Electrochemical\nBehaviors of Ultramicro Triangular\nPipettes

Ultramicro pipettes with circular orifices have practically\nbecome\ncommon probes in exploring the microscopic world, yet the versatility\nof differently shaped pipettes is undermined in the pore family. Herein,\nultramicro triangular pipettes with a pseudotriangular-shaped orifice\nwere fabricated by laser-pulling triangular quartz capillaries and\ncharacterized by microscopic and electrochemical methods. Then, the\ndifferences in the electrochemical behaviors of triangular and circular\npores were revealed through experiments and simulations. A liquid/liquid\ninterface was supported first at a triangular pipette, and the facilitated\npotassium ion transfer reactions exhibited steady-state voltammetric\nresponses. An empirical equation for triangular pores between the\ndiffusion-limited current and the side length (<i>a</i>)\nof the orifice was evaluated, and the corresponding mass transfer\ncoefficient of ion ingress was estimated as <i>m</i><sub>Tri</sub> = 8.05<i>D</i>/<i>a</i>. As for ion\negress transfer, the tip angle and pore shape would affect the diffusion\nregime and the ion distribution, where the mass transfer would be\nenhanced at the corners of a triangular pipette with a large tip angle.\nTriangular submicropores and nanopores were employed to detect particle\ntranslocations at a high capture rate, though the events had broader\ndistributions and lower charges than those of circular pores. These\nfindings demonstrate the shape effect in triangular pores that promotes\nthe mass transfer rate of interfacial ion transfer reactions and the\ncapture rate of ionic blockades. The universal laser-pulling method\ncould make ultramicro pores of arbitrary shapes accessible in fundamental\nstudies and applicable as chemical sensors.