(Invited) Diamond Electrodes for Sensitive Electrochemical Detection

Abstract

Boron-doped diamond (BDD) electrodes are known to have excellent electrochemical properties, such as wide potential window and low background current, as well as extreme physical/chemical stability. Based on these properties, the BDD electrodes are expected to be used for sensitive electrochemical detection in various research fields including bioelectrochemistry. Usually, BDD electrodes are prepared by deposition of a polycrystalline BDD thin film on a conductive silicon wafer substrate, and thus obtained as an inflexible macro-electrode. In order to expand application fields of BDD electrodes for sensitive electrochemical detection, we have developed screen-printed BDD electrodes and BDD microring electrodes. 1. Screen-printed BDD electrodes Screen-printed BDD electrodes were developed as a low-cost, light-weight, flexible, disposable and sensitive electrochemical electrode. An ink containing BDD powder (BDDP, particle size < 1 μm) and polyester (PES) resin binder was prepared and was subjected to screen printing to obtain a polyimide film-based screen-printed BDD electrode. In comparison with conventional carbon-printed electrode, the BDDP-printed electrode was found to show low background current, leading to large signal-to-background (S/B) ratio. Electrochemical properties of the BDDP-printed electrode was changed drastically by the PES/BDDP ratio of the ink. The BDDP-printed electrode showed planar electrode-type behavior at small PES/BDDP ratios. At a BDDP-printed electrode with large PES/BDDP ratios, however, microelectrode-type voltammetric behavior was observed due to the random microelectrode array effect. The S/B ratio for the voltammetric detection of ascorbic acid was found to be in the order BDDP-printed electrode (PES/BDDP = 1.0) > BDDP-printed electrode (PES/BDDP = 0.3) > conventional polycrystalline BDD electrode. 2. BDD microring electrodes BDD microring electrodes were developed for electrochemical detection at a micrometer-scale local space. A quartz glass rod was pulled to prepare a quartz glass needle with a tip diameter of ca. 200 nm. BDD thin film was deposited on the needle tip to obtain BDD microelectrode. After deposition of an insulating layer on the electrode surface, the tip was cut by focused ion beam to obtain microring electrode. Diameter of the BDD microring electrode was ca. 5 μm. Oxygen reduction reaction current at a platinum microelectrode in the presence of bovine serum albumin (BSA) was found to be reduced by 58% from the current in the absence of BSA. In contrast, the current reduction was found to be 20% at the BDD microring electrode, showing good durability to electrode fouling by the presence of BSA.