A photosensitive surface capable of inducing electrophysiological changes in NG108-15 neurons.

Retinal prostheses promise to be a viable therapy for many forms of blindness. Direct stimulation of neurons using an organic light-sensitive, self-assembled monolayer surface offers a simple alternative to conventional semiconductor technology. For this purpose we have derivatized an indium tin oxide (ITO) substrate with the photosensitive dye, NK5962, using 3-(aminopropyl)trimethoxysilane (APTMS) as cross-linker. The surface was characterized through contact angle goniometry, electrochemical impedance spectroscopy, grazing angle infrared and ultraviolet-visible spectrophotometry. NG108-15 neurons were grown on the ITO-APTMS-NK5962 surface and neural responses from electrical stimulation vs. photostimulation through the ITO-APTMS-NK5962 surface were measured using patch clamp electrophysiology. Under these conditions, photostimulation of depolarized cells caused an approximate 2-fold increase in voltage-gated sodium (Na(+)) current amplitude at a membrane potential of -30mV. Our results demonstrate the feasibility of stimulating neurons, grown on light-sensitive surfaces, with light impulses, which ultimately may facilitate the fabrication of a simple, passive retinal prosthetic.

Absorption and fluorescence of 2,5-diarylidenecyclopentanones in acidic media: evidence for excited-state proton transfer.

Spectroscopic properties for a series of 2,5-diarylidenecyclopentanones in weak and strong acid environments are reported. Electronic absorption and fluorescence spectra have been measured for the all-E configurations of 2,5-dibenzylidenecyclopentanone (1), 2,5-bis(3-phenylallylidene)cyclopentanone (2), and 2,5-bis(5-phenylpenta-2,4-dienylidene)cyclopentanone (3) in acetic acid and sulfuric acid solutions. The spectroscopic evidence indicates that in 96% sulfuric acid 1, 2, and 3 are protonated both in the ground state and on the S1 potential energy surface. This assignment is supported by Zerner's intermediate neglect of differential overlap (ZINDO) and time-dependent density functional theory (TD-DFT) calculations. In glacial acetic acid, 1, 2, and 3 are unprotonated in the ground state. The absence of observable fluorescence from 1 in glacial acetic acid indicates that S1 is npi, whereas the observation of fluorescence from 2 and 3 in acetic acid is consistent with S1 being pipi. A combination of spectroscopic data, molecular orbital calculations, and fluorescence lifetime measurements indicate that 2 and 3 undergo intermolecular excited-state proton transfer in glacial acetic acid and diluted sulfuric acid solutions. Photochemical studies reveal that, unlike its behavior in organic solvents, 1 does not undergo efficient E,E --> E,Z photoisomerization in 96% sulfuric acid.