A Si/Ge based, single mode, mid-infrared optical waveguide, is used as an evanescent sensor in liquid matrix. The selectivity is achieved by the use of quantum cascade lasers (QCLs) tuned to the maximum absorption of a given analyte. The cocaine detection in human saliva at 5.81 microns is chosen as a pilot application to demonstrate the technology. Light emitted from the QCL is butt coupled into the Si/Ge waveguide. The waveguide is passing through the detection part of the micro-fluidic sample preparatory/handler, and interacting with the analyte, it is collected and guided into the mid infrared quantum cascade detector QCD.
Andras Kis, Fedele Tagarelli, Dmitrii Unuchek, Zhe Sun, Juan Francisco Gonzalez Marin, Cheol Yeon Cheon