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Publications (103)
Doubly deuterated water (D2O) exhibits two distinct nuclear spin-isomers, ortho and para, which have not much been studied and there is hardly any information about the spin-exchange processes of D2O. Here, we investigated the nuclear-spin quantum states of D2O in gas phase by evaluating the ortho-to-para ratio (OPR) using high-resolution cavity ri...
The investigation of stable isotopes finds applications in a vast array of fields. The measurement of isotopic ratios in natural environments such as oceans, atmosphere and geological samples assists in identification of sources and sinks of compounds. On the other hand, isotopic labeling of compounds helps to study the role of different species in...
We have detected spin-dependent splitting of light, the signature of the photonic spin Hall
effect (PSHE), via quantum weak measurements on two types of thin films with architected
columnar morphology. Specifically, we fabricated columnar thin films (CTFs) comprising
parallel tilted nanocolumns and chiral sculptured thin films (CSTFs) comprising pa...
Insight into the aggregation kinetics of gold nanoparticles (GNPs) is critical for developing a colorimetric assay extensively used in chemical and biomolecular sensing. The aggregation of NPs plays a significant role in many natural and industrial processes, demanding comprehensive perceptions of the aggregation kinetics at a solid-liquid interfac...
Nitrogen dioxide (NO 2 ) is an important air pollutant due to its environmental impact and adverse effects on human health. It is released into the atmosphere primarily through anthropogenic activities. Here, we report on the development of a simple, compact, and cost-effective robust optical detection method exploiting cavity-enhanced absorption s...
We employed the wavelength-interrogated surface plasmon resonance (SPR) method to characterize the real-time kinetics of urea-urease hydrolysis reaction in response to a CO2-free N2 environment and CO2-enriched ambient reaction medium. We established that a simple label-free SPR probe could accurately extract kinetic parameters from the nature of t...
We employed the wavelength-interrogated surface plasmon resonance (SPR) method to characterize the real-time kinetics of urea-urease hydrolysis reaction in response to a CO2-free N2 environment and CO2-enriched ambient reaction medium. We established that a simple label-free SPR probe could accurately extract kinetic parameters from the nature of t...
Conventional endoscopic biopsy tests are not suitable for early detection of the acute onset and progression of peptic ulcer as well as various gastric complications. This also limits its suitability for widespread population-based screening and consequently, many people with complex gastric phenotypes remain undiagnosed. Here, we demonstrate a new...
High-resolution ro-vibrational spectroscopic features of nitric oxide (NO) are particularly interesting because of the unpaired electron and non-zero nuclear spin of the nitrogen atom. Here, ultra-sensitive cavity ring-down spectroscopy (CRDS) coupled with an external-cavity quantum cascade laser (EC-QCL) radiation source was employed to measure th...
Quantum dots (QDs) or luminescent semiconductor nanocrystals possess size-tunable elegant electro-optical properties, broad absorption spectra and narrow emission ranging from UV to NIR region, high fluorescent quantum yields, fluorescence intermittency, resistance to photobleaching, and significant Stoke shift, which are the prerequisite for the a...
We report a novel scheme for sensitivity-enhanced liquid phase cavity ring-down spectroscopy (CRDS) exploiting the two-dimensional transition metal dichalcogenides (2D-TMDCs) based surface plasmon resonance (SPR). We investigated the performance of the proposed sensing scheme by monitoring water isotopologues i.e. D2O (heavy water) and H2O on the S...
Pristine Antimony tungstate nanoparticles prepared via a simple hydrothermal process showcase interesting photocatalytic efficiency, degrading Methylene Blue (MB) completely in 180 min under visible light. In this study, the impact on crystalline quality and related optical properties as well as photocatalytic efficiency of antimony tungstate due t...
Pristine Antimony tungstate nanoparticles prepared via a simple hydrothermal process showcase interesting photocatalytic efficiency, degrading Methylene Blue (MB) completely in 180 min under visible light. In this study, the impact on crystalline quality and related optical properties as well as photocatalytic efficiency of antimony tungstate due t...
![The [Na(H2O)4]n⁺ found in 1 with ellipsoids at 50% probability](publication/359608651/figure/fig5/AS:1164519141322763@1654654407535/The-NaH2O4n-found-in-1-with-ellipsoids-at-50-probability_Q320.jpg)
A family of dioxidovanadium(V) complexes (1–4) of the type [Na(H2O)x]⁺[VVO2(HL¹⁻⁴)]⁻ (x = 4, 4.5 and 7) where HL²⁻ represents the dianionic form of 2-hydroxybenzoylhydrazone of 2-hydroxyacetophenone (H2L¹, complex 1), 2-hydroxy-5-methylacetophenone (H2L², complex 2), 2-hydroxy-5-methoxyacetophenone (H2L³, complex 3) and 2-hydroxy-5-chloroacetopheno...
A high-sensitive optical detection method was designed and developed at 7.8 μm mid-IR region by coupling a room-temperature operated continuous wave (cw) external-cavity quantum cascade laser (EC-QCL) with an astigmatic multipass cell. The detection strategy operates in the principle of wavelength modulation spectroscopy with second harmonic detect...
We report the direct experimental evidence of the photonic spin Hall shift (PSHS) in monolayer M o S 2 for a fundamental Gaussian beam via a weak measurement scheme involving definite preselection and postselection spin states. We find that the PSHS is largely dependent on the angle of incidence, postselection angles, and polarization states along...
We developed a mid-IR 2 f -wavelength modulation spectroscopy (WMS) detection system combining a continuous wave external-cavity quantum cascade laser (QCL) at 5.2 μ m and an astigmatic multipass cell. The high-sensitivity performance of the 2 f -WMS system was validated by simultaneously probing the strongest interference-free absorption lines of...
Selectivity is one of the most crucial figures of merit in trace gas sensing, and thus a comprehensive assessment is necessary to have a clear picture of sensitivity, selectivity, and their interrelations in terms of quantitative and qualitative views. Recent reviews on gas sensors/techniques are limited to specific sensors, sensors with unconventi...
Dideutero-methane ¹²CH2D2 is unique among all the methane isotopomers because of its asymmetric-top nature. Here, we first report the fine ro-vibrational gas-phase spectra of ¹²CH2D2 isotopomer in the a-type ν9 (B2-symmetry) fundamental band near 7.8 µm using ultra-sensitive cavity ring-down spectroscopy (CRDS) instrument in the mid-infrared spectr...
The optical excitation of plasmonic oscillation at metal-dielectric interface has widely been utilized for selective detection of molecules by tracking the change of the refractive index (RI) of the medium...
We report a robust technique to fabricate a cost-efficient Raman substrate which is composed of polyvinylpyrrolidone (PVP) coated gold nanoparticles layer on commercial aluminum foil. The layer of metal nanoparticles on the aluminum foil, i.e., the nanoparticle-on-mirror (NPoM) structure was fabricated by spraying nanoparticle colloidal solution di...
We report the experimental evidence of the Imbert-Fedorov (IF) shift in monolayer MoS2 for a fundamental Gaussian beam. Using Jones vector formalism, we have shown a novel, to the best of our knowledge, pathway to apply the quantum weak measurement technique for easy and accurate determination of the IF shift. We have revealed the dependence of IF...
Here, we report the analytical observations of adsorption behaviour of the most abundant stable isotopes of CO2 (12C16O2, 13C16O2 and 12C16O18O) and H2O vapour (H216O, H217O, H218O and HD16O) in emeraldine salt form of Polyaniline (ES-PANI) using optical cavity-enhanced absorption spectroscopy technique. Isotopic investigation showed a preferential...
We report the direct experimental evidences of l-doublet fine splittings between the parity doublet e and f sub-states of β-site isotopomer of nitrous oxide (¹⁵N¹⁴N¹⁶O) in the (12²0)←(02²0) ro-vibrational transition for l = 2 (i.e. Δ state) vibrational state in the mid-IR 7.8 µm spectral region. Due to extremely small splittings it remains a challe...
A simple, convenient, and surfactant free synthesis technique for Au nanoparticles (NPs) embedded in ZnO matrix is reported. At room temperature, a dramatic eight times enhancement of the deep level emission (DLE) in contrast to near band edge (NBE) emission was seen as compared to the pristine ZnO NPs with part per billion by weight (ppbw) additio...
The spectroscopic features of l-type doublets of the site-specific ¹⁵N-isotopomers of nitrous oxide (N2O) are interesting to study as it would reveal the effect of l-type doubling in different branches of the transition band and on the spectroscopic parameters. Here, we have explored various spectroscopic features that are influenced by the l-type...
Water vapor, the most important greenhouse gas in the atmosphere, has four natural stable isotopologues (H2¹⁶O, H2¹⁷O, H2¹⁸O and HD¹⁶O), and their isotopic compositions can be used as hydrological tracers. But the underlying processes and pattern-dynamics of the isotopic compositions of atmospheric water vapor and precipitation in response to vario...
Cavity ring-down spectroscopy (CRDS), one of the most fascinating analytical techniques, has found widespread applications in a variety of research fields. It is a direct, ultra-sensitive and quantitative laser absorption spectroscopy technique which measures the rate of absorption of molecular species instead of the magnitude of absorption in an o...
Over the past few decades, the progress in applications of quantum cascade laser (QCL) spectroscopy has accelerated with breathtaking way since its discovery in 1994. The unique properties of QCL such as certain access in mid-IR spectral range, narrow emission pure spectrum, and wide tuning capabilities have enabled to develop new-generation analyt...
We predict the spatial and angular Goos-Hänchen (GH) and Imbert-Fedorov (IF) shifts in partial (PR) and total internal reflection (TIR) conditions for fundamental Gaussian mode beams of a wide range of wavelength (400–1300 nm) impinging upon a graphene-coated dielectric surface. The GH and IF shifts turn out to be extremely dependent upon the chemi...
The book highlights recent developments in the field of spectroscopy by providing the readers with an updated and high-level of overview. The focus of this book is on the introduction to concepts of modern spectroscopic techniques, recent technological innovations in this field, and current examples of applications to molecules and materials releva...
We report the direct experimental evidence of the Goos–Hänchen (GH) shift in monolayer molybdenum disulphide (MoS2) for a Gaussian beam via the quantum weak measurement scheme. We demonstrate the dependence of the GH shift in monolayer MoS2 on the angle of incidence including the critical angle in the total internal reflection condition. We have al...
In recent times, the need for high-sensitive detection has grown drastically as more and more applications of molecular sensing are being explored. Cavity ring-down spectroscopy (CRDS) is one of the new age and robust techniques which has revolutionized the field of molecular detection, particularly gas-phase analysis. In this short review, we have...
Methane (CH4) and hydrogen sulfide (H2S) are two major trace molecules in exhaled air of IBS (Irritable Bowel Syndrome)-affected individuals. In this study, we have utilized a mid-IR continuous wave (cw) external cavity (EC)-quantum cascade laser (QCL) coupled cavity ring-down spectrometer (CRDS) for monitoring CH4 and H2S in exhaled air of human s...
In this paper, we measured the absolute line intensities and air broadening coefficients of several rotationally resolved lines in the P and R branches of the allowed (ν4+ν5)⁰ and forbidden (ν4+ν5)² vibrational combinational bands of C2H2 at room temperature 296K. These measurements were performed using an external-cavity quantum cascade laser (EC-...
Water, the major body fluid in humans, has four main naturally occurring isotopologues, H2¹⁶O, H2¹⁷O, H2¹⁸O and H²H16O (i.e. HD16O) with different masses. The underlying mechanisms of the isotope-specific water-metabolism in human gastrointestinal (GI) tract and respiratory system are largely unknown and remained illusive for several decades. Here,...
Measurements of high-resolution spectroscopic line parameters in the ν4 fundamental band of ¹³CH4 isotopomer of methane (CH4) occurring at 7.5 µm mid-IR spectral region are important for the studies of remote sensing of the Earth and planetary atmospheres at different conditions. Here, a continuous wave (cw) external-cavity quantum cascade laser (E...
We report on the development of a simple, linear optical cavity-based system combining evanescent wave (EW) with high-sensitive cavity ring-down spectroscopy (CRDS) technique using a diode laser at 644 nm and a right-angled prism for evanescent field generation on prism surface. We characterized the set-up in detail and achieved an optimum ring-dow...
The underlying mechanisms of the triple-oxygen (¹⁶O, ¹⁷O and ¹⁸O) isotopic content of deuterated (D) isotopologues of water in H-D exchange reactions in the gas-phase, yet remain elusive. Herein, we have demonstrated the high-resolution gas-phase spectral analysis of doubly (D2O) and singly (HDO) deuterated isotopologues of water in the region arou...
Cavity ring-down spectroscopy (CRDS) is a direct quantitative absorption technique that utilizes an enhanced light-matter interaction length inside a high-finesse optical resonator for ultrasensitive trace gas monitoring with high-spatial and temporal resolutions. The CRDS technique, first pioneered in 1988, has been evolved over the times to emerg...
The invention of quantum cascade laser (QCL) technology rejuvenates the spectroscopic monitoring of trace gas species providing an unprecedented access to the ‘molecular fingerprint region’ covering mid-infrared (mid-IR) spectral range of 3–25 μm. The recent technological advancements of QCL fulfil all the critical parameters as an ideal optical so...
The fine rotational-vibrational spectra of long-chain molecules like 1,3-butadiene are very closely spaced and highly overlapped. Such investigations require high-sensitive techniques to avoid overlapping and adequate resolution to observe their fine structure spectra. In this work, we have utilized a high-resolution external cavity-quantum cascade...
The simultaneous monitoring of three stable isotopes of hydrogen sulphide (H2S), i.e. H2³²S, H2³³S, and H2³⁴S, within a single laser scan of 0.4 cm⁻¹ has been achieved by means of a continuous-wave (cw) external-cavity quantum cascade laser (EC-QCL) coupled to high-resolution cavity ring-down spectroscopy (CRDS) near 7.5 μm. The measurement precisi...
We report the isotope selective diffusion of carbon dioxide (CO2) gas through large aspect ratio (length: diameter = 20:1) and porous one dimensional (1D) nanostructure of tungsten oxide (WO3). This novel effect was demonstrated in an ensemble of binary oxide, WO3 nanostructures with large surface area. When atmospheric CO2, which has two major sta...
The active Ni(II) centre of metalloenzyme urease forms a coordination with substrate urea prior to the hydrolysis of urea. The present study provided the direct experimental evidences of isotope preferential coordination between Ni(II) metal centre of urease enzyme and substrate urea, which eventually alters the product yield. Furthermore, in-vitro...
We have extensively studied Goos–Hänchen (GH) and Imbert–Fedorov (IF) shifts for reflection of a fundamental Gaussian beam using transfer matrix method. By considering a dielectric slab coated with monolayer of transition metal dichalcogenides (TMDC), we theoretically investigate the potential role of four different TMDC monolayers (WS2, WSe2, MoS2...
Over the past several decades, it has been generally believed that the microbial nitrification and denitrification are not significant processes in human gastrointestinal tract. Moreover, the underlying physiological link between exhaled nitrous oxide (N<sub>2</sub>O) and aerobic denitrification in the gastric environment is still largely unknown....
We report a detailed theoretical study of the Goos–Hänchen (GH) shift for a fundamental Gaussian beam on the surface coated with monolayer (ML) molybdenum disulfide (MoS2), a promising two-dimensional transition metal dichalcogenide (2D-TMDC) and a direct band-gap semiconductor. A general model has been developed to predict the GH shifts on ML-MoS2...
We report a room-temperature continuous-wave (cw) mode-hop-free (MHF) external-cavity quantum cascade laser (EC-QCL) based mid-infrared methane (CH4) sensor operating between 7.5 and 8 µm in the mid-IR molecular fingerprint region. We utilized the 2f-wavelength modulation spectroscopy (2f-WMS) for high sensitive monitoring of atmospheric CH4. The s...
Helicobacter pylori causes several gastrointestinal diseases and may also contribute to the development of type 2 diabetes (T2D). Several studies suggest that there might be a potential link between H. pylori infection and T2D, but it still remains the subject of debate. Here, we first report the cumulative effect of H. pylori infection and T2D by...
We demonstrate a mid-infrared detection strategy with 1f-normalized 2f-wavelength modulation spectroscopy (WMS-2f/1f) using a continuous wave (CW) external-cavity quantum cascade laser (EC-QCL) operating between 7.5 and 8 µm. The detailed performance of the WMS-2f/1f detection method was evaluated by making rotationally resolved measurements in the...
We report on the performance of a widely tunable continuous wave mode-hop-free external-cavity quantum cascade laser operating at λ ~ 5.2 µm combined with cavity ring-down spectroscopy (CRDS) technique for high-resolution molecular spectroscopy. The CRDS system has been utilized for simultaneous and molecule-specific detection of several environmen...
We investigated the l-type doubling in the (14²0) ← (02²0) weak hot band transition of carbonyl sulphide (OCS) for l = 2 (i.e. Δ state) vibrational state. High-resolution spectroscopic measurements of l-doublet splittings of OCS were carried out using cavity ring-down spectroscopy (CRDS) technique employing a continuous-wave (cw) external-cavity qu...
We report on the development of a mid-infrared cavity ring-down spectrometer (CRDS) coupled with a continuous wave (cw) external cavity quantum cascade laser (EC-QCL), operating between 6.0 μm to 6.3 μm, for high-resolution spectroscopic studies of ammonia (NH3) which served as a bench-mark molecule in this spectral region. We characterized the EC-...
The underlying mechanisms towards the progression of end-stage renal disease (ESRD) in chronic kidney disease (CKD) are poorly understood and it still remains a major clinical stumbling block for early detection of CKD. Most patients with CKD pass through ESRD with the necessity of frequent hemodialysis (HD) treatment. At present, plasma urea and c...
We developed a mid-infrared continuous-wave cavity ring-down spectroscopy technique coupled with an external-cavity mode-hop-free quantum cascade laser working at 7.5 μm. We, subsequently, tested the system by measuring 12CH4 and 13CH4 isotopes of methane (CH4).
We developed a cavity ring-down spectroscopy system utilizing a room-temperature, mode-hop-free, continuous wave external-cavity quantum cascade laser for high-resolution and high-sensitive molecular spectroscopic study of ammonia molecule in the spectral region covering 6.0-6.3 μm.
The oxygen-18 isotopic (¹⁸O) composition in CO2 provides important insight into the variation of rate in isotopic fractionation reaction regulated by carbonic anydrase (CA) metalloenzyme. This work aims to employ ¹⁸O-isotope ratio-based analytical method for quantitative estimation of CA activity in erythrocytes for clinical testing purposes. Here,...
A number of atmospheric pollutants and greenhouse gases have strong fundamental vibrational transitions within the spectral range of 7.5–8 µm, which marks the region as particularly important for trace gas sensing. Here, we report the development of a mid-infrared continuous-wave (cw) cavity ring-down spectroscopy (CRDS) technique coupled with an e...
Nitric oxide (NO) plays a key role in the development of peptic ulcer disease (PUD). Conversely, the gastric pathogen Helicobacter pylori colonizes the human stomach and contributes to the development of non-ulcer dyspepsia (NUD) and PUD. But, the underlying relation between molecular NO in exhaled breath and H. pylori associated NUD and PUD largel...
Urease, a metalloenzyme, requires carbon dioxide (CO2) for its activation. But, whether this activation is isotope-specific to ¹²CO2 or ¹³CO2, is not yet known and even the potential role of CO2 in the enzymatic activity of urease is poorly understood. Here, we provide direct experimental evidence that the catalytic activity of urease exhibits a un...
A new method to replace commercially prepared ¹³C-labelled glucose with naturally available ¹³C-enriched substrates could result in promotion of the clinical applicability of the isotopic breath test for detection of type 2 diabetes (T2D). Variation of the carbon-13 isotope in human breath depends on the ¹³C enrichment in the diet taken by subjects...
Nitrous oxide (N2O) is an important anthropogenic emitted greenhouse gas in the atmosphere that can contribute to the ozone destruction. Considering its environmental importance, the real-time monitoring and molecule-specific detection of atmospheric N2O with high sensitivity have received much attention in the 21st century. In this study, a widely...
The inability to envisage the acute onset and progression of type 1 diabetes (T1D) has been a major clinical stumbling block and an important area of biomedical research over the last few decades. Therefore there is a pressing need to develop a new and an effective strategy for early detection of T1D and to precisely distinguish T1D from type 2 dia...
The 13C-urea breath test (13C-UBT), developed a few decades ago, is widely used as a non-invasive diagnostic method to detect only the presence of the gastric pathogen Helicobacter pylori infection; however, the actual disease state, i.e. whether the person harbouring H. pylori has peptic ulcer disease (PUD) or non-ulcerous dyspepsia (NUD), is stil...
The gastric pathogen Helicobacter pylori utilizes molecular hydrogen (H2) as a respiratory substrate during colonization in the gastric mucosa. However, the link between molecular H2 and the pathogenesis of peptic-ulcer disease (PUD) and non-ulcerous dyspepsia (NUD) by the enzymatic activity of H. pylori still remains mostly unknown. Here we provid...
There is a pressing need to develop a novel early-detection strategy for the precise evolution of small intestinal bacterial overgrowth (SIBO) in irritable bowel syndrome (IBS) patients. The current method based on a hydrogen breath test (HBT) for the detection of SIBO is highly controversial. HBT has many limitations and drawbacks. It often fails...
A high-resolution cavity ring-down spectroscopic (CRDS) system based on a continuous wave (cw) mode-hop-free (MHF) external-cavity quantum cascade laser (EC-QCL) operating at λ∼5.2 μm has been developed for ultrasensitive detection of nitric oxide (NO). We report the performance of the high-resolution EC-QCL based cw-CRDS instrument by measuring th...
A residual gas analyzer (RGA) coupled with a high vacuum chamber has been explored to measure atmospheric CO2 entrapped in aminosilanes modified clay nanotubes. Ambient CO2 uptake efficacy together with stability of these novel adsorbents comprised of both primary and/or secondary amine sites, has been demonstrated at standard ambient temperature a...
New strategies for an accurate and early detection of insulin resistance are important to delay or prevent the acute onset of type 2 diabetes (T2D). Currently, insulin sensitivity index (ISI0,120) is considered to be a viable invasive method of whole-body insulin resistance for use in clinical settings in comparison with other invasive sensitivity...
The gastric pathogen Helicobacter pylori utilize glucose during metabolism, but the underlying mechanisms linking to oxygen-18 ((18)O) and carbon-13 ((13)C)-isotopic fractionations of breath CO2 during glucose metabolism are poorly understood. Using the excretion dynamics of (18)O/(16)O and (13)C/(12)C-isotope ratios of breath CO2, we found that in...
With the aim to capture and subsequent selective trapping of CO2, a nanocomposite has been developed through selective modification of the outer surface of the halloysite nanotubes (HNTs) with an organosilane to make the nanocomposite a novel solid-phase adsorbent to adsorb CO2 from the atmosphere at standard ambient temperature and pressure. The p...
Carbonic anhydrase (CA), a well-characterized metalloenzyme, is associated with oxygen-18 ( (18)O)-isotopic fractionations of CO2. To investigate how CA activity links the (18)O of breath CO2 to pre-diabetes (PD) and type 2 diabetes (T2D) during metabolism, we studied pre- and post-dose CA activities in erythrocytes with simultaneous monitoring of...
We report for the first time the time-dependent excretion kinetics of 18O/16O isotope ratios of CO2 in exhaled breath samples using an optical cavity-enhanced integrated cavity output spectroscopy (ICOS) method for the detection of Helicobacter pylori (H. pylori) infection in human stomach. We observed the large differences of the oxygen-18 isotopi...
