No abstract

Electro‐optical neural interface technologies provide great potential and versatility in neuroscience research. High temporal resolution of electrical neural recording and high spatial resolution of optical neural interfacing such as calcium imaging or optogenetics complimentarily benefit the way information is accessed from neuronal networks. To develop a hybrid neural interface platform, it is necessary to build transparent, soft, flexible microelectrode arrays (MEAs) capable of measuring electrical signals without light‐induced artifacts. In this work, flexible and transparent ultrathin (<10 nm) gold MEAs are developed using a biocompatible polyelectrolyte multilayer (PEM) metallic film nucleation‐inducing seed layer. With the polymer seed layer, the thermally evaporated ultrathin gold film shows good conductivity while providing high optical transmittance and excellent mechanical flexibility. In addition, strong electrostatic interaction via the PEM alters the electrode‐electrolyte interfaces, thereby reducing the electrode impedance and baseline noise level. With a simple modification of the fabrication process of the MEA using biocompatible materials, both excellent transmittance, and electrochemical interface characteristics are achieved, which is promising for efficient electro‐optical neural interfaces.

Implications: Extreme caution should be applied when examining data about subgroups within the 'Asian' category.

Various temperature sensitive biological mechanisms have been utilized for new biomedical engineering tools such as neuromodulation, cancer cell hyperthermia or photothermal therapy. Optically transparent and high spatio‐temporal resolution temperature sensors are needed to precisely analyze the biological effects that occur in response to the temperature changes. In this work, semi‐transparent p‐NiO/n‐ZnO heterojunction diode‐based temperature sensors with 100 µm‐diameter ultrathin transparent Au/Ag metal anodes is introduced. The fabricated diode temperature sensors accurately measure temperature changes from 25 to 80 °C, which is of significant interest in many biomedical engineering applications. The sensors also exhibit adequate transparency over the entire visible light spectrum for biomedical imaging including fluorescent microscopy. Low‐power operation of the temperature sensor (<0.2 nW) is achieved to avoid a self‐heating effect. The micro‐scale spatial resolution of the transparent temperature sensors is especially useful for cellular resolution bio‐imaging, optical neural recording, and optical bio‐modulation where transparency and high‐resolution temperature sensing are necessary.

Optical neuromodulation is a versatile neural stimulation technology that enables highly localized excitatory or inhibitory stimulation of neuronal activities. Photothermal neural stimulation using thermoplasmonic metallic nanoparticles for light to heat conversion has been suggested as an optical neural stimulation technology without genetic modification. Optical fibers implementing the thermoplasmonic effect were recently developed for localized neural stimulation, and the successful demonstration of localized neural stimulation in vitro was reported. However, before photothermal neural stimulation is further applied in the brains of live animals and ultimately in human trials, a safety analysis must carefully be performed for the thermal effect of stimulation in vivo. With the complexity of the physical structure and different thermal properties of the brain and surrounding body, the resulting thermal effect could vary despite the same power of light delivered to the optical fiber. In addition, dynamic thermal properties of the brain such as the daily blood perfusion rate change or metabolic heat generation must also be carefully considered for the precise implementation of photothermal neural stimulation. In this work, an in-depth computational analysis was conducted of the photothermal effects using a thermoplasmonic optical fiber for in vivo neural stimulation. The effects of the experimental design and stimulation protocols on the thermal effect in the brain were analyzed. We believe that the results provide a good experimental guideline for safely conducting photothermal neural stimulation using the thermoplasmonic optical fiber technology.