(Keynote) Oxygen Sensing Microfluidic Structures for Biomedical and Environmental Science Research

Planar optode films consisting of a fluorescent dye in a polymer film can be incorporated into microfluidic structures to map out oxygen concentrations while microfluidic devices set up gradients and environmental conditions that are relevant to biomedical or natural biogeochemical systems. Gradients of molecular oxygen are of particular interest due to the fact that many important biological processes either occur at interfaces or are regulated by the flux of oxygen and other resources. Hence, oxygen sensing microfluidic devices can be used to investigate microbial behavior related to carbon cycling, or microbial communities in the gut where the interface with the host tissue is microoxic. In addition, oxygen sensing microfluidic devices may be useful in mammalian cell or tissue culture where favorable conditions must be maintained. Practical issues in developing and fabricating microfluidic structures with inherent oxygen sensing capability include multiple parameters, including incorporation of sensing elements in microfluidics, imaging oxygen concentrations by fluorescence, and relating oxygen imaging data to spatial structure of the microfluidic channels, all in useful structures that create biologically relevant microenvironments. We will describe multiple approaches to meeting these challenges, including gas impermeable silicon-on-glass structures where the fluorescent signals are only observed where microfluidic channels occur, and solvent imprinting lithography where sensing dyes can be incorporated in thermoplastics in a single process that enables sensor dye impregnation, channel imprinting, and cover plate bonding. These methods are discussed with regard to structures including pore network and gradient generation microfluidic structures.