Probe Beam Deflection of Isotachophoresis on Miniaturized Planar Glass Devices

Abstract

Much effort is currently being applied to the miniaturization of analytical equipment. One potentially valuable area of research is miniaturization of electro separation systems using planar substrates with microchannels typically of 50 μm depth. In the work at UMIST such systems are being developed for isotachophoresis in which analytes are separated into discrete zones. The concentration of the zones can be determined by the zone length and therefore precise measurements of the zone boundaries are required.

The novel aspect of this work is the use of a laser beam deflection technique for detection of zone boundaries in isotachophoresis performed on miniaturized planar glass devices. Laser based detectors are ideal for miniaturized devices as laser beams with good spatial coherence can be focused to a very small spot with no loss of power. Fabrication of these planar glass devices was carried out in-house using micromachining methods and a fluorosilicic acid etch rather than a conventional HF etch.

The objectives of the work presented here are to achieve sensitive detection of picoliter volumes in isotachophoresis. Zone boundaries are detected by the deflection of the beam caused by refractive index changes as the zone crosses the probe beam The deflection is recorded on a CCD array in the far field.

The experimental data presented shows that the proposed laser probe method can successfully determine zone boundaries and hence zone lengths in a precise manner meaning low concentrations of sample can be detected in very small volumes.