High-quality CuInS ₂/ZnS quantum dots for in vitro and in vivo bioimaging

The exploration of biocompatible quantum dots (QDs) for biomedical imaging is currently one of the fastest growing fields of nanotechnology. This strategy overcomes the intrinsic toxicity of well-developed II-VI and other semiconductor QDs (Cd, Hg, Pb, Se, Te, As, etc.) that remains a major obstacle to their clinical use. In this report, we synthesized high-quality CuInS ₂/ZnS (CIS/ZnS) QDs without using conventional toxic heavy metals. These QDs exhibited improved photoluminescence (PL) properties, with tunable emission peaks ranging from 550 to 800 nm and a maximum PL quantum yield (QY) up to 80%. Next, we explored the effective loading of the prepared oil-soluble CIS/ZnS QDs using biodegradable folate-modified N-succinyl-N′-octyl chitosan (FA-SOC) micelles. Targeting efficacy of the resulting QDs-loaded micelles to tumors using in vitro and in vivo optical imaging techniques was also investigated. The results show that the micelle platform allowed successful formulation of these oil-soluble QDs in water, while retaining the morphology, crystal structure, and PL of the initial CIS/ZnS QDs. This study demonstrates the versatility of using the biocompatible CIS/ZnS QDs across different spatial scales (in vitro cell imaging and in vivo small animal imaging) for multicolor biological imaging applications.