Incorporating fluorescent CdTe nanocrystals into a hydrogel via hydrogen bonding:: Toward fluorescent microspheres with temperature-responsive properties

Fluorescent microspheres were constructed by incorporating CdTe nanocrastals (NCs), costabilized by both thioglycerol and thioglycolic acid, into poly(N-isopropylacrylamide) (PNIPAM) microspheres through hydrogen bonding between the ligands capped on CdTe NCs and the PNIPAM chains. The loading capacity of PNIPAM was found to be dependent on the incubation temperature. Under optimized conditions the average spatial distance between CdTe NCs loaded into hydrogel spheres is still greater than that required for Forster energy transfer between CdTe NCs; therefore, very little change in the photoluminescence of CdTe NCs was observed after they were loaded into PNIPAM micropheres. Multiplex optical encoding was realized by loading differently sized NCs into single gel spheres. The emission color of the resultant fluorescent spheres was mainly determined by the ratio of differently sized NCs incorporated. Although CdTe NCs in the hydrogel increased the cross-linking degree of the PNIPAM network, the volume of the resultant composite spheres remained tunable against temperature. Therefore, Forster energy transfer between differently sized NCs loaded can be initiated by increasing the environmental temperature, creating a temperature-responsive emission.