[Analytical Chemistry] Use of ice nucleating proteins for improved performance of freeze thaw valves
Currently, reliable valving on integrated microfluidic devices fabricated from rigid materials is confined to expensive and complex methods. Freeze thaw valves (FTVs) can provide a low cost, low complexity valving mechanism, but reliable implementation has been greatly hindered by the lack of ice nucleation sites within the valve body’s small volume. Work to date has required very low temperatures (on the order of -40 °C or colder) to induce freezing without nucleation sites, making FTVs impractical due to instrument engineering challenges. Here we report the use of ice nucleating proteins (INPs) to induce ice formation at relatively warm temperatures in microfluidic devices. Microfluidic channels were filled with buffers containing femtomolar INP concentrations from Pseudomonas syringae. The channels were cooled externally with simple, small-footprint Peltier thermoelectric coolers (TECs), and the times required for channel freezing (valve closure) and thawing (valve opening) were measured. Under optimized conditions in plastic chips, INPs made sub 10 s actuations possible at TEC temperatures as warm as 13 °C. Additionally, INPs were found to have no discernible inhibitory effects in model enzyme linked immunosorbent assays or polymerase chain reactions, indicating their compatibility with microfluidic systems that incorporate these widely used bioassays. FTVs with INPs provide a much needed, reliable valving scheme for rigid plastic devices with low complexity, low cost, and no moving parts on the device or instrument. The reduction in freeze time, accessible actuation temperatures, chemical compatibility, and low complexity make the implementation of compact INP-based FTV arrays practical and attractive for the control of integrated biochemical assays.
Joseph C Gaiteri, W. Hampton Henley, Nathan A Siegfried, Thomas H. Linz, and J. Michael Ramsey Anal. Chem., Just Accepted Manuscript DOI: 10.1021/acs.analchem.7b00556 Publication Date (Web): May 3, 2017 Copyright © 2017 American Chemical Society