Thin-film plastics used in microfluidic channels for microscopy imaging in low resource settings

The use of microfluidic channels as an imaging platform within microscopy systems provides the potential for a low-cost point-of-care system. Glass is traditionally used as a binding substrate for polydimethylsiloxane (PDMS) channels because of its optical favorability, however its cost and mechanical properties make it less than ideal. Glass' range of thicknesses (174 microns to 1mm) can create the issues of increased fragility at the lower thicknesses and induced optical aberrations at the higher thicknesses, respectively. Therefore, a thin optically transparent plastic becomes a favorable low-cost substitute for a binding substrate. Plastics such as polycarbonate, polyester, and polyvinylchloride were studied as potential substitutes based on a combination of their material and optical characteristics. Studied material characteristics include the thermal expansion of the material along with the bond strength between the plastic and PDMS. Resolution limitations caused by the plastic materials were measured using a 1951 U.S. Air Force target and portable microscopy system. Preliminary data suggests that when trying to resolve features as small as 0.78 microns, 0.254mm thick polycarbonate performed better than 1mm thick glass. To determine the optical limitations of the plastic substrate PDMS microchannel as an imaging platform, whole blood infected with Plasmodium falciparum was viewed through the channel within the same portable system, and individual blood cells and malaria parasites were attempted to be resolved. Results suggest the use of a thin-film plastic as the substrate for microfluidic channels provides a robust low-cost imaging platform.