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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].

Durable and safe energy storage is required for the next generation of miniature bioelectronic devices, in which aqueous electrolytes are preferred due to the advantages in safety, low cost, and high conductivity. While rechargeable aqueous batteries are among the primary choices with relatively low power requirements, their lifetime is generally limited to a few thousand charging/discharging cycles as the electrode material can degrade due to electrochemical reactions. Electrical double layer capacitors (EDLCs) possess increased cycling stability and power density, although with as-yet lower energy density, due to quick electrical adsorption and desorption of ions without involving chemical reactions. However, in aqueous solution, chemical reactions which cause electrode degradation and produce hazardous species can occur when the voltage is increased beyond its operation window to improve the energy density. Diamond is a durable and biocompatible electrode material for supercapacitors, while at the same time provides a larger voltage window in biological environments. For applications requiring higher energy density, diamond-based pseudocapacitors (PCs) have also been developed, which combine EDLCs with fast electrochemical reactions. Here we inspect the properties of diamond-related materials and discuss their advantages and disadvantages when used as EDLC and PC materials. We argue that further optimization of the diamond surface chemistry and morphology, guided by computational modelling of the interface, can lead to supercapacitors with enhanced performance. We envisage that such diamond-based supercapacitors could be used in a wide range of applications and in particular those requiring high performance in biomedical applications.

Neural recording, stimulation, and biochemical sensing using semiconducting electrodes in both electrical and optical domains are discussed. Their differences from metallic electrodes from the application and characterization perspective are highlighted.

Semiconducting electrodes are increasingly utilised for neural interfacing applications, such as neural recording, stimulation, and photomodulation. To characterise the performance of these electrodes, photoelectrochemical analysis is often undertaken in biologically relevant electrolytes. These include electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and for photomodulation applications, photocurrent (PC) measurements. From such measurements, it is possible to deduce key properties of semiconductor surfaces, such as electrochemical impedance and capacitance, as well as mechanisms of charge transfer. To extract these parameters from the experimental data, equivalent electrical circuit modelling is often employed, but usually only for a single technique at a time which often misses key insights about the processes occurring at the electrode-electrolyte interface. Here we present an equivalent circuit model that simultaneously describes the results from CV, EIS, and PC transient measurements. Using semiconducting nitrogen-doped ultrananocrystalline diamond (N-UNCD) electrodes in saline solution, we show that the model describes physical mechanisms that occur at the interface with electrolyte, encompassing the space charge region, the electrical double layer, and the electrolyte. Using the model we are able to optimise parameters relevant for neural interfacing and suggest that this framework may assist in the characterisation of other semiconducting electrodes.

Site‐specific integration (SSI) cell line systems are gaining popularity for biotherapeutic development and production. Despite the proven advantages for these expression hosts, the SSI system is still susceptible to rare off‐target events and potential vector rearrangements. Here we describe the development process of an SSI cell line for production of an IgG1 monoclonal antibody (mAb‐086). During cell line generational studies to assess suitability of clone C10 for commercial purposes, restriction fragment lengths of genomic DNA harboring the light chain (LC) were not in agreement with the predicted size. We first confirmed that the SSI landing‐pad achieved occupancy of the desired expression plasmid. Additional investigation revealed that random integration had occurred, resulting in the acquisition of a partial copy of the LC and a full‐length copy of the heavy chain (HC) at a different locus in the host genome. This off‐target event had no impact on the genotypic consistency and phenotypic stability of the cell line, the production process, or the drug substance product quality. Given the genetic, phenotypic, and process consistency of the cell line, clone C10 was deemed suitable as a manufacturing cell line.

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