Optofluidic surface enhanced Raman spectroscopy microsystem for sensitive and repeatable on-site detection of chemical contaminants.

We demonstrate highly sensitive detection of real-world food and water contaminants using a portable and automated optofluidic surface enhanced Raman spectroscopy (SERS) microsystem. The optofluidic SERS device utilizes a porous microfluidic matrix formed by packed silica microspheres to concentrate silver nanoparticles and adsorbed analyte molecules, resulting in greatly improved SERS detection performance. In addition, a passive micromixer that mixes silver nanoparticles into the sample solution is integrated into the device for improved automation. Furthermore, two optical fibers are integrated into the device and aligned to the detection volume to improve the automation as compared to confocal SERS, which requires focusing and alignment. The device exhibits up to 2 orders of magnitude improvement in SERS performance as compared to conventional microfluidic SERS in an open channel. Using the optofluidic SERS device, the food contaminant melamine was detected in low concentrations, with an estimated limit of detection (LOD) of 63 ppb, while the fungicide thiram was detected down to an estimated LOD of 50 ppt. In both cases, the reported results meet the U.S. federal requirements. Additionally, it is shown that the device continues to exhibit excellent performance even when mated to a commercially available portable spectrometer for the trace detection of thiram. This combination of the optofluidic SERS microsystem with a portable spectrometer will lead to highly sensitive and automated sensing systems for on-site detection of food and water contaminants in the field.