Diamond possesses many favorable properties for biochemical sensors, including biocompatibility, chemical inertness, resistance to biofouling, an extremely wide potential window, and low double-layer capacitance. The hardness of diamond, however, has hindered its applications in neural implants due to the mechanical property mismatch between diamond and soft nervous tissues. Here, we present a flexible, diamond-based microelectrode probe consisting of multichannel boron-doped polycrystalline diamond (BDD) microelectrodes on a soft Parylene C substrate. We developed and optimized a wafer-scale fabrication approach that allows the use of the growth side of the BDD thin film as the sensing surface. Compared to the nucleation surface, the BDD growth side exhibited a rougher morphology, a higher sp 3 content, a wider water potential window, and a lower background current. The dopamine (DA) sensing capability of the BDD growth surface electrodes was validated in a 1.0 mM DA solution, which shows better sensitivity and stability than the BDD nucleation surface electrodes. The results of these comparative studies suggest that using the BDD growth surface for making implantable microelectrodes has significant advantages in terms of the sensitivity, selectivity, and stability of a neural implant. Furthermore, we validated the functionality of the BDD growth side electrodes for neural recordings both in vitro and in vivo. The biocompatibility of the microcrystalline diamond film was also assessed in vitro using rat cortical neuron cultures.

This paper reports the fabrication and characterization of an optical neuro-stimulator array that consists of 32-channel microscale light-emitting diodes (µ-LEDs) coupled with microscale reflectors for intensity enhancement. The hemi-spherical micro-reflector is able to collect the rear side emission of LED while also acting as a collimator to focus the diverged LED light, aiming toward driving power minimization through light intensity increase, for wireless neuro-stimulator applications. The micro-reflector was constructed by wet etching of silicon followed by aluminum coating as the reflective mirror. The reflective cavity was filled with polydimethylsiloxane (PDMS) that acts as the planarization polymer to facilitate device integration with the µ-LED chip. Deviation of hemi-spherical geometry cavities due to the uneven lateral and vertical etching rate was shown, and the surface morphology was characterized experimentally. Optical intensity enhancement was studied in both simulation and experiments, demonstrating that the micro-reflector enables 65% intensity enhancement. The reflector-coupled LED had an operating temperature increase of <1 • C, well within the ANSI/AAMI safety limit for biomedical implants. The potential of the stimulator for use in optogenetics was validated by in vitro experiments.

No abstract

No abstract