Radial sample preconcentration

In this paper we present a radial sample preconcentration strategy enabled by axisymmetric concentration polarization in a microfluidic chamber on a uniform nanoporous film. Sample analytes are focused into the centre, creating a concentrated plug that is injected vertically into the microfluidic analysis layer. No balancing pressure driven flows or tangential fields are required, and the process has essentially zero footprint on the analysis layer. An electrokinetic loading scheme enables repeat loading/concentration cycles, and a finned radial chamber geometry dampens instabilities and accommodates larger volumes. Modelling results indicate over 1800-fold concentration increases are possible in 10 s, for high mobility buffers and high applied field strength. At moderate field strength and buffer mobility, experiments demonstrate a 168-fold increase in concentration of FITC-BSA protein in 36 s.