectrophotometer and fluorescence spectrophotometer. The results are as follows: Figure 8 As shown.

[0033] Depend on Figure 8As shown in A (Abs), the UV-Vis absorption spectrum exhibits a characteristic peak at 300 nm. The excitation spectrum (Ex) of the Fe / Mo-CDs1 nanozyme shows two distinct absorption bands located at 245 nm and 315 nm, respectively. This is characteristic of heteroatom-doped carbon dot systems, confirming the success of metal doping and the formation of active sites. Figure 8 As shown in Figure B, the Fe / Mo-CDs1 nanozyme aqueous solution emitted strong blue fluorescence under 315 nm ultraviolet light irradiation. This result indicates that the carbon dot possesses excellent fluorescence properties.

[0034] The time-dependent changes in absorbance catalyzed by Fe / Mo-CDs1 nanozymes of different concentrations were evaluated. The specific steps were as follows: A series of Fe / Mo-CDs1 nanozyme solutions of different concentrations (30-240 μg / mL) were mixed with 0.2 M NaAc buffer (adjusting the pH to 4.0), followed by the sequential addition of 0.5 mM TMB and 200 mM H2O2. The total volume of the reaction system was then brought to 3.0 mL using the same buffer. The reaction system was incubated at room temperature in the dark. Immediately after the reaction started, the absorbance was continuously monitored over time (1-20 min) at 652 nm using a UV-Vis spectrophotometer. The results are shown below. Figure 9 As shown.

[0035] like Figure 9 As shown, the absorbance of the reaction system first increases and then decreases with the increase of nanozyme concentration, reaching a peak at a concentration of 210 μg / mL. The absorbance reaches its maximum value after 18 min of reaction, indicating that this concentration is the optimal concentration for catalytic activity under the experimental conditions.

[0036] The effect of different temperatures on the catalytic activity of Fe / Mo-CDs1 nanozymes was evaluated. The specific steps were as follows: The Fe / Mo-CDs1 nanozyme concentration was fixed at 210 μg / mL in a 0.2M NaAc buffer system at pH 4.0. Then, 0.5 mM TMB and 200 mM H2O2 were added sequentially, bringing the total volume to 3.0 mL. The reaction system was incubated at 20-65°C in the dark for 18 min, and the absorbance at 652 nm was measured. The results are shown below. Figure 10 As shown.

[0037] like Figure 10 As shown, the absorbance of the reaction system reaches its peak at 35 °C, indicating that this temperature is the optimal temperature for catalytic activity.

[0038] The effect of different pH values ​​on the catalytic activity of Fe / Mo-CDs1 nanozymes was evaluated. The specific steps were as follows: A series of 0.2 M NaAc buffer solutions with different pH values ​​(3.5-7.0) were used to fix the Fe / Mo-CDs1 nanozyme concentration at 210 μg / mL. Then, 0.5 mM TMB and 200 mM H2O2 were added sequentially, bringing the total volume to 3.0 mL. The reaction system was incubated at the optimal temperature of 35 °C in the dark for 18 min, and the absorbance at 652 nm was measured. The results are as follows: Figure 11 As shown.

[0039] like Figure 11 As shown, the absorbance of the reaction system reaches its peak at pH 4.0, indicating that this pH is the optimal acidity or alkalinity for catalytic activity.

[0040] Depend on Figure 9-11 It can be seen that the Fe / Mo-CDs1 nanozyme exhibits good stability under different temperature, concentration and pH conditions.

[0041] The enzymatic properties of Fe / Mo-CDs1 nanozymes were tested using TMB as a chromogenic substrate. Under the optimal experimental conditions (optimal nanozyme concentration, optimal temperature, and optimal pH), the peroxidase-like activity of Fe / Mo-CDs1 nanozymes was systematically studied. The specific steps were as follows: Fe / Mo-CDs1 nanozymes (210 μg / mL) were added to NaAc buffer (0.2 M, pH adjusted to 4.0), followed by the sequential addition of TMB (final concentration 0.5 mM) and hydrogen peroxide (final concentration 200 mM); the total reaction volume was adjusted to 3.0 mL using NaAc buffer. The mixture was incubated at room temperature for 18 min, and the color change was observed. The absorbance at 652 nm was recorded using a UV-Vis spectrophotometer to assess the catalytic activity. To evaluate the feasibility of detecting HQ in the reaction system, the above reaction system was used, and HQ was introduced as an inhibitor. The specific steps were as follows: Under the same experimental conditions, in a system containing Fe / Mo-CDs1 nanozyme (final concentration 210 μg / mL), TMB (final concentration 0.5 mM), and H2O2 (final concentration 200 mM), analysis was performed using a UV-Vis spectrophotometer. HQ (0.5 μM) was added, and the mixture was incubated at room temperature for 18 min. The color change was observed, and the analysis was performed again using a UV-Vis spectrophotometer. The results are as follows: Figure 12 As shown.

[0042] Depend on Figure 12 It is known that Fe / Mo-CDs1 nanozyme can efficiently catalyze the oxidation of substrate TMB by H2O2 under acidic conditions (pH 4.0) to generate blue oxTMB, which has a characteristic absorption peak at a wavelength of 652 nm.

[0043] Steady-state kinetics of Fe / Mo-CDs1 nanozymes were analyzed under optimized conditions (pH 4.0, 35°C). The specific steps were as follows: First, while maintaining a constant hydrogen peroxide concentration, the TMB concentration was varied (0.5-6.0 mM); conversely, while keeping the TMB concentration constant (0.2-2.0 mM), the hydrogen peroxide concentration was varied, thus constructing two reaction systems. The Fe / Mo-CDs1 nanozyme concentration was maintained at 210 μg / mL, and the total volume was 3.0 mL. Immediately after reaction initiation, the absorbance was monitored in real-time at 652 nm using a UV-Vis spectrophotometer. The initial reaction rate (V0) at each substrate concentration was calculated based on the slope of the initial linear phase of the reaction. Kinetic parameters (Km and Vmax) were calculated by fitting the Michaelis-Menten equation: V = Vmax[S] / (Km + [S]), where V is the initial rate, [S] is the substrate concentration, Vmax is the maximum reaction rate, and Km represents the Michaelis constant. The results are shown below. Figure 13 As shown.

[0044] Depend on Figure 13 It can be seen that the POD-like activity of Fe / Mo-CDs1 nanozyme follows the typical Michaelis-Menten model, showing extremely high affinity and excellent catalytic efficiency for the substrates TMB and H2O2.

[0045] (II) Construction and Application of Dual-Signal Sensing System A colorimetric / fluorescence dual-mode dual-signal sensing system was constructed. The specific detection steps are as follows: Fe / Mo-CDs1 nanozyme (30 μg / mL) was added to NaAc buffer (0.2 M, pH 4.0) in sequence, followed by the addition of TMB (final concentration 0.5 mM) and hydrogen peroxide (final concentration 200 mM) to prepare a standard reaction mixture, thus obtaining the colorimetric / fluorescence dual-mode dual-signal sensing system. HQ detection was performed using the constructed sensing system in colorimetric mode. The specific steps were as follows: Different concentrations of HQ (0.25-2.0 μM) were added as inhibitors to the standard reaction system, and the total reaction volume was adjusted to 3.0 mL with NaAc buffer. The mixture was incubated at 35°C in the dark for 30 min. The absorbance at 652 nm was measured using a UV-Vis spectrophotometer, and the corresponding color change was recorded. The test was performed in triplicate, and the average of the three results was taken as the final result. The results are shown below. Figure 14 As shown in Figure A, a linear relationship between HQ concentration and absorbance was plotted with HQ concentration on the x-axis and absorbance on the y-axis. The results are as follows. Figure 14 As shown in B, during this process, the color change of the system was observed, and the results are as follows. Figure 14 As shown in C.

[0046] Depend on Figure 14 It can be seen that when the HQ concentration increases from 0.25 μM to 2.0 μM, the characteristic absorption intensity at 652 nm wavelength shows a systematic decrease (Figure A), the standard curve is y = 0.06486 + 0.24354x, and the R² is 0.97414 (Figure B). This is accompanied by a visual gradient of color changing from deep blue to colorless (Figure C).

[0047] HQ detection was performed using the constructed sensing system in fluorescence mode. The specific steps were as follows: HQ solutions of different concentrations (0.1-1.0 μM) were added to the standard reaction system as inhibitors, and the total reaction volume was adjusted to 3.0 mL with NaAc buffer. The mixture was incubated at 35°C in the dark for 30 min. The fluorescence emission spectra were recorded at an excitation wavelength of 315 nm. The experiment was performed in triplicate, and the average of the three results was taken as the final result. The results are shown below. Figure 15 As shown in Figure A, a linear relationship between HQ concentration and fluorescence intensity at 402 nm wavelength was plotted, with HQ concentration on the x-axis and fluorescence intensity at 402 nm wavelength on the y-axis. The results are as follows. Figure 15 As shown in B.

[0048] Depend on Figure 15 It can be seen that there is a good linear correlation between fluorescence intensity (y) and HQ concentration (x) (Figure A), and the fitting equation y=1.46949+1.18123x has an R² of 0.99534 (Figure B).

[0049] (III) Test of hydroquinone content in actual samples The content of p-diol in actual HQ samples was determined using the colorimetric / fluorescence dual-mode dual-signal sensing system constructed in (II). Specifically, recovery and precision tests were conducted in fluorescence mode and colorimetric mode, respectively. The specific steps for the recovery test in fluorescence mode are as follows: accurately weigh 0.11 g of cream, disperse it in 10 mL of ethanol, sonicate for 20 min, and then filter it through a 0.22 μm membrane; store the filtrate at 4℃ in the dark; during detection, add an appropriate amount of sample solution to the reaction mixture, which contains sodium acetate buffer (0.2 M, pH 4.0), Fe / Mo-CDs1 nanozyme (30 μg / mL), TMB (0.5 mM), and H2O2 (200 mM), and adjust the total volume to 3.0 mL with NaAc buffer, and record the fluorescence intensity (λex / λem = 315 / 402 nm) using a fluorescence spectrophotometer; the recovery test is performed by adding three concentrations (0.2 μM, 0.4 μM, and 0.6 μM) of HQ standard solution to the sample under the same conditions, and perform three parallel determinations. The recovery rate was calculated using the following formula: Recovery rate (%) = (Measured concentration - Initial concentration) / Added concentration × 100%, where the measured concentration, initial concentration, and added concentration represent the measured concentration of HQ in the spiked sample, the original HQ concentration in the sample, and the added HQ concentration, respectively. The results are shown in Table 1. The relative standard deviation (RSD) was calculated using the formula: Relative standard deviation (%) = (Standard deviation / Average) × 100%, and the results are shown in Table 1. The specific steps for the recovery test in colorimetric mode are as follows: Similar to the fluorescence mode, accurately weigh 0.11 g of the cream, disperse it in 10 mL of ethanol, sonicate for 20 min, and then filter through a 0.22 μm membrane; store the filtrate at 4℃ protected from light. During detection, add an appropriate amount of sample solution to the reaction mixture, which contains sodium acetate buffer (0.2 M, pH 4.0), Fe / Mo-CDs1 nanozyme (30 μg / mL), TMB (0.5 mM), and H2O2 (200 mM). Adjust the total volume to 3.0 mL with NaAc buffer, and record the absorbance at 652 nm using a UV spectrophotometer. The recovery test was performed by adding three concentrations (0.2 μM, 0.4 μM, and 0.6 μM) of HQ standard solution to the sample under the same conditions, with three parallel determinations. The recovery rate was calculated using the following formula: Recovery rate (%) = (Measured concentration - Initial concentration) / Added concentration × 100%, where the measured concentration, initial concentration, and added concentration represent the measured concentration of HQ in the spiked sample, the original HQ concentration in the sample, and the added HQ concentration, respectively. The results are shown in Table 1. The relative standard deviation (RSD) was calculated using the formula: Relative standard deviation (%) = (Standard deviation / Average) × 100%, and the results are shown in Table 1.

[0050] Table 1. Tests on the recovery and precision of hydroquinone content determination in actual samples (n=3) As shown in Table 1, both colorimetric and fluorescence methods achieved recoveries ranging from 90.2% to 98.7%, with relative standard deviations (RSDs) below 4.5%. These results demonstrate the high accuracy and precision achieved in such a complex cosmetic matrix, strongly confirming the excellent analytical reliability of the Fe / Mo-CDs1 nanozyme of this application and laying a solid foundation for its practical application in cosmetic safety monitoring and quality control.

[0051] The above embodiments are merely illustrative of the technical solutions and effects of the present invention and are not intended to limit the scope of the invention. Those skilled in the art can modify or alter the embodiments without departing from the spirit and scope of the invention. Any equivalent modifications or substitutions made based on the technical concept of the present invention should fall within the protection scope of the present invention.

Claims

1. A method for preparing an iron / molybdenum-doped carbon dot nanoszyme, characterized in that, The preparation method of the iron / molybdenum doped carbon dot nanozyme includes the following steps: S1. Mix solid trivalent iron source, solid nitrogen source, solid carbon sulfur source and solid molybdenum source, grind them and perform solvent-free in-situ carbonization to obtain powder; S2. Dissolve the powder in water, sonicate it, and filter it through a filter membrane to obtain the iron / molybdenum doped carbon dot nanozyme.

2. The preparation method of the iron / molybdenum-doped carbon dot nanoszyme according to claim 1, characterized in that, In step S1, the molar ratio of the solid trivalent iron source, solid nitrogen source, solid carbon-sulfur source and solid molybdenum source is 0.5-2.0: 4.0-6.0: 0.5-1.5: 0.3-0.

4.

3. The preparation method of the iron / molybdenum-doped carbon dot nanoszyme according to claim 1, wherein, In step S1, the solid trivalent iron source is selected from at least one of ferric chloride, ferric nitrate, and ferric sulfate.

4. The preparation method of the iron / molybdenum-doped carbon dot nanoszyme according to claim 1, wherein, In step S1, the solid nitrogen source is selected from urea.

5. The preparation method of the iron / molybdenum-doped carbon dot nanoszyme according to claim 1, wherein, In step S1, the solid carbon-sulfur source is selected from 2,2'-dithiodibenzoic acid.

6. The preparation method of the iron / molybdenum-doped carbon dot nanoszyme according to claim 1, wherein, In step S1, the solid molybdenum source is selected from ammonium molybdate tetrahydrate.

7. The preparation method of the iron / molybdenum-doped carbon dot nanoszyme according to claim 1, wherein, In step S2, the temperature of the solvent-free in-situ carbonization is 180-220℃, and the time of the solvent-free in-situ carbonization is 18-26h.

8. The method for preparing the iron / molybdenum-doped carbon dot nanoszyme according to claim 1, wherein, In step S2, the duration of the ultrasonic treatment is 15-25 minutes.

9. An iron / molybdenum doped carbon dot nanozyme prepared according to the method described above.

10. The use of the iron / molybdenum doped carbon nanoparticle nanozyme as described in claim 9 in the preparation of products for detecting the content of hydroquinone and / or ascorbic acid and / or hydrogen peroxide and / or glutathione.

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