Contactless conductivity detection of small ions in a surface micro‐machined CE chip

Abstract

A microchip is presented which is capable of CE separations and is built using exclusively thin film deposition techniques, fully compatible with microelectronics batch processing. Standard photolithography provides control of the spacing between electrodes used in conductivity measurement and overall channel geometry. Fluid channels are arranged as a double-T injector with a 50 microm offset at the arm intersection. The chip's performance was tested using concentrations of sodium chloride and calcium chloride ranging from 1 microM to 1 mM in a 5-mM MES/histidine buffer. Separations were performed by applying different voltages to reservoirs positioned at the four fluid channel openings. Conductivity detection was performed by applying a small AC voltage (1 Vrms) to the insulated electrodes positioned inside the fluid channels. A computer running LabVIEW controlled the AC signal generation, data acquisition and storage. Measurements indicated that the chip's detection limit was below 1 microM for both sodium and calcium cations.

Contactless conductivity detection for analytical techniques: Developments from 2010 to 2012

“…New procedures were described in the last two years for the fabrication of PMMA , PDMS , glass , and hybrid glass/PDMS microchips employing C 4 D. For MCE‐C 4 D devices, the precise geometry of the sensing electrodes and their positioning close to the separation channel are of key importance and much more critical than for standard capillaries and several new approaches for their fabrication have been described in the last two years. Zhao et al used thermal bonding of two glass wafers for microchip fabrication.…”

On-chip capacitively coupled contactless conductivity detection using “injected” metal electrodes

“…A number of approaches for integrated contactless electrodes in LOC devices have been reported. These include the fabrication of micro-uidic chips on top of printed circuit boards [9][10][11][12] and glass wafers 13 containing microscale electrodes. Alternate methods have mounted the electrodes in external housings 14,15 and others have reported the deposition of metal layers onto previously etched glass wafer surfaces to form electrodes in the same plane as the analysis channels.…”

Capacitively coupled contactless conductivity detection on microfluidic systems—ten years of development

“…Shang et al reported the fabrication of a MCE-C 4 D with insulated detection electrodes. 44 Chromium electrodes were formed using an e-beam evaporator and a 100 nm SiO 2 layer provided the electrical insulation. The insulating layer was deposited by plasma-enhanced chemical vapour deposition (PECVD).…”