Triple-Barrel Ultramicroelectrodes for Multipurpose, Submilliliter Electroanalysis

Abstract

Here, we have developed and applied a triple-barrel microelectrode. This device incorporates a platinum disk working electrode, a platinum disk counter electrode, and a low-leakage Ag/AgCl reference electrode into a small probe. We demonstrate that the incorporated low-leakage reference electrode shows similar voltammetry, potentiometry, and drift when compared to a commercial reference electrode in bulk solution. We also demonstrate the versatility of such a small three-channel system via voltammetry in nanoliter droplets and through electroanalysis of captured aerosols. Finally, we demonstrate the probe's potential utility in single-cell electroanalysis by making measurements within salmon eggs.

Figure 1.

(a) Schematic and (b) photograph of the triple-barrel UME, consisting of a triple-barrel capillary tube with 25 μm platinum disks sealed into one end, forming the three electrode surfaces. One disk is the working electrode (green lead), one is the counter electrode (red lead), and the third is the tip of the bipolar Ag/AgCl reference electrode (white lead). (c) 5X magnified image of the tip of the triple-barrel UME, showing the three platinum disks sealed in a triangle.

Figure 2.

Cyclic voltammograms taken in (a) a bulk solution of 50 mM ferricyanide and 50 mM ferrocyanide in 1 M KCl using the triple-barrel UME (blue) and the triple-barrel UME when the reference lead is attached to a commercial Ag/AgCl reference electrode (orange) at 50 mV/s, (b) a 750 nL droplet of 50 mM ferricyanide and 50 mM ferrocyanide in 1 M KCl pipetted onto the tip of the triple-barrel UME at 100 mV/s, (c) a 1 M KCl droplet pipetted onto the tip of the triple-barrel UME after 5 s of an aerosol of 300 mM ferricyanide and 300 mM ferrocyanide in ultrapure water was sprayed into the droplet at 100 mV/s, and (d) a single salmon egg after 3 h of incubation in a solution of 10 mM ferricyanide and 10 mM ferrocyanide in 1 M KCl at 100 mV/s.

Figure 3.

Cyclic voltammograms taken in a single salmon egg after 3 h of incubation in a solution of 10 mM ferricyanide and 10 mM ferrocyanide in 1 M KCl at 100 mV/s using the (blue) internal Ag/AgCl reference or (orange) external Ag/AgCl reference electrode to demonstrate the effects of the cellular membrane potential.