Highly ordered fluorescent rings by “breath figures” on patterned substrates using polymer-free CdSe quantum dots

Highly ordered and strongly fluorescent 2-dimensional arrays of cadmium selenide (CdSe) quantum dots (QDs) were obtained on gold substrates using a simple method combining microcontact printing and “breath figures” techniques. In this process, water vapor was condensed on chemically patterned Au substrates to form ordered arrays of droplets. When the water droplet arrays were submerged in a chloroform solution of CdSe QDs, the QDs were spontaneously assembled at the droplet surface and were then turned into uniform ring structures after solvent evaporation. The size and shape of the rings could be readily tuned by varying the pattern dimensions and assembly conditions. More complicated patterns were obtained by introducing sample vibration and changing the QD concentration. This process did not require grafting the QDs with polymer and the produced ring array had ideal topography that avoids substrate-induced florescence quenching.