Speaker – Pankaj Arora (EE11D036)
Surface Plasmon (SP) based label-free sensing may be used to estimate the refractive index and thickness of sub-wavelength thick dielectric analytes, due to the strong conﬁnement of ﬁelds resulting in enhanced interaction with analytes.
In this talk, colorimetric sensing using real and Fourier Plane microscopic images of hybrid mode SPs, excited on engineered 1D and 2D low aspect ratio (~0.1) periodic plasmonic nanostructures will be presented.
The key ideas that will be presented are as follows :-
- The periodic plasmonic nanostructures with periods ≈ resonance wavelength, were designed to exhibit transmission resonances (or transmission peaks) in visible spectrum at normal incidence, without using Extra Ordinary Transmission phenomena. This resulted in larger fabrication tolerances, feature sizes and lesser swing for the same resonance wavelengths.
- The structures were fabricated using conventional planar material processing techniques. Inclusion of a homogeneous metal layer below the periodic structures resulted in mitigating the charging effects during electron beam lithography.
- The structures exhibited a polarization rotation of 90° mediated by differential phase retardation in the hybrid mode due to TE and TM components.
- This was used to design and develop a dark field microscope for imaging SP excitation in real and Fourier plane (FP).
- Thin dielectric films with known bulk parameters, were coated on fabricated structures. The images obtained during control experiments provided an index resolution of 10-5 RIU for 60 nm thick film.
- To avoid image registration problem for accurate sensing, FP images were used for sensing. The structures were designed to couple first order diffraction to SP excitation and hence the direct zeroth order transmission could be removed from analysis, which is not possible in real plane images. The method also distinguishes between refractive index and thickness induced surface modification.
- The structures were used to image surface functionalization using 2 nm thick thiol group layer, 7 nm thick mouse anti-human IgG (antibody) and binding to a 5 nm thick human IgG (antigen), to prove the limits of sensing.
- Opto-fluidic integration using microfluidic channels on the fabricated structures was performed.
- We demonstrate stain free imaging of interface of colorless miscible and immiscible liquids flowing in laminar flow regime in the microfluidic channels.
The purpose of the work is to establish the foundation of stain-free color contrast imaging sensors, possibly to avoid fluorescence tagging.
On Thursday, 4th February 2016 at 3:00 p.m. in the EE Seminar Hall (ESB 244)
(Dr. Ananth Krishnan)