(Invited) Fluorescent Frequency Domain Oxygen Sensing and Gradient Imaging within Microfluidic Structures

Abstract

Development of microsensors and microfluidics have proceeded in parallel for a number of decades. The incorporation of chemical sensing within microfluidic structures presents specific challenges, however. As one of the most important electron acceptors in biology, oxygen is of particular interest as a as a factor many processes, down to the pore scale. Microfluidic structures offer unique opportunities to create microenvironments that 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. Here we describe approaches to sense oxygen concentrations and gradients within microfluidic structures, using localized films of fluorescent oxygen sensing dyes and frequency domain fluorescent lifetime imaging. Of particular interest is to design systems where the fluorescent images also match the microfluidic spatial structure within the device. This is a concern because the simplest conventional approach, sandwiching a polymer film containing an oxygen sensing dye between a cover plate and a structured base plate produces a fluorescent signal across the entire device, including (mostly) areas that have nothing to do with the microfluidic structure. By contrast, we are pursuing approaches where the fluorescent signal is only seen in microchannel areas. Diverse approaches will be contrasted for fabricating and imaging oxygen sensing microfluidic structures, including pore network structures as models for natural systems at the pore scale.