Isotachophoretic Preconcentration on Paper-Based Microfluidic Devices

Paper substrates have been widely used to construct 
point-of-care lateral flow immunoassay diagnostic devices and more recently in microfluidic paper analytical devices. Paper
 based microfluidic devices are robust and relatively simple to operate,
 compared to channel microfluidic devices, which is perhaps their greatest
 advantage and the reason devices such as lateral flow immunoassays have reached a high level of commercial
 success. However, paper devices may not be well suited for integrated
 sample preparation, such as sample extraction and preconcentration, 
which may be required in complex samples with low analyte concentrations. We will present our work on integration of isotachophoresis (ITP) onto nitrocellulose-based paper microfluidic devices with the goal to improve the 
limit of detection of immunoassays.  ITP is a powerful electrokinetic technique that has been widely used in traditional lab-on-a-chip devices to simultaneously separate and concentrate variety of ionic compounds.  ITP takes advantage of a simple electrolyte system, high electrophoretic mobility leading and low electrophoretic mobility trailing electrolytes, and a constant electric field. We show that ITP on nitrocellulose is capable of up to a 1000 fold increase in initial sample concentration and up to 60% extraction from 100 μL samples and more than 80% extraction from smaller sample volumes. ITP can improve the analytical sensitivity of immunoassays by significantly increasing the concentration of the target at the test zone resulting in a dramatic increase in the surface reaction rate and equilibrium binding. We apply ITP to a Group-A Streptococcal (bacteria that causes Strep throat) immunoassay diagnostic and demonstrate a two order of magnitude improvement of the limit of detection over commercially available rapid immunoassay based lateral flow diagnostic tests.