Neurotransmitters are one of the most critical biomolecules in the brain. They play a vital role in preserving neurophysiological processes such as cognition, memory, and behavior. For example, the abnormal levels of neurotransmitters may result in severe neurological disorders such as Parkinson's disease, schizophrenia, and Huntington's disease. In the case of Parkinson's disease, most patients have lost more than 80% of their production of dopamine neurotransmitter. Stem cell-based therapy to create dopamine-producing (dopaminergic) neurons that can be implanted into patients has emerged as a promising approach for treating Parkinson's disease. The functionality of stem cell-derived dopaminergic neurons can be confirmed by the detection of dopamine. The proposed biosensing system has the capability of real-time monitoring of stem cell differentiation by detecting neurotransmitters. It will accelerate the development of stem cell therapies by removing some bottlenecks in current stem cell therapies. Moreover, the proposed biosensor will be an excellent sensing platform to advance research and development in regenerative medicine and neuroscience.The scientific goal of this proposal is to investigate how stem cells can generate a neural interface with functional neurons by detecting neurotransmitters selectively and effectively. Conventional neurotransmitter detection methods suffer from non-specific sensing and lack of in situ analysis. Addressing current challenges in the detection of neurotransmitters, a novel in situ nano-biosensor using graphene oxide-covered nanostructure arrays as a platform to real-time monitor mature neuronal differentiation of stem cells will be developed by detecting the secreted neurotransmitters in a noninvasive manner. For this purpose, the proposal focuses on the synthesis of chemically well-defined graphene oxide-nanostructures and the development of graphene-based hybrid nanoelectrode arrays to generate stable and reproducible signals. The developed novel graphene-based hybrid nanoelectrode arrays detect dopamine molecules selectively and sensitively using surface-enhanced Raman scattering technique. Raman dye (graphene oxide)-labeled aptamers targeting dopamine molecules are attached to the surface of graphene oxide-covered nanostructure arrays through the pi-pi interactions, resulting in a Raman enhancement from the graphene oxide nanostructures. The loss of binding affinity between nucleotides and the Raman dye (malachite green molecules)-labeled aptamers after the dye-labeled aptamers reacted with dopamine will consequently decrease the Raman signal for quantitative analysis. The whole processes enable the detection of low concentration of dopamine in the neural interface. Upon successful completion, the proposed nano-biosensing system will facilitate the study of a biological phenomenon by monitoring cell secretions from complex biological matrices. The proposal takes advantage of the graphene functionalized surface and the highly selective bio-recognition elements to fabricate a novel hybrid graphene-nanostructure-based real-time sensing system to act as a multi-purpose sensor platform for the detection of a variety of molecules. Given the challenges of in situ detection of neurotransmitters at the single cell level, this surface-enhanced Raman scattering-based detection method can represent a unique tool for investigating single-cell mechanisms associated with dopamine, or other neurotransmitters, and their roles in neurological processes.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.
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