Near-IR micro-fluidic sensing by total internal reflective diffraction

This work studies how the sensitivity of a recently reported novel integrated micro-fluidic system [1] can be improved optimizing the conditions of measurements. The considered lab-on-a-chip system is based on a diffraction grating, operating under total internal reflection and illuminated by near-IR light (1.55 μm). The interaction between the evanescent field of the totally reflected light with dipoles of the analyte results in phase and amplitude changes in the reflected diffraction orders. In this work the dependence of the sensing signal on the measured diffraction order, polarization of the light and angle of incidence are investigated. The conditions giving highest sensitivity are determined. The feasibility of the integrated micro-fluidic system for analysis of nano-dispersions is demonstrated by samples of oil-based dispersion of composite CuFe2O4 nanoparticles. A resolution toward the CuFe2O4 concentration of 0.1 wt.% is obtained. The possibilities for further increase of the sensitivity are discussed.