A Reactive Peptidic Linker for Self-Assembling Hybrid Quantum Dot−DNA Bioconjugates

Self-assembly of proteins, peptides, DNA, and other biomolecules to semiconductor quantum dots (QD) is an attractive bioconjugation route
that can circumvent many of the problems associated with covalent chemistry and subsequent purification. Polyhistidine sequences have
been shown to facilitate self-assembly of proteins and peptides to ZnS-overcoated CdSe QDs via complexation to unoccupied coordination
metal sites on the nanocrystal surface. We describe the synthesis and characterization of a thiol-reactive hexahistidine peptidic linker that can
be chemically attached to thiolated-DNA oligomers and mediate their self-assembly to CdSe−ZnS core−shell QDs. The self-assembly of
hexahistidine-appended DNA to QDs is probed with gel electrophoresis and fluorescence resonance energy transfer techniques, and the
results confirm high-affinity conjugate formation with control over the average molar ratio of DNA assembled per QD. To demonstrate the
potential of this reactive peptide linker strategy, a prototype QD−DNA−dye molecular beacon is self-assembled and tested against both specific
and nonspecific target DNAs. This conjugation route is potentially versatile, as altering the reactivity of the peptide linker may allow targeting
of different functional groups such as amines and facilitate self-assembly of other nanoparticle−biomolecule structures.