Preparation of low fluorescence loss Multishell-QDs@SiO2-COOH and its application to quantitative immunoassay

Abstract

The demand for precise and sensitive detection has promoted the rapid development of QDs with good biocompatibility. QDs modified with silicon dioxide can effectively isolate the external environment without affecting the fluorescence performance of QDs while endowing them with biocompatibility. However, the existing silica modification methods suffers from significant fluorescence loss and relatively poor stability of QDs. In this paper, multishell-QDs@SiO₂-COOH (MS-QDs@SiO₂-COOH) with low fluorescence loss (quantum yield reduction value is about 11 %) is successfully prepared by using high self-fluorescence stability core/multishell QDs in the reverse microemulsion system. By adjusting the content of silicon source and the ratio of carboxylation reagent, the thickness of silica shell within the range of 6–12 nm and the carboxyl groups on the surface can be controlled, and MS-QDs@SiO₂-COOH has good stability, which can meet the detection applications requirements with different particle sizes and carboxyl content. Using the prepared MS-QDs@SiO₂-COOH as a fluorescent labeling material, the construction of a quantum dot-based fluorescence-linked immunosorbent assay (QLISA) has successfully achieved quantitative detection of C-reactive protein, showing a good linear relationship (R² = 0.992) in a wide range of 1–2000 ng/mL, with a detection limit of 0.9 ng/mL, and good recovery rates of 92.8–102.4 %. This study provides a new method for the application of QDs in quantitative detection.