Towards optical neuromodulation using nitrogen-doped ultrananocrystalline diamond photoelectrodes

TL;DR

This study enhances nitrogen-doped ultrananocrystalline diamond electrodes' near-infrared photoresponsivity through oxygen treatments, significantly improving their potential for optical neuromodulation and neuronal stimulation.

Contribution

It demonstrates that oxygen furnace annealing greatly increases photoresponsivity of N-UNCD electrodes, advancing their application in optical neuromodulation.

Findings

Oxygen furnace annealing improves photoresponsivity by 200 times.

Surface chemical changes are key to enhanced photoresponse.

Photocurrent levels are sufficient for neuronal stimulation within safety limits.

Abstract

Nitrogen-doped ultrananocrystalline diamond (N-UNCD) is a form of diamond electrode with near-infrared photoresponsivity, making it well suited for physiological applications. N-UNCD's photoresponsivity is strongly influenced by its surface. While it is known that oxygen treatment provides a higher photoresponsivity, a better understanding of its surface processes is needed to tailor the material for optical neuromodulation. This work examines the impact of various oxygen treatment methods, with aim of creating oxygen rich surfaces with different chemical and structural properties. Surface characterisation methods along with electrochemical and photoelectrochemical measurements and modelling were used to investigate the films. It was found that oxygen furnace annealing resulted in orders of magnitude improvement in the near-infrared photoresponsivity, to 3.75 +/- 0.05 uA/W. This translates to an approximate 200 times increase in the photocurrent compared to the untreated surface. This enhancement in photocurrent is largely due to the changes in the chemical species present at the surface. The photocurrent is estimated to be sufficient for extra-cellular stimulation of brain neurons within the safe optical exposure limit, positioning N-UNCD as an excellent candidate to be used in next-generation photoelectrodes for photobiomodulation.