Preparation of “pomegranate”-like QD/SiO2/poly(St-co-MAA) fluorescent nanobeads in two steps to improve stability and biocompatibility

Fluorescent nanobeads are widely used due to their advantages of visualization, sensitivity and the quantitative measurement of target analytes. In terms of their applications, the stability and biocompatibility of fluorescent nanobeads are very important. In this work, “pomegranate”-like QD/SiO2/poly(St-co-MAA) (QSIP-COOH) nanobeads were synthesized by two-step strategies. First, quantum dots (QDs) were covered by a silica layer using the reverse hydrolysis method to form a core–shell structure like the seed and flesh of a pomegranate, and then a poly(St-co-MAA) layer was formed as the skin of the pomegranate. The structure and morphology of nanobeads were investigated by FTIR, TG, TEM and HRTEM. The results confirmed that QSIP-COOH nanobeads had a pomegranate structure with a QD core, an intermediate silica shell, and a carboxylated polystyrene outermost shell. TEM and HRTEM results showed that the size of the typical product was about 170 nm with the QDs of about 8 nm and the MPS-modified QD/SiO2 (QSI-CC) of about 27 nm, respectively. The in vitro cytotoxicity test showed that nanobeads had desirable stability and good biocompatibility, which made them applicable for various bioassays and diagnostics. Here, QSIP-COOH fluorescent nanobeads were applied to immunochromatography test strip (ICTS) and the result proved that QSIP-COOH fluorescent nanobeads could be used for the sensitive detection of immune human chorionic gonadotropin (HCG).