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Author: search.filters.author.Gupta, Raj KumarSubject: search.filters.subject.Surface plasmon resonance

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    Measurement of optical anisotropy in ultrathin films using surface plasmon resonance
    (Elsevier, 2016-01) Manjuladevi, V.; Gupta, Raj Kumar
    The optical phenomenon, surface plasmon resonance (SPR) is employed for the measurement of optical anisotropy in the ultrathin films fabricated through Langmuir–Blodgett (LB) and self-assembled monolayer (SAM) techniques onto 50 nm gold film supported on BK7 glass substrates. The resonance angle (RA) is measured using a home built setup in Kretschmann configuration. The LB films and SAM can provide a single layer of highly ordered and organized molecules on the two dimensional surface. If the film forming molecules are anisotropic, their organization in the LB films and SAM can yield an anisotropic film due to tilt of the molecules with respect to the surface normal. The SPR spectra are recorded for the two orthogonal directions of the film with respect to the plane of incidence. The spectra are simulated by modeling the Fresnel's reflection from 4-layers viz., prism, gold, ultrathin films and air; and the real and imaginary parts of refractive index are estimated. Our study shows the metallic and dielectric nature of the LB films of bundles of single walled carbon nanotubes (SWCNTs) when the long axis of SWCNTs are aligned parallel and perpendicular to plane of incidence, respectively. The optical anisotropy was estimated from the change in real part of refractive index (Δnr) of the ultrathin films measured in the orthogonal directions. In addition, we have also studied such optical anisotropy in the LB film of cadmium-stearate and self-assembled monolayer of octadecanethiol.
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    Surface plasmon resonance sensor based on a new opto-mechanical scanning mechanism
    (Elsevier, 2016-05) Gupta, Raj Kumar; Manjuladevi, V.
    Surface plasmon resonance (SPR) is employed as one of the key phenomena in biological, chemical and gas sensors. In this paper, we report development of a Kretschmann configuration based SPR sensing instrument by adopting a unique opto-mechanical scanning mechanism. The new scanning mechanism ensures portable, very low-cost and sensitive SPR sensor. In contrary to the traditional scanning mechanism, we utilized a rotating mirror for changing angle of incidence, and a quadrant photodiode (QPD) for recording reflected intensity. In order to achieve constant spot measurement on the sensing area (gold surface) for a fixed referencing, the prism-sensor assembly is translated vertically in a highly controlled manner governed by a feedback mechanism. In the feedback mechanism, the deflection of reflected beam is quantified by the QPD, and the prism-sensor assembly is translated vertically so as to regain the original set point. The SPR spectra of different materials deposited onto the gold surface using different techniques were collected and studied. Using the developed SPR instrument with pure gold sensing surface, the lowest detectable concentration of the sucrose in aqueous medium was found to be 100 femto-molar. The sensitivity of the instrument was estimated using the different concentration of aqueous solutions of sucrose with known refractive indices, and it was found to be around 52.6°/RIU. These studies indicate a high resolution and good sensitivity of the instrument.