An insulator-based dielectrophoresis (iDEP) is a label-free method that has been extensively utilized for manipulation of nanoparticles, cells, and biomolecules. University of Cincinnati engineers have developed a new iDEP approach that can rapidly trap nanoparticles at the close proximity of a glass nanopipette’s tip by applying 10 V/cm direct current (DC) across the pipette’s length. The trapping mechanism was systemically studied using both numerical modeling and experimental observations. The results showed that the particle trapping was determined to be controlled by three dominant electrokinetic forces including dielectrophoretic, electrophoretic and electroosmotic force. Furthermore, the effect of the ionic strength, the pipette’s geometry, and the applied electric field on the entrapment efficiency was investigated. To show the application of their device in biomedical sciences, the developers demonstrated the successful entrapment of fluorescently tagged liposomes and unlabeled plasma-driven exosomes from the PBS solution. Also, to illustrate the selective entrapment capability of the device, 100 nm liposomes were extracted from the PBS solution containing 500 nm polystyrene particles at the tip of the pipette as the voltage polarity was reversed.
(a) A schematic of the nanopipette-DEP device. The ionic current across the pipette and the trajectory of the particles were simultaneously recorded. (b) (i) Microscopic image of entrapment as 10 V/cm was applied with the positive bias at the base of the pipette after 100 seconds. (b) (ii) The conductance measurements across the 1 μm pore as the particles accumulate by the tip. (c) (i) Microscopic image of few particles entrapment as negative 10 V/cm bias was applied at the base of the pipette after 100 seconds. (c) (ii) The corresponding conductance measurements across the 1 μm pore. (d) The correlation between the magnitude of electric field and the number of trapped particles after 100 seconds. The suspending medium was 10 mM KCl (pH = 7.0).