Transparent vertical nanotube electrode arrays on graphene for cellular recording and optical imaging

Here, we report the fabrication of transparent multichannel vertical nanotube electrode arrays for detecting cellular activity and optically imaging neuronal networks. To fabricate these transparent electrode arrays, position- and morphology-controlled ZnO nanotube arrays consisting of ultrathin nanowalls were grown on transparent graphene layers and coated with Ti/Au metal layers. Using these multichannel arrays, electrophysiological signals were individually recorded from primary mouse hippocampal neurons and recorded distinctive intracellular potential-like signals. Moreover, the transparent electrode array enabled fluorescence imaging of neuron cell bodies and neurite connections. This transparent graphene- and nanotube-based recording device is proposed to greatly increase the versatility of capabilities for investigating neuronal activity through simultaneous recording and imaging of neuron cultures. The figure depicts a new type of transparent electrode recording array made of vertically aligned zinc oxide nanotubes grown on graphene (top middle). The nanotubes are formed by sharp nanowalls to penetrate the cell (top left) while transparent graphene layers allow imaging the neurons using with conventional microscopy (top right). As a result, simultaneous recording of electrical signals was obtained from multiple neurons at single-cell resolution. Moreover, the signals had distinguishable waveforms that implicated extracellular- and intracellular-like electrophysiological voltage changes (bottom).