Facile synthesis of high-quality CuInZnxS2+x core/shell nanocrystals and their application for detection of C-reactive protein

Highly photoluminescent (PL) CuInZnxS1+x nanocrystals (NCs) and CuInZnxS1+x/ZnS core/shell NCs were successfully synthesized by a facile colloidal method. First, a facile and reliable non-injection method for the synthesis of photoluminescent CuInZnxS2+x NCs was developed with inexpensive reagents. The relative PL quantum yields (QYs) of CuInZnxS2+x NCs could reach up to 30%, with tunable emissions in the range 580–780 nm. Then, CuInZnxS2+x/ZnS core/shell NCs were synthesized and showed greatly improved optical properties, the PL QY of the CuInZnxS2+x/ZnS NCs can reach up to 60%. Even in the near-infrared region, the PL QY still can achieve up to 45% due to the successful controlled red shift of PL during the ZnS shell growth process. More importantly, such core/shell NCs can be transferred into water successfully using amphiphilic oligomer (polymaleic acid n-hexadecanol ester) as a surface coating agent by an organic-aqueous phase transfer method and the PL QYs can be well controlled over 40%. Furthermore, a biosensor system (lateral flow immunoassays system, LFIA) for the detection of C-reactive protein (CRP) was developed by using this water-soluble CuInZnxS2+x/ZnS core/shell NCs as fluorescent label and a nitrocellulose filter membrane for lateral flow. The results showed that such CuInZnxS2+x/ZnS core/shell NCs were excellent fluorescent labels to detect CRP. The detection sensitivity for CRP could reach 1 ng mL−1.