Fluorescence correlation spectroscopy study of protein transport and dynamic interactions with clustered-charge peptide adsorbents

Ion-exchange chromatography (IEX) relies on electrostatic interactions between the adsorbent and the adsorbate, and is used extensively in protein purification. Conventional IEX utilizes ligands that are singly charged and randomly dispersed over the adsorbent, creating a heterogeneous distribution of potential adsorption sites. Clustered-charge ion exchangers exhibit higher affinity, capacity, and selectivity than their dispersed-charge counterparts of the same total charge density. In the present work, we monitored the transport behavior of an anionic protein near clustered-charge adsorbent surfaces using Fluorescence Correlation Spectroscopy. We can resolve protein free diffusion, hindered diffusion and association with bare glass, agarose-coated, and agarose-clustered peptide surfaces, demonstrating that this method can be used to understand and ultimately optimize clustered charge adsorbent and other surface interactions at the molecular scale.