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The aim of this project was to develop high performance polymer microfluidic chips with reduced complexity for
Electrospray Ionization Mass Spectrometry (ESI-MS) analysis. This paper presents the fabrication and testing of
developed hot embossed open channel polymer microfluidic chips for ESI-MS. Hot embossing was done using a laser
machined steel tool and an electroformed nickel tool on polystyrene (PS) and polycarbonate (PC) substrates. Stable
electrosprays were generated at microchannel exits of replicated microchips without cover using a high voltage
difference between a positive stainless steel electrode in the reservoir and a negative aluminum plate. Electrospray
parameters such as; nozzle tip distance from counter electrode, ESI onset potential and duration were investigated. For
open channel systems, the results show that the electric field for stable ES directly relates to the distance between the
channel tip and counter electrode, onset potential applied and to the flow velocity of the test solution in the
microchannel. Fluid is delivered as a result of electroosmosis due to an applied electric field and capillary action,
thereby eliminating the need for external pressure devices. From experimental results, for an open-channel of 100μm
width, 100μm depth, length 12.5mm attached to an open reservoir of diameter 2 mm, the optimum distance between the
channel exit tip and counter electrode is 1.2 mm for initiation of electrospray at voltage of ~2000 volts. The laser
machined steel tool was found to be more durable than the nickel tool for PS/PC microstructure fabrication.
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