Protein A/G-Based Surface Plasmon Resonance Biosensor for Regenerable Antibody-Mediated Capture and Analysis of Nanoparticles

Characterization of nanoparticles (NPs) and their subpopulations in heterogeneous samples is of utmost importance, for example, during the initial design of targeted NP therapies and the different phases of their production cycle. Biological NPs such as extracellular vesicles (EVs) have shown promise in improving the drug delivery capabilities compared to traditional NP-based therapies, for example, in treating cancer and neurodegenerative diseases. This work presents a general antibody-mediated surface capture and analysis protocol for NPs using a Protein A/G-functionalized surface plasmon resonance biosensor. The use of anti-streptavidin antibodies allows regenerable capture of biotin-containing NPs such as large unilamellar vesicles commonly used as drug delivery vehicles. Furthermore, the use of antibodies directed against glycophorin A and B (CD235a and b) enabled diffusion-limited specific surface capture of red blood cell-derived extracellular vesicles (RBC EVs). RBC EVs showed the efficacy of the biosensor in the determination of size and bulk concentration of NP subpopulations isolated from a complex biological matrix. The mean size of the surface-captured RBC EVs was comparable to the corresponding sizes derived for the entire EV population measured with well-established NP sizing techniques, namely, nanoparticle tracking analysis and dynamic light scattering. Taken together, the Protein A/G-functionalized biosensor provides a generic alternative to the existing NP-capturing sensors based on, for example, covalent antibody attachment, hydrophobic surfaces or biotin-capped self-assembled monolayers.