Pulse-clamp technique for single neuron stimulation electrode characterization

Miniaturized electrodes, structures and devices are necessary to achieve high target selectivity during stimulation in single neuron networks, while significant charge transfer is still demanded. A reliable test method is required to evaluate charge injection capability for high resolution neural stimulation applications that demand both a large amount of charge injection and a small electrode size. A circuit designed for the pulse-clamp technique was employed to characterize the electrode charge-storage capability of microelectrodes of sizes smaller than 300 µm in diameter. The circuit allows different electrodes and surface modifications to be quickly and accurately compared. Pulse-clamp measurements are performed on planar microelectrodes in 154 mM phosphate buffered saline (PBS) solution with 400 µs long pulses at charges up to 40 nC. The pulse-clamp and cyclic voltammetry results of sputtered iridium oxide film (SIROF) electrodes of different sizes show charge losses of less than 3% and a superior reversible charge injection capability compared to platinum microelectrodes of the same size, even at higher charge density levels.