Sensitive Optical Absorbance Measurements on a Microfluidic Device Using Conductivity-based Photothermal Detection

We have implemented a photothermal absorbance strategy where optical absorbance induced solvent temperature increases are monitored using electrolyte conductivity. This method produces a response that is independent of pathlength, assuming thermal conductivity issues can be neglected, and has been suggested to be an interesting approach for use in capillary-based systems, but sensitivity was found to be limited [1,2]. Incorporating metal thin film electrodes into a microfluidic device has proven to be a sensitive and effective conductivity device for photothermal detection [3]. Optimization and application of this device will be discussed.