Microfluidic devices are also being fabricated using PMMA to create a chip that could inject a sample analyte plug containing many metallic species in various molecular forms (e.g. copper, lead, manganese, cadmium, etc.) through a molecular gate (i.e. NCAM membrane) and into a microfluidic separation channel. As the analyte plug would move along the separation channel, it would separate into various bands and a detector (i.e. two parallel plate capacitive sensors in a modified Wheatstone bridge arrangement probed at the resonant frequency) would sense each band as it passed. The device consists of three separate microfluidic layers that contains one or more microfluidic channels per layer. These layers are separated in the vertical direction by NCAMs (nano-capillary array membranes) that serve as molecular gates across which sample plugs could be injected and separated bands could be collected.
Various strategies are being explored to immobilize DNAzyme on PMMA and glass, such as biotin-streptavidin interaction and amine-aldehyde chemistry. To form the enclosed chip, a PDMS microchannel structure is aligned onto the glass so that the microchannels bisect the predeposited DNA sites. The fluorescence in the channel is quenched upon hybridization with the quencher strand, while the fluorescence that is sealed beneath PDMS continues to act as an internal reference. In the presence of lead, a fluorescence increase is observed with the reaction of Pb2+ with the complex. The sensing chemistry can be regenerated by hybridization of DNAzyme with more substrate strand in the channel. This device is an important step toward detecting multiple heavy metal ions with a single injection by introducing different DNAzymes at different locations on a single molecular gated device. Efforts to immobilize Pb-specific DNAzyme in the PMMA microfluidic devices and to study the Pb detection activity in the microchannel using fluorescence microscopy will be described.