Red diode laser induced fluorescence detection with a confocal microscope on a microchip for capillary electrophoresis

A highly sensitive laser induced fluorescence (LIF) detection system based on a 635 nm laser diode and cyanine-5 (Cy-5) dye, is described for use with a planar, microfluidic, capillary electrophoresis (CE) chip. The CE-chip i s able to determine a protein biological threat agent simulant, ovalbumin ( Ov), by performing an immunoassay separation of Cy-5 labeled anti-ovalbumin from its complex with Ov, in under 30 s. A confocal, epiluminescent detect ion system utilizing a photomultiplier tube gave optimum results with a 400 mu m pinhole, an Omega 682DF22 emission filter, a 645DRLP02 dichroic mirro r, a 634.54 +/- 5 nm excitation filter, and a Power Technology ACM08 635 MI laser operated at 11.2 mW. Using this detector, a microchip CE device with a separation efficiency of 42 000 plates and an etch depth of 20 mu m, gav e a concentration detection limit of 9 pM Cy-5. This limit corresponds to t he determination of 4560 injected molecules and detection of 900 of these m olecules, given a probe volume of 1.6 pi and a probing efficiency of 20%. ( C) 2000 Elsevier Science S.A. All rights reserved.