Valving Microfluidic Devices
Currently, reliable valving on integrated microfluidic devices fabricated from rigid materials is confined to expensive and complex methods. In a paper recently published in Analytical Chemistry, researchers in the Ramsey Group demonstrate the use of trace quantities of ice-nucleating protein, INP, additive buffers to enhance the performance of freeze-thaw valves, FTVs.
FTVs, to date, have been impractical for microfluidics and have found little use commercially or in academic research due to the impractical temperatures needed to achieve actuation, freezing, in small volumes containing smooth surfaces, in essence, few ice forming nucleation sites. The lack of nucleation sites leads to slow and uncertain actuation times. It was found that sub-picomolar concentrations of INPs from Pseudomonas syringae in typical bioassay buffers reduce the time and variability for FTVs to switch to the "off state" when used with plastic microfluidic devices.The work also shows that actuation temperatures of FTVs can be increased from -45 ℃ to -13 ℃ with sub-10 s switching times, reducing the power and complexity of the thermal technology used for actuation. 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.
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.