Integration of a carbon microelectrode with a microfabricated palladium decoupler for use in microchip capillary electrophoresis/ electrochemistry

Abstract

A method to integrate a carbon microelectrode with a microfabricated palladium decoupler for use in microchip capillary electrophoresis (CE) is detailed. As opposed to previous studies with decouplers for microchip CE, the working electrode material, which is made by micromolding of a carbon ink, is different from the decoupling electrode material (palladium). The manner in which the working electrode is made does not add additional etching or lithographic steps to the fabrication of the glass electrode plate. The hybrid poly(dimethylsiloxane)/glass device was characterized with fluorescence microscopy and by monitoring the CE-based separation of dopamine. Hydrodynamic voltammograms exhibited diffusion-limited currents occurring at potentials above +1.0 V. It was also shown that the half-wave potential does not shift as the separation potential is changed, as is the case in nondecoupled systems. Gated injections of dopamine in a 25 mM boric acid buffer (pH 9.2) showed a linear response from 200 to 5 microM (r2 = 0.9992), with a sensitivity of 5.47 pA/microM and an estimated limit of detection of 2.3 microM (0.621 fmol, S/N = 3). This is the first report of coupling a carbon electrode with a decoupler in microchip CE.

Simplified current decoupler for microchip capillary electrophoresis with electrochemical and pulsed amperometric detection

“…The mechanism preventing flow down these channels is under investigation. It should be noted, however, that these results are consistent with the work of Kovarik et al [49] when they sealed PDMS over a raised carbon electrode.…”

“…A detection limit of 500 nM was achieved, in part due to the use of a Pd working electrode. Microfabrication of two different electrode materials onto a single substrate for use as a decoupler and a working electrode does not only improve sensitivity but also increase the overall microchip cost and fabrication complexity [40,43,49,50].…”

Use of micromolded carbon dual electrodes with a palladium decoupler for amperometric detection in microchip electrophoresis

“…As seen in the previous work, an alignment marker was used to reproducibly align the electrophoresis PDMS channel with the electrode plate [17,26]. The mark was aligned with the bottom of the decoupler, using a stereomicroscope to guarantee a constant distance of 1.2 mm between the bottom of the decoupler and the beginning of the buffer waste reservoir.…”

“…2. Once sealed, the dual microelectrodes were fabricated based on previously published methods [17,34]. Briefly, commercially available carbon ink and solvent thinner (Ercon) were mixed so that the volume of the added thinner was 0.2% v/w of the initial ink weight.…”

“…Importantly, the working electrodes remain in the separation channel. Our group [17,26] and others [15,27,28] have utilized palladium electrodes for decoupling in microchip electrophoresis, as palladium can effectively absorb and dissipate hydrogen produced at an electrophoretic cathode up to field strengths of 1200 V/cm [26].…”