# Photothermal Transport for Guiding Nanoparticles Through the Vitreous Humor

## TL;DR

A new method uses light and a dye to guide nanoparticles in the eye's vitreous humor, improving drug delivery to the retina.

## Contribution

This is the first demonstration of guided light-controlled nanoparticle transport in the vitreous using clinical modalities.

## Key findings

- Photothermal transport guides nanoparticles toward laser-illuminated areas in the vitreous.
- Thermal convection is the main driver of nanoparticle motion, with thermophoresis playing a minor role.
- Optimization parameters include dye concentration, particle size, and laser fluence.

## Abstract

Visual impairments affect over 2.2 billion people worldwide, yet delivering drugs to the posterior segment of the eye, including the retina, remains a major challenge. Intravitreal injection, the standard administration route, often results in suboptimal drug diffusion through the vitreous, limiting drug access to the retina. While various strategies have been explored to enhance the mobility of drug molecules and nanomedicines (drugs encapsulated in nanoparticles) in the vitreous, no method has demonstrated guided transport. Here, we investigate photothermal transport of nanoparticles in the vitreous using a pulsed laser and indocyanine green, both clinically approved modalities. We show that photothermal transport guides nanoparticles from one location in the vitreous toward the laser‐illuminated area, away from the injection spot. Multiple‐particle tracking and numerical simulations reveal that this motion is predominantly driven by thermal convection, with thermophoresis contributing to a lesser extent. We identified parameters for optimization, including dye concentration, particle size, distance from the laser focus, and laser fluence. These findings establish a novel and clinically relevant paradigm for light‐guided drug delivery in the eye. To our knowledge, this is the first demonstration of guided light‐controlled particle transport in the vitreous using ocular dyes and pulsed lasers routinely applied in ophthalmology.

Nanosecond laser irradiation of the clinically approved dye indocyanine green (ICG) enables light‐guided nanoparticle transport within the vitreous humor. The combined use of ICG and pulsed laser illumination induces localized convection and thermophoresis, directing particles toward illuminated regions. This study demonstrates controllable photothermal transport within the vitreous using clinical modalities, opening avenues for light‐guided drug delivery in ophthalmology.