Multi-unit recording with iridium oxide modified stereotrodes in Drosophila melanogaster

Background: Drosophila is a very favorable animal model for the studies of neuroscience. However, itremains a great challenge to employ electrophysiological approaches in Drosophila to study the neuronalassembly dynamics in vivo, partially due to the small size of the Drosophila brain. Small and sensitivemicroelectrodes for multi-unit recordings are greatly desired.New method: We fabricated micro-scale stereotrodes for electrical recordings in Drosophila melanogaster.The stereotrodes were modified with iridium oxide (IrO2) under a highly controllable deposition proce-dure to improve their electrochemical properties. Electrical recordings were carried out using the IrO2stereotrodes to detect spontaneous action potentials and LFPs in vivo.Results: The IrO2electrodes exhibited significantly higher capacitance and lower impedance at 1 kHz.Electrical recording with the IrO2stereotrodes in vivo demonstrated an average signal-to-noise ratio(SNR) of 7.3 and a significantly improved LFP sensitivity. 5 types of different neurons recorded were clearlyseparated. Electrophysiological responses to visual and odor stimulation were also detected, respectively.Comparison with existing method(s): The most widely used electrodes for electrical recording in Drosophilaare glass microelectrode and sharpened tungsten microelectrode, which are typically used for single-unit recordings. Although tetrode technology has been used to record multi-neuronal activities fromDrosophila, the fabricated IrO2stereotrodes possess smaller geometry size but exhibited comparablerecording signal-to noise ration and better sorting quality.