Biotin-4-Fluorescein Based Fluorescence Quenching Assay for Determination of Biotin Binding Capacity of Streptavidin Conjugated Quantum Dots. Bioconjugate Chem

bS Supporting Information ABSTRACT: The valency of quantum dot nanoparticles conju-gated with biomolecules is closely related to their performance in cell tagging, tracking, and imaging experiments. Commer-cially available streptavidin conjugates (SAv QDs) are the most commonly used tool for preparing QD-biomolecule conju-gates. The fluorescence quenching of biotin-4-fluorscein (B4F) provides a straightforward assay to quantify the number of biotin binding sites per SAv QD. The utility of this method was demonstrated by quantitatively characterizing the biotin bind-ing capacity of commercially available amphiphilic poly(acrylic acid) Qdot ITK SAv conjugates and poly(ethylene glycol) modifiedQdot PEG SAv conjugates with emission wavelength