Millisecond CdS nanocrystal nucleation and growth studied by microfluidics with in situ spectroscopy

Abstract

Microfluidic methods allowing fast mixing allow studying fast chemical reactions on the millisecond time scale. Here the kinetics of nucleation and growth of thioglycerol- and l-cysteine-capped CdS quantum dots is investigated using a continuous-flow microfluidic device in combination with in situ microscopy and spectroscopic techniques. A microfluidic device is developed to three-dimensionally focus a central aqueous Cd2+-stream, which is completely enclosed by a water buffer layer, into a stream of aqueous S2−. Diffusion-limited nucleation and growth of CdS nanoparticles occurs in the buffer layer downstream the reaction channel which can be followed by in situ confocal laser scanning microscopy and UV-Vis absorption spectroscopy on the time scale of the first 1–100 ms, giving direct and unique insights into early colloidal crystal nucleation and growth processes.