The behaviour of platinum, iridium and ruthenium electrodes in strong chloride solutions

Electrochemical attack and corrosion of platinum electrodes in dielectrophoretic diagnostic devices

Though the advances in microelectronic device fabrication have realized new capabilities in integrated analytical and diagnostic platforms, there are still notable limitations in point-of-care sample preparation. AC electrokinetic devices, especially those leveraging dielectrophoresis (DEP), have shown potential to solve these limitations and allow for sample-to-answer in a single point-of-care device. However, when working directly with whole blood or other high conductance (~ 1 S/m) biological fluids, the aggressive electrochemical conditions created by the electrode can fundamentally limit the device operation. In this study, platinum wire-based electrode devices spanning circular polytetrafluorethylene (PTFE) wells and a planar microarray device with sputtered platinum electrodes were tested in plasma and PBS buffers of differing concentration across a wide range of frequencies and electric field intensities (AC voltages) to determine their respective safe regions of operation and to gain an understanding about the failure mechanisms of this class of device. At frequencies of 10 kHz and below, the upper bound of operation is the degradation of electrodes due to electrochemical attack by chlorine overcoming the native platinum oxide passivation. At higher frequencies, 100 kHz and above, the dielectric loss and subsequent heating of the buffer will boil before the electrodes suffer observable damage, due to the slow irreversible reaction kinetics. Effective dielectrophoretic capture of small biological particles at these frequencies is limited, and heat/oxidative denaturation of target material are a major concern. A new class of smaller devices, ones capable of high throughput at voltages low enough to maintain the integrity of the platinum passivation layer, is needed to mitigate these fundamental limitations.

Development of a selective chloride sensing platform using a screen-printed platinum electrode

A new and selective voltammetric method for chloride determination is proposed, based on platinum and chloride interactions. A screen-printed platinum electrode (SPPtE) functions as a sensing platform, which promotes the formation of chloro-adsorbed species on the electrode surface, acting as an effective means of anion-determination in several matrices. The pretreatment of the SPPtE and careful control of the cathodic stripping voltammetric parameters yielded a well-defined electrochemical signal. This cathodic peak was due to the adsorption of chlorine, which had previously been oxidized from chloride anions in the initial anodic deposition step. It offers a simple, low-cost, fast, reproducible (RSD < 6%) and precise method for selective chloride determination, with limit of detection of 0.76 mM, and a sensitivity of - 24.147 µA mM ^-1 for a broad determination range of up to 150 mM. Chloride determination was correctly performed with single drops of environmental, pharmaceutical and food samples. In addition, the sensor was successfully adapted as a flexible screen-printed platinum electrode sensor using Gore-Tex^® as support for printing.