A microfluidic device with integrated fluorimetric detection for flow injection analysis

Abstract

This work describes the development of flow analysis microsystems with integrated fluorimetric detection cells. Channels (width of 300-540 microm and depth of 200-590 microm) were manufactured by deep-UV lithography in urethane-acrylate (UA) resin. Plastic optical fibers (diameter of 250 microm) were coupled to a 2.0-mm-long detection channel in order to guide the excitation radiation from an LED (470 nm) and collect the emitted radiation at a right angle towards a photomultiplier. A single-line miniaturized system, with a total internal volume of 10.4 microL, was evaluated by means of standard fluorescein solutions (0.53-2.66 micromol L(-1), pH 8.5). The analytical signals presented a linear relationship in the concentration range studied, with a relative standard deviation of 1.9% (n = 5), providing a detection limit of 0.37 micromol L(-1) and an analytical frequency of 60 samples/h, using a flow rate of 60 microL min(-1). Optical microscopy images and videos acquired in real time for the hydrodynamic injection of 130 and 320 nL of sample solutions indicated the good performance of the proposed sampling strategy. Another microsystem with a total internal volume of 38 microL was developed, incorporating a confluence point for two solutions. This device was applied to the determination of the total concentration of Ca(2+) and Mg(2+) in commercial mineral waters using the calcein method. Microscopy images and videos demonstrated the mixing efficiency of the solutions in the microchannels. A linear relationship was observed for the analytical signal in the Ca(2+) concentration range from 25 to 125 micromol L(-1), with relative standard deviations of 3.5%. The analysis of mineral waters with the proposed system provided results that did not differ significantly from those obtained by the EDTA titration method at a confidence level of 95%. These results demonstrate the viability of developing micro flow injection systems with an integrated fluorimetric detection cell.