Preparation of Non-enzymatic L-cysteine Sensor Based on Modified Glassy Carbon and Gold Electrodes

• Main Authors: Farrel Gunawan, 吳端陽
• Other Authors: Meng-Jiy Wang
• Format: Others
• Language: en_US
• Published: 2016
• Online Access: http://ndltd.ncl.edu.tw/handle/96197666825753616162

碩士 === 國立臺灣科技大學 === 化學工程系 === 104 === The development of effective strategy to perform electrochemical determination of l-cysteine (L-cys) is of great importance for physiological and clinical diagnosis of various diseases owing to the abnormal level of L-cys. In this study, the application of electrochemical method aim to perform simple, accurate, and fast detection of L-cys using glassy carbon (GCE) and gold electrodes (AuE). Since direct use of bare GCE and AuE possessed problems of insufficient sensitivity and specificity, two designs of sensors for electrochemical determination of L-cys which are copper-silver fibers composite (500-Ag-Cu/PVP fibers) incorporated in Prussian blue-chitosan modified on GCE (Cu-Ag-PB-Chi/GCE) and copper electrodeposited on AuE (Cu/AuE) were prepared in order to address those problems. The modified layer of GCE was made under three steps: (1) preparation of 500-Ag-Cu/PVP fibers involving electrospinning, crosslinking, thiol-functionalization, silver-ions loading, heat reduction and copper electroless plating, (2) chemical synthesis of PB, and (3) preparation of chitosan solution (Chi). The as-prepared 500-Ag/PVP fibers, 500-Ag-Cu/PVP fibers, chemically synthesized PB, and Chi were used to fabricate: PB-Chi, Ag-PB–Chi, and Cu-Ag-PB–Chi/ GCE. The surface modification on the electrodes were evaluated by different analytical methods. Surface morphology observation by SEM revealed that after heat reduction allow to load silver-ions on PVP fibers (Ag+-RSH-CL-PVP fibers), where the structure of fibers was maintained. Meanwhile, by means of copper electroless plating, the 500-Ag-Cu/PVP fibers which possessed thicker average diameter than 500-Ag/PVP fibers was generated. The thiol-functionalization process was confirmed by FTIR that the peaks corresponded to the functional group of Si-O-Si and Si-O-CH3 were found. Moreover, XRD pattern results declared that the as-prepared 500-Ag/PVP and 500-Ag-Cu/PVP fibers reveal the crystalline phases of Ag and both Cu and Ag, respectively. The three modified GCE were characterized by cyclic voltammetry to investigate the current responses toward L-cys. The results of CV response of L-cys revealed the following findings: (1) PB-Chi/GCE was the least sensitive to L-cys, (2) Ag-PB-Chi/GCE exhibited higher current response than that of PB-Chi/GCE (1.2 times fold higher), and (3) Cu-Ag-PB-Chi/GCE owned a significant increase of sensitivity toward L-cys, as compared to that of PB-Chi (1.8 times fold increase) and Ag-PB-Chi/GCE (1.5 times fold increase). This improvement implied the contribution of synergetic effects of catalytic behavior of 500-Ag-Cu/PVP fibers in electrooxidation of L-cys. The sensing performance of Cu-Ag-PB-Chi/GCE was examined by amperometric test under optimized conditions. The Cu-Ag-PB-Chi/GCE showed two linear ranges over conentrations of 40-1800 and 1800-2500 µM with corresponding sensitivities of 0.1501 and 0.0707µA.µM-1cm-2, respectively, with the detection limit of 1.42 µM. According to interference tests, Cu-Ag-PB-Chi/GCE was selective toward L-cys and showed negligible response to sucrose, glucose, citric acid, oxalic acid, urea (concentration ratio L-cys to interferent= 1:1), uric acid, and EDTA (concentration ratio L-cys to interferent= 10:1). The second objective of this thesis is to prepare L-cys sensor based on Cu/AuE. The Cu/AuE was developed by potentiostatic deposition of metallic Cu from a precursor solution onto AuE. The surface morphology and crystallinity of the Cu/AuE were studied by SEM and XRD, respectively. According to SEM observation, the homogeneous coverage of copper layer on AuE was obtained for longer deposition time (≥ 480 s). In addition, dendrites structure of copper can be produced when high overpotential (≤ -0.7 V) was applied. XRD pattern of Cu/AuE confirmed that copper was successfully electro-deposited on the surface without the presence of its corresponding oxide forms. For further assessments, AuE was electrodeposited at -0.4 V for 480 s from solution containing 0.005 M of CuSO4 and 0.3 M Na2SO4, concerning the highest amperometric response resulted from Cu/AuE farbricated under these parameters. The electrochemical characteristics of Cu/AuE were investigated using cyclic voltammetry tests. Based on CV results, the Cu/AuE displayed a prominent anodic peak ascribed for electrooxidation of L-cys, indicating greater electrooxidation activity toward L-cys than bare AuE. The amperometric test run under optimized conditions showed that the Cu/AuE had lowest detection limit of 0.21 µM and two linear ranges between 1-400 and 400-1800 µM with corresponding sensitivities of 1.0493 and 0.5090 µA.µM-1.cm-2, respectively. Additionally, the Cu/AuE also exhibited high specificity to L-cys, as minor influence from sucrose, glucose, citric acid, oxalic acid, urea, EDTA (concentration ratio L-cys to interferent= 1:1), and uric acid (concentration ratio L-cys to interferent= 40:1) to the L-cys signal.