(755a) Characterization of Biologically Modified Nanomaterials with Analytical Ultracentrifugation

Rigorous regulatory hurdles will be encountered for the commercialization of biologically modified nanomaterials designed to detect and treat human disease. Robust analytical techniques will be needed to assure the quality of these nanomaterial products and to detect manufacturing problems that may impact the efficacy and safety of nanoparticle-based therapeutics. Aggregation of nanoparticle-based therapeutics will likely be of paramount concern, much as it is today for the biotechnology industry in the manufacture of protein therapeutics. It is well known that even small changes in protein product formulation can result in aggregation that can lead to adverse, even life-threatening, immune reactions in patients. Techniques such as light scattering (LS) and size exclusion chromatography (SEC) are widely used for ascertaining aggregate formation, however, they can have difficultly in resolving low concentrations of aggregates (LS) or suffer from matrix interactions (SEC). Analytical ultracentrifugation (AUC) is a well-established protein analysis tool that allows accurate measurement of aggregation of samples over wide concentration and formulation ranges. This talk will describe the application of AUC to the analysis of biologically modified nanomaterials. The model system examined in this work consists of 10 nm gold particles derivatized with thiol-terminated thymidine homo-oligomers varying in length from 5 to 30 bases The DNA-derivatized gold particles were centrifuged in pure water as well as aqueous 1 molar sodium chloride and 1 molar magnesium chloride solutions. Keeping DNA surface coverage constant and switching from pure water to either 1 molar sodium chloride or 1 molar magnesium chloride, the sedimentation velocity of particles derivatized with 20 and 30 base homo-oligomers increased modestly. This behavior suggests an inward folding of the DNA for strands greater than 10 bases in length when salt cations are present. Sedimentation velocity was found to be independent of the cation's charge. As the length of the homo-oligomer was increased from 5 to 30 bases, the sedimentation coefficient of the nanomaterials was found to decrease by a factor of 2. Systematic decreases in DNA surface coverage were accompanied by an increase in the material's sedimentation velocity. This behavior is interpreted as the DNA strands adopting a more compact conformation as their distance to neighboring strands increases. The concentration of aggregated nanomaterial was systematically increased in a non-aggregated sample to demonstrate the detection limit of the centrifuge.