Electrochemical Behaviors of Ultramicro Triangular Pipettes

Ultramicro pipettes with circular orifices have practically become common probes in exploring the microscopic world, yet the versatility of differently shaped pipettes is undermined in the pore family. Herein, ultramicro triangular pipettes with a pseudotriangular-shaped orifice were fabricated by laser-pulling triangular quartz capillaries and characterized by microscopic and electrochemical methods. Then, the differences in the electrochemical behaviors of triangular and circular pores were revealed through experiments and simulations. A liquid/liquid interface was supported first at a triangular pipette, and the facilitated potassium ion transfer reactions exhibited steady-state voltammetric responses. An empirical equation for triangular pores between the diffusion-limited current and the side length (a) of the orifice was evaluated, and the corresponding mass transfer coefficient of ion ingress was estimated as m_Tri = 8.05D/a. As for ion egress transfer, the tip angle and pore shape would affect the diffusion regime and the ion distribution, where the mass transfer would be enhanced at the corners of a triangular pipette with a large tip angle. Triangular submicropores and nanopores were employed to detect particle translocations at a high capture rate, though the events had broader distributions and lower charges than those of circular pores. These findings demonstrate the shape effect in triangular pores that promotes the mass transfer rate of interfacial ion transfer reactions and the capture rate of ionic blockades. The universal laser-pulling method could make ultramicro pores of arbitrary shapes accessible in fundamental studies and applicable as chemical sensors.