Modulating electrode kinetics for discrimination of dopamine by PEDOT:COOH interface doped with negatively-charged tri-carboxylate.

Abstract

The rapidly developing field of conducting polymers in organic electronics has many implications for bioelectronics. For biosensing applications, tailoring the functionalities of the conducting polymer s surface is an efficient approach to improve both sensitivity and selectivity. Here, we demonstrated a facile and economic approach for the fabrication of a high-density, negatively-charged carboxylic acid group-functionalized PEDOT (PEDOT:COOH) using an inexpensive ternary carboxylic acid, citrate, as a dopant. The polymerization efficiency was significantly improved by addition of LiClO4 as a supporting electrolyte yielding a dense PEDOT:COOH sensing interface. The resulting PEDOT:COOH interface had a high surface density of carboxylic acid groups of 25.75 \uf06dM/cm2 as quantified by the toluidine blue O (TBO) staining technique. The dopamine response measured with the PEDOT:COOH sensing interface was characterized by cyclic voltammetry with a significantly reduced \uf072Ep of 90 mV and a 3 fold increase in the Ipa value compared with the non-functionalized PEDOT sensing interface. Moreover, the cyclic voltammetry and electrochemical impedance spectroscopy results demonstrated the increased electrode kinetics and highly selective discrimination of dopamine (DA) in the presence of the interferents ascorbic acid (AA) and uric acid (UA) resulted from the introduction of negatively-charged carboxylic acid groups. The negatively-charged carboxylic acid groups could favor the transfer, preconcentration and permeation of positively charged DA to deliver improved sensing performance, while repelling the negatively-charged AA and UA interferents. The PEDOT:COOH interface facilitate measurement of dopamine over the range of 1 - 85 µM, with a sensitivity of 0.228 µA µM-1, which is 4.1 times higher than that of a non-functionalized PEDOT electrode (0.055 µA µM-1). Our results demonstrate the feasibility of a simple and economic fabrication of a high density PEDOT:COOH interface for chemical sensing, which also has the potential for coupling with other bio-recognition molecules via the carboxylic acid moieties for the development of a range of advanced PEDOT-based biosensors.