Electrochemical micro-electrode arrays for measurement of transient concentration gradients of hydrogen peroxide

Understanding biological processes such as neurotransmitter release and reuptake in neurons, glucose transport for adapted cell metabolism in cancer cells involves measuring dynamic concentration gradients with diffusion time constants varying from a few hundred milliseconds to a few minutes. [1] Many prior electrochemical sensor reports utilize single electrodes, and achieve spatial information using techniques such as the self-referencing approach, which employs a moving probe. These approaches suffer from setup complexity, poor temporal and spatial resolution and poor suitability for portable, multi-analyte, high throughput applications. [2] In this work, an array of individually addressable platinum micro-electrodes was employed for amperometric measurement of transients and gradients with fast response time and good spatial resolution. The target analyte, hydrogen peroxide (H₂O₂), is the secondary species generated in enzymatic reactions (e.g. glucose with glucose oxidase), and is responsible for the redox reaction that lead to electrode current in such systems. Since the reaction constant for oxidation of H₂O₂ is large, the associated current response approximates the inherent response time of the sensor electrodes. In order to generate local gradients/transients, and eventually to mimic cellular function, a large platinum disk electrode (LPE) was used as a bias-controlled H₂O₂ sink [3], with time constants as low as 1s.