Summary Unmodified neurons can be directly stimulated with light to produce action potentials, but such techniques have lacked localization of the delivered light energy. Here we show that gold nanoparticles can be conjugated to high-avidity ligands for a variety of cellular targets. Once bound to a neuron, these particles transduce millisecond pulses of light into heat which changes membrane capacitance, depolarizing the cell and eliciting action potentials. Compared to non-functionalized nanoparticles, ligand-conjugated nanoparticles highly resist convective washout, and enable photothermal stimulation with lower delivered energy and resulting temperature increase. Ligands targeting three different membrane proteins were tested; all showed similar activity and washout resistance. This suggests that many types of ligands can be bound to nanoparticles, preserving ligand and nanoparticle function, and that many different cell phenotypes can be targeted by appropriate choice of ligand. The findings have applications as an alternative to optogenetics, and potentially for therapies involving neuronal photostimulation.

The voltage-gated proton channel Hv1 plays a critical role in the fast proton translocation that underlies a wide range of physiological functions, including the phagocytic respiratory burst, sperm motility, apoptosis, and metastatic cancer. Both voltage activation and proton conduction are carried out by a voltage-sensing domain (VSD) with strong similarity to canonical VSDs in voltage-dependent cation channels and enzymes. We set out to determine the structural properties of membrane-reconstituted human proton channel (hHv1) in its resting conformation using electron paramagnetic resonance spectroscopy together with biochemical and computational methods. We evaluated existing structural templates and generated a spectroscopically constrained model of the hHv1 dimer based on the Ci-VSD structure at resting state. Mapped accessibility data revealed deep water penetration through hHv1, suggesting a highly focused electric field, comprising two turns of helix along the fourth transmembrane segment. This region likely contains the H + selectivity filter and the conduction pore. Our 3D model offers plausible explanations for existing electrophysiological and biochemical data, offering an explicit mechanism for voltage activation based on a one-click sliding helix conformational rearrangement.V oltage-gated proton channels (hHv1) represent a remarkable evolutionary adaptation of canonical voltage sensing domain (VSD). In hHv1, both voltage-sensing and ion (H + ) conduction are carried out by a single domain, and undergo a global conformational rearrangement (1, 2). In humans, hHv1 is widely expressed and required for a variety of physiological processes (3), including optimal reactive oxygen species production by NADPH oxidase (4-6), B-cell proliferation and differentiation (7), and regulation of human sperm motility (8). hHv1 folds as an antiparallel four-helix bundle with its fourth transmembrane segment (S4) containing three putative gating charges. Just as in the VSDs from ion channels and enzymes, the positively charged S4 moves outwardly in response to a depolarization (9). Beyond sensing the transmembrane voltage, S4 reorientation in hHv1 participates in the formation of a protonselective permeation pathway responsible for the generation of the proton currents that underlie its multiple physiological functions (10, 11).Despite high sequence similarity and a common structural blueprint, VSDs from ion channels and enzymes display a wide range of electrophysiological properties; these include large variations in effective gating charge (z = ∼0.9 to ∼3.6 e − ) and midpoints of activation (V 1/2 = ∼−150 to ∼+150 mV). Existing VSD crystal structures (12-16) have provided key data on the arrangement and orientation of the transmembrane helices S1-S4, while at the same time revealed a considerable structural heterogeneity-particularly, the number and positions of both the gating charges and their compensating countercharges in relation to the hydrophobic "plug" or "gasket" electrically separating the intra-and extrace...

In this work, we investigate the emission and absorbance properties of the novel water-soluble cationic conjugated polymer poly{2,5-bis[3-(N,N,N-triethylammonium bromide)-1-oxapropyl]-1,4-phenylenevinylene}, denoted here as P2, in the presence of varying amounts of the anionic surfactant sodium dodecylsulfate (SDS). We show that the absolute photoluminescence quantum efficiency (PLQE), the absorption wavelength, and the emission wavelength of an aqueous solution of P2 can be adjusted according to the surfactant/polymer ratio in aqueous solution. In particular, we show that the addition of SDS to P2 increases the polyelectrolyte's PLQE to approximately 40%. An observed red shift in the emission spectra upon addition of the surfactant is attributed to the reduction in electrostatic repulsive interactions between side chains that minimize the benzene ring twisting along the backbone structure. At the surfactant's critical micelle concentration, the P2 chains wrap around the outer surface of the SDS micelles. This work has implications on the development of new stable poly(p-phenylenevinylene)-based photovoltaic and electroluminescent materials with tunable optical properties.

Clinical methods used to assess the electrical activity of excitable cells are often limited by their poor spatial resolution or their invasiveness. One promising solution to this problem is to optically measure membrane potential using a voltage-sensitive dye, but thus far, none of these dyes have been available for human use. Here we report that indocyanine green (ICG), an infrared fluorescent dye with FDA approval as an intravenously administered contrast agent, is voltage-sensitive. The fluorescence of ICG can follow action potentials in artificial neurons and cultured rat neurons and cardiomyocytes. ICG also visualized electrical activity induced in living explants of rat brain. In humans, ICG labels excitable cells and is routinely visualized transdermally with high spatial resolution. As an infrared voltage-sensitive dye with a low toxicity profile that can be readily imaged in deep tissues, ICG may have significant utility for clinical and basic research applications previously intractable for potentiometric dyes.