The central nervous system (CNS), the most complex and dynamic network found in nature, is composed of billions of neurons with trillions of dendritic spines and synapses, including pre- and postsynaptic terminals. The postsynaptic side of synapses can take the form of dendritic spines, which are small, actin-rich protrusions that serve as sites of postsynaptic contact and signal integration for most of the excitatory synapses in the CNS. Synapses relay signals between neighboring neurons in large neuronal networks, underscoring their vital function in the CNS. Not surprisingly, abnormalities in dendritic spines/synapses are associated with a number of CNS disorders, including Fragile-X syndrome, Down?s syndrome, Alzheimer?s disease, autism, schizophrenia, and epilepsy, glaucoma, and intellectual disorders. It is, therefore, crucial to understand the relationships between the functional connectivity map of neuronal networks and the physiological or pathological functions of individual synapses and neurons. To address this challenge, we propose to integrate two-dimensional flexible graphene membranes with scanning photocurrent microscopy to probe electrical activities of individual synapses and neurons in the retina and brain, two of the three components of the CNS. A unique advantage of graphene is that its whole volume is exposed to the environment, which maximizes its sensitivity to local electrochemical potential change. For example, graphene transistors are capable of detecting individual gas molecules, due to its high surface-area-to-volume ratio and high electron mobility (100 to 1000 times higher than silicon). The high electron mobility also enables graphene transistors to operate at very high frequencies (up to 500 GHz), leading to high temporal resolution. Because of its strength and flexibility, graphene membranes can adhere to cell membranes or tissue slices to achieve high electrical sensitivity. Furthermore, monolayer graphene transmits more than 97% of incident light, making it ideal to be used as transparent electrical devices that are compatible with optical imaging techniques. In addition, graphene transistors and electrodes have demonstrated the capability of stable operation at stretching up to 9%. As such, we propose to create an unprecedented neurotechnology through a rare combination of flexible graphene transistors and scanning photocurrent microscopy to simultaneously study the electrical activities of a large population of synapses and neurons in vitro, in situ, and in vivo. This technology will allow us to decipher the functional connectivity map of neuronal networks with high spatiotemporal resolution and high throughput.
Exploring the relationships between the functional connectivity map of neuronal networks and the physiological or pathological functions of individual synapses and neurons is the central goal of contemporary neuroscience. In the proposed research, we are integrating graphene transistors with scanning photocurrent microscopy to simultaneously investigate the electrical activities of a large population of individual synapses and neurons in the retina and brain with high spatiotemporal resolution and electrical sensitivity. These fundamental studies will provide an in-depth understanding of synapse formation and maintenance, cognitive behavior and the neurobiological basis for various neurological disorders.
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