Motile Artificial Chromatophores: Light-Triggered Nanoparticles for Microdroplet Locomotion and Color Change

Gold nanoparticles coated with a poly(N-isopropylacrylamide) (pNIPAM) shell undergo reversible dis/assembly below and above the critical temperature of 32 degrees C. Loading these particles into microdroplets at high density creates light-driven artificial chromatophores. Triggering the nanoparticle assembly gives dramatic color changes from nanoparticle localization at the base of the droplets, resembling zebrafish melanophores. These reversible chromatophore states can be switched by both bulk and optical heating, explored here in individual microdroplets and in large cm(2) areas of close-packed droplets. Illuminating chromatophores off-center with a tightly focused beam results in droplet locomotion via two separate mechanisms, Marangoni interfacial shear and gas bubble propulsion, depending on optical power.