Engineering Quantum Dot (Cadmium Sulfide) on Antibodies for Fluoroimmunoassays

Abstract

Antibodies are good escorts for a therapeutic and diagnostic tool against many diseases as well as for targeting drug delivery and in immunohistochemistry. Cysteine-capped cadmium sulfide (quantum dot) nanoparticles have wide applications in immunohistochemistry due to their unique physical, chemical, and fluorescent properties. In this study, polyclonal antibodies against transferrin (as ligand), doxorubicin (anticancer drug), and H. pylori (cancer-causing agent) were developed in rabbits and purified. Purified antibodies were labeled with cadmium sulfide (CdS) quantum dot (QD) and used as a fluorescent-labeled marker for one-step identification in diagnosis and therapeutics. Cysteine-capped CdS QDs were synthesized in the presence of taurine (antioxidant) and characterized by FTIR, VSM, DLS, and TEM. CdS nanoparticles are monodisperse with a narrow size range below 7 nm and showed an increase of almost 30 nm after conjugation to IgG. The binding of QD-labeled antibodies was observed and confirmed by binding on MDA-MB 231 cancer cells, mouse liver tissue, mouse tumor tissue, and H. pylori under a fluorescent microscope. QD-labeled antibodies gave sharp fluorescence after binding with their respective targets. Intensity of fluorescence with quantum dot enhances many folds as compared to that of traditional fluorescent-labeled compounds. Experiments are underway to target transferrin and doxorubicin and to analyze the role of H. pylori in a mouse model of gastric cancer.