Our team works on developing ultrathin optoelectronic devices for biomedical implants that can stimulate biophysical processes [1-9]. All these devices rely on near infrared irradiation in the tissue transparency window to actuate nanoscale organic semiconductor components. Our motivation is to provide a minimalistic wireless implant which can perform the duty of standard implantable electrodes, but without invasive wiring [3]. The devices we fabricate are not only wireless, but also 100-1000 times thinner than most existing technologies. Making implants have as small as possible mechanical footprint improves the efficacy of bioelectronic medical treatments by minimizing the risk for inflammation and making surgical implantation less invasive.

While organic semiconductors provide a promising platform for cellular photostimulation, understanding of the mechanisms occurring at a semiconductor/electrolyte interface is a complex problem. Organic semiconductor thin films can afford charging of electrolytic double layers or faradaic reactions. The magnitude of these two effects will depend on the thermodynamics of the materials used in the devices, in particular the nature of the cathodic and anodic components of the device, as well as the capacitance. Through judicious selection of materials one can obtain high photovoltages which can either drive efficient charging of double layer capacitors or faradaic reactions. The former is used to generate displacement currents which can capacitively couple with the cell membrane potential of nearby cells – this can be used to stimulate action potentials. Our experiment and model converge to create a detailed picture of how such devices, known as organic electrolytic photocapacitors, work to affect the gating of ion channels. This device can mimic biphasic current-pulse neurostimulation and thus transduces an optical signal into directly-evoked action potentials in neurons. On the other hand, the other block of our research efforts is directed at devices which, when stimulated with light, perform faradaic chemistry. We focus on the delivery of controlled amounts of reactive oxygen species (mostly peroxide). We aim to study the effects of photoelectrochemically-generated peroxides on physiological processes, with the hope of developing novel therapeutic approaches to neurodegenerative diseases.