The role of volume transport and near-surface alignment in particled-based target capture.

We investigate the processes that determine the overall association rate in particle-based target capture, i.e. experiments in which bio-functional particles capture biological targets. We describe a theoretical framework and experiments that separate the processes of volume transport, near-surface alignment, and chemical binding. To quantify these processes, different types of actuation are applied, in a model system of fluorescent nanoparticles captured by magnetic microparticles. Compared to passive thermal transport, fluid agitation increases the reaction rate by more than an order of magnitude, implying a higher encounter frequency and a higher near-surface alignment probability. Active rotation of capture particles enhances the near-surface alignment probability per encounter by a factor four. The developed understanding lays the foundation for novel ultra-high-sensitive bioanalytical assay technologies for small sample volumes.