Department of Physics

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Subject: search.filters.subject.Surface plasmon resonance (SPR)

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    Sensing Through Surface Plasmon Resonance Technique
    (Springer, 2017-03) Gupta, Raj Kumar
    The optical phenomenon, surface plasmon resonance (SPR) has become extremely popular owing to its high sensitivity, label-free and non-destructive measurement towards any molecular specific interaction. This is one of the widely used phenomena for biological, chemical and gas sensing devices. There are different ways that the SPR phenomenon can be employed for such sensing applications. In this chapter, we will review some of the important SPR techniques and their applications in sensing.
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    Surface Plasmon Resonance Study Of Langmuir-blodgett Films Of Stearic Acid
    (CIB Tech, 2012) Manjuladevi, V.; Gupta, Raj Kumar
    Stearic acid is one of the commonly studied fatty acid. It exhibits interesting behavior on surfaces. The Langmuir Blodgett films of stearic acid were fabricated on solid substrates. We have developed a surface plasmon resonance (SPR) instrument in the Kretschmann configuration. The change in SPR angle due to molecular specific interaction is potentially employed for sensing application. In this paper we report our studies on SPR of stearic acid deposited on solid substrates. We find a significant change in the resonance angle.
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    Electrochemical Surface Plasmon Resonance for Efficient Sensing and Analysis
    (CRC Press, 2023) Gupta, Raj Kumar; Manjuladevi, V.
    The optical phenomenon of surface plasmon resonance (SPR) is widely used for a variety of applications viz. sensing, drug-target interactions and dielectrics in material science. Several sensing applications based on optical perception do exhibit a change in electrochemical behavior. Therefore, integrating electrochemical platform in SPR measurement may ensure a simultaneous observation of the optical and electrochemical responses. The sensing platform based on such multiparameters is more reliable in decision making and therefore it can be a potential transducer for the next generation of sensing. This chapter briefly discusses the fundamentals of SPR and electrochemical SPR (eSPR), instrumentation and a variety of sensing applications.
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    The Effect of Relative In-Plane Twisting in Graphene Bilayer on Sensing Using Surface Plasmon Resonance
    (Springer, 2022-12) Manjuladevi, V.; Gupta, Raj Kumar
    Surface plasmon resonance (SPR) is generally observed by the excitation of surface plasmon polaritons on the metal (Au/Ag) surface. In order to utilize the SPR phenomenon for sensing application, the metal surface is functionalized with suitable ligands. Although such functionalization can enhance the specific adsorption capability of the sensor however due to the large thickness of the ligands, the plasmonic field of the metal surface becomes less sensitive towards the adsorption of analytes. In the next generation SPR-based sensor, graphene can be utilized not only as plasmonic material but also as a suitable ligand for attracting analytes through π-π interaction. In this article, we present our theoretical simulation studies on the observation of the SPR phenomenon using graphene monolayer (MLG), bilayer graphene (BLG), and in-plane twisted layers of BLG (T-BLG) as plasmonic materials deposited over zinc-selenide substrate. The Kretschmann configuration under wavelength interrogation setup was simulated, and SPR wavelength for graphene systems/water interface was estimated. The bio-sensing simulation was performed, and the sensing parameters viz. sensitivity, figure-of-merit (FOM), and plasmonic field for different graphene systems were obtained. Interestingly, the excellent sensing parameters were found in T-BLG system with relative in-plane twist angle near to magic angle viz. 1°. The enhancement is due to strong coupling between the layers twisted at the magic angle. This study demonstrates that the MLG, BLG and T-BLG can be employed as a standalone layer system for not only the generation of plasmonic fields but also enhanced sensing due to its intrinsic interactions with bio-analytes.
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    3D Graphene-Based Optical Sensors
    (Springer, 2023-07) Gupta, Raj Kumar; Manjuladevi, V.
    3D graphene (3DG) has been utilized as a functional material for the development of gas and chemical sensors. The sensor based on optical phenomena such as surface plasmon resonance (SPR) offers label-free measurements at a very high resolution and sensitivity. It is essential for any sensor to exhibit a very high analyte adsorption capability and good perceptibility to measure changes in electrical and optical properties due to such adsorption. Although SPR is extremely sensitive, 3DG is one of the potential functional materials which can exhibit a high analyte adsorption capability. Therefore, the use of 3DG as a functional layer in SPR devices can ensure a next-generation sensor. The Kretschmann configuration in angular interrogation-based SPR sensors may offer a sensitivity of the order of 10–8 RIU. In the SPR sensor, the extent of the plasmonic field over the metallic surface is limited to a few hundred nanometres. The excellent adsorption capability of 3D graphene can be employed for bio-sensing applications. However, due to the bulk nature of 3DG, the plasmonic field during SPR-based sensing decays rapidly into the porous structure of the 3DG, and therefore, the measurement becomes unresponsive even after the efficient adsorption of the analytes. Therefore, the layer of 3D graphene can be grown over the gold surface by some bottom-up deposition mechanism with control over the thickness. The bottom-up deposition mechanism may yield monolayer, bilayer, and twisted bilayer graphene which also exhibit excellent bio-sensing merits.
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    Facile layered structure of sensing chip of a prism–based surface plasmon resonance device
    (Elsevier, 2022) Manjuladevi, V.; Gupta, Raj Kumar
    Surface plasmon resonance (SPR) is a popular optical phenomenon for sensing application owing to its capability for label-free measurement which offers very high resolution and sensitivity. The traditional prism based Kretschmann configuration employs a sensing chip consists of a glass substrate deposited with 50 nm thick gold/silver layer. The parameters of the figure-of-merit (FOM) of an SPR sensor are a quality factor, signal-to-noise ratio, and the strength of the plasmonic field over the gold surface. In this article, we present a simulation work on a facile SPR sensor chip that yields a high FOM as compared to the traditional SPR sensor chip. We introduced a metallic intermediate layer (IML) in the traditional SPR chip and optimized the performance with respect to the material and thickness of IML. We optimized the thickness of the glass substrate such that the plasmonic field generated in the IML can couple with the outer gold film (OGF). Such coupling enhances the overall plasmonic field over the OGF by 112%.
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    Photoinduced modulation of refractive index in Langmuir-Blodgett films of azo-based H-shaped liquid crystal molecules
    (Elsevier, 2022-10) Manjuladevi, V.; Gupta, Raj Kumar
    The development of optically active area consisting of organic molecules are essential for the devices like optical switches and waveguides, as it can be easily maneuvered by the application of suitable electromagnetic (EM) waves. In this article, we report the development of a photoactive surface by the deposition of a single layer of Langmuir-Blodgett (LB) film of a novel H-shaped liquid crystal (HLC) molecule. The synthesized HLC molecules possess azo-groups and nitro-groups. The azo-group can be isomerized (trans–cis transformation) by irradiating them with ultraviolet (UV) light. The nitro-group can provide sufficient amphiphilicity to the HLC molecules to form a stable Langmuir monolayer at air–water interface. The Langmuir monolayer of the HLC molecules exhibited gas and liquid-like phases. A single layer of LB film of HLC molecules was deposited on a gold chip of a home-built surface plasmon resonance (SPR) instrument. The azo-groups of the molecules in LB film was excited by UV irradiation leading to a change in morphology due to trans–cis transformation. Such a change in morphology can lead to a miniscule change in refractive index (RI) of the LB film. SPR is a label free and highly sensitive optical phenomenon for the measurement of such changes in RI. In our studies, we found systematic changes in the resonance angle of the LB film of HLC molecules as a function of intensity of the UV irradiation. We measured switch-on and switch-off intensity which may suggest that the LB film of HLC molecules can find applications in optical switches or waveguides.
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    Refractive index of graphene AA and AB stacked bilayers under the influence of relative planar twisting
    (IOP, 2021-10) Manjuladevi, V.; Gupta, Raj Kumar
    The optical properties of graphene in monolayer and bilayer structure is essential for the development of optical devices viz surface plasmon resonance (SPR) based bio-sensors. The band structure of the twisted bilayer graphene (BLG) is remarkably different than the normal AA or AB stacking. This provides an opportunity to control the optical and electrical properties of BLG by applying an in-plane twist to one of the layer relative to other in a BLG system. Here, we calculated the refractive index (RI) of AA and AB stacking of BLG system using density functional theory. Though the spectrum for AA stacking shows some similarity with that of monolayer graphene, the spectrum for AB stacking was found to be remarkably different. The spectrum of AB stacked layer is red-shifted and the absorption peaks in low energy regime increases nearly by three-folds. A large dependency of the twist angle on RI of twisted BLG were found. Based on the calculation, a schematic of phase diagram showing material behavior of such twisted BLG systems as a function of twist angle and photon energy was constructed. The twisted AA stacked BLG shows largely dielectric behavior whereas the twisted AB stacked BLG shows predominately semimetallic and semiconducting behavior. This study presents a RI landscape of twisted BLG dependent on important parameters viz photon energy and inplane relative twist angle. Our studies will be very useful for the design and development of optical devices employing BLG systems particularly SPR based bio-sensors which essentially measures change in RI due to adsorption of analytes.