| Abstract
| - We have used confocal fluorescence microscopy with single molecule sensitivity to characterize uptake andrelease of fluorescent protein (mEosFP) molecules by individual spherical polyelectrolyte brush (SPB)nanoparticles that were immobilized on a glass surface. The SPB particles consisted of a solid core particleof 100 nm diameter onto which long polyelectrolyte chains were affixed. They could be loaded with up to30 000 mEosFP molecules in a solvent of low ionic strength. The concentration dependence of protein loadingcan be described with a simple bimolecular binding model, characterized by an equilibrium dissociationcoefficient of 0.5 μM. Essentially complete release of the bound proteins was observed after increasing theionic strength by adding 250 mM NaCl to the solvent. Fluorescence emission spectra and time-resolvedfluorescence intensity decays were measured on individual, mEosFP-loaded SPB nanoparticles, and also onthe dissolved mEosFP before and after adsorption. These results indicate that the mEosFP molecules remainedstructurally intact in this procedure. Hence, the present investigation demonstrates unambiguously thatpolyelectrolyte-mediated protein adsorption onto SPB particles presents a viable process for proteinimmobilization.
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