Impact and Customers
Our work establishes metrics for measurement quality and reproducibility for cell-based assays within microfluidic devices. Many novel microfluidic devices are being created that permit new measurements or enable new biological functions to be tested; however, characterizations necessary to benchmark the quality and reproducibility of these novel systems are often lacking. Companies that hope to market new instruments and products associated with medical diagnostic and therapeutic applications will require methods to validate the capabilities of these nascent technologies. We published a framework for cell-based measurements in microfluidic devices in Analytical Chemistry in 2011. A follow-up study was published in Lab on a Chip (2012). Both the FBI and the Bioterrorism Response Laboratory at the Massachusetts Department of Public Health are interested in using this assay for analysis of ricin activity.
Microfluidic devices were constructed from polydimethylsiloxane (PDMS) using standard techniques. We designed a simple test bed device with a single inlet and a large number of chambers for cells. The inlet channel branches into eight columns of chambers, and each column contains eight 1.1 mm diameter chambers for a total of 64 chambers. African green monkey kidney epithelial (Vero) cells transfected to express green fluorescent protein (GFP) were loaded into the device to create a gradient of cell densities across the columns of chambers, thus enabling us to test whether cell density had any effect on the assay readout and to determine measurement confidence limits as a function of cell density. We studied GFP expression in the cells with quantitative time-lapse fluorescence microscopy, monitoring the rate at which GFP degrades in cells after they are treated with a reversible ribosome inhibitor, cycloheximide (CHX). The rate of decay of GFP fluorescence in cells is a measure of the effect of CHX, which blocks protein synthesis. The GFP decay rates upon CHX injection in microfluidic devices were compared with results from larger scale culture conditions of cells in 35 mm polystyrene dishes and in dishes coated with PDMS. Cell proliferation and migration rates were calculated from single-cell tracking measurements.