Browsing by Author "Sen, Tapasi"

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    DNA Origami Directed Au Nanostar Dimers for Single-Molecule Surface-Enhanced Raman Scattering
    (American Chemical Society, 2017) Tanwar, Swati; Haldar, Krishna Kanta; Sen, Tapasi; Tanwar, S.; Haldar, K.K.; Sen, T.
    We demonstrate the synthesis of Au nanostar dimers with tunable interparticle gap and controlled stoichiometry assembled on DNA origami. Au nanostars with uniform and sharp tips were immobilized on rectangular DNA origami dimerized structures to create nanoantennas containing monomeric and dimeric Au nanostars. Single Texas red (TR) dye was specifically attached in the junction of the dimerized origami to act as a Raman reporter molecule. The SERS enhancement factors of single TR dye molecules located in the conjunction region in dimer structures having interparticle gaps of 7 and 13 nm are 2 ? 1010 and 8 ? 109, respectively, which are strong enough for single analyte detection. The highly enhanced electromagnetic field generated by the plasmon coupling between sharp tips and cores of two Au nanostars in the wide conjunction region allows the accommodation and specific detection of large biomolecules. Such DNA-directed assembled nanoantennas with controlled interparticle separation distance and stoichiometry, and well-defined geometry, can be used as excellent substrates in single-molecule SERS spectroscopy and will have potential applications as a reproducible platform in single-molecule sensing. ? 2017 American Chemical Society.
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    DNA Origami-Templated Bimetallic Core-Shell Nanostructures for Enhanced Oxygen Evolution Reaction
    (American Chemical Society, 2022-04-15T00:00:00) Kaur, Gagandeep; Biswas, Rathindranath; Haldar, Krishna Kanta; Sen, Tapasi
    Hydrogen generation through electrocatalytic water splitting offers promising technology for sustainable and clean energy production as an alternative to conventional energy sources. The development of highly active electrocatalysts is of immense interest for improving the efficiency of gas evolution, which is strongly hindered due to the sluggish kinetics of oxygen evolution reaction (OER). Herein, we present the design of Ag-coated Au nanostar (core-shell-type Au@Ag nanostar) monomer structures assembled on rectangular DNA origami and study their electrocatalytic activities through OER, which remains unexplored. Our designed DNA origami-templated bimetallic nanostar catalyst showed excellent OER activity and high stability without using any external binder and exhibited a current density of 10 mA cm-2at a low overpotential of 266 mV, which was smaller than those of ss-DNA-functionalized Au@Ag nanostars and DNA origami-templated pure Au nanostars. Our results reveal that DNA origami-assembled core-shell Au@Ag nanostars show better electrocatalytic performance as compared to pure-core Au nanostars immobilized on DNA origami, owing to the presence of a highly conductive Ag layer. Such controlled assembly of bimetallic nanostructures on a DNA origami template can provide additional electrochemical surface area and a higher density of active sites resulting in enhanced electrocatalysis. � 2022 American Chemical Society. All rights reserved.
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    Interfacial design of gold/silver core-shell nanostars for plasmon-enhanced photocatalytic coupling of 4-aminothiophenol
    (Royal Society of Chemistry, 2021-10-02T00:00:00) Kaur, Gagandeep; Tanwar, Swati; Kaur, Vishaldeep; Biswas, Rathindranath; Saini, Sangeeta; Haldar, Krishna Kanta; Sen, Tapasi
    Chemical reactions under mild conditions mediated by localized surface plasmon resonance (LSPR) of metals have emerged as a functional research field. In the present study, we report an interfacial designing procedure for the fabrication of a class of bimetallic hybrid nanomaterials as a profoundly active photocatalyst for the conversion of para-aminothiophenol (PATP) into 4,4?-dimercaptoazobenzene. For this purpose, core-shell nanostars composed of gold (core) and silver (shell) (Au/Ag NSs) were utilized as both surface-enhanced Raman scattering substrate and plasmon driven catalyst under 532 nm laser excitation. Au/Ag NSs with sharp tips display excellent surface-enhanced Raman scattering (SERS) efficiency of PATP. Employing the SERS study, it has been found that PATP rapidly converts into its dimerized product DMAB within few seconds by surface photochemical reaction in the Au-Ag heterojunction of core-shell nanostars. Au/Ag NSs with multiple sharp tips exhibit intense LSPR and highly strong electric fields are created at the tips, which enables the generation of hot electrons responsible for the rapid conversion reaction. Such well-designed interfacial bimetallic nanostars could have potential applications in surface enhanced spectroscopy, biosensing, and photoinduced surface catalysis. This journal is � The Royal Society of Chemistry.
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    Interfacial Engineering of CuCo2S4/g-C3N4Hybrid Nanorods for Efficient Oxygen Evolution Reaction
    (American Chemical Society, 2021-07-29T00:00:00) Biswas, Rathindranath; Thakur, Pooja; Kaur, Gagandeep; Som, Shubham; Saha, Monochura; Jhajhria, Vandna; Singh, Harjinder; Ahmed, Imtiaz; Banerjee, Biplab; Chopra, Deepak; Sen, Tapasi; Haldar, Krishna Kanta
    Altering the morphology of electrochemically active nanostructured materials could fundamentally influence their subsequent catalytic as well as oxygen evolution reaction (OER) performance. Enhanced OER activity for mixed-metal spinel-type sulfide (CuCo2S4) nanorods is generally done by blending the material that has high conductive supports together with those having a high surface volume ratio, for example, graphitic carbon nitrides (g-C3N4). Here, we report a noble-metal-free CuCo2S4 nanorod-based electrocatalyst appropriate for basic OER and neutral media, through a simple one-step thermal decomposition approach from its molecular precursors pyrrolidine dithiocarbamate-copper(II), Cu[PDTC]2, and pyrrolidine dithiocarbamate-cobalt(II), Co[PDTC]2 complexes. Transmission electron microscopy (TEM) images as well as X-ray diffraction (XRD) patterns suggest that as-synthesized CuCo2S4 nanorods are highly crystalline in nature and are connected on the g-C3N4 support. Attenuated total reflectance-Fourier-transform infrared (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy studies affirm the successful formation of bonds that bridge (Co-N/S-C) at the interface of CuCo2S4 nanorods and g-C3N4. The kinetics of the reaction are expedited, as these bridging bonds function as an electron transport chain, empowering OER electrocatalytically under a low overpotential (242 mV) of a current density at 10 mA cm-2 under basic conditions, resulting in very high durability. Moreover, CuCo2S4/g-C3N4 composite nanorods exhibit a high catalytic activity of OER under a neutral medium at an overpotential of 406 mV and a current density of 10 mA cm-2. � 2021 American Chemical Society.
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    Shell thickness matters! Energy transfer and rectification study of Au/ZnO core/shell nanoparticles
    (Academic Press Inc., 2016) Haldar, Krishna Kanta; Sen, Tapasi
    In the present study we report the influence of shell thickness on fluorescence resonance energy transfer between Au/ZnO core-shell nanoparticles and Rhodamine 6G dye by steady-state and time-resolved spectroscopy and rectification behaviours. Au/ZnO core-shell nanoparticles with different shell thickness were synthesized in aqueous solution by chemically depositing zinc oxide on gold nanoparticles surface. A pronounced effect on the photoluminescence (PL) intensity and shortening of the decay time of the dye in presence of Au/ZnO core-shell nanoparticles is observed. The calculated energy transfer efficiencies from dye to Au/ZnO are 62.5%, 79.2%, 53.6% and 46.7% for 1.5 nm, 3 nm, 5 nm and 8 nm thickness of shell, respectively. Using FRET process, the calculated distances (r) are 117.8, 113.2 ? 129.9 ? and 136.7 ? for 1.5 nm, 3 nm, 5 nm and 8 nm thick Au/ZnO core-shell nanoparticles, respectively. The distances (d) between the donor and acceptor are 71.0, 57.8, 76.2 and 81.6 ? for 1.5 nm, 3 nm, 5 nm and 8 nm thick core-shell Au/ZnO nanoparticles, respectively, using the efficiency of surface energy transfer (SET). The current-voltage (I-V) curve of hybrid Au/ZnO clearly exhibits a rectifying nature and represents the n-type Schottky diode characteristics with a typical turn-on voltage of between 0.6 and 1.3 V. It was found that the rectifying ratio increases from 20 to 90 with decreasing the thickness of the shell from 5 nm to 3 nm and with shell thickness of 8 nm, electrical transport through the core-shell is similar to what is observed with pure ZnO samples nanoparticles. The results indicated that the Au/ZnO core-shell nanoparticles with an average shell thickness of 3 nm exhibited the maximum energy transfer efficiencies (79.2%) and rectification (rectifying ratio 90). ? 2016