Signal Amplification in a Microchannel from Redox Cycling with Varied Electroactive Configurations of an Individually Addressable Microband Electrode Array
by Lewis, P. M.; Sheridan, L. B.; Gawley, R. E.; Fritsch, I.
Amperometric detection at microelectrodes in lab-on-a-chip (LOAC) devices lose advantages in signal-to-background ratio, reduced ohmic iR drop, and steady-state signal when volumes are so small that diffusion fields reach the walls before flux becomes fully radial. Redox cycling of electroactive species between multiple, closely spaced microelectrodes offsets that limitation and provides amplification capabilities. A device that integrates it microchannel with an individually addressable microband electrode array has been used to study effects of signal amplification due to redox cycling in a confined, static solution with different configurations and numbers of active generators and collectors. The microfabricated device consists of a 22 mu m high, 600 mu m wide microchannel containing an array of 50 mu m wide, 600 mu m long gold microbands, separated by 25 mu m gaps, interspersed with an 800 mu m wide counter electrode and 400 mu m wide passive conductor, with it distant but on-chip 400 mu m wide pseudoreference electrode. Investigations involve solutions of potassium chloride electrolyte containing potassium ferrocyanide. Amplification factors were as high as 7.60, even with these microelectrodes of fairly large dimensions (which are generally less expensive, easier, and more reproducible to fabricate), because of the significant role that passive and active (instrumentally induced) redox cycling plays in confined volumes of enclosed microchannels. The studies are useful in optimizing designs for LOAC devices.