CN110849850A - Quantum dot-nanochannel-based copper ion detection method - Google Patents
Quantum dot-nanochannel-based copper ion detection method Download PDFInfo
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Abstract
The invention provides a copper ion detection method based on quantum dot-nanochannels, which comprises the following steps: preparing a CdSe @ ZIF-8/PAA film; the CdSe @ ZIF-8/PAA film is used for manufacturing a chip matched with an inverted fluorescence microscope, the chip comprises a liquid storage tank, the CdSe @ ZIF-8/PAA film is positioned in the liquid storage tank, a working electrode is further arranged in the liquid storage tank, and the working electrode is electrically connected with an electrochemical workstation; adding electrolyte solution and Cu into the liquid storage tank2+A solution, said electrochemical station applying a potential to effect Cu2+Enrichment, the liquid storage tank is subjected to fluorescence spectrum scanning through the inverted fluorescence microscope, and spectrum signals are obtained to realize the Cu-based concentration2+Detection of (3). The detection method provided by the invention is convenient to operate and low in cost, and not only can detect trace copper ions, but also can visualize the detection process.
Description
Technical Field
The invention relates to the technical field of chemical sensing, in particular to a copper ion detection method based on quantum dot-nano channels.
Background
Copper ion (Cu)2+) Is a very important and essential trace element in the living body, but Cu is contained in the human body2+The concentration of (C) must be kept within a certain range if Cu2+Excessive intake of the drug can lead to damage of kidney or liver, gastrointestinal dysfunction, neurodegenerative diseases and cell metabolism destruction. With the increasing discharge of industrial wastewater and coal mine acid wastewater, Cu2+Pollution also affects various aspects of human life, such as: food, drinking water and various industrial products. To date, Cu2+There are many methods of quantitative analysis of (c), for example: atomic absorption spectrometry, high performance liquid chromatography, ion chromatography, anodic stripping voltammetry, and the like. However, these methods have certain disadvantages in that they require expensive and complicated instruments and cumbersome sample processing procedures, and cannot achieve visualization effects.
Therefore, for general routine detection, it is very meaningful to develop a method which is convenient to operate and low in cost, and can detect trace copper ions and visualize the detection process.
Disclosure of Invention
The invention aims to solve the problems that the copper ion detection method in the prior art is complicated in process, cannot be visualized and the like to a certain extent.
In order to solve the problems, the invention provides a copper ion detection method based on quantum dot-nano channel, comprising the following steps:
preparing a CdSe @ ZIF-8/PAA film;
the CdSe @ ZIF-8/PAA film is used for manufacturing a chip matched with an inverted fluorescence microscope, the chip comprises a liquid storage tank, the CdSe @ ZIF-8/PAA film is positioned in the liquid storage tank, a working electrode is further arranged in the liquid storage tank, and the working electrode is electrically connected with an electrochemical workstation;
adding electrolyte solution and Cu into the liquid storage tank2+A solution, said electrochemical station applying a potential to effect Cu2 +Enriching, feeding into the liquid storage tank by the inverted fluorescence microscopeScanning line fluorescence spectrum and acquiring spectrum signals to realize Cu contrast2+Detection of (3).
Optionally, the spectral signal is varied with Cu2+Increase in concentration and decrease in Cu2+The measured value of the concentration is obtained from the acquired spectral signal by solving the following equation:
y＝6143.76-992.76logx，
wherein y is a spectral signal, and x is Cu2+The concentration of (c).
Optionally, the Cu2+The concentration of the solution is in the range of 0.01pM to 1. mu.M, the Cu2+The detection limit of (2) was 0.004 pM.
Optionally, the preparing the CdSe @ ZIF-8/PAA film comprises the steps of:
and (2) placing the PAA film between two semi-electrolytic tanks and communicating the two semi-electrolytic tanks, adding CdSe quantum dots and a zinc nitrate solution into one semi-electrolytic tank, simultaneously adding the CdSe quantum dots and a 2-methylimidazole solution with the same volume into the other semi-electrolytic tank, sealing for 22-26h, taking out the film, ultrasonically washing with ultrapure water, and finally drying to obtain the CdSe @ ZIF-8/PAA film.
Optionally, the volume ratio of the CdSe quantum dots, the zinc nitrate solution and the 2-methylimidazole solution is 1: (1-50): (1-6).
Optionally, the preparation method of the CdSe quantum dot includes:
adding 3-mercaptopropionic acid into the cadmium chloride solution, controlling the pH value to be 10-11, uniformly stirring, adding a sodium hydroselenide solution under the protection of nitrogen, reacting for 7-9h at 90-100 ℃, and then separating and purifying to obtain the CdSe quantum dots.
Optionally, the manufacturing of the chip adapted to the inverted fluorescence microscope by using the CdSe @ ZIF-8/PAA film includes:
mixing polydimethylsiloxane and a curing agent according to the weight ratio of 10:1, uniformly stirring and pouring the mixture on a template, vacuumizing and heating the mixture to perform a curing reaction, and demolding to obtain a polydimethylsiloxane plate;
respectively arranging a first micropore and a second micropore which are matched with the micro-channel of the inverted fluorescence microscope on the two polydimethylsiloxane plates, wherein the first micropore and the second micropore are suitable for forming a cross channel;
and respectively cleaning the two polydimethylsiloxane plates according to the sequence of ethanol and ultrapure water, then drying, placing the CdSe @ ZIF-8/PAA film between the two polydimethylsiloxane plates, and bonding the CdSe @ ZIF-8/PAA film with the polydimethylsiloxane plates at the cross channel through ultraviolet irradiation to obtain the cross chip.
Optionally, the applying of the potential through the electrochemical workstation realizes Cu2+Enrichment, comprising: the electrochemical workstation applies a potential of 5V.
Optionally, the measurement conditions of the fluorescence spectrum include that the excitation wavelength is 450nm, and the spectrum scanning range is 480-650 nm.
Optionally, the electrolyte solution is a 1mmol/L KCl solution, a 1mmol/L PBS solution or a 1mmol/L NaCl solution.
Compared with the prior art, the quantum dot-nanochannel-based copper ion detection method provided by the invention has the following advantages:
(1) according to the invention, CdSe quantum dots are added into a solution containing a ZIF-8 precursor, so that a ZIF-8 framework is assembled around the quantum dots, the quantum dots are embedded into the ZIF-8 framework and are filled in a PAA nano channel together to form a quantum dot-nano channel (CdSe @ ZIF-8) film, the CdSe @ ZIF-8 film is used for preparing a sensor, and the quantum dots have high fluorescence efficiency, high sensitivity and high selectivity on copper ion detection and the enrichment effect of the nano channel on copper ions are utilized, so that on one hand, the sensing signal and specificity of a fluorescence probe are enhanced, and the high sensitivity and high selectivity on the copper ions are detected; on the other hand, the copper ions interact with hydroxyl groups of the CdSe quantum dots, so that the fluorescence of the CdSe @ ZIF-8/PAA film is quenched, and the detection process is visualized.
(2) The copper ion detection method provided by the invention has the advantages of simple structure, low cost, mild reaction conditions, high response speed and good linear detection range (0.01pM-1 mu M) for copper ions, and the detection limit can be as low as 0.004pM due to the electric field enrichment effect of the nanochannel.
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FIG. 1 is a flow chart of a method for detecting copper ions according to an embodiment of the present invention;
FIG. 2 is a schematic structural diagram of a cross-type chip according to an embodiment of the present invention;
FIG. 3 is a diagram illustrating the detection of Cu with different concentrations by synthesizing CdSe @ ZIF-8 solutions with different volume ratios according to an embodiment of the present invention2+And a linear plot of fluorescence intensity versus concentration of: (a) and (g) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:1: 1; (b) and (h) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:2: 2; (c) and (i) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:3: 3; (d) and (j) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:4: 4; (e) and (k) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:5: 5; (f) and (l) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Plot of fluorescence versus linearity at 1:6: 6;
FIG. 4(a) is an SEM of ZIF-8 according to an embodiment of the present invention; FIG. 4(b) SEM picture of CdSe @ ZIF-8 according to an embodiment of the present invention;
FIG. 5(a) is a TEM image of CdSe quantum dots according to the embodiment of the present invention; FIG. 5(b) is a HRTEM image of a CdSe quantum dot; FIG. 5(c) is a TEM image of ZIF-8; FIG. 5(d) is a TEM image of CdSe @ ZIF-8;
FIG. 6 is an EDS spectrum of CdSe @ ZIF-8 according to an embodiment of the present invention;
FIGS. 7(a) and (c) are fitting curves of fluorescence decay of CdSe quantum dots according to the embodiment of the present invention; FIGS. 7(b) and (d) are fitting curves of fluorescence decay of CdSe @ ZIF-8 according to examples of the present invention;
FIG. 8(a) is a complete XPS spectrum of a sample according to an embodiment of the present invention; FIG. 8(b) is an XPS spectrum of the Cd3d and N1s peaks of CdSe quantum dots, CdSe @ ZIF-8, and CdSe @ ZIF-8/PAA films according to an embodiment of the present invention;
FIG. 9 is an inverted fluorescence microscope image of an embodiment of the invention, wherein (a) is a pure PAA film; (b) is a ZIF-8/PAA film; (c) is a CdSe @ ZIF-8/PAA film; (d) cu at a concentration of 1. mu.M2+The treated CdSe @ ZIF-8/PAA film;
FIG. 10 shows Cu concentrations in accordance with an embodiment of the present invention2+A fluorescence microscopy image of the treated CdSe @ ZIF-8/PAA film array nanochannel, wherein (a)0 pM; (b)0.01 pM; (c)0.1 pM; (d)1 pM; (e)10 pM; (f)100 pM; (g)1 nM; (h)10 nM; (i)100 nM; (j)1 mu M;
FIG. 11(a) shows different Cu embodiments of the present invention2+A spectral signal corresponding to the concentration; FIG. 11(b) shows the spectrum signal and Cu according to the embodiment of the present invention2+Linear relationship of concentration (0.01 pM-1. mu.M);
FIG. 12(a) shows Cu2+(1. mu.M) and other metal ions (Zn)2+、Pb2+、Mn2+、Fe3+、Co2+、Cd2+And Ba 2+10 μ M) corresponding fluorescence profile; FIG. 12(b) other Metal ions and Cu2+Corresponding fluorescence histograms.
Description of reference numerals:
the material comprises 1-PAA film, 2-CdSe quantum dots, 3-ZIF-8 particles, 4-PDMS plate, 5-first micropores and 6-second micropores.
Detailed Description
It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
In addition, the terms "comprising," "including," "containing," and "having" are intended to be non-limiting, i.e., that other steps and other ingredients can be added that do not affect the results. Materials, equipment and reagents are commercially available unless otherwise specified.
Zeolite imidazole framework (ZIF-8) is a ZIF series of metal-organic framework material having a structure formed from metal ions Zn2+And imidazolyl ligands, can grow freely in the nanochannel and fill the nanochannel without being restricted by the channel pore size; while the porous anodic aluminum oxide (PAA) film is a nano-channel array with high densityThe nano-channel has stable aperture and good physical and chemical properties, can provide a stable carrier for the ZIF-8 material, and can functionalize the inner surface of the pore channel by modifying the interior of the pore channel. The ZIF-8/PAA film can be used as a membrane electrode to improve the sensitivity of an electrochemical sensor, and in some literatures, the ZIF-8/PAA film is mentioned to have the effect of Pb2+Has strong adsorption capacity, but has strong Cu adsorption capacity2+The detection effects are not obvious, and the detection effects are based on that ZIF-8 has acidic and basic functional groups and can adsorb pollutants with different properties, so that the detection result can only be displayed by an instrument and cannot achieve the visual effect.
In order to solve the problems, the invention provides a quantum dot-nanochannel-based copper ion detection method, which comprises the steps of preparing a quantum dot-nanochannel (CdSe @ ZIF-8) composite material and preparing the CdSe @ ZIF-8 composite material into an electrochemical sensor. The fluorescence of CdSe quantum dots in the CdSe @ ZIF-8/PAA film can be quenched by utilizing the copper ions, and the nano-channel has certain selective adsorbability on the copper ions, so that the adsorption property can play an enrichment role on the copper ions, and the sensing signal and specificity of a fluorescent probe are greatly enhanced, therefore, the copper ions can be detected by an electrochemical sensor made of the CdSe @ ZIF-8 composite material, the detection method can detect trace copper ions, the detection process can be visualized, and the detection method has ultrahigh sensitivity and selectivity.
In order to make the aforementioned objects, features and advantages of the present invention comprehensible, embodiments accompanied with figures are described in detail below.
Referring to fig. 1-2, a method for detecting copper ions based on quantum dots-nanochannels includes the steps of:
s1, preparing a CdSe @ ZIF-8/PAA film;
s2, preparing an electrochemical sensor: the chip matched with the inverted fluorescence microscope is manufactured by utilizing the CdSe @ ZIF-8/PAA film, the chip comprises a liquid storage tank, the CdSe @ ZIF-8/PAA film is positioned in the liquid storage tank, a working electrode is also arranged in the liquid storage tank, and the working electrode is electrically connected with the electrochemical workstation;
s3, copper ion (Cu)2+) Detection of (2):adding electrolyte solution and Cu into the liquid storage tank2+Solution, electrochemical station applying potential to realize Cu2+Enrichment, fluorescence spectrum scanning is carried out on the liquid storage tank through an inverted fluorescence microscope, and spectrum signals are obtained to realize the Cu2+Detection of (3).
According to the embodiment of the invention, the synthesized cadmium selenide (CdSe) quantum dots are added into a solution containing a zeolite imidazole framework (ZIF-8) precursor, so that a ZIF-8 framework is assembled around the quantum dots, the quantum dots are embedded into the ZIF-8 framework and are filled in a porous anodic aluminum oxide (PAA) nano channel together to form a quantum dot-nano channel (CdSe @ ZIF-8) film, the CdSe @ ZIF-8 film is prepared into an electrochemical sensor, and the quantum dots have high fluorescence efficiency, high sensitivity and high selectivity on copper ion detection and the enrichment function of the nano channel on copper ions, so that on one hand, the sensing signal and specificity of a fluorescence probe are enhanced, and the high sensitivity and high selectivity on the copper ions are detected; on the other hand, the copper ions interact with hydroxyl groups of the CdSe quantum dots, so that the fluorescence of the CdSe @ ZIF-8/PAA film is quenched, and the detection process is visualized.
In step S1, a CdSe @ ZIF-8/PAA film is prepared by an in-situ growth method, and ZIF-8 particles embedded with CdSe quantum dots are modified into a nanochannel of a PAA film, wherein the step includes preparation of the PAA film, synthesis of the CdSe quantum dots, and preparation of the CdSe @ ZIF-8/PAA film using a self-made PAA film and CdSe quantum dots as raw materials. The method specifically comprises the following steps:
s11 preparation of PAA film
The PAA film is prepared by adopting a two-step anodic oxidation method, and the specific steps are as follows:
1) cutting an aluminum sheet into a required shape, then performing ultrasonic treatment for 4-5min respectively according to the sequence of 1mol/L NaOH aqueous solution, ultrapure water and absolute ethyl alcohol, and drying by nitrogen; 2) anodic oxidation: performing first anodic oxidation under the conditions of using a phosphoric acid solution with the concentration of 0.4M as an electrolyte and the voltage of 100V, wherein the first anodic oxidation time is 2 h; after the first anodic oxidation is finished, taking out the aluminum sheet and placing the aluminum sheet in the mixed solution of 1.8 wt% of chromic acid and 6 wt% of phosphoric acidPerforming water bath at 60 deg.C for 40-50 min; then, carrying out second anodic oxidation under the conditions that a phosphoric acid solution with the concentration of 0.4M is used as an electrolyte and the voltage is 100V to obtain an aluminum oxide film, wherein the second anodic oxidation time is 8 h; 3) placing the oxidized alumina film in stannous chloride (SnCl)2) In the solution, stannous chloride with higher concentration (a small amount of hydrochloric acid can be added to accelerate the replacement reaction rate) is used for removing aluminum on the back of the aluminum oxide film until a light yellow transparent film is seen, the reaction is stopped, ultrapure water is used for ultrasonic treatment for about one minute to remove all residues, and the steps are repeated for a plurality of times until the aluminum base is completely removed (namely the aluminum film becomes transparent and yellowish), so that the PAA film is obtained. Placing the prepared PAA film in ultrapure water for 10-12H to soak out oxalic acid in the PAA film, and then placing the PAA film in 5 wt% phosphoric acid (H)3PO4) and water bath at 40 deg.C for 30min, pore-expanding the PAA membrane, air drying with anhydrous ethanol, and storing at low temperature for subsequent use.
S12 synthesis of CdSe quantum dots
In the embodiment of the invention, the preparation steps of the CdSe quantum dots comprise: to cadmium chloride (CdCl)2) Adding 3-mercaptopropionic acid into the solution, controlling the pH value to be 10-11, stirring uniformly, adding sodium hydroselenide solution under the protection of nitrogen, reacting for 7-9h at 90-100 ℃, and then separating and purifying to obtain the CdSe quantum dots
Specifically, the method comprises the following steps: 1) 0.0913g of CdCl were weighed out2Dissolving in a beaker with ultrapure water and fixing the volume to 100mL to obtain 0.004M CdCl2Adding 35 mu L of 3-mercaptopropionic acid (3-MPA) into a beaker, controlling the pH value of the solution to be 10-11 by using 1M NaOH solution, placing the mixed solution into a 500mL three-neck flask, assembling the three-neck flask into a condensation reflux device, setting the condensation reflux temperature to be 5 ℃, and introducing N2 into the reflux device; 2) 0.078g of selenium (Se) powder and 0.140g of sodium borohydride (NaBH) were added in sequence to a 50mL conical flask with a stopper4) And 3mL of ultrapure water, covering a plug, and reacting in an ice water bath for 30min to obtain a clear and transparent sodium hydrogen selenide (NaHSe) solution; 3) adding the prepared NaHSe solution (200 mu L) into a three-neck flask protected by nitrogen, and heating for 8 hours in a water bath at the temperature of 95 ℃ to prepare CdSe quantum dots; 4) completion of the reactionAnd then, adding 200mL of absolute ethyl alcohol into the CdSe quantum dot solution, centrifuging for 25min at 9000r/min, removing supernatant, dissolving precipitate with ultrapure water to obtain a purified CdSe quantum dot solution, and storing at 4 ℃ for later use.
Synthesis of S13, CdSe @ ZIF-8/PAA film
Placing the PAA film in the middle of two semi-electrolytic baths and connecting the two semi-electrolytic baths, and adding CdSe quantum dots and zinc nitrate (Zn (NO)3)2·6H2O) solution is added into one half electrolytic tank, meanwhile, CdSe quantum dots and 2-methylimidazole solution with the same volume are added into the other half electrolytic tank, sealing is carried out for 22-26h, then the membrane is taken out, ultra-pure water is used for ultrasonic washing, and finally drying is carried out to obtain the CdSe @ ZIF-8/PAA membrane.
Wherein, in the preparation process of the S13CdSe @ ZIF-8 film, CdSe quantum dots and Zn (NO)3)2And mIm, the inventors prepared CdSe @ ZIF-8 mixtures and tested the mixtures on Cu to obtain the appropriate volume ratios of the three2+And (3) detecting the proportion with the best effect, and calculating and obtaining the optimal reaction condition of the CdSe @ ZIF-8 film. The embodiment of the optimized experimental conditions provided by the embodiment of the invention is as follows:
synthesis of S14, CdSe @ ZIF-8 mixture
The specific procedure for the synthesis of the CdSe @ ZIF-8 mixture was as follows: 1) dissolve 1.027g of Zn (NO) in 10mL of ultrapure water3)2·6H2O, Zn (NO) at 49mM3)2A solution; 2) 2.271g of mIm was dispersed in 10mL of ultrapure water to prepare a 39.5mM mIm solution; 3) adding CdSe quantum dots to Zn (NO)3)2mIm to form orange suspension, centrifuging, washing with ultrapure water for 3 times, and drying at 60 deg.C overnight to obtain CdSe @ ZIF-8 mixture.
CdSe and Zn (NO) are added according to the preparation method of the step S143)2And mIm are synthesized into CdSe @ ZIF-8 solution respectively in the volume ratio of 1:1:1, 1:2:2, 1:3:3, 1:4:4, 1:5:5 and 1:6: 6. Then, Cu of different concentrations2+Adding into CdSe @ ZIF-8 solutionIn (1), the reaction time is 30 min. Then, the fluorescence spectrum detection is performed with 450nm as the excitation wavelength and 480-650nm as the wavelength range. Selecting CdSe @ ZIF-8 to Cu2+The ratio with the best detection effect is the optimal ratio, and the CdSe @ ZIF-8/PAA film is prepared according to the ratio.
FIG. 3 is a diagram illustrating the detection of Cu with different concentrations by synthesizing CdSe @ ZIF-8 solutions with different volume ratios according to an embodiment of the present invention2+And a linear relationship graph of fluorescence intensity and concentration of (a) and (g) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:1: 1; (b) and (h) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:2: 2; (c) and (i) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:3: 3; (d) and (j) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:4: 4; (e) and (k) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:5: 5; (f) and (l) is V [ CdSe ]]:V[Zn(NO3)2]:V[mIm]Graph of fluorescence curves and linearity at 1:6: 6. As can be seen from the figure, CdSe quantum dots, Zn (NO)3)2mIm, the volume ratio of which is 1:1:1, is used for Cu with different concentrations2+The results of the fluorescence detection of (2) are shown in FIG. 3(a), and it can be seen from the graph that Cu is included2+The fluorescence intensity gradually decreases with increasing concentration. Fluorescence intensity as ordinate, Cu2+The results are plotted on the abscissa, and are shown in FIG. 3(g), where it can be seen that the concentration is in the range of 10 to 1000nMCu2+Fluorescence intensity and Cu in the concentration range2+The logarithm of the concentration has good linear relation, and the linear correlation coefficient is R2＝0.98。
CdSe quantum dots, Zn (NO)3)2And mIm, detecting Cu with different concentrations by using CdSe @ ZIF-8 mixed solution synthesized by the three in a volume ratio of 1:2:22+The fluorescence curve of (A) is shown in FIG. 3(b), and it can be seen from the graph that Cu is included2+The fluorescence intensity gradually decreases with increasing concentration of (2). Fluorescence intensity as ordinate, Cu2+Concentration is plotted on the abscissa, and the results are obtainedAs shown in FIG. 3(h), it can be seen that the fluorescence intensity and Cu were observed in the concentration range of 10 to 1000nM2+The logarithm of the concentration has good linear relation, and the linear correlation coefficient is R2＝0.99。
When CdSe quantum dots, Zn (NO)3)2mIm at volume ratios of 1:3:3, 1:4:4, 1:5:5 and 1:6:6, although Cu is shown in FIGS. 3(c) -3(f)2+The fluorescence of the synthesized CdSe @ ZIF-8 was quenched and the intensity was reduced, but as shown in FIGS. 3(i) -3(l), the fluorescence intensity was correlated with that of Cu2+The concentration relationship deviates from linearity.
Therefore, in summary, it can be seen that CdSe quantum dots, Zn (NO)3)2And mIm, whereby the preparation of CdSe @ ZIF-8/PAA is also a choice for this volume ratio.
That is, step S13 specifically includes: 2.5mLCdSe quantum dots and 10mL of 49mM zinc nitrate (Zn (NO)3)2·6H2O) solution was added to one of the half-cells while 2.5mLCdSe quantum dots and 10mL of a 39.5mM 2-methylimidazole solution (mIm) were added to the other half-cell, sealed for 24h, and then the film was taken out, ultrasonically washed 3 times with ultrapure water, and dried at 60 ℃ for 1h to obtain CdSe @ ZIF-8/PAA film.
To characterize the ability of CdSe quantum dots and ZIF-8 particles to be modified in PAA films, the inventors also provided examples of preparing ZIF-8, ZIF-8/PAA films to characterize the synthesized CdSe quantum dots, PAA films, ZIF-8, CdSe @ ZIF-8, ZIF-8/PAA films, and CdSe @ ZIF-8/PAA films, further illustrating the properties of the CdSe @ ZIF-8 films prepared by the examples of the present invention. The following are described by way of example:
synthesis of S15 and ZIF-8
The specific process for synthesizing ZIF-8 is as follows: 1) 1.027g of zinc nitrate (Zn (NO) was dissolved in 70mL of ultrapure water3)26H2O) to form a 49mM zinc nitrate solution; 2) 2.271g of a 2-methylimidazole solution (mIm) was dispersed in 70mL of ultrapure water to form a 39.5mM mIm solution; 3) mixing the obtained zinc nitrate solution and mIm solution uniformly, stirring for 2 hr to obtain white suspension, centrifuging the white suspension, and washing with ultrapure water for 3 timesAnd dried at 110 ℃ for 12 hours to obtain ZIF-8 white powder.
Preparation of S16, ZIF-8/PAA film
Preferably, the ZIF-8/PAA film is prepared by an in-situ growth method. Firstly, the prepared PAA membrane is placed between two self-made semi-electrolytic membranes and two self-made semi-electrolytic cells. 49mMZn (NO)3)2·6H2The methanolic solution of O was added to one half of the cells and the same volume of 39.5mM mIm solution (methanol as reagent) was added to the other half of the cells; then sealed for 72h and replaced by Zn (NO) every 24h3)2·6H2Methanol solution of O and mIm solution; and finally, taking out the membrane, ultrasonically washing the membrane for 3 times by using a large amount of methanol, and drying the membrane for 1h at the temperature of 110 ℃ to obtain the ZIF-8/PAA membrane.
As shown in FIG. 4, FIG. 4(a) is an SEM photograph of ZIF-8 synthesized using water as a solvent, and FIG. 4(b) is an SEM photograph of CdSe @ ZIF-8. As can be seen from the figure, the prepared ZIF-8 particles have a flaky structure and are uniform in size; the shape of the synthesized CdSe @ ZIF-8 is also a sheet structure, which is similar to the structure of the synthesized ZIF-8, and this shows that the addition of quantum dots does not affect the nano-channel structure of the ZIF-8.
FIG. 5, taken in conjunction with FIG. 5, is a TEM image of ZIF-8, CdSe quantum dots, and CdSe @ ZIF-8. Among them, fig. 5(a) is a TEM image of the CdSe quantum dot, and it can be seen that the shape of the CdSe quantum dot is nearly spherical and the quantum dot is significantly aggregated; FIG. 5(b) is an HRTEM image of a CdSe quantum dot from which many extra small stripes can be observed, indicating that the structure of the CdSe quantum dot is purely crystalline; FIG. 5(c) is a TEM image of ZIF-8, from which it can be seen that the prepared ZIF-8 has a plate-like shape, which is the same as the result of the SEM image of ZIF-8; FIG. 5(d) is a TEM image of CdSe @ ZIF-8, from which it can be seen that the morphology of CdSe @ ZIF-8 is similar to that of ZIF-8, and that CdSe quantum dots are immobilized in the ZIF-8 framework.
To confirm the presence of cadmium (Cd), selenium (Se) and zinc (Zn) in the CdSe @ ZIF-8 sample, the sample was analyzed using an energy scattering X-ray fluorescence spectrometer (EDS), and the results are shown in FIG. 6. from FIG. 6, it can be seen that Cd, Se and Zn peaks are present in the EDS spectrum, which further illustrates that CdSe quantum dots are immobilized in the ZIF-8 structure.
Carrying out transient fluorescence detection on the synthesized CdSe quantum dots and CdSe @ ZIF-8, monitoring a fluorescence decay curve at a luminescence maximum value, and fitting through three exponential functions to obtain:
wherein, tau1、τ2And τ3Represents the time constant, B1、B2And B3The weights are indicated, respectively, and the data are shown in table 1.
TABLE 1 fitting of fluorescence decay fitting curves
Mean fluorescence lifetime (. tau.)av) Calculated by the following formula:
calculated mean fluorescence lifetime τ of CdSe quantum dotsavAn average fluorescence lifetime τ of 39.29ns, CdSe @ ZIF-8avIs 30.74 ns. The experimental result shows that the fluorescence lifetime of CdSe @ ZIF-8 is smaller than the average fluorescence lifetime of CdSe quantum dots, and the possible reason is that the CdSe quantum dots are embedded in a ZIF-8 framework, so that the energy transfer rate of ZIF-8 is lower.
Meanwhile, in connection with FIG. 7, FIGS. 7(a) and (c) are fitting curves of fluorescence decay of CdSe quantum dots with fitting coefficient x21.112, close to 1, indicates a good fit. FIGS. 7(b) and (d) are fitting curves of the fluorescence decay of CdSe @ ZIF-8 with fitting coefficient x21.199, close to 1, indicates a better fit. This shows that the calculated values of the average fluorescence lifetimes of the CdSe quantum dots and CdSe @ ZIF-8 have certain reliability.
In addition, in order to further confirm that CdSe quantum dots and ZIF-8 can be modified into PAA films, the prepared PAA films, CdSe quantum dots, ZIF-8, CdSe @ ZIF-8, ZIF-8/PAA films and CdSe @ ZIF-8/PAA films were analyzed using XPS, and the results are shown in FIG. 8.
As can be seen from fig. 8(a), in the XPS curve of ZIF-8, significant Zn2p, O1s, N1s, and C1s peaks can be observed; from the XPS curve of the PAA film, significant O1s, C1s, Al2s, and Al2p peaks were observed; from XPS curves of CdSe quantum dots, significant Cd3d, Se3p3, N1s, and O1s peaks can be observed, consistent with the reference; from the XPS curve of CdSe @ ZIF-8, a significant Cd3d peak was observed in addition to the significant Zn2p, O1s, N1s and C1s peaks; from the XPS curve of the ZIF-8/PAA film, not only significant Zn2p, O1s, N1s, and C1s peaks, but also Al2s and Al2p peaks were observed; from the XPS curve of the CdSe @ ZIF-8/PAA film, not only significant Zn2p, O1s, N1s, C1s, Al2s and Al2p peaks, but also significant Cd3d peaks were observed.
Because the Cd3d peak and the N1s peak are difficult to distinguish in the whole graph, the data of the Cd3d peak and the N1s peak are amplified, and an enlarged graph is shown in 8(b), and the two Cd3d peaks of the CdS quantum dot, namely Cd3d3 and Cd3d5, can be seen from the graph, and the corresponding binding energies of the two peaks are 411.7eV and 405 eV. The patterns of the CdSe @ ZIF-8 and CdSe @ ZIF-8/PAA films not only have two Cd3d peaks, but also have an N1s peak. Thus, in summary, it can be shown that ZIF-8 and CdSe quantum dots have been successfully modified into PAA films.
Specifically, the step S2 of preparing the electrochemical sensor includes fabricating a cross chip that can be used on an inverted fluorescence microscope, so as to observe the PAA film, the ZIF-8/PAA film, and the CdSe @ ZIF-8/PAA film, which are prepared in the above embodiments, through the inverted microscope, and determine the fluorescence property of the prepared sample. The cross chip is formed by bonding two linear micro channels and a porous alumina membrane nano channel, wherein four small holes connected with the micro channels are formed in the chip. The device is equivalent to two self-made half electrolytic cells, and can provide reaction sites for subsequent electrolyte solution, working electrodes and the like. In addition, the micro-channel-nano-channel composite chip constructed by combining the micro-channel and the nano-channel can also realize the enrichment and detection of target objects in a micro sample.
Preparing a chip matched with an inverted fluorescence microscope by using the CdSe @ ZIF-8/PAA film, wherein the step S2 specifically comprises the following steps:
1) mixing a Polydimethylsiloxane (PDMS) monomer and a curing agent according to a volume ratio of 10:1, uniformly stirring, pouring on a template, vacuumizing for 10min to remove bubbles, heating at 70 ℃ for 2h to cure the PDMS, and demolding from the template to obtain a PDMS plate 4;
2) the two PDMS plates 4 are respectively provided with a first micropore 5 and a second micropore 6 which are matched with the micro-channel of the inverted fluorescence microscope, the first micropore 5 and the second micropore 6 are suitable for forming a cross channel, and the cross channel forms a liquid storage tank which is connected with the micro-channel;
3) cleaning and drying two PDMS plates 4 provided with a first micropore 5 and a second micropore 6 by using acetone, ethanol and ultrapure water in sequence; and (3) placing the CdSe @ ZIF-8/PAA film between the two dried clean PDMS plates 4, placing the PDMS plates in an ultraviolet irradiator for ultraviolet irradiation for 15min, and bonding the CdSe @ ZIF-8/PAA film with the PDMS plates 4 at the cross channel to obtain a cross chip, thereby completing the preparation of the electrochemical sensor.
As shown in FIG. 2, the CdSe @ ZIF-8/PAA film includes a PAA film 1, and ZIF-8 particles 3 embedded with CdSe quantum dots 2, which are modified in a nano-channel of the PAA film 1.
Wherein, still put working electrode in the liquid storage pond, working electrode and electrochemistry workstation electricity are connected. During detection, the CHI660E electrochemical workstation applied a detection potential of 5V to the working electrode. In an embodiment of the invention, the working electrode is a platinum (Pt) electrode.
Cu of step S32+In the detection, the cross chip prepared in step S2 was bonded to a 0.4mM clean glass plate, and 1mM electrolyte solution and Cu were added to the liquid reservoir of the cross chip2+Solution, electrochemical workstation applying 5V potential to realize Cu2+Enriching, placing on an objective table of an inverted microscope, performing fluorescence spectrum scanning by the inverted fluorescence microscope, exciting by using blue light, and observing the change of green fluorescence. Observation of Cu2+The fluorescence intensity of the CdSe @ ZIF-8/PAA film array nano-channel changes when the solution is added, and the observed fluorescence intensity change is converted into a spectrum through a spectrometerFigure, quantitative analysis is carried out to realize the aim of Cu2+Detection of (3).
Blue light excitation is used for observation by an inverted fluorescence microscope, green fluorescence is generated by the CdSe @ ZIF-8/PAA film, and the central wavelength of a spectrometer is set to be 545 nm.
The electrolyte solution may be a 1mmol/L KCl (potassium chloride) solution, a 1mmol/L PBS (phosphate buffer salt) solution, or a 1mmol/L NaCl (sodium chloride) solution.
To understand the fluorescence properties of the prepared CdSe @ ZIF-8/PAA films, observations were made using an inverted fluorescence microscope (blue light excitation) and the results are shown in FIG. 9. FIG. 9(a) is a fluorescence microscope photograph of a pure PAA film, from which it can be seen that no fluorescence is generated by the pure PAA film at an exposure time of 200 ms. FIG. 9(b) is a fluorescence microscope photograph of a ZIF-8/PAA film, from which it can be seen that the ZIF-8/PAA film does not generate fluorescence at an exposure time of 200 ms. FIG. 9(c) is a fluorescence microscope photograph of a CdSe @ ZIF-8/PAA film, from which it can be seen that at an exposure time of 200ms, the CdSe @ ZIF-8/PAA film can generate green fluorescence, which is mainly caused by the fluorescence effect of CdSe quantum dots. FIG. 9(d) shows the use of 1. mu. MCu2+The fluorescence pattern after processing the CdSe @ ZIF-8/PAA film shows that the green fluorescence of the CdSe @ ZIF-8/PAA film disappears, which indicates that the Cu is coated on the surface of the film2+The fluorescence of the CdSe @ ZIF-8/PAA film can be quenched; that is, the CdSe @ ZIF-8/PAA film array nano-channel can be used for Cu2+Detection of (3).
It is understood that the ZIF-8/PAA material has a strong adsorption effect on cations, and the imidazole structure and Cu in the ZIF-8/PAA material2+Has complexation between them, so that the CdSe @ ZIF-8/PAA film is coated with Cu2+Has strong adsorption effect to make Cu2+Enriched in CdSe @ ZIF-8/PAA film surface and enriched in Cu2+Can react with groups on the surface of the quantum dot material to form a complex with inactive fluorescence but active ultraviolet, and finally inhibits the fluorescence of the quantum dot through an internal filtering effect, so that a fluorescence quenching phenomenon occurs. The quantum dot-nanochannel-based copper ion detection method provided by the embodiment of the invention has the advantages of simple device preparation process, low cost, mild reaction conditions, fluorescence inhibition and Cu2+Synergistic effect of enrichmentThe sensitivity of the sensing probe can be greatly improved, the response speed is high, the detection is convenient, the period is short, the stability is high, and the reproducibility is good.
To further explore the use of quantum dot-nanochannel based electrochemical sensors for the detection of Cu2+The sensitivity of (3), in step S3, may include the steps of:
s31 sensitivity analysis
The method specifically comprises the following steps: during the detection, Cu with the concentration of 0-1 mu M is added into the liquid storage tank2+The solution is applied with 5V potential by using an electrochemical workstation, and under the action of electric field force, Cu2+Will enter and concentrate in the nanochannel. Due to Cu2+The fluorescence of CdSe @ ZIF-8 can generate quenching effect, and Cu with different concentrations can be observed by an inverted microscope2+The fluorescence intensity of the CdSe @ ZIF-8/PAA film array nano-channel changes when the solution is added.
As can be seen from FIG. 10, in conjunction with FIGS. 10-11, with Cu2+The green fluorescence gradually darkens or even is completely quenched as the concentration increases. FIG. 11 is a spectrum signal converted by a spectrometer from the change of a fluorescence signal observed by a fluorescence microscope, and it can be seen from FIG. 11(a) that the spectrum signal is varied with Cu2+The concentration decreased with increasing concentration, and FIG. 11(b) shows the spectrum signal and Cu2+Graph of concentration dependence, from which the spectral signal is seen to be Cu2+The logarithm of the concentration is linear. The equation is defined as y-6143.76-992.76 logx (nM), where y is the spectral signal and x is Cu2+The correlation coefficient of this equation is 0.97. For Cu due to electric field enrichment of nano channel2+The detection limit of (A) is as low as 0.004 pM.
For characterizing CdSe @ ZIF-8/PAA film array nano-channel pair Cu2+In the detecting of step S3, the method may include the steps of:
s32, CdSe @ ZIF-8/PAA film array nanochannel selectivity research
Selective to Cu2+The detection is very important, and the fluorescence property of the quantum dot-nano channel electrochemical sensor based on the CdSe @ ZIF-8/PAA film is attributed to the CdSe @ ZIF-8 material, so that the CdSe @ ZIF-8 material can pass throughThe selectivity of the mixed solution determines the selectivity of the CdSe @ ZIF-8/PAA film.
The method specifically comprises the following steps: as described in the synthesis of the S14-CdSe @ ZIF-8 mixture with CdSe quantum dots, Zn (NO)3)2mIm, preparing CdSe @ ZIF-8 solution with the volume ratio of 1:2:2, and then adding 1 mu Cu into the CdSe @ ZIF-8 solution respectively2+And 10 μ M of other metal ion, the other metal ion being Zn2+、Pb2+、Mn2+、Fe3+、Co2+、Cd2+And Ba2+And the reaction time is 30min, and finally, the fluorescence spectrum detection is carried out by taking 450nm as the excitation wavelength and taking the wavelength range of 480-.
FIG. 12(a) shows Cu in combination with FIG. 122+(1. mu.M) and other metal ions (e.g. Zn)2+、Pb2+、Mn2+、Fe3+、Co2 +、Cd2+And Ba 2+10 μ M) corresponding fluorescence profile; FIG. 12(b) shows other metal ions and Cu2+Corresponding fluorescence histogram, wherein error bars were obtained by calculating the results of three experiments. As can be seen from the figure, when Cu is present2+The fluorescence intensity of the CdSe @ ZIF-8 solution was significantly reduced at 1. mu.M, while other metal ions (Zn) were present at 10. mu.M2+、Pb2+、Mn2+、Fe3+、Co2+、Cd2+And Ba2+) The decrease of the fluorescence intensity of the CdSe @ ZIF-8 solution was not significant, which indicates that the CdSe @ ZIF-8 solution was not significant for Cu2+Has good selectivity. Thus, CdSe @ ZIF-8/PAA film array nano-channel sensor pair Cu2+Has good selectivity. The high selectivity is mainly attributed to the enrichment of ZIF-8 in the selective adsorption of heavy metal ions and the CdSe quantum dot on Cu2+Selectively sensing the synergy of both.
According to the quantum dot-nanochannel-based copper ion detection method provided by the embodiment of the invention, quantum dots are successfully embedded on a ZIF-8 framework, and ZIF-8 particles embedded with CdSe quantum dots are modified into a nanochannel of a PAA film to obtain the CdSe @ ZIF-8/PAA film. The functionalized CdSe @ ZIF-8/PAA film not only retains the excellent fluorescence characteristics and sensing selection of quantum dotsSelectively and reserve the Cu of the ZIF-8/PAA material2+Strong adsorption property of (1). The CdSe @ ZIF-8/PAA film can powerfully and selectively enrich target analytes and is used as a sensor for detecting Cu2+The detection range is good (0.01pM-1 mu M), and the detection limit can be as low as 0.004pM due to the electric field enrichment effect of the nano-channel; at the same time, the sensor pair Cu2+Has good selectivity in detection. The detection method is economical, simple, high in sensitivity and visual, and can be used for detecting Cu in food and environment2+Provides a new approach.
Although the present disclosure has been described above, the scope of the present disclosure is not limited thereto. Various changes and modifications may be effected therein by one of ordinary skill in the pertinent art without departing from the spirit and scope of the present disclosure, and these changes and modifications are intended to be within the scope of the present disclosure.
Claims (10)
1. A copper ion detection method based on quantum dots-nano channels is characterized by comprising the following steps:
preparing a CdSe @ ZIF-8/PAA film;
the CdSe @ ZIF-8/PAA film is used for manufacturing a chip matched with an inverted fluorescence microscope, the chip comprises a liquid storage tank, the CdSe @ ZIF-8/PAA film is positioned in the liquid storage tank, a working electrode is further arranged in the liquid storage tank, and the working electrode is electrically connected with an electrochemical workstation;
adding electrolyte solution and Cu into the liquid storage tank2+A solution, said electrochemical station applying a potential to effect Cu2+Enrichment, the liquid storage tank is subjected to fluorescence spectrum scanning through the inverted fluorescence microscope, and spectrum signals are obtained to realize the Cu-based concentration2+Detection of (3).
2. The method of claim 1, wherein the spectral signal is related to Cu2+Increase in concentration and decrease in Cu2+The measured value of the concentration is obtained by solving the following equation according to the acquired spectral signal:
y＝6143.76-992.76logx，
wherein y is a spectral signal, and x is Cu2+The concentration of (c).
3. The method according to claim 2, wherein the Cu is selected from the group consisting of Cu, and Cu2+The concentration of the solution is in the range of 0.01pM to 1. mu.M, the Cu2+The detection limit of (2) was 0.004 pM.
4. The method of claim 1, wherein the preparing a CdSe @ ZIF-8/PAA film comprises the steps of:
and (2) placing the PAA film between two semi-electrolytic tanks and communicating the two semi-electrolytic tanks, adding CdSe quantum dots and a zinc nitrate solution into one semi-electrolytic tank, simultaneously adding the CdSe quantum dots and a 2-methylimidazole solution into the other semi-electrolytic tank, sealing for 22-26h, taking out the film, ultrasonically washing with ultrapure water, and finally drying to obtain the CdSe @ ZIF-8/PAA film.
5. The method for detecting copper ions according to claim 4, wherein the volume ratio of the CdSe quantum dots, the zinc nitrate solution and the 2-methylimidazole solution is 1: (1-50): (1-6).
6. The method for detecting copper ions according to claim 4, wherein the preparation method of the CdSe quantum dots comprises the following steps:
adding 3-mercaptopropionic acid into the cadmium chloride solution, controlling the pH value to be 10-11, uniformly stirring, adding a sodium hydroselenide solution under the protection of nitrogen, reacting for 7-9h at 90-100 ℃, and then separating and purifying to obtain the CdSe quantum dots.
7. The method for detecting copper ions according to claim 1, wherein the step of forming a chip adapted to an inverted fluorescence microscope using the CdSe @ ZIF-8/PAA film comprises the steps of:
mixing polydimethylsiloxane and a curing agent according to the weight ratio of 10:1, uniformly stirring and pouring the mixture on a template, vacuumizing and heating the mixture to perform a curing reaction, and demolding to obtain a polydimethylsiloxane plate;
respectively arranging a first micropore and a second micropore which are matched with the micro-channel of the inverted fluorescence microscope on the two polydimethylsiloxane plates, wherein the first micropore and the second micropore are suitable for forming a cross channel;
and respectively cleaning the two polydimethylsiloxane plates according to the sequence of ethanol and ultrapure water, then drying, placing the CdSe @ ZIF-8/PAA film between the two polydimethylsiloxane plates, and bonding the CdSe @ ZIF-8/PAA film with the polydimethylsiloxane plates at the cross channel through ultraviolet irradiation to obtain the cross chip.
8. The method of claim 1, wherein the applying of the potential through the electrochemical workstation effects Cu ion detection2+Enrichment, comprising: the electrochemical workstation applies a potential of 5V.
9. The method for detecting copper ions according to any one of claims 1 to 8, wherein the measurement conditions of the fluorescence spectrum are: the excitation wavelength is 450nm, and the spectral scanning range is 480 nm and 650 nm.
10. The method of claim 9, wherein the electrolyte solution is a 1mmol/LKCl solution, a 1mmol/L PBS solution, or a 1mmol/L NaCl solution.
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