Critical flocculation concentrations, binding isotherms, and ligand exchange properties of peptide-modified gold nanoparticles studied by UV-visible, fluorescence, and time-correlated single photon counting spectroscopies

Protocols for modifying gold nanoparticles with peptide-bovine serum albumin (BSA) conjugates are described within. The resulting constructs were characterized using a number of techniques including static fluorescence spectroscopy and time-correlated single photon counting spectroscopy (TCSPC) in order to quantify peptide-BSA binding isotherms, exchange rates, critical flocculation concentrations, and the composition of mixed peptide-BSA monolayers on gold nanoparticles. TCSPC has proven to be a powerful technique for observing the microenvironment of protein-gold nanoparticle conjugates because it can distinguish between surface-bound and solution-phase species without the need for separation steps. Full characterization of the composition and stability of peptide-modified metal nanoparticles is an important step in their use as intracellular delivery vectors and imaging agents.