以分子模版修飾電極感測尼古丁、兒茶素 與辨識酪胺酸

Abstract

本研究中主要分為四大部份，首先我們以二氧化鈦（TiO2）為拓印基材，在目標分子（template）—尼古丁（nicotine, NIC）的存在下，使之均勻混，將尼古丁分子模版（molecularly imprinted polymer, MIP）製備於銦錫氧化物（indium tin oxide, ITO）導電玻璃上，再經由高溫燒結以固定TiO2並去除包覆於TiO2內之尼古丁而形成一尼古丁分子模版修飾電極（ITO/TiO2[NIC]），為增加修飾電極之靈敏度，再將3,4-ethylenedioxythiophene (EDOT)以電聚合法鍍於ITO/TiO2[NIC]之上，形成一具有良好導電度之尼古丁分子模版修飾電極（ITO/TiO2[NIC]/PEDOT），並以PEDOT薄膜催化尼古丁之能力，以定電位的方式（chronoamperometry）來感測尼古丁。而ITO/TiO2[NIC]/PEDOT電極之線性感測範圍為0~5 mM，靈敏度為31.4 μA/ mM•cm2，感測下限為11.1 μM（S/N=3），分子模版之拓印效率為1.24。此外，本研究更利用掃瞄式電化學顯微鏡（scanning electrochemical microscopy, SECM）以白金探針為工作電極，利用赤血鹽與黃血鹽之氧化還原對來判別分子模版修飾電極之表面形態。 第二部分之研究導入微機電（micro-electro-mechanical-system, MEMS）製程，製備三極式微電極，除工作電極之基材與參考電極改為白金與Ag/AgCl外，尼古丁分子模版修飾電極之製備方式與第一部分所提及相同。此外，我們同樣以定電位法感測尼古丁，線性感測範圍為0~5 mM，靈敏度為28.32 μA/ mM•cm2，感測下限為5.19 μM（S/N=3），分子模版之拓印效率為7.54。

第三部分之研究以苯胺aniline (AN)作為單體、兒茶素（(+)-catechin, (+)-C）為模版，以電聚合方式包覆分子模版於導電玻璃ITO上作為分子模版修飾電極（ITO/PAN[(+)-C]），並以定電位法感測兒茶素，線性感測範圍為0~50 μM，靈敏度為45.9 μA/ mM•cm2，感測下限為5 μM（S/N=3），而分子模版之拓印效率為1.46。 最後，將利用分子模版之技術分別以D與L-酪胺酸（tyrosine, Tyr）作為模版，拓印於氧化鋁（Al2O3）基材內，並使其鍍於氟錫氧化物（fluorine tin oxide, FTO）導電玻璃上，分別製備成FTO/Al2O3[D-Tyr]與FTO/Al2O3[L-Tyr]兩分子模版修飾電極，而後，同第一部分所提，將導電高分子PEDOT鍍於修飾電極上以增加感測器之靈敏度，FTO/Al2O3[D-Tyr]與FTO/Al2O3[L-Tyr]。對於L與D-酪胺酸辨識之實驗，我們利用具有選擇性質之分子模版孔洞利用循環伏安法（cyclic voltammetry, CV）來作D與L-酪胺酸之辨識。對於FTO/Al2O3[D-Tyr] /PEDOT與FTO/Al2O3[L-Tyr] /PEDOT兩模版修飾電極對其模版之光學選擇率（enatioselectivity, E.S.）分別為1.79與1.42。此外，我們更藉由SECM所作模版之吸附實驗來印證模版與其相對應電極間之吸附狀況。

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-.