Carbon nanodot-hybridized silica nanospheres assisted immunoassay for sensitive detection of Escherichia coli

Carbon dots (CDs) are intrinsically luminescent nanomaterials that have many potential applications in biosensing technologies due in part to their high photostability and fluorescent properties. However, attempts to integrate CDs into immunosorbent assays have been deterred by challenges preventing quantum yield augmentation and surface functionalization. To address these issues, we fabricated carbon dot-encapsulated silica nanospheres (CSNs) using a facile one-pot synthesis method. The enclosing silica matrix rendered extensive material stability to the nanospheres and abated quenching by nonradiative decay to cause considerable signal amplification. Nanosphere hybridization to antibodies permitted their use in solid-phase immunoassays as tracers. Here, we demonstrate the suitability of CSN-based immunosorbent assays as a point-of-care technique for the detection of foodborne pathogens through E. coli O157:H7 quantitation experiments. After optimization, detection limit of E. coli O157:H7 was determined to be 2.4 CFU mL−1. The estimated recoveries were in the range of 91.7–110.5% in spiked samples, which indicated that the developed method is capable for detecting E. coli O157:H7 in food samples. The nanosphere tracers described herein, and the methods used to create them, may be beneficial tools for the development of new pathogen biosensing strategies. •CSNs presented enhanced brightness and stability.•The fluorescence of CSNs showed stability due to the protection of the silica shell.•The CSNs were used as an ideal signal label for immunoassay-detection of E.coli O157:H7.•A low detection limit of E.coli O157:H7 could be determined to be 2.4 CFU/mL.