Enhanced Sensitivity of Graphene Probes in Detection of Electrical Activities of Retina

Graphene has triggered tremendous interest in biosensing due to its superior electrical, mechanical and optical properties. For example, the high electron mobility and transparent nature of graphene allow for sensing of electrical activities with simultaneous high-resolution optical imaging. Here, we report on real-time extracellular electrical activity recording of retinal ganglion cells (RGCs) with flexible graphene electrodes integrated into perforated microfluidic platforms, which represents the first attempt of applying flexible graphene probes in retina study that can simultaneously monitor extracellular spiking activities from multiple channels with a high temporal and spatial resolution. Our results show under identical conditions, the graphene electrodes exhibit a higher electrical sensitivity than the gold counterparts with approximately 2.5 fold enhancement in the recorded spiking amplitude. Moreover, when RGCs are stimulated with high K⁺ concentration, they display a strong response with the firing rate first increasing and then ceasing, likely be due to the potassium-induced neural depolarization. Under light stimulation, we observed three distinct response patterns: ON, OFF, and ON-OFF, which reflects how different types of RGCs behave in response to light mediated by cone-shaped photoreceptors. Moreover, the observed spiking waveforms can be divided into two groups: the biphasic waveform usually as a result of direct contact between the electrode and soma, and the triphasic waveform that is likely from an isolated axon in contact with the electrode. Our results suggest that graphene electrodes can be a promising candidate for the electrophysiology studies of the retina and offer a route to engineering two-dimensional materials based flexible biosensors.