Assembling quantum dots via critical Casimir forces

•Critical Casimir forces, arising from solvent density fluctuations near a critical point, can assemble quantum dot in solution.•The assembly is reversible upon lowering the temperature away from the critical point.•The temperature-sensitive assembly is monitored by dynamic light scattering.•Assembly is driven by properties of the solution.

Programmed assembly of colloidal inorganic nanocrystal superstructures is crucial for the realization of future artificial solids as well as present optoelectronic applications. Here, we present a new way to assemble quantum dots reversibly using binary solvents. By tuning the temperature and composition of the binary solvent mixture, we achieve reversible aggregation of nanocrystals in solution induced by critical Casimir forces. We study the temperature-sensitive quantum-dot assembly with dynamic light scattering. We show that careful screening of the electrostatic repulsion by adding salt provides a further parameter to tune the reversible assembly.