On-chip label-free plasmonic based imaging microscopy for microfluidics.

In this work, we demonstrated on-chip label-free imaging microscopy using real and Fourier Plane (FP) microscopic dark field images of Surface Plasmons (SP), excited on engineered 1D and 2D low aspect ratio periodic plasmonic nanostructures. The periodic plasmonic nanostructures with period almost equal to resonance wavelength, were engineered to exhibit transmission resonances as transmission peaks in visible spectrum at normal incidence, without using extraordinary optical transmission phenomena. The plasmonic nanostructures exhibited a polarization rotation of 90 degree mediated by differential phase retardation in the SP mode due to Transverse Electric and Magnetic components. This was used to develop a dark field on-chip plasmonic polarization microscope for imaging SP excitation in real and Fourier planes. After successful integration of these plasmonic nanostructures with SU- 8 based microfluidic channels, a real-time monitoring of label free on chip sensing was demonstrated. Label-free on-chip imaging for interface of colorless miscible and immiscible analytes flowing on plasmonic nanostructures in the microfluidic channels were performed using color-selective filtering nature of plasmonic nanostructures. Since the imaging is realized on a chip and does not need any complicated and bulky arrangement, it will be well suited for on-chip point of care diagnostics.