Researches On Bimetallic Nanocrystals For Electrochemical Sensing Applications

In this dissertation,a series of bimetallic alloy nanocrystals were designed and prepared to address the issues of low catalytic activity,poor selectivity and high cost of conventional single-component noble metal catalysts.And the high sensitivity detection of small biomolecules based on electrochemical sensors was carried out.The effects of bimetallic composition and nanostructure on electrochemical catalytic performance were investigated.The sensing mechanism of the prepared bimetallic nanocrystalls during electrochemical detection is in-depth studied.Herein,a series of electrochemical biosensors for detection of carbamate pesticides,dopamine and prostate cancer markers of AMACR were developed.The main results of this work can be surmarized and listed as follows.1)The exploitation of Aux Rh1-x alloy nanocrystals for specifically and directly identifying carbamate pesticides was reported for the first time and could be easily further developed to meet the specific needs of emergency intoxication cases.In this study,Au_xRh_1-x alloy nanocrystals with a tunable composition were synthesized and then employed for the electrocatalytic oxidation of carbamate pesticides.Compared with other Au_xRh_1-x samples and monometallic analogues,the Au42Rh58 sample with an optimized composition showed advances in terms of its electrocatalytic activity.According to electrochemical assessments,we discovered that the Au42Rh58 sample had specific responses to carbaryl.Typical common existing substances including glucide,amino acids,metal ions,and OP pesticides showed no interference in carbaryl determination.Moreover,Au42Rh58 nanocrystals displayed a considerable response towards 1 n M carbaryl without the assistance of acetylcholinesterase（ACh E）,cholinesterase（Ch E）or other biochemical recognition elements.The observed high-efficiency detection was driven by electrocatalyzing the hydrolysis product of carbaryl in a strong alkaline solution.Au42Rh58 alloy nanocrystals with high catalytic activity and good selectivity are promising sensing materials for the detection of trace levels of carbaryl.Furthermore,Au42Rh58 alloy nanocrystals with uniform shape and narrow size distribution could be used in micro/nanoelectrode fabrication technology such as in screenprinting or ink-jetting or in the further design and implementation of real-time identification systems。2)The free aldehyde group of imidazole-2-carboxaldehyde（ICA）ligand in ZIF-90 frameworks demonstrated a specific capture capability towards dopamine through covalent bonding.Moreover,the negative charges on the surface of ZIF-90 crystals are apt to attract dopamine molecules（prone to be protonated at physiological p H）and circumvent the entry of anionic biological interferences via electrostatic interaction.Given these characteristics,combined with its high catalytic efficiency,ZIF-90 is found to be a promising candidate material for electrochemical sensing of dopamine with good selectivity.Although the Schiff-base induced mechanism is pivotal for dopamine measurements,the developed sensing material displays different response behaviours towards other neurotransmitters and amino acid compounds.The dissimilarity in chemical structures as well as the resulting different electrochemical sensing behaviours was included in the discussion of this dissertation.The Pt₄₁Rh₅₉ alloy nanocatalyst lowered the barriers involved in electrocatalysis of dopamine,and thus increases the sensing efficiency.The synergetic effect caused by Pt₄₁Rh₅₉/ZIF-90 nanocomposite endowed it a low detection limit of 1 n M and good specificity.Also,the measurement of dopamine in bovine serum albumin（BSA）buffer solution indicates that the developed Pt₄₁Rh₅₉/ZIF-90 nanocomposite has the potential for practical dopamine sensing application.3)Early diagnosis of prostate cancer is crucial for the successful treatment.This research focused on the development of electrochemical biosensor targeting alpha-methylacyl-Co Aracemase（AMACR）,an emerging prostate cancer biomarker.Herein,bimetallic nanocrystals were applied for the construction of electrochemical biosensor.With the assistance of electrochemical detection experiments,the competitive adsorption effect of bimetallic nanocrystals for different bio-molecules would be studied.The sensing mechanism and performance of bimetallic nanocrystals was explored based on enzymatic reaction of AMACR.Based on the optimized sensing materials,printable ink was prepared,and its intrinsic physical properties including viscosity,density and surface tension were optimized.The exploited printable ink could be deposited on flexible substrate for microsensor chips fabrication based on screen-printing technology,further design and implement real time identification system.The motivation of this study is to design,construct,and test a rapid and sensitive electrochemical based AMACR biosensor capable of detecting minute quantities of AMACR in biofluids.The sampling analysis of human plasma indicates that the developed microsensor could effectively differentiate between prostate cancer patients and health controls with a high diagnostic specificity and sensitivity.Another important enzyme,dihydronicotinamide adenine dinucleotide（NADH）was also found to be abnormally expressed in cancer cells,and then was used as second marker to validate the testing results.The simultaneous determination of AMACR and NADH under the redox potential regulation could achieve high diagnosis accuracy.This biosensor and the detection mechanism explored herein possess great potential to enhance the early clinical diagnosis of prostate cancers,and to monitor metastatic progression and disease recurrence in patients with metastatic disease.