Recent advances in upconversion technology have enabled optogenetic neural stimulation using remotely applied optical signals, but limited success has been demonstrated for neural inhibition by using this method, primarily due to the much higher optical power and more redshifted excitation spectrum that are required to work with the appropriate inhibitory opsin proteins. To overcome these limitations, core−shell−shell upconversion nanoparticles (UCNPs) with a hexagonal phase are synthesized to optimize the doping contents of ytterbium ions (Yb 3+ ) and to mitigate Yb-associated concentration quenching. Such UCNPs' emission contains an almost three-fold enhanced peak around 540−570 nm, matching the excitation spectrum of a commonly used inhibitory opsin protein, halorhodopsin. The enhanced UCNPs are utilized as optical transducers to develop a fully implantable upconversion-based device for in vivo tetherless optogenetic inhibition, which is actuated by near-infrared (NIR) light irradiation without any electronics. When the device is implanted into targeted sites deep in the rat brain, the electrical activity of the neurons is reliably inhibited with NIR irradiation and restores to normal level upon switching off the NIR light. The system is further used to perform tetherless unilateral inhibition of the secondary motor cortex in behaving mice, achieving control of their motor functions. This study provides an important and useful supplement to the upconversion-based optogenetic toolset, which is beneficial for both basic and translational neuroscience investigations.

Nowadays, MXenes have received extensive concern as a prominent electrode material of electrochemical capacitors. As two important factors to the capacitance, the influence of the intrinsical terminations (F, O and OH) and coordination atoms (C and N) is investigated using first-principles calculations. According to the density of states aligned with the standard hydrogen electrode, it turns out that a Ti3CNO2 monolayer is proven to show an obvious pseudocapacitive behavior, while the bare, F and OH terminated Ti3CN monolayers may only present electrochemical double layer characters in an aqueous electrolyte. Moreover, the illustration of molecular orbitals over the Fermi level are mainly contributed by the d-orbitals of Ti atoms coordinated with O and N atoms, indicating that the redox pseudocapacitance of the Ti3CNO2 monolayer is promoted by the coordination N atoms. Then the superiority of N bonded Ti atoms in accepting charges can be visualized through the charge population. Further, the larger ratio of C/N in the coordination environment of Ti atoms indicates that more electrons can be stored. Our investigation can give an instructional advice in the MXenes-electrode production.

The intrinsic charge storage capability of a series of transition metal dichalcogenides (TMDs) (MS2, M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Zr, Nb, Mo, Tc, Hf, Ta, W, Re, and MoX2, X = S, Se, Te) is investigated using density functional theory calculations. A map for pseudocapacitor electrodes is provided, depending on the demands of high conductivity and a remarkable peak of density of states (DOS) in the range of the electrolyte window. The calculated DOS suggests that most of the T phase structures are superior to H phase in electroconductibility. The charge storage capability is represented by the number of gaining or losing electrons calculated by integrating DOS in the electrolyte window. MS2 (M = Ti, V, Cr, Fe, Nb, Mo, Tc) of the T phase is conductive and gains electrons easily with considerable valence state change of the TM atom, showing a redox pseudocapacitance character as a cathode. Meanwhile, CoS2–H and MoSe2–T are promising anode materials. Moreover, the chalcogen (S, Se, Te) with different electronegativity and work function will result in the changes of Fermi level and surface polarization of MoX2, leading to the shift of their DOS in the electrolyte window. In another way, the metallic hydrogenated H phase of MoS2 (MoS2H2) with conductivity should have enhanced advanced electrochemical performance.

Many cellular programs of neural development are under combinatorial regulation by different chemoattractive or chemorepulsive factors. Here, we describe a microfluidic platform that utilizes well-controlled three-dimensional (3D) diffusion to generate molecular gradients of varied steepness in a large array of hydrogel cylinders, allowing high-throughput 3D chemotactic assays for mechanistic dissection of steepness-dependent neuronal chemotaxis. Using this platform, we examine neuronal sensitivity to the steepness of gradient composed of netrin-1, nerve growth factor, or semaphorin3A (Sema3A) proteins, and reveal dramatic diversity and complexity in the associated chemotactic regulation of neuronal development. Particularly for Sema3A, we find that serine/threonine kinase-11 and glycogen synthase kinase-3 signaling pathways are differentially involved in steepness-dependent chemotactic regulation of coordinated neurite repellence and neuronal migration. These results provide insights to the critical role of gradient steepness in neuronal chemotaxis, and also prove the technique as an expandable platform for studying other chemoresponsive cellular systems.