Transparent, low-autofluorescence microECoG device for simultaneous Ca2+ imaging and cortical electrophysiology in vivo
Multimodal neuroimaging approaches are beneficial to discover brain functionalities at high spatial and temporal resolution. In our work, a novel material composition of microECoG device relying on Parylene HT and indium-tin-oxide (ITO) is presented that facilitates two-photon imaging of Ca2+ signals and concurrent recording of cortical EEG. Long-term stability of the interfaces of the transparent microdevice is confirmed in vitro by electrochemical and mechanical tests. The outstanding optical properties, like high transmittance and low auto-fluorescent are proven by fluorimetric measurements. Spatial resolution of fluorescent two-photon imaging through the microECoG device is presented in transgenic hippocampal slices, while concurrent recording of Ca2+ signals and cortical EEG is demonstrated in vivo. Photoartefacts and photodegradation of the materials are also investigated in detail to provide safety guidelines for further use in two-photon in vivo imaging schemes. Two-photon imaging of Ca signals can be safely performed through the proposed transparent ECoG device, without significant distortion in the dimensions of detected neuronal structures or in the temporal signaling. In chronic use, we demonstrated that fluorescent Ca signals of individual neurons can be clearly recorded even after 51 days. Our results give a firm indication that highly transparent microECoG electrode arrays made of Parylene HT/ITO/Parylene HT multilayer are excellent candidates for synergetic recording of optical signals and EEG from intact brains with high resolution and free of electrical and optical artefacts.