Light-addressable electrochemical sensors for neurotransmitter sensing

Electrochemical sensors are important for a variety of applications. However, they suffer from physical constraints, as each electrode requires a dedicated wire. Although arrays of 500 electrodes have been reported, achieving high-density electrochemical measurements is still difficult. In a light-addressable electrode, electrochemical processes occur only when the electrode is illuminated. Light-addressable electrodes could potentially solve many of the drawbacks of traditional electrode arrays, as light is used to spatially confine the redox process to only a small part of the electrode and only one connection is needed. It could also allow for new, faster electrochemical imaging techniques. We show the fabrication and characterizations of light-addressable electrodes that are simple to produce, inexpensive and scalable. Moreover, the method does not require clean room techniques. We synthesize the electrodes by depositing Au nanoparticles on n-type Si and characterize them in catechol, dopamine and ferrocene methanol using three illumination conditions (Total illumination, local illumination and no illumination). When a voltage is applied under no illumination conditions, the electrode does not pass significant current. However, when the whole electrode surface is illuminated, the peak current increases roughly two orders of magnitude. When only a small part of the electrode is illuminated, the current is roughly one order of magnitude lower than when overall illumination is used. For a simple redox event, peak current is directly proportional to electrode area. Smaller peak currents suggest that the active electrode surface area is being reduced. These results pave the way for future experiments, such as measuring dopamine release by a cell.