Morphology-dependent light-triggered assembly of azobenzene-functionalized gold colloids and their intracellular retention.

Abstract

Understanding how controllable colloidal states influence nanoparticle behavior at the nano-bio interface is important for designing responsive nanomaterials with programmable intracellular retention and clearance profiles. However, achieving programmable assembly while resolving the coupled roles of particle motion, ligand switching, interparticle forces, and morphology remains challenging. Here, we develop azobenzene-functionalized gold photoresponsive colloids that undergo light-triggered assembly through an "accelerate-and-lock" mechanism. In the dispersed state, trans-azobenzene ligands maintain colloidal stability through steric repulsion. Under 365 nm UV irradiation, photothermal heating of the gold cores enhances Brownian motion and interparticle collisions, while trans-to-cis isomerization weakens steric stabilization, lowers the DLVO energy barrier, and enables van der Waals-mediated locking into stable aggregates. This coupling drives the transition from stochastic diffusion to collective assembly. Assembly kinetics and cluster structure depend strongly on particle morphology: isotropic gold nanospheres form compact clusters, whereas anisotropic nanorods and nanotriangles produce looser aggregates because of orientational constraints, rotational diffusion, and geometric frustration. In cells, switching from dispersed particles to larger clusters increases intracellular retention by approximately eightfold through size-exclusion effects. This work establishes a surface-chemistry-regulated active-colloid platform and shows how photothermal motion, ligand conformation, interaction barriers, and particle geometry collectively govern assembly and nano-bio interfacial behavior.

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