Rakesh S. Moirangthem

Nano-imprint gold grating as refractive index sensor

Large scale of fabrication of plasmonic nanostructures has been a challenging task due to time consuming process and requirement of expensive nanofabrication tools such as electron beam lithography system, focused ion beam system, and extreme UV photolithography system. Here, we present a cost-effective fabrication technique so called soft nanoimprinting to fabricate nanostructures on the larger sample area. In our fabrication process, a commercially available optical DVD disc was used as a template which was imprinted on a polymer glass substrate to prepare 1D polymer nano-grating. A homemade nanoimprinting setup was used in this fabrication process. Further, a label-free refractive index sensor was developed by utilizing the properties of surface plasmon resonance (SPR) of a gold coated 1D polymer nano-grating. Refractive index sensing was tested by exposing different solutions of glycerol-water mixture on the surface of gold nano-grating. The calculated bulk refractive index sensitivity was found to be...

Efficient Simulation for Light Scattering from Plasmonic Core-Shell Nanospheres on a Substrate for Biosensing

We have developed an efficient numerical method to investigate light scattering from plasmonic nanospheres on a substrate covered by a shell, based on the half-space Green’s function approach. We use this method to study optical scattering from DNA molecules attached to metallic nanoparticles on a substrate and compare with the experiment. We obtain fairly good agreement between theoretical predictions and the measured ellipsometric spectra. The metallic nanoparticles were used to detect the binding with DNA molecules in a microfluidic setup via spectroscopic ellipsometry (SE), and a detectable change in ellipsometric spectra was found when DNA molecules are captured on a Au nanoparticle surface. Our theoretical simulation indicates that the coverage of the Au nanosphere by a submonolayer of DNA molecules, which is modeled by a thin layer of dielectric material, can indeed lead to a small but detectable change in ellipsometric spectra. Our studies demonstrated the ultrasensitive capability of SE for sensing the submonolayer coverage of DNA molecules on Au nanospheres.

Flexible and disposable plasmonic refractive index sensor using nanoimprint lithography

Nanostructure based plasmonic sensors are highly demanding in various areas due to their label-free and real-time detection capability. In this work, we developed an inexpensive flexible plasmonic sensor using optical disc nanograting via soft UV-nanoimprint lithography (UV-NIL). The polydimethylsiloxane (PDMS) stamp was used to transfer the nanograting structure from digital versatile discs (DVDs) to flexible and transparent polyethylene terephthalate (PET) substrate. Further, the plasmonic sensing substrate was obtained after coating a gold thin film on the top of the imprinted sample. The surface plasmon resonance (SPR) modes excited on gold coated nanograting structure appeared as a dip in the reflectance spectra measured at normal incident of white light in ambient air medium. Electromagnetic simulation based on finite element method (FEM) was used to understand and analyze the excited SPR modes and it is a very close agreement with the experimental results. The bulk refractive index (RI) sensing was performed by the sensor chip using water-glycerol mixture with different concentrations. Experimentally, the bulk RI sensitivity was found to be 797±17 nm/RIU.

Influence of magnesium fluoride (MgF2) layer on a conventional surface plasmon resonance sensor

In this work, a numerical study of Surface Plasmon Resonance (SPR) sensor has been done by using Magnesium Fluoride (MgF2) layer on a conventional Kretschmann configuration. The prism was coated with smooth gold thin film of thickness 50u2005nm followed by MgF2 layer. To obtain the maximum reflection dips in the SPR modes, the thickness of MgF2 layer is optimized by varying it from 200-800u2005nm. Our calculations also reveal that SPR modes corresponding to gold-MgF2 layer are very sensitive to the changes in the surrounding medium as compared to the traditional SPR device. The sensing performance of the proposed nano-plasmonic sensor is theoretically calculated using bulk refractive index sensing. Such bilayer device (gold-MgF2) is expected to take an important role on the field of chemical and biological sensing.