CN108240976B - Fluorescence analysis method for detecting dopamine by using double-emission-ratio fluorescent quantum dot probe - Google Patents
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Abstract
The invention relates to a fluorescence analysis method for detecting dopamine by using a double-emission-ratio fluorescent quantum dot probeDA as the response signal of ratiometric fluorescent probe, r-QDs @ SiO2As a stable internal standard of a fluorescent probe, then the PDA and the r-QDs @ SiO2The double emission ratio fluorescence sensor was assembled, and the concentration of dopamine was detected by the double emission ratio fluorescence analysis method.
Description
Technical Field
The invention relates to a fluorescence analysis method for detecting dopamine by using a double-emission-ratio fluorescent quantum dot probe, belonging to the technical field of preparation of environment functional materials.
Background
Dopamine (DA) is a catecholamine neurotransmitter, which is secreted by the human central nervous system, often found in the central nervous, hormonal and cardiovascular systems, and plays an important role in human behavioral responses and brain functions, such as sensory and neuro-information transmission. The abnormal concentration of dopamine in a biological system can cause a series of neurological diseases and cause great harm to human health. It is common that hypersecretion of dopamine causes failure of energy metabolism and sudden neurological death in the human body; the lack of dopamine secretion can lead to the body to lose control of muscles, and the attention of the body cannot be focused even on the Parkinson's disease. Therefore, in recent years, a method for detecting the concentration of dopamine has become a research hotspot of researchers.
In recent years, common dopamine detection methods include electrochemical detection, ultraviolet-visible spectrum detection, high performance liquid chromatography and fluorescence probe methods (organic dyes and quantum dots), but the methods have certain limitations, such as complex preparation process, complicated instrument procedures, use of organic solvents and toxic substances, and the like, so that development of a simple, non-toxic, low-cost and efficient detection method is very necessary.
Fluorescence is now of interest to many researchers due to its simple process and low cost. The ratio fluorescence detection method is one of the methods, compared with the traditional fluorescence method, the ratio fluorescence detection method is more direct and has more obvious visual detection effect, the ratio fluorescence detection means that the ratio of two fluorescence emission intensities changes along with the change of a target analyte, and the visual change is very obvious after the action of a trace target object and is easy to distinguish. One outstanding advantage of ratiometric fluorescence detection is that the range of dynamic response is increased by the change in intensity ratio, and by establishing an internal standard, interference from other factors is greatly reduced, and quantitative detection of target analytes is achieved. The fluorescent nanoparticles in such fluorescent compositions are generally classified into two categories, inorganic fluorescent nanoparticles (FINs) and organic fluorescent nanoparticles (FONs). The inorganic fluorescent nanoparticles are quantum dots serving as fluorescent substances, and the Quantum Dots (QDs) are novel luminescent nano materials, have the characteristics of wide excitation range, narrow emission peak position, high luminous efficiency, adjustable peak position and the like, and are ideal fluorescent probes. Quantum Dots (QDs), i.e., semiconductor nanocrystals with a radius less than or close to the exciton bohr radius, spherical or nearly spherical nanoparticles with a size in the range of 1-10nm, which are aggregates of atoms and molecules on the nanometer scale. When the size of three dimensions is reduced below the critical size, the energy is fully quantized, so that the quantum dots are called as quantum dots, and have good fluorescence, so that the quantum dots are widely applied to target object detection in the biological field and other fields. However, many inorganic nanoparticles are not degradable and harmful to organisms, so that how to overcome this difficulty in the aspect of inorganic fluorescent nanoparticles becomes a hot point of research for many researchers. The organic fluorescent material is regarded as having good prospects in the aspects of biodegradability, biocompatibility and modifiability, but still has many problems, such as complex preparation, long time consumption and certain toxicity of raw materials.
In recent years, a number of articles have reported a novel dopamine assay for determining the concentration of poly-dopamine (PDA) oxidatively synthesized under alkaline conditions by measuring its light absorption, which is rapid and straightforward and inexpensive. Dopamine is reported to self-polymerize into poly-dopamine under alkaline conditions and to deposit on the surface of various substances, much like natural melanin polymers. These reports share the same thing, and all measure the concentration of DA by measuring the light absorption of the oxidized synthesis product using an oxidizing agent as a reagent.
According to the inspiration of the above article, poly dopamine fluorescence particles with green fluorescence are used as response signals for detecting dopamine, silicon dioxide nano silicon spheres are used for embedding red cadmium telluride quantum dots (r-QDs @ SiO2) as internal standards of a dual emission ratio fluorescence probe, so that the internal standards do not cause any harm or pollution and provide color background for visual detection, and green fluorescence dopamine particles with different depths can be generated according to different concentrations of dopamine to perform fluorescence detection on the concentration of dopamine by a dual emission ratio fluorescence method.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provides a fluorescence analysis method for detecting dopamine by using a double-emission ratio fluorescence quantum dot probe.
The technical scheme adopted by the invention is as follows:
a fluorescence assay method using a dual emission ratio fluorescent quantum dot probe for the detection of dopamine, the method comprising the steps of:
(1) adding sodium borohydride (NaBH4) and tellurium powder into a centrifuge tube, pricking a small hole on a centrifuge tube cover by using a needle to discharge excessive hydrogen in the reaction, and then adding 1-2mL of secondary distilled water to completely dissolve the solid; placing the centrifugal tube in an ultrasonic machine for ultrasonic reaction, wherein the final white transparent liquid is the required precursor NaHTe solution;
(2) injecting the precursor NaHTe solution obtained in the step (1) into a hydrated cadmium chloride (CdCl2 & 2.5H2O) aqueous solution in the presence of thioglycolic acid (TGA) which is subjected to nitrogen introduction and oxygen removal under the condition of nitrogen introduction and oxygen removal, and carrying out reflux reaction on the mixed solution under the condition of nitrogen protection to obtain the required red fluorescent quantum dot;
(3) adding the red fluorescent quantum dots obtained in the step (2) into a mixed solution of n-hexanol, cyclohexane and Triton X-100, stirring uniformly, adding tetraethyl orthosilicate, continuing stirring, then adding ammonia water, reacting at room temperature to prepare silicon dioxide nanospheres (r-QDs @ SiO2) embedding the red fluorescent quantum dots, finally adding 2-3mL of acetone for demulsification, centrifuging, removing supernatant, washing for several times, and drying to obtain r-QDs @ SiO2 without impurities;
(4) respectively mixing 10g/L of polyethyleneimine solution with dopamine solutions with different concentrations, standing at room temperature to obtain polydopamine fluorescent nanoparticles with different dark and light green fluorescence, recording the growth time of the polydopamine fluorescent nanoparticles, and putting the polydopamine fluorescent nanoparticles obtained by reaction into a dialysis bag for dialysis to obtain pure polydopamine fluorescent nanoparticles;
(5) adjusting the pH value of the polydopamine fluorescent nanoparticle solution obtained in the step (4) to 7.0 by using 0.1M dilute hydrochloric acid solution, respectively adding the r-QDs @ SiO2 obtained in the step (3) to obtain a dual-emission ratio fluorescent probe, directly detecting the fluorescence intensity of the dual-emission ratio fluorescent probe, obtaining a linear relation graph of the dopamine concentration and the fluorescence intensity of the dual-emission ratio fluorescent probe through linear fitting, and detecting the dopamine concentration in an unknown sample according to the linear relation graph.
Wherein the molar ratio of the sodium borohydride to the tellurium powder in the step (1) is 4-6: 1.
wherein the pH of the CdCl2 & 2.5H2O aqueous solution added with thioglycolic acid (TGA) in the step (2) is 10.5-11.5; wherein the mole ratio of CdCl2 & 2.5H2O, TGA and NaHTe is 1: 2.0-2.5: 0.4-0.6, wherein the molar weight of the NaHTe is obtained according to the molar weight of the tellurium powder in the step (1); the reflux reaction temperature is 100-130 ℃.
Wherein the volume ratio of the red fluorescent quantum dot solution, the hexanol, the cyclohexane and the triton X-100 in the step (3) is 1:4-6:18-20: 4-6; the volume ratio of the added tetraethyl orthosilicate to the ammonia water to the quantum dots is 15-30: 1; the stirring time is 2-3 hours; the reaction time is 20-28 hours.
Wherein the mass-to-volume ratio of the silicon oxide nanospheres embedding the red fluorescent quantum dots to the green fluorescent poly-dopamine fluorescent nanoparticles in the step (5) is 6-10 mg: 100-.
The invention has the technical advantages that: the method takes red fluorescent cadmium telluride quantum dots synthesized by water phase as optical materials, utilizes the hydrolysis of tetraethyl orthosilicate to embed the optical materials, protects the optical materials and forms an internal standard material, and on the basis, green polydopamine fluorescent nanoparticles are mixed to form the dual-emission ratio type fluorescent probe. The internal red fluorescent quantum dots are protected by the silicon oxide, the influence of external factors is little, the fluorescence intensity is basically unchanged, and the external green fluorescent polydopamine nanoparticles are in a growth state due to the polyethyleneimine and the dopamine. The color of the solution gradually changes from colorless to green, dopamine solutions with different concentrations and polyethyleneimine with the same concentration can generate polydopamine fluorescent nanoparticles with different shades and greens, and after r-QDs @ SiO2 is added, the color of the solution gradually changes from red to green according to the concentration of the dopamine from low to high, so that visual detection of the dopamine is realized. Therefore, the quantum dot dual-emission ratio type fluorescent probe obtained by the invention has good optical performance and the capability of realizing visual and rapid detection of the dopamine content.
Drawings
FIG. 1 is a flow chart of the preparation of CdTeQDs.
FIG. 2a is a transmission electron micrograph of the polydopamine fluorescent nanoparticles (A), and FIG. 2B is a transmission electron micrograph of r-QDs @ SiO2 (B).
FIG. 3 is an infrared spectrum of dopamine (a) and polydopamine (b).
FIG. 4 is a diagram showing the synthesis process and reaction mechanism of r-QDs @ SiO 2-PDA.
FIG. 5a is a graph of the fluorescence spectrum of PDA; FIG. 5b is a graph showing the fluorescence spectrum of r-QDs @ SiO 2; FIG. 5c is a graph showing the fluorescence spectrum of r-QDs @ SiO 2-PDA.
FIG. 6 is a graph of response time for PDA.
FIG. 7a is a graph of the change in fluorescence intensity of a dual emission ratio fluorescent probe with increasing dopamine concentration;
FIG. 7b is a graph showing the change in fluorescence intensity of PDA that fluoresces green with increasing dopamine concentration.
Detailed Description
The invention is further illustrated by the following examples.
Example 1:
(1) adding 60.6mg of sodium borohydride (NaBH4) and 51.04mg of tellurium powder into a centrifuge tube, pricking a small hole on the centrifuge tube cover by using a needle to discharge excessive hydrogen in the reaction, and then adding 1.5mL of secondary distilled water to completely dissolve the solid; and placing the centrifugal tube in an ultrasonic machine for ultrasonic reaction for 2 hours, wherein the final white transparent liquid is the required precursor NaHTe solution.
(2) Injecting the precursor NaHTe solution obtained in the step (1) into aqueous solution of cadmium chloride hydrate (CdCl 2.2.5H 2O) in the presence of 138.5 mu L thioglycolic acid (TGA) subjected to nitrogen introduction and oxygen removal under the condition of nitrogen introduction and oxygen removal, adding CdCl 2.2.5 H2O228.34mg, and carrying out reflux reaction on the mixed solution at 120 ℃ for 85H under the condition of nitrogen protection to obtain the required red fluorescent quantum dot.
(3) Adding 800 mu L of red fluorescent quantum dots obtained in the step (2) into a mixed solution of 3.2mL of n-hexanol, 14.4mL of cyclohexane and 3.2mL of Triton X-100, stirring uniformly, adding 1.2mL of tetraethyl orthosilicate, continuing stirring, then adding 1.2mL of ammonia water, reacting at room temperature for 20h to prepare r-QDs @ SiO2, finally adding 2mL of acetone for demulsification, centrifuging, removing a supernatant, washing for several times, and drying to obtain the r-QDs @ SiO2 without impurities.
(4) Mixing 10g/L of polyethyleneimine solution with 10-80 mu M of dopamine solution, standing at room temperature for 3h to obtain polydopamine fluorescent nanoparticles with different shades of green fluorescence, recording the growth process of the polydopamine fluorescent nanoparticles, and putting the polydopamine particles obtained by reaction into a dialysis bag for dialysis for 24h to obtain pure polydopamine fluorescent nanoparticles.
(5) And (3) adjusting the pH of the polydopamine fluorescence nanoparticle solution obtained in the step (4) to 7.0 by using a 0.1M dilute hydrochloric acid solution, respectively adding 6mg of r-QDs @ SiO2 obtained in the step (3) to obtain a dual-emission ratio fluorescence probe, directly detecting the fluorescence intensity of the dual-emission ratio fluorescence probe, obtaining a linear relation graph of the dopamine concentration and the fluorescence intensity of the dual-ratio fluorescence probe through linear fitting, and further detecting the dopamine concentration in an unknown sample according to the linear relation graph.
Wherein the molar ratio of the sodium borohydride to the tellurium powder in the step (1) is 4: 1.
wherein the pH of the CdCl 2.2.5H 2O aqueous solution added with thioglycolic acid (TGA) in the step (2) is 10.5; wherein the mole ratio of CdCl2 & 2.5H2O, TGA and NaHTe is 1: 2.0: 0.4, wherein the molar weight of the NaHTe is obtained according to the molar weight of the tellurium powder in the step (1); the reflux reaction temperature was 120 ℃.
Wherein the volume ratio of the red fluorescent quantum dot solution, the hexanol, the cyclohexane and the triton X-100 in the step (3) is 1:4:18: 4; the volume ratio of the added tetraethyl orthosilicate to the ammonia water to the quantum dots is 15:15: 1; the stirring time is 2 hours; the reaction time was 20 hours.
Wherein the mass-to-concentration ratio of the silicon oxide nanoparticles embedding the red fluorescent quantum dots to the dopamine solution in the step (5) is 6 mg: 10-80 μ M.
Example 2:
(1) adding 75.7mg of sodium borohydride (NaBH4) and 51.04mg of tellurium powder into a centrifuge tube, pricking a small hole on the centrifuge tube cover by using a needle to discharge excessive hydrogen in the reaction, and then adding 1.5mL of secondary distilled water to completely dissolve the solid; and placing the centrifugal tube in an ultrasonic machine for ultrasonic reaction for 2 hours, wherein the final white transparent liquid is the required precursor NaHTe solution.
(2) Injecting the precursor NaHTe solution obtained in the step (1) into aqueous solution of cadmium chloride hydrate (CdCl 2.2.5H 2O) in the presence of 115.44 mu L thioglycolic acid (TGA) which is subjected to nitrogen and oxygen introduction and removal under the condition of nitrogen introduction and oxygen removal, adding CdCl 2.2.5H 2O152.23mg, and carrying out reflux reaction on the mixed solution at 120 ℃ for 85H under the condition of nitrogen protection to obtain the required red fluorescent quantum dot.
(3) Adding 800 mu L of red fluorescent quantum dots obtained in the step (2) into a mixed solution of 4.0mL of n-hexanol, 15.2mL of cyclohexane and 4.0mL of Triton X-100, stirring uniformly, adding 1.6mL of tetraethyl orthosilicate, continuing stirring, then adding 1.6mL of ammonia water, reacting at room temperature for 24h to prepare r-QDs @ SiO2, finally adding 2.5mL of acetone for demulsification, centrifuging, removing a supernatant, washing for several times, and drying to obtain the r-QDs @ SiO2 without impurities.
(4) Mixing 10g/L of polyethyleneimine solution with 10-80 mu M of dopamine solution respectively, standing at room temperature for 3h to obtain polydopamine fluorescent nanoparticles with different shades of green fluorescence, recording the growth process of the polydopamine fluorescent nanoparticles, and putting the polydopamine particles obtained by reaction into a dialysis bag for dialysis to obtain pure polydopamine fluorescent nanoparticles.
(5) And (3) adjusting the pH of the polydopamine fluorescence nanoparticle solution obtained in the step (4) to 7.0 by using a 0.1M dilute hydrochloric acid solution, respectively adding 8mg of r-QDs @ SiO2 obtained in the step (3) to obtain a dual-emission ratio fluorescence probe, directly detecting the fluorescence intensity of the dual-emission ratio fluorescence probe, obtaining a linear relation graph of the dopamine concentration and the fluorescence intensity of the dual-ratio fluorescence probe through linear fitting, and further detecting the dopamine concentration in an unknown sample according to the linear relation graph.
Wherein the molar ratio of the sodium borohydride to the tellurium powder in the step (1) is 5: 1.
wherein the pH of the CdCl 2.2.5H 2O aqueous solution added with thioglycolic acid (TGA) in the step (2) is 11.5; wherein the mole ratio of CdCl2 & 2.5H2O, TGA and NaHTe is 1: 2.5: 0.6, wherein the molar weight of the NaHTe is obtained according to the molar weight of the tellurium powder in the step (1); the reflux reaction temperature was 120 ℃.
Wherein the volume ratio of the red fluorescent quantum dot solution, the hexanol, the cyclohexane and the triton X-100 in the step (3) is 1:5:19: 5; the volume ratio of the added tetraethyl orthosilicate to the ammonia water to the quantum dots is 20:20: 1; the stirring time is 3 hours; the reaction time was 24 hours.
Wherein the mass-to-concentration ratio of the silicon oxide nanoparticles embedding the red fluorescent quantum dots to the dopamine solution in the step (5) is 8 mg: 10-80 μ M.
Example 3:
(1) adding 90.9mg of sodium borohydride (NaBH4) and 51.04mg of tellurium powder into a centrifuge tube, pricking a small hole on the centrifuge tube cover by using a needle to discharge excessive hydrogen in the reaction, and then adding 1.5mL of secondary distilled water to completely dissolve the solid; and placing the centrifugal tube in an ultrasonic machine for ultrasonic reaction for 2 hours, wherein the final white transparent liquid is the required precursor NaHTe solution.
(2) Injecting the precursor NaHTe solution obtained in the step (1) into aqueous solution of cadmium chloride hydrate (CdCl 2.2.5H 2O) in the presence of 133 mu L thioglycolic acid (TGA) for nitrogen and oxygen introduction, adding CdCl 2.2.5H 2O182.67mg, and carrying out reflux reaction on the mixed solution at 130 ℃ for 72H under the condition of nitrogen protection to obtain the required red fluorescent quantum dot.
(3) Adding 800 mu L of red fluorescent quantum dots obtained in the step (2) into a mixed solution of 4.8mL of n-hexanol, 16.0mL of cyclohexane and 4.8mL of Triton X-100, stirring uniformly, adding 2.4mL of tetraethyl orthosilicate, continuing stirring, then adding 2.4mL of ammonia water, reacting at room temperature for 28h to prepare r-QDs @ SiO2, finally adding 3mL of acetone for demulsification, centrifuging, removing a supernatant, washing for several times, and drying to obtain the r-QDs @ SiO2 without impurities.
(4) Mixing 10g/L of polyethyleneimine solution with 10-80 mu M of dopamine solution respectively, standing at room temperature for 3h to obtain polydopamine fluorescent nanoparticles with different shades of green fluorescence, recording the growth process of the polydopamine fluorescent nanoparticles, and putting the polydopamine particles obtained by reaction into a dialysis bag for dialysis to obtain pure polydopamine fluorescent nanoparticles.
(5) And (3) adjusting the pH of the polydopamine fluorescence nanoparticle solution obtained in the step (4) to 7.0 by using a 0.1M dilute hydrochloric acid solution, respectively adding 10mg of r-QDs @ SiO2 obtained in the step (3) to obtain a dual-emission ratio fluorescence probe, directly detecting the fluorescence intensity of the dual-emission ratio fluorescence probe, obtaining a linear relation graph of the dopamine concentration and the fluorescence intensity of the dual-ratio fluorescence probe through linear fitting, and further detecting the dopamine concentration in an unknown sample according to the linear relation graph.
Wherein the molar ratio of the sodium borohydride to the tellurium powder in the step (1) is 6: 1.
wherein the pH of the CdCl 2.2.5H 2O aqueous solution added with thioglycolic acid (TGA) in the step (2) is 11.2; wherein the mole ratio of CdCl2 & 2.5H2O, TGA and NaHTe is 1: 2.4: 0.5, wherein the molar weight of the NaHTe is obtained according to the molar weight of the tellurium powder in the step (1); the reflux reaction temperature was 120 ℃.
Wherein the volume ratio of the red fluorescent quantum dot solution, the hexanol, the cyclohexane and the triton X-100 in the step (3) is 1:6:20: 6; the volume ratio of the added tetraethyl orthosilicate to the ammonia water to the quantum dots is 30:30: 1; the stirring time is 4 hours; the reaction time was 28 hours.
Wherein the mass-to-concentration ratio of the silicon oxide nanoparticles embedding the red fluorescent quantum dots to the dopamine solution in the step (5) is 10 mg: 10-80 μ M.
Test example 1: 50mgr-QDs @ SiO2 was added to a colorimetric tube containing 10mL of distilled water to form a solution, 10 to 80. mu.M of the dopamine solution was dissolved in a calibrated test tube containing 5mL of 10g/L polyethyleneimine solution, respectively, after standing for 3 hours, the solution in this test tube was adjusted to pH 7 with 0.1M of dilute hydrochloric acid solution, and then 200. mu.L of r-QDs @ SiO2 solution was added to the test tube in this order and mixed well. And then transferred to a quartz cuvette for fluorescence detection.
Fig. 1 is a flow chart of preparation of red fluorescent quantum dots.
As can be seen from the transmission electron micrograph of FIG. 2, both the PDA and the r-QDs @ SiO2 have good dispersibility, and the size of the r-QDs @ SiO2 is uniform.
Fig. 3 is an infrared spectrum of dopamine (a) and polydopamine (b). The successful synthesis of the polydopamine fluorescent nanoparticles can be seen by comparing the infrared spectrograms of dopamine and polydopamine.
Wherein, on the dopamine infrared spectrogram (a), the 1450-1600cm < -1 > shows an absorption peak which is a skeleton stretching vibration peak on a dopamine benzene ring. The absorption peak appearing at 1285cm-1 is the stretching vibration peak of the C-O bond of the phenolic hydroxyl group on the dopamine. The absorption peaks of 2954cm-1 and 3035cm-1 are the stretching vibration peaks of C-H bonds on dopamine. Compared with an infrared spectrum of dopamine, an amino stretching vibration peak appears at 1654cm < -1 > on the infrared spectrum (b) of polydopamine, and the stretching vibration peak of a benzene ring framework is weakened due to the appearance of the amino stretching vibration peak. Infrared analysis proves that the reaction of the polyethyleneimine and the dopamine occurs, and the polydopamine nano-particles are successfully prepared.
FIG. 4 is the experimental synthesis process and mechanism diagram of this experiment.
In fig. 5, a is a green fluorescent polydopamine particle, b is a silica sphere in which a red quantum dot is embedded, and c is a fluorescence spectrum of a mixed solution of the two.
FIG. 6 is a fluorescence spectrum of the polydopamine fluorescent nanoparticles at different growth times, from which we can determine that the growth time of polydopamine is 3 h.
FIG. 7a is a graph of fluorescence intensity for a two-ratio fluorescent probe as the concentration of dopamine increases, and FIG. 7b is a graph of fluorescence intensity for a monochromatic fluorescent probe as the concentration of dopamine increases.
The result shows that the double-emission-ratio fluorescent probe synthesized by the specification has good optical detection capability and visual detection effect on dopamine.
Claims (4)
1. A fluorescence analysis method for detecting dopamine by using a double-emission-ratio fluorescent quantum dot probe is characterized by comprising the following steps of: the method comprises the following steps:
(1) adding sodium borohydride and tellurium powder into a centrifuge tube, pricking a small hole on a centrifuge tube cover by using a needle to discharge excessive hydrogen in the reaction, and then adding 1-2mL of secondary distilled water to completely dissolve the solid; placing the centrifugal tube in an ultrasonic machine for ultrasonic reaction, wherein the final white transparent liquid is the required precursor NaHTe solution;
(2) injecting the precursor NaHTe solution obtained in the step (1) into a hydrated cadmium chloride aqueous solution which is subjected to nitrogen introduction and oxygen removal and has thioglycollic acid, and carrying out reflux reaction on the mixed solution under the condition of nitrogen protection to obtain the required red fluorescent quantum dot;
(3) adding the red fluorescent quantum dots obtained in the step (2) into a mixed solution of n-hexanol, cyclohexane and Triton X-100, stirring uniformly, adding tetraethyl orthosilicate, continuing stirring, then adding ammonia water, reacting at room temperature to prepare silicon dioxide nanospheres embedding the red fluorescent quantum dots, finally adding 2-3mL of acetone for demulsification, centrifuging, removing a supernatant, washing for several times, and drying to obtain r-QDs @ SiO2 without impurities;
(4) respectively mixing 10g/L of polyethyleneimine solution with dopamine solutions with different concentrations, standing at room temperature to obtain polydopamine fluorescent nanoparticles with different dark and light green fluorescence, recording the growth time of the polydopamine fluorescent nanoparticles, and putting the polydopamine fluorescent nanoparticles obtained by reaction into a dialysis bag for dialysis to obtain pure polydopamine fluorescent nanoparticles;
(5) adjusting the pH value of the polydopamine fluorescent nanoparticle solution obtained in the step (4) to 7.0 by using 0.1M dilute hydrochloric acid solution, respectively adding the r-QDs @ SiO2 obtained in the step (3) to obtain a dual-emission ratio fluorescent probe, directly detecting the fluorescence intensity of the dual-emission ratio fluorescent probe, obtaining a linear relation graph of the dopamine concentration and the fluorescence intensity of the dual-emission ratio fluorescent probe through linear fitting, and detecting the dopamine concentration in an unknown sample according to the linear relation graph.
2. The fluorescence analysis method for detecting dopamine by using the dual-emission-ratio fluorescent quantum dot probe according to claim 1, characterized in that: the molar ratio of the sodium borohydride to the tellurium powder in the step (1) is 4-6: 1.
3. the fluorescence analysis method for detecting dopamine by using the dual-emission-ratio fluorescent quantum dot probe according to claim 1, characterized in that: the pH value of the CdCl2 & 2.5H2O aqueous solution added with thioglycolic acid in the step (2) is 10.5-11.5; wherein the mole ratio of CdCl2 & 2.5H2O, TGA and NaHTe is 1: 2.0-2.5: 0.4-0.6, wherein the molar weight of the NaHTe is obtained according to the molar weight of the tellurium powder in the step (1); the reflux reaction temperature is 100-130 ℃.
4. The fluorescence analysis method for detecting dopamine by using the dual-emission-ratio fluorescent quantum dot probe according to claim 1, characterized in that: the volume ratio of the quantum dot solution, the hexanol, the cyclohexane and the triton X-100 in the step (3) is 1:4-6:18-20: 4-6; the volume ratio of the added tetraethyl orthosilicate to the added ammonia water to the red fluorescent quantum dot solution is 15-30: 1; the stirring time is 2-3 hours; the reaction time is 20-28 hours.
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