A sensing platform for highly sensitive immunoassay based on metal-enhanced fluorescence of CdSe@ZnS

Abstract

Insufficient sensitivity caused by low radiative intensity of employed fluorescent material is the main obstacle toward early accurate diagnosis of fatal diseases when applying fluorescence analysis. Herein, we have developed a dual amplification procedure to overcome this issue. We first synthesize high-quality CdSe@ZnS@SiO2 core/shell quantum dots (QDs) with type-I band alignment to confine the carrier wave functions, thus ensuring high quantum yield (∼ 80%). The fluorescence intensity of those QDs is further amplified by localized surface plasmon resonance effect enabled by gold nanoparticles. We finally construct CdSe@ZnS@SiO2 and Au@SiO2 immune sandwich biosensor platform, and take C-reaction protein (CRP) as a test case. It is shown that this biosensor platform exhibits a wide detecting range between 0.5 and 100 ng/mL, and detecting limit of 0.076 ng/mL. We further apply this detecting scheme in serum and actual clinical, competing performance compared with the prevailing standard measurements in hospital has been obtained. Both experiment and the finite element analysis (FEA) approach calculation results indicate that a highly enhanced electric field between Au@SiO2 and CdSe@ZnS@SiO2 enhances the radiative recombination rates of the QDs@SiO2 and decreases the fluorescence lifetime of that. The fluorescence intensity amplification scheme proposed herein is of great significance for the real-time and high-sensitivity early detection of biomarkers in the biomedicine.