CONTROLLED FUNCTIONALIZATION OF WATER-SOLUBLE SEMICONDUCTOR QUANTUM DOTS FOR BIOCONJUGATION

Abstract

He one-stage procedure using carbodiimide condensation was proposed for the controlled functionalization of water-soluble semiconductor quantum dots (QDs) with azide groups. A controlled variation in the surface density of the functional groups and zeta-potential was demonstrated by functionalization of anionic (carboxylic) and similar zwitterionic polymer-encapsulated CdSe/ZnS core-shell QDs. Ethanolamine-O-sulfate (EOS), aminotetraethylene glycol (H₂N-[TEG]-OH) and aminotetraethylene glycol azide (H2N-[TEG]-N₃) were utilized as modifiers. Functionalization was investigated by studying the kinetics of the organic dye JOE conjugation with QDs using the strain-promoted azide-alkyne cycloaddition (SPAAC) reaction. The reactivity of QDs towards SPAAC has been found to be nearly proportional to the relative density of the surface azide groups, and the QDs zeta-potential correlates with the ratio of the modifiers. It was shown that azido groups on the surface of QDs can be easily and under mild conditions transformed into primary amino groups using tris(2-carboxyethyl)phosphine (TCEP) as a reducing agent. The applicability of surface-functionalized QDs for bioconjugation was demonstrated by their conjugation with dye-labeled bovine serum albumin (BSA).