Thick-Shell CdSe/ZnS/CdZnS/ZnS Core/Shell Quantum Dots for Quantitative Immunoassays

Colloidal quantum dots (QDs) have been broadly applied as fluorescent labeling materials in the fields of bio-imaging, sensing, and detection, in which the optical performances and stability of the utilized QDs are vital. Despite significant efforts in developing such materials, it is still challenging to fabricate QDs with high photoluminescence quantum yields (PL QYs) while concurrently possessing high particle and optical stabilities, limiting the further development of QD-based biological labeling and detection techniques. Herein, we report a synthesis of giant CdSe/ZnS/CdZnS/ZnS core/shell QDs with an ultrathick shell (∼36 monolayers) and high PL QYs (>80%). We further employ the as-synthesized QDs for C-reactive protein detection, which reach nearly a 3-fold enhancement in detection sensitivity (∼0.41 ng/mL) and a 2-fold increase in shelf life, in comparison to the traditional thick-shell QDs (i.e., CdSe/CdS/ZnS core/shell QDs) or commercially available core/shell QDs. We postulate that the performance improvements in protein detection are due to the use of the developed core/shell QDs with high particle stability and PL QYs and large surface area (facilitating surface antibody coupling). Our study demonstrates the viability of applying high-quality core/shell QDs for protein detection with high sensitivity and accuracy.