Electronic Quantification of Protein Biomarkers Based on Bead Aggregate Sizing

We demonstrate a novel protein sensing method using detection of bead aggregates of different sizes in a micro-fluidic impedance cytometer. We utilize micro-fabricated coplanar electrodes at the base of our micro-channel to measure the impedance. When the single beads or bead aggregates pass through the electrodes, a difference in impedance change is detected. We measure these signals using a lock-in amplifier. Due to the difference in impedance change for unbound beads compared with protein-bound bead aggregates, we can differentiate the two types from each other electronically. We demonstrate proof-of-concept using streptavidin and biotin coated beads.