Determination of EOF of PMMA microfluidic chip by indirect laser-induced fluorescence detection

A simplified method for mobility determination of electroosmotic flow (EOF) of polymethyl methacrylate (PMMA) microfluidic chips is developed with indirect laser-induced fluorescence detection (IDLIFD). Based on the interval between the beginning of separation and the apex of converse peak, the present technique highlights in circumventing the great demand for sensitivity and baseline stability of routine methods. IDLIFD is performed by a home-made laser-induced fluorescence detector of confocal optical configuration, mainly composed of a 473 nm laser diode double-pumped solid state laser (LD-DPSSL) and a 520 nm band-pass interference filter. Amino acetate (NH4Ac) solution containing Vitamin B2 is used as the background fluorescent reagent (BFR) solution. The pre-treatment procedures of chip inter-surface and the voltage program of injection and separation are studied. Reasons for the low background fluorescent response during injection are also discussed. Even this phenomenon has a good effect on the accurate recording of the interval between the baseline starting of separation and the lowest point of the converse peak. The results demonstrate that the reciprocals of EOF mobility (υeo) of PMMA microfluidic chip are in line with the ion strength of background electrolyte (BGE) solution. Furthermore, the υeo of PMMA material is related to the pH of BGE solution. Compared with those results obtained from the Current-Monitoring method, no apparent difference has been found.