CN110186884B - Visual molecularly imprinted nanosensor and preparation and application thereof - Google Patents
Visual molecularly imprinted nanosensor and preparation and application thereof Download PDFInfo
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Abstract
The invention belongs to the fields of materials, analytical chemistry and food safety, and particularly relates to a molecular imprinting ratio fluorescence nanosensor based on dual fluorescence emission, a preparation method thereof and application of the molecular imprinting ratio fluorescence nanosensor in visual detection of folic acid in food. The visualized molecular imprinting nano sensor is a dual fluorescence emission molecular imprinting nano sensor with a core-shell structure, which is obtained by performing sol-gel polymerization imprinting on the surface of silicon dioxide nano particles through a one-step method, embedding red fluorescent cadmium telluride quantum dots (CdTe QDs) and folic acid with self-blue fluorescence, and taking a cavity for eluting the folic acid as an identification site. Compared with the traditional two-step method for preparing the molecular imprinting ratio fluorescence sensor, the preparation method provided by the invention is simpler, avoids complicated synthesis steps and shortens the experimental period. In addition, the sensor prepared by the method can detect folic acid in a high-sensitivity, high-selection and self-correction manner, provides rich fluorescence color evolution, and realizes visual detection of a target object.
Description
Technical Field
The invention belongs to the fields of materials, analytical chemistry and food safety, and particularly relates to a molecular imprinting ratio fluorescence sensor based on dual fluorescence emission, a preparation method thereof and application of the molecular imprinting ratio fluorescence sensor in visual detection of folic acid in food.
Background
Folic acid is a water-soluble vitamin and has important clinical significance for human health. It plays an important physiological role in cellular metabolism as an important coenzyme factor, and is involved in nucleic acid and erythrocyte formation, cell replication and tissue growth. In addition, folic acid, as a dietary supplement, is currently recommended by adults in the United states for a daily intake of 400 μ g. The lack of folic acid of pregnant women can cause fetal neural tube malformation; excessive folic acid intake can affect the absorption of other nutrients, e.g. B12Zinc, causing other health problems. With the gradual improvement of food safety awareness, the development of a method capable of rapidly, conveniently and reliably detecting the folic acid content in food is urgent.
The molecular imprinting technology is to prepare a polymer with specific recognition performance on a specific target molecule, namely, a Molecular Imprinted Polymer (MIPs), by utilizing the principle of antigen-antibody combination. Compared with antibodies with specific recognition function, the MIPs have the advantages of high physical and chemical stability, low cost, easy preparation and the like, and have the characteristics of high predetermination, strong recognition, wide applicability and the like. The fluorescence nano-sensing has the advantages of high sensitivity, simple operation and short response time, and is beneficial to the detection of trace substances. In recent years, molecular imprinting technology and fluorescence detection have attracted great interest to researchers and have been rapidly developed. Therefore, in combination with the high specificity and the high sensitivity of the two, the preparation of the molecular imprinting fluorescence sensor is expected to be applied to the rapid visual detection of the nutrition enhancer in the complex matrix. However, the traditional molecular imprinting fluorescence sensor only has one emission peak and is easily interfered by other various irrelevant factors (such as detection substrate, instrument fluctuation, photobleaching and the like) to limit accurate quantitative detection; in addition, as the concentration of the target substance changes, only the change of the fluorescence brightness of the target substance can be caused, and the more direct color change cannot be provided visually.
Ratiometric fluorescence sensing achieves analyte detection by comparing the change in fluorescence intensity of two different luminophores before and after addition of the analyte. The basic principle is as follows: the assay substrate may be subjected to quantitative detection by causing a change in fluorescence intensity at one wavelength (response signal) while the fluorescence intensity at the other wavelength remains constant or undergoes a change opposite to the response signal, and then correlating the change in the ratio of the two peak intensities with the concentration of the assay substrate. This not only weakens the interference of external factors and improves the reliability of the analysis, but also shows the macroscopic fluorescence color change through the change of the fluorescence intensity ratio, so the naked eye detection becomes possible in the molecular imprinting technology. However, the synthesis process of the core-shell type molecular imprinting ratio fluorescence sensing is complicated at present, and generally involves two steps, namely embedding reference fluorescence into silica nanoparticles and then imprinting on the surface of the silica nanoparticles, namely embedding before imprinting; or the core-shell type single-emission molecularly imprinted fluorescent sensing and the silica nanoparticles embedded with the reference fluorescence are prepared respectively, namely the preparation is carried out firstly and then the mixing is carried out.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to provide a molecular imprinting ratio fluorescence nano-sensor based on a one-pot method, and preparation and application thereof in visual detection of folic acid.
In order to achieve the purpose, the invention adopts the technical scheme that:
a visualized molecular imprinting nano sensor is characterized in that sol-gel polymerization imprinting is carried out on the surfaces of silicon dioxide nano particles through a one-step method, red fluorescent cadmium telluride quantum dots (CdTe QDs) and folic acid with spontaneous blue fluorescence are embedded, and a cavity for eluting folic acid is used as a recognition site to obtain the double-fluorescence emission folic acid imprinting microsphere with a core-shell structure.
The obtained sensor has dual-emission fluorescence, and the emission ranges are respectively 440-460nm under the 365 excitation wavelength
And 610 and 620 nm.
A preparation method of a visual molecularly imprinted nano-sensor comprises the steps of adding red fluorescent cadmium telluride quantum dots (CdTe QDs), folic acid and 3-aminopropyl triethoxysilane (APTES) into a solution containing silicon dioxide nano-particles, stirring for 1-2h, continuously adding Tetraethoxysilane (TEOS) and ammonia water to perform sol-gel polymerization reaction for 10-12h in a dark environment, precipitating a product after reaction by a centrifugal method, discarding supernatant, repeatedly eluting folic acid in the precipitate by 24mL of methanol to obtain folic acid imprinted microspheres with a core-shell structure, and re-dispersing the folic acid imprinted microspheres in 6mL of ultrapure water.
The total volume of the sol-gel polymerization reaction system is controlled to be 20-22 mL; wherein the dosage of the silicon dioxide nano particle solution, the CdTe QDs, the folic acid, the APTES, the TEOS and the ammonia water is respectively 1-2mL, 3-5mL, 8-10mL, 37-75 μ L, 50-100 μ L and 50-100 μ L.
Adding ammonia water into a water/ethanol mixed solution, stirring for 10-30min, uniformly mixing, adding an ethanol solution of Tetraethoxysilane (TEOS) one drop by using a constant-pressure dropping funnel, stirring for reaction for 10-12h, centrifuging the obtained product, removing a supernatant, washing the precipitate with ethanol, and finally dispersing in 50mL of ultrapure water again for later use.
The concentration of the silicon dioxide nano particles is 1.2-1.5 mg/mL; the total volume of the water/ethanol mixed solution is 80-100mL, and the volume ratio is 5: 3; the volume of the TEOS ethanol solution is 25-30mL, wherein the volume of TEOS accounts for 2% -3%.
The concentration of the folic acid is 1-1.2 g/L; the concentration of the NaOH ethanol solution is as follows: 0.01-0.02 mol.L-1The ethanol accounts for 20-30% of the total volume.
The application of a visual molecular imprinting nano sensor in detecting folic acid which is a nutrition enhancer in food and biological samples and serum.
The sensor is arranged in a liquid to be detected, red fluorescence CdTe QDs in the sensor is used as a response signal, the fluorescence intensity of the red fluorescence CdTe QDs is reduced along with the increase of the concentration of a target object, the blue fluorescence of the target object folic acid is gradually enhanced, and the visual naked eye detection of the folic acid is realized through the change of the intensity ratio of two different emission peaks.
The invention has the beneficial effects that:
1) according to the invention, the core-shell type molecularly imprinted ratio fluorescence sensing is constructed by adopting one-step sol-gel polymerization for the first time, so that the mass transfer rate is improved, the synthesis process is simplified, the molecularly imprinted polymer is prevented from being synthesized for many times, the experiment period is shortened, and the experiment cost is reduced.
2) The sensor quenches the fluorescence of red CdTe QDs by specific recognition of folic acid; further, in the detection, photoinduced electron transfer occurs between the red CdTe QDs and the analyte folic acid, the fluorescence of the red CdTe QDs is gradually quenched along with the increase of the concentration of the folic acid, and the blue fluorescence of the folic acid is gradually enhanced, so that the ratio detection of the folic acid is realized, the fluorescence color is changed from red-pink-purple to blue, and the visual detection of the folic acid is realized.
3) The sensor fully exerts the advantages of high selectivity of molecular imprinting polymerization and high sensitivity, self-correction, interference resistance and the like of a ratiometric fluorescence technology, develops a convenient, rapid and reliable quantitative method for detecting folic acid, and provides abundant color change for qualitative detection; the folic acid detection range of the sensor is 0.23-113 mu M, and the detection line is as low as 4.8 nM; the sensor overcomes the defects of easy interference, instability and the like of the traditional single-fluorescence sensor, and has important application value in the detection and control of nutrition enhancers in food and other fields.
Drawings
Fig. 1 is a schematic diagram of a process for preparing a visualized molecular imprinting nanosensor according to an embodiment of the invention.
FIG. 2 shows silica nanoparticles (SiO)2) Profile maps of folate imprinting ratio fluorescence sensors (FL-MIPs) and non-imprinting ratio fluorescence sensors (FL-NIPs).
FIG. 3 is a fluorescence spectrum and fluorescence color evolution of folate detected by a folate blotting ratio fluorescence sensor (FL-MIPs) according to an embodiment of the present invention under different dosage conditions, wherein the dosage of FL-MIPs is 50 μ L,100 μ L,125 μ L, and 150 μ L from A-E.
FIGS. 4A and C are the fluorescence spectra and fluorescence color changes of folic acid detected by a folate blotting ratio fluorescence sensor (FL-MIPs) and a non-blotting ratio fluorescence sensor (FL-NIPs), respectively, according to the present invention. B and D are fitting relation graphs of the ratio change of the fluorescence intensity and the folic acid concentration corresponding to the B and D respectively.
FIG. 5 shows fluorescence intensity ratio and fluorescence color change of folic acid blotting ratio fluorescence sensors (FL-MIPs) and non-blotting ratio fluorescence sensors (FL-NIPs) after different analogs are identified, and the concentration of each substance is 20mg L-1. The inset shows the concentration ratio of carbamazepine/folic acid (C)MTX/CFA) The ratio of fluorescence intensity of folate blot ratio fluorescence sensors (FL-MIPs) under the conditions was varied.
Detailed Description
The invention is further explained below with reference to the figures and examples.
The sensor of the invention shows the emission ranges of 440-460nm and 610-620nm under the excitation wavelength of 365nm, which respectively correspond to the self-blue fluorescence of folic acid and the red fluorescence of CdTe QDs, wherein the former is used as reference fluorescence, and the latter is used as response fluorescence for the detection of folic acid. Under the optimal condition, the fluorescence spectrum of the solution is measured by a fluorescence spectrophotometer, the peak intensity of an emission peak is read, and the corresponding relation between the change of the fluorescence intensity ratio and the concentration of the folic acid is calculated, so that the quantitative detection of the folic acid is carried out. In addition, when the sensor detects folic acid, the red fluorescence is gradually quenched, and the blue autofluorescence is gradually enhanced, so that the fluorescence color is gradually changed from red to blue, and the sensor can be used for visual detection of folic acid. The sensor prepared by the invention can detect folic acid with high selectivity and high sensitivity, and provides color evolution and self-correction functions; and the simple one-pot method for constructing the core-shell sensor improves the mass transfer rate, avoids the complicated synthesis process, greatly shortens the experimental period, saves the experimental cost, and can be more widely applied to the detection of various nutrition enhancers.
Example 1
A preparation method of a visual molecularly imprinted nanosensor (see figure 1) comprises the following steps:
(1)1g·L-1preparation of a folic acid solution: firstly, 0.01 mol.L is prepared-1Sodium hydroxide ethanol solution to 500mL ethanol solution (volume fraction of 20%) was added 200mg sodium hydroxide. 100mL of this solution was taken and 100mg of folic acid was added to obtain 1 g.L-1A folic acid solution.
(2) A folic acid imprinting ratio fluorescence sensor (FL-MIPs) was prepared by adding 8mL of ultrapure water, 37. mu.LAPTES, and 8mL of the above folic acid to 1mL of a silica nanoparticle solution, stirring the mixture for 1 hour to form a prepolymerization mixture, adding 50. mu.L of LTEOS and 50. mu.L of ammonia water, and reacting the mixture in a dark environment for 10 to 12 hours. After the reaction is finished, the product is centrifuged (8000rpm, 10 minutes), the supernatant is discarded, and then the template molecular folic acid in the precipitate is repeatedly eluted by 24mL of methanol to obtain the ratio fluorescence nano-sensing of the core-shell type folic acid blot, and the nano-sensing is dispersed in 6mL of water for later use. Meanwhile, non-blotting specific fluorescence sensors (FL-NIPs) were used as controls, and prepared by the same method as above, except that no template molecular folic acid was added during the preparation process.
Application example 2
1) Respectively taking 100 mu L of the silicon dioxide nano particles, the folic acid imprinting ratio fluorescence sensors (FL-MIPs) and the non-imprinting ratio fluorescence sensors (FL-NIPs) obtained in the embodiment, respectively diluting by 1000 times, then respectively dispersing on a copper net washed by ethanol, drying, and observing the copper net loaded with the diluted substances by using a transmission electron microscope; (see upper layer of FIG. 2)
2) Respectively taking 100 mu L of the solutions of the silicon dioxide nano particles, the folic acid imprinting ratio fluorescence sensors (FL-MIPs) and the non-imprinting ratio fluorescence sensors (FL-NIPs) obtained in the embodiment, respectively diluting by 100 times, then respectively dispersing the diluted solutions on a silicon wafer cleaned by ethanol, drying, and observing the silicon wafer loaded with the diluted substances by using a scanning electron microscope; (see FIG. 2 bottom layer)
FIG. 2 shows silica nanoparticles, a folate imprinting ratio fluorescence sensor, and a non-imprinting ratio fluorescence sensor, respectively, wherein the silica nanoparticles have an average diameter of about 75-85nm, and the folate imprinting ratio fluorescence sensor and the non-imprinting ratio fluorescence sensor have no significant difference in morphology and size, and have rough surfaces with an average particle diameter of about 90 nm. It is thus computationally known that a shell thickness of about 5-8nm, sites located on the imprinting surface improve accessibility to template molecular folate, while a thin imprinted shell facilitates rapid recognition of the target molecule.
Application example 3
Folic acid trace ratio fluorescence sensors (FL-MIPs) obtained in the above examples with different volumes of 50. mu.L, 100. mu.L, 125. mu.L and 150. mu.L are respectively added with different concentrations of folic acid, wherein the concentrations of folic acid are 0,1,5,10,20,30,40 and 50mg L in sequence-1Then, the volume was increased to 1mL with ultrapure water, and after mixing them uniformly, the mixture was reacted for 10min, and then the fluorescence spectrum (excitation wavelength: 365nm, slit width 5/5nm) of each sample was measured with a fluorescence spectrophotometer.
As shown in FIGS. 3A-E corresponding to FL-MIPs with volumes of 50. mu.L, 100. mu.L, 125. mu.L and 150. mu.L, respectively, it can be seen that as the concentration of folic acid increases, the red fluorescence is quenched and the blue fluorescence is enhanced. As shown in the graph A, when the dosage of FL-MIPs is 50 mu L, the color of the solution is changed from initial red to purple to blue, and is mostly blue; as the volume of FL-MIPs increases, the red color increases slightly, but still predominates in red and blue (fig. B); however, excessive FL-MIPs mask the blue fluorescence, mostly in red (FIGS. D and E). Thus, these four cases all reduce the change in fluorescence colorAnd (5) changing the range. When the dosage volume of FL-MIPs is 125 mu L, the folic acid concentration is increased from 0 to 50mg L-1The fluorescence color of the sample changed to red-pink-purple-blue, and was uniformly distributed.
Application example 4
125 μ L of the folic acid blotting ratio fluorescence sensors (FL-MIPs) and non-blotting ratio fluorescence sensors (FL-NIPs) obtained in the above examples were taken, added with folic acid of different concentrations, and then made to 1mL with ultrapure water, wherein the folic acid concentrations were 0.1,1,5,10,15,20,25,30,35,40,45 and 50mg L in this order-1After mixing well, the reaction was carried out for 10min, and then the fluorescence spectrum of each sample was measured by a fluorescence spectrophotometer (excitation wavelength: 365nm, slit width 5/5 nm).
As shown in FIG. 4A, the fluorescent nano-sensor with molecular imprinting ratio emits two fluorescence peaks at 449 nm and 617nm, respectively, under 365nm wavelength excitation. With the increase of the concentration of folic acid, the red fluorescence intensity is gradually reduced, while the blue fluorescence intensity is gradually increased, which directly leads to the gradual transition of the fluorescence color change from red to blue, and the distinguishable and obvious color change can be seen by naked eyes, thereby visually detecting folic acid. As shown in the graph B, the change of the ratio of fluorescence intensity and the concentration of folic acid (0.1-50mg L-1) are in a linear relationship, the linear correlation coefficient (r2) is 0.992, the correlation coefficient of polynomial fitting reaches 0.999, and the detection limit is 9.8 nM. As shown in FIG. 4C, the blue fluorescence in FL-NIPs gradually increases with the folic acid concentration, but the red fluorescence intensity does not change significantly, and the quenching degree is far lower than FL-MIPs, resulting in a greatly reduced fluorescence color change range. As shown in FIG. 4D, good linear and polynomial fits were also shown between the ratio change of fluorescence intensity in FL-NIPs and folate concentration, and the correlation coefficients all reached above 0.99(r2), thereby calculating the imprinting factor as 2.24. This result demonstrates the presence of recognition sites specific for folate in FL-MIPs but not in FL-NIPs.
Application example 5
125 μ L of the folic acid blotting ratio fluorescence sensors (FL-MIPs) and the non-blotting ratio fluorescence sensors (FL-NIPs) obtained in the above examples were added to 20mg L of each-1Folic acid, tranexamic acid (MTX for short), and ungualThe fluorescence spectrum of each sample was measured by a fluorescence spectrophotometer (excitation wavelength: 365nm, slit width 5/5nm) after the volume of oxabenayl aminopyrimidine (TMP), cysteine (Cys), histidine (His), arginine (Arg), glutamic acid (Glu) and vitamin C (Vc) was adjusted to 1mL with ultrapure water and mixed uniformly for 10 min. (see FIG. 5).
As shown in FIG. 5, the fluorescence intensity ratio of the folate blot ratio fluorescence sensor (FL-MIPs) has the greatest influence, because FL-MIPs contain a large number of blot sites completely matched with folic acid in terms of structure size, configuration, functional groups and the like, so that target molecular folic acid is specifically recognized, while other analogues are difficult to enter into the blot cavity and only can perform nonspecific binding, so that the quenching degree is low, and the fluorescence intensity is not greatly changed. Meanwhile, the ratio change of the FL-NIPs by various analogs has little influence, because no specific recognition site exists on the surface of the FL-NIPs, and the recognition between the FL-NIPs is only non-specific recognition.
Application example 6
125 μ L of the folate blot ratio fluorescence sensor (FL-MIPs) obtained in the above example was added with different concentration ratios of tranexamic acid/folic acid (C)MTX/CFA) Then, the volume was adjusted to 1mL with ultrapure water, and after mixing uniformly, the reaction was carried out for 10min, and then the fluorescence spectrum of each sample was measured with a fluorescence spectrophotometer. Wherein the concentration of folic acid is fixed to 20mg L-1The concentration ratio of the carbamoylic acid/the folic acid is 0,1, 2, 3, 4 and 5 in sequence. (excitation wavelength: 365nm, slit width 5/5 nm). (see FIG. 5 for inset)
As shown in the interpolated graph in FIG. 5, the ratio of the fluorescence intensity of the trace rate fluorescence sensors (FL-MIPs) changes considerably as the concentration of the methotrexate increases, and the result proves that the trace rate fluorescence sensors (FL-MIPs) have higher selectivity for the target folic acid.
Claims (6)
1. A visual molecular imprinting nano sensor is characterized in that: the visible molecular imprinting nano sensor is used for embedding red fluorescent cadmium telluride quantum dots and folic acid with spontaneous blue fluorescence on the surface of silicon dioxide nano particles through sol-gel polymerization imprinting by a one-step method, and a cavity for eluting folic acid is used as an identification site to obtain the dual-fluorescence emission folic acid imprinting microsphere with a core-shell structure;
the preparation method of the visual molecularly imprinted nanosensor comprises the following steps: adding red fluorescent cadmium telluride quantum dots, folic acid and 3-aminopropyltriethoxysilane into a solution containing silicon dioxide nanoparticles, stirring for 1-2h, continuously adding tetraethoxysilane and ammonia water after uniform mixing to perform sol-gel polymerization reaction for 10-12h in a dark environment, precipitating a product by using a centrifugal method after the reaction, removing supernatant, eluting folic acid to obtain folic acid imprinted microspheres with a core-shell structure, and re-dispersing the folic acid imprinted microspheres in 6mL of ultrapure water.
2. The visual molecularly imprinted nanosensor of claim 1, characterized by: the total volume of the sol-gel polymerization reaction system is controlled to be 20-22 mL; wherein the dosage of the silicon dioxide nano particle solution, the CdTe QDs, the folic acid, the APTES, the TEOS and the ammonia water is respectively 1-2mL, 3-5mL, 8-10mL, 37-75 μ L, 50-100 μ L and 50-100 μ L.
3. The visual molecularly imprinted nanosensor of claim 1, characterized by: adding ammonia water into a water/ethanol mixed solution, stirring for 10-30min, uniformly mixing, adding an ethyl orthosilicate ethanol solution drop by using a constant-pressure dropping funnel, stirring for reaction for 10-12h, centrifuging an obtained product, removing a supernatant, washing a precipitate with ethanol, and finally dispersing in 50mL of ultrapure water again for later use.
4. The visual molecularly imprinted nanosensor of claim 3, characterized in that: the concentration of the silicon dioxide nano particles is 1.2-1.5 mg/mL; the total volume of the water/ethanol mixed solution is 80-100mL, and the volume ratio is 5: 3; the volume of the TEOS ethanol solution is 25-30mL, wherein the volume of TEOS accounts for 2% -3%.
5. The visual molecularly imprinted nanosensor of claim 1, characterized by: the folic acid solution is prepared by dissolving folic acid in NaOH ethanol solution.
6. The visual molecularly imprinted nanosensor of claim 5, wherein: the concentration of the folic acid is 1-1.2 g/L; the concentration of the NaOH ethanol solution is as follows: 0.01-0.02 mol.L-1The ethanol accounts for 20-30% of the total volume.
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