Coaxial-like three-dimensional nanoelectrodes for biological applications

Three-dimensional nanostructures are becoming the standard tools for interfacing cells with biosensors and other devices. A morphology that develops in three dimensions leads to the engulfment of the nanostructures by the cell, reducing the cleft and largely improving the cell/material coupling and sealing. The recording of action potentials from electrogenic cells, as well as biomolecular sensing of generic biological samples, can benefit from 3D nano-objects due to the improved bio-interface. In this context, we present here a novel fabrication technique for producing 3D vertical nanostructures that can be tuned both in material composition and shape, being thus suitable for a large variety of applications, from SERS spectroscopy and microfluidics to intracellular recording. The technique is based on focus ion beam milling and gold electrodeposition. This combination allows to fabricate coaxial-like nanocylinders with a metallic core and an insulating shell. Moreover, the metallic core can be structured as a hollow donut to act as nano-channel, or as a bulky head to increase the contact surface. The nanostructure coupling with cells is evaluated by fluorescence imaging, SERS spectroscopy and FIB/SEM cross-section imaging of HL-1 cardiac cells cultured on the devices.