A dual-emission carbon dot hydrogel film and a preparation method and application thereof

Abstract

The application discloses a kind of double-emission carbon dot hydrogel film and its preparation method and application, it is related to analysis detection and functional material technical field.The double-emission carbon dot hydrogel film with polyvinyl alcohol hydrogel as carrier, wherein uniformly dispersed with the double-emission carbon dot (O-CDs) synthesized with L-glutamic acid and o-phenylenediamine as precursor.O-CDs has dual emission peak of 400 nm and 530 nm under 375 nm excitation.Double-emission carbon dot hydrogel film is applied in Cu 2+ And Ag + Portable visual detection, which is a dual-mode measurement based on RGB, including fluorescence colorimetric assay in solution and smartphone-assisted visual detection film.The dual-mode strategy does not require sophisticated instruments, and can achieve rapid, reliable and simultaneous detection of Cu 2+ And Ag + Within 10 min, breaking through the limitations of traditional single-mode detection, and providing a robust platform for on-site metal ion monitoring.

Description

Technical Field

[0001] This invention relates to the fields of analytical testing and functional materials technology, specifically to a dual-emission carbon dot hydrogel film, its preparation method, and its application. Background Technology

[0002] Currently, the study focuses on heavy metal ions Cu in water or food. 2+ and Ag + The detection mainly relies on the following types of technologies:

[0003] Large-scale precision instrument methods, such as atomic absorption spectrometry (AAS), inductively coupled plasma mass spectrometry (ICP-MS), and inductively coupled plasma optical emission spectrometry (ICP-OES), are standard laboratory methods with low detection limits and high accuracy. However, these methods rely on large instruments, making rapid on-site testing difficult. Instruments like AAS and ICP-MS are bulky, expensive, and require specialized operators and laboratory conditions, making them unsuitable for grassroots units, field operations, or emergency scenarios.

[0004] Traditional colorimetric and photometric methods: utilizing colorimetric reagents and Cu 2+ and Ag + A color reaction occurs, and the absorbance is measured quantitatively using a spectrophotometer. However, this type of method is mostly for the detection of single metal ions and cannot simultaneously distinguish Cu. 2+ and Ag + Most existing fluorescent or colorimetric probes are designed for a specific metal ion, or different metal ions produce similar signals, leading to difficulties in detecting Cu. 2+ and Ag + It cannot simultaneously quantify and differentiate, and its adaptability to complex samples is poor.

[0005] Fluorescent probe detection: This method utilizes fluorescent materials such as small organic molecule probes, metal complexes, quantum dots, and carbon dots to enhance / quench the fluorescence of target ions or induce spectral shifts, thus achieving fluorescence detection. However, this type of method suffers from poor single-channel signal anti-interference capability and insufficient quantitative accuracy. Many fluorescent probes rely solely on single-wavelength emission intensity changes, making them susceptible to influences such as light source intensity, probe concentration, and imaging conditions, resulting in insufficient reproducibility and quantitative accuracy, making truly reliable on-site monitoring difficult. Liquid-phase probes are not convenient for portability and long-term storage. Traditional liquid-phase detection methods using "probe solution + cuvette" suffer from leakage, volatilization, and microbial contamination issues, making them inconvenient for transportation and long-term storage, and also unsuitable for one-time, standardized on-site testing.

[0006] Smartphone-assisted detection technology combines fluorescent probes or test strips with a smartphone camera to achieve on-site quantitative or semi-quantitative detection using RGB values, but it mostly focuses on single ions or single emission channels. Furthermore, smartphone detection methods are still imperfect; some existing smartphone-assisted methods remain at the subjective judgment stage of "taking a picture and looking at the color," lacking stable solid / hydrogel carriers and a systematic RGB quantitative analysis process, resulting in large measurement deviations and insufficient repeatability.

[0007] Therefore, it is necessary to develop a method that can simultaneously, rapidly, and visually detect Cu. 2+ and Ag + Portable detection materials and methods that are easy to carry, have good stability, and strong anti-interference capabilities have important practical application value. Summary of the Invention

[0008] To address the aforementioned problems, this invention provides a dual-emission carbon dot hydrogel film, its preparation method, and its applications. By integrating dual-emission carbon dots, a hydrogel film, smartphone RGB analysis, and a portable light source, it achieves Cu... 2+ and Ag + Rapid, simultaneous, and visualized on-site inspection.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] One object of the present invention is to provide a method for preparing a dual-emission carbon dot hydrogel film, comprising the following steps:

[0011] S1: Preparation of dual-emission carbon dots: L-glutamic acid and o-phenylenediamine were dissolved in anhydrous ethanol and ultrasonically treated to form a homogeneous solution. The homogeneous solution was then transferred to a polytetrafluoroethylene-lined autoclave for reaction. After the reaction was completed, the solution was naturally cooled to room temperature, centrifuged, and filtered to obtain an orange-red dual-emission carbon dot solution (O-CDs solution).

[0012] S2: Preparation of polyvinyl alcohol solution: Polyvinyl alcohol (PVA) is dissolved in ultrapure water and heated and stirred until completely dissolved to obtain a PVA solution;

[0013] S3: Forming of hydrogel film: After removing air bubbles from PVA solution, add O-CDs solution to obtain a mixture; after the mixture is fully mixed and degassed by magnetic stirring, inject it into a 12-well culture plate and perform three rounds of continuous freeze-thaw cycles to obtain the dual-emission carbon dot hydrogel film (PVA@O-CDs hydrogel film).

[0014] Further, in step S1, the molar ratio of L-glutamic acid to o-phenylenediamine is 1:2; the reaction temperature is 210℃, the reaction time is 10 h; the centrifugation speed is 8000 r / min, and the reaction time is 20 min.

[0015] Furthermore, in step S2, the solid-liquid ratio of polyvinyl alcohol to ultrapure water is 1:10 (g:mL); the heating temperature is 95℃; and the stirring time is 4 h.

[0016] Further, in step S3, the removal of bubbles from the polyvinyl alcohol solution specifically involves: maintaining the polyvinyl alcohol solution at 37°C for 20 min; the volume ratio of the PVA solution to the O-CDs solution after bubble removal is 7:3; the freeze-thaw cycle is: maintaining at -20°C for 20 h, then switching to 25°C and maintaining for 4 h.

[0017] Another object of the present invention is to provide a PVA@O-CDs hydrogel film prepared by the above preparation method, wherein the film uses PVA hydrogel as a carrier, and dual-emission carbon dots are uniformly dispersed in the PVA hydrogel; the dual-emission carbon dots have two fluorescence emission peaks at 400 nm and 530 nm when excited at a wavelength of 375 nm. 2+ It can quench 400 nm emission while enhancing 530 nm emission, while Ag + This will quench both types of emission, thereby achieving F in ratio fluorescence detection. 530 / F 400 Self-calibration of the (F2 / F1) response.

[0018] Another object of the present invention is to provide an O-CDs solution and / or PVA@O-CDs hydrogel film prepared by the aforementioned preparation method in Cu 2+ and Ag + Applications in portable visual inspection.

[0019] Furthermore, the portable visual detection is an RGB-based dual-mode measurement, including fluorescence colorimetric determination in solution and smartphone-assisted visual detection of thin films.

[0020] Furthermore, the smartphone-assisted visualization detection film includes a darkroom, a 365 nm UV lamp, and a smartphone. During detection, a cuvette containing the sample to be tested and the PVA@O-CDs hydrogel film is placed in the darkroom, the UV lamp is turned on, and images are captured in real time via the smartphone. The RGB values ​​are extracted using an application, and the target ion Cu is quantified based on the RGB values ​​and a preset calibration curve. 2+ and Ag + The concentration.

[0021] Furthermore, the fluorescence colorimetric assay in the solution integrates a portable device with Wi-Fi communication. The core components include a dual sample chamber, an LED excitation light source, a color sensor, an electronic module, and a cuvette. A smartphone serves as a remote terminal for data display and interaction. The electronic module is based on a microcontroller and includes a resistor and an LCD module. Before detection, the O-CDs solution and BR buffer are incubated at room temperature for 2 minutes to obtain the O-CDs sensor solution. During detection, the cuvette containing the O-CDs sensor solution and the test solution is placed in the dual sample chamber. The LED light source excites the sample to generate a fluorescence response, which is captured by the color sensor and converted into RGB values. These RGB values ​​are then transmitted to the smartphone for quantitative analysis of Cu based on a preset calibration curve. 2+ and Ag + The concentration.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0023] This invention provides a dual-mode measurement based on RGB, including fluorescence colorimetric determination in solution and smartphone-assisted visualization detection of thin films, for the simultaneous and rapid detection of Cu. 2+ and Ag + Based on this dual-mode, fluorescence colorimetry achieves Cu detection within a linear range of 1–100 μM. 2+ The detection limit is 0.014 μM, Ag + The detection limit was 0.120 μM, and the recoveries were 99.80–101.10% and 99.60–100.50%, respectively, with RSDs all below 3.90%. The detection range for smartphone-assisted hydrogel films was extended to 1–1000 μM, Cu 2+ and Ag + The limits of detection were 0.071 μM and 0.230 μM, respectively, maintaining a good recovery rate of 98.70–100.80% with an RSD of less than 4.59%. This dual-mode strategy requires no sophisticated instruments and can achieve detection of Cu within 10 min. 2+ and Ag + Its rapid, reliable, and synchronous detection breaks through the limitations of traditional single-mode detection, providing a robust platform for on-site metal ion monitoring. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the synthesis and detection application process of O-CDs-based fluorescent sensing materials. A: Schematic diagram of O-CDs and PVA@O-CDs preparation; B: Cu based on the O-CDs sensor solution. 2+ / Ag + Visualized portable detection; C: Cu based on PVA@O-CDs hydrogel film sensor 2+ / Ag + Visualized portable detection;

[0025] Figure 2 The image shows the characterization results of O-CDs, where A: TEM image; B: particle size distribution histogram; C: EDS elemental analysis; D: XRD diffraction pattern; E: FT-IR spectrum; F: XPS measurement scan.

[0026] Figure 3 O-CDs, O-CDs + Cu 2+ Complex and O-CDs + Ag + High-resolution XPS spectra of the complex, where A~C represent the C 1s, N 1s, and O 1s spectra of O-CDs, respectively; D~F represent the O-CDs + Cu... 2+ C 1s, N 1s, O 1s plots; G~I represent O-CDs + Ag + The C 1s, N 1s, and O 1s plots;

[0027] Figure 4 The optical properties of O-CDs, where A: O-CDs, O-CDs + Cu 2+ O-CDs+ Ag + A: UV-Vis absorption spectrum of O-CDs and fluorescence emission spectrum of O-CDs (λex = 375 nm); B: Fluorescence emission spectrum of O-CDs under different excitation wavelengths; C: Photographs of O-CDs solution under fluorescent and UV lamps.

[0028] Figure 5 The results show the optimized detection conditions for O-CDs, where A: fluorescence emission spectra of the O-CDs sensor at different dilution factors (10, 30, 50, 80, 100, 300); B: fluorescence intensity ratio F2 / F1 (F...) of the O-CDs sensor under different pH values ​​(2~12). 530 / F 400 C: Change graph; C: Detection of Ag by O-CDs sensor under different incubation times (0~40 min) + and Cu 2+ The graph shows the variation of the fluorescence intensity ratio F2 / F1; D: Detection of Ag by O-CDs sensor under different incubation temperatures (20~60℃). + and Cu 2+ The graph showing the change in the fluorescence intensity ratio F2 / F1;

[0029] Figure 6 For O-CDs sensor to detect Cu 2+ and Ag + The standard calibration curve, where A: Cu2+ Fluorescence emission spectra of O-CDs with increasing concentration; B: F2 / F1 ratio and Cu 2+ Linear relationship of concentration; C: Green-red intensity ratio (G / R) and Cu 2+ Linear relationship of concentration; D: Cu 2+ Detect the corresponding CIE chromaticity diagram; E: Ag at different concentrations + Fluorescence emission spectra of O-CDs under certain conditions; F: F2 / F1 ratio and Ag + Linear relationship of concentration; G: Green-blue intensity ratio (G / B) and Ag + Linear relationship of concentration; H:Ag + Detect the corresponding CIE chromaticity map;

[0030] Figure 7 For O-CDs sensors to Cu 2+ / Ag + The selectivity and anti-interference ability, where A: fluorescence emission spectra of O-CDs in the presence of different ions; B: F2 / F1 ratio corresponding to different ions, with the same letter in the figure indicating no significant difference ( P >0.05);

[0031] Figure 8 To use a PVA@O-CDs hydrogel sensor to detect Cu 2+ and Ag + Visual inspection and quantitative analysis were performed, including A: G / R intensity ratio and Cu. 2+ Linear relationship of concentration; B: Cu 2+ Detect the corresponding CIE chromaticity diagram; C: G / B intensity ratio and Ag + Linear relationship of concentration; D: Ag + Detect the corresponding CIE chromaticity map;

[0032] Figure 9 For dual-mode sensors with different Cu concentrations 2+ and Ag + Visualized color response images under the given conditions, where the A:O-CDs sensor solution changes with Cu 2+ Color change graph of concentration (0~100 μM) increasing; B: O-CDs sensor solution with Ag + Color change graph of increasing concentration (0~100 μM); C: PVA@O-CDs hydrogel sensor with Cu 2+ Color change graph of increasing concentration (0~1 mM); D: PVA@O-CDs hydrogel sensor with Ag + Color change graph of increasing concentration (0~1 mM). Detailed Implementation

[0033] To make the objectives and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are only for explaining the invention and are not intended to limit the invention.

[0034] Unless otherwise specified, the instruments, reagents, and materials used in the following embodiments are all conventional instruments, reagents, and materials already available in the prior art and can be obtained through legitimate commercial channels. Unless otherwise specified, the experimental methods and detection methods used in the following embodiments are all conventional experimental methods and detection methods already available in the prior art.

[0035] The experimental equipment and reagents used in the following examples are as follows:

[0036] Experimental equipment: The morphological characteristics of O-CDs were analyzed using transmission electron microscopy (TEM, JEM-F200, JEOL, Japan). X-ray diffraction patterns were obtained using X-ray diffraction (XRD, D8 Advance, Bruker, Germany). Surface elemental composition and chemical state were determined using Fourier transform infrared spectroscopy (FT-IR, Nicolet iS20, Thermo Fisher Scientific, USA) and X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi, Thermo Scientific, USA), respectively. Optical properties were analyzed using fluorescence spectroscopy (F97 Pro, Shanghai Lengguang Technology Co., Ltd., China) and ultraviolet-visible absorption spectroscopy (UV-2300II, Shanghai Taikepu Scientific Instruments Co., Ltd., China). Sample dispersion was performed using an ultrasonic bath (KH5200DE, Kunshan Hechuang Ultrasonic Instruments Co., Ltd., China). Centrifugation was performed using a centrifuge (H1850, Hunan Xiangyi Laboratory Instrument Development Co., Ltd., China), and pH adjustment was performed using a pH meter (ST2100, OHAUS, USA).

[0037] Experimental reagents: L-glutamic acid, o-phenylenediamine, and polyvinyl alcohol (PVA) were purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. (Shanghai, China). Ethanol was provided by Tianjin Tianli Chemical Reagent Co., Ltd. (Tianjin, China). Glacial acetic acid and sodium hydroxide were purchased from Tianjin Damao Chemical Reagent Factory (Tianjin, China). Commercially available mineral water, lake water, and tap water samples were collected from the campus of Longdong University (Qingyang, China). All reagents were of analytical grade and could be used directly without further purification. Ultrapure water was used throughout the experiment.

[0038] 1. Example 1

[0039] Preparation of dual-emission carbon dot hydrogel films

[0040] S1: Synthesis of O-CDs: L-glutamic acid (0.111 g) and o-phenylenediamine (0.162 g) were dissolved in 25.00 mL of anhydrous ethanol and sonicated at 100 Hz for 15 min to form a homogeneous solution. The mixture was then transferred to a 100 mL PTFE-lined autoclave and heated at 210 °C for 10 h. Figure 1 A). After naturally cooling to room temperature, centrifuge at 8000 r / min for 20 min. Filter the supernatant through a 0.22 μm microporous membrane to obtain the O-CDs solution, which is stored at 4℃ for subsequent experiments.

[0041] S2: Dissolve 2.00 g of polyvinyl alcohol in 20.00 mL of ultrapure water and stir continuously at 95℃ for 4 h to obtain a PVA solution;

[0042] S3: Synthesis of PVA@O-CDs hydrogel film: After removing air bubbles by maintaining a 10% (w / v) PVA solution at 37℃ for 20 min, 7.00 mL of the solution was added to 3.00 mL of O-CDs solution to obtain a mixture. The mixture was then thoroughly mixed and degassed by magnetic stirring at 500 r / min for 30 min and injected into a 12-well culture plate. The physical gelation process was promoted by implementing three consecutive freeze-thaw cycles: each cycle was maintained at -20℃ for 20 h, followed by maintenance at 25℃ for 4 h, resulting in a light pink dual-emission carbon dot hydrogel film, named PVA@O-CDs hydrogel film, which was stored at 4℃ for subsequent experiments.

[0043] 2. Building sensors and developing portable devices

[0044] (1) Constructing a sensor

[0045] Construction of the O-CDs sensor: 2.00 mL of O-CDs solution was mixed with 1.00 mL of Britton-Robinson (BR) buffer (pH 7.0) at room temperature and vortexed for 2 min to obtain the O-CDs sensor solution. When detecting different targets, the emission intensities at 400 nm (F1) and 530 nm (F2) were recorded at an excitation wavelength of 375 nm. The detection performance of the sensor was evaluated by the ratio signal (F2 / F1) and the change in solution color.

[0046] Construction of the PVA@O-CDs hydrogel sensor: The PVA@O-CDs hydrogel film prepared above is itself a PVA@O-CDs hydrogel sensor. When detecting different target analytes, the PVA@O-CDs hydrogel film was immersed in target analyte solutions of different concentrations, and its color change was observed under 365 nm ultraviolet light irradiation. The detection performance of the sensor was evaluated based on the color change.

[0047] The two sensors described above represent two different types: one solution-based and the other thin-film-based. The thin-film sensor, formed by integrating O-CDs sensors into PVA to create a gel, offers greater convenience. Both sensors can be integrated into portable devices for detection, serving as a comparison between them.

[0048] (2) Develop portable devices

[0049] The developed portable device integrates a PVA@O-CDs hydrogel film and an O-CDs sensor solution, providing RGB-based dual-mode measurements, including fluorescence colorimetric determination in the solution (O-CDs sensor solution) and smartphone-assisted visualization of the detection film (PVA@O-CDs hydrogel film), for the simultaneous and rapid detection of Cu. 2+ and Ag + .

[0050] The smartphone-assisted visual inspection system for thin films integrates a darkroom, a 365 nm ultraviolet lamp, and smartphone components. For example... Figure 1 As shown in Figure C, this platform is specifically designed to minimize ambient light interference, which can significantly affect image attributes such as brightness, hue, saturation, and exposure. Its detection process is as follows:

[0051] ① Launch the “Color Grab” application on your smartphone; ② Place the cuvette containing the PVA@O-CDs hydrogel film and the sample in a dark chamber; ③ Turn on the UV lamp, take a real-time image through the observation window with your smartphone, and extract the RGB values ​​through the application; ④ Quantify the target ion concentration based on the RGB values ​​and the preset calibration curve.

[0052] Fluorescence colorimetric determination in solution is performed using a portable device that integrates Wi-Fi communication (such as...). Figure 1 (As shown in B). The core components include dual sample chambers, an LED excitation light source, an electronic module (based on an ESP32 microcontroller, equipped with resistors and an LCD module), and cuvettes. A smartphone (Huawei Nova 12) serves as a remote terminal for data display and interaction. The system operation follows the following procedure:

[0053] ① System activation: After power-on, the microcontroller automatically connects to the local Wi-Fi network. The user opens a dedicated WeChat mini-program on their mobile phone to detect and pair the sensor device; ② Sample loading: The cuvette containing O-CDs and the analyte is placed into the sample chamber; ③ Automatic detection and data transmission: The LED light source excites the sample to produce a fluorescence response. The integrated color sensor captures the signal, converts it into RGB values, and transmits it to the mini-program in real time via Wi-Fi; ④ Quantitative analysis: The mini-program converts the RGB values ​​into corresponding ion concentrations using a pre-calibrated standard curve, directly displays the results, and records all data for subsequent analysis.

[0054] 3. O-CDs + Cu 2+ Complex and O-CDs + Ag + Preparation of the complex

[0055] O-CDs + Cu 2+ The preparation method of the complex is as follows: First, prepare BR buffer (pH=7.0), and dilute the newly synthesized O-CDs solution 30 times with anhydrous ethanol (optimal dilution factor) to serve as the O-CDs working solution; then prepare Cu at different concentrations. 2+ Standard solution (0–100 μM). Accurately transfer 2.00 mL of the above O-CDs working solution, add 1.00 mL of BR buffer (pH 7.0), mix well, and pre-incubate at room temperature for 2 min to stabilize the system. Add 2.00 mL of Cu at a specific concentration to the stabilized mixture. 2+ Standard solution. Incubate the mixture at room temperature for 10 min. During this process, Cu 2+ Coordination occurs between the oxygen-containing functional groups on the surface of O-CDs, reaching coordination equilibrium, thereby enabling the in-situ preparation of stable "O-CDs + Cu" in solution. 2+ "complex".

[0056] O-CDs + Ag + The preparation method of the complex is as follows: Prepare Ag at different concentrations. + Standard solution (0–100 μM). Then, accurately transfer 2.00 mL of the above O-CDs working solution, add 1.00 mL of BR buffer (pH 7.0), mix well, and pre-incubate at room temperature for 2 min. Add 2.00 mL of Ag at a specific concentration to the above mixture. + Standard solution. Incubate the mixture at room temperature for 10 min. During this process, Ag... + The reaction involves specific binding / coordination with functional groups on the surface of O-CDs to reach a reaction equilibrium, thereby producing stable "O-CDs + Ag". + "complex".

[0057] 1. Experimental Example 1

[0058] Material characterization

[0059] The morphology and structural properties of O-CDs were comprehensively characterized using TEM. For example... Figure 2 As shown in Figure A, O-CDs exhibit a spherical morphology with a uniform particle size distribution and good dispersibility. Their particle size ranges from 0.5 to 3.5 nm, with an average size of 1.8 nm. Figure 2 B). EDS analysis ( Figure 2 C) shows that the main component of O-CDs is carbon (C), accounting for 99.34%, with the remainder being trace amounts of nitrogen (N, 0.38%) and oxygen (O, 0.28%). Due to the limited precision of EDS in the quantitative analysis of elements such as C, N, and O, XPS technology was further used to verify its elemental composition. XRD analysis was used to assess the crystallinity of O-CDs. Figure 2 As shown in Figure D, the XRD pattern exhibits a broad diffraction peak at 2θ = 21.59°, indicating the amorphous nature of the carbon structure. The surface functional groups of the O-CDs were characterized by FT-IR. Figure 2 In the FT-IR full spectrum shown in E, the characteristic absorption peak is located at 3313.59 cm⁻¹. -1 (Stretching vibrations of OH and NH), 2972.18 cm -1 (OH stretching vibration), 2880.82 cm -1 (CH stretching vibration), 1378.97 cm -1 (CH deformation vibration), 1087.04 cm -1 and 1045.14 cm -1 (CO stretching vibration), and 879.96 cm -1 (NH bending vibration). These characteristics indicate that O-CDs possess hydrophilic functional groups, including hydroxyl, amino, carboxyl, and aromatic groups.

[0060] XPS analysis provided us with a deeper understanding of the chemical groups and bonding structures of O-CDs. XPS measurement of scanning spectra ( Figure 2 F) Three significant peaks were observed at binding energies of 284 eV (C 1s), 399 eV (N 1s), and 532 eV (O 1s), a result that corroborates the findings of EDS. High-resolution spectroscopy further elucidates the detailed chemical state: the C 1s spectrum ( Figure 3 A) After deconvolution, characteristic peaks of CC / C=C (284.0 eV) and OC=O (285.3 eV) were revealed; N 1s spectrum ( Figure 3B) Identified pyridine nitrogen (398 eV) and pyrrole nitrogen (399.4 eV); O 1s spectrum ( Figure 3 C) was resolved to consist of chemisorbed oxygen (530.9 eV), C=O (531.5 eV), and CO (532.2 eV). These XPS results are consistent with the FT-IR characterization results, confirming that O-CDs are composed of O- and N-containing functional aromatic sps. 2 The structural domains and surface hydroxyl groups together enhance its hydrophilicity and support its dual-emission fluorescence properties.

[0061] 2. Optical properties

[0062] like Figure 4 As shown in Figure A, the UV-vis absorption spectra of O-CDs exhibit three significant peaks at 216.5 nm, 239 nm, and 280 nm. These spectral features can be attributed to the π-π* electronic transitions of the aromatic carbon-carbon double bond (C=C) and the n-π* electronic transitions of the carbonyl (C=O) and hydroxyl (OH) functional groups. This spectroscopic evidence confirms the presence of conjugated structural domains and aromatic ring structures in O-CDs. Under excitation at 375 nm, O-CDs exhibit a dual emission spectrum with peaks at 400 nm and 530 nm. In aqueous solution, these O-CDs appear deep red under sunlight, while emitting strong orange-red fluorescence under ultraviolet light, such as... Figure 4 As shown in Figure C, the optimal excitation wavelength was determined by collecting emission spectra within the excitation range of 345–405 nm. Figure 4 (B) As the excitation wavelength increases, the emission intensity at 400 nm gradually decreases, while the emission intensity at 530 nm gradually increases. Notably, the positions of the two emission peaks remain unchanged, indicating the presence of multiple emission states or surface emission centers. All subsequent references to Cu... 2+ and Ag + The ratio sensing experiments all used 375 nm as the excitation wavelength because it can provide well-separated dual emission peaks, which is beneficial for ratio fluorescence detection.

[0063] 3. Condition Optimization

[0064] By systematically optimizing multiple parameters such as dilution factor, pH value, incubation temperature, and time, the O-CDs sensor's detection of Cu was significantly improved. 2+ and Ag + Detection sensitivity of ions. Changes in fluorescence ratios under different experimental conditions were recorded to determine the optimal parameters. A series of experimental conditions were used: dilution factors (10, 30, 50, 80, 100, 300 times); BR buffer solution with pH values ​​of 2.0–12.0; incubation temperatures of 20–60℃ (in increments of 5℃); and incubation times of 0–40 min. Figure 5As shown in Figure A, the fluorescence intensity at 400 nm peaks at a 30-fold dilution, and further dilution leads to a gradual decrease in intensity; therefore, a 30-fold dilution is determined to be the optimal condition. Figure 5 As shown in B, the fluorescence ratio F2 / F1 remained stable in the pH range of 2 to 8, but decreased significantly in the pH range of 9 to 12. Therefore, pH 7 was selected as the optimal condition for subsequent detection. Figure 5 The C-value showed that the F2 / F1 ratio rose rapidly in the first 10 minutes and then stabilized, indicating that an equilibrium had been reached. Therefore, 10 minutes was determined to be the optimal incubation time. Temperature stability was further evaluated by monitoring the F2 / F1 ratio within the temperature range of 20–60 °C. Figure 5 D). The F2 / F1 ratio remained nearly constant, demonstrating its excellent thermal stability and suitability for various temperature conditions. Based on these results, subsequent experiments were conducted using an O-CDs sensor diluted 30-fold at pH 7.0, incubated at room temperature (25°C) for 10 min.

[0065] 4. Calibration model based on fluorescence ratio detection

[0066] To construct an integrated sensing platform, three calibration models were developed: the F2 / F1 ratio method based on fluorescence ratios, the RGB mode of fluorescence colorimetry, and the RGB mode of smartphone imaging. The F2 / F1 ratio method in fluorescence spectroscopy serves as a high-precision reference standard. RGB values ​​of the O-CDs sensor are extracted using a portable device for on-site visual analysis. In the PVA@O-CDs hydrogel sensor, color changes are captured using a smartphone camera for solid-state visual detection.

[0067] The specific steps of the F2 / F1 ratio method based on fluorescence spectroscopy are as follows: 2.0 mL of freshly prepared O-CDs solution was mixed with 1.00 mL of pH 7.0 BR buffer and incubated at room temperature for 2 min to obtain the O-CDs sensor. 2.0 mL of standard metal ion solutions of different concentrations (0, 1, 5, 10, 20, 40, 60, 80, and 100 μM) were added to the O-CDs sensor. After incubation at room temperature for 10 min, the fluorescence intensities of F2 and F1 were recorded, and the F2 / F1 ratio was calculated. A calibration curve was established with concentration as the x-axis and fluorescence intensity ratio as the y-axis to evaluate the dual-ion detection capability of the O-CDs sensor. Furthermore, Cu with the same concentration gradient (0–100 μM) was used… 2+ and Ag + The standard solutions were applied to the fluorescence colorimetric RGB mode of the solution system and the smartphone RGB mode of the thin film (0~1000 μM), respectively. By plotting a standard curve with ion concentration as the x-axis and color ratio as the y-axis, the visual quantitative detection of metal ions was achieved.

[0068] like Figure 6 As shown in A, when Cu 2+ When the concentration changes from 0 to 100 μM, the fluorescence intensity of F1 shows a decreasing trend, while the fluorescence intensity of F2 shows an increasing trend. Figure 6 B shows the F2 / F1 ratio and Cu 2+ Concentration showed a significant linear correlation, with a coefficient of determination (R²). 2 The concentration reached 0.997, which can be expressed by the equation F2 / F1 = 1.4586 + 0.031c (where c represents the concentration). The limit of detection (LOD) was calculated to be 0.011 μM using the formula LOD = 3σ / S, where σ is the standard deviation of the blank sample and S is the slope of the calibration curve. Figure 6 As shown in E, with Ag + With increasing concentration (1–100 μM), the intensities of both F1 and F2 decreased. Analysis showed that the F2 / F1 ratio was related to Ag... + The concentration shows a linear relationship (R0). 2 =0.994), such as Figure 6 As shown in Figure F, its equation is F2 / F1 = 0.6275 + 0.0028c, and the detection limit is 0.067 μM. The sensor's excellent sensitivity and clear fluorescence response characteristics make it an ideal foundation platform for colorimetric visual inspection devices.

[0069] 5. Anti-interference capability

[0070] By optimizing the conditions, potential interfering metal ions (Al) 3+ Fe 2+ Fe 3+ Mn 2+ Na + Co 2+ Mg 2+ NH4 + Zn 2+ K + The standard solution of Cu was introduced at a concentration of 10 times. 2+ and Ag + The selectivity and anti-interference capability of the developed O-CDs sensing system were evaluated by testing the solution. Specifically, 2.0 mL of each ion solution was mixed with 2.0 mL of O-CDs working solution and 1.0 mL of BR buffer, and incubated for 10 min. The fluorescence intensity ratio (F2 / F1) was recorded to evaluate the response to Cu. 2+ and Ag + It exhibits selectivity and resistance to interference from other coexisting ions.

[0071] The selectivity and anti-interference characteristics of the O-CDs-based sensing system were evaluated in the presence of various potential interfering factors. Figure 7As shown in Figure A, the O-CDs sensor detects Cu. 2+ It exhibits a clear ratio fluorescence response, while for Ag... + This exhibits a quenching response, thus confirming its selectivity for these specific metal ions. Statistical analysis shows that Cu... 2+ and Ag + The change in the ion-induced fluorescence intensity ratio F2 / F1 was significantly different compared to that of potential interfering substances. P <0.05)( Figure 7 B). These results demonstrate that sensing systems employing O-CDs have extremely strong anti-interference capabilities against potential interference.

[0072] 6. Cu 2+ and Ag + Visual detection

[0073] Cu based on RGB dual-mode measurement as described above. 2+ and Ag + Visual detection is achieved, and the detection limit for each mode is calculated using a calibration model to realize semi-quantitative detection. For example... Figure 6 As shown in Figure C, Cu in the O-CDs sensor was analyzed by RGB fluorescence colorimetry. 2+ The G / R ratio obtained at that time showed a linear relationship in the concentration range of 0~100 μM (R 2 =0.995). The correlation expression is G / R = 0.783 + 0.0022c, with a detection limit of 0.014 μM. In the formula, G represents the color intensity value of the green channel in the fluorescence image acquired by a smartphone or portable device; R represents the color intensity value of the red channel in the acquired fluorescence image; G / R represents the ratio of the green to red channel color intensities; and c represents the Cu content in the test system. 2+ The concentration. Figure 9 A shows the effect of Cu 2+ As the concentration increases, the color changes visually from pink to green, a phenomenon consistent with the coordinate changes observed in the International Commission on Illumination (CIE) chromaticity diagram. Figure 6 D), thus confirming the visual detection Cu 2+ The feasibility of ions. Similarly, Ag in solution. + The fluorescence colorimetric RGB mode (expressed as G / B values) also exhibits high linearity in the 1–100 μM range (RB). 2 = 0.996)( Figure 6The formula G / B = 1.0475 + 0.0058c has a detection limit of 0.120 μM, where G represents the color intensity value of the green channel in the fluorescence image acquired by a smartphone or portable device; B represents the color intensity value of the blue channel in the acquired fluorescence image; G / B represents the color intensity ratio of the green and blue channels; and c represents the Ag content in the test system. + The concentration. Figure 9 B shows the solution with Ag + The color shift from pink to orange as concentration increases corresponds to a coordinate shift in the CIE chromaticity diagram. Figure 6 H), thus verifying Ag + Feasibility of ion visual detection. A portable hydrogel sensor suitable for smartphones, in RGB mode, has RGB values ​​related to Cu. 2+ and Ag + There is a correlation between ion concentrations. For example... Figure 8 As shown in Figure A, the G / R ratio and Cu in the range of 1~1000 μM are... 2+ The ion concentrations show a strong linear relationship, with a correlation coefficient (R0). 2 The limit of detection was 0.997. The calibration equation was G / R = 0.522 + 0.423c, and the limit of detection was 0.071 μM. Similarly, Figure 8 C shows the G / B ratio and Ag. + Ion concentrations showed a linear correlation within the same concentration range, with an R² value of 0.994. The calibration equation was G / B = 0.805 + 4.681c, and the detection limit was 0.230 μM. Figure 9 C demonstrated a PVA@O-CDs hydrogel sensor in Cu 2+ The color change phenomenon upon addition. The observed phase transition is in high agreement with the coordinate shift in the CIE chromaticity diagram. Figure 8 (B) confirms that the PVA@O-CDs hydrogel sensor can be used in Cu 2+ Visual detection. Similarly, Ag + Color change when added ( Figure 9 D) and changes in the CIE diagram ( Figure 8 D) Matches, confirming Ag + Feasibility of visual inspection. These results demonstrate the successful integration of portable PVA@O-CDs hydrogel sensors with smartphone reading systems.

[0074] 7. Analysis of actual samples

[0075] Empirical tests were conducted on various water samples, including mineral water, lake water, and tap water, to verify the effectiveness of this method for Cu. 2+ and Ag +Feasibility of ion quantification. Each sample was centrifuged at 8000 r / min for 20 min, followed by filtration through a 0.22 μm microporous membrane. The processed samples were properly labeled and stored at 4℃ for subsequent analysis. Cu at concentrations of 0, 10, and 20 μM were added according to the standard addition method. 2+ and Ag + Standard solutions were injected into the O-CDs sensor for fluorescence colorimetric determination in solution (RGB mode). Additionally, a smartphone-assisted PVA@O-CDs hydrogel sensor was used to determine the concentrations of 0, 100, and 200 μM samples (RGB mode). RGB values ​​were acquired using a dual-mode portable device, and Cu in the samples was determined according to a preset calibration curve. 2+ and Ag + Concentration. Recovery rates were calculated to validate the precision of the fluorescence colorimetric method versus the hydrogel colorimetric method in complex matrices.

[0076] Fluorescence colorimetric RGB mode for Cu 2+ The recovery rate was 99.80%~101.10%, for Ag + The recoveries ranged from 99.60% to 100.50%, with relative standard deviations (RSDs) of 0.69% to 1.70% and 0.88% to 3.90%, respectively (Table 1). The recovery rate of Cu in smartphone RGB mode... 2+ The recovery rate was 98.70%~100.80%, for Ag + The recoveries ranged from 99.85% to 100.75%, with RSDs of 0.51% to 4.59% and 0.07% to 2.70%, respectively. These results demonstrate that the O-CDs sensing system can detect Cu in complex real-world samples. 2+ and Ag + It exhibits good precision and repeatability, demonstrating great potential in the field of environmental monitoring. Furthermore, both the fluorescence colorimetric RGB mode and the smartphone RGB mode demonstrate satisfactory detection performance, providing a convenient and rapid platform for on-site visual detection of heavy metal ions.

[0077] Table 1. Liquid-phase O-CDs sensor and gel-phase PVA@O-CDs hydrogel sensor for Cu 2+ Ag + Recovery rate test (n=3)

[0078]

[0079] 8. Sensing Mechanism

[0080] FT-IR and XPS analyses revealed the presence of aromatic ring structures on the O-CDs surface. These O-CDs surfaces not only possess extensive conjugated sp... 2The region is also rich in oxygen- and nitrogen-containing functional groups. (Cu) 2+ With Ag + Ions can form chelates with these functional groups, thereby constructing complex structures and altering the fluorescence properties of O-CDs. Regarding Cu... 2+ and Ag + UV absorption spectra, fluorescence spectra, and FT-IR and XPS data of ions and O-CDs, such as Figure 2 As shown in E, O-CDs and Cu 2+ and Ag + The FT-IR spectrum of the formed complex is at 1645 cm⁻¹ -1 The presence of an additional peak at this location indicates the presence of characteristic C=C skeletal stretching vibration peaks specific to aromatic benzene rings. Furthermore, a peak at 1378 cm⁻¹ was also identified in O-CDs. -1 and 3329 cm -1 The characteristic peaks at this location correspond to a large number of amino and carboxyl groups. These hydrophilic groups significantly enhance the hydrophilicity of O-CDs. Considering the carbonization polymerization process using o-phenylenediamine as a precursor, the abundant amino groups in o-phenylenediamine (many of which have lone pairs of electrons) may quench the fluorescence of O-CDs through photoinduced electron transfer (PET). These results suggest that O-CDs may detect Cu through π-π stacking interactions. 2+ and Ag + and through its amino group with Cu 2+ and Ag + The interaction of ions produces the PET effect. The effect of O-CDs detection solution on Cu... 2+ Further studies on the fluorescence response showed that adding Cu to the O-CDs detection medium... 2+ Subsequently, 375 nm excitation led to the detection of F in the solution by O-CDs. 400 weaken and F 530 Enhancement. Contrast. Figure 3 C and Figure 3 F shows that Cu 2+ It coordinated with oxygen-containing functional groups on the surface of O-CDs; simultaneously, in contrast... Figure 3 B and Figure 3 The N 1s spectrum of E shows that the addition of Cu... 2+ Subsequently, the binding energy of nitrogen shifted significantly (from 398 eV and 399.4 eV to 398.2 eV and 399.1 eV, respectively), indicating that Cu 2+ It also exhibits strong coordination interactions with nitrogen-containing functional groups (such as amino groups) on the surface of O-CDs. 2+ Co-coordinated with oxygen- and nitrogen-containing functional groups to form O-CDs + Cu 2+The complex may quench the fluorescence emission of O-CDs at 400 nm through the PET effect. Conversely, the yellow fluorescence emission of O-CDs at 530 nm is primarily attributed to the luminescence of the carbon core. Analysis Figure 3 A and Figure 3 D shows that O-CDs + Cu 2+ The C1s spectrum of the complex was unaffected, indicating that Cu 2+ The effect on the 530 nm yellow fluorescence emitted by the carbon core is negligible. Therefore, with the F of O-CDs... 400 As the value decreases, the luminescence of the system gradually changes from F... 530 Fluorescence-dominant, leading to a significant enhancement in fluorescence emission. This is observed in the O-CDs detection solution for Ag. + Further analysis of the fluorescence response indicated that the addition of Ag... + Subsequently, the 375 nm excitation simultaneously caused F 400 and F 530 The value decreased. (Comparison) Figure 3 G and Figure 3 I can see that Ag + It interacted with carbon- and oxygen-containing surface groups; further comparison Figure 3 B and Figure 3 The N 1s spectrum of H shows that the addition of Ag... + Subsequently, the binding energy of nitrogen also shifted significantly (from 398 eV and 399.4 eV to 398.5 eV and 399.8 eV, respectively), confirming that Ag... + Coordination bonds also occurred with nitrogen-containing groups (such as amino groups) on the surface of O-CDs. Therefore, Ag + It forms complexes with O-CDs through co-coordination with carbon-, oxygen-, and nitrogen-containing surface groups, potentially quenching the fluorescence emission of O-CDs at 400 nm via the PET effect. However, the yellow fluorescence emission of O-CDs at 530 nm is mainly attributed to carbon core luminescence. (Contrast) Figure 3 A and Figure 3 G is visible O-CDs + Ag + The C 1s state in the system changes, indicating that Ag + Significantly affecting the 530 nm yellow fluorescence originating from the carbon core. Therefore, when the F of O-CDs... 400 When it weakens, F 530The LOD also decreases accordingly. Based on the above inferences regarding the metal ion detection mechanism of O-CDs detection solutions, this solution has practical significance for the rapid detection of heavy metal ions using O-CDs. The hierarchical phenomenon exhibited by LOD can be attributed to the differences in signal resolution and matrix effects. The ratio detection mode using fluorescence spectroscopy achieves the lowest LOD due to the high spectral resolution of the fluorometer and the accurate calibration of the F2 / F1 ratio. In contrast, the LOD of the RGB mode of fluorescence colorimetry in the solution phase is slightly higher, which stems from the fact that the accuracy of RGB signal extraction by portable devices is not as high as the spectral analysis capability of fluorescence instruments. In addition, the smartphone RGB mode in the hydrogel phase exhibits the highest LOD, both because the polyvinyl alcohol hydrogel hinders ion diffusion and because smartphone cameras have lower resolution compared to analytical instruments.

[0081] This invention uses O-CDs as the core, constructing a PVA hydrogel solid-phase support system and an integrated module for RGB quantitative analysis of a 365 nm light source, dark chamber, and smartphone. This forms a dual ion detection scheme with both specific recognition and on-site quantitative capabilities. The feasibility and innovation of this technical route stem from the differentiated characteristics of the material's luminescence mechanism and the synergistic support of the system engineering design. The O-CDs are prepared via a one-step solvothermal method using L-glutamic acid and o-phenylenediamine, exhibiting two distinguishable emission peaks at a 375 nm excitation wavelength, located at F... 400 and F 530 At this location, spectral analysis indicates that F 400 It mainly relies on the luminescence properties of O-CDs surface functional groups, and is more sensitive to surface coordination and the PET effect, while F 530 Cu exhibits intrinsic luminescence primarily from the carbon nucleus, resulting in higher stability. Based on this structure-dependent luminescence characteristic, Cu... 2+ With Ag + Cu induces spectral response differentiation through differentiated coordination and electronic dissipation pathways. 2+ Preferentially binds to functional groups on the surface of O-CDs, leading to F 400 Significant quenching and F 530 Relative enhancement, Ag + This causes a stronger perturbation to the electronic state of the carbon nucleus, resulting in F 400 With F 530 The synchronous quenching, this "opposite / same-direction" spectral response difference provides a basis for constructing F 530 / F 400 Ratio-based detection modes provide a clear physicochemical basis, enabling Cu detection in a two-dimensional signal space. 2+ With Ag + The effective differentiation and parallel quantification of these ions have solved the technical bottleneck that a single emission channel cannot simultaneously identify two types of ions.

[0082] To extend the self-calibration advantages of laboratory ratio fluorescence to on-site detection scenarios, this invention establishes a cross-dimensional mapping method of "spectral signal - mobile phone RGB image". By suppressing ambient light interference through a dark box structure and fixing the relative geometric positions of the light source, sample, and camera, combined with RGB channel signal extraction, exposure parameter locking, and white balance calibration, dimensionless ratios such as G / R and G / B are correlated with laboratory standard curves. This constructs a mutually referential quantitative closed loop between two detection modes: "solution-portable RGB device" and "gel-smartphone", overcoming the core limitation of traditional visual detection being "easy to qualitative but difficult to quantitative". The pain points are as follows: The introduction of PVA hydrogels forms a stable solid microenvironment through freeze-thaw physical cross-linking. On the one hand, it restricts the migration and diffusion of O-CDs sensors, reducing batch-to-batch errors caused by solvent evaporation and microbial contamination. On the other hand, by regulating the ion diffusion rate, it achieves an optimized balance between response time and detection sensitivity, providing a reasonable explanation for the hierarchical characteristics of LOD. Fluorescence spectrometers achieve the lowest LOD due to their high spectral resolution, followed by portable RGB devices. The gel-smartphone mode is constrained by both ion diffusion rate and imaging resolution, resulting in a slightly higher LOD, but it still meets the needs of rapid on-site detection.

[0083] For Cu in actual samples 2+ With Ag + In coexistence scenarios, this invention will F 400 F 530 The mapping relationship between the ion concentrations and the RGB channels is considered as a linear or piecewise linear combination of the two ion concentrations. Simultaneous calculation of the two components in a single measurement is achieved through binary regression analysis or partial least squares algorithm. Matrix effects are corrected using the standard addition method, and the coefficient of determination (R²) is employed. 2 The robustness of the model was validated using three indicators: spiked recovery rate and RSD; to effectively address common interfering substances in real water samples (such as Cl). - To mitigate the effects of turbidity and background fluorescence caused by organic ligands, suspended matter, etc., this invention specifies corresponding anti-interference measures in its methodology and operational procedures. These include pretreatment steps such as centrifugation and filtration to ensure sample clarity, and effective suppression of these effects by setting blank controls and performing background subtraction in RGB signal analysis. Regarding device preparation and process control, the sensitivity of detection is improved by optimizing detection conditions such as incubation temperature, time, and pH. This detection system comprehensively covers the process from sensor preparation and signal acquisition to quantitative analysis, and is suitable for detecting Cu in samples such as drinking water, surface water, and food contact material extracts. 2+ With Ag + Rapid screening and on-site law enforcement evidence collection. In summary, this invention constructs a Cu... through mechanistic differential response and ratiometric readout strategy of O-CDs. 2+ With Ag +The core technology of "simultaneous differentiation and quantification" enables the transfer of laboratory precision to field testing through PVA hydrogel solidification and engineered packaging of light source-dark box-mobile phone. Cross-mode calibration and full-process quality control mechanisms ensure the repeatability of test results. Furthermore, systematic constraints and compensation for interference factors, system drift, equipment aging, and batch consistency further ensure the reliability of the solution under real complex samples and long-term operating conditions, laying the foundation for its industrial-scale application.

[0084] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a dual-emission carbon dot hydrogel film, characterized in that: Includes the following steps: S1: Preparation of dual-emission carbon dots: L-glutamic acid and o-phenylenediamine were dissolved in anhydrous ethanol and ultrasonically treated to form a homogeneous solution; The homogeneous solution was then transferred to a polytetrafluoroethylene-lined autoclave and reacted at 210°C for 10 h. After the reaction, it was naturally cooled to room temperature, centrifuged at 8000 r / min for 20 min, and filtered to obtain a dual-emission carbon dot solution. The molar ratio of L-glutamic acid to o-phenylenediamine was 1:

2. S2: Preparation of polyvinyl alcohol solution: Polyvinyl alcohol is dissolved in ultrapure water and heated and stirred at 95°C for 4 h until completely dissolved to obtain a polyvinyl alcohol solution; the solid-liquid ratio of polyvinyl alcohol to ultrapure water is 1:10 in g:mL. S3: Forming of hydrogel film: After removing air bubbles from polyvinyl alcohol solution, add dual-emission carbon dot solution to obtain a mixture; after the mixture is thoroughly mixed and degassed by magnetic stirring, inject it into a 12-well culture plate and implement three rounds of continuous freeze-thaw cycles to obtain the dual-emission carbon dot hydrogel film. The process of removing air bubbles from the polyvinyl alcohol solution involves: maintaining the polyvinyl alcohol solution at 37°C for 20 min; the volume ratio of the polyvinyl alcohol solution after bubble removal to the dual-emission carbon dot solution is 7:3; the freeze-thaw cycle is: maintaining at -20°C for 20 h, then switching to 25°C and maintaining for 4 h.

2. The dual-emission carbon dot hydrogel film prepared by the preparation method according to claim 1, characterized in that: The film uses polyvinyl alcohol hydrogel as a carrier, in which dual-emission carbon dots are uniformly dispersed; the dual-emission carbon dots have two fluorescence emission peaks at 400 nm and 530 nm when excited at a wavelength of 375 nm.

3. The application of the dual-emission carbon dot hydrogel film as described in claim 2, characterized in that: Dual-emission carbon dot hydrogel film in Cu 2+ and Ag + Applications in portable visual inspection.

4. The application according to claim 3, characterized in that: The portable visual inspection is a smartphone-assisted visual inspection thin film mode in RGB-based dual-mode measurement.

5. The application according to claim 4, characterized in that: The smartphone-assisted visualization detection film includes a darkroom, a 365 nm UV lamp, and a smartphone. During detection, a cuvette containing the sample to be tested and a dual-emission carbon dot hydrogel film is placed in the darkroom. The UV lamp is activated, and images are captured in real time via the smartphone. The RGB values ​​are extracted using an application, and the target ion Cu is quantified based on the RGB values ​​and a preset calibration curve. 2+ and Ag + The concentration.

6. The application of the dual-emission carbon dot solution as described in claim 1, characterized in that: Dual-emission carbon dot solution in Cu 2+ and Ag + Applications in portable visual inspection.

7. The application according to claim 6, characterized in that: The portable visual detection method is a solution fluorescence colorimetric measurement mode based on RGB dual-mode measurement. This solution fluorescence colorimetric measurement integrates a portable device with Wi-Fi communication. The core components include dual sample chambers, an LED excitation light source, a color sensor, an electronic module, and a cuvette. A smartphone serves as a remote terminal for data display and interaction. The electronic module is based on a microcontroller and includes a resistor and an LCD module. Before detection, a dual-emission carbon dot solution is incubated with BR buffer at room temperature for 2 minutes to obtain a dual-emission carbon dot sensor solution. During detection, a cuvette containing the dual-emission carbon dot sensor solution and the test solution is placed in the dual sample chamber. The sample is excited by the LED light source to generate a fluorescence response. The color sensor captures the signal and converts it into RGB values, which are then transmitted to a smartphone for quantitative analysis of Cu based on a preset calibration curve. 2+ and Ag + The concentration.

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