Hybrid Electro-Plasmonic Neural Stimulation with Visible-Light-Sensitive Gold Nanoparticles.

Biomedical prosthetics utilizing electrical stimulation have limited, effective spatial resolution due to spread of electrical currents to surrounding tissue, causing nonselective stimulation. So, precise spatial resolution is not possible for traditional neural prosthetic devices, such as cochlear implants. More recent, alternative methods utilize optical stimulation, mainly infrared, sometimes paired with nanotechnology for stimulating action potentials. Infrared stimulation has its own drawbacks, as it may cause collateral heating of surrounding tissue. In previous work, we employed a plasmonic method for stimulation of electrically excitable neuroblastoma cell line, which had limited success. Here, we report the development of a hybrid electro-plasmonic stimulation platform for spatially and temporally precise neural excitation to address the above deficiencies. Primary trigeminal neurons were co-stimulated In Vitro in a whole-cell patch-clamp configuration with sub-threshold-level short duration (1-5 ms) electrical and visible light pulses (1-5 ms, 1-5 V, 10 Hz). The visible light pulses were aimed at a gold-nanoparticle coated nanoelectrode placed alongside the neuron, within 2 µm distance. Membrane action potentials were recorded with tri-fold higher success rate and five-fold better post-stimulation cell recovery rate than with pure optical stimulation alone. Also, electrical stimulus current input was being reduced by up to 40%. The sub-threshold levels of electrical stimuli in conjunction with visible light (532 nm) reliably triggered trains of action potentials. This single-cell hybrid activation was reliable and repeatable, without any damage as observed with pure optical stimulation. This work represents an empirical cellular study of the action potential membrane effects produced by the cultured primary sensory trigeminal neurons when co-stimulated with plasmonic and hybrid stimulation. Our hybrid neurostimulation method can be used towards development of high-acuity neural modulation prosthetic devices, tunable for individual needs, which would qualify as a preferred alternative over traditional electrical stimulation technologies.