Microchip Electrophoresis with Enhanced Dark‐Field Illumination Detection for Fast Separation of Native Single Super‐Paramagnetic Nanoparticles

Fast microchip electrophoretic ( ME ) separation of native super‐paramagnetic nanoparticles ( SPMNPs ) with different functional groups ( i.e .,  NH 2 ,  OH , and  COOH ) was investigated at the single‐particle level using enhanced dark‐field illumination detection with high signal‐to‐noise ratio. The dynamics provide evidence of the random motion of individual native nanoparticles and their real‐time velocities within a microchip with or without an electric field. The SPMNPs were introduced into the microchip by magnetic force, and separation was performed at different electric field strengths; neither low (≤30 V/cm) nor high (≥70 V/cm) applied electric field strengths provided separation above baseline (resolution > 1.5) due to the random motion of the nanoparticles. Based on the optimized separation conditions obtained at the single‐particle level, the individual SPMNPs were separated successfully from the model nanoparticle mixture within ~75 s using differences in acid dissociation constants and zeta potentials.