Thermal lens microscopy as a detector in microdevices

The small length scales that make microfluidics attractive are also the source of some very stringent constraints, especially with respect to the detection approach used. The low concentrations often analyzed in microfluidic devices require highly sensitive detection methods that are effective even in vanishingly small sample volumes. Over the years, many detection approaches have been developed for microfluidics. The majority of these methods rely upon optical phenomena, with the most common being fluorescence detection. Fluorescence detection is well suited to microfluidics because it is both flexible and sensitive; however, it does have shortcomings. Weak fluorescence of targets, autofluorescence of materials, and photobleaching are a few of the issues that have to be dealt with when working with fluorescence detection. Another option that eliminates all of these problems is thermal lens microscopy (TLM), a photothermal spectroscopy technique. TLM is a flexible, sensitive detection approach for nonfluorescent molecules that is capable of carrying out single-molecule detection to label-free in vivo quantification. Despite the potential benefits of TLM, it is still an underutilized detection approach. We hope this review will help broaden the use of TLM for microchip-based CE, as well as a host of other microfluidic applications.