Abstract
Dual carbon electrodes (DCEs) are quickly, easily, and cheaply fabricated by depositing pyrolytic carbon into a quartz theta nanopipet. The size of DCEs can be controlled by adjusting the pulling parameters used to make the nanopipet. When operated in generation/collection (G/C) mode, the small separation between the electrodes leads to reasonable collection efficiencies of ca. 30%. A three-dimensional finite element method (FEM) simulation is developed to predict the current response of these electrodes as a means of estimating the probe geometry. Voltammetric measurements at individual electrodes combined with generation/collection measurements provide a reasonable guide to the electrode size. DCEs are employed in a scanning electrochemical microscopy (SECM) configuration, and their use for both approach curves and imaging is considered. G/C approach curve measurements are shown to be particularly sensitive to the nature of the substrate, with insulating surfaces leading to enhanced collection efficiencies, whereas conducting surfaces lead to a decrease of collection efficiency. As a proof-of-concept, DCEs are further used to locally generate an artificial electron acceptor and to follow the flux of this species and its reduced form during photosynthesis at isolated thylakoid membranes. In addition, 2-dimensional images of a single thylakoid membrane are reported and analyzed to demonstrate the high sensitivity of G/C measurements to localized surface processes. It is finally shown that individual nanometer-size electrodes can be functionalized through the selective deposition of platinum on one of the two electrodes in a DCE while leaving the other one unmodified. This provides an indication of the future versatility of this type of probe for nanoscale measurements and imaging.
Highlights
Dual-electrode systems are widely used to study the kinetics of redox reactions.[15,16] Usually, but not exclusively,[17,32] such devices operate in an amperometric/voltammetric mode, where each electrode is held at a potential to oxidize or reduce a target species of interest, and the current measured at each electrode relates to the flux of that active species, arriving at the electrode
(3D) finite element method (FEM) simulation of nanoscale (100−1000 nm) dual carbon electrodes (DCEs) based on the probe geometry observed in scanning electron micrograph (SEM) images of
A full and C) consists of two planar semielliptical electrodes description of the FEM simulation, including Figure S1 of the separated by a septum and surrounded by glass
Summary
(3D) FEM simulation of nanoscale (100−1000 nm) DCEs based on the probe geometry observed in SEM images of DCEs were fabricated with a high success rate (ca. 85%, based on more than 100 made) on the day of use, with approximately typical nanoscale DCEs (e.g., Figure 1B) to estimate the probe 3 min required per tip. From which electrode sizes for different currents can be determined, were constructed from the FEM model, and these are shown in Figure S2 and section S7 of the Supporting Information This highlights that the G/C experiments are sensitive to the probe size. Simulation results for approach curves, with the probe perfectly aligned to the surface (which is an approximation as already discussed), to both insulating and conducting substrates were calculated and are shown in black in Figure 3 (panels A and B) These show the same topological features as observed in the experimental results, most obviously the increase in collection current when approaching an insulating substrate. This highlights the possibility of using DCEs for electrochemical sensing which, with further developments, may allow multicomponent chemical analysis at the nanoscale
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