An optofluidic dye concentration detector based on the pulsed photoacoustic effect

We report the development of an opto-acousto-fluidic platform by combining an illumination source in the form of a pulsed laser, a microfluidic channel, and an ultrasound transducer to detect photoacoustic signals generated from the fluid sample inside the channel. We study the effect of the channel dimensions on the emitted acoustic signals using methylene blue solution, a dye of immense interest in processing industry, as a target fluid and select an appropriate channel for further studies. We vary the concentration of the methylene blue dye and collect the corresponding photoacoustic signals. We find that the measured acoustic signal strength varies linearly with the increasing dye concentration, thus making this measurement scheme a potential dye concentration detector. This is a significant finding as it paves the way for developing a miniaturized photoacoustic detector for onsite sensing of dye concentration and perhaps even an online monitoring system which will be radical departure for current analysis methods using bench top bulky and expensive analytical tools.