Molecularly Imprinted Modified Electrodes for Nicotine and (+)-Catechin Sensings and Tyrosine Recognition

• Main Authors: Cheng-Tar Wu, 吳政達
• Other Authors: Kuo-Chuan Ho
• Format: Others
• Language: en_US
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/99079452614082291025

碩士 === 國立臺灣大學 === 化學工程學研究所 === 94 === In the first part of this study, amperometric detection of nicotine (NIC) was carried out on a titanium dioxide (TiO2)/poly(3,4-ethylenedioxythiophene) (PEDOT) modified electrode by molecularly imprinted technique. The sensing material was prepared by coating a mixture of TiO2 colloid and the analyte, NIC, on a planar indium tin oxide electrode (ITO) followed by sintering. In order to improve the conductivity of the substrate, PEDOT was coated on the sintered electrode (ITO/TiO2[NIC]) by in-situ electrochemical polymerization of the EDOT monomer. Finally the NIC imprinted TiO2 electrode (ITO/TiO2[NIC]/PEDOT) was obtained. The linear detection range (LDR) for the NIC oxidation on the ITO/TiO2[NIC]/PEDOT electrode was between 0 to 5 mM, with a sensitivity, limit of detection (LOD), and imprinting efficiency (I.E.) of 31.35 μA/mM•cm2, 11.1 μM (S/N = 3) and 1.24 respectively. Moreover, scanning electrochemical microscopy (SECM) was employed to distinguish the surface morphology of the imprinted and the non-imprinted electrode using Fe(CN)63-/ Fe(CN)64- as a redox probe on a platinum tip. In the second part, a micro-electro-mechanical-system (MEMS) technology was employed to fabricate an on-chip three-electrode system. NIC was also electrochemically detected on a modified microelectrode made by molecular imprinting technique. The fabrication method of NIC imprinted electrode was similar to the first part, except that the working (ITO) and reference (Ag/AgCl/sat’d KCl) electrodes were replaced with Pt bar and Ag/AgCl, respectively. The NIC imprinted electrode was denoted as Pt/TiO2[NIC]/PEDOT. The LDR for NIC oxidation on the microelectrode was up to 5 mM, with a sensitivity, LOD and I.E. of 28.32 μA/mM•cm2, 5.19 μM, and 7.54 respectively. Furthermore, the SECM was also employed to distinguish the surface morphologies of the unmodified bar Pt and the Pt/TiO2[NIC]/PEDOT microelectrode by using Fe(CN)63-/ Fe(CN)64- as the redox couple. In the third part, (+)-catechin, abbreviated as (+)-C, was incorporated into polyaniline (PAN) thin film by acid protection mechanism which avoids the oxidation of (+)-C. The modified electrode was prepared by electropolymerizing (+)-C with aniline on an ITO electrode to form a (+)-C imprinted PAN modified electrode. After the template was extracted, a (+)-C MIP modified electrode (ITO/PAN/[(+)-C]) was obtained. Amperometric method was employed to detect (+)-C with the concentration varying from 0 to 150 μM. A LDR was obtained, which showed the relationship between the net steady-state current and the (+)-C concentration ranging from 0 to 50 μM at the ITO/PAN/[(+)-C] electrode. A LOD of 5 μM along with a sensitivity of 45.9 μA/mM∙cm2 was obtained for the ITO/PAN[(+)-C] electrode. In the last part, the recognition electrode was prepared by mixing either D or L-tyrosine (Tyr) with Al2O3 colloid, followed by the deposition onto a conducting fluorine tin oxide (FTO, sheet resistivity of 15 Ω/sq.) electrode by a glass rod to form both FTO/Al2O3[D-Tyr] and FTO/Al2O3[L-Tyr] electrodes respectively. PEDOT was deposited by electropolymerization onto FTO/Al2O3[D-Tyr] and FTO/Al2O3[L-Tyr] to enhance the sensitivity of the modified electrode, and the higher sensitivity electrodes were denoted as FTO/Al2O3[D-Tyr]/PEDOT and FTO/Al2O3[L-Tyr]/PEDOT. Afterward, cyclic voltammetry (CV) method was used to recognize for D and L-Tyr on the imprinted electrode. The enatioselectivities Abstract VII (E.S.) of FTO/Al2O3[D-Tyr] and FTO/Al2O3[L-Tyr] were 1.79 and 1.42, respectively. Further, SECM topography lended support for the higher adsorption ability of D-Tyr onto the FTO/Al2O3[D-Tyr]/PEDOT surface than that of L-Tyr under different adsorption times via the redox current responses of Fe(CN)6 3-/ Fe(CN)6 4-.