Method for detecting allura red in food by using difunctional sulfur nanodots

Abstract

The invention provides a method for detecting allura red in food by using difunctional sulfur nanodots. According to the invention, a fluorescence detection method for quantitative detection and identification of allura red (AR) is developed by utilizing dual functions of S-dots, and the S-dots are both a fluorescence indicator and a decomposition reagent of the AR. The fluorescence of the S-dots is quenched by AR, and the mechanism is a static quenching effect. In addition, due to the synergistic decomposition effect of S-dots and an etching reagent (H2O2 solution) on AR, quenched fluorescence is gradually recovered. According to the fluorescent response of S-dots to AR, AR as low as 5 nM can be quantitatively detected, and AR in food pigments can be distinguished by observing fluorescence recovery. Detection and identification of AR in actual food samples such as soda drinks, coated chocolates and fruity milk candies are realized. A new clue is provided for the design of a chemical sensor, and the method has great application potential in the aspect of guaranteeing food safety.

Description

Technical Field

[0001] The invention relates to the technical field of nano analysis, in particular to a method for detecting allura red in food by using dual-functional sulfur nanodots. Background Art

[0002] Allura Red (AR), also known as E129 food additive, is a monoazo synthetic food colorant with the advantages of excellent color stability, water solubility, and low microbial contamination. It is widely used in many foods, such as candy, baked goods, and soft drinks. AR was introduced in the early 1980s, and the Joint FAO / WHO Expert Committee on Food Additives announced that its acceptable daily intake is 7 mg per kilogram of human body weight. Recent studies have shown that continuous use of AR can lead to serious health complications such as allergies, angioedema, attention deficit, anxiety, and urticaria. Therefore, AR is banned in many countries and regions, such as Denmark, Belgium, France, Germany, Switzerland, Sweden, Austria, and Norway. Therefore, in order to ensure the quality of food and the safety of consumers, there is an urgent need to monitor the content of AR in food.

[0003] In recent years, a variety of methods have been developed to detect and identify AR, among which high performance liquid chromatography combined with ultraviolet, diode array detection or mass spectrometry has become the most popular technology due to its excellent separation and identification capabilities. However, they are still limited by the cumbersome and time-consuming detection process and dependence on complex equipment and technicians. Fluorescence methods have the advantages of simple operation, low cost, fast detection speed, high sensitivity, and non-destructive detection, and have great development potential. Researchers have reported AR fluorescence assays using organic dyes, carbon dots, and metal nanoclusters as fluorescent probes. For example, Vijeata et al. reported the detection of AR and other types of food pigments by recording the quenching fluorescence signal of blue-emitting carbon dots. Zhuang et al. reported peptide-modified gold nanoclusters as fluorescent probes for the detection of AR. However, most of these studies used fluorescent nanomaterials as signal probes.

[0004] In this work, we proposed a fluorescence detection method that can quantitatively detect AR and distinguish it from commonly used food pigments, using bifunctional sulfur nanodots (S-dots), in which the sulfur nanodots act as a fluorescence indicator and decomposition agent for AR. The sulfur nanodots exhibit strong blue emission, which is effectively quenched by AR, which contributes to its extensive and strong absorption in the blue-green region. AR can be quantitatively detected by recording the quenched fluorescence signal of S dots. The fluorescence quenching follows the SQE mechanism, has good detection tolerance to common interferences, and relatively poor selectivity and discrimination ability for other types of food pigments. The identification of AR in food pigments was achieved by observing the fluorescence recovery of S dots triggered by the decomposition effect of S dots on AR. The fluorescence method also shows good practical application potential through the detection of AR in various food samples (soda drinks, coated chocolates, fruit-flavored milk candies, and fruit juice candies). Based on this, the present invention provides a bifunctional sulfur nanodot material, which can be used for quantitative detection of AR. Summary of the invention

[0005] The purpose of the present invention is to provide a method for detecting allura red in food using bifunctional sulfur nanodots. The method uses bifunctional sulfur nanodots to detect AR, has the advantages of high sensitivity and selectivity, non-toxic detection materials and reagents, and good stability, and the bifunctional sulfur nanodot material can also decompose AR.

[0006] The present invention is achieved in that:

[0007] The bifunctional sulfur nanodots provided by the present invention are prepared by subjecting a mixed solution of sublimated sulfur, sodium hydroxide and PEG-400 to a one-step heat treatment and then to a H2O2 passivation treatment.

[0008] Specifically, the preparation method of the bifunctional sulfur nanodot material comprises the following steps:

[0009] (a) Sublimed sulfur (1.4 g), sodium hydroxide (4.0 g), PEG-400 (3 mL), and pure water (50 mL) were added into a three-necked round-bottom flask to obtain a mixed solution;

[0010] (b) The reaction temperature of the mixed solution in step (a) is adjusted to 90° C., and the mixture is reacted for 72 hours in a condensation reflux device, and then H 2 O 2 is added to passivate the surface thereof to obtain a bifunctional sulfur nanodot material.

[0011] The invention first etches sublimated sulfur into nanometer-level particles by using NaOH, and then adds H2O2 to passivate the surface thereof to obtain dual-functional sulfur nanodots.

[0012] The dual-functional sulfur nanodot material prepared by the invention can be used for detecting AR-containing substances and decomposing AR.

[0013] A method for selectively detecting a substance containing AR comprises the following steps:

[0014] (a) AR aqueous solutions of different concentrations were prepared; bifunctional sulfur nanodot materials were used as detection objects and mixed with AR aqueous solutions of different concentrations, and fluorescence spectra were measured at 25°C to calculate the fluorescence change ratio; the linear equation of the fluorescence change ratio and AR concentration was determined with AR concentration as the horizontal axis and the fluorescence change ratio as the vertical axis;

[0015] (b) mixing the sample to be tested with the AR standard solution to obtain a mixed solution to be tested, mixing the mixed solution to be tested with the bifunctional sulfur nanodot material, measuring the fluorescence spectrum, and calculating the fluorescence change ratio;

[0016] (c) Calculate the content of AR in the sample according to the linear equation in step (a).

[0017] Preferably, in steps (a) and (b), the fluorescence data at the peak of the fluorescence spectrum at 433 nm is selected to calculate the fluorescence change ratio. The fluorescence change ratio refers to (F0-F) / F0, wherein F is the fluorescence data at 433 nm after the reaction of the bifunctional sulfur nanodots with allura red, and F0 refers to the fluorescence data of the bifunctional sulfur nanodots at 433 nm.

[0018] Preferably, in step (a), AR aqueous solutions of different concentrations are mixed with the bifunctional sulfur nanodot material and then tested immediately at 25°C.

[0019] Preferably, in step (b), the mixed solution to be tested is mixed with the bifunctional sulfur nanodot material and then tested immediately at 25°C.

[0020] Preferably, in step (a), the ratio of the fluorescence change at 433 nm is linearly related to the AR aqueous solution within a certain concentration range: when the AR concentration is 0.01 μM to 3 μM and 15 μM to 400 μM, (F0-F) / F0=0.11lg[AR]+0.27, R 2 =0.978 and (F0-F) / F0=0.45lg[AR]-0.20, R 2 = 0.991. The limit of detection (LOD) was as low as 5 nM.

[0021] Preferably, in step (b), the concentration of the AR standard solution is set so that the AR concentration in the mixed solution to be tested is in the range of 15 μM to 400 μM, and then in step (c), the AR concentration in the mixed solution to be tested is calculated according to the linear equation (F0-F) / F0=0.45lg[AR]-0.20, and the spiked recovery rate is further obtained according to the concentration of the AR standard solution to obtain the AR content in the sample to be tested.

[0022] The bifunctional sulfur nanodot material provided by the present invention can not only detect the content of AR by quenching, but also decompose AR. After the bifunctional sulfur nanodot material decomposes AR, the fluorescence of the bifunctional sulfur nanodot is enhanced again, that is, the fluorescence after quenching is restored.

[0023] The use of bifunctional sulfur nanodot materials to decompose AR-containing substances in the present invention is demonstrated by the following means:

[0024] (1) A 2 mM AR aqueous solution was prepared; the bifunctional sulfur nanodot material was used as a detection substance and mixed with the AR aqueous solution. The fluorescence spectrum was measured at 25°C as the reaction time changed. The fluorescence spectrum showed that the fluorescence intensity increased with the increase of reaction time, indicating that the bifunctional sulfur nanodots decomposed AR, so that the sulfur nanodot fluorescence was quenched and then recovered.

[0025] (2) Prepare a 2 mM AR aqueous solution; use the bifunctional sulfur nanodot material as a test object, mix it with the AR aqueous solution, adjust the pH of the mixed solution to 1-14, and measure the absorption spectrum at 60°C as the reaction time changes. From the absorption spectrum, it can be seen that as the reaction time increases, the absorbance decreases, indicating that the bifunctional sulfur nanodots decompose AR.

[0026] By measuring the fluorescence spectra at different reaction times at 25°C and the absorption spectra at 60°C, it can be concluded that the bifunctional sulfur nanodot material can decompose substances containing AR.

[0027] Preferably, in step (2), the pH of the mixed solution is adjusted to 12.

[0028] Preferably, in step (1), fluorescence data at the peak of the fluorescence spectrum at 433 nm is collected.

[0029] Preferably, in step (2), the absorption data at the absorption spectrum peak of 500 nm is collected.

[0030] The present invention designs a water-soluble bifunctional sulfur nanodot material, which is non-toxic, has the ability to recognize AR-related substances, and conducts effective signal transduction, achieves low background signals, and has sensitive detection and selectivity for AR and substances containing AR.

[0031] The raw material cost used in the preparation of the dual-functional sulfur nanodot material of the present invention is low, the preparation method is simple, easy to operate, and can be mass-produced. The detection system of the present invention does not contain toxic reagents and materials such as organic molecules and heavy metals, has a wide detection range, high sensitivity, high selectivity, can realize the analysis and detection of AR in food, and has a wide range of potential application value. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a transmission electron microscopy image of the bifunctional sulfur nanodots prepared in Example 1 of the present invention.

[0033] Figure 2 1 and 2. These are the fluorescence spectrum and AR absorption spectrum of the bifunctional sulfur nanodots measured in Example 2 of the present invention.

[0034] Figure 3 This is a fluorescence spectrum diagram of the bifunctional sulfur nanodots detecting AR at different reaction temperatures in Example 3 of the present invention.

[0035] Figure 4 This is a fluorescence spectrum diagram of the bifunctional sulfur nanodots in Example 4 of the present invention detecting different concentrations of AR.

[0036] Figure 5 This is a fluorescence ratio diagram of the bifunctional sulfur nanodots detecting AR at different pH values ​​in Example 5 of the present invention.

[0037] Figure 6 This is the absorption spectrum of the bifunctional sulfur nanodots decomposing AR at different reaction temperatures in Example 6 of the present invention.

[0038] Figure 7 This is the absorption spectrum of the decomposition of AR by the bifunctional sulfur nanodots at different reaction times in Example 7 of the present invention.

[0039] Figure 8 This is the absorbance graph of AR decomposition by bifunctional sulfur nanodots at different pH values ​​in Example 8 of the present invention.

[0040] Fig. 9 Graphs showing the fluorescence spectra of AR decomposed by bifunctional sulfur nanodots at different reaction times in Example 9 of the present invention.

[0041] Fig.10 Graphs showing the fluorescence spectra of AR decomposed by bifunctional sulfur nanodots at different reaction times in Example 10 of the present invention.

[0042] Fig.11 This is a graph showing the anti-interference ability results when using the dual-functional sulfur nanodot material to detect AR in Example 11 of the present invention.

[0043] Fig.12 This is a graph showing the selectivity results when using the bifunctional sulfur nanodot material to identify AR in Example 12 of the present invention.

[0044] Fig.13 This is a linear correlation curve between the fluorescence change ratio of the bifunctional sulfur nanodots and the AR concentration in Example 13 of the present invention. DETAILED DESCRIPTION

[0045] The present invention is further described below in conjunction with examples. The following examples are only for illustration and are not intended to limit the scope of protection of the present invention in any way.

[0046] The processes and methods not described in detail in the following examples are conventional methods known in the art, and the reagents used in the examples are all analytically pure or chemically pure, and can be purchased commercially or prepared by methods well known to those of ordinary skill in the art. The following examples all achieve the purpose of the present invention.

[0047] Example 1

[0048] 1.4 g of sublimated sulfur, 4.0 g of sodium hydroxide, 3.0 mL of PEG-400 and 50 mL of high-purity water were mixed, the resulting mixed solution was heated to 90° C., stirred for 72 hours, cooled to room temperature, and a hydrogen peroxide solution (30%) was added thereto until blue fluorescence appeared under ultraviolet light, and then the addition was stopped to obtain a bifunctional sulfur nanodot (S-dots) aqueous solution.

[0049] The bifunctional sulfur nanodots aqueous solution was dispersed by ultrasonic treatment and then dropped onto a copper grid. It was then naturally dried and characterized by TEM. The results are shown in the figure. Figure 1 As shown. Figure 1 It can be seen that the embodiment of the present invention successfully synthesized the dual-functional sulfur nanodot material, and the particle size of the prepared sulfur nanocluster material was 5.0 nm.

[0050] Example 2

[0051] 150 μL of the sulfur nanodot solution obtained in Example 1 was added with distilled water to 1 mL, and the fluorescence spectrum at an excitation wavelength of 300 nm to 400 nm was measured at 25°C. The results are as follows: Figure 2 As shown in Figure 2, the emission peak has a maximum red shift, showing a fluorescence spectrum with typical S-dot fluorescence characteristics. Figure 2 It can be seen from the fluorescence excitation spectrum and emission spectrum that the optimal excitation wavelength of sulfur nanodots is 350nm, and there is an emission peak at 433nm under the optimal excitation wavelength. Figure 2 The absorption spectrum of AR is also shown in the figure. The fluorescence emission spectrum and excitation spectrum of S-dots are completely covered by the UV-visible absorption spectrum of AR.

[0052] Example 3

[0053] 300 μL of 2 mM AR aqueous solution was mixed with 150 μL of the bifunctional sulfur nanodot solution obtained in Example 1, and distilled water was added to 1 mL. The mixture was reacted at different temperatures, and the fluorescence spectra were measured after 2 h of reaction. The results are as follows: Figure 3The fluorescence intensity at the emission peak position was selected to calculate the normalized intensity (i.e., F / F0, where F is the fluorescence intensity after the reaction and F0 is the fluorescence intensity at point S before the reaction). The results are shown in Table 1. Figure 3 As can be seen from Table 1, the fluorescence normalized intensity at the emission peak position at 25°C is the lowest, indicating that the bifunctional sulfur nanodots are most strongly quenched by AR at 25°C, and 25°C is the optimal condition for the test.

[0054] Table 1

[0055] Reaction temperature Normalized Intensity 25℃ 0.12 37℃ 0.78 40℃ 0.79 50℃ 0.68 60℃ 0.60 70℃ 0.51 80℃ 0.55 90℃ 0.83 100℃ 0.86

[0056] Example 4

[0057] 300 μL of AR aqueous solution of different concentrations (0, 0.00003, 0.00017, 0.0003, 0.0017, 0.003, 0.05, 0.1, 0.17, 0.23, 0.3, 0.37, 0.43, 0.5, 0.7, 0.8, 1.0, 1.33, 2.0, 3.0 mM) were mixed with 150 μL of the sulfur nanodot solution obtained in Example 1, distilled water was added to 1 mL, reacted at 25°C, measured immediately, and fluorescence spectra were collected. The results are shown in FIG. Figure 4 As shown. Figure 4 It can be seen that with the increase of AR concentration, the fluorescence intensity gradually decreases.

[0058] Example 5

[0059] 300 μL of 2 mM AR aqueous solution was mixed with 150 μL of sulfur nanodot solution obtained in Example 1, and distilled water was added to 1 mL. Fifteen portions were prepared and the pH was adjusted to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10.6, 11, 12, 13, and 14 with HCl and NaOH, respectively. The reaction was carried out at 25°C, and the fluorescence spectrum was measured immediately and collected. The results are shown in FIG. Figure 5 shown. Figure 5 In the vertical axis, F is the fluorescence intensity after the reaction, and F0 is the fluorescence intensity of the sulfur nanodots before the reaction. Figure 5 It can be seen that the pH value of this experiment is applicable in a wide range.

[0060] Example 6

[0061] 300 μL of 2 mM AR aqueous solution was mixed with 150 μL of sulfur nanodot solution obtained in Example 1, distilled water was added to 1 mL, and the mixture was reacted at different temperatures. The absorption spectra were measured immediately and collected. The results are as follows: Figure 6 The absorbance at 500nm is selected and the results are shown in Table 2. Figure 6 As can be seen from Table 2, 60°C is the best condition for the test.

[0062] Table 2

[0063] Reaction temperature Absorbance 25℃ 3.52 37℃ 3.48 45℃ 2.85 60℃ 2.12 75℃ 2.18

[0064] Example 7

[0065] 300 μL of 2 mM AR aqueous solution was mixed with 150 μL of sulfur nanodot solution obtained in Example 1, distilled water was added to 1 mL, and the mixture was reacted at 60°C. As the reaction time changed, the absorption spectrum was collected. The results are as follows: Figure 7 The absorbance at 500nm is selected and the results are shown in Table 3. Figure 7 As can be seen from Table 3, AR is gradually degraded as the reaction time changes.

[0066] Table 3

[0067] Reaction time Absorbance 0h 2.03 0.5h 1.17 1h 0.63 1.5h 0.22 2h 0.12 2.5h 0.03

[0068] Example 8

[0069] 300 μL of 2 mM AR aqueous solution was mixed with 150 μL of sulfur nanodot solution obtained in Example 1, and distilled water was added to 1 mL. Fifteen portions were prepared and the pH was adjusted to 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 10.6, 11, 12, 13, and 14 with HCl and NaOH, respectively. The reaction was carried out at 60°C for 2 h, and then the absorption spectrum was collected. The results are shown in FIG. Figure 8 And as shown in Table 4. Figure 8 The vertical axis is the absorbance at 500nm in the absorption spectrum. Figure 8 As can be seen from Table 4, the best condition is when the pH is adjusted to 12 (although the absorbance is also 0 when the pH is 13, the smaller the pH value, the smaller the effect, so pH 12 is selected as the best condition).

[0070] Table 4

[0071] pH Absorbance 1 1.55 2 2.24 3 2.21 4 2.19 5 2.24 6 2.19 7 2.22 8 2.19 9 2.00 10 1.17 10.6 0.12 11 0.06 12 0 13 0 14 0.43

[0072] Example 9

[0073] 300 μL of 2 mM AR aqueous solution was mixed with 150 μL of sulfur nanodot solution obtained in Example 1, and distilled water was added to 1 mL. Fluorescence spectra were collected at 25°C as the reaction time changed. The results are as follows: Fig. 9 The fluorescence intensity at the emission peak position was selected and the normalized intensity was calculated. The results are shown in Table 5. Fig. 9 As can be seen from Table 5, as the reaction time increases, the fluorescence intensity gradually increases.

[0074] Table 5

[0075]

[0076]

[0077] Example 10

[0078] 300 μL of 2 mM AR aqueous solution was mixed with 150 μL of sulfur nanodot solution obtained in Example 1, and distilled water was added to 1 mL. Two portions were prepared and reacted at 25°C for 0 h and 3 h. Fluorescence spectra were collected respectively. The results are shown in FIG. Fig.10 shown. Fig.10 The fluorescence spectrum of the sulfur nanodot solution obtained in Example 1 at 25°C without adding AR aqueous solution is also shown in Table 6. The fluorescence intensity at the emission peak position is selected and the normalized intensity is calculated. The results are shown in Table 6. Fig.10 As can be seen from Table 6, the fluorescence intensity can be enhanced to 98% after 3 hours of reaction.

[0079] Table 6

[0080] Reaction time Normalized Intensity 0h 0.01 3h 0.98

[0081] Embodiment 11

[0082] Citric acid (CA), sodium citrate (SC), galactose (Gal), sucrose (Sucrose), potassium sorbate (PS), glucose (Glu), ascorbic acid (Vc), glycine (Gly), Na + , K + Mg 2+ 、SO4 2- 、SO3 2- , S 2- 、S2O3 2- 、S2O8 2- 、HPO4 2- 、HCO3 - Mix with 150 μL of the sulfur nanodot solution obtained in Example 1, add distilled water to 1 mL; add 2 mM citric acid (CA), sodium citrate (SC), galactose (Gal), sucrose (Sucrose), potassium sorbate (PS), glucose (Glu), ascorbic acid (Vc), glycine (Gly), Na + , K + Mg 2+ 、SO4 2- 、SO3 2- , S 2- 、S2O3 2- 、S2O8 2- 、HPO4 2- 、HCO3 -Mix with 300 μL of 2 mM AR aqueous solution and 150 μL of sulfur nanodot solution obtained in Example 1, add distilled water to 1 mL; react at 25°C, transfer them to fluorescence cuvettes, measure the fluorescence spectrum immediately, select the fluorescence intensity at the emission peak position, calculate the fluorescence ratio (F / F0), and the anti-interference ability results are as follows: Fig.11 As shown. Fig.11 It can be seen that the effects of these interferences on the fluorescence intensity of S dots and their recognition ability for AR are almost negligible.

[0083] Example 12

[0084] AR solution with a concentration of 2 mM, methyl orange (MO), brilliant green (BG), tartrazine (TRZ), basic fuchsin (BF) were mixed with 150 μL of the sulfur nanodot solution obtained in Example 1, and distilled water was added to 1 mL. The reaction was carried out at 25°C for 0 h and 3 h, and the mixture was transferred to a fluorescence cuvette, the fluorescence spectrum was measured, the fluorescence intensity at the emission peak position was selected, and the fluorescence ratio was calculated. The selectivity results are shown in FIG. Fig.12 As shown. Fig.12 As can be seen, methyl orange (MO), brilliant green (BG), tartrazine (TRZ), and basic fuchsin (BF) can also effectively quench the fluorescence of S-dots, however, these food pigments cannot produce recovered fluorescence signals, which enables people to identify AR in commonly used food pigments by recording the quenching of S dots and the subsequent recovery of fluorescence signals.

[0085] Example 13

[0086] Prepare a 2mM AR solution, dilute it to different concentrations, mix it with 150μL of the sulfur nanodot solution obtained in Example 1, add distilled water to 1mL, and react at 25°C. Then transfer it to a fluorescence cuvette, measure the fluorescence spectrum immediately, select the fluorescence intensity at the emission peak position, calculate the fluorescence change ratio (F0-F) / F0, and make a linear correlation curve between the fluorescence change ratio and the AR concentration. The results are as follows: Fig.13 shown.

[0087] from Fig.13 It can be seen that the fluorescence change ratio at the emission peak position of 433nm is linearly related to the AR aqueous solution within a certain concentration range: when the AR concentration is 0.01μM~3μM and 15μM~400μM, (F0-F) / F0=0.11lg[AR]+0.27, R 2 =0.978 and (F0-F) / F0=0.45lg[AR]-0.20, R 2 = 0.991. The limit of detection (LOD) was as low as 5 nM.

[0088] When the AR concentration is in the range of 3 to 15 μM, the AR concentration and the fluorescence change ratio at the emission peak position are not linearly related, and the above linear formula cannot be directly applied at this time. To solve this problem, a certain amount of AR standard solution can be added to the solution to be tested, so that the AR concentration in the mixed solution after adding the AR standard solution is in the range of 15 μM to 400 μM, and then the fluorescence change ratio of the mixed solution is measured, and then the AR concentration in the mixed solution is solved according to (F0-F) / F0=0.45lg[AR]-0.20, and then the spike recovery rate can be obtained. According to the spike recovery rate, the AR content in the solution to be tested can be obtained.

[0089] Embodiment 14

[0090] Food samples from local supermarkets, including carbonated drinks, chocolates, and different types of candies, were collected and processed by ultrasound, filtration, and the like. Then, 150 μL of AR standard solutions (specified and recovered) of different concentrations were mixed with 150 μL of diluted food samples and 150 μL of the sulfur nanodot solution obtained in Example 1, and distilled water was added to 1 mL. The mixture was reacted at 25°C and transferred to a fluorescence cuvette. The fluorescence spectrum was immediately measured, the fluorescence intensity at the emission peak position was selected, the fluorescence change ratio was calculated, and the concentration of AR in the food samples was quantitatively detected using the standard curve obtained in Example 13. The results are shown in Table 7 below.

[0091] Table 7

[0092]

[0093]

[0094] The present invention proposes a fluorescence detection method that can quantitatively detect AR and distinguish it from commonly used food pigments, using bifunctional sulfur nanodots (S-dots), in which the sulfur nanodots serve as a fluorescent agent and a decomposition agent for AR. The sulfur nanodots exhibit strong blue emission, which is effectively quenched by AR, which contributes to its extensive and strong absorption in the blue-green region. AR can be quantitatively detected by recording the quenched fluorescence signal of the S dots. Fluorescence quenching follows the SQE mechanism, has good detection tolerance to common interferences, and relatively poor selectivity and discrimination ability for other types of food pigments. The identification of AR in food pigments is achieved by observing the fluorescence recovery of the S dots triggered by the decomposition effect of the S dots on AR. The fluorescence method also shows good practical application potential by detecting AR in various food samples (soda drinks, coated chocolates, fruit-flavored toffees, and soft candies).

Claims

1. A method for detecting allura red in food using bifunctional sulfur nanodots, characterized in that: The steps include: (a) preparing aqueous solutions of Allura Red of different concentrations; (b) The bifunctional sulfur nanodot materials were mixed with different concentrations of allura red aqueous solutions, and the fluorescence spectra were measured at 25°C to calculate the fluorescence change ratio; (c) using the concentration of allura red as the abscissa and the fluorescence change ratio as the ordinate, a linear equation of the fluorescence change ratio and the allura red concentration was established; (d) mixing the food to be tested with an allura red standard solution to obtain a mixed solution to be tested, mixing the mixed solution to be tested with a bifunctional sulfur nanodot material, measuring the fluorescence spectrum at 25° C., and calculating the fluorescence change ratio; (e) calculating the content of allura red in the food according to the fluorescence change ratio obtained in step (d) in combination with the linear equation in step (c).

2. The method for detecting allura red in food using bifunctional sulfur nanodots according to claim 1, characterized in that: In steps (b) and (d), the fluorescence data at the peak of the fluorescence spectrum at 433 nm is selected to calculate the fluorescence change ratio, which refers to (F0-F) / F0, wherein F is the fluorescence data at 433 nm after the bifunctional sulfur nanodots react with allura red, and F0 refers to the fluorescence data of the bifunctional sulfur nanodots at 433 nm.

3. The method for detecting allura red in food using bifunctional sulfur nanodots according to claim 2, characterized in that: In step (c), the ratio of the fluorescence change at 433 nm is linearly related to the allura red aqueous solution within a certain concentration range: when the allura red concentration C AR When the concentration is 0.01μM~3μM and 15μM~400μM, (F0-F) / F0=0.11lgC AR +0.27 and (F0-F) / F0=0.45lgC AR The linear regression equation is -0.

20.

4. The method for detecting allura red in food using bifunctional sulfur nanodots according to claim 3, characterized in that: In step (d), the concentration of the added allura red standard solution is set so that the allura red concentration in the test mixture is in the range of 15 μM to 400 μM. In step (e), the linear regression equation (F0-F) / F0=0.451 g C is further used. AR -0.20 to calculate the concentration of allura red in the mixed solution to be tested, and then combined with the concentration of the added allura red standard solution, the content of allura red in the food to be tested is calculated.

5. The method for detecting allura red in food using bifunctional sulfur nanodots according to claim 1, characterized in that: In steps (b) and (d), the fluorescence spectra of the allura red aqueous solutions of different concentrations, the test mixture and the bifunctional sulfur nanodot material are immediately measured at 25°C after being mixed.

6. A method for identifying allura red in food using bifunctional sulfur nanodots, characterized in that: The steps include: (a) Mix the food to be tested with the bifunctional sulfur nanodot solution and add distilled water to a set volume; (b) Fluorescence spectra were immediately measured at 25 °C; (c) The fluorescence spectrum was measured again after reacting at 25 °C for 3 h; (d) If the fluorescence signal at the emission peak position of the bifunctional sulfur nanodots in the fluorescence spectrum in step (b) is quenched, and then the fluorescence signal is restored after reacting for 3 hours in step (c), it is determined that the food contains allura red.

7. The method according to claim 1 or 6, characterized in that: The bifunctional sulfur nanodots used were prepared by a mixed solution of sublimated sulfur, sodium hydroxide and PEG-400 through a one-step heat treatment and then a H2O2 passivation treatment.

8. The method for detecting allura red in food using bifunctional sulfur nanodots according to claim 7, characterized in that: The preparation method of the bifunctional sulfur nanodots comprises the following steps: (a) mixing sublimed sulfur, sodium hydroxide, PEG-400 and pure water; (b) The mixed solution in step (a) is heated to 90° C. and reacted for 72 hours, and then H 2 O 2 is added for passivation treatment to obtain a bifunctional sulfur nanodot material.

9. The method for detecting allura red in food using bifunctional sulfur nanodots according to claim 8, characterized in that: In step (b), H2O2 is added until blue fluorescence appears under ultraviolet light and then the addition is stopped.

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