Sub-zeptomole detection in a microfabricated glass channel by thermal-lens microscopy

A thermal-lens microscope which we developed was applied to an ultramicro quantity determination of a dye in an aqueous solution filling a microchannel (150 mu m wide and 100 mu m deep) fabricated in a quartz glass substrate. The detection volume, which corresponded to the confocal volume, was estimated to be 1.3 fl. The detection limit of the dye molecules was 160 ymol, and the calibration line showed good linearity in the sub-zmol-to-zmol region. This detection sensitivity is equivalent to that of laser-induced fluorometry. The thermal-lens signal measured in the microchannel was more stable than that measured in a liquid micro space between a slide glass and a cover glass, which was much wider than the microchannel. This may have been due to a suppression of convection in the microchannel. The thermal lens method can be applied to non-fluorescent chemical species, and is thus very suitable detection method for integrated chemistry systems.