CN111504969B - Preparation method and application of fluorescent sensor based on carbon dot-quantum dot ratio - Google Patents

Preparation method and application of fluorescent sensor based on carbon dot-quantum dot ratio Download PDF

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CN111504969B
CN111504969B CN202010358457.5A CN202010358457A CN111504969B CN 111504969 B CN111504969 B CN 111504969B CN 202010358457 A CN202010358457 A CN 202010358457A CN 111504969 B CN111504969 B CN 111504969B
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付海燕
王硕
时琼
陈亨业
兰薇
佘远斌
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South Central Minzu University
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Abstract

The invention belongs to the technical field of nano material preparation, and particularly relates to a preparation method and application of a fluorescent sensor based on a carbon dot-quantum dot ratio. According to the invention, CdTe quantum dots wrapped by mercaptosuccinic acid and carbon dots doped with sulfur are mixed in a specific ratio to obtain the nano fluorescent sensor with high sensitivity and high specificity to silver ions. The ratiometric fluorescent sensor can be specifically combined with silver ions and generates a fluorescence quenching effect, and has the advantages of better stability, quicker response and lower detection limit. The preparation method has the advantages of simple process, environmental protection, low cost, easy popularization, industrial production and wide application prospect.

Description

Preparation method and application of fluorescent sensor based on carbon dot-quantum dot ratio
Technical Field
The invention belongs to the technical field of nano material preparation, and particularly relates to a preparation method and application of a fluorescent sensor based on a carbon dot-quantum dot ratio.
Background
Carbon dots are carbon-based zero-dimensional materials, and have been widely used in the fields of chemical analysis, environmental monitoring, medical imaging, energy development and the like due to their outstanding optical properties, biocompatibility, low cost, low toxicity and chemical inertness. At present, a plurality of methods for synthesizing carbon dots are available, such as an arc discharge method, a laser ablation method, an electrochemical synthesis method and the like, but the method for synthesizing the carbon dots by a hydrothermal method in a common laboratory has the advantages of simplicity in operation, high repeatability, environmental friendliness and the like. The quantum dot is a novel semiconductor nano material, has size effect, quantum confinement effect, macroscopic quantum tunneling effect, surface effect and the like, and shows different physicochemical properties due to the difference of the particle size and the appearance of the quantum dot. As a fluorescent material, the quantum dot has the advantages of wide absorption spectrum, narrow emission spectrum, high quantum yield and the like, and is often superior to the traditional organic fluorescent dye. The synthesis method of the quantum dots can be roughly divided into three categories, namely a microemulsion method, a thermal decomposition method and a hydrothermal method, the quantum dots are synthesized by the hydrothermal method in a common laboratory, the shape and the particle size of the quantum dots can be effectively controlled, and the method is environment-friendly. Silver ions have a broad-spectrum bactericidal effect, have a certain degree of killing effect on common bacteria and fungi in life, and are widely applied to the fields of medicine and daily necessities. Although silver ions are not bioaccumulating toxicants, silver ions in the human body can combine with amines, imidazoles, and carboxyl groups into various metabolite groups and even inactivate mercaptoenzymes, thereby inducing liver and kidney damage, stimulating eyes, skin, respiration, changing blood cells, and growth retardation in children. Traditional silver ion detection methods include Atomic Absorption Spectroscopy (AAS), X-ray spectroscopy (XRF), inductively coupled plasma atomic emission spectroscopy (IEP-AES), potentiometric titration, etc., but these methods have the disadvantages of expensive instruments, complex operation, time consumption, etc., are not acceptable by the people, and are difficult to popularize. According to the existing literature method, a new fluorescent sensor method for rapidly identifying silver ions based on carbon dots-quantum dots is not reported in the literature, so that a silver ion detection method which is better in stability, faster in response, lower in detection limit and suitable for industrial production needs to be established.
Disclosure of Invention
Based on the defects of the prior art, the invention aims to provide a preparation method and application of a fluorescent sensor based on a carbon dot-quantum dot ratio; according to the invention, CdTe quantum dots wrapped by mercaptosuccinic acid and carbon dots doped with sulfur are used as ratiometric fluorescent probes, and the carbon dots are mixed in a specific proportion to form the nano fluorescent sensor based on the carbon dots-quantum dots, the sensor can be specifically combined with silver ions to generate a fluorescence quenching effect, and the sensor has the advantages of better stability, quicker response and lower detection limit. The preparation method has the advantages of simple process, environmental protection, low cost, easy popularization and suitability for industrial production.
A preparation method of a fluorescent sensor based on a carbon dot-quantum dot ratio comprises the following steps:
(1) dissolving cadmium chloride and mercaptosuccinic acid in a proper amount of ultrapure water, adjusting the pH of the solution to 8.00 +/-0.10 by using sodium hydroxide, then introducing nitrogen and stirring in ice bath for a period of time (preferably 20 minutes); sequentially adding sodium tellurite and sodium borohydride, and uniformly stirring; transferring the clear solution into a reaction kettle, putting the reaction kettle into an oven with the temperature of 180-220 ℃ for reaction, taking out the reaction kettle after 40-60 minutes to obtain a CdTe quantum dot fluorescent probe which emits red light with the emission wavelength of 620-650 nm and emits blood under a 365nm ultraviolet lamp, wherein the particle size of the CdTe quantum dot fluorescent probe is 4 +/-0.5 nm;
(2) mixing concentrated sulfuric acid and mercaptosuccinic acid, refluxing for at least 2 hr (preferably 4 hr), cooling, adding the mixture into ultrapure water, and ice-bath; adding a small amount of organic solvent with the boiling point not higher than 50 ℃ into the reaction solution for many times, fully shaking, and distilling to remove the organic solvent; adding excessive ammonium hydroxide (the ammonium hydroxide preferably adopts ammonia water with the concentration of 20-30 wt%), standing for at least 36 hours (preferably 48 hours), performing vacuum drying (preferably at 60 ℃) to obtain light yellow solid powder, and re-dissolving the light yellow solid powder in ultrapure water to obtain sulfur element-doped carbon dots with the emission wavelength of 438 +/-1 nm, wherein the particle size of the sulfur element-doped carbon dots is 2 +/-0.5 nm;
(3) and (3) mixing the sulfur element-doped carbon dots obtained in the step (2) with the CdTe quantum dots wrapped by the mercaptosuccinic acid obtained in the step (1) to obtain a mixed solution, so as to obtain the carbon dot-quantum dot ratio fluorescence sensor with the double composite nano effect.
Furthermore, the ratio of the amounts of the cadmium chloride, the mercaptosuccinic acid and the sodium tellurite in the step (1) is 1.0 (1.2-1.5) to 0.2, and preferably, the emission wavelength of the CdTe quantum dot fluorescent probe in the step (1) is 630-645 nm.
Furthermore, the mass ratio of the cadmium chloride to the sodium borohydride in the step (1) is 1 (0.4-0.8).
Further, in the step (2), the concentrated sulfuric acid is 98 wt% sulfuric acid, and the ratio of the concentrated sulfuric acid to mercaptosuccinic acid is 1mL (2-4) mg.
Further, the organic solvent with the boiling point not higher than 50 ℃ is added in the step (2) for the purpose of retaining the carbon point precursor, and the organic solvent is dichloromethane, petroleum ether or diethyl ether.
Further, the concentration of the CdTe quantum dots wrapped by the mercaptosuccinic acid in the mixed solution obtained in the step (3) is 7.3 multiplied by 10-8～1.46×10-5mol·L-1The concentration of carbon dots doped with sulfur element is 3.3X 10-7～6.6×10-6g·L-1The mixed solution formed under the condition is stable, and the fluorescence intensity ratio is moderate (namely, the fluorescence intensity of the quantum dots and the carbon dots is about 1: 1).
The carbon dot-quantum dot ratio fluorescence sensor prepared by the preparation method is applied to rapid recognition of silver ions. Dissolving the carbon dot-quantum dot ratio fluorescence sensor in 0.1 mol/L solution with pH of 7.50-8.00-1PBSAnd (4) quantitatively detecting silver ions in the buffer solution.
Further, the carbon dot-quantum dot ratio fluorescence sensor detects silver ions by the following steps: to a 1.5mL cuvette, 100 μ L of the prepared carbon dot-quantum dot ratio fluorescence sensor was added, 800 μ LpH ═ 7.50 of 0.1mol · L-1And (3) uniformly mixing the PBS buffer solution, adding 100 mu L of unknown sample solution, setting the excitation wavelength to be 360nm, and performing fluorescence spectrum measurement at 380-695nm for 2 min. The obtained fluorescence intensity ratio F438/F640And regression curve F438/F640＝0.0013C(Ag+) And+ 0.7840, the corresponding silver ion concentration can be obtained.
The carbon dot-quantum dot ratio fluorescence sensor has the advantages of high sensitivity, good specificity and simple operation. The CdTe quantum dots wrapped by thioglycolic acid have gradually reduced fluorescence intensity along with the increase of the concentration of silver ions, and even are quenched to the end. The fluorescence intensity of the sulfur-doped carbon dots can not change along with the concentration of silver ions, and compared with the traditional single quantum dot fluorescence sensor, the carbon dot-quantum dot-based ratio fluorescence sensor has the advantages of higher stability, quicker response, lower limit of detection (LOD), and higher precision due to the fact that the interference of the background is reduced. LOD of the invention is 31.8 nmol.L-1The method is mainly applied to the detection of the silver ions in the environmental water sample and the drinking water, and can also be used for the detection of the silver ions in the human body and the like. The LOD of the Environmental Protection Agency (EPA) to the silver ion in the drinking water is 900 nmol.L-1WHO's specification for silver ions is 460 nmol.L-1. The method has lower LOD than that of EPA and WHO response.
The method is simple and rapid, has high repeatability and wide application prospect, and can be put into industrial production.
Drawings
Fig. 1 is a schematic diagram of a novel carbon dot-quantum dot fluorescent nano sensor for detecting silver ions in example 1.
Fig. 2 is a transmission electron microscope picture of CdTe and carbon dots wrapped by mercaptosuccinic acid in the novel carbon dot-quantum dot fluorescent nanosensor of example 1, both of which are nanosphere particles with particle diameters of 4 ± 0.5nm and 2 ± 0.5nm, respectively. (the left picture is quantum dot, the right picture is carbon dot)
FIG. 3: (a) the graph shows the mid-infrared spectra of carbon dots, quantum dots, and mixtures thereof in example 1, with wavelength on the abscissa and transmittance on the ordinate; (b) the figure shows the new carbon dot-quantum dot fluorescent nano-sensor and different concentrations of silver ions (0, 10, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650 nmol.L) in example 1-1) The horizontal axis represents wavelength and the vertical axis represents absorbance in the ultraviolet spectra before and after combination.
According to the intermediate infrared spectrogram, the surfaces of the quantum dots and the carbon dots are modified with rich oxygen-containing functional groups; according to the ultraviolet spectrogram, the ultraviolet spectrum of the carbon dot-quantum dot fluorescent nano sensor is not obviously changed after the carbon dot-quantum dot fluorescent nano sensor reacts with silver ions with different concentrations, which shows that the reaction of the carbon dot-quantum dot fluorescent nano sensor and the silver ions is possibly caused by electron transfer effect, and the form of the carbon dot-quantum dot is not damaged.
FIG. 4 shows fluorescence spectra before and after combining the novel carbon dot-quantum dot fluorescence nanosensor of example 1 with silver ions of different concentrations, with the abscissa as wavelength and the ordinate as fluorescence intensity, wherein F438Maximum fluorescence intensity, F, corresponding to the carbon point640The maximum fluorescence intensity corresponding to the quantum dots.
FIG. 5 shows the new carbon-quantum-dot fluorescence nano-sensor pair of high concentration silver ions (10) in example 1-5mol·L-1pH 7.50), the reaction was extremely sensitive and rapid, and was stable at 1 minute. A reaction time of 1 minute is a preferred condition.
FIG. 6 is a bar graph of response intensity of the novel carbon dot-quantum dot fluorescent nano-sensor in example 1 to silver ions with relatively low concentration and other 14 metal ions with relatively high concentration (where "texture" refers to the Mixture of the aforementioned 15 metal ions), and it can be seen from the graph that the carbon dot-quantum dot system has very strong response to silver ions with low concentration, has substantially no response to other metal ions with high concentration, and still does not detect the system after other metal ions are mixed with silver ionsThe interference is generated when the silver ions are detected, which shows that the novel carbon dot-quantum dot fluorescent nano sensor has strong specificity to the metal silver ions. (silver ion concentration 1X 10)-6mol·L-1The concentration of other metal ions is 1X 10-5mol·L-1The solutions were prepared with ultra pure water, pH 7.50, reaction time 1 min)
Fig. 7 is a graph of the linear result of the response of the novel carbon dot-quantum dot fluorescent nano-sensor in example 1 to silver ions in a certain concentration range, and the linear equation is as follows: f438/F640＝0.0013C(Ag+)+0.7840. (the linear range of silver ions is 10 to 650 nmol. L)-1pH 7.50, reaction time 1 min)
According to the triple noise method, the LOD 3 0.0138/0.0013 31.8nmol L is obtained by combining the slope of the linear equation-1。
FIG. 8 shows the new carbon-quantum-dot fluorescence nano-sensor pair of high concentration silver ions (10) in example 1-5mol·L-1) The graph shows that the reaction has very different intensities under different pH conditions, weak response under acidic conditions, strong response under neutral and alkaline conditions, and good condition at pH 7.50. Wherein F0And F1Respectively represent the fluorescence intensity of the quantum dots before and after the reaction. (reaction time 1 minute)
Detailed Description
The present invention will be described in further detail with reference to specific examples below so that those skilled in the art can more clearly understand the present invention. The following should not be construed as limiting the scope of the claimed invention.
The chemicals and solvents used in the examples were all analytical grade. The stirring mode adopts a magnetic stirrer. The fluorescence spectrum measurement conditions are that the emission wavelength is 380-695nm, the excitation wavelength is 360nm, and the slit width is 10 nm.
Example 1: the preparation method of the carbon dot-quantum dot-based nano fluorescence sensor is shown in a schematic diagram in figure 1, and comprises the following steps:
(1) synthesizing CdTe quantum dots wrapped by mercaptosuccinic acid:
cadmium chloride pentahydrate (0.1142g,12.5 mmol. multidot.L)-1The concentration of the substance in the solution after dissolution is the same as below) and mercaptosuccinic acid (0.0979g,16.3 mmol. multidot.L)-1) Dissolving the mixture in 40mL of ultrapure water, and stirring for 15 minutes at normal temperature and normal pressure to fully dissolve the mixture; adjusting the pH of the solution to 8.00 with sodium hydroxide, introducing nitrogen and stirring in ice bath for 20 minutes; sodium tellurite (0.0221g,2.5 mmol. multidot.L) was added-1) After stirring for 15 minutes, an appropriate amount of sodium borohydride (0.0113g,7.5 mmol. multidot.L) was added-1) Continuously stirring for 10 minutes; transferring the clear solution into a reaction kettle, putting the reaction kettle into a 200 ℃ oven for reaction, and taking out after 50 minutes. Cooling to room temperature to obtain the quantum dots with the concentration of 7.3 × 10 and capable of emitting red fluorescence under a 365nm ultraviolet lamp-6mol·L-1CdTe quantum dots.
(2) And (3) synthesizing sulfur-doped carbon dots:
5mL of concentrated sulfuric acid (98 wt%) and 15mg of mercaptosuccinic acid are mixed and refluxed for 4 hours, and after the reactant is cooled to room temperature, the reactant is poured into 20mL of ultrapure water and ice-cooled for 45-60 minutes by using ice cubes. Dichloromethane was added to the reaction in small portions, after each addition, shaking thoroughly to leave the carbon dot precursor in the organic phase, then the dichloromethane was removed by rotary evaporation, and a 25 wt% excess of concentrated ammonia (20mL) was added and allowed to stand for 48 hours. Vacuum drying at 60 deg.C to obtain light yellow solid (S-CDs), and re-dissolving in ultrapure water to obtain a solution with concentration of 6.6 × 10-6g·L-1。
(3) Preparing a carbon dot-quantum dot nano fluorescent sensor:
diluting the CdTe quantum dots wrapped by the mercaptosuccinic acid obtained in the step (1) by 2.5 times (namely 2.92 multiplied by 10) with ultrapure water- 6mol·L-1) Mixing with the sulfur-doped carbon dots obtained in the step (2) in an equal volume ratio, and shaking up to obtain the stable carbon dot-quantum dot nano fluorescent sensor (wherein the concentration of the CdTe quantum dots is 1.46 multiplied by 10)-6mol·L-1The concentration of carbon dots is 3.3X 10-6g·L-1) And putting the mixture into a refrigerator for refrigeration and standby.
In 1The 5mL cuvette was charged with 100 μ L of the carbon dot-quantum dot nanofluorescent sensor prepared in step (3), 900 μ L of 0.1mol · L with pH 7.50-1And (3) mixing the PBS buffer solution, reacting for 1 minute, and measuring the fluorescence intensity of the PBS buffer solution, wherein the fluorescence intensity of the carbon dots is 700-750 a.u., and the fluorescence intensity of the quantum dots is 900-1000 a.u.
Example 1 the CdTe quantum dots obtained in step (1) are different in pH of the solution compared to ZL201811395826.7 "method for detecting silver ions and serine using a paper chip based on CdTe quantum dots modified with mercaptosuccinic acid" in example 1, and the difference is that the pH of the solution is different, so that the combination form of the quantum dots and the groups is directly affected, and the quantum dots formed by combination in different forms have different physicochemical properties (color, fluorescence intensity, etc.).
Detecting silver ions by using the prepared carbon dot-quantum dot nano fluorescent sensor:
to a 1.5mL cuvette, 100 μ L of the carbon dot-quantum dot nanofluorescent sensor prepared in step (3) was added, 800 μ L of 0.1mol · L with pH of 7.50-1PBS buffer solution, 100. mu.L of silver ions of different concentrations (concentration of 10, 50, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650 nmol. L. respectively)-1Solutions were prepared with analytically pure silver nitrate, ultrapure water). The excitation wavelength is set to be 360nm, fluorescence spectrometry is carried out at 380-695nm, and the reaction time is 2min, as shown in FIG. 4. As the concentration of silver ions is increased, the fluorescence of the sulfur element doped carbon point at 438nm does not change, but the fluorescence of the mercaptosuccinic acid-coated CdTe at 640nm is gradually weakened and even quenched to the end, and the concentration range of the silver ions is 10 nmol.L-1～650nmol·L-1Has good linearity, R209998, as in fig. 7.
Silver ions with different concentrations are prepared by using human plasma, bovine serum, lake water and Longjing tea as solution matrixes (the pH value of the solution is adjusted to 7.50 by using a buffer solvent), and the silver ions are detected by using a carbon dot-quantum dot ratiometric fluorescent probe. Table 1 shows the labeling of the novel carbon dot-quantum dot fluorescence nano-sensor on silver ions in different substrate environments (Ag standard is 10 nmol. L prepared from analytically pure silver nitrate and ultrapure water)-1、350nmol·L-1And 650 nmol.L-1Silver nitrate solution), wherein human plasma and bovine serum stock solution are centrifuged at 10000r/min for 10 minutes to obtain supernatant, lake water is filtered through a 0.22 mu m microporous filter membrane to obtain filtrate, and Longjing tea is soaked in boiling water. As can be seen from the recovery rate result table, the recovery rate of the experiment is 96.2-102.0%, the recovery rate result is between 95-105%, and the result is better.
TABLE 1 Ag in real samples+Labeled recovery detection
Figure BDA0002474270760000071

Claims (7)

1. A preparation method of a fluorescent sensor based on a carbon dot-quantum dot ratio is characterized by comprising the following steps:
(1) synthesizing CdTe quantum dots wrapped by mercaptosuccinic acid:
dissolving cadmium chloride and mercaptosuccinic acid in ultrapure water, adjusting the pH of the solution to 8.00 +/-0.10, introducing nitrogen, stirring in an ice bath for a period of time, sequentially adding sodium tellurite and sodium borohydride, and uniformly stirring; transferring the clear solution into a reaction kettle, putting the reaction kettle into a 180-ion 220 ℃ oven for reaction for 40-60 minutes, and taking out the reaction kettle to obtain a CdTe quantum dot fluorescent probe which emits red light with the emission wavelength of 620-650 nm and emits blood under a 365nm ultraviolet lamp, wherein the particle size of the CdTe quantum dot fluorescent probe is 4 +/-0.5 nm;
(2) and (3) sulfur-doped carbon dot synthesis:
mixing concentrated sulfuric acid and mercaptosuccinic acid, refluxing for at least 2 hours, cooling, adding the mixture into ultrapure water, and carrying out ice bath; adding a small amount of organic solvent with the boiling point not higher than 50 ℃ into the reaction solution for many times, fully shaking, and distilling to remove the organic solvent; adding excessive ammonium hydroxide, standing for at least 36 hours, vacuum drying to obtain light yellow solid powder, and redissolving in ultrapure water to obtain sulfur element doped carbon dots with emission wavelength of 438 +/-1 nm, wherein the particle size of the carbon dots is 2 +/-0.5 nm;
(3) preparing a carbon dot-quantum dot ratio fluorescence sensor:
mixing the sulfur-doped carbon dots obtained in the step (2) with CdTe quantum dots wrapped by mercaptosuccinic acid obtained in the step (1) to obtain a mixed solution, thereby obtaining the carbon dot-quantum dot ratio fluorescence sensor with the double composite nano effect;
the mass ratio of the cadmium chloride, the mercaptosuccinic acid and the sodium tellurite in the step (1) is 1.0 (1.2-1.5) to 0.2; the mass ratio of the cadmium chloride to the sodium borohydride in the step (1) is 1 (0.4-0.8);
in the step (2), the concentrated sulfuric acid is 98 wt% sulfuric acid, and the ratio of the concentrated sulfuric acid to mercaptosuccinic acid is 1mL (2-4) mg.
2. The preparation method according to claim 1, wherein the concentration of the mercaptosuccinic acid-coated CdTe quantum dots in the mixed solution of the step (3) is 7.3 x 10-8～1.46×10-5 mol·L-1The concentration of carbon dots doped with sulfur element is 3.3X 10-7～6.6×10-6 g·L-1。
3. The preparation method of claim 1, wherein the emission wavelength of the mercaptosuccinic acid-coated CdTe quantum dot fluorescent probe in the step (1) is 630-645 nm.
4. The method according to claim 1, wherein the organic solvent is dichloromethane, petroleum ether or diethyl ether.
5. The application of the carbon dot-quantum dot ratio fluorescence sensor prepared according to any one of the preparation methods of claims 1 to 4 in the rapid identification of silver ions.
6. The use of claim 5, wherein the carbon dot-quantum dot ratio fluorescence sensor is dissolved in PBS buffer solution with pH = 7.50-8.00 to quantitatively detect silver ions.
7. According toThe use of claim 6, wherein the carbon dot-quantum dot ratio fluorescence sensor has a detection limit of 31.8 nmol.L for silver ions-1。
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