A beveled working electrode coupled to a sandglass shape detection cell: A strategy to improve the sensitivity of electrochemiluminescence detection in microchip electrophoresis

Abstract

A beveled working electrode (WE) with a sandglass shape electrochemiluminescence (ECL) detection cell based on tris(2,2′-bipyridyl)ruthenium(II) (TBR) for microchip capillary electrophoresis (MCE) was described in this paper. The beveled WE was readily fabricated from a platinum (Pt) wire (0.3mm diameter). The microchip comprised of three layers: top polydimethylsiloxane (PDMS) layer, middle glass plate, and bottom glass coverslip. The middle layer was a glass wafer on which the injection and separation channels were etched; meanwhile, an inverted funnel hole was made by a coniform drill, and a snot which was used to hold a guide tube aligning to the separation channel outlet was fabricated by a clubbed drill. The top layer was PDMS block containing four holes that connected injection channels and separation channel terminals, respectively. The two layers were bonded after their surfaces were processed by a plasma cleaner. The bottom layer was a coverslip (0.17mm thick) which covered the inverted funnel hole in the middle layer with epoxy resin. The beveled WE was inserted into the guide tube and immobilized using melt adhesive. A Pt wire acted as a counter electrode (CE) was penetrated through the PDMS layer perpendicularly to the WE, with a 1.5-mm long portion left inside the detection cell. Proline was used to evaluate the developed MCE–ECL microdevice with the limit of detection down to 0.2μM (S/N=3). The detection sensitivity was found to be improved remarkably, compared to the conventional disk electrode.