In neuroscience research, it is crucial to measure action potentials accurately with high spatiotemporal resolution and sensitivity. Current approaches rely on electrodes or optogenetics. New approaches providing higher spatial resolution close to a single neuron, immunity to biological noise, and lesser tissue damage during measurements are always desired. Here, we present a feasibility study on a novel label-free integrated approach by combining the electro-optic (EO) properties of lithium niobate (LN) with a microring resonator (MRR) and coherent detection to enable highly sensitive and precise measurement of action potentials. Specifically, we discuss the feasibility of this so-called opto-probe by carrying the action potential signal with light modulation and beating it through homodyne detection to detect weak signals. The MRR structure obtains the modulation of the light through the refractive index change of LN under the electric field generated by the action potential. Then, at the homodyne detection part, the action potential information is extracted from the beating of these two signals by mixing the modulated signal with a local oscillator signal. We estimate that the electric field generated by action potentials as small as 15 μV is detectable with high resolution. Furthermore, the spatial resolution of the opto-probe can reach up to 249 electrodes/mm2 when configured as an array, which offers scalability and potential for multiplexed sensing applications. The research findings present a promising advancement towards a novel tool that overcomes the limitations of electrode-based methods, enabling highly accurate and precise measurements of action potentials and enhancing our understanding of neuronal activity in the brain.
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