(Invited) A Spontaneously Generated Electrical Charge of an Aqueous Droplet by Pipetting and Its Use of a Self-Powered Sensor

Recently, we reported that pipetting always dispenses an electrically charged aqueous droplet by spontaneous electrical charging process between the pipet tip inner surface and the aqueous droplet. The amount of an electrical charge depends on the constituents of the droplet, on coating material of a pipet tip, and on atmospheric humidity. It is clarified that this spontaneous electrical charging of an aqueous droplet is originated from the electrical charge separation between the droplet and the pipet tip inner surface through performing consecutive measurement of the electrical charge amount of the pipet tip and the droplet during a pipetting process. Since this unexpected electrification phenomenon could influence the localization and combination of charged bio-molecules inside the aqueous solution, controlling and suppressing the spontaneous electrification phenomenon are important. To suggest the way to suppress the electrification phenomenon, a graphene-based nanocomposite coated pipet tip, which we called a zeta-pipet tip, is fabricated, as a proof-of-concept example to reduce the zeta potential of the pipet tip inner surface. Since the electrical charge is always spontaneously generated in the case of solid-water contact, it could be potentially utilized with a self-powered sensor.