Fig. 2

Fabrication and characterization of the nexFET. a The nexFET is fabricated in dual-barrel quartz nanopipettes by a pyrolytic carbon deposition in one of the barrels, followed by electrodepositing of PPy at the carbon-coated nanopipette tip. SEM images at each stage of the fabrication process are shown in b quartz double barrels after nanopipette pulling (scale bar 100 nm, inset 20 μm). c One barrel coated with carbon after pyrolytic deposition (scale bar 100 nm) and, d electropolymerized PPy, acting as a gate electrode, deposited on top of the carbon electrode and surrounding the opening of the nanopore (scale bar 100 nm). e Linear sweep voltammograms recorded at both carbon surface uncoated and coated tips using 1mM ferrocenemethanol as redox mediator. The three fold increase in limiting current of the surface coated tip confirmed the extension of the carbon electrode around the open barrel for forming the PPy gate. f Gate current and gate voltage plots in a representative device as monitored over timer during PPy electropolymerization, showing increasing gate current with each successive PPy deposition cycle (as indicated by the arrow). The total deposition time for this particular device was 6 s. The inset illustrates the electrode configuration used. g Nanopore (drain-source) I-Vs of the open barrel as monitored during electropolymerization of PPy indicating decrease of the initial nanopore conductance (1) with each successive deposition cycles (2–6) (as indicated by the arrow). The inset shows the decrease of the initial nanopore current (1) over time with each successive deposition cycle (2–6). h I-Vs for five representative nanopore devices that show very different initial ion transport characteristics. i Decrease in nanopore current over time during controllable deposition of PPy until the set-point ionic current (1 nA) is reached for the same devices as in h. j I-Vs of the same devices following ionic current feedback deposition confirming reproducibility of the open pore current. Note that there is some variation at negative V _DS due to geometrical differences in the nanopipettes