Robust synthesis of bright multiple quantum dot-embedded nanobeads and its application to quantitative immunoassay

In this paper, semiconductor nanocrystal quantum dot-based nanobeads with strong luminescence and high stability were prepared by a novel controllable synthetic route. CdSe/ZnS core/shell quantum dots (QDs) were first attached onto the surface of silica spheres, then encapsulated by silica and functional hydrophilic groups. Eventually, nanostructured SiO2@QDs@SiO2-COOH beads were formed. This convenient method shows high repeatability, which can precisely control the loading density of QDs in a single SiO2 sphere and minimize the loss of QDs. In view of their structure-based advantages, SiO2@QDs@SiO2-COOH nanobeads exhibited approximately 50 times stronger photoluminescence (PL) than single QDs, which have similar quantum yields. Stability studies revealed that the SiO2@QDs@SiO2-COOH nanobeads showed robustness against harsh conditions, such as acid etching and high temperature. Furthermore, such SiO2@QDs@SiO2-COOH nanobeads were used as excellent label material for high sensitive and quantitative assay. A quantitative quantum dot-based fluorescence-linked immunosorbent assay (QLISA) with high sensitivity for C-reactive protein (CRP) detection was established successfully by utilizing fluorescent nanobeads as probes. SiO2@QDs@SiO2-COOH nanobeads showed great improvement on the detection intensity, sensitivity, and linear range. The excellent linearity of quantitative detection of CRP has been established in the range of 0.5 ng mL(-1) and 1000 ng mL(-1), and the limit of detection (LOD) can be as low as 0.32 ng mL(-1). All these results indicates that the SiO2@QDs@SiO2-COOH nanobeads have a great application prospect for in vitro diagnostics.