Polyaniline-modified electrodes prepared with sulfonated polyelectrolytes by layer-by-layer techniques for biosensing

• Main Authors: Yin-Hou Chen, 陳盈豪
• Other Authors: Yi-Chang Chung
• Format: Others
• Language: zh-TW
• Published: 2006
• Online Access: http://ndltd.ncl.edu.tw/handle/87611210802573863747

碩士 === 義守大學 === 生物技術與化學工程研究所碩士班 === 94 === Polyaniline (PAni) has been used frequently for the construction of bio-sensors. However, a prime limitation is its instability at basic or neutral pH because of the loss of its electrochemical activity and conductivity. In this study, three available sulfonated polyanions serving as the counterion and providing an acidic microenvironment to stabilize PAni, are used to fabricate an amperometric sensor for ammonium ion deteection. Additionally, the electrodes were coated in multilayered polyelectrolytes using layer-by-layer techniques. And they were stabilized by crosslinking reactions on the out-most surfaces to prevent dissolution in aqueous solution. Furthermore, the multilayered electrodes were rendered to encapsure and immobilize urease for serving as urea sensors. In this study, the electrodes were fabricated by immersing gold-coated alumina plates into the mixture of sulfonated polyelectrolytes and aniline solution, and then electropolymerized under cyclic voltammetric (CV) control in a potential range of -0.2 V to 0.8V. The polyaniline thickness was determined by the number of scan cycles. Two modified electrode sys-tems were developed: Au/PAni-Poly(sodium 4-styrene-sulfonate) (PSS), and Au/PAni-Poly(vinyl sulfate, Potassium salt) (PVS), compared with the Nafion-coated electrode system. Nafion used to be a common ion-sensitive membrane due to its high proton conductivity. However, its high cost and limited solubility has constrained its uses. PVS and PSS are water-soluble polymers, easily incorporating with PAni to form the composites. Surface analysis by electron spectroscopy for chemical analysis (ESCA) and scan-ning electron microscope (SEM), and the electrochromic property for the PAni composites provided the convenient tools to characterize the electrode fabrication. ESCA analysis illustrated that the sulfur peak at 168 eV was de-rived from the sulfonate groups, verifying that the water-soluble polyelec-trolytes can be deposited and adsorbed on the electrode as polyaniline form-ing. Also the SEM photographs of PAni/polyelectrolyte composites showed that the pores between particles were filled with some nanoparticles, leading to an increase of effective electrode area. Reversible color changes were ob-served between green (reduced state) and blue (oxidized state) with the ap-plication of the potentials between -0.8 and 0.8 V to the PAni/polyelectrolyte composites. On the aspect of sensing ammonium ions, CV and chronoamperometry (CA) methods were applied for detecting various concentration of ammo-nium solution. The modified electrodes exhibited electroactivity of PAni in ammonium ion detection and also showed the linear dependence of reduc-tion current on the ammonium ion concentration in a range of 0-400 mM, with the sensitivity of 6.17±0.099 μA(mM)-1cm-2. The pH effect was found insignificant to the response (ranging from pH 6.9 to 7.6). For increasing the stability of the electrodes, the diazo-resin (DAR) was introduced to the coat on the outmost layer and then cured by UV irradiation, forming the covalent network between the layers of polyelectrolytes, and giving a 90 % of re-mained sensitivity after detecting 4 times. On the application of urea detection, the LbL structures of electrodes were prepared by encapsulating naturally charged enzyme using cationic Poly(allylamine hydrochloride) (PAH). Water Contact angle measurement showed a zigzag profile of contact angle between PAH and the enzyme (or PSS), verifying the formation of LbL multilayer. The electrode system of PSS-PAni/PSS/(PAH/Urease)5 was prepared and found that linear relation-ship between the current response and the urea concentration ranging from 60-130 mg/Dl with the sensitivity of 1.203±0.028 μA dL(mg)-1cm-2. As con-sidering the electrode stabilization, DAR was used on the outmost electrode surface, however, UV curing process possibly denatured the immobilized urease. Thus, the multilayer systems were change to introduce epoxyl chain-ended poly(ethylene glycol) (PEGDE) to immobilize the urease layers, forming the PSS-PAni/PSS/(PAH/PEG/Urease)n modified electrodes. It was found that the electrode having one bilayer (n=1) displayed the linear de-pendence of current response on the urea concentration ranging from 0.5-9 mg/dL with the sensitivity of 0.197±0.061 μA dL(mg)-1cm-2; and that having two bilayer (n=2) displayed the linear dependence ranging from 0.5-30 mg/dL of urea concecntration with 0.125±0.022 μA dL(mg)-1cm-2 sensitivity, showing the detectable range was dependent and controllable on the number of enzyme layers.