A Quantitative Label-Free Displaying Method of Neuronal Firing via Optical Phase Information

Abstract

A label-free real-time detection method of neuronal firing is studied in this paper. The relation between the optical phase variation and membrane potential of a neuron model is investigated. The nature of action potential is the transmembrane flow of ions, e.g. Na+ and K+, on both sides of the cell membrane. That is, the ion concentration in the cell body has large change during the generation of action potential. The variation of ion concentration will further affect the refractive index and the phase distribution of a sample is affected by the related refractive index distribution. Therefore, the variation of phase is actually induced by the variation of ion concentration in the cell body. In other words, the neuron firing can be described via optical phase information. To explore the correlation between the neuronal firing activities and the variation of optical phase, a phase imaging experiment is designed and implemented. Firstly, the phase distribution of the simulation model in the solution with different concentration is obtained. Then, the phase value of sampling point in the solution of different concentration is obtained and the phase has linear relation with Na+ ion concentration by fitting analysis. Finally, the quantity associated with Na+ ion concentration in the neuronal model is replaced with the phase value. The experimental result and the subsequent simulation agree well with the theoretical analysis. This work could give a basis to extract and express the real-time information of membrane potential visually with label-free approaches.