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.
We present both experimental and theoretical studies for investigating DNA molecules attached on metallic nanospheres. We have developed an efficient and accurate numerical method to investigate light scattering from plasmonic nanospheres on a substrate covered by a shell, based on the Green’s function approach with suitable spherical harmonic basis. Next, we use this method to study optical scattering from DNA molecules attached to metallic nanoparticles placed on a substrate and compare with experimental results. 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 Au nanoparticles. Our theoretical simulation indicates that the coverage of Au nanosphere by a submonolayer of DNA molecules, which is modeled by a thin layer of dielectric material (which may absorb light), can lead to a small but detectable spectroscopic shift in both the Ψ and Δ spectra with more significant change in Δ spectra in agreement with experimental results. Our studies demonstrated the ultrasensitive capability of SE for sensing submonolayer coverage of DNA molecules on Au nanospheres. Hence the spectroscopic ellipsometric measurements coupled with theoretical analysis via an efficient computation method can be an effective tool for detecting DNA molecules attached on Au nanoparticles, thus achieving label-free, non-destructive, and high-sensitivity biosensing with nanoscale resolution.
We experimentally investigated Zinc oxide (ZnO) nanowires (NWs) on flat Si substrate and ZnO NWs on Au
nanoislands attached on a Si substrate via hydrothermal technique, pursuing surface enhanced Raman scattering (SERS).
Au nanoislands were formed by thermal annealing of a Au thin film deposited on Si substrate. ZnO NWs were then
grown on two types of substrates (with and without Au nanoislands) and thermally annealed together. During the thermal
annealing process, the ZnO NWs were coupled to Au nanoislands. After the thermal annealing, strong SERS
enhancement was observed of ZnO NWs on Au nanoislands. Over 30 times enhancement in SERS was found when the
initial Au layer thickness was 40 nm.
An optical label free and high sensitivity plasmonic biosensor using nanoimprint metallic binary grating is presented
based on the phase information of the ellipsometry signal. Plasmonic binary grating was prepared by using soft nanoimprinting
technique which significantly reduce the fabrication cost and can be realized for a transition from a
laboratory-scale method to full-scale technology. The bulk sensitivity measurement from this 1D binary metallic grating
gives a value of refractive index resolution of 1.06×10-7 RIU. Such a highly sensitive plasmonic biochip was used to
investigate the adsorption of bio-molecules on the nanostructure surface in dynamic mode by monitoring the change in
polarization state or phase of reflected light in the ellipsometry measurement as a sensing signal.
A label free, non-destructive and high sensitivity biosensor with sub-nanometer thickness resolution is presented. We
investigate various sequences of DNA attached on gold nanoparticles (AuNPs) on top of a layer of self assembling
molecules. A strategy to amplify localized surface plasmon resonance (LSPR) response is made by sandwiching DNA
sequences between two AuNPs. We monitor the induced changes in polarization state or phase of reflected light from the
surface as a function of the photon energy as a sensor signal by using ellipsometry and compare that with theoretical
simulation.
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