Electrochemical detection of insulating beads at subattomolar concentration via magnetic enrichment in a microfluidic device.

We report electrochemical detection of collisions between individual magnetic microbeads, present at subattomolar concentrations, and electrode surfaces. This limit of detection is 4 orders of magnitude lower than has been reported previously, and it is enabled by using a magnetic field to preconcentrate the microbeads prior to detection in a microfluidic electrochemical cell. Importantly, the frequency of collisions between the microbeads and the electrode is not compromised by the low concentration of microbeads. These findings represent an unusual case of detecting individual electrochemical events at very low analyte concentration. In addition to experiments supporting these claims, finite-element simulations provide additional insights into the nature of the interactions between flowing microbeads and their influence on electrochemical processes.