Lab-on-a-chip systems with three dimensional microelectrodes

This paper reports on the development and testing of a self-contained portable electrochemical (EC) detection platform capable of monitoring heavy metals (Pb, Cu etc.). Towards this end, a lab-on-a-chip (LOC) device was fabricated by etching a microchannel system into a soda lime glass substrate and incorporating photo-lithographically patterned radial gold microelectrodes at the end of the designated separation channel. The first pair of electrodes was modified into a single 3D microelectrode whose high surface area is ideal for effective pre-concentration of metals ions in a sample stream, while the other 2 pairs were unmodified and used as planar "sensing" electrodes. Proper control of plating and stripping voltages at the 3D microelectrode yielded initial pre-concentration and subsequent release of Cu/sup 2+/ ions, which were then detected downstream at the one of the planar electrodes.

I. Introduction

During the last decade, pocket-sized analytical platforms fabricated using microfabrication techniques, commonly known as “lab-on-a-chip” (LOC) devices, have become commercially available. These chips, in combination with portable electronics, are applicable in “point of care” analyses of body fluids and general forensics, as well as field applications such as pollution monitoring, identification of explosives or process control in chemical industries [1]–[4]. In principle, the LOC approach offers numerous advantages in addition to portability such as minimal reagent consumption, high efficiency and throughput, low power consumption, batch fabrication and overall lower cost. All of these factors are further enhanced when combined with specific benefits offered by the incorporation of electrochemical detection (ECD) into the design. This detection mechanism offers well-characterized analyte/electrode combinations, low cost, portability, and perhaps most importantly, the ability to customize electrode geometry and materials. This last attribute in particular makes possible the development of customized intelligent sensor suites capable of remote analysis and routine unsupervised monitoring. Example applications could be industrial toxic waste control, water stream monitoring, and battlefield detection of chemical/biological agents.