Neural micro-electrode arrays that are transparent over a broad wavelength spectrum from ultraviolet to infrared could allow for simultaneous electrophysiology and optical imaging, as well as optogenetic modulation of the underlying brain tissue. The long-term biocompatibility and reliability of neural micro-electrodes also require their mechanical flexibility and compliance with soft tissues. Here we present a graphene-based, carbon-layered electrode array (CLEAR) device, which can be implanted on the brain surface in rodents for high-resolution neurophysiological recording. We characterize optical transparency of the device at >90% transmission over the ultraviolet to infrared spectrum and demonstrate its utility through optical interface experiments that use this broad spectrum transparency. These include optogenetic activation of focal cortical areas directly beneath electrodes, in vivo imaging of the cortical vasculature via fluorescence microscopy and 3D optical coherence tomography. This study demonstrates an array of interfacing abilities of the CLEAR device and its utility for neural applications.

The development of efficient non-platinum group metal (non-PGM) catalysts for oxygen reduction reaction (ORR) is of paramount importance for clean and sustainable energy storage and conversion devices. The major bottleneck in developing Fe-N-C materials as the leading non-PGM catalysts lies in the poor understanding of the nature of active sites and reaction mechanisms. Herein, we report a scalable metal organic framework-derived Fe-N-C catalyst with high ORR activity demonstrated in practical H 2 /air fuel cells, and an unprecedented turnover frequency (TOF) in acid in rotating disk electrode. By characterizing the catalyst under both ex situ and operando conditions using combined microscopic and spectroscopic techniques, we show that the structures of active sites under ex situ and working conditions are drastically different. Resultantly, the active site proposed here, a non-planar ferrous Fe-N 4 moiety embedded in distorted carbon matrix characterized by a high Fe 2+/3+ redox potential, is in contrast with those proposed hitherto derived from ex situ characterizations. This site reversibly switches to an in-plane ferric Fe-N 4 moiety poisoned by oxygen adsorbates during the redox transition, with the population of active sites controlled by the Fe 2+/3+ redox potential. The unprecedented TOF of the active site is correlated to its near-optimal Fe 2+/3+ redox potential, and essentially originated from its favorable biomimetic dynamic nature that balances the site-blocking effect and O 2 dissociation. The porous and disordered carbon matrix of the catalyst plays pivotal roles for its measured high ORR activity by hosting high population of reactant-accessible active sites. 50In situ characterizations reveal that the biomimetic dynamic nature of the Fe-N-C active site with a near-optimal Fe 2+/3+ redox potential formed upon pyrolysis accounts for its high ORR activity by balancing the site-blocking effect and O 2 dissociation.

Today's consumer electronics, such as cell phones, tablets and other portable electronic devices, are typically made of non-renewable, non-biodegradable, and sometimes potentially toxic (for example, gallium arsenide) materials. These consumer electronics are frequently upgraded or discarded, leading to serious environmental contamination. Thus, electronic systems consisting of renewable and biodegradable materials and minimal amount of potentially toxic materials are desirable. Here we report high-performance flexible microwave and digital electronics that consume the smallest amount of potentially toxic materials on biobased, biodegradable and flexible cellulose nanofibril papers. Furthermore, we demonstrate gallium arsenide microwave devices, the consumer wireless workhorse, in a transferrable thin-film form. Successful fabrication of key electrical components on the flexible cellulose nanofibril paper with comparable performance to their rigid counterparts and clear demonstration of fungal biodegradation of the cellulose-nanofibril-based electronics suggest that it is feasible to fabricate high-performance flexible electronics using ecofriendly materials.

No abstract