BITS Faculty Publications
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Item Plasmonic Au Nanoparticles Coated on ReS2 Nanosheets for Visible-Near-Infrared Photodetectors(ACS, 2022-07) Hazra, ArnabEven though there are various reports on the fabrication of flexible photodetectors, still there is a need for the development of high-performance photodetectors. In recent years, the plasmonic photodetection technique has emerged as one of the prominent solutions to enhance photodetection performance. In this work, a flexible and high-performance broadband (visible-near-infrared (NIR)) plasmonic photodetector is demonstrated by integrating gold (Au) nanoparticles (NPs) on two-dimensional (2D) ReS2 nanosheets. Fabricated Au-NPs/ReS2 showed an approximately 15-fold enhancement in the photodetection performance compared to pristine ReS2. Photoresponsivity of the fabricated Au-NPs/ReS2 device in visible (Vis) and NIR regions is ∼2.1 and ∼1.3 A W–1, respectively. Significant enhancement in the photosensing performance of the device could be a combined effect of multiple factors, including localized surface plasmon resonance and effective charge transfer at the interface of Au-NPs and ReS2. The response speed of the fabricated device is approximately 200 ms. Furthermore, theoretical understanding of light interaction with Au-NPs is studied, and also electromagnetic simulations are performed using Lumerical Finite Difference Time Domain Multiphysics simulation to investigate the plasmon coupling effect of Au-NPs on 2D ReS2 nanosheets. To further understand the photodetection mechanism, the energy band diagram of the Au-NPs/ReS2 interface is drawn using ultraviolet photoelectron spectroscopy measurements.Item Synthesis of Normal and Inverted Gold−Silver Core−Shell Architectures in β-Cyclodextrin and Their Applications in SERS(ACS, 2007-07-04) Pande, SurojitBeta-cyclodextrin (β-CD) in alkaline solution has been observed to produce mono- and bimetallic nanoparticles of silver and gold and to provide in-house stability to both types of particles. Thus, the weak reducing capability of the β-CD molecule (oxidation occurs at +1.33 V vs Ag/AgCl) and its unique kinetic control over the evolution of both normal and inverted core−shell bimetallic architectures have been established. The structure and composition of the bimetallic particles were characterized by UV−visible spectroscopy, transmission electron microscopy, high-resolution transmission electron microscopy, electron dispersive spectroscopy, and X-ray photoelectron spectroscopy. Bimetallic core−shell particles containing silver shells have been shown to provide an elegant SERS-active substrate compared to the corresponding monometallic nanoparticles, and therefore, they highlight the importance of electronic ligand effects on the enhancement of the Raman signals of molecular probes on nanostructured metallic surfaces.Item Decoration of Carbon Nitride Surface with Bimetallic Nanoparticles (Ag/Pt, Ag/Pd, and Ag/Au) via Galvanic Exchange for Hydrogen Evolution Reaction(ACS, 2017-08-21) Pande, SurojitHere, we propose the synthesis of AgPt, AgPd, and AgAu bimetallic nanoparticles (NPs) on a carbon nitride (C3N4) surface via a galvanic exchange technique for the hydrogen evolution reaction (HER). Prior to the synthesis of C3N4/AgPt, AgPd, and AgAu, Ag NPs were synthesized on a C3N4 surface. For the synthesis of Ag NPs, initially Ag+ ions were adsorbed and then reduced by NaBH4 resulting in the decoration of Ag NPs. These Ag NPs were then subjected to galvanic exchange where sacrificial Ag was replaced by Pt2+, Pd2+, and Au3+ to fabricate AgPt, AgPd, and AgAu NPs. The galvanic exchange reaction occurs on a solid substrate, which favored slow exchange of Ag and resulted in the transformation of Ag into AgPt, AgPd, and AgAu alloys. The synthesized heterostructures were characterized with the help of PXRD, XPS, TEM, FESEM, and EDS techniques. All the materials were applied for hydrogen evolution using 0.5 M H2SO4 solution. C3N4/AgPt shows efficient electrocatalytic activity as it requires only −150 mV potential to attain current density of 10 mA/cm2. Bimetallic catalysts synthesized through galvanic exchange proved very efficient as compared to monometallic C3N4/Ag.Item Exploration of Electrostatic Field Force in Surface-Enhanced Raman Scattering: An Experimental Investigation Aided by Density Functional Calculations(ACS, 2008-10-27) Basu, MrinmoyeeSurface chemical properties of metal nanoparticles must be tunable to create chemical specificity and are a key prerequisite for successful sensing and imaging platforms. To relate surface enhanced Raman scattering (SERS) to electrostatic field force, a simple colloidal chemistry approach has been deliberately exploited for syntheses of gold nanoparticles with negative and positive surface charges to study their interactions with charged analytes. We took up the challenge with sulfur-containing analytes because “Au−S” interaction is well-known. Thiocyanate ion, −SCN−, a well-known SERS analyte, has been proved to be chemically ligated/anchored on positively charged gold nanoparticles surface owing to favorable electrostatic attraction. The Au−S vibrational band at ∼240 cm−1 and blue-shifting of the −C≡N stretching frequency by ∼46 cm−1 in conjunction with its intensity enhancement by an order of ∼103 in the SERS spectrum clearly illustrate a chemisorption phenomenon. In contrast, physisorption of the −SCN− ion becomes evident on negatively charged colloid. Again, methylene blue has been shown to remain engrossed on the negatively charged gold surfaces. However, the electrostatic field force could not be accounted for from fluorescence quenching while methylaminopyrene was introduced because of the distance-dependence effect. The feasibility of such coordinative/chemical attachment also has been examined theoretically by density functional theory (DFT). Moreover, employment of this DFT calculation has been performed on five different metal−molecule interaction models to fruitfully interpret the experimental SERS findings and also the orientation of the SERS analyte. The observed Raman signals have been assigned from the potential energy distributions in terms of internal coordinates of adsorbate from the output of DFT calculations. The results thus provide a benchmark illustration of the value of DFT for aiding interpretation of adsorbate vibrational spectra attainable by using SERS.Item Chelate Effect in Surface Enhanced Raman Scattering with Transition Metal Nanoparticles(ACS, 2009-12-17) Basu, MrinmoyeeOver the years, several protocols have been designed to achieve surface enhanced Raman scattering (SERS) from noble/coinage metal nanoparticles preferably with silver and gold owing to the local electromagnetic field enhancement near their surface. However, the higher value of the imaginary component of the dielectric constant and the coupling between conduction and interband electron transitions result in poor SERS intensity for transition metals. Therefore, a good number of approaches such as the development of various surface roughening procedures have been made to increase the SERS sensitivity involving transition metal nanoparticles. This letter reports that chelating ligands such as 1,10-phenanthroline, ethylenediammine, and so forth have been found to be superior alternatives to bring forth the SERS activity from “3d” block transition metal nanoparticles (nickel and cobalt). Thus, a comparative account of SERS efficiency derived from these materials as well as from coinage metal nanoparticles engaging chelating and nonchelating (e.g., pyridine) ligands becomes intriguing.Item Synthesis of Monometallic (Au and Pd) and Bimetallic (AuPd) Nanoparticles Using Carbon Nitride (C3N4) Quantum Dots via the Photochemical Route for Nitrophenol Reduction(ACS, 2016) Basu, Mrinmoyee; Gangopadhyay, Subhashis; Pande, SurojitIn this study, we report the synthesis of monometallic (Au and Pd) and bimetallic (AuPd) nanoparticles (NPs) using graphitic carbon nitride (g-C3N4) quantum dots (QDs) and photochemical routes. Eliminating the necessity of any extra stabilizer or reducing agent, the photochemical reactions have been carried out using a UV light source of 365 nm where C3N4 QD itself functions as a suitable stabilizer as well as a reducing agent. The g-C3N4 QDs are excited upon irradiation with UV light and produce photogenerated electrons, which further facilitate the reduction of metal ions. The successful formation of Au, Pd, and AuPd alloy nanoparticles is evidenced by UV–vis, powder X-ray diffraction, X-ray photon spectroscopy, and energy-dispersive spectroscopy techniques. The morphology and distribution of metal nanoparticles over the C3N4 QD surface has been systematically investigated by high-resolution transmission electron microscopy (HRTEM) and SAED analysis. To explore the catalytic activity of the as-prepared samples, the reduction reaction of 4-nitrophenol with excellent performance is also investigated. It is noteworthy that the synthesis of both monometallic and bimetallic NPs can be accomplished by using a very small amount of g-C3N4, which can be used as a promising photoreducing material as well as a stabilizer for the synthesis of various metal nanoparticles.Item Decoration of Carbon Nitride Surface with Bimetallic Nanoparticles (Ag/Pt, Ag/Pd, and Ag/Au) via Galvanic Exchange for Hydrogen Evolution Reaction(ACS, 2017-08-21) Basu, Mrinmoyee; Pande, SurojitHere, we propose the synthesis of AgPt, AgPd, and AgAu bimetallic nanoparticles (NPs) on a carbon nitride (C3N4) surface via a galvanic exchange technique for the hydrogen evolution reaction (HER). Prior to the synthesis of C3N4/AgPt, AgPd, and AgAu, Ag NPs were synthesized on a C3N4 surface. For the synthesis of Ag NPs, initially Ag+ ions were adsorbed and then reduced by NaBH4 resulting in the decoration of Ag NPs. These Ag NPs were then subjected to galvanic exchange where sacrificial Ag was replaced by Pt2+, Pd2+, and Au3+ to fabricate AgPt, AgPd, and AgAu NPs. The galvanic exchange reaction occurs on a solid substrate, which favored slow exchange of Ag and resulted in the transformation of Ag into AgPt, AgPd, and AgAu alloys. The synthesized heterostructures were characterized with the help of PXRD, XPS, TEM, FESEM, and EDS techniques. All the materials were applied for hydrogen evolution using 0.5 M H2SO4 solution. C3N4/AgPt shows efficient electrocatalytic activity as it requires only −150 mV potential to attain current density of 10 mA/cm2. Bimetallic catalysts synthesized through galvanic exchange proved very efficient as compared to monometallic C3N4/Ag.Item Decoration of Carbon Nitride Surface with Bimetallic Nanoparticles (Ag/Pt, Ag/Pd, and Ag/Au) via Galvanic Exchange for Hydrogen Evolution Reaction(ACS, 2017) Basu, Mrinmoyee; Pande, SurojitHere, we propose the synthesis of AgPt, AgPd, and AgAu bimetallic nanoparticles (NPs) on a carbon nitride (C3N4) surface via a galvanic exchange technique for the hydrogen evolution reaction (HER). Prior to the synthesis of C3N4/AgPt, AgPd, and AgAu, Ag NPs were synthesized on a C3N4 surface. For the synthesis of Ag NPs, initially Ag+ ions were adsorbed and then reduced by NaBH4 resulting in the decoration of Ag NPs. These Ag NPs were then subjected to galvanic exchange where sacrificial Ag was replaced by Pt2+, Pd2+, and Au3+ to fabricate AgPt, AgPd, and AgAu NPs. The galvanic exchange reaction occurs on a solid substrate, which favored slow exchange of Ag and resulted in the transformation of Ag into AgPt, AgPd, and AgAu alloys. The synthesized heterostructures were characterized with the help of PXRD, XPS, TEM, FESEM, and EDS techniques. All the materials were applied for hydrogen evolution using 0.5 M H2SO4 solution. C3N4/AgPt shows efficient electrocatalytic activity as it requires only −150 mV potential to attain current density of 10 mA/cm2. Bimetallic catalysts synthesized through galvanic exchange proved very efficient as compared to monometallic C3N4/Ag.Item Biosynthesized Protein-Capped Silver Nanoparticles Induce ROS-Dependent Proapoptotic Signals and Prosurvival Autophagy in Cancer Cells(ACS, 2017) Panwar, Jitendra; Rahaman, Inamur; Chowdhury, RajdeepIn recent years, the use of silver nanoparticles (AgNPs) in biomedical applications has shown an unprecedented boost along with simultaneous expansion of rapid, high-yielding, and sustainable AgNP synthesis methods that can deliver particles with well-defined characteristics. The present study demonstrates the potential of metal-tolerant soil fungal isolate Penicillium shearii AJP05 for the synthesis of protein-capped AgNPs. The particles were characterized using standard techniques, namely, UV–visible spectroscopy, transmission electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The anticancer activity of the biosynthesized AgNPs was analyzed in two different cell types with varied origin, for example, epithelial (hepatoma) and mesenchymal (osteosarcoma). The biological NPs (bAgNPs) with fungal-derived outer protein coat were found to be more cytotoxic than bare bAgNPs or chemically synthesized AgNPs (cAgNPs). Elucidation of the molecular mechanism revealed that bAgNPs induce cytotoxicity through elevation of reactive oxygen species (ROS) levels and induction of apoptosis. Upregulation of autophagy and activation of JNK signaling were found to act as a prosurvival strategy upon bAgNP treatment, whereas ERK signaling served as a prodeath signal. Interestingly, inhibition of autophagy increased the production of ROS, resulting in enhanced cell death. Finally, bAgNPs were also found to sensitize cells with acquired resistance to cisplatin, providing valuable insights into the therapeutic potential of bAgNPs. To the best of our knowledge, this is the first study that provides a holistic idea about the molecular mechanisms behind the cytotoxic activity of protein-capped AgNPs synthesized using a metal-tolerant soil fungus.Item Superior Bactericidal Efficacy of Fucose-Functionalized Silver Nanoparticles against Pseudomonas aeruginosa PAO1 and Prevention of Its Colonization on Urinary Catheters(ACS, 2018-08-10) Panwar, JitendraPseudomonas aeruginosa, a Gram-negative rod-shaped bacterium is a notorious pathogen causing chronic infections. Its ability to form antibiotic-resistant biofilm has raised the need for the development of alternative treatment approaches. An ideal alternate can be silver nanoparticles known for their strong yet tunable bactericidal activity. However, their use in commercial in vivo medicine could not see the light of the day because of the unwanted toxicity of silver in the host cells at higher concentrations. Thus, strategies which can modulate the bacterial cell–silver nanoparticle interactions thereby reducing the amount of nanoparticles required to kill a typical number of bacterial cells are utmost welcomed. The current work showcases one such strategy by functionalizing the silver nanoparticles with l-fucose to increase their interactions with the LecB lectins present on P. aeruginosa PAO1. The advantage of this approach lies in the higher bactericidal and antibiofilm activity of fucose-functionalized silver nanoparticles (FNPs) as compared to the citrate-capped silver nanoparticles (CNPs) of similar size and concentrations. The superior bactericidal potential of FNPs as demonstrated by fluorescence-assisted cell sorting, confocal laser scanning microscopy, and transmission electron microscopy analyses may be attributed to the higher reactive oxygen species generation and oxidative membrane damage. Additionally, FNPs prevented the formation of biofilms by downregulating the expression of various virulence genes at lower concentrations as compared to CNPs. The practical applicability of the approach was demonstrated by preventing bacterial colonization on artificial silicone rubber surfaces. These results can be extrapolated in the treatment of catheter-associated urinary tract infections caused by P. aeruginosa. In conclusion, the present work strongly advocates the use of antivirulence targets and their corresponding binding residues for the augmentation of the bactericidal effect of silver nanoparticles.