(672e) Single Particle Virus Isoelectric Point Determination with Chemical Force Microscopy

Virus surface characteristics plays a key role in virus sorption processes, but there is very limited information in the literature on viral surface properties. One important surface characteristics is the isoelectric point (pI), which corresponds to the pH where the net charge on the virus particle is zero. The surface charge of virus particles is pH dependent, which dictates the mobility and controls the colloidal behavior in virus sorption processes. While traditional characterization methods, including zeta potential and viral adsorption to a charged surface chemistry, have been used to study viral surface charges and determine the pI of virus, they are bulk measurements that are limited by virus purification methods. The single particle method of chemical force microscopy (CFM) allows not only the quantitation of the virus surface charges, but can probe the effect of purification on the charge. CFM can measure the isoelectric point of complicated virus particles by using an AFM probe terminated with ionizable groups.

The model non-enveloped porcine parvovirus (PPV) and enveloped bovine viral diarrhea virus (BVDV) were used to demonstrate the use of CFM for viral particles. The change of adhesion forces measured as a function of pH is due to a change of virus surface electrostatic properties. The liquid environment used during CFM helps to maintain a more natural form of the virus without deformation, disassembly, or dehydration. The pI of each virus determined by CFM was also compared with that determined by traditional surface characterization method zeta potential. With a thorough understanding of virus surface characteristics, virus purification and future virus removal process could be significantly improved to specifically targeting viral particles. This will lead to improvements in virus removal, purification and detection.