Browsing by Author "Rajneesh Kumar"

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A contemporary overview on quantum dots-based fluorescent biosensors: Exploring synthesis techniques, sensing mechanism and applications
(Elsevier B.V., 2025) Anushka Yadav; Priyanka Dogra; Pinky Sagar; Monika Srivastava; Amit Kumar Srivastava; Rajneesh Kumar; Sanjay Kumar Srivastava
In the epoch of bioinformatics, pivotal biomedical scrutiny and clinical diagnosis hinge upon the unfolding of highly efficacious biosensors for intricate and targeted identification of specific biomolecules. In pursuit of developing robust biosensors endowed with superior sensitivity, precise selectivity, rapid performance, and operational simplicity, semiconductor QDs have been acknowledged as pivotal and advantageous entities. In this review, we present a comprehensive analysis of the latest unfolding within the domain of QDs used in fluorescent biosensors for the detection of diverse biomolecular entities, encompassing proteins, nucleic acids, and a range of small molecules, with an emphasis on the synthesis methodologies of QDs employed and mechanism behind sensing. Additionally, this review delves into several pivotal facets of QD-based fluorescent biosensors in detail, such as surface functionalization methodologies aimed at enhancing biocompatibility and improving target specificity. The challenges and future perspectives of QD-based fluorescent biosensors are also considered, emphasizing the necessity of ongoing multidisciplinary research to realize their full potential in enhancing personalized medicine and biomedical diagnostics. © 2025 Elsevier B.V.
A smartphone-enabled colorimetric sensor based on VS2 quantum dots for Rapid and on-site detection of ferric ions
(Elsevier B.V., 2025) Anushka Yadav; Pinky Sagar; Monika Srivastava; Amit Kumar Srivastava; Rajneesh Kumar; Sanjay Kumar Srivastava
This research delves into the holistic hydrothermal synthesis of VS2 QDs and their subsequent utilization as a fluorescent probe for the subtle detection of ferric ions (Fe3+) in practical sample matrices. The detection paradigms harness a colorimetric sensing mechanism, amplified by smartphone-enabled analytical integration for improved precision and real-time monitoring. A comprehensive suite of analytical characterization techniques has been employed, revealing that the as-synthesized VS2 QDs feature a surface densely populated with functional groups. While the VS2 QDs showcase interactions with multifarious metal ions in aqueous media, they set forth a pronounced and selective fluorescent quenching response toward Fe3+ ions, markedly surpassing their interactions with other metal ions. The developed sensing probe exhibits a linear detection range spanning from 0 – 90 μM, with a LOD as low as 2.25 μM, also exhibits exceptional sensitivity (KD ∼ 0.8 × 104 M−1) and remarkable selectivity for Fe3+ ions, harnessing the intrinsic photoluminescent characteristics of VS2 QDs. In addition, a sophisticated portable smartphone platform, integrated with a radiometric fluorescence probe specifically tailored for in-situ detection of Fe3+ at the point of care, exhibits a LOD of approximately 5.05 μM, a value that resides below the prescribed safety threshold. Thus, the proposed probe stands to function as an exceptionally potent sensing apparatus for the precise quantification of Fe3+ in complex real-world samples. © 2024 Elsevier B.V.
Alkali metal ion codoped Eu3+ activated yttrium orthovanadate with tunable photoluminescence properties for LEDs and anti-counterfeiting applications
(Elsevier Ltd, 2025) Anuradha; Arpita Dwivedi; Satyam Upadhyay; Amit Kumar Srivastava; Monika Srivastava; Rajneesh Kumar; Sanjay Kumar Srivastava
The present experimental report articulates a comprehensive investigation on the synthesis, structural, and photoluminescence characteristics of M0.05,Eu0.05:Y0.90VO4 (M = Li+, Na+, K+) nanophosphors synthesised by auto-combustion approach, for optical display and anticounterfeiting technologies. Various characterization tools such as X-ray diffractometer (XRD), Transmission Electron Microscope (TEM), Scanning Electron Microscope (SEM), Fourier transform infra-red (FTIR) Spectroscope, and Raman spectroscope have been employed to understand the morphology and crystal structure of M0.05,Eu0.05:Y0.90VO4 (M = Li+, Na+, K+) nanophosphor, which reveals the formation of a pure tetragonal structure and well crystalline phase. Moreover, the UV–Vis spectra, suggests that the as-synthesised material substantiated to possess an energy band gap of ∼3.6 eV conjecturing it as a wide-band material, and the refractive index (n) of the prepared samples has been deduced as ∼ 2.1. Among all alkali ions, Li+-codoped sample exhibits the most intense PL spectra. The enhancement in PL intensity has been observed due to the energy transfer of VO43−→Eu3+ and the codoping of lithium ions acts as a good charge compensator. For the optimized sample CIE coordinates has been found as (0.59, 0.39) and CCT value as 1712 K, which suggest it as a prospective candidate for the warm LEDs. The optimized sample has further been investigated for the visualization of Latent fingerprint on glass slide and as security ink. It displays efficient applicability as a well-defined ridge features up to level III. Henceforth, the as-synthesised Li0.05,Eu0.05:Y0.90VO4 nanophosphor may potentially be applied for multipurpose applications. © 2024 Elsevier Ltd and Techna Group S.r.l.
Effect of La Doping on NiCr2O4Properties and Catalytic Applications toward Decolorization of 4-Nitrophenol
(IOP Publishing Ltd, 2022) G. Rajeswari; N. Prabavathi; A. Prakasam; Rajneesh Kumar; S. Geetha; P. Tamizhdurai; Zeid A. Alothman; Ahmed muteb Aljuwayid; U. Rajaji
We report the successful synthesis of urea as a fuel for low-temperature microwave combustion-based synthesis of NiCr2O4 and La-doped NiCr2O4. Synthesis parameters include the kind of precursor, fuel, and container, as well as how external heat is provided to achieve the combustion reaction. Crystal structures, morphology, surface area, solar cells, Fourier-transform infrared spectrometry, and catalytic activity were used to characterize the products. No impurities phase formed in the as-synthesized NiCr2O4 sample, confirmed by XRD. Surface area was measured with a Brunauer Emmet Teller adsorption isotherm. Schottky and Frenkel formation energies have been investigated. This demonstrates the time needed for full decolorization of 4-Nitrophenol (yellow color) by NiCr2O4 and La-doped NiCr2O4. The La-doped NiCr2O4 (0.03%) showed the greatest catalytic activity compared to pristine and other La-doped NiCr2O4. The decolorization occurs in 10 min. The chemical hardness and surface area of the chromites appear to be important in determining catalytic performance. For multi oxide systems, the counter-doped ions in the A and B sites may alter the metal ion-oxide bond, promoting this partial oxidation process at the interface. The results suggest multiple research subjects focusing on such materials for the future. © 2022 Electrochemical Society Inc.. All rights reserved.
Enhance photoluminescence properties of Ca-Eu:Y2O3@SiO2 core–shell nanomaterial for the advanced forensic and LEDs applications
(Elsevier B.V., 2023) Arpita Dwivedi; Anuradha; Monika Srivastava; Amit Srivastava; Rajneesh Kumar; Sanjay Kumar Srivastava
The divalent (Ca2+)-doped Eu:Y2O3@SiO2 core–shell luminescent nanophosphors have been synthesised by a cost-effective combustion technique. Various characterizations were carried out to confirm the successful formation of the core–shell structure. The TEM micrograph reveals the thickness of the SiO2 coating over Ca-Eu:Y2O3 as ∼25 nm. The optimal value of silica coating over the phosphor has been obtained as 10 vol%(TEOS) of SiO2, with this value increasing fluorescence intensity by 34 %. Phosphor exhibits CIE coordinates as x = 0.425, y = 0.569 and a CCT value as ∼2115 K with color purity and the respective CRI of 80 % and 98 %, respectively, which make the core–shell nanophosphor suitable for warm LEDs, and other optoelectronic applications. Further, the core–shell nanophosphor has been investigated for the visualisation of latent finger prints and as security ink. The findings point towards the prospective future application of nanophosphor materials for anti-counterfeiting purposes and latent finger prints for forensic purposes. © 2023 Elsevier B.V.
Enhanced dielectric and electrical properties of polystyrene-2% divinyl benzene (PDB) embedded in SrTiO3-Poly (vinylidene fluoride) three phase composite films
(Elsevier GmbH, 2022) N.P. Yadav; Bibhuti B. Sahu; Tarun Yadav; Rajneesh Kumar; Amit Pathak; G.N. Pandey; Srikanta Moharana
A facile solution casting technique has been employed to fabricate ceramic SrTiO3; STO particle and polystyrene-2% divinyl benzene (PDB) filled three phase composite films using poly(vinylidene fluoride) (PVDF) matrix. The frequency dependence of dielectric and electrical properties of the three phase PVDF-STO-PDB composite films of various weight percentage of PDB (fPDB) were analyzed. With the small change in the AC conductivity and dielectric loss the dielectric constant of the PVDF-STO-PDB composite systems is improved noticeably. The experimental results suggested that, the introduction of 10 wt% of PDB particles in the PVDF-STO composites enhanced the dielectric constant (≈76) and suppressed dielectric loss value (< 0.5) at 100 Hz. This may be attributed to the addition of PDB particles improved the establishment of polarization. The morphological analysis depicts that the PDB particles are uniformly dispersed and well compatibility between filler particles and polymer matrix which may be ascribed to the minimization of dielectric loss of the resultant composites. Further, the strong interaction between PDB particles and PVDF matrix at the interface is the crucial factor in the improvement of the dielectric and electrical properties. The percolation theory was used to elucidate the dielectric and electrical performance of PVDF-STO-PDB composites. It is noticed that the three phase PVDF-STO-PDB composite films exhibited an insulator-conductor transition with percolation threshold of fPDB = 5 wt%. The three phase composites with high dielectric constant (≈76) at percolation threshold might be helpful to understand the influence of PDB particles on the interfaces between the ceramics and polymer matrix. This work will provide an easy and effective solution to fabricate high performance three phase composites to the development of high energy storage applications. © 2022 Elsevier GmbH
Facile construction of MoS2 decorated CdS hybrid heterojunction with enhanced hydrogen generation performance
(Elsevier B.V., 2024) R. Sridevi; A. Prakasam; P.M. Anbarasan; Rajneesh Kumar; M. Karthik; K. Deepakvijay
Promoting the charge separation to improve photocatalytic performance of semiconductor photocatalysts is very important in the field of artificial photosynthesis. Here, a novel MoS2/CdS 2D–2D ultrathin nanosheet heterostructure was fabricated via a one-pot solvothermal route. The obtained 2D–2D MoS2/CdS nanojunction has not only provided large contact areas, but also shortened the charge transport distance, resulting in significantly enhanced photocatalytic H2 evolution property. The composites that were synthesized were examined using X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM), Transmission electron microscope (TEM), UV-vis diffuse reflectance spectra (DRS), Photoluminescence (PL) and X-ray photoelectron spectra (XPS) analysis. By optimizing the 2D MoS2 amounts in the heterojunction, the 5 wt.% 2D/2D MoS2/CdS heterojunction displayed the maximal photocatalytic H2 evolution rate of 4449 μmolh−1g−1 under visible light irradiation in the presence of lactic acid as the sacrificial reagent, which was 6 times higher than that of pristine 2D CdS. Based on the photoelectrochemical and photoluminescence spectra tests, it could be deduced that the charge separation and transfer of 2D/2D MoS2/CdS heterojunction was tremendously improved, and the recombination of photoinduced electron-hole pairs was effectively impeded. Moreover, the 2D MoS2 was used as a cocatalyst to provide the abundant active sites and lower the overpotential for H2 generation reaction. The current work would offer an insight to fabricate the 2D/2D heterojunction photocatalysts for splitting H2O into H2. © 2024 The Author(s)
Molecular geometries, vibrational spectra and electronic properties of biphenyl nematic liquid crystals: a quantum chemical analysis
(Taylor and Francis Ltd., 2023) Nagendra Prasad Yadav; Anil Kumar Vishwkarma; Ajit Kumar Maddheshiya; Tarun Yadav; Srikanta Moharana; Rajneesh Kumar; Amit Pathak; Pankaj Kumar Tripathi
The present work reports the vibrational spectroscopic signature, thermodynamics, and natural bond orbital analysis (NBO) of 4-Cyano-4-pentylbiphenyl (5CB) and 4-Cyano-4'-hexyl diphenyl (6CB) liquid crystals. The optimization of both compounds (5CB and 6CB) has been performed at DFT/B3LYP/6-31++G(d, p) level of theory. Most of the vibrational modes have wavenumbers in the expected range. The comparison of vibrational frequencies of both compounds has been made. Subsequently, the different thermodynamical parameters and electronic properties have been calculated and discussed in detail. The NBO analysis has been performed to check the stability of the electronic structures. The UV visible, HOMO- LUMO, MEP, and charge analysis has been performed. Moreover, the strong electronic transition from HOMO to LUMO (97% of MO contribution) has been predicted for 5CB and 6CB at 289 nm with oscillator strengths of 0.7242 and 0.7286, respectively. The MEP plots of both 5CB and 6CB are almost the same and show that strong electrophilic substitution would take place near the N atom attached to the CN group. The energy gap of 5CB and 6CB compounds is found to be 4.65eV. Molecules with large energy gaps are less polarizable and are termed as hard molecules, having low chemical reactivity and high kinetic stability. © 2023 Informa UK Limited, trading as Taylor & Francis Group.
Morphologies, crystal structure and antibacterial properties of chromium substituted zinc oxide nanoparticles synthesized by microwave method
(Elsevier Ltd, 2021) A. Prakasam; P.M. Anbarasan; R. Azhagu Raj; C. Ragupathi; Rajneesh Kumar
In this paper, we report on the synthesis on pure and Cr doped ZnO particles via the microwave method. Pure and Cr doped ZnO produced are monodisperse and versatile and were characterized with the help of FT-IR, XRD, SEM/EDX and TEM methods. Pure and Cr doped ZnO particles are crystalline in nature and average sizes were between 20 and 30 nm. Furthermore, the present work clearly indicated that the surface area to volume ratio and particle size variation of green ZnO nanoparticles are accountable for significantly increased antibacterial behaviour. © 2021 Elsevier Ltd. All rights reserved.
Perovskite Metal Oxides: Synthesis, Properties, and Applications
(Elsevier, 2023) Srikanta Moharana; Tanmaya Badapanda; Santosh Kumar Satpathy; Ram Naresh Mahaling; Rajneesh Kumar
Perovskite Metal Oxides: Synthesis, Properties and Applications provides an overview on the topic, including the synthesis of various types of perovskites, their properties, characterization and application. The book reviews the applications of this category of materials for photovoltaics, electronics, biomedical, fuel cell, photocatalyst, sensor, energy storage and catalysis, along with processing techniques of perovskite metal oxides with a focus on low-cost and high-efficiency methods, including various properties and probable applications in academia and industry. Other sections discuss strategies to improve the functionality of perovskite metal oxide materials, including chemical methods and controlling the size, shape and structure of the materials. Finally, applications of perovskite metal oxides in energy conversion and storage, sensing and electronics are covered. © 2023 Elsevier Inc. All rights reserved.
RIXS, XES and XAS studies for electronic structure of rare earth and alkaline earth modified manganite
(Elsevier B.V., 2022) Mahmoud Abu-Samak; Upendra Kumar; A.M. Quraishi; Rajneesh Kumar; Shalendra Kumar; S. Dalela; M. Ayaz Ahmad; B.L. Choudhary; P.A. Alvi
This article reports on the RIXS (Resonant inelastic X-ray scattering), XES (X-ray emission spectroscopy), and XAS (X-ray absorption spectroscopy) of the LaSr2Mn2O7, La0.95Ba0.05MnO3, and La1.2(BaCa)1.8Mn2O7 at 40 K, 100 K and 300 K. The RIXS spectra of these samples show the presence of Mn in different valence states (Mn2+, Mn3+, and Mn4+) which is associated with the Jahn-Teller distortion due to overlapping between O2− and the unpaired electrons of transition metal Mn. It has also been noticed that the distortion observed in different valence states of Mn with O2− is found to be suppressed with dropping and the temperature. So, based on aforementioned studies, the Manganites have been considered as a strongly correlated magnetic system which would be useful in magnetic device applications. © 2021 Elsevier B.V.
Spectroscopic Investigation of Electron-Releasing Functional Groups Substituted N-Iso-Butyl, S-2-Nitro-1-Phenylethyl Dithiocarbamate–A DFT Approach
(Taylor and Francis Ltd., 2022) Tarun Yadav; Goutam Brahmachari; Indrajit Karmakar; Saumen Saha; Joydeep Chowdhury; Amit Pathak; Rajneesh Kumar; R. Sharma; Ricardo R. F. Bento; Nagendra P. Yadav
Quantum chemical calculations have been carried out to explore structural and spectroscopic properties of some derivatives of N-iso-butyl, S-2-nitro-1-phenylethyl dithiocarbamate molecule in neutral and cationic forms. Electron-releasing groups (Me, OH and OMe) are considered to explore their effect on geometrical parameters, vibrational spectra and electronic properties of N-iso-butyl, S-2-nitro-1-phenylethyl dithiocarbamate. All the computations were performed at DFT/B3LYP level of Gaussian09 suite. The Raman spectra at different laser exciting frequencies are presented. The potential energy distributions of the considered derivatives were calculated by using the normal coordinate analysis method. The NBO calculations were performed to study the donor-acceptor interactions, HOMO-LUMO, electronic structure and hyper-conjugative interaction energies. The vibrational contribution of various thermodynamical parameters, viz, entropy, specific heat and free energy have also been presented and discussed in detail. Moreover, we have also explored the effect of temperature at specific heat and partition function of these molecules. Molecular docking studies have been performed to understand the nature of the interactions and the probable binding sites of NSD, NSD-Me, NSD-OH and NSD-OMe molecules in the active pockets of the 2KCE receptor. © 2021 Taylor & Francis Group, LLC.
Stability Analysis and Controlling Chaos of Fractional-Order Three-Species Food Chain Model with Fear
(Springer, 2021) Amit K. Mishra; Rajneesh Kumar; Vijay K. Yadav
In this article, stability analysis and chaos control of three species food chain model have been studied in the fractional order case. The fractional order three-species food chain model with fear term is the extension work of Panday et al. (Int J Bifurc Chaos 28:1850009, 2018), where they discussed the stability analysis and control of chaos of the model under several conditions. The stability analysis is done using Routh–Hurwitz condition and Matignon theorem for fractional order differential equations. The analysis has been done for the fractional-order of a three species food chain model with and without fear terms k1 and k2. If the fear terms are neglected in the considered model then the model is reduced to Hastings-Powell model. The chaos control is done using Lyapunov stability theory, the equilibrium points of the system are computed and stability is obtained in the system. The results are obtained through numerical simulation. © 2021, The Author(s), under exclusive licence to Springer Nature India Private Limited.
Streaming Instability Generation in Lunar Plasma Environment
(Institute of Electrical and Electronics Engineers Inc., 2022) Mehul Chakraborty; Vipin K. Yadav; Rajneesh Kumar
Plasma instabilities are the non-linear processes occurring in plasmas when excess energy gets accumulated in a plasma system which is unable to hold it. There are almost 60 known plasma instabilities in nature. © 2022 International Radio Science Union (URSI).
Study of array plasma antenna parameters
(American Institute of Physics Inc., 2018) Rajneesh Kumar; Prince Kumar
This paper is aimed to investigate the array plasma antenna parameters to help the optimization of an array plasma antenna. Single plasma antenna is transformed into array plasma antenna by changing the operating parameters. The re-configurability arises in the form of striations, due to transverse bifurcation of plasma column by changing the operating parameters. Each striation can be treated as an antenna element and system performs like an array plasma antenna. In order to achieve the goal of this paper, three different configurations of array plasma antenna (namely Array 1, Array 2 and Array 3) are simulated. The observations are made on variation in antenna parameters like resonance frequency, radiation pattern, directivity and gain with variation in length and number of antenna elements for each array plasma antenna. Moreover experiments are also performed and results are compared with simulation. Further array plasma antenna parameters are also compared with monopole plasma antenna parameters. The study of present paper invoke the array plasma antenna can be applied for steering and controlling the strength of Wi-Fi signals as per requirement. © 2018 Author(s).
The effect of energetic electrons in lunar ionosphere on the streaming plasma instability around moon
(American Institute of Physics, 2024) Vipin K. Yadav; Mahima Agarwal; Mehul Chakraborty; Rajneesh Kumar
The analytical study of the two-stream instability (TSI) generation is carried out in the lunar ionosphere. The solar wind is considered an electron beam, which interacts with the lunar ionosphere, generated due to the photoionization of the lunar neutrals by the extreme ultraviolet component of the solar radiation. In this interaction process, the lunar electrons constitute the background plasma as the ion population is considerably low in the lunar plasma environment. In the present study along with the non-energetic (“cold”) electrons, which are in the majority, a fraction of energetic electrons (“hot”) of the total lunar electron population are also considered and the fraction of energetic electrons is taken in the range of 1%-25% of the total lunar electron count. The particle-in-cell simulations suggest that the presence of energetic electrons in the lunar plasma environment hastens the electron bunching during the interaction with the incoming solar wind electrons during the TSI. The energetic electrons in the lunar plasma environment are capable of triggering non-linear phenomena, such as the generation of lunar plasma waves. The inclusion of hot electrons in the lunar plasma ambiance changes the scenario for the TSI to occur in the lunar ionosphere, and the analysis shows that it modifies the TSI dispersion relation and can have a significant impact on the growth and decay of the TSI and its threshold for generation in a lunar plasma environment. © 2024 Author(s).
Two-stream instability generation in the lunar ionosphere
(Elsevier Ltd, 2023) Mehul Chakraborty; Vipin K. Yadav; Rajneesh Kumar
The Two-stream Instability (TSI) generation is studied analytically in the lunar ionosphere. The TSI is a tiny perturbation in the electron plasma density, due to which an electric field grows with time and this growth is facilitated by the electron plasma in the background. In lunar ionosphere, the TSI comes into existence when the solar wind interacts unhindered with the tenuous lunar electron plasma in the surface bound exosphere. In this study, the conditions which allow the TSI to form and the subsequent instability growth with time i.e. the growth factor, is estimated. Initially, the threshold condition for the TSI to take place is determined. Thereafter, the solar wind and lunar plasma parameter contribution to trigger TSI is investigated along with the effect of these parameters in the evolution of TSI. The plasma TSI evolution with the passage of time is also depicted in phase space diagram with Particle-In-Cell simulations. © 2022 COSPAR