Modulation of neuronal firing: what role can nanotechnology play?

The foremost interest of neuroscience is to find better ways to control neural activity at a single-cell and network level. A successful and punctual neural modulation lies at the basis of any therapeutic strategy for the prevention or recovery of potentially any neurological disorder. Nowadays, clinical neuromodulation at the cortical level finds its benchmark in microelectrodes such as the Utah and Michigan arrays, while deep brain stimulation (DBS) therapies still rely on the macroscale of bulky and invasive multisite electrodes. Notwithstanding, the huge efforts of the scientific community to develop less invasive neuroscientific tools that could preserve a relevant therapeutic efficacy, very few novel strategies stand out as the actual breakthrough. The potential of nanostructured materials for neuronal stimulation lies in their size and in the variety of mechanisms and interactions that unravel at the nanoscale. Nanotechnological solutions attracted the neuroscientific community looking for higher spatial resolution, specificity and low invasiveness for diagnostics and therapeutics. Despite the great promise demonstrated by nanotechnology in vitro, only a few nanoformulations have reached to date in vivo testing or clinical trials, being furthermore mostly intended for imaging and drug delivery. Here, we highlight the state of the art of the few nanotechnological strategies for neural modulation that reached in vivo characterizations, discussing the advantages compared with the current stimulation methods that might open a path toward a proficient use of nanotechnology in this field. Given the increasing number of scientific communications regarding cells and tissues, we propose here an overview of promising nanotechnological tools that already demonstrated a potential for in vivo therapeutic strategies. In particular, we focus our attention on active nanostructured devices and colloidal nanostructures.