A simple example is light-induced zeta potential neutralization that can lead to the self-assembly of nanoparticles into clusters due to the absence of electrostatic stabilization. Interestingly, hybridization in nanostructures has also led to both photo-and magneto-responsive nanostructures. Similarly, if the solvent medium is photo-responsive, a light induced processes can lead to the assembly of nanoparticles that are stably dispersed. Kundu et al. demonstrated that the reversible light induced modulation of acidity (pH) of a medium is possible by photoconversion of a photo-responsive molecule. This change of pH results in zeta potential reduction by H + removal from the nanoparticle surfaces with COOH terminated ligands, thereby leading to clustering the nanoparticles, Figure (b). Similar pH sensitive Au nanoparticle clustering triggered by light was demonstrated by He et al. where Au nanoparticles functionalized with guanidiniocarbonyl pyrrole carboxylate zwitterion (GCPZ) molecules reversibly assemble at neutral pH due to surface charge minimization. When the particles are trapped at the air-liquid interface, re-arrangement of the particles can also be induced by cis-trans photoisomerization of photo-responsive surfactants. Shown for microparticles in Figure (c), such photosensitive surfactants allow dynamic switching of the particle organization between a highly crystalline (under light) and a disordered (in the dark) phase with a fast response time (crystallization in ~10 s, disassembly in ~1 min) . Such an assembly-disassembly method can be applied for particles regardless of the size if they are trapped at the interface. Apart from the chemical routes, light induced assembly can also be driven by physical effects such as photothermal, Marangoni convection, optofluidic convection, near-field optical force, etc., because of the illumination.