Fabrication and evaluation of a 3-dimensional microchip device where carbon microelectrodes individually address channels in the separate fluidic layers

A fabrication method that results in a 3-dimensional fluidic device containing poly(dimethylsiloxane) (PDMS) -embedded microelectrodes that individually address each layer is described. The two electrode-containing layers and the polycarbonate membrane are reversibly sealed together, eliminating the need for plasma oxidation during device assembly, while enabling simultaneous amperometric detection in membrane-separated fluidic channels. The electrodes were characterized using microchip-based flow analysis. It was found that PDMS-embedded electrodes have a limit of detection (400 nM for catechol) that is 5-fold lower than that reported for microchip-based flow analysis with similar electrodes in a hybrid PDMS–glass device. The selectivity of the carbon ink microelectrodes can be tuned by a simplified modification procedure; this was demonstrated by the selective detection of nitric oxide over possible interferents. Finally, the ability to monitor processes occurring in separate layers of a 3-dimensional device was shown by the simultaneous detection of catechol on either side of the polycarbonate membrane. The electrode response in each fluidic channel was found to be linear as a function of concentration and the transport between layers could be controlled by varying the linear velocities of each fluidic channel. The ability to fabricate and operate this type of 3-dimensional device will be useful for the development of cell-based in vivo mimics that involve the transport of molecular messengers and/or pharmaceuticals across layers of immobilized cells.