LDHNS composite membrane modified electrode and electrochemical identification of methionine enantiomer thereof
阅读说明：本技术 Ldhns复合膜修饰电极及其对蛋氨酸对映体的电化学鉴别 (LDHNS composite membrane modified electrode and electrochemical identification of methionine enantiomer thereof ) 是由 詹天荣 丁瑶 王军 王闰夏 王超 于 2021-08-02 设计创作，主要内容包括：本发明公开了一种钴铝类水滑石纳米片@金纳米簇/羧甲基-β-环糊精复合膜修饰电极及其制备方法和鉴别检测蛋氨酸对映体的应用。在甲酰胺中合成超薄的钴铝类水滑石纳米片,在其表面静电吸附AuCl-(4)～(-)和羧甲基-β-环糊精,经硼氢化钠原位还原制备钴铝类水滑石纳米片@金纳米簇/羧甲基-β-环糊精纳米复合物,采用滴涂法制备了相应的复合膜修饰电极。所得修饰电极发挥了类水滑石纳米片、金纳米簇和羧甲基-β-环糊精的协同作用,实现了对蛋氨酸对映体的鉴别和高灵敏检测,其中L-蛋氨酸检测的线性范围为2×10～(-8)～2×10～(-5)mol/L,检测限为10nmol/L；D-蛋氨酸检测的线性范围为2×10～(-7)～2×10～(-5)mol/L,检测限为61nmol/L。该修饰电极的制备简单,能实现对蛋氨酸手性对映体的高灵敏鉴别和检测。(The invention discloses a cobalt-aluminum hydrotalcite nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite membrane modified electrode, a preparation method thereof and application of the modified electrode in identification and detection of methionine enantiomer. Synthesizing ultrathin cobalt-aluminum hydrotalcite nano-sheet in formamide, and electrostatically adsorbing AuCl on the surface of the ultrathin cobalt-aluminum hydrotalcite nano-sheet 4 ‑ And carboxymethyl-beta-cyclodextrin, preparing the cobalt-aluminum hydrotalcite nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin nano compound by sodium borohydride in-situ reduction, and preparing the corresponding composite film modified electrode by adopting a dripping method. The obtained modified electrode exerts the synergistic effect of the hydrotalcite-like nano-sheet, the gold nano-cluster and the carboxymethyl-beta-cyclodextrin, realizes the identification and the high-sensitivity detection of methionine enantiomer, wherein the linear range of the L-methionine detection is 2 multiplied by 10 ‑8 ～2×10 ‑5 mol/L, the detection limit is 10 nmol/L; the linear range of D-methionine detection was 2X 10 ‑7 ～2×10 ‑5 mol/L, detection limit is 61 nmol/L. The modified electrode is simple to prepare, and can realize high-sensitivity identification and detection of methionine chiral enantiomers.)
1. The hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite membrane modified electrode is characterized in that the hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite membrane modified electrode is formed by taking a glassy carbon electrode as a substrate electrode and taking the hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin as an electrode modification material; the hydrotalcite-like nano-sheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin is obtained by carrying out electrostatic adsorption on AuCl on hydrotalcite-like nano-sheets after being stripped in formamide4 -And carboxymethyl-beta-cyclodextrin, and then reducing and growing the gold nanoclusters in situ to obtain the gold nanoclusters; the glassy carbon electrode is marked as GCE; the hydrotalcite-like nano-sheet is a cobalt-aluminum hydrotalcite-like nano-sheet and is marked asLDHNS; marking the gold nanoclusters as AuNCs; the carboxymethyl-beta-cyclodextrin is marked as CMCD;
the preparation method of the hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite film modified electrode comprises the following specific steps:
(a) preparation of LDHNS material
Mixing Co (NO)3)2·6H2O and Al (NO)3)3·9H2Dissolving O in a mixed solvent of formamide and water with a certain volume according to a certain molar ratio, slowly titrating with a proper amount of 0.7mol/L NaOH solution to maintain the pH of the solution at 8.5, aging for half an hour, centrifugally washing the obtained LDHNS colloidal solution, and dispersing the solution in a mixed solvent of 25mL formamide and 15mL deionized water to prepare an LDHNS stock solution for later use;
(b) preparation of LDHNS @ AuNCs/CMCD
Adding 2.4mL of LDHNS stock solution in the step (a) into 9.6mL of formamide-water mixed solvent, and firstly adding 2mL of 10mM fresh HAuCl4Stirring the aqueous solution and the CMCD dispersion solution to react for 1 to 5 hours, and quickly dropwise adding 0.6mL of 200mM NaBH under the condition of vigorous stirring4Stirring the solution at room temperature for 1h, centrifuging at 10000rpm for 5min, and washing with deionized water to obtain LDHNS @ AuNCs/CMCD;
(c) preparation of GCE modified by LDHNS @ AuNCs/CMCD composite film
Polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing the LDHNS @ AuNCs/CMCD composite material prepared in the step (b) in deionized water to prepare a dispersion liquid with the concentration of 1mg/mL, dropwise coating 2-20 mu L of the dispersion liquid on the surface of the GCE treated in the step (c), and naturally drying at room temperature to obtain the LDHNS @ AuNCs/CMCD composite film modified GCE.
2. The hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite membrane modified electrode as claimed in claim 1, wherein the Co (NO) in preparation method step (a)3)2·6H2O and Al (NO)3)3·9H2The molar ratio of O is 2: 1; formyl radicalsThe content of formamide in the mixed solvent of amine and water is 62.5 percent, and the total volume is 40 mL; the content of formamide in the formamide-water mixed solvent in the step (b) is 62.5 percent; the CMCD dispersion liquid is 462mg CMCD dispersed in 1mL deionized water; in the LDHNS @ AuNCs/CMCD, the LDHNS has an obvious lamellar structure, a rough surface and a thickness of 5-10nm, the transverse dimension of the LDHNS is 100-200 nm, the AuNCs are uniformly distributed on a hydrotalcite substrate, and the particle size of the LDHNS is 5-10 nm; in the step (c), the polishing of the substrate electrode adopts aluminum oxide powder on chamois to polish in sequence, and the time of ultrasonic cleaning is 30 s.
3. The hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite membrane modified electrode of claim 1 or 2, which is used for identifying and detecting methionine chiral enantiomers, it is characterized in that 0.1mol/L phosphate buffer solution with pH 6.0 is used as supporting electrolyte, the modified electrode is added into an electrolytic cell after being incubated in electrolyte solution containing different amounts of L-methionine and D-methionine, and (3) taking the modified electrode as a working electrode, detecting by using a differential pulse voltammetry to respectively obtain linear regression equations of the oxidation peak currents and the concentrations of the oxidation peak currents of the L-methionine and the D-methionine, measuring the oxidation peak currents of the L-methionine and the D-methionine in the sample to be detected by using the same method, and substituting the oxidation peak currents into the linear regression equations to obtain the contents of the L-methionine and the D-methionine in the sample to be detected.
The technical field is as follows:
the invention relates to a cobalt-aluminum hydrotalcite nanosheet @ AuNCs/carboxymethyl-beta-cyclodextrin modified electrode; the invention also relates to a preparation method of the modified electrode and an application of the modified electrode in electrochemical identification of amino acid enantiomers.
Background art:
chiral molecules, also known as enantiomers, have the same elemental composition and major physicochemical properties, but differ greatly in metabolic processes, physiological toxicity and pharmacological activity. Usually, only one chiral molecule is effective, while the other chiral molecule is ineffective, or even exhibits the opposite effect. Methionine is essential amino acid of animal body, and can maintain growth and nitrogen balance of animal body, prevent and treat liver diseases and poisoning caused by arsenic and benzene, and lack of methionine in livestock and poultry can cause dysplasia, weight loss, liver and kidney function reduction, muscle atrophy, fur deterioration, etc. Methionine is an optically active compound, and is classified into D-form and L-form. The L form is easy to be absorbed in animal body, and the D form can participate in the synthesis of protein only after being converted into the L form by enzyme. Therefore, establishing a method for identifying and detecting D/L methionine enantiomer with good stability and high sensitivity is particularly important. In order to solve the problem, various analysis methods such as capillary electrophoresis, high performance liquid chromatography, circular dichroism, colorimetry, fluorescence and the like are established to realize sensitive identification and detection of enantiomers. However, these methods have limited their use due to time consuming, expensive instruments and reagents, and complicated procedures performed by skilled technicians. The electrochemical method has the advantages of quick response, high sensitivity, good selectivity, low cost, simple and convenient operation, time saving and the like, provides selection for identifying and detecting enantiomers, and therefore, the method for finding the electrode suitable for modifying the nano composite membrane is an effective method for improving the sensitivity and the stability of the electrode.
Cyclodextrin (CD) is a natural macrocyclic oligosaccharide with a hydrophobic inner cavity and a hydrophilic outer cavity. The CD has lower cost and excellent performance, and can effectively adsorb enantiomers selectively into hydrophobic cavities thereof to form a host-guest inclusion compound. Due to the poor conductivity of CD, the direct construction of electrochemical sensors using it does not achieve good results. Efficient electrochemical chiral sensors not only require the identification of each enantiomer, but also require improved response signals, and thus the construction of chiral sensors using conjugated materials through the combination of enantioselectivity and electrochemical properties has become an option. Carboxymethyl-beta-cyclodextrin (CMCD) is a derivative of CD, has stronger compatibilization capacity and higher stability, and is generally used for compounding with other nano materials to form conjugated materials.
Hydrotalcite-like compounds (LDHs) are two-dimensional layered nanomaterials, which have a positive sheet charge and are widely used in recent years to immobilize negatively charged biomolecules. Compared with other inorganic matrixes, LDH has abundant chemical components, adjustable structural characteristics and intercalation performance, and is an effective host nanostructure for fixing guest molecules. However, LDH has the defects of easy aggregation, poor conductivity, insufficient exposure of catalytic active sites and the like, and the specific surface area of the LDH can be improved by stripping the LDH into LDH ultrathin nano sheets, and the catalytic sites of the LDH ultrathin nano sheets can be fully exposed, so that the electrochemical catalytic performance of the LDH can be improved. However, the LDH ultrathin nanosheets in the exfoliated state are easy to aggregate and recover into LDH bulk states in an aqueous medium, and can only be used in the form of colloidal solution, so that the deep development of hydrotalcite-like compounds in the electrochemical field is greatly limited. The gold nanocluster is proved to be a catalyst with high activity and high selectivity due to the advantages of good conductivity, small size, controllability and the like. In electrochemical detection, the gold nanoclusters can improve the conductivity of the electrode, improve the transfer speed of electrons and provide a large number of active sites. However, the small size of the gold nanoclusters causes problems of instability, easy aggregation and the like when the sensor is constructed, and the electrochemical performance of the gold nanoclusters is influenced.
In order to solve the defects existing when the materials are used independently, the invention aims to adsorb AuCl on the ultrathin CoAl-LDH nano-sheets in an electrostatic way4 -And carboxymethyl-beta-cyclodextrin, growing gold nanoclusters through in-situ chemical reduction to prepare an LDHNS @ AuNCs/CMCD nano compound, modifying GCE by adopting the compound, fully playing the synergistic effect of modified electrode materials, improving the conductivity, fully exposing the active site of an electrocatalyst, realizing selective recognition and sensitive detection on methionine enantiomer, further widening the linear detection range, reducing the detection limit, and improving the stability and sensitivity.
The invention content is as follows:
aiming at the defects of the prior art and the requirements of research and application in the field, one of the purposes of the invention is to provide a modified electrode made of a hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite material, namely, a corresponding modified electrode made of an LDHNS @ AuNCs/CMCD composite film.
The invention also aims to provide a preparation method of the hydrotalcite-like nano-sheet @ gold nano-cluster/carboxymethyl-beta-cyclodextrin composite material modified electrode, which comprises the following specific steps:
(a) preparation of LDHNS material
Mixing Co (NO)3)2·6H2O and Al (NO)3)3·9H2Dissolving O in a mixed solvent of formamide and water with a certain volume according to a certain molar ratio, slowly titrating with a proper amount of 0.7mol/L NaOH solution to maintain the pH of the solution at 8.5, aging for half an hour, centrifugally washing the obtained LDHNS colloidal solution, and dispersing the solution in a mixed solvent of 25mL formamide and 15mL deionized water to prepare an LDHNS stock solution for later use;
(b) preparation of LDHNS @ AuNCs/CMCD
Adding 2.4mL of LDHNS stock solution in the step (a) into 9.6mL of formamide-water mixed solvent, and firstly adding 2mL of 10mM fresh HAuCl4Stirring the aqueous solution and the CMCD dispersion solution for reaction for 1-5h, and quickly dropwise adding 0.6mL of 200mM NaBH under the condition of vigorous stirring4Stirring the solution at room temperature for 1h, centrifuging at 10000rpm for 5min, and washing with deionized water to obtain LDHNS @ AuNCs/CMCD;
(c) preparation of GCE modified by LDHNS @ AuNCs/CMCD composite film
Polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing the LDHNS @ AuNCs/CMCD composite material prepared in the step (b) in deionized water to prepare a dispersion liquid with the concentration of 1mg/mL, dropwise coating 2-20 mu L of the dispersion liquid on the surface of the GCE treated in the step (c), and naturally drying at room temperature to obtain the LDHNS @ AuNCs/CMCD composite film modified GCE.
Wherein the preparation method step (a) is described in the description of Co (NO)3)2·6H2O and Al (NO)3)3·9H2The molar ratio of O is 2: 1; the content of formamide in the mixed solvent of formamide and water is 62.5%, and the total volume is 40 mL; the content of formamide in the formamide-water mixed solvent in the step (b) is 62.5 percent; the CMCD dispersion liquid is 462mg CMCD dispersed in 1mL deionized water; in the LDHNS @ AuNCs/CMCD, the LDHNS has an obvious lamellar structure, a rough surface and a thickness of 5-10nm, the transverse dimension of the LDHNS is 100-200 nm, the AuNCs are uniformly distributed on a hydrotalcite substrate, and the particle size of the LDHNS is 5-10 nm; in the step (c), the polishing of the substrate electrode adopts aluminum oxide powder on chamois to polish in sequence, and the time of ultrasonic cleaning is 30 s.
The third purpose of the invention is to provide the application of the hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite material modified electrode in identification and detection of methionine chiral enantiomers, it is characterized in that 0.1mol/LpH 6.0.0 phosphate buffer solution is used as supporting electrolyte, the modified electrode is added into an electrolytic cell after being incubated in electrolyte solutions containing different amounts of L-methionine and D-methionine, and (3) taking the modified electrode as a working electrode, detecting by using a differential pulse voltammetry to respectively obtain linear regression equations of the oxidation peak currents and the concentrations of the oxidation peak currents of the L-methionine and the D-methionine, measuring the oxidation peak currents of the L-methionine and the D-methionine in the sample to be detected by using the same method, and substituting the oxidation peak currents into the linear regression equations to obtain the contents of the L-methionine and the D-methionine in the sample to be detected.
Compared with the prior art, the invention has the following beneficial effects:
(a) the hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite material is prepared by directly carrying out electrostatic adsorption of AuCl on hydrotalcite-like nanosheets synthesized in formamide through a one-step method4 -After the gold nanoclusters are grown in situ with carboxymethyl-beta-cyclodextrin to prepare the LDH @ AuNCs/CMCD nano compound, complex steps such as LDH stripping are avoided, and the preparation method is simple;
(b) the hydrotalcite-like nanosheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite material modified electrode plays a synergistic effect of each component in the aspect of electrocatalysis of L-methionine and D-methionine: the carboxymethyl-beta-cyclodextrin can effectively and selectively adsorb various compounds into a hydrophobic cavity of the carboxymethyl-beta-cyclodextrin to form a host-guest inclusion compound, and can realize chiral recognition on D-/L-methionine due to different binding affinities of the carboxymethyl-beta-cyclodextrin and different chiral amino acids; in order to improve the electrochemical response of CMCD, gold nanoclusters (AuNCs) and LDHs with good biocompatibility and a large number of active sites are selected to be compounded with the CMCD. The obtained electrochemical sensor can realize the identification and detection of the enantiomer, improve the response signal and improve the electrochemical performance.
(c) The hydrotalcite-like nano-sheet @ gold nanocluster/carboxymethyl-beta-cyclodextrin composite material modified electrode has a wider linear range (L-methionine 2 multiplied by 10) in the aspect of detecting D-/L-methionine enantiomer-8～2×10-5mol/L, D-methionine 2X 10-7～2×10-5mol/L) and lower detection limit (L-methionine 10nmol/L, D-methionine 61nmol/L), so that the chiral recognition of methionine enantiomer can be well realized, and the detection method has good stability and high sensitivity.
Description of the drawings:
FIG. 1 is a TEM image of LDHNS @ AuNCs/CMCD complex prepared in example 1 of the present invention at different magnifications.
FIG. 2 shows the results of differential pulse voltammetry of GCE (A) corresponding to comparative example 1, CMCD/GCE (B) corresponding to comparative example 2, LDHNS @ AuNCs/GCE (C) corresponding to comparative example 3, and LDHNS @ AuNCs/CMCD/GCE (D) corresponding to example 1 in a 0.1mol/L phosphate buffer solution of pH 6.0 containing a mixture of 0.1 mmol/LL-methionine and D-methionine, wherein the a curve corresponds to L-methionine, and the b curve corresponds to D-methionine.
FIG. 3 shows GCE (a), CMCD/GCE (b), LDHNS @ AuNCs/GCE (c) and LDHNS @ AuNCs/CMCD/GCE (d) in the presence of 10.0mmol/L [ Fe (CN)6]-3/-4And electrochemical impedance plots in 0.1mol/LKCl solution.
FIG. 4 is a differential pulse voltammogram of the L-methionine enantiomer at different concentrations, with L-methionine concentration sequentially 2X 10, on the corresponding LDHNS @ AuNCs/CMCD/GCE of example 1-8、5×10-8、1×10-7、5×10-7、1×10-6、5×10-6、1×10-5、1.2×10-5、1.5×10-5、2×10-5mol/L(a～j)。
FIG. 5 is a differential pulse voltammogram of D-methionine enantiomer at different concentrations on the corresponding LDHNS @ AuNCs/CMCD/GCE of example 1, with the D-methionine concentration being 2X 10 in order-7、5×10-7、1×10-6、5×10-6、1×10-5、1.2×10-5、1.5×10-5、2×10-5mol/L(a～h)。
FIG. 6 is a graph showing the linear relationship between L-methionine concentration and peak current.
FIG. 7 is a graph showing the linear relationship between the D-methionine concentration and the peak current.
The specific implementation mode is as follows:
for a further understanding of the invention, reference will now be made to the following examples and drawings, which are not intended to limit the invention in any way.
Example 1:
(a) preparation of LDHNS material
Mixing Co (NO)3)2·6H2O and Al (NO)3)3·9H2O is as follows: dissolving 1mol ratio in 40mL mixed solvent of formamide and water (the content of formamide is 62.5%), wherein the concentration of total metal ions is 75mmol/L, slowly titrating with 0.7mol/L NaOH solution to maintain the pH of the solution at 8.5, aging for half an hour, centrifugally washing the obtained LDH colloidal solution, dispersing the LDH colloidal solution in a mixed solution of 25mL formamide and 15mL deionized water, and preparing LDHNS stock solution for later use;
(b) preparation of LDHNS @ AuNCs/CMCD
Taking 2.4mL of the LDHNS stock solution in the step (a), adding the LDHNS stock solution into 9.6mL of formamide-water mixed solvent (the content of formamide is 62.5%), and firstly adding 2mL of 10mM fresh HAuCl4The aqueous solution and 1mL of CMCD aqueous dispersion (CMCD content: 462mg) were stirred for 2h, and 0.6mL of 200mM NaBH was added dropwise rapidly under vigorous stirring4Stirring the solution at room temperature for reaction for 1h, and centrifuging at 10000rpm for 5min to obtain LDH @ AuNCs/CMCD;
(c) preparation of LDH @ AuNCs/CMCD composite material modified GCE
Polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing the LDHNS @ AuNCs/CMCD composite material prepared in the step (b) in deionized water to prepare a dispersion liquid with the concentration of 1mg/mL, dropwise coating 5 mu L of the dispersion liquid on the surface of the GCE treated in the step (c), and naturally drying at room temperature to obtain the LDHNS @ AuNCs/CMCD composite film modified GCE.
Example 2:
(a) preparation of LDHNS material
Prepared according to the method and conditions of step (a) in example 1;
(b) preparation of LDHNS @ AuNCs/CMCD
Prepared according to the method and conditions of step (b) in example 1;
(c) preparation of GCE modified by LDHNS @ AuNCs/CMCD composite material
Polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing the LDHNS @ AuNCs/CMCD composite material prepared in the step (b) in deionized water to prepare a dispersion liquid with the concentration of 1mg/mL, dropwise coating 2 muL of the dispersion liquid on the surface of the GCE treated in the step (c), and naturally drying at room temperature to obtain the LDHNS @ AuNCs/CMCD composite film modified GCE.
Example 3:
(a) preparation of LDHNS material
Prepared according to the method and conditions of step (a) in example 1;
(b) preparation of LDHNS @ AuNCs/CMCD
Prepared according to the method and conditions of step (b) in example 1;
(c) preparation of GCE modified by LDHNS @ AuNCs/CMCD composite material
Polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing the LDHNS @ AuNCs/CMCD composite material prepared in the step (b) in deionized water to prepare a dispersion liquid with the concentration of 1mg/mL, dropwise coating 8 muL of the dispersion liquid on the surface of the GCE treated in the step (c), and naturally drying at room temperature to obtain the LDHNS @ AuNCs/CMCD composite film modified GCE.
Example 4:
(a) preparation of LDHNS material
Prepared according to the method and conditions of step (a) in example 1;
(b) preparation of LDHNS @ AuNCs/CMCD
Prepared according to the method and conditions of step (b) in example 1;
(c) preparation of GCE modified by LDHNS @ AuNCs/CMCD composite material
Polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing the LDHNS @ AuNCs/CMCD composite material prepared in the step (b) in deionized water to prepare a dispersion liquid with the concentration of 1mg/mL, dropwise coating 10 mu L of the dispersion liquid on the surface of the GCE treated in the step (c), and naturally drying at room temperature to obtain the LDHNS @ AuNCs/CMCD composite film modified GCE.
Example 5:
(a) preparation of LDHNS material
Prepared according to the method and conditions of step (a) in example 1;
(b) preparation of LDHNS @ AuNCs/CMCD
Prepared according to the method and conditions of step (b) in example 1;
(c) preparation of GCE modified by LDHNS @ AuNCs/CMCD composite material
Polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing the LDHNS @ AuNCs/CMCD composite material prepared in the step (b) in deionized water to prepare a dispersion liquid with the concentration of 1mg/mL, dropwise coating 12 mu L of the dispersion liquid on the surface of the GCE treated in the step (c), and naturally drying at room temperature to obtain the LDHNS @ AuNCs/CMCD composite film modified GCE.
Comparative example 1:
directly using naked GCE.
Comparative example 2:
polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing analytically pure CMCD in deionized water to prepare a dispersion liquid with the concentration of 1mg/mL, dropwise coating 5 mu L of the dispersion liquid on the surface of the treated GCE, and naturally drying at room temperature to obtain CMCD/GCE;
comparative example 3:
(a) preparation of LDHNS material
Prepared according to the method and conditions of step (a) in example 1;
(b) preparation of LDHNS @ AuNCs
Dispersing the stock solution obtained in step (a) in formamide solution, and adding 2mL of 10mM fresh HAuCl4The aqueous solution was stirred for 2h to mix well and 0.6mL of 200mM NaBH was added dropwise rapidly under vigorous stirring4Stirring the solution at room temperature for 1h, and centrifuging at 10000rpm for 5min to obtain LDHNS @ AuNCs;
(c) preparation of GCE modified by LDHNS @ AuNCs composite material
Polishing the substrate electrode into a mirror surface, ultrasonically cleaning the mirror surface by using ultrapure water, and naturally drying the mirror surface at room temperature to obtain the well-treated GCE; ultrasonically dispersing the LDHNS @ AuNCs composite material prepared in the step (b) in deionized water to prepare dispersion liquid with the concentration of 1mg/mL, dropwise coating 5 mu L of the dispersion liquid on the surface of the GCE treated in the step (c), and naturally drying at room temperature to obtain the LDHNS @ AuNCs composite film modified GCE.
FIG. 1 is a TEM image of LDHNS @ AuNCs/CMCD complex prepared in example 1 of the present invention at different magnifications. From A, it can be observed that the bottom-evident fold structure of LDH, AuNCs are relatively uniformly distributed on the hydrotalcite matrix, the particle size is about 5-10nm, but there are some aggregation cases. B. C, D are enlarged views of different sizes, respectively. In addition, HR-TEM images of single aucns showed one-dimensional lattice fringes (fig. D). At a pitch of 0.22nm, the presence of lattice fringes corresponding to the (111) crystal plane can be clearly seen. CMCD is an organic molecule and is therefore not represented in TEM images.
Example 6:
using the LDHNS @ AuNCs/CMCD/GCE prepared in example 1 as a working electrode, a platinum wire as a counter electrode and an Ag/AgCl electrode as a reference electrode, GCE, CMCD/GCE, LDHNS @ AuNCs/CMCD/GCE corresponding to comparative example 1, comparative example 2, comparative example 3 and working electrode corresponding to example 1 were used as comparisonThen, differential pulse voltammetry was performed in 0.1mol/L phosphate buffer pH 6.0 containing 0.1mmol/L L-methionine and D-methionine, respectively (curve a is L-methionine, and curve b is D-methionine), and the results are shown in FIG. 2. From FIG. 2A, it can be seen that both D-and L-Met have a weak and similar oxidation peak at 0.47V bare GCE due to their similar structural and chemical properties. Although no significant difference in peak potential was observed due to the host-guest recognition ability of CMCD and the different binding affinities of CMCD to D-/L-Met in FIG. 2B, the peak currents of D-and L-Met were increased to different extents, and the peak current response of L-Met was significantly higher than that of D-Met, the ratio of the peak current response of L-Met to that of D-Met, i.e., IL/IDAbout 1.35. Therefore, the CMCD modified electrode has certain capacity of detecting and identifying Met chiral isomers, but the identification efficiency is not ideal due to small current ratio, which is probably because the CMCD amount adsorbed by GCE is too small to effectively identify L-and D-Met. FIG. 2C shows that similar large peak currents occur for the D-and L-Met chiral isomers, but ILAnd IDThe difference is small, and the differential detection of the methionine isomer can not be realized. In addition, the electrochemical reaction of methionine enantiomer on LDHNS @ AuNCs/GCE was studied, and as shown in FIG. 2D, the peak current of D-/L-Met was further increased, and ILAnd IDIs further increased by the ratio ofL/IDAbout 2.48. The LDHNS @ AuNCs/CMCD has higher stereoselectivity, and can improve the capability of enantioselective recognition on a working electrode.
FIG. 3 shows GCE (a), CMCD/GCE (b), LDHNS @ AuNCs/GCE (c) and LDHNS @ AuNCs/CMCD/GCE (d) in the presence of 10.0mmol/L [ Fe (CN)6]-3/-4And electrochemical impedance plot in 0.1mol/L KCl solution. As can be seen from the figure, the spectrum is divided into two parts, where a semicircle under high frequency corresponds to the effective electron transfer control process, and the diameter of the semicircle represents the electron transfer resistance (Ret); while the linear part of the lower frequency band corresponds to the solute diffusion control process. The fitted charge transfer resistance (R) of comparative example 2 to CMCD/GCE (curve b, 780 Ω) due to poor CMCD conductivityct) Is superior to the bare board GCE of comparative example 1 (curve a, 1300. omega.), onlyComparative example 3LDHNS @ AuNCs/GCE (curve c) shows excellent electrochemical performance, improves the conductivity of the modified electrode, promotes electron transfer, and improves RctAbout 220 omega, so the LDHNS @ AuNCs/CMCD nano composite material is obtained by compounding CMCD and LDHNS @ AuNCs. While for the LDHNS @ AuNCs/CMCD/GCE of example 1 (curve d), R is compared to the LDHNS @ AuNCs/GCE modified electrodectThe value is slightly increased, probably caused by poor conductivity of the CMCD, but compared with the CMCD/GCE modified electrode, the conductivity is obviously improved, and the purposes of improving the conductivity of the modified electrode and promoting electron transfer are achieved.
Increasing the concentration of L-methionine and D-methionine, increasing the current of oxidation peak, obtaining the linear relation curve of the concentration of L-methionine and D-methionine and the current of oxidation peak, and determining the detection limit of L-methionine and D-methionine according to the related sensitivity determination rule. The optimal condition for measuring the L-methionine and the D-methionine is phosphate buffer solution with pH of 6.0, and the concentrations of the L-methionine and the D-methionine measured by differential pulse voltammetry are in a good linear relation with oxidation peak current within a certain range.
FIG. 4 is a differential pulse voltammogram of L-methionine at different concentrations on the corresponding LDHNS @ AuNCs/CMCD/GCE of example 1. It can be seen that the response value current of L-methionine is gradually increased along with the increase of the concentration in the concentration range of the experiment, which indicates that the modified electrode prepared by the invention can realize the quantitative detection of L-methionine.
FIG. 5 is a differential pulse voltammogram of D-methionine at different concentrations on the corresponding LDHNS @ AuNCs/CMCD/GCE of example 1. It can be seen that the response value current of D-methionine is gradually increased along with the increase of the concentration in the concentration range of the experiment, which shows that the modified electrode prepared by the invention can realize the quantitative detection of D-methionine.
As shown in FIG. 6, L-methionine has different linear relations in the range of 0.02 to 1 μ M and in the range of 1 to 20 μ M, I (μ A) ═ 1.66342c (μ M) -1.81824 (R)20.99567) and I (μ a) -0.3518c (μ M) -3.34577 (R)20.98581) with a detection limit of 10 nM. .
As shown in FIG. 7, D-methionine is in the range of 0.2 to EThe linear relationship between 5 mu M and 5-20 mu M is I (mu A) ═ 0.45934c (mu M) -1.63381 (R)20.99938) and I (μ a) -0.18123c (μ M) -3.04395 (R)20.99402) with a detection limit of 61 nM.
As can be seen from Table 1, after the LDHNS @ AuNCs/CMCD nano composite is adopted to modify the substrate electrode, the linear range of the electrode in the identification and detection of L-methionine and D-methionine is close to or superior to that of the existing modified electrode, but the detection limit is obviously lower than that of the existing modified electrode, so that the LDHNS @ AuNCs/CMCD composite membrane modified electrode has sensitive electrocatalytic performance on the L-methionine and the D-methionine, and therefore, the LDHNS @ AuNCs/CMCD composite membrane modified electrode shows better stability and sensitivity.
The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.
Table 1 shows the comparison of the L-methionine and D-methionine detection performance of LDHNS @ AuNCs/CMCD/GCE obtained by the invention with other electroanalysis methods