Development of pipette tips to control the spontaneously generated charge of droplets

Recently, we first reported that a conventional pipetting always dispenses a charged droplet by spontaneous electrical charging. Given that this electrification phenomenon is undesired in fluid dispensing industries that utilize pipettes, the amount of electric charge should be controlled. In this paper, we report two different methods of control the charge of a droplet dispensed from the pipette tip. In a passive method, we fabricate a graphene coated pipette tip for reducing the zeta potential of the pipette tip inner surface resulting in reduced electric charge. In an active method, the electrode-deposited pipette tip is developed so as to precisely adjust the charge of the droplet by applying the proper voltage. This work would provide a powerful charge control platform to the droplet-based analysis.