Robust monolithic silica-based on-chip electro-osmotic micro-pump

A robust, compact, on-chip, electro-osmotic micro-pump (EOP) for micro-flow analysis, based on parallel, encased, 10 × 0.1 mm I.D. monolithic silica capillary columns has been developed. A 15 × 40 × 2 mm poly(methyl methacrylate) (PMMA) chip, containing a total of nine parallel EOP systems was fabricated, allowing the use of single, double or triple monolithic columns to produce increased flow as required. The monolithic silica was compatible with both aqueous and organic solvents without swelling or shrinking problems, with the triple column EOP capable of generating flow of up to 0.6 μL min−1 under zero pressure load and over 0.1 μL min−1 with an applied pressure of ca. 2.4 bar using an applied voltage of just 2 kV. Current generated at the 2 kV applied voltage for a 2 mM acetate buffer solution (pH 4.5) was under 4 μA, allowing stable, bubble-free flow. The developed triple column EOP was incorporated within a micro-fluidic chip (5.0 × 2.0 × 0.4 cm) integrated with a second single 10 × 0.1 mm column EOP, for combined sample injection and simple on-chip micro-flow analysis.