Optofluidic multi-measurement system for the online monitoring of lubricant oil

We show a detection system that simultaneously allows absorbance (ABS), laser-induced fluorescence (LIF) and scattering detection excited by two different laser sources at 405 nm and 450 nm. The heart of the system consists of a mass manufacturable polymer optofluidic chip. The chip is mounted in an optical detection assembly that aligns the chip to the rest of the system, seals the chip from leakage, fixes the position and connects the channels to the rest of the fluidic system. The fluidics exhibit a reduced susceptibility to perturbations caused by air bubbles, this is accomplished by making use of a serpentine channel layout. For coumarin 480, detection limits of 100 nM and 10 pM are observed for ABS and LIF respectively. An effective detection range of 4000 down to 1 nephelometric turbidity units is shown for the detection of scattered light. The viscous behaviour of the sample is analysed by a secondary FFT processing step of which the result is further processed by multivariate data analysis. This allows the identification of samples and prediction of their quality parameters. We apply this system for the monitoring of lubricant oil, demonstrating its ability to compete with spectroscopic detection techniques. The low-cost approach and multi-measurement architecture shown in this paper pave the way for miniaturized on-line monitoring of liquids in an industrial environment.