Near-infrared excitation of nitrogen-doped ultrananocrystalline diamond photoelectrodes in saline solution

Abstract

Receipt date:PACS indexing codes: 87. 85.eg, 42.70.Km, 73.40.Mr, is a promising material for a variety of neural interfacing applications, due to its unique combination of high conductivity, bioinertness, and durability. One emerging application for N-UNCD is as a photoelectrode material for high-precision optical neural stimulation. This may be used for the treatment of neurological disorders and for implantable bionic devices such as cochlear ear implants and retinal prostheses. N-UNCD is a well-suited material for stimulation photoelectrodes, exhibiting a photocurrent response to light at visible wavelengths with a high charge injection density [A. Ahnood, A. N. Simonov, J. S. Laird, M. I. Maturana, K. Ganesan, A. Stacey, M. R. Ibbotson, L. Spiccia, and S. Prawer, Appl. Phys. Lett. 108, 104103 (2016)]. In this study, the photoresponse of N-UNCD to near-infrared (NIR) irradiation is measured. NIR light has greater optical penetration through tissue than visible wavelengths, opening the possibility to stimulate previously inaccessible target cells. It is found that N-UNCD exhibits a photoresponsivity which diminishes rapidly with increasing wavelength and is attributed to transitions between mid-gap states and the conduction band tail associated with the graphitic phase present at the grain boundaries. Oxygen surface termination on the diamond films provides further enhancement of the injected charge per photon, compared to as-grown or hydrogen terminated surfaces. Based on the measured injected charge density, we estimate that the generated photocurrent of oxygen terminated N-UNCD is sufficient to achieve extracellular stimulation of brain tissue within the safe optical exposure limit.The use of light-based techniques for neural stimulation is an area of growing interest, with potential applications in the treatment of neurological disorders and in implantable bionic devices [1][2][3][4]. In particular, optically-driven electrodes have the potential to offer wireless stimulation with much greater spatial resolution than conventional electrically-driven electrodes [2]. This approach relies on the transduction of light into electrical signals in order to stimulate neural tissue, caused by the separation of photo-excited charge carriers in a semiconducting electrode [2]. Materials such as photoconductive silicon [5][6][7][8], conductive polymers [9][10][11], and quantum dots [12][13][14] have been extensively studied for this purpose. However, these photoactive surfaces have often been found to exhibit limited biostability or produce cytotoxic reactions [15][16][17][18][19][20].

Single-Step Fabrication Method toward 3D Printing Composite Diamond–Titanium Interfaces for Neural Applications

“…As a result, the CIC values are 526 μC cm –2 and 215 μC cm –2 for TiD 50 and TiD 30 , respectively. These values are very high and comparable to other diamond electrodes, such as the N-UNCD electrodes with a CIC value of 1 mC cm –2 and the iridium oxide electrode with a charge value of 4 mC cm –2 , − as presented in Table .…”

Diamond Supercapacitors: Towards Durable, Safe, and Biocompatible Aqueous-Based Energy Storage

“…For instance, hydrogen terminated diamond causes upward band bending at the surface so that the valence band overlaps with the energy distribution of the oxygen redox couple, increasing the Faradaic reaction rate and producing surface hole conductivity ( Chakrapani et al, 2007 ). On the other hand, oxygen terminated diamond exhibits less band bending and so overlaps less with the energy levels of redox species, leading to lower reactivity and greater capacitive behavior ( Chakrapani et al, 2007 ; Chambers et al, 2020 ; Falahatdoost et al, 2021 ). This has important implications for diamond composite pseudocapacitors in particular, where the surface chemistry is thought to play a major role in their operational stability ( Kovalenko et al, 2010 ; Yang et al, 2016 ).…”

Translational considerations for the design of untethered nanomaterials in human neural stimulation

“…This class of nanomaterials is a promising tool for many biomedical applications in imaging, diagnostics, and therapeutics [55,56]. Since carbon nanomaterials show low toxicity with neurons in vitro [57][58][59][60] and remarkable physical and electrical properties, their main research applications have been directed towards neuroregeneration [55,[61][62][63]. They have also been used as interface materials for recording and stimulation of neural tissue as components of a larger, tethered system [64,65].…”

“…However, most studies involving these nanomaterials are not focused on the central nervous system (CNS), and have rarely been tested in vivo [56]. Furthermore, novel carbon nanomaterials such as nitrogen-doped ultrananocristalline diamonds have been recently developed and suggested for in vivo use, as they have shown promising preliminary results in vitro for optical neurostimulation [60].…”