CN110596086A - Colorimetric and/or SERS detection of pesticide residue and preparation method of detection colloid - Google Patents

Colorimetric and/or SERS detection of pesticide residue and preparation method of detection colloid Download PDF

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Publication number
CN110596086A
CN110596086A CN201910861615.6A CN201910861615A CN110596086A CN 110596086 A CN110596086 A CN 110596086A CN 201910861615 A CN201910861615 A CN 201910861615A CN 110596086 A CN110596086 A CN 110596086A
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colloid
polyvinyl alcohol
gold nanoparticle
pesticide
colorimetric
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CN110596086B (en
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黄梅珍
孔丽丽
陈婕
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Shanghai Jiaotong University
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Shanghai Jiaotong University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/62—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light
    • G01N21/63—Systems in which the material investigated is excited whereby it emits light or causes a change in wavelength of the incident light optically excited
    • G01N21/65—Raman scattering
    • G01N21/658—Raman scattering enhancement Raman, e.g. surface plasmons
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/75—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated
    • G01N21/77—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator
    • G01N21/78—Systems in which material is subjected to a chemical reaction, the progress or the result of the reaction being investigated by observing the effect on a chemical indicator producing a change of colour
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N33/00—Investigating or analysing materials by specific methods not covered by groups G01N1/00 - G01N31/00
    • G01N33/02—Food
    • G01N33/025—Fruits or vegetables

Abstract

The invention discloses a method for colorimetric and/or SERS detection of pesticide residues and preparation of a detection colloid, which comprises the following steps: preparing polyvinyl alcohol-gold nanoparticle colloid; establishing a concentration colorimetric method standard calibration curve of the pesticide to be detected related to the polyvinyl alcohol-gold nanoparticle colloid; measuring the concentration of the pesticide to be detected remained in the fruit and vegetable sample to be detected according to the standard calibration curve of the concentration colorimetric method; and/or performing surface enhanced Raman spectrum detection on the surface of the fruit and vegetable sample to be detected dripped with the polyvinyl alcohol-gold nanoparticle colloid by adopting a Raman spectrometer to confirm fingerprint spectrum information of the fruit and vegetable sample. The preparation method comprises the following steps: and mixing the polyvinyl alcohol powder with the gold nanoparticle solution to obtain polyvinyl alcohol-gold nanoparticle colloid. By the method, the colorimetric process is stable and controllable, so that the stability and the accuracy of a detection system are improved; in addition, the sensitivity is improved, and the in-situ detection is realized.

Description

Colorimetric and/or SERS detection of pesticide residue and preparation method of detection colloid
Technical Field
The invention relates to the technical field of food safety detection, in particular to a colorimetric and/or SERS detection method for pesticide residues and a preparation method of a detection colloid.
Background
Pesticides have been widely used in the control of pests and regulating plant growth. However, pesticide residues are potentially harmful to the environment and even cause health problems such as neurotoxicity, liver disease, and even cancer. Therefore, the method has important significance for realizing in-situ detection of pesticide residues in fruits and vegetables. Analytical methods such as gas chromatography, liquid chromatography, high performance liquid chromatography and mass spectrometry have been widely used for detection of pesticide residues, and detection results of these methods have high accuracy and are considered as gold standards. However, the above methods suffer from several disadvantages, they are often expensive, time consuming and dependent on specialized personnel.
Currently, colorimetric methods based on gold nanoparticle (AuNPs) solutions have been applied to the detection of pesticide residues. The method utilizes aggregation-dispersion of AuNPs to realize colorimetric detection of pesticide molecules: the interaction (electrostatic adsorption and chemical interaction) between pesticide molecules and AuNPs causes the dispersed AuNPs to aggregate, thereby causing the plasma resonance wavelength of the AuNPs to move to the long wavelength direction, and the color of the AuNPs solution is changed from wine red to purple and finally to blue. Within a certain range, the higher the concentration of the pesticide, the more obvious the shift of the AuNPs plasma resonance wavelength and the change of the color of the AuNPs solution. Therefore, the pesticide concentration can be measured by the change of the AuNPs plasma wavelength and the observation of the solution color. The colorimetric method for measuring the pesticide has the advantages of high sensitivity detection, quick response, naked eye distinguishing and the like, and is suitable for large-area visual quick detection of pesticide residues on the surfaces of fruits and vegetables. However, the colorimetric process based on the AuNPs solution is usually fast and strong, under the induction of pesticides with different concentrations, the AuNPs solution changes from wine red to blue, and is in a colorless and transparent excessive aggregation state after a period of time, so that the determination time is difficult to grasp, and the determination accuracy is influenced; in addition, most colorimetric methods are performed on liquid samples in test tubes, and are not suitable for in-situ detection of pesticide residues on the surfaces of fruits and vegetables.
In recent years, Surface Enhanced Raman Spectroscopy (SERS) is considered to be a reliable method for rapid and nondestructive detection of analytes, and can acquire "fingerprint" spectrum information of pesticide molecules to be detected, rapidly judge the types of pesticides, and have specificity. Based on the colorimetric method for large-area visual measurement of concentration distribution, SERS can be confirmed and verified aiming at certain points. AuNPs, as nanomaterials with localized surface plasmon resonance properties, are one of the most commonly used enhancement substrates in SERS. At present, some researches on combination of colorimetry and SERS based on AuNPs solutions exist, however, in the researches, SERS measurement is carried out on a liquid sample to be measured by transferring the liquid sample to a gold-plated glass slide for SERS detection, and in-situ measurement is not achieved.
To sum up, the problem that exists in pesticide detection of present color comparison/SERS combined technology is: 1. the measuring object is mainly a liquid sample, and the measurement of pesticides in fruits and vegetables (solid) is limited; 2. the colorimetric reaction is violent and uncontrollable, so that the determination time is difficult to master and the determination precision is influenced; 3. in situ measurement of SERS was not achieved.
Disclosure of Invention
The invention provides a method for colorimetric and/or SERS detection of pesticide residues and a preparation method of detection colloid aiming at the problems in the prior art, and polyvinyl alcohol-gold nanoparticle colloid (PVA-Au) is designed and prepared to be used as a colorimetric and SERS dual sensor. Polyvinyl alcohol (PVA) has physical characteristics of optical transparency, strong water solubility, stickiness and the like, PVA-Au obtained by mixing PVA powder and AuNPs solution is colloidal, and the colorimetric process can be stable and controllable, so that the stability and accuracy of a detection system are improved; meanwhile, the PVA-Au probe is easy to attach to the surface of a sample to be detected, so that the PVA-Au probe is in closer contact with pesticide molecules to be detected, the sensitivity is improved, and the in-situ detection is realized.
In order to solve the technical problems, the invention is realized by the following technical scheme:
the invention provides a colorimetric and/or SERS detection method for pesticide residues, which comprises the following steps:
s11: preparing polyvinyl alcohol-gold nanoparticle (PVA-Au) colloid;
s12: establishing a concentration colorimetric method standard calibration curve of the pesticide to be detected related to the polyvinyl alcohol-gold nanoparticle colloid;
s13: measuring the concentration of the pesticide to be detected remained in the fruit and vegetable sample to be detected according to the standard calibration curve of the concentration colorimetric method; and/or performing surface enhanced Raman spectroscopy detection on the surface of the fruit and vegetable sample to be detected dripped with the polyvinyl alcohol-gold nanoparticle colloid by using a Raman spectrometer to confirm fingerprint spectrum information of the fruit and vegetable sample to be detected so as to determine the type of pesticide to be detected;
preferably, the S11 further includes: and mixing the polyvinyl alcohol powder with the gold nanoparticle solution to obtain polyvinyl alcohol-gold nanoparticle colloid.
Preferably, the S11 further includes:
s111: adding a sodium citrate solution with a preset volume and a preset concentration into a tetrachloroauric acid solution with a preset boiling volume and a preset concentration, and stopping adding after continuing boiling for a preset time;
s112: cooling the solution obtained in the step S111 to room temperature, centrifuging at a preset rotating speed for a preset time, and removing a supernatant to obtain a gold nanoparticle solution;
s113: adding polyvinyl alcohol powder into the gold nanoparticle solution obtained in the step S112, and stirring until uniform mixing is achieved, so that polyvinyl alcohol powder-gold nanoparticle colloid is obtained.
Preferably, the mass-to-volume ratio of the polyvinyl alcohol powder to the gold nanoparticle solution is 5 mg: 2 ml.
Preferably, the step S113 of adding polyvinyl alcohol powder into the gold nanoparticle solution obtained in the step S112, and stirring the mixture until the mixture is uniformly mixed further includes: and adjusting the pH value of the colloid after uniform mixing to a preset pH value.
Preferably, the adjusting the PH value of the uniformly mixed colloid in S113 to a preset PH value specifically includes: adding dilute HCl or dilute HNO3And adjusting the pH value of the colloid after uniform mixing to a preset pH value.
Preferably, the preset pH value is weakly acidic, and the optimal pH value is 5, wherein the polyvinyl alcohol powder-gold nanoparticle colloid is uniformly distributed at the pH value and is more sensitive to colorimetric determination of pesticides.
Preferably, the S12 specifically includes:
s121: preparing pesticide solutions to be detected with different concentrations, spraying the pesticide solutions to the surfaces of fruits and vegetables, and drying to obtain fruit and vegetable samples to be detected for pesticide residues;
s122: dripping polyvinyl alcohol powder-gold nanoparticle colloid with preset volume on the surface of the fruit and vegetable sample obtained in the step S121, after the reaction is stable, acquiring a photo of the surface of the fruit and vegetable sample by using a camera under LED light sources with a first wavelength and a second wavelength, reading a gray value of the photo, and calculating the reflectivity of the fruit and vegetable sample according to the gray value;
s123: and (3) making a concentration calibration curve according to the relation between the ratio of the reflectivity obtained under the irradiation of the LED light source with the first wavelength to the reflectivity obtained under the irradiation of the LED light source with the second wavelength and the concentration of the pesticide solution to be detected.
Preferably, the selection method of the first wavelength and the second wavelength in S122 is: by measuring the ultraviolet absorption spectrum of the polyvinyl alcohol powder-gold nanoparticle colloid, the absorption peak of the polyvinyl alcohol powder-gold nanoparticle colloid is found to move from a first wavelength to a second wavelength in the presence of the pesticide to be detected, so that the first wavelength and the second wavelength are obtained.
Preferably, the method for calculating the reflectivity R according to the gray-scale value in S122 is: r (λ) ═ G-Gd)/(Gr-Gd. Wherein λ is the wavelength of the LED, G is the gray value of the sample image captured by the CCD camera under the LED light source, Gr is the gray value of the reference plane image obtained under the same LED light source, and Gd is the gray value of the reference plane image obtained in the darkroom.
The invention also provides a preparation method of the detection colloid for pesticide residue, which comprises the following steps:
s81: and mixing the polyvinyl alcohol powder with the nano gold particle solution to obtain polyvinyl alcohol-gold nano particle colloid.
Preferably, the S81 further includes:
s811: adding a sodium citrate solution with a preset volume and a preset concentration into a tetrachloroauric acid solution with a preset boiling volume and a preset concentration, and stopping adding after continuing boiling for a preset time;
s812: cooling the solution obtained in the step S811 to room temperature, centrifuging at a preset rotating speed for a preset time, and removing a supernatant to obtain a gold nanoparticle solution;
s813: adding polyvinyl alcohol powder into the gold nanoparticle solution obtained in the step S812, and stirring to be uniformly mixed to obtain polyvinyl alcohol powder-gold nanoparticle colloid.
Preferably, the mass-to-volume ratio of the polyvinyl alcohol powder to the gold nanoparticle solution is 5 mg: 2 ml.
Preferably, the step of adding polyvinyl alcohol powder into the gold nanoparticle solution obtained in step S812 in step S813, and stirring the mixture until the mixture is uniformly mixed further includes: and adjusting the pH value of the colloid after uniform mixing to a preset pH value.
Preferably, the adjusting the PH of the uniformly mixed colloid in S813 to a preset PH specifically includes: adding dilute HCl or dilute HNO3And adjusting the pH value of the colloid after uniform mixing to a preset pH value.
Preferably, the preset PH value is weakly acidic, and most preferably, the preset PH value is 5, and the polyvinyl alcohol powder-gold nanoparticle colloid is more stable and more uniformly distributed at the preset PH value.
Compared with the prior art, the invention has the following advantages:
(1) according to the method for preparing the colorimetric and/or SERS detection colloid of pesticide residues and the detection colloid, the polyvinyl alcohol-gold nanoparticle colloid (PVA-Au) is prepared to serve as a colorimetric and SERS dual sensor, and the PVA-Au colloid is more stable than a traditional AuNPs solution, is not easy to deteriorate and is convenient to store for later use; in addition, the PVA-Au colloid ensures that the colorimetric detection process is stable and controllable, and is beneficial to accurate determination;
(2) according to the method for preparing the pesticide residue colorimetric and/or SERS detection colloid, the prepared PVA-Au colloid has viscosity and is easy to attach to the surface of a sample to be detected, and the PVA-Au is promoted to be in close contact with molecules to be detected, so that the sensitivity of determination is improved, and in-situ colorimetric/SERS determination is realized;
(3) the method for colorimetric and/or SERS detection of pesticide residues and preparation of the detection colloid provided by the invention is suitable for detection of fruits and vegetables with different colors, and has the advantages of high sensitivity, quick response and naked eye visibility.
Of course, it is not necessary for any product in which the invention is practiced to achieve all of the above-described advantages at the same time.
Drawings
Embodiments of the invention are further described below with reference to the accompanying drawings:
FIG. 1 is a flow chart of the colorimetric detection method of pesticide residue of example 1 of the present invention;
fig. 2 is a flowchart of a SERS detection method of pesticide residues according to example 2 of the present invention;
FIG. 3 is a flow chart of the colorimetric and SERS detection method of pesticide residue according to example 3 of the present invention;
FIGS. 4a and 4b are scanning electron micrographs of a PVA-Au nanoparticle colloid according to an embodiment of the present invention, with a scale of 200 nm;
FIG. 5 is an absorption spectrum of a polyvinyl alcohol-gold nanoparticle colloid in the presence of different concentrations of thiram according to an embodiment of the present invention;
FIGS. 6a and 6b are graphs showing the reflectance ratio of AuNPs solution to PVA-Au colloid as a function of reaction time for different concentrations of thiram residues according to an embodiment of the present invention;
FIG. 7 is a standard calibration curve for thiram concentration colorimetry in accordance with an embodiment of the present invention;
FIG. 8 is a Fumeishu SERS spectrum collected in situ on an apple according to an embodiment of the present invention.
Detailed Description
The following examples are given for the detailed implementation and specific operation of the present invention, but the scope of the present invention is not limited to the following examples.
Example 1:
this example describes the colorimetric detection method of pesticide residue according to the present invention in detail with reference to fig. 1, which comprises the following steps as shown in fig. 1:
s11: preparing polyvinyl alcohol-gold nanoparticle (PVA-Au) colloid;
s12: establishing a concentration colorimetric method standard calibration curve of the pesticide to be detected related to PVA-Au colloid;
s13: and measuring the concentration of the pesticide to be detected remained in the fruit and vegetable sample to be detected according to the standard calibration curve of the concentration colorimetric method.
Example 2:
this embodiment describes the method for SERS detection of pesticide residue according to the present invention in detail with reference to fig. 2, as shown in fig. 2, which includes the following steps:
s11: preparing polyvinyl alcohol-gold nanoparticle (PVA-Au) colloid;
s12: establishing a concentration colorimetric method standard calibration curve of the pesticide to be detected related to the polyvinyl alcohol-gold nanoparticle colloid;
s14: and (3) carrying out surface enhanced Raman spectrum detection on the surface of the fruit and vegetable sample to be detected dripped with the PVA-Au colloid by using a Raman spectrometer to confirm fingerprint spectrum information of the fruit and vegetable sample to be detected so as to determine the type of the pesticide to be detected.
Example 3:
this example describes the colorimetric and SERS detection method of pesticide residue according to the present invention in detail with reference to fig. 3, as shown in fig. 3, which includes the following steps:
s11: preparing polyvinyl alcohol-gold nanoparticle (PVA-Au) colloid;
s12: establishing a concentration colorimetric method standard calibration curve of the pesticide to be detected related to the polyvinyl alcohol-gold nanoparticle colloid;
s13: measuring the concentration of the pesticide to be detected remained in the fruit and vegetable sample to be detected according to the standard calibration curve of the concentration colorimetric method;
s14: and (3) carrying out surface enhanced Raman spectrum detection on the surface of the fruit and vegetable sample to be detected dripped with the polyvinyl alcohol-gold nanoparticle colloid by using a Raman spectrometer to confirm fingerprint spectrum information of the fruit and vegetable sample to be detected so as to determine the type of the pesticide to be detected.
In the above embodiment, the sequences of S13 and S14 may be interchanged, or S14 may be performed first, and then S13 may be performed.
In a preferred embodiment, S11 further includes: polyvinyl alcohol (PVA) powder and gold nanoparticle solution (AuNPs solution) are mixed to obtain polyvinyl alcohol-gold nanoparticle colloid.
In a preferred embodiment, S11 further includes:
s111: rapidly adding 3ml of 1% (w/w) sodium citrate solution into boiling 100ml of 0.25mM tetrachloroauric acid solution, continuously boiling for 30min, and stopping heating;
s112: naturally cooling the solution obtained in the step S111 to room temperature, centrifuging at the rotating speed of 1000rpm for 10min, removing supernatant, and obtaining a lower-layer concentrated part which is an AuNPs solution;
s113: and adding the PVA powder into the AuNPs solution, stirring until the PVA powder and the AuNPs solution are uniformly mixed to obtain PVA-Au, and sealing the PVA-Au in a centrifugal tube for storage.
In the above embodiments, the parameters of the various solutions and powders, the parameters of the rotation speed and the parameters of the time may be changed according to the needs.
In a preferred embodiment, the mass-to-volume ratio of the PVA powder to the AuNPs solution in S113 is 5 mg: 2 ml.
In a preferred embodiment, the step S113 further includes, after the step of uniformly mixing: and adjusting the pH value of the colloid after uniform mixing to a preset pH value. Preferably, the preset pH value is weakly acidic, and the optimal pH value is 5, wherein the polyvinyl alcohol powder-gold nanoparticle colloid is uniformly distributed at the pH value and is more sensitive to colorimetric determination of pesticides.
In a preferred embodiment, the method for adjusting PH comprises: adding dilute HCl or dilute HNO3And adjusting the pH value of the colloid after uniform mixing to a preset pH value. Of course, in different embodiments, other acidic solutions or alkaline solutions may be added to adjust the PH, and are not described herein.
In a preferred embodiment, S12 further includes:
s121: preparing pesticide solutions to be detected with different concentrations, spraying the pesticide solutions to the surfaces of fruits and vegetables, and drying to obtain fruit and vegetable samples to be detected for pesticide residues;
s122: dripping polyvinyl alcohol powder-gold nanoparticle colloid with preset volume on the surface of the fruit and vegetable sample obtained in the step S121, after the reaction is stable, collecting a photo of the surface of the fruit and vegetable sample by using a camera under LED light sources with a first wavelength and a second wavelength, reading a gray value of the photo, and calculating the reflectivity of the fruit and vegetable sample according to the gray value;
s123: and (3) making a concentration calibration curve according to the relation between the ratio of the reflectivity obtained under the irradiation of the LED light source with the first wavelength to the reflectivity obtained under the irradiation of the LED light source with the second wavelength and the concentration of the pesticide solution to be detected.
In a preferred embodiment, the selection method of the first wavelength and the second wavelength in S122 is as follows: by measuring the ultraviolet absorption spectrum of the polyvinyl alcohol powder-gold nanoparticle colloid, the absorption peak of the polyvinyl alcohol powder-gold nanoparticle colloid is found to move from a first wavelength to a second wavelength in the presence of the pesticide to be detected, so that the first wavelength and the second wavelength are obtained.
In the preferred embodiment, the method for calculating the reflectivity R according to the gray-level value in S122 is as follows: r (λ) ═ G-Gd)/(Gr-Gd. Wherein λ is the wavelength of the LED, G is the gray value of the sample image captured by the CCD camera under the LED light source, Gr is the gray value of the reference plane image obtained under the same LED light source, and Gd is the gray value of the reference plane image obtained in the darkroom.
The above examples are specifically described below by taking thiram pesticide as an example, and fig. 4a shows a scanning electron microscope image of PVA-Au without adding thiram pesticide, and the dispersion is compared, and fig. 4b shows a scanning electron microscope image of PVA-Au with adding thiram pesticide, and the aggregation is compared. S12 specifically includes:
s121: accurately preparing thiram solutions with different concentrations, spraying the thiram solutions on the surfaces of fruits and vegetables, and naturally drying at room temperature to obtain fruit and vegetable samples with thiram residues;
s122: directly dripping 10 mu L of PVA-Au colloid on the surface of a fruit and vegetable sample, after the reaction is stable, acquiring photos of the fruit and vegetable sample by using a monochromatic CCD camera under LED light sources with a first wavelength and a second wavelength, measuring the reflectivity of the fruit and vegetable sample, and making a concentration calibration curve according to the relation between the reflectivity ratio and the thiram concentration; the absorption spectra of the PVA-Au colloid in the presence of different concentrations of thiram are given in FIG. 5, where the concentrations of thiram are: 0,100,500, 2000 ppb;
s123: and (3) preparing a concentration calibration curve according to the relation between the ratio of the reflectivity obtained under the irradiation of the LED light source with the first wavelength to the reflectivity obtained under the irradiation of the LED light source with the second wavelength and the concentration of the thiram solution.
In the preferred embodiment, the concentration of the thiram solution prepared in S121 is 5,10,50,100,500,1000,2000ppb, respectively.
In the preferred embodiment, the UV absorption spectrum of PVA-Au colloid is measured, and the absorption peak of PVA-Au colloid is shifted from 520nm to 620nm in the presence of thiram, so that LEDs with the wavelengths of 520nm and 620nm are selected as the light source. In different embodiments, the selected wavelength may be different according to actual measurement when the pesticide is different in type.
In a preferred embodiment, the reflectance is expressed as R (λ) ═ G-Gd)/(Gr-Gd. Wherein λ is the wavelength of the LED, G is the gray value of the sample image captured by the CCD camera under the LED light source, Gr is the gray value of the reference plane image obtained under the same LED light source, and Gd is the gray value of the reference plane image obtained in the darkroom. In the above embodiment, the reflectance ratio is R (520)/R (620). Fig. 6a and 6b show the comparative results of different concentrations of thiram residues in this example, and the reflectivity ratio of AuNPs solution to PVA-Au colloid changes with reaction time. Fig. 6a illustrates that the reflectivity ratio of AuNPs solution rapidly increases with the reaction time after different concentrations of thiram residue remain, and stabilizes at a similar ratio after 15min, and the thiram residue concentration can hardly be judged according to the reflectivity ratio. In FIG. 6b, the PVA-Au colloid in the presence of different concentrations of thiram has stable reflectance ratio R (520)/R (620) after about 11min, and the greater the reflectance ratio R (520)/R (620) is, the greater the reflectance ratio is, the thiram residual concentration can be determined according to the reflectance ratio. Compared with AuNPs solution, the PVA-Au colloid ensures that the colorimetric detection process is stable and controllable, and is beneficial to accurate determination.
Taking determination of thiram pesticide residues in three fruits and vegetables including pear (yellow), apple (red) and vegetable (green) as an example, fig. 7 shows a standard calibration curve diagram of thiram concentration colorimetry of fruit and vegetable samples of the embodiment; figure 8 shows the thiram SERS spectrum collected in situ on apple. The concentration of thiram is 5 ppm. Table 1 shows the colorimetric calibration curve equation, the fitting degree (R2) and the lowest detection Limit (LOD) of the thiram concentration in the fruit and vegetable samples of the embodiment.
TABLE 1
The determination result shows that the PVA-Au colloid is suitable for colorimetric determination of thiram (pKa 7.82) residues in fruit and vegetable samples with different colors, and meanwhile, the PVA-Au colloid can be used as an SERS substrate to obtain the fingerprint spectrum information of thiram in situ, and can be confirmed and verified aiming at certain points on the basis of large-area visual concentration distribution measurement.
Example 4:
this example describes in detail the preparation method of the colloid for detecting pesticide residue according to the present invention, which comprises the following steps:
s81: and mixing the polyvinyl alcohol powder with the nano gold particle solution to obtain polyvinyl alcohol-gold nano particle colloid.
In a preferred embodiment, S81 further includes:
s811: rapidly adding 3ml of 1% (w/w) sodium citrate solution into boiling 100ml of 0.25mM tetrachloroauric acid solution, continuously boiling for 30min, and stopping heating;
s812: naturally cooling the solution obtained in the step S811 to room temperature, centrifuging at the rotating speed of 1000rpm for 10min, removing supernatant, and obtaining AuNPs solution as a lower-layer concentrated part;
s813: and adding the PVA powder into the AuNPs solution, stirring until the PVA powder and the AuNPs solution are uniformly mixed to obtain PVA-Au, and sealing the PVA-Au in a centrifugal tube for storage.
In the above embodiments, the parameters of the various solutions and powders, the parameters of the rotation speed and the parameters of the time may be changed according to the needs.
In a preferred embodiment, the mass-to-volume ratio of the PVA powder to the AuNPs solution in S813 is 5 mg: 2 ml.
In a preferred embodiment, the step S813 further includes, after the step of uniformly mixing: and adjusting the pH value of the colloid after uniform mixing to a preset pH value. Preferably, the predetermined pH is 5.
In a preferred embodiment, the method for adjusting PH comprises: adding dilute HCl or dilute HNO3And adjusting the pH value of the colloid after uniform mixing to a preset pH value. Of course, in different embodiments, other acidic solutions or alkaline solutions may be added to adjust the PH, and are not described herein.
The principle of the above example for determining pesticides with acidity coefficients pKa > 5 is: (1) colorimetric detection: the surface of the PVA-Au colloid is coated with citrate ions to present negative charges, and the PVA-Au is uniformly and stably dispersed in a weak acid system by electrostatic repulsion. pesticide molecules with pKa > 5 will be protonated and carry a high positive charge in such systems, for example: thiram (pKa ═ 7.82) contains 2 tertiary amine groups, and is easily protonated and positively charged in a weakly acidic system. Thus, in the presence of the pesticide (pKa > 5), the effect of electrostatic attraction causes the PVA-Au to change from a dispersed state to an aggregated state. The plasma resonance wavelength of the PVA-Au colloid shifts to the long wavelength direction, and the color of the PVA-Au colloid changes from wine red to purple and finally to blue. Within a certain range, the higher the concentration of the pesticide (pKa > 5), the more obvious the shift of the plasma resonance wavelength of the PVA-Au colloid and the change of the colloid color. The measurement of the concentration of the pesticide (pKa > 5) is realized by the change of the plasma wavelength of the PVA-Au colloid and the change of the colloid color. (2) SERS detection: the PVA-Au colloid is used as a nano material with the local surface plasma resonance characteristic, can be used as an SERS enhanced substrate, can effectively amplify a Raman signal of a target molecule, and is suitable for directly detecting the target molecule on the surface of a sample.
The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and not to limit the invention. Any modifications and variations within the scope of the description, which may occur to those skilled in the art, are intended to be within the scope of the invention.

Claims (10)

1. A colorimetric and/or SERS detection method of pesticide residues, comprising:
s11: preparing polyvinyl alcohol-gold nanoparticle colloid;
s12: establishing a concentration colorimetric method standard calibration curve of the pesticide to be detected related to the polyvinyl alcohol-gold nanoparticle colloid;
s13: measuring the concentration of the pesticide to be detected remained in the fruit and vegetable sample to be detected according to the standard calibration curve of the concentration colorimetric method; and/or performing surface enhanced Raman spectrum detection on the surface of the fruit and vegetable sample to be detected dripped with the polyvinyl alcohol-gold nanoparticle colloid by adopting a Raman spectrometer to confirm fingerprint spectrum information of the fruit and vegetable sample.
2. The colorimetric and/or SERS detection method of pesticide residues according to claim 1, characterized in that the S11 further comprises: and mixing the polyvinyl alcohol powder with the gold nanoparticle solution to obtain polyvinyl alcohol-gold nanoparticle colloid.
3. The colorimetric and/or SERS detection method of pesticide residues according to claim 2, characterized in that the S11 further comprises:
s111: adding a sodium citrate solution with a preset volume and a preset concentration into a tetrachloroauric acid solution with a preset boiling volume and a preset concentration, and stopping adding after continuing boiling for a preset time;
s112: cooling the solution obtained in the step S111 to room temperature, centrifuging at a preset rotating speed for a preset time, and removing a supernatant to obtain a gold nanoparticle solution;
s113: adding polyvinyl alcohol powder into the gold nanoparticle solution obtained in the step S112, and stirring until uniform mixing is achieved, so that polyvinyl alcohol powder-gold nanoparticle colloid is obtained.
4. The colorimetric and/or SERS detection method for pesticide residues as claimed in claim 3, wherein the step of adding polyvinyl alcohol powder into the gold nanoparticle solution obtained in the step S112 in the step S113 and stirring the mixture until the mixture is uniformly mixed further comprises the following steps: and adjusting the pH value of the colloid after uniform mixing to a preset pH value.
5. Root of herbaceous plantThe colorimetric and/or SERS detection method for pesticide residues according to claim 4, wherein the adjusting of the pH value of the uniformly mixed colloid in S113 to a preset pH value is specifically: adding dilute HCl or dilute HNO3And adjusting the pH value of the colloid after uniform mixing to a preset pH value.
6. The colorimetric and/or SERS detection method of pesticide residues according to claim 4 characterized by the fact that the preset PH value is weakly acidic.
7. The colorimetric and/or SERS detection method of pesticide residues according to any of claims 1 to 6, characterized in that the S12 comprises in particular:
s121: preparing pesticide solutions to be detected with different concentrations, spraying the pesticide solutions to the surfaces of fruits and vegetables, and drying to obtain fruit and vegetable samples to be detected for pesticide residues;
s122: dripping polyvinyl alcohol powder-gold nanoparticle colloid with preset volume on the surface of the fruit and vegetable sample obtained in the step S121, after the reaction is stable, acquiring a photo of the surface of the fruit and vegetable sample by using a camera under LED light sources with a first wavelength and a second wavelength, reading a gray value of the photo, and calculating the reflectivity of the fruit and vegetable sample according to the gray value;
s123: and (3) making a concentration calibration curve according to the relation between the ratio of the reflectivity obtained under the irradiation of the LED light source with the first wavelength to the reflectivity obtained under the irradiation of the LED light source with the second wavelength and the concentration of the pesticide solution to be detected.
8. The colorimetric and/or SERS detection method for pesticide residues according to claim 7, wherein the first and second wavelengths in S122 are selected by: by measuring the ultraviolet absorption spectrum of the polyvinyl alcohol powder-gold nanoparticle colloid, the absorption peak of the polyvinyl alcohol powder-gold nanoparticle colloid is found to move from a first wavelength to a second wavelength in the presence of the pesticide to be detected, so that the first wavelength and the second wavelength are obtained.
9. A method for preparing a colloid for detecting pesticide residues, wherein the prepared colloid for detecting the pesticide residues is used for the colorimetric and/or SERS detection method of the pesticide residues according to any one of claims 1 to 8, and comprises the following steps:
s81: and mixing the polyvinyl alcohol powder with the gold nanoparticle solution to obtain polyvinyl alcohol-gold nanoparticle colloid.
10. The method for preparing colloid for detecting pesticide residue according to claim 9, wherein the S81 further comprises:
s811: adding a sodium citrate solution with a preset volume and a preset concentration into a tetrachloroauric acid solution with a preset boiling volume and a preset concentration, and stopping adding after continuing boiling for a preset time;
s812: cooling the solution obtained in the step S811 to room temperature, centrifuging at a preset rotating speed for a preset time, and removing a supernatant to obtain a gold nanoparticle solution;
s813: adding polyvinyl alcohol powder into the gold nanoparticle solution obtained in the step S812, and stirring to be uniformly mixed to obtain polyvinyl alcohol powder-gold nanoparticle colloid.
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