Cationic Polyelectrolyte Adsorption onto Anionic Nanoparticles Analyzed with Frequency-Domain Scanning Fluorescence...

An improved small-circle scanning fluorescence correlation spectroscopy (sFCS) technique is introduced by combining acousto-optical laser scanning with fitting the autocorrelation function in the frequency domain. The technique is validated using both simulation and experimental data on various fluorescent nanoparticles, including polystyrene beads, CdSe/CdS quantum dots, and lipid nanoparticles. Then, the sFCS method is used to investigate the adsorption of in-house synthesized poly(2-guanidinoethyl methacrylate) (PGUMA) polymers on polystyrene beads as a model system for polymer-coated particles in biomedical and gene delivery applications. Using the particle diffusion and illumination beam waist values obtained from our sFCS analysis, regions of polymer concentrations are identified where polymer-particle complexes remain stable. An increase in hydrodynamic size is also observed with the molecular mass of the adsorbed polymer. Beyond quantifying polymer-particle stability and hydrodynamic size, the sFCS technique offers the advantage of not requiring a time-consuming calibration step for the measurement volume, unlike standard FCS.