PH-responsive multi-band fluorescent nanofiber sensor and preparation method and application thereof

Abstract

The invention discloses a pH-responsive multi-band fluorescent nanofiber sensor as well as a preparation method and application thereof. The sensor takes lignin-containing cellulose nanofibers as a carrier and is loaded with gold nanoclusters reduced and coordinated by soybean peptide. By regulating the reaction pH and inducing a local thermal field through near-infrared laser (808 nm), three fluorescent nanofibers with emission wavelengths of red (600-630 nm), turquoise (495-515 nm) and blue (450-480 nm) are directionally synthesized on the surfaces of the nanofibers. After being mixed according to a specific proportion, the sensor generates remarkable multi-band synergistic fluorescence response to pH stimulation, blue fluorescence is stable within the pH range of 2-13, turquoise fluorescence is converted into blue within the pH range of 8-13, and red fluorescence is subjected to two-stage conversion from red to turquoise to blue within the pH range of 2-13. The unique multicolor superposition effect realizes wide-range, visual and anti-interference pH detection.

Description

Technical Field

[0001] This invention belongs to the field of fluorescence sensor technology, specifically relating to a pH-responsive multi-band fluorescent nanofiber sensor, its preparation method, and its application. Background Technology

[0002] The core advantage of multi-band fluorescent nanosensors lies in their use of multi-band fluorescent nanomaterials to introduce multiple fluorescent response signals with non-overlapping emission wavelengths, significantly broadening the sensor's colorimetric range and information capacity. This design allows the sensor to generate rich and distinguishable fluorescence color changes by superimposing multiple narrow emission bands, thereby achieving highly specific identification and differentiation of target analytes. Therefore, multi-band fluorescent nanosensors possess significant potential for spectral and visual differentiation, providing a unique solution for the simultaneous detection or high-precision quantification of multiple targets in complex matrices. However, constructing high-performance multi-band fluorescent nanosensors faces key challenges. The fluorophores used to assemble the sensor need to have similar excitation wavelengths, narrow emission bands, and sufficient distance between emission centers. Therefore, selecting spectrally compatible fluorescent components and developing effective strategies to overcome the assembly challenges between multiple components are crucial for sensor performance. In recent years, researchers have fabricated proportional fluorescence sensors by combining gold nanoclusters with carbon dots or fluorescent reagents. However, these sensors typically use two or more substances, forming heterojunctions, which often suffer from drawbacks such as high energy loss, poor compatibility, and poor stability at the heterojunction. Therefore, it is essential to develop ratiometric fluorescence sensors with multiple gold nanoclusters forming a homogeneous interface. Currently, how to prepare homogeneous interface fluorescence sensors using the same ligand remains a challenge.

[0003] This invention utilizes a single ligand, soybean peptide, as a reducing agent to successfully synthesize three gold nanoclusters with different emission wavelengths growing along fibers, constructing a multi-band fluorescent nanofiber sensor. The gold nanoclusters not only possess precisely tunable emission wavelengths but also exhibit excellent photoluminescence properties, making them excellent candidates for constructing ideal sensing platforms. In sensor applications, the superposition effect of these three emission wavelengths enables the sensor to generate clearly distinguishable blue, cyan-green, and red fluorescent signals. This material exhibits good selectivity and sensitivity, showing promising application prospects in pH detection. Summary of the Invention

[0004] The present invention aims to provide a pH-responsive multi-band fluorescent nanofiber sensor and its preparation method. This sensor produces significant multi-band fluorescence color changes in response to pH stimulation (blue is stable, cyan-green → blue, red → cyan-green → blue), realizing wide-range and visualized pH detection, and solving the problems of narrow detection range and incompatibility of heterogeneous interfaces in existing single fluorescent sensors.

[0005] The above-mentioned objectives of the present invention are achieved through the following technical solutions:

[0006] This invention provides a pH-responsive multi-band fluorescent nanofiber sensor, which is composed of a mixture of blue fluorescent nanofibers, cyan-green fluorescent nanofibers, and red fluorescent nanofibers. Under pH stimulation, the blue fluorescent nanofibers show no significant change in fluorescence color within the pH range of 2-13; the cyan-green fluorescent nanofibers gradually transition from cyan-green to blue within the pH range of 8-13; and the red fluorescent nanofibers exhibit a two-stage response within the pH range of 2-13, transitioning from red to cyan-green and then gradually to blue.

[0007] The blue, cyan, and red fluorescent nanofibers were obtained by growing gold nanoclusters with three different fluorescence properties along lignin-containing cellulose nanofibers. The lignin-containing cellulose nanofibers were used as a carrier and mixed with chloroauric acid, which was then adsorbed by the nanofibers. A uniformly oriented gold ion-loaded layer is formed on the surface of nanofibers, and soybean peptides are added as ligands and reducing agents. Under near-infrared laser irradiation, lignin absorbs light and generates a local thermal field, which activates the reducing activity of soybean peptides. Soybean peptides are reduced to form gold cores. By adjusting the pH of the reaction, the indole ring of tryptophan and the phenolic hydroxyl group of tyrosine in soybean peptide molecules combine with the gold core to form a core-shell structure, resulting in blue fluorescent nanofibers with gold nanoclusters growing along nanofibers. The imidazole ring of histidine in soybean peptide molecules combines with the gold core to form a core-shell structure, resulting in green fluorescent nanofibers with gold nanoclusters growing along nanofibers. The breaking of the disulfide bond of cysteine ​​in soybean peptide molecules exposes thiol groups, which combine with the gold core to form a core-shell structure, resulting in red fluorescent nanofibers with gold nanoclusters growing along cellulose nanofibers.

[0008] This invention also provides a method for preparing the above-mentioned pH-responsive multi-band fluorescent nanofiber sensor, comprising the following steps:

[0009] S1. Preparation of blue fluorescent nanofibers: A lignin-containing cellulose nanofiber dispersion was added to a chloroauric acid aqueous solution under nitrogen protection and mixed, and then mixed with a soybean peptide solution; the pH was adjusted to 10-13, and the reaction system temperature was raised to 70 ℃-80 ℃ by near-infrared laser irradiation and the reaction was carried out for 10-12 h to obtain a blue fluorescent nanofiber dispersion in which gold nanoclusters grow along the nanofibers;

[0010] S2. Preparation of bluish-green fluorescent nanofibers: Lignin-containing cellulose nanofibers were added to a chloroauric acid aqueous solution under nitrogen protection and mixed, and then mixed with soybean peptide solution; the pH was adjusted to 7-9, and the reaction system temperature was raised to 50 ℃-60 ℃ by near-infrared laser irradiation for 6-8 h to obtain a bluish-green fluorescent nanofiber dispersion in which gold nanoclusters grow along the nanofibers.

[0011] S3. Preparation of red fluorescent nanofibers: lignin-containing cellulose nanofibers were added to a chloroauric acid aqueous solution under nitrogen protection and mixed, and then mixed with soybean peptide solution; the pH was adjusted to 2-6, and the reaction system temperature was raised to 50 ℃-60 ℃ by near-infrared laser irradiation for 6-8 h to obtain a red fluorescent nanofiber dispersion in which gold nanoclusters grow along the nanofibers.

[0012] S4. Preparation of pH-responsive multi-band fluorescent nanofiber sensor: The blue fluorescent nanofiber dispersion obtained in step S1, the cyan-green fluorescent nanofiber dispersion obtained in step S2, and the red fluorescent nanofiber dispersion obtained in step S3 are mixed at a volume ratio of 1:1-20:1-20 to obtain the pH-responsive multi-band fluorescent nanofiber sensor.

[0013] Further, in step S1, the concentration of the chloroauric acid aqueous solution is 10 mM, the concentration of the soybean peptide solution is 45-90 mg / mL, and the volume ratio of the chloroauric acid aqueous solution to the soybean peptide solution is 1:3.

[0014] Further, in step S2, the concentration of the chloroauric acid aqueous solution is 10 mM, the concentration of the soybean peptide solution is 40-80 mg / mL, and the volume ratio of the chloroauric acid aqueous solution to the soybean peptide solution is 1:3.

[0015] Further, in step S3, the concentration of the chloroauric acid aqueous solution is 10 mM, the concentration of the soybean peptide solution is 30-70 mg / mL, and the volume ratio of the chloroauric acid aqueous solution to the soybean peptide solution is 1:3.

[0016] Furthermore, in step S1, the wavelength of the near-infrared laser is 808 nm, and the power density is 2. .

[0017] Furthermore, in step S2, the wavelength of the near-infrared laser is 808 nm, and the power density is 1. .

[0018] Furthermore, in step S3, the wavelength of the near-infrared laser is 808 nm, and the power density is 1. .

[0019] The pH-responsive multi-band fluorescent nanofiber sensor of the present invention can be applied to pH detection.

[0020] The present invention has the following beneficial effects:

[0021] (1) In this invention, lignin-containing cellulose nanofibers are used as photothermal materials and carriers for the directional synthesis of gold nanoclusters, and soybean peptides are used as ligands and reducing agents. The lignin-containing cellulose nanofibers selectively adsorb A uniformly oriented gold ion-loaded layer is formed on the surface of the nanofibers. The lignin on the nanofibers releases heat by absorbing energy from near-infrared laser light, generating a localized thermal field around the nanofibers. This thermal field activates the reduction activity of soybean peptides, and the adsorbed lignin on the nanofibers... Preferably reduced to form a gold core, the gold nanoclusters in soybean peptide molecules are then controlled by adjusting the pH of the reaction. This allows the indole ring of tryptophan and the phenolic hydroxyl group of tyrosine in the soybean peptide molecule to combine with the gold core to form a core-shell structure, resulting in blue fluorescent nanofibers where gold nanoclusters grow along nanofibers. Similarly, the histidine imidazole ring in the soybean peptide molecule combines with the gold core to form a core-shell structure, resulting in cyan-green fluorescent nanofibers where gold nanoclusters grow along nanofibers. Finally, the breaking of the disulfide bond in cysteine ​​in the soybean peptide molecule exposes a thiol group, which combines with the gold core to form a core-shell structure, resulting in red fluorescent nanofibers where gold nanoclusters grow along cellulose nanofibers. The emission wavelengths of the prepared blue, cyan-green, and red fluorescent nanofibers are 450-480 nm (blue), 495-515 nm (cyan-green), and 600-630 nm (red), respectively. Under pH stimulation, the blue, cyan-green, and red fluorescent nanofibers exhibit fluorescence color changes: no significant color change, a gradual transition from cyan-green to blue, and a transition from red to cyan-green and then back to blue, respectively.

[0022] (2) This invention prepares a pH-responsive multi-band fluorescent nanofiber sensor by mixing three types of fluorescent nanofibers in a certain proportion. Through the synergistic response of multi-color fluorescence, a multi-color superposition effect is generated to achieve pH sensing. Under pH stimulation, the blue fluorescent nanofiber shows no significant change in fluorescence color within the pH range of 2-13, and can be used as an internal reference signal to eliminate interference from ambient light fluctuations; the cyan-green fluorescent nanofiber gradually transitions from cyan-green to blue within the pH range of 8-13; the red fluorescent nanofiber exhibits a two-stage response within the pH range of 2-13, transitioning from red to cyan-green and then gradually to blue. By adjusting the mixing ratio of the three nanofibers and the pH, a color gradient change that can be observed by the naked eye can be presented. Through internal reference calibration, multi-signal synergistic feedback, and visualization output, the problem of narrow detection range of existing single fluorescent sensors is solved.

[0023] (3) This invention uses only soybean peptides as reducing ligands, which breaks through the inherent limitations of heterogeneous systems and eliminates the compatibility barrier of heterogeneous interfaces.

[0024] (4) The present invention uses cellulose nanofibers containing lignin as a carrier to avoid the agglomeration of gold nanoclusters in the subsequent reduction, which would cause uneven nanocluster size, and at the same time avoid fluorescence quenching caused by gold nanocluster agglomeration.

[0025] (5) The present invention uses biomass materials cellulose nanofibers and soybean peptides as raw materials, which have the triple functions of reducing agent, stabilizer and functional template. Compared with the traditional toxic reagent synthesis process, it is simple, environmentally friendly and low cost. Attached Figure Description

[0026] Figure 1 The fluorescence spectra of the three fluorescent nanofibers prepared in Example 1 are shown. The emission wavelengths of the blue fluorescent nanofiber (BLUE-CNC), the cyan-green fluorescent nanofiber (GREEN-CNC), and the red fluorescent nanofiber (RED-CNC) are 450-480 nm (blue), 495-515 nm (cyan-green), and 600-630 nm (red), respectively. Detailed Implementation

[0027] The present invention will be described in more detail below through specific embodiments, which are intended to explain the invention and not to limit it.

[0028] All reagents and materials used in the following examples were commercially available. The lignin-containing cellulose nanofiber dispersion (L-CNC) used in Examples 1-3 was purchased from Tianjin Wood Elf Biotechnology Co., Ltd., wherein the mass percentage of lignin was 35% and the mass percentage of cellulose nanofiber was 3%.

[0029] Example 1

[0030] The preparation method of a pH-responsive multi-band fluorescent nanofiber sensor in this embodiment is as follows:

[0031] S1. Preparation of cellulose nanofiber functional matrix solution: 15 mL of L-CNC was added to 30 mL of 10 mM chloroauric acid aqueous solution under nitrogen protection to obtain cellulose nanofiber functional matrix solution.

[0032] S2. Preparation of multicolor fluorescent nanofibers:

[0033] a) Preparation of blue fluorescent nanofibers: 0.675 g of soybean peptide powder was dissolved in 15 mL of deionized water, and a clear soybean peptide solution was formed by ultrasonic-assisted dissolution. This solution was then mixed with 15 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH of the mixture was adjusted to 13 with NaOH. A near-infrared laser (808 nm, 2...) was then used to analyze the solution. Irradiation was used to raise the temperature of the reaction system to 70 °C and react for 12 h.

[0034] b) Preparation of bluish-green fluorescent nanofibers: 0.75 g of soybean peptide powder was dissolved in 15 mL of deionized water, and the solution was dissolved by ultrasonication to form a clear soybean peptide solution. This solution was then mixed with 15 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH was adjusted to 9 with NaOH, and the solution was then analyzed using a near-infrared laser (808 nm, 1...). Irradiation was used to raise the temperature of the reaction system to 60 °C and react for 6 h.

[0035] c) Preparation of red fluorescent nanofibers: 1.35 g of soybean peptide powder was dissolved in 15 mL of deionized water, and the solution was dissolved by ultrasonic assistance to form a clear soybean peptide solution. This solution was then mixed with 15 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH was adjusted to 2 with HCl, and the solution was then analyzed using a near-infrared laser (808 nm, 1...). Irradiation was used to raise the temperature of the reaction system to 60 °C and react for 6 h.

[0036] S3. Purification of fluorescent nanofibers: After the reaction solution in step S2 was cooled to room temperature, it was subjected to ultrafiltration centrifugation (centrifuge tubes with molecular weight cutoffs of 5 kD, 5 kD, and 1 kD, rotation speed of 10,000 rpm, and time of 15 min) to remove unreacted substances and other impurities, and purified dispersions A, B, and C were obtained respectively.

[0037] S4. The purified dispersions A, B, and C are mixed in a volume ratio of 1:5:10 and ultrasonically dispersed (40kHz, 300W) to form a uniform suspension. The suspension is then allowed to stand for 24 h to complete the self-assembly of the hydrogen bond network, thus obtaining the pH-responsive multi-band fluorescent nanofiber sensor.

[0038] The performance tests and results are as follows:

[0039] The pH value of the pH-responsive multi-band fluorescent nanofiber sensor prepared in this example was adjusted using HCl or NaOH. When the pH value was 2, 3, 4, 5, and 6, the sensor showed pink fluorescence; when the pH value was 7, 8, and 9, the sensor showed blue-green fluorescence; and when the pH value was 10, 11, 12, and 13, the sensor showed bright blue fluorescence.

[0040] As can be seen, the pH-responsive multiband fluorescent nanofiber sensor prepared in this embodiment exhibits pink fluorescence under acidic conditions (pH 2-6), blue-green fluorescence under neutral and weakly alkaline conditions (pH 7-9), and bright blue fluorescence under strongly alkaline conditions (pH 10-13). The pH-responsive multiband fluorescent nanofiber sensor of this embodiment is suitable for wide-range pH detection.

[0041] Example 2

[0042] The preparation method of a pH-responsive multi-band fluorescent nanofiber sensor in this embodiment is as follows:

[0043] S1. Preparation of cellulose nanofiber functional matrix solution: 15 mL of L-CNC was added to 24 mL of 10 mM chloroauric acid aqueous solution under nitrogen protection to obtain cellulose nanofiber functional matrix solution.

[0044] S2. Preparation of multicolor fluorescent nanofibers:

[0045] a) Preparation of blue fluorescent nanofibers: 1.2 g of soybean peptide powder was dissolved in 24 mL of deionized water, and a clear soybean peptide solution was formed by ultrasonic-assisted dissolution. This solution was then mixed with 13 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH of the mixture was adjusted to 12 with NaOH. A near-infrared laser (808 nm, 2...) was then used to analyze the solution. Irradiation was used to raise the temperature of the reaction system to 75 °C and react for 11 h.

[0046] b) Preparation of bluish-green fluorescent nanofibers: 0.96 g of soybean peptide powder was dissolved in 24 mL of deionized water, and a clear soybean peptide solution was formed by ultrasonic-assisted dissolution. This solution was then mixed with 13 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH was adjusted to 8 with NaOH, and the solution was then analyzed using a near-infrared laser (808 nm, 1...). Irradiation was used to raise the temperature of the reaction system to 55 °C and react for 7 h.

[0047] c) Preparation of red fluorescent nanofibers: 1.92 g of soybean peptide powder was dissolved in 24 mL of deionized water, and a clear soybean peptide solution was formed by ultrasonic-assisted dissolution. This solution was then mixed with 13 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH was adjusted to 4 with HCl, and the solution was then analyzed using a near-infrared laser (808 nm, 1...). Irradiation was used to raise the temperature of the reaction system to 55 °C and react for 7 h.

[0048] S3. Purification of fluorescent nanofibers: After the reaction solution in step S2 was cooled to room temperature, it was subjected to ultrafiltration centrifugation (centrifuge tubes with molecular weight cutoffs of 5 kD, 5 kD, and 1 kD, rotation speed of 10,000 rpm, and time of 15 min) to remove unreacted substances and other impurities, and purified dispersions A, B, and C were obtained respectively.

[0049] S4. The purified dispersions A, B, and C are mixed at a volume ratio of 1:20:1 and ultrasonically dispersed (40kHz, 300W) to form a uniform suspension. The suspension is then allowed to stand for 24 h to complete the self-assembly of the hydrogen bond network, thus obtaining the pH-responsive multi-band fluorescent nanofiber sensor.

[0050] The performance tests and results are as follows:

[0051] The pH value of the pH-responsive multi-band fluorescent nanofiber sensor prepared in this example was adjusted using HCl or NaOH. When the pH value was 2, 3, 4, 5, and 6, the sensor showed a bluish-green (whitish) fluorescence; when the pH value was 7, 8, and 9, the sensor showed a blue-green fluorescence; and when the pH value was 10, 11, 12, and 13, the sensor showed a blue fluorescence.

[0052] As can be seen, the pH-responsive multiband fluorescent nanofiber sensor prepared in this embodiment exhibits bluish-green (whitish) fluorescence under acidic conditions (pH 2-6), blue-green fluorescence under neutral and weakly alkaline conditions (pH 7-9), and blue fluorescence under strongly alkaline conditions (pH 10-13). The pH-responsive multiband fluorescent nanofiber sensor of this embodiment is suitable for wide-range pH detection.

[0053] Example 3

[0054] The preparation method of a pH-responsive multi-band fluorescent nanofiber sensor in this embodiment is as follows:

[0055] S1. Preparation of cellulose nanofiber functional matrix solution: 5 mL of L-CNC was added to 10 mL of 10 mM chloroauric acid aqueous solution under nitrogen protection to obtain cellulose nanofiber functional matrix solution.

[0056] S2. Preparation of multicolor fluorescent nanofibers:

[0057] a) Preparation of blue fluorescent nanofibers: 0.55 g of soybean peptide powder was dissolved in 10 mL of deionized water, and the solution was dissolved by ultrasonic assistance to form a clear solution. This solution was then mixed with 5 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH of the mixture was adjusted to 10 with NaOH. A near-infrared laser (808 nm, 2...) was used for the final mixing. Irradiation was used to raise the temperature of the reaction system to 80 ℃ and react for 10 h.

[0058] b) Preparation of bluish-green fluorescent nanofibers: 0.3 g of soybean peptide powder was dissolved in 10 mL of deionized water, and the solution was dissolved by ultrasonic assistance to form a clear solution. This solution was then mixed with 5 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH was adjusted to 7 with NaOH, and the solution was then analyzed using a near-infrared laser (808 nm, 1...). Irradiation was used to raise the temperature of the reaction system to 50 °C and react for 8 h.

[0059] c) Preparation of red fluorescent nanofibers: 0.7 g of soybean peptide powder was dissolved in 10 mL of deionized water, and the solution was dissolved by ultrasonic assistance to form a clear solution. This solution was then mixed with 5 mL of the cellulose nanofiber functional matrix solution obtained in step S1. Thorough mixing was achieved by isothermal oscillation. The pH was adjusted to 6 with HCl, and the solution was then analyzed using a near-infrared laser (808 nm, 1...). Irradiation was used to raise the temperature of the reaction system to 50 °C and react for 8 h.

[0060] S3. Purification of fluorescent nanofibers: After the reaction solution in step S2 was cooled to room temperature, it was subjected to ultrafiltration centrifugation (centrifuge tubes with molecular weight cutoffs of 5 kD, 5 kD, and 1 kD, rotation speed of 10,000 rpm, and time of 15 min) to remove unreacted substances and other impurities, and purified dispersions A, B, and C were obtained respectively.

[0061] S4. The purified dispersions A, B, and C are mixed in a volume ratio of 1:1:20 and ultrasonically dispersed (40kHz, 300W) to form a uniform suspension. The suspension is then allowed to stand for 24 h to complete the self-assembly of the hydrogen bond network, thus obtaining the pH-responsive multi-band fluorescent nanofiber sensor.

[0062] The performance tests and results are as follows:

[0063] The pH value of the pH-responsive multi-band fluorescent nanofiber sensor prepared in this example was adjusted using HCl or NaOH. When the pH value was 2, 3, 4, 5, and 6, the sensor showed pink fluorescence; when the pH value was 7, 8, and 9, the sensor showed cyan-green fluorescence; and when the pH value was 10, 11, 12, and 13, the sensor showed bright blue fluorescence.

[0064] As can be seen, the pH-responsive multiband fluorescent nanofiber sensor prepared in this embodiment exhibits pink fluorescence under acidic conditions (pH 2-6), bluish-green fluorescence under neutral and weakly alkaline conditions (pH 7-9), and bright blue fluorescence under strongly alkaline conditions (pH 10-13). The pH-responsive multiband fluorescent nanofiber sensor of this embodiment is suitable for wide-range pH detection.

Claims

1. A pH-responsive multi-band fluorescent nanofiber sensor, characterized in that: The sensor is composed of a mixture of blue fluorescent nanofibers, cyan-green fluorescent nanofibers, and red fluorescent nanofibers. Under pH stimulation, the blue fluorescent nanofibers show no significant change in fluorescence color within the pH range of 2-13; the cyan-green fluorescent nanofibers gradually transition from cyan-green to blue within the pH range of 8-13; and the red fluorescent nanofibers exhibit a two-stage response within the pH range of 2-13, transitioning from red to cyan-green and then gradually to blue. The blue, cyan, and red fluorescent nanofibers were obtained by growing gold nanoclusters with three different fluorescence properties along lignin-containing cellulose nanofibers. The lignin-containing cellulose nanofibers were used as a carrier and mixed with chloroauric acid, which was then adsorbed by the nanofibers. A uniformly oriented gold ion-loaded layer is formed on the surface of nanofibers, and soybean peptides are added as ligands and reducing agents. Under near-infrared laser irradiation, lignin absorbs light and generates a local thermal field, which activates the reducing activity of soybean peptides. Soybean peptides are reduced to form gold cores. By adjusting the pH of the reaction, the indole ring of tryptophan and the phenolic hydroxyl group of tyrosine in soybean peptide molecules combine with the gold core to form a core-shell structure, resulting in blue fluorescent nanofibers with gold nanoclusters growing along nanofibers. The imidazole ring of histidine in soybean peptide molecules combines with the gold core to form a core-shell structure, resulting in greenish-blue fluorescent nanofibers with gold nanoclusters growing along nanofibers. The breaking of the disulfide bond of cysteine ​​in soybean peptide molecules exposes thiol groups, which combine with the gold core to form a core-shell structure, resulting in red fluorescent nanofibers with gold nanoclusters growing along cellulose nanofibers.

2. A method for preparing a pH-responsive multi-band fluorescent nanofiber sensor, characterized in that, Includes the following steps: S1. Preparation of blue fluorescent nanofibers: A lignin-containing cellulose nanofiber dispersion was added to a chloroauric acid aqueous solution under nitrogen protection and mixed, and then mixed with a soybean peptide solution; the pH was adjusted to 10-13, and the reaction system temperature was raised to 70 ℃-80 ℃ by near-infrared laser irradiation and the reaction was carried out for 10-12 h to obtain a blue fluorescent nanofiber dispersion in which gold nanoclusters grow along the nanofibers; S2. Preparation of bluish-green fluorescent nanofibers: Lignin-containing cellulose nanofibers were added to a chloroauric acid aqueous solution under nitrogen protection and mixed, and then mixed with soybean peptide solution; the pH was adjusted to 7-9, and the reaction system temperature was raised to 50 ℃-60 ℃ by near-infrared laser irradiation for 6-8 h to obtain a bluish-green fluorescent nanofiber dispersion in which gold nanoclusters grow along the nanofibers. S3. Preparation of red fluorescent nanofibers: lignin-containing cellulose nanofibers were added to a chloroauric acid aqueous solution under nitrogen protection and mixed, and then mixed with soybean peptide solution; the pH was adjusted to 2-6, and the reaction system temperature was raised to 50 ℃-60 ℃ by near-infrared laser irradiation for 6-8 h to obtain a red fluorescent nanofiber dispersion in which gold nanoclusters grow along the nanofibers. S4. Preparation of pH-responsive multi-band fluorescent nanofiber sensor: The blue fluorescent nanofiber dispersion obtained in step S1, the cyan-green fluorescent nanofiber dispersion obtained in step S2, and the red fluorescent nanofiber dispersion obtained in step S3 are mixed at a volume ratio of 1:1-20:1-20 to obtain the pH-responsive multi-band fluorescent nanofiber sensor.

3. The method for preparing a pH-responsive multi-band fluorescent nanofiber sensor according to claim 2, characterized in that: In step S1, the concentration of the chloroauric acid aqueous solution is 10 mM, the concentration of the soybean peptide solution is 45-90 mg / mL, and the volume ratio of the chloroauric acid aqueous solution to the soybean peptide solution is 1:

3.

4. The method for preparing a pH-responsive multi-band fluorescent nanofiber sensor according to claim 2, characterized in that: In step S2, the concentration of the chloroauric acid aqueous solution is 10 mM, the concentration of the soybean peptide solution is 40-80 mg / mL, and the volume ratio of the chloroauric acid aqueous solution to the soybean peptide solution is 1:

3.

5. The method for preparing a pH-responsive multi-band fluorescent nanofiber sensor according to claim 2, characterized in that: In step S3, the concentration of the chloroauric acid aqueous solution is 10 mM, the concentration of the soybean peptide solution is 30-70 mg / mL, and the volume ratio of the chloroauric acid aqueous solution to the soybean peptide solution is 1:

3.

6. The method for preparing a pH-responsive multi-band fluorescent nanofiber sensor according to claim 2, characterized in that: In step S1, the wavelength of the near-infrared laser is 808 nm, and the power density is 2. .

7. The method for preparing a pH-responsive multi-band fluorescent nanofiber sensor according to claim 2, characterized in that: In step S2, the wavelength of the near-infrared laser is 808 nm, and the power density is 1. .

8. The method for preparing a pH-responsive multi-band fluorescent nanofiber sensor according to claim 2, characterized in that: In step S3, the wavelength of the near-infrared laser is 808 nm, and the power density is 1. .

9. The application of the pH-responsive multi-band fluorescent nanofiber sensor according to claim 1 or the pH-responsive multi-band fluorescent nanofiber sensor prepared by the preparation method according to any one of claims 2-8 in pH detection.

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