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.