Preparation of multi-shell structured fluorescent composite nanoparticles for ultrasensitive human procalcitonin detection

In this paper, we reported the preparation of carboxyl functionalized quantum dots (QDs)-embedded silica nanoparticles by combining layer-by-layer (LbL) self-assembly technique and a multi-layer protection method. Preformed SiO 2 nanoparticles synthesized via the Stöber method were first alternately deposited with positively charged polyelectrolyte (poly(diallyl dimethylammonium chloride), PDDA) and negatively charged CdSe/ZnS QDs by LBL method and further coated by a silica shell. Then, the functionalization of SiO 2 @PDDA@QDs@SiO 2 nanoparticles with hydrophobic hydrocarbons and biocompatible oligomers impart optical imaging properties and good colloidal stability in aqueous solutions at a wide range of pH, PBS buffer, and under thermal treatment. In addition, these newly developed multi-shell structured nanoparticles coupled with specific antibodies were successfully applied in detecting procalcitonin (PCT) antigens using fluorescent lateral flow immunoassay (LFIA). The naked-eye detection limit of fluorescence nanoparticles could achieve 0.1 ng mL −1 of PCT antigens, which was about two hundred times higher than that of colloidal gold-based method.