A ratiometric fluorescent nanoprobe Si / CdTeNPs, a paper chip, and its applications

Abstract

The application provides a ratio fluorescent nano probe Si / CdTe NPs, a paper chip and application thereof, wherein the probe Si / CdTe NPs is obtained by mixing Si dots and CdTe quantum dots in a buffer solution with a pH value of 6-9, the final concentration of the Si dots is 20-100 μg / mL, and the final concentration of the CdTe quantum dots is 8-20 nM. 2‑ The fluorescence intensity of the probe at λem=488nm increases with the increase of the concentration of S 620 , while the fluorescence intensity at λem=620nm is quenched, the correlation between the fluorescence intensity ratio (F 488 ) and the concentration of S 2‑ is a negative linear relationship, and the detection limit is 0.3 μM. In order to realize portable detection, the Si / CdTe NPs are further placed into a carrier to prepare a visual paper chip, and the freshness of high-protein food can be monitored in a portable mode.

Description

Technical Field

[0001] This invention belongs to the field of food detection technology, specifically relating to a ratiometric fluorescent nanoprobe Si / CdTe NPs, a paper chip, and their applications. Background Technology

[0002] Food safety has always been a major public concern. With the continuous improvement of living standards, people's demand for fresh, protein-rich foods is also constantly increasing. However, high-protein foods are prone to spoilage during storage, mainly due to the presence of harmful microorganisms and endogenous enzymes, which can lead to contamination. During the spoilage process, a large amount of volatile gases are produced. Hydrogen sulfide (H2S), a common toxic gas with a rotten egg odor, plays a significant role in the spoilage of high-protein foods. Therefore, abnormal levels of hydrogen sulfide are generally considered a key indicator for assessing the quality of high-protein foods in the early stages of storage. Furthermore, excessive and prolonged exposure to hydrogen sulfide concentrations exceeding 10 ppm can have serious harmful effects on human health, leading to symptoms such as dizziness, nausea, and vomiting. In addition, hydrogen sulfide is closely associated with diabetes, Alzheimer's disease, and Down syndrome. Therefore, developing an efficient, reliable, and accurate method for monitoring hydrogen sulfide concentration is of great significance for ensuring food safety.

[0003] Due to its high volatility and rapid decomposition and metabolism, hydrogen sulfide detection methods face significant challenges. Currently, the main methods for hydrogen sulfide detection include gas chromatography, high-performance liquid chromatography, and electrochemical methods. While these methods can detect hydrogen sulfide quickly and accurately, they have limitations such as high cost, the need for skilled technicians, complex preparation procedures, and lengthy detection cycles. Furthermore, they lack portable detection capabilities. Therefore, there is an urgent need to develop portable sensors to identify low levels of hydrogen sulfide in rotten food. Currently, fluorescent nanoprobes are widely used in food safety analysis. They possess various advantages, such as rapid reaction, high specificity, harmless properties, and visibility, enabling the quantitative analysis of biomarkers. In an excellent study, Xiao et al. used H… +A ratiometric fluorescent nanoprobe with a "double-bond lock" was constructed in response to BODIPY dye and cationic cyanocyanine Cy7Cl dye. This probe accurately reflects the freshness of meat during storage by measuring changes in fluorescence signal and solution color. Ratiometric fluorescent nanoprobes can also be improved for portable detection. For example, Lu et al. developed a multicolor ratiometric fluorescent colorimetric paper sensor that effectively monitors mercury ions and sulfides by combining fluorescent probes composed of carbon quantum dots and CdZnTe quantum dots with a hydrogel. The freshness of food can be quickly detected using a smartphone by analyzing RGB (red, green, blue) values. Recently, Deng et al. developed a usable sensing platform by immobilizing ratiometric fluorescent nanoprobes bound to Rh6G and UiO-66-NH2 on a gelatin hydrogel matrix. This portable platform enables semi-quantitative detection of nitrite in meat products using fluorescence and visible light nanocolorimetry. These results demonstrate the remarkable potential of fluorescent nanoprobes in developing smart sensors for food safety assessment. In summary, researchers are primarily focused on developing portable detection methods that require simpler preparation processes and offer excellent selectivity, higher sensitivity, and greater stability. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention aims to provide a ratiometric fluorescent nanoprobe Si / CdTeNPs, a paper chip, and its applications.

[0005] The specific technical solution of this invention is as follows:

[0006] The present invention provides a ratiometric fluorescent nanoprobe Si / CdTe NPs, which is obtained by mixing Si dots and CdTe quantum dots in a buffer solution with a pH of 6-9, wherein the final concentration of the Si dots is 20-100 μg / mL and the final concentration of the CdTe quantum dots is 8-20 nM.

[0007] Furthermore, the final concentration of the Si dots is 50 μg / mL, and the final concentration of the CdTe quantum dots is 8-20 nM;

[0008] Preferably, the final concentration of the Si dots is 50 μg / mL, and the final concentration of the CdTe quantum dots is 20 nM.

[0009] Furthermore, the Si point is prepared by mixing aztreonam and N-[3-(trimethoxyphenyl)propyl]ethylenediamine in ultrapure water, and reacting the resulting mixed solution at 150-200℃ for 5-30 min, wherein the final concentration of aztreonam is 10-37.5 mM.

[0010] Preferably, the final concentration of aztreonam is 12.5-25 mM;

[0011] Preferably, the final concentration of aztreonam is 25 mM;

[0012] Preferably, the resulting mixed solution is reacted at 175-200℃ for 5-30 min;

[0013] Preferably, the resulting mixed solution is reacted at 175-200℃ for 25 min;

[0014] Preferably, the resulting mixed solution is reacted at 175°C for 25 min;

[0015] And / or, when preparing the CdTe quantum dots, cadmium chloride is used as the cadmium source and sodium tellurite is used as the tellurium source.

[0016] Another aspect of the present invention provides a paper chip based on ratiometric fluorescent nanoprobes Si / CdTe NPs, which is prepared from the ratiometric fluorescent nanoprobes Si / CdTe NPs and a carrier.

[0017] Furthermore, the carrier is sodium carboxymethyl cellulose.

[0018] Another aspect of the present invention provides a method for preparing the paper chip based on ratiometric fluorescent nanoprobes Si / CdTe NPs. The preparation method is as follows: the carrier is dissolved in boiling water and cooled to 35-45°C. Then, the Si / CdTe NPs are added, and after rapid stirring, the mixture is poured into a mold, cooled to room temperature, placed in a -80°C refrigerator for 2-6 hours, and then freeze-dried. After demolding, the chip is obtained.

[0019] Another aspect of the present invention provides the ratiometric fluorescent nanoprobe Si / CdTe NPs or the paper chip in S 2- Applications in the visual detection of freshness in high-protein foods.

[0020] Another aspect of the present invention provides an S 2- The detection method includes the following steps:

[0021] The ratiometric fluorescent nanoprobes Si / CdTe NPs or the paper chip were incubated with sodium sulfide solutions of different concentrations at room temperature for 2-3 minutes, and then the fluorescence intensity ratio (F) at 620 nm and 488 nm was measured. 620 / F 488 ), draw S 2- A standard curve relating concentration to fluorescence intensity ratio;

[0022] The ratiometric fluorescent nanoprobes Si / CdTe NPs or the paper chip were incubated with the sample at room temperature for 2-3 minutes. Then, the fluorescence intensity ratio at 620 nm and 488 nm was measured. Based on the standard curve, the S0 of the sample was calculated. 2- concentration.

[0023] Furthermore, the S 2- The detection limit is 0.3 μM.

[0024] Another aspect of the present invention provides a visual detection method for the freshness of high-protein foods, comprising the following steps:

[0025] (1) The ratiometric fluorescent nanoprobe Si / CdTe NPs or the paper chip based on the ratiometric fluorescent nanoprobe Si / CdTe NPs are placed in the same space with fresh high-protein food at 4°C or room temperature for storage time of m days, where m is a positive integer. Under ultraviolet light irradiation, the color change of the paper chip is observed, and the fluorescence photos of the paper chip at different storage times are recorded using a smartphone. The fluorescence photos are arranged in ascending order of storage days to form a visual fluorescence colorimetric card indicating the freshness of high-protein food; or, different fluorescence photos are converted into RGB values ​​using a smartphone color picker APP. The linearity of the ratio (B / R) of the blue (B) / red (R) channel depends on the hydrogen sulfide concentration. The B / R of high-protein food at different storage times is obtained, and a standard curve of B / R versus hydrogen sulfide concentration is constructed.

[0026] (2) The ratiometric fluorescent nanoprobe Si / CdTe NPs or the paper chip based on the ratiometric fluorescent nanoprobe Si / CdTe NPs are placed in the same space as the high-protein food to be tested and stored. Under ultraviolet light irradiation, a fluorescence image of the paper chip is obtained. The fluorescence image obtained in step (2) is compared with the visual fluorescence colorimetric card indicating the freshness of the high-protein food described in step (1). The freshness of the high-protein food can be visually detected. Alternatively, the color of the fluorescence image can be converted to RGB color using a smartphone color picker APP. The ratio of the blue (B) / red (R) channel (B / R) is substituted into the standard curve constructed in step (1) to calculate the S of the high-protein food to be tested. 2- concentration.

[0027] The beneficial effects of this invention are as follows:

[0028] 1. This invention provides a mixed-ratio fluorescent nanoprobe Si / CdTe NPs, which encapsulates Si / CdTe NPs through the electrostatic interaction between Si dots and CdTe quantum dots. Compared with single fluorescent nanoprobes, this probe has advanced properties. The fluorescence intensity of Si / CdTe NPs at λem = 488 nm increases with S... 2-The fluorescence intensity increases with increasing concentration, but is quenched at λem = 620 nm, and the fluorescence intensity ratio (F) is higher. 620 / F 488 ) and S 2- The correlation between concentrations is negatively linear; the fluorescence intensity of the probe Si / CdTe NPs is related to the concentration of S. 2- The concentration exhibits rapid response, high sensitivity, and excellent selectivity, with a detection limit of 0.3 μM. Furthermore, this invention uses N-[3-(trimethoxyphenyl)propylethylenediamine (DAMO) and aztreonam as Si sources to prepare environmentally friendly, low-photobleaching Si dots; and uses cadmium chloride and sodium tellurite as the respective sources of cadmium and tellurium to synthesize CdTe quantum dots (QDs) with high brightness, broad absorption spectrum, and large Stokes shift characteristics.

[0029] 2. This invention constructs a paper chip based on Si / CdTe NPs, prepared by embedding Si / CdTe NPs in a carrier. This paper chip possesses an ideal porous structure, good particle dispersibility, ideal chemical stability, and excellent fluorescence performance, enabling portable monitoring of the freshness of high-protein foods. When monitoring hydrogen sulfide generated during the spoilage process of real samples, the color change of this paper chip is positively correlated with the concentration of hydrogen sulfide captured. As the sample spoils, the fluorescence color of the paper chip under ultraviolet (UV) irradiation gradually changes from purplish-red to blue. Using the chip created in this invention to detect the freshness of high-protein foods has high accuracy. In summary, the Si / CdTe NP-based paper chip, due to its excellent portability, fast response time, and simple operation, shows great potential in visually and accurately monitoring the H2S content in high-protein foods, providing a reliable and portable method for assessing hydrogen sulfide concentration in high-protein foods, thus introducing a promising strategy for food freshness monitoring in the field of food safety monitoring. Attached Figure Description

[0030] Figure 1 Schematic diagram of Si / CdTe NPs ratio fluorescent paper chip (A) preparation and (B) application in monitoring the freshness of high-protein foods. Si dots were prepared using DAMO and aztreonam. Cd... 2+ CdTe quantum dots were synthesized using NAC, Na₂TeO₃, and NaBH₄. Si / CdTe NPs were encapsulated through the electrostatic interaction between Si and CdTe quantum dots. Subsequently, the Si / CdTe NPs were mixed with CMC-Na and poured into a mold to prepare a ratiometric paper chip based on Si / CdTe NPs. When the ratiometric paper chip came into contact with hydrogen sulfide generated from the deterioration of a real sample, the chip's fluorescence color changed from purplish-red to blue.

[0031] Figure 2Preparation and characterization of Si spots. (A) Optimization of Si spot preparation methods, including aztreonam concentration, reaction time, and reaction temperature. (B) TEM images, (C) FT-IR spectra, (D) XRD spectra, and (E) XPS analysis of Si spots. (F) Interference of various ions, amino acids, and biomolecules on the fluorescence intensity of Si spots. (G) Fluorescence intensity of Si spots stored at 4°C for different time intervals.

[0032] Figure 3 High-resolution XPS spectra of Si points. High-resolution O1s(A), N1s(B), C1s(C), and Si 2p(D) XPS spectra.

[0033] Figure 4 Transmission electron microscopy image of CdTe quantum dots.

[0034] Figure 5 Synthesis and characterization of Si / CdTe NPs. (A) Optimization of CdTe quantum dot concentration in Si / CdTe NPs preparation. (B) Fluorescence spectra of Si and CdTe quantum dots at different pH values. (C) Fluorescence spectra of Si / CdTe NPs at different pH values. (D) Analysis of fluorescence intensity and intensity ratio of CdTe quantum dots and Si dots in Si / CdTe NPs at different pH values. (E) Transmission electron microscopy images of Si / CdTe NPs. (F) Size distribution of Si, CdTe quantum dots, and Si / CdTe NPs.

[0035] Figure 6 .Si / CdTe NPs for S 2- The fluorescence response. (A) Fluorescence spectra of Si / CdTe NPs in Tris buffer containing different concentrations of sodium sulfide. The fluorescence response of Si / CdTe NPs was analyzed. 2- (B) Calibration curve for detection. (C) Presence of sodium sulfide (S) 2- Fluorescence lifetime decay curves of CdTe quantum dots at a concentration of 20 μM or in their absence. (D)S 2- Studies on the selectivity of detection. 2- The concentration was 20 μM, and the concentration of interfering molecules was 200 μM. (E)Si / CdTe NPs and (F)CdTe QDs were used to target S... 2- Visual detection was performed. Si / CdTe NPs or CdTe QDs were incubated with 0–60 μM light and fluorescence was detected under 365 nm UV light, captured by a smartphone camera. “ns” indicates no significant difference, *** indicates P-value < 0.001, and **** indicates P-value < 0.0001.

[0036] Figure 7 .CdTe quantum dot pairs S 2-The fluorescence response of CdTe quantum dots. (A) Fluorescence spectra of CdTe quantum dots in Tris buffer containing different concentrations of sodium sulfide. (B) Detection of S by CdTe quantum dots. 2- The calibration curve.

[0037] Figure 8 With or without S 2- The UV-Vis absorption spectra of Si / CdTe NPs.

[0038] Figure 9 Detection of hydrogen sulfide using a Si / CdTe NPs-based paper chip. Color of the Si / CdTe NPs-based paper chip under sunlight (A) and ultraviolet light (B). Color of the CMC-Na chip under sunlight (C) and ultraviolet light (D). (E) Detection of hydrogen sulfide using a Si / CdTe NPs-based paper chip. All photos were taken with a smartphone camera.

[0039] Figure 10 The freshness of protein-rich foods was detected using Si / CdTe NPs paper chips. Shrimp (A) and beef (B) samples were incubated with Si / CdTe NPs or CdTe QDs-based paper chips at 4°C and room temperature, respectively. The color changes of the paper chips were then detected under 365nm ultraviolet light. All photos were taken with a smartphone camera.

[0040] Figure 11 Semi-quantitative analysis of the freshness of high-protein foods based on the blue / red (B / R) ratio of paper chips. (A, B) B / R ratios of paper chips and shrimp after incubation at 4℃ and room temperature for 27 h, respectively. (C, D) B / R ratios of paper chips and beef after incubation at 4℃ and room temperature for 36 h, respectively. "ns" indicates no significant difference, * indicates P < 0.05, ** indicates P < 0.01, *** indicates P < 0.001, **** indicates P < 0.0001.

[0041] Figure 12 The freshness of high-protein foods was determined using a commercial hydrogen sulfide gas detector. The freshness of (A) shrimp (4°C, room temperature, 27 h) and (B) beef (4°C, room temperature, 36 h) was determined using the hydrogen sulfide gas detector. Detailed Implementation

[0042] To better understand the present invention, it is now further described with reference to the following embodiments and accompanying drawings. The embodiments are for illustrative purposes only and do not limit the invention in any way. In the embodiments, all original reagents and materials are commercially available, and experimental methods not specifically specified are conventional methods and conditions well known in the art, or according to the conditions recommended by the instrument manufacturer.

[0043] 1. Chemicals and materials

[0044] N-(β-aminoethyl)-γ-aminopropylmethyldimethoxysilane (DAMO), L-glutathione, N-acetyl-l-cysteine ​​(NAC), glucose, urea, proline, threonine, serine, tyrosine, and tris(hydroxymethyl)aminomethane hydrochloride (Tris-HCl) were purchased from Sigma. Sodium chloride was purchased from Solanum Biotech Co., Ltd. Sodium dihydrogen phosphate was purchased from Sangon Biotech (Shanghai) Co., Ltd. Sodium carbonate was purchased from Sinopharm Chemical Reagent Co., Ltd. Copper sulfate and calcium nitrate were purchased from Shanghai Lingfeng Chemical Reagent Co., Ltd. Ammonium chloride was supplied by Xilong Chemical Co., Ltd. Glutamic acid and sodium sulfide were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Potassium chloride was purchased from Shanghai Maclean Biochemical Technology Co., Ltd.

[0045] 2. Instruments for characterizing Si dots, CdTe quantum dots, and Si / CdTeNPs

[0046] Microwave system (bio-stimulator) + Si dots and CdTe quantum dots were synthesized. The size and morphology of Si dots, CdTe quantum dots, and Si / CdTe NPs were characterized using a JEOL-F200 microscope (JEOL, Beijing, China). UV-Vis absorption spectra were measured using a U-3900H spectrophotometer. Fluorescence spectra were collected using a F-7100 fluorescence spectrophotometer (Hitachi, Tokyo, Japan). FTIR spectra of the samples were obtained using a Nicolet iS20 Fourier transform infrared (FTIR) spectrometer (Thermo Fisher Scientific, Watson, Massachusetts, USA). X-ray diffraction (XRD) spectra were measured using a UltimaVI XRD system (Rigaku, Tokyo, Japan). X-ray photoelectron spectra (XPS) of the samples were recorded using a K-Alpha spectrometer (Thermo Fisher Scientific, Watson, Massachusetts, USA).

[0047] Example 1

[0048] 1. Preparation and characterization of Si points

[0049] The Si points were prepared using microwave-assisted synthesis, based on previous research with minimal modifications. In short, aztreonam was first mixed with N-[3-(trimethoxyphenyl)propyl]ethylenediamine (DAMO) in ultrapure water. The mixture was then transferred to a glass vial in a microwave synthesizer, pre-stirred for 2 min, and reacted at a specific temperature for a specified time. Subsequently, the reaction product was completely mixed with acetonitrile at a volume ratio of 1:4, and then centrifuged at 8000 rpm for 15 min. The centrifuged particles were washed twice with acetonitrile and dried at 70 °C for 30 h to obtain the Si points. The product was stored at 4 °C for subsequent experiments.

[0050] The properties of Si points play a crucial role in fluorescence calibration and significantly influence detection sensitivity. This embodiment optimizes the preparation conditions of Si points, including the final concentration of aztreonam, reaction temperature, and reaction time. Gradient optimization revealed that when DAMO reacts with 25 mM aztreonam at 175 °C for 25 min, the synthesized Si points exhibit the strongest fluorescence emission peak at 488 nm under 370 nm excitation. Figure 2 A). In this embodiment, the morphological characterization of the Si points was also performed using transmission electron microscopy (TEM), such as... Figure 2 As shown in Figure B, the synthesized Si points are almost spherical, uniformly dispersed, and have an average diameter of 2.99 nm.

[0051] FTIR measurements were used to characterize the surface groups at Si sites. For example... Figure 2 As shown in C, at 3433.8cm- 1 Strong OH and NH vibrational and stretching peaks appeared at 2932.6 cm⁻¹. -1 The peak appearing at 1621.2 cm⁻¹ may be related to the stretching vibrations of methylene and methyl groups. Furthermore, the peak at 1621.2 cm⁻¹... -1 and 1392.0cm -1 The strong intensity peak at 1046.5 cm⁻¹ may be related to the C=O stretching of the carboxyl group, while the peak at 1046.5 cm⁻¹ is more pronounced. -1 The bands at this location mainly originate from CO and Si-O. Furthermore, at 919.6 cm⁻¹... -1 A peak caused by CH stretching was also observed at the Si point. These observations indicate the presence of numerous hydrophilic oxygen-adding functional groups on the prepared Si point surface, which greatly contributes to the good water dispersibility of the Si points. Furthermore, the presence of distinct characteristic diffraction peaks clearly demonstrates the good crystallinity of the Si points. Figure 2 D).

[0052] The elemental composition and valence state distribution were investigated using XPS. The full-range XPS spectrum of Si showed five main peaks at binding energies of 531.25, 398.75, 283.75, 168.75, and 101.25 eV, corresponding to O1s, N1s, C1s, S2p, and Si2p, respectively. Figure 2 E). The high-resolution XPS spectrum of the O 1s spectrum showed peaks at 530.8, 531.9, and 533.4 eV, which were attributed to C=O, Si-O, and CO, respectively. Figure 3 A). At 399.2 eV, the peak in the N 1s spectrum can be attributed to CN ( Figure 3 B). C 1s shows peaks at 284.8, 286.4, and 288.6 eV, corresponding to the CC / CH, CN / CO, and C=O values ​​at the Si point, respectively. Figure 3C). Furthermore, the Si 2p peak at 102.1 eV corresponds to the Si-O (C) peak at the Si point. Figure 3 D). These results indicate that there are abundant functional groups at the Si point.

[0053] The stability of Si points in solution is a key factor in the preparation of ratiometric fluorescent nanoprobes. Therefore, this study investigated the stability of Si points by introducing interfering substances such as metal ions, amino acids, and biomacromolecules. For chemical stability analysis, Si points were first incubated with metal ions and amino acids (100 μM), respectively, and then the fluorescence intensity was measured. In storage stability testing, Si points were stored at room temperature for a specific period, and then the fluorescence intensity was measured. The results showed that the addition of interfering substances had no significant effect on fluorescence, indicating that the Si points possess good chemical stability. Figure 2 F). After being stored at room temperature for 30 days, the Si sites retained approximately 98% of their initial fluorescence intensity (F). Figure 2 These results demonstrate that the Si point exhibits good chemical and storage stability, and holds great potential for the analysis of complex samples.

[0054] 2. Preparation and characterization of CdTe quantum dots

[0055] First, solution A was prepared by dissolving 73 mg of cadmium chloride and 147 mg of N-acetyl-L-cysteine ​​(NAC) in 38 mL of ultrapure water, and the pH was adjusted to 9.0. Solution B was prepared by dissolving 5 mg of sodium borohydride and 11 mg of sodium tellurite in 1 mL of ultrapure water. Then, solutions A and B were mixed and transferred to a glass bottle in a microwave synthesizer. After pre-stirring for 2 min, the mixture was reacted at 175 °C for 1 min. The generated CdTe quantum dots were purified by centrifugation (10000 rpm, 3 min) using an ultrafiltration tube and washed three times with ultrapure water. The product was then stored at 4 °C for subsequent experiments.

[0056] Transmission electron microscopy images of CdTe quantum dots are shown below. Figure 4 As shown.

[0057] 3. Preparation and characterization of ratiometric fluorescent nanoprobes Si / CdTe NPs

[0058] Si / CdTe NPs are encapsulated by self-assembly of Si dots and CdTe quantum dots, specifically by mixing Si dots and CdTe quantum dots in Tris-HCl buffer.

[0059] This embodiment optimized the CdTe quantum dot concentration in the preparation of Si / CdTe NPs. During the encapsulation process, Si dots were mixed with different concentrations of CdTe quantum dots in Tris-HCl buffer (pH 7.4). The final concentration of Si dots was 50 μg / mL, and the final concentrations of CdTe quantum dots were 4, 8, and 20 nM. The fluorescence characteristics of the assembled Si / CdTe NPs were compared. It was found that when the final concentration of Si dots was 50 μg / mL and the final concentration of CdTe quantum dots was 20 nM, both Si dots and CdTe quantum dots exhibited strong fluorescence intensity in the Si / CdTe NPs. Figure 5 A). Subsequently, Si / CdTe NPs prepared from Si dots with a final concentration of 50 μg / mL, CdTe quantum dots with a final concentration of 20 nM, and Si / CdTe quantum dots with a final concentration of 50 μg / mL and 20 nM respectively were incubated in solutions with a pH of 6–9 for 2 min, and then the fluorescence intensity was measured to study the pH stability within the pH range of 6–9. Figure 5 As shown in Figure B, the fluorescence intensity of individual CdTe quantum dots increased significantly as the pH value changed from 6 to 9. In contrast, CdTe quantum dots in Si / CdTe NPs exhibited good pH stability. Figure 5 C), fluorescence intensity ratio (F) 620 / F 488 The change from pH 6 to 9 is very small. Figure 5 D), this may be due to the passivation and protection of the Si point.

[0060] Transmission electron microscopy was used to analyze the surface morphology and size of CdTe quantum dots and Si / CdTe NPs nanoprobes. Images show that CdTe quantum dots (… Figure 4 ) and Si / CdTe NPs ( Figure 5 The E) are all nearly spherical and uniformly distributed, with dimensions of approximately 3.44 nm and 21.78 nm, respectively. Compared to Si dots and CdTe quantum dots, Si / CdTe NPs are significantly larger ( Figure 5 F), which may be due to the interaction and aggregation of two different groups of particles. In summary, the synthesized Si / CdTe NPs exhibit good pH stability and morphological uniformity after self-assembly, and can be used for subsequent experiments.

[0061] Example 2

[0062] S based on ratiometric fluorescent nanoprobes Si / CdTe NPs 2- Detection:

[0063] 3 μL of Si (50 mg / mL) and 3 μL of CdTe QDs (20 μM) were mixed in Tris-HCl buffer (pH 7.4), and the volume was adjusted to 3 mL to prepare Si / CdTe NPs. The mixture was then divided into 10 separate test tubes, each containing a different concentration of sodium sulfide (Na₂S) solution. After incubation at room temperature for 2 min, the ratio of fluorescence intensity at 620 nm to 488 nm was measured. For selectivity analysis, the Si / CdTe NPs were further mixed with Cl₂S solution. - ,PO4 3- NO3 - SO4 2- CO3 2- L-glutathione (L-GSH) and N-acetylcysteine ​​(NAC) were incubated at room temperature for 2 min, and finally, the ratio of fluorescence intensity at 620 nm to 488 nm was measured.

[0064] Si / CdTe NPs for S 2- fluorescence response, such as Figure 6 As shown in A, with S 2- As the concentration increased from 0 to 30 μM, the fluorescence intensity at λem = 488 nm gradually increased, while the fluorescence intensity at λem = 620 nm decreased. The fluorescence intensity ratio (F...) 620 / F 488 ) and S 2- The concentration showed a negative linear correlation, and the detection limit was 0.3 μM. Figure 6 B). Further comparisons were made of CdTe quantum dots with different concentrations of S. 2- Fluorescence changes during incubation showed that the fluorescence intensity of CdTe quantum dots ranged from 2.5 to 15.0 μM. 2- Concentration showed a negative linear correlation ( Figure 7 These results indicate that the encapsulation of Si dots is beneficial for CdTe quantum dots paired with S. 2- The response had no significant impact.

[0065] In addition, the pairing of CdTe quantum dots with S was also studied. 2- The fluorescence response mechanism. For example... Figure 6 As shown in C, S 2- The addition of [a substance] led to a significant decrease in fluorescence lifetime. Furthermore, the addition of S [a substance] resulted in a significant decrease in fluorescence lifetime. 2- Afterwards, the UV-Vis absorption spectra of Si / CdTe NPs did not change significantly. Figure 8 These results indicate that S 2-This may have caused the dynamic quenching of CdTe quantum dots. Selectivity is considered an important indicator for evaluating the feasibility of a detection system. To assess this parameter, various substances (various ions, glutathione, and N-acetylcysteine) were tested. The results showed that Si / CdTe NPs did not show a significant response to other substances. Figure 6 D) indicates its influence on S 2- The detection has good selectivity.

[0066] To further verify the feasibility of Si / CdTe NPs in detecting S in real samples, they were applied to tap water. 2- The determination of the added parameters was performed. The results demonstrate the reliability of Si / CdTe NPs for practical applications, proven by recoveries ranging from 90.8% to 102.1% (Table S1). The results also indicate that the ratiometric fluorescent nanoprobes in S... 2- It exhibits high sensitivity, significant selectivity, and excellent versatility in detection.

[0067] Table S1. Method for recovering S from tap water 2-

[0068]

[0069] To achieve visual inspection, Si / CdTe NPs and CdTe quantum dots were respectively subjected to different concentrations of S. 2- Incubate, then detect fluorescence under 365nm UV light. Visual analysis shows that with S... 2- As the concentration increases, the color of the solution changes from purplish-red to blue. Figure 6 E and 6F). The blue / red (B / R) light ratio of Si / CdTe NPs changed more significantly than that of CdTe QDs, indicating that Si / CdTe NPs have better performance in visual detection of S. 2- It has better sensitivity.

[0070] Example 3

[0071] 1. Preparation of paper chips

[0072] To expand the practical applications of Si / CdTe NPs, this embodiment develops a portable Si / CdTe NPs-based paper chip for convenient on-site screening of hydrogen sulfide. CMC-Na is a water-soluble sodium salt of carboxymethyl cellulose, forming a transparent colloidal solution in water. It exhibits good biocompatibility, biodegradability, and non-toxicity. Therefore, this embodiment selects CMC-Na as a potential carrier for preparing Si / CdTe NPs-based paper chips. The encapsulated Si / CdTe NPs were prepared according to the method described in Example 2. The paper chip was synthesized according to the previously reported method with some modifications. Briefly, 125 mg of CMC-Na was dissolved in 10 mL of boiling water with constant stirring to ensure complete dissolution. The solution was then cooled to approximately 40°C, and the encapsulated Si / CdTe NPs were added. After rapid stirring, the composite hydrogel solution was poured into a mold, cooled to room temperature, and placed in a -80°C freezer for 3 hours. Subsequently, they were freeze-dried for 30 hours to form the paper chip. After demolding, a paper chip based on Si / CdTe NPs was obtained.

[0073] The prepared Si / CdTe NPs-based paper chip appears as a milky white solid foam shape under sunlight. Figure 9 A), reflects a purplish-red color under ultraviolet light ( Figure 9 B). Furthermore, the relatively sparse and porous surface of the paper chip creates a favorable environment for gas adsorption and successful binding with the fluorescent probe. For comparison, this embodiment fabricated a CMC-Na chip (containing no Si / CdTe NPs), controlling the chip to be transparent under sunlight (…). Figure 9 C), under ultraviolet light, it can only reflect blue ( Figure 9 D). Schematic diagram of the fabrication of paper chips based on Si / CdTe NPs and their application in monitoring the freshness of high-protein foods, as shown in the figure. Figure 1 As shown.

[0074] 2. Detection of hydrogen sulfide using paper chips

[0075] To detect hydrogen sulfide using a paper-based microarray, Si / CdTe NPs-based microarrays were first placed in petri dishes containing sodium sulfide solutions of varying concentrations (100 μL). After incubation at room temperature for 30 min, the Si / CdTe NPs-based microarrays absorbed the hydrogen sulfide gas released from the sodium sulfide solution, causing the microarray's color to change from purplish-red to blue. The concentration of hydrogen sulfide was then preliminarily determined based on this color change, thus achieving semi-quantitative detection of hydrogen sulfide gas.

[0076] The results showed that as the sodium sulfide concentration increased, the fluorescence of the chip changed from purplish-red to blue. Figure 9E), which indicates that the chip has significant potential for visual detection of hydrogen sulfide.

[0077] 3. Analysis of real samples

[0078] To evaluate the potential applications of Si / CdTe NPs-based paper chips, this embodiment selected shrimp and beef to assess the potential feasibility of using Si / CdTe NPs-based paper chips in real-world sample detection. The shrimp and beef samples were obtained from Shenzhen Elephant Fresh Technology Co., Ltd. During the analysis, the samples and Si / CdTe NPs-based paper chips were placed in sealed petri dishes and stored at 4°C and room temperature for a period of time. Then, the color change of the paper chips was detected under 365nm ultraviolet light. In addition, a monochromatic paper chip containing only CdTe quantum dot probes was used as a control. Simultaneously, a hydrogen sulfide gas detector (Shenzhen Zhongyou Shengshi Technology Co., Ltd., Shenzhen, China) was used to detect the samples to verify the accuracy of the established method.

[0079] like Figure 10 As shown, the fluorescence of the chip changes from purplish-red to blue with increasing storage time. Furthermore, compared to CdTe quantum dots, the paper chip based on Si / CdTe NPs can detect the presence of hydrogen sulfide earlier. Further analysis of the blue / red (B / R) light ratio of the paper chip confirms that Si / CdTe NPs have better sensitivity. Figure 11 The paper-based chip using Si / CdTe NPs was also compared with an H2S detector. A significant correlation was observed between fluorescence changes and hydrogen sulfide concentration values, indicating that the method of this invention has high accuracy. Figure 12 In summary, paper-based chips based on Si / CdTe NPs can sensitively and effectively detect the freshness of high-protein foods, and have great potential for practical applications.

[0080] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art can make other variations or modifications based on the above description.

Claims

1. A ratiometric fluorescent nanoprobe Si / CdTe NPs in S 2- Its application in the detection or visual detection of freshness in high-protein foods is characterized by, The ratiometric fluorescent nanoprobes Si / CdTe NPs were obtained by mixing Si dots and CdTe quantum dots in a buffer solution with a pH of 6-9. The final concentration of the Si dots was 20-100 μg / mL, and the final concentration of the CdTe quantum dots was 8-20 nM. The Si point is prepared by mixing aztreonam and DAMO in ultrapure water, and reacting the resulting mixed solution at 150-200ºC for 5-30 min. The final concentration of aztreonam is 10-37.5 mM. And / or, when preparing the CdTe quantum dots, cadmium chloride is used as the cadmium source and sodium tellurite is used as the tellurium source.

2. The application according to claim 1, characterized in that, The final concentration of the Si dots is 50 μg / mL, and the final concentration of the CdTe quantum dots is 20 nM; The final concentration of aztreonam was 12.5-25 mM; the resulting mixed solution was reacted at 175-200ºC for 5-30 min.

3. The application according to claim 2, characterized in that, The final concentration of aztreonam was 25 mM; the resulting mixed solution was reacted at 175-200ºC for 25 min.

4. A paper chip based on ratiometric fluorescent nanoprobes Si / CdTe NPs in S 2- Its application in the detection or visual detection of freshness in high-protein foods is characterized by, The paper chip is prepared from the ratiometric fluorescent nanoprobe Si / CdTe NPs and the carrier as described in any one of claims 1-3; The carrier is sodium carboxymethyl cellulose.

5. An application as described in claim 4, characterized in that, The paper chip based on ratiometric fluorescent nanoprobes Si / CdTe NPs is prepared as follows: the carrier is dissolved in boiling water and cooled to 35-45ºC. Then, the Si / CdTe NPs according to any one of claims 1-3 are added, and after rapid stirring, the mixture is poured into a mold, cooled to room temperature, placed in a -80°C refrigerator for 2-6 hours, and then freeze-dried. After demolding, the paper chip is obtained.

6. A kind of S 2- The detection method is characterized by, The detection method includes the following steps: The ratiometric fluorescent nanoprobe Si / CdTe NPs described in claim 1 or the Si / CdTe NPs-based paper chip described in claim 4 were incubated with sodium sulfide solutions of different concentrations at room temperature for 2-3 min. Then, the fluorescence intensity ratio at 620 nm and 488 nm was measured, and S was plotted. 2- A standard curve relating concentration to fluorescence intensity ratio; The ratiometric fluorescent nanoprobe Si / CdTe NPs described in claim 1 or the Si / CdTe NPs-based paper chip described in claim 4 were incubated with the sample to be tested at room temperature for 2-3 min. Then, the fluorescence intensity ratio at 620 nm and 488 nm was measured. Based on the standard curve, the S0 of the sample to be tested was calculated. 2- concentration.

7. The detection method according to claim 6, characterized in that, The S 2- The detection limit is 0.3 μM.

8. A visual detection method for the freshness of high-protein foods, characterized in that, Includes the following steps: (1) The paper chip based on the ratiometric fluorescent nanoprobe Si / CdTe NPs described in claim 1 or the ratiometric fluorescent nanoprobe Si / CdTe NPs described in claim 4 is placed in the same space with fresh high-protein food at 4°C or room temperature for a storage time of m days, where m is a positive integer. Under ultraviolet light irradiation, the color change of the paper chip is observed, and the fluorescence photos of the paper chip at different storage times are recorded using a smartphone. The fluorescence photos are arranged in ascending order of storage days to form a visual fluorescence colorimetric card indicating the freshness of high-protein food. Alternatively, different fluorescence photos are converted into RGB values ​​using a smartphone color picker APP. The linearity of the ratio B / R of the blue B / red R channels depends on the hydrogen sulfide concentration. The B / R of high-protein food at different storage times is obtained, and a standard curve of B / R versus hydrogen sulfide concentration is constructed. (2) Place the ratiometric fluorescent nanoprobe Si / CdTe NPs described in claim 1 or the paper chip based on ratiometric fluorescent nanoprobe Si / CdTe NPs described in claim 4 in the same space as the high-protein food to be tested and store it. Under ultraviolet light irradiation, obtain a fluorescence photograph of the paper chip. Compare the visual fluorescence colorimetric card indicating the freshness of the high-protein food described in step (1) with the fluorescence photograph obtained in step (2) to achieve visual detection of the freshness of the high-protein food; or, convert the color of the fluorescence photograph to RGB color through a smartphone color picker APP, substitute the ratio B / R of the blue B / red R channels into the standard curve constructed in step (1), and calculate the S of the high-protein food to be tested. 2- concentration.

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