Measuring protein binding to individual hydrogel nanoparticles with single-nanoparticle surface plasmon resonance imaging microscopy

The specific binding and uptake of protein molecules to individual hydrogel nanoparticles is measured with real-time single-nanoparticle surface plasmon resonance imaging (SPRI) microscopy. Nanoparticles that adsorb onto chemically modified gold thin films interact with traveling surface plasmon polaritons and create individual point diffraction patterns in the SPRI microscopy differential reflectivity images. The intensity of each point diffraction pattern depends on the integrated refractive index of the nanoparticle; an increase in this single nanoparticle point diffraction intensity (Δ%RNP) is observed for nanoparticles that bind proteins. SPRI adsorption measurements can be used to measure an average increase in Δ%RNP that can be correlated with bulk dynamic light scattering measurements. Moreover, the distribution of Δ%RNP values observed for individual nanoparticles can be used to learn more about the nature of the protein-nanoparticle interaction. As a first example, the binding of the lectin Concanavalin A to 180 nm N-Isopropylacrylamide hydrogel nanoparticles that incorporate a small percentage of mannose sugar monomer units is characterized