Capture and Release of Protein–Nanoparticle Conjugates by Reversible Covalent Molecular Linkers

A hybrid approach to covalently detachable molecules for nanoparticle capture and release from several custom-functionalized surfaces is described. This new surface chemistry capability provides a means for reversible binding of functionalized nanoparticles without relying on costly nucleic acid-based complexation. A new surface linker motif was devised wherein custom molecules were synthesized with components for surface anchoring, cleavage, and target capture through biotin–streptavidin binding. All capture-and-release chemistry is performed using physiological conditions (aqueous, pH 7). Covalent cleavage of linker molecules was achieved through incorporation of a tunable orthogonal reversible covalent (TORC) hydrazone functional group which underwent exchange with a competitive hydrazide aided by an aniline catalyst. The influence of the linker architecture on hydrazone exchange and nanoparticle release was probed by altering the distance between hydrazone and biotin groups using different length PEG spacers. Cleavable linkers were used to functionalize microwells, magnetic separation beads, and gold-coated glass surfaces. Upon functionalization, all surface types bound streptavidin and conjugated nanoparticles regardless of the linker structure. Conversely, the extent of hydrazone exchange as well as release of nanoparticles were influenced both by the hydrazone surface density and the linker molecular structure.