A Wireless Photometric Probe to Capture Calcium Activities During Hippocampal Seizures in Freely Moving Mice

Exploring the coding mechanisms of the nervous system and their associated functions holds great value in neuroscience research. Specifically, monitoring deep-brain neuronal activities with high specificity and minimal invasiveness is crucial. In this study, the development and application of a wireless photometric probe system is presented to monitor calcium (Ca²⁺) dynamics in the hippocampus during seizure events in freely moving mice. The probe integrates thin-film, microscale optoelectronic devices, including a micro light-emitting diode (micro-LED) and a photo detector, to excite and capture fluorescent emissions of the genetically encoded Ca²⁺ indicator (GCaMP). Wavelength-selective optical designs minimize the spectral crosstalk and optimize the detection of green fluorescence signals. Additionally, a portable, miniaturized wireless circuit module powers the devices and remotely transmits data. In vitro experiments validate the probe's capability to detect fluorescence signals in both ambient and aqueous environments, while in vivo experiments reveal its efficacy in capturing Ca²⁺ dynamics during seizure occurrences provoked by electrical stimulations as well as drug administrations in the hippocampus of behaving mice. The wireless photometric probe system developed here offers a promising tool for neuroscience research, particularly in studying complex behaviors and disease models in freely moving animals.