Tip-Functionalized Gold Nanorod Micropillar Arrays for Millisecond-Resolved Photothermal Neuromodulation Toward Retinal Prosthetic Applications.

Photothermal stimulation using plasmonic nanomaterials presents a promising alternative to electrical stimulation in retinal prostheses, addressing various functional limitations associated with electrical methods. However, many photothermal strategies utilize dispersed nanoparticles randomly accumulated on target locations and do not demonstrate millisecond-scale thermal dynamics. Herein, a flexible polydimethylsiloxane (PDMS) micropillar array with gold nanorods (GNRs), immobilized at the pillar tips, is introduced to create a deterministic and conformal platform that spatially localizes photothermal transduction at the neuron-device interface. Using infrared thermography with millisecond resolution, we map the rapid heating events at the pillar tips following near-infrared (NIR) pulse stimulation. This provides, to our knowledge, the first experimental verification of such rapid transients in GNR-based neuromodulation. Finite element modeling shows that the photothermal response is spatially confined, producing physiologically relevant temperature increase of 2-6°C, sufficient to modulate neuronal activities while minimizing off-target heating. Retinal progenitor cells cultured on these arrays demonstrate biocompatibility, proliferating and adapting morphologically by extending dendrites and attaching to the interface, while exhibiting consistent calcium responses under NIR actuation. These confirm both biocompatibility and functional activation. Together, these results establish a new class of deterministic, conformal, and light-addressable photothermal interfaces for high-resolution retinal prostheses.