Study On Highly Selective Detection Of Amino Acids By Using Ultrastructure Metal Nanocomposite Membranes

Amino acids and nitrogen-containing molecules are closely related to human life activities,physical capacity,and metabolism since abnormal body amino acid contents will cause diseases.Therefore,it is of great significance to establish a rapid and accurate method for detecting nitrogen-containing molecules such as amino acids.Based on this,in this paper,a glassy carbon electrode modified with composite film which consists carbon nanomaterials with high sensitivity and specificity and novel metal nanomaterials was prepared,and a new method for amino acid detection was established,which can detect three substances including L-Tyrosine(L-Tyr),L-Tryptophan(L-Trp)and dopamine(DA).The constructed composite electrode and detecting method are valuable in the field of biological analysis,and the main contents are as follows:1.A selective and highly sensitive detection method for L-tyrosine based on ultra-micro nanostructured CuS nanosheet composite film modified electrode was established.Nanometer-sized copper sulfide has remarkable properties such as metal like electrical conductivity and electrocatalytic activity.In this work,ultrathin copper sulfide nanosheets(CuS NS)were synthesized and employed to modify on surface of glassy carbon electrode(GCE)combining with chitosan(CS)and acidified multi-walled carbon nanotubes(F-MWCNTs).Scanning electron microscopy(SEM)and transmission electron microscopy(TEM)showed that the shape of CuS NS was hexagon with side length of 13.33±0.67 nm and thickness of 4.50±0.58 nm.The electrochemical characteristics of different nanocomposite modified electrodes were examined by using cyclic voltammetry(CV)and differential pulse voltammetry(DPV),indicating that the modified electrode of CuS NS-CS/F-MWCNTs/GCE possessed good electrocatalytic activity towards oxidation of L-tyrosine(L-Tyr).Under the optimal condition,the modified electrode exhibited a wide linear response range for L-Tyr(0.08?1.0 ?M)with a detection limit of 4.9 nM.No obvious interferences from coexisted two-fold of L-tryptophan and 50-fold of other amino acids could be observed,indicating its good selectivity.The electrode also had good repeatability,reproducibility and stability.Compared with a commercial instrument analytical method,HPLC,the electrode can be successfully applied to the determination of L-Tyr in pig serums with a recovery rate of 95.7%? 102.6%,and its test results are in good agreement with that of HPLC,showing its promising application value.2.Based on the above CuS nanosheet structure composite membrane,a novel electrochemical sensing method based on formaldehyde mediation for the high selectivity detection of L-tryptophan(L-Trp)was established.In this work,the intermediate product(2,3,4,9-tetrahydro-lH-pyrido[3,4-b]indole-3-carboxylic acid)is formed by the Pictet-Spengler reaction between the vehicle of formaldehyde(HCHO)and L-trp,which caused the oxidation potential of L-Trp to move,it can effectively avoid the interference of oxidation peak of L-Tyr,achieving highly selective detection of L-Trp.Using this method,The prepared copper sulfide nanosheet/chitosan/acidified carbon nanotube composite film(CuS NS/CS/F-MWCNTs)modified electrode was formed by using hexagonal copper sulfide nanosheets with a side length of 10.46±0.65 nm and a thickness of about 5.27±0.74 nm.It was used to detect L-Trp based on the reaction of formaldehyde.The linear range is 8.0×10-7 mol/L?6.0×10-5 mol/L andthe lower limit is 4.6×10-8 mol/L.The method doesn't interfere with the coexistence of 50-fold concentration including L-tyrosine and other amino acids,and it was applied to the detection of tryptophan in pig serum.The recoveries were 94.5%?102.6%,indicating that the method has high sensitivity and good selectivity.The detection of L-Trp has potential applications in the field of bioanalysis value.3.A ultrastructured three-dimensional octagonal PtCu bimetallic nanoframe was prepared by self-assembly,and loaded onto carbon nano-dots/graphene quantum dots composites to obtain 3D-PtCu/CNDs/GQDs/GCE composite electrodes for selective detection of L-tyrosine and dopamine.The morphology of 3D-PtCu was characterized by TEM.The results showed that the morphology of 3D-PtCu is conposed of a cube with a side length of 8.47±0.47 nm and eight symmetric claws with a length of 7.20±0.38 nm.The electrochemical behaviors of L-Tyr and DA were studied by CV and differential DPV.The results showed that 3D-PtCu/CNDs/GQDs/GCE has good electrocatalytic oxidation characteristics for L-Tyr and DA.In the 0.10 mol/L PBS buffer solution(pH=5.5),the response peak current of the modified electrode has a good linear relationship with the concentration of L-Tyr and DA,and the linear range of L-Tyr is 2.0×11-7 mol/L?10×10-5 mol/L,the lower limit of detection is 6.4×10-8 mol/L(S/N=3);the linear range of DA is 30×10-7 mol/L?1.0×10-5 mol/L and the detection limit is 7.2×10-8 mol/L(S/N=3).This electrode was used for the determination of L-Tyr and DA in pig serum samples,and the recoveries were 95.9%?107.4%,97.2%?105.7%,respectively.This indicates that the modified electrode is potential to be applied in the field of bioanalysis and detection.