Tolerance analysis of a micro-optical detection system for on-line monitoring of lubricant oils

We present a functional prototype of a micro-optical detection unit for both absorbance and laser-induced fluorescence analysis in fused silica capillaries. Absorbance detection allows concentration measurements ranging from 0.6 micro-M to 12 mM, whereas fluorescence detection enables concentration measurements from 6 pM up to 0.6 mM. We make use of non-sequential optical ray tracing simulations combined with statistical design methodology to perform a complete tolerance analysis for manufacturability and we demonstrate experimentally that the efficiency of the system is insensitive to reasonable misalignment and fabrication errors of its building blocks. The possibility of using standard fabrication techniques to prototype and replicate this miniaturized plastic detection system, as well as its wide measurement range make it a good candidate for applications where low-cost and portable systems are needed to measure small volumes of liquid samples with low-level concentrations. As an example we demonstrate the use of the system for the optical characterization and differentiation of nanoliter volumes of lubricant oils.