Single Photon Counting Technique Research Articles

Peering into cloud physics using ultra-fine resolution radar and lidar systems

Abstract Cloud microphysical processes, such as droplet activation, condensational growth, and collisional growth, play a central role in the evolution of clouds and precipitation. Accurate representations of these processes in numerical models are challenging partially due to incomplete understanding of them at the process-level arising from limited systematic observations. Most surface-based active remote sensors, including today’s operational cloud radars and lidars, have a resolution on the order of tens of meters. This resolution is insufficient to resolve cloud microphysical processes that manifest at finer (meter and sub-meter) scales. A new set of ultra-high-resolution ground-based radar and lidar systems have been developed to address this observational gap. The newly developed 94-GHz cloud radar has a range resolution down to 2.8 m, or a factor of 10 finer than typical radars, using a large bandwidth and quadratic phase coding techniques. The lidar has a range resolution down to 10 cm, or a factor of 100 finer than typical lidars, using a time-gated time-correlated single photon counting technique. Such high-resolution observations were previously only achievable through in situ aircraft measurements. Even then, aircraft measurements do not permit continuous long-term cloud observation as is possible with ground-based remote sensing instruments. In this study, the first-light cloud observations from the new radar and lidar systems are shown to reveal detailed cloud structures that conventional sensors could only perceive in a bulk sense, thus providing new avenues to investigate cloud microphysical processes and their impact on weather and climate.

Bismuth (Bi3+) based lead-free halide perovskitoid for light driven applications: A potential low-toxic alternative for lead (Pb2+)

Bismuth-based perovskite-like materials are recognised as feasible optoelectronic alternatives to lead-based perovskites. High toxicity and limited environmental stability of Pb-based perovskite are the principal hurdles for their practical use, whereas Bismuth (Bi3+) based materials exhibit relatively low toxicity. In this study, we fabricated (FPEA)BiI4 (FPEA = Fluorophenylethyl amine, as a hydrophobic aromatic spacer) and explored its compatibility in the field of photocatalysis and solar cells. UV–Vis, photoluminescence (PL) and time-correlated single photon counting (TCSPC) techniques were used to understand the optoelectronic properties of the material. These fabricated thin films were used towards toxic MBT remediation. Solar cells (in n-i-p configuration) were also fabricated using (FPEA)BiI4 and their photo conversion efficiency (PCE) was tested under AM1.5 illumination.

Quantifying distortion in time-correlated single photon counting: a universal parameter.

One major drawback of the classic time-correlated single photon counting (TCSPC) technique is pileup-related distortion. To keep it under a reasonable level, the maximum count rate has to be reduced, posing a serious limitation to the overall measurement speed. This means that there is an intrinsic trade-off between speed and distortion: either count rate is raised, but distortion is worsened, or distortion is minimized at the expense of speed. In both cases, it is impossible to precisely evaluate the degree of distortion introduced. Here comes our new, to the best of our knowledge, figure of merit, which is able to provide a numerical estimate of the distortion whatever the signal shape is, marking a real turning point in the way of doing TCSPC. In this article, this new parameter will be defined and its effectiveness will be demonstrated by means of mathematical computations.

Two-photon excited luminescence of sulfur quantum dots for heavy metal ion detection.

Spectrally-resolved third-order nonlinear optical properties of water-dispersed sulfur quantum dots (SQDs) were investigated in the wavelength range from 740 nm to 820 nm with the two-photon excited emission technique using a tunable femtosecond laser system. The maximum value of the two-photon absorption (TPA) cross-section (σ2) for ∼5.4 nm size SQDs was found to be 185 GM (Goeppert-Mayer unit), while the two-photon brightness (σ2 × η) was found to be 1.5 GM at 780 nm, the wavelength being in the first biological transmittance window. The TPA properties are presented here as appropriate cross-sections normalized per molecular weight which enables meaningful comparison of the nonlinear factors of the studied quantum dots with those of various nanomaterials. The optimized TPA properties of these hydrophilic colloidal SQDs may be potentially useful for detection of Fe3+ metal ions. The experimentally determined limit of Fe3+ detection for both one- and two-photon regime was 10 μmol L-1 (0.6 μg mL-1). Förster resonance energy transfer between SQDs as donors and Fe3+ metal ions as acceptors was confirmed as one of the possible detection mechanisms using a time-correlated single photon counting technique.

Modulation of excimer formation and photostability of avobenzone inside the nanocavities of cyclodextrins

Avobenzone (AVZ), a UVA filter, is extensively used in sunscreen lotion and protects the skin from harmful UVA radiation. Despite their importance in sunscreen formulation, less attention has been given to its light induced excited state properties. Herein, we have explored the photophysical properties of AVZ in aqueous solutions and cyclodextrins (CDs) complexes by employing steady-state, time-resolved fluorescence, and molecular modelling tools followed by photostability analysis. AVZ exhibits dual emission from monomer and excimer forms in aqueous solutions. Spectroscopic studies revealed that AVZ forms multiple inclusion complexes with β-CD and γ-CD depending upon the host’s cavity size. These versatile host–guest complexes resulted in the modulation of the excimer formation of AVZ. The presence of α-CD and β-CD complexes with AVZ inhibited the excimer forms. In contrast, γ-CD facilitated excimer formation because its larger cavity could encapsulate the AVZ dimer. Stoichiometry and association constants for multiple host–guest complexes were determined using Benesi-Hildebrand (BH) plot. Job’s plot was used to confirm the stoichiometry of complexes. Time correlated single photon counting (TCSPC) technique was used to depict the excited state lifetime values of AVZ:CD inclusion complexes. Furthermore, these inclusion complexes were characterized by Fourier transform-infrared (FT-IR) spectroscopy, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Molecular docking followed by semiempirical calculations confirm the experimental results on stoichiometries and binding constants of host–guest complexes. UV light-induced absorption kinetics revealed that the photostability of AVZ inside the β-CD cavity is much better than other inclusion complexes of CDs. Overall, the present study helps us in further understanding of excited state behavior of AVZ inside hydrophobic nanocavities.

Pulse-sampling fluorescence lifetime imaging: evaluation of photon economy.

This Letter presents an experimental study comparing the photon rate and photon economy of pulse sampling fluorescence lifetime imaging (PS-FLIm) with the conventional time-correlated single photon counting (TCSPC) technique. We found that PS-FLIm has a significantly higher photon detection rate (200 MHz) compared with TCSPC (2-8 MHz) but lower photon economy (4-5 versus 1-1.3). The main factor contributing to the lower photon economy in PS-FLIm is laser pulse variability. These results demonstrate that PS-FLIm offers 25× faster imaging speed than TCSPC while maintaining room light rejection in clinical settings. This makes PS-FLIm a robust technique for clinical applications.

Photoluminescence of high energy xenon ion irradiated magnesium aluminate spinel single crystals

Laser confocal microscopy technique (60 ps laser pulse excitation at 445 nm) and a time-correlated single photon counting (TCSPC) technique have been used to study the photoluminescence (PL) in 152 MeV Xe ion irradiated MgAl2O4 single crystals. It was shown that radiation defects produced by swift xenon ions give rise to broad luminescence band positioned in the 470–800 nm wavelength range. The measurements of the PL decay curves have evidenced that lifetime of defect-related PL signal gradually increases from 6 to 10 ns in 500–620 nm spectral range and decreases with ion fluence increasing. The decrease of the luminescence intensity observed after fluences ∼1013 cm−2 is attributed to overlapping of individual ion track core regions.

Exploring novel and fast stability or sameness evaluation tool for different categories of injectable formulations

The establishment of drug product stability and sameness is the heart of generic formulation development. For regulatory filing, various instrumental methods are used on a case basis to establish the generic and innovator product sameness in multiple aspects. Here in the present study, we explored the applicability of the Time-correlated single photon counting (TCS-PC) technique as a fast, reliable, and nondestructive method for establishing the sameness of three different categories of injectable formulations, namely, Amphotericin B liposome for injection, enoxaparin injection, and iron sucrose injection. All three category formulations were evaluated in their native and artificially induced post degradation state to identify the discrimination power of the used instrumental techniques. The degradation of materials were confirmed by high performance liquid chromatography (HPLC). Based on the product category, pre and post-degradation samples were evaluated by selective instrumental methods like differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), fluorescence spectroscopy, particle size analysis by dynamic light scattering (DLS), small angle X-ray scattering (SAXS), Raman spectroscopy, inductively coupled plasma optical-emission spectrometry (ICP-OES) and circular dichroism study. All pre and post-degradation samples were further analyzed by TCS-PC. We observed that, TCS-PC can identify the differences between the initial and post degradation samples in very less time with promising discrimination power across the different injectable formulation types. Thus TCS-PC can be used as a fast and promising stability or sameness evaluation tool for different injectable drug products.

Detection of high-frequency gravitational waves using high-energy pulsed lasers

We propose a new method for detecting high-frequency gravitational waves (GWs) using high-energy pulsed lasers. Through the inverse Gertsenshtein effect, the interaction between a GW and the laser beam results in the creation of an electromagnetic signal. The latter can be detected using single-photon counting techniques. We compute the minimal strain of a detectable GW which only depends on the laser parameters. We find that a resonance occurs in this process when the frequency of the GW is twice the frequency of the laser. With this method, the frequency range 1013–1019 Hz is explored non-continuously for strains for current laser systems and can be extended to with future generation facilities.

Strong localization and suppression of Anderson modes in an asymmetrical optical waveguide.

In this paper, transverse Anderson localization of light waves in a 3D random network is achieved inside an asymmetrical type optical waveguide, formed within a fused-silica fiber by capillary process. Scattering waveguide medium originates from naturally formed air inclusions and Ag nanoparticles in rhodamine dye doped-phenol solution. Multimode photon localization is controlled by changing the degree of the disorder in the optical waveguide to suppress unwanted extra modes and obtain only one targeted strongly localized single optical mode confinement at the desired emission wavelength of the dye molecules. Additionally, the fluorescence dynamics of the dye molecules coupled into the Anderson localized modes in the disordered optical media are analyzed through time resolved experiments based on a single photon counting technique. The radiative decay rate of the dye molecules is observed to be enhanced up to a factor of about 10.1 through coupling into the specific Anderson localized cavity within the optical waveguide, providing a milestone for investigation of transverse Anderson localization of light waves in 3D disordered media to manipulate light-matter interaction.

Real time reconstruction of the fast electron spectrum from high intensity laser plasma interaction using gamma counting technique

X-ray and gamma fluxes from the high intensity laser-plasma interaction are extremely short, well beyond temporal resolution of any detectors. If laser pulses come repetitively, the single photon counting technique allows to accumulate the photon spectra, however, its relation to the spectrum of the initial fast electron population in plasma is not straightforward. We present efficient and fast approach based on the Geant4 package that significantly reduces computer time needed to re-construct the high energy tail of electron spectrum from experimental data accounting for the pileup effect. Here, we first tabulate gamma spectrum from monoenergetic electron bunches of different energy for a given experimental setup, and then compose the simulated spectrum. To account for the pileups, we derive analytical formula to reverse the data. We also consider errors coming from the approximation of the initial electron spectrum by the sum of monoenergetic impacts, the finite range of the electron spectrum, etc. and give estimates on how to choose modelling parameters to minimize the approximation errors. Finally, we present an example of the experimental data treatment for the case of laser-solid interaction using 50 fs laser pulse with intensity above 1018 W/cm2.

Quantifying the interactions of micellar drug delivery system components with albumin using time-resolved fluorescent methods.

The least requirement for the bioavailability of an active pharmaceutical ingredient (API) is its solubility in aqueous media. The solubilization of poorly soluble drugs is one of the key challenges of drug formulation development. Micellar drug delivery systems (MM-DDS) are efficient in solubilizing such APIs, are well tolerated by patients upon administration, are cost efficient and easy to produce. However, the number of marketed drugs is very limited. One problem identified by a reflection paper on this topic by the European Medicines Agency (EMA) is the number of different transformations of MM-DDS upon dilution by intravenous administration. The release of an API from MM-DDS and its subsequent binding to plasma proteins such as human serum albumin (HSA) determines the fate of the API in a human body. Tracking and characterization of such binding processes in a multicomponent system opens the door to understanding the drug - blood-components interaction. In this project we develop a label free time-resolved fluorescence tracking method to investigate the interaction of small molecules (API, MM-DDS components) with albumin. In detail, the data is collected using a time-correlated single-photon counting (TCSPC) technique at 280-nm excitation. Quenching of tryptophan fluorescence through Förster resonance energy transfer (FRET) to an API reveals information about the binding process. Affinity constants and stoichiometry can be obtained by global fitting of the titration curves and confirmed by the means of support plane analysis.

Unusual similarity of DNA solvation dynamics in high-salinity crowding with divalent cations of varying concentrations.

Double-stranded DNA bears the highest linear negative charge density (2e- per base-pair) among all biopolymers, leading to strong interactions with cations and dipolar water, resulting in the formation of a dense 'condensation layer' around DNA. Interactions involving proteins and ligands binding to DNA are primarily governed by strong electrostatic forces. Increased salt concentrations impede such electrostatic interactions - a situation that prevails in oceanic species due to their cytoplasm being enriched with salts. Nevertheless, how these interactions' dynamics are affected in crowded hypersaline environments remains largely unexplored. Here, we employ steady-state and time-resolved fluorescence Stokes shifts (TRFSS) of a DNA-bound ligand (DAPI) to investigate the static and dynamic solvation properties of DNA in the presence of two divalent cations, magnesium (Mg2+), and calcium (Ca2+) at varying high to very-high concentrations of 0.15 M, 1 M and 2 M. We compare the results to those obtained in physiological concentrations (0.15 M) of monovalent Na+ ions. Combining data from fluorescence femtosecond optical gating (FOG) and time-correlated single photon counting (TCSPC) techniques, dynamic fluorescence Stokes shifts in DNA are analysed over a broad range of time-scales, from 100 fs to 10 ns. We find that while divalent cation crowding strongly influences the DNA stability and ligand binding affinity to DNA, the dynamics of DNA solvation remain remarkably similar across a broad range of five decades in time, even in a high-salinity crowded environment with divalent cations, as compared to the physiological concentration of the Na+ ion. Steady-state and time-resolved data of the DNA-groove-bound ligand are seemingly unaffected by ion-crowding in hypersaline solution, possibly due to ions being mostly displaced by the DNA-bound ligand. Furthermore, the dynamic coupling of cations with nearby water may possibly contribute to a net-neutral effect on the overall collective solvation dynamics in DNA, owing to the strong anti-correlation of their electrostatic interaction energy fluctuations. Such dynamic scenarios may persist within the cellular environment of marine life and other biological cells that experience hypersaline conditions.

Structural isomerism induces pH dependent AIE-coupled ESIPT: an in-depth spectroscopic exploration with application in amine vapor sensing.

A novel excited state intramolecular proton transfer probe 3-(benzo[d]thiazol-2-yl)-4-hydroxy-5-methoxybenzaldehyde (3BTHMB) was synthesized and characterized using NMR, ESIMS and single crystal diffraction studies. The steady state and time resolved studies using the time correlated single photon counting (TCSPC) technique revealed that 3BTHMB shows ESIPT reaction with a time constant of 0.10-0.15 ns and longer local emission and anion emissions of time constants 0.5-2.0 ns and 3.0-4.0 ns, respectively, that co-exist in polar solution. In a polar protic solution like methanol, the ESIPT process is damped. Interestingly, 3BTHMB shows aggregation induced emission (AIE) solely in an acidic environment, evidenced by the enhanced quantum yield of emission (∼35%) in acidic solution as well as a long lifetime component of 7.4 ns that corresponds to the lifetime in the solid state. The AIE phenomenon was explored using the DLS technique where enhancement of the hydrodynamic radius in an acidic medium was observed. The judicious positioning of the formyl group in 3BTHMB gives the mentioned probe to show AIE in an acidic medium, as opposed to its previously reported structural isomer BTHMB, which showed no AIE phenomenon as well as its parent molecule 2-(benzo[d]thiazol-2-yl)-6-methoxyphenol (TMP), which showed AIE in neutral pH. The AIE property of 3BTHMB was exploited by successful and rapid detection of amine vapor in the solid state, qualitative ratiometric detection of aqueous pH, by observing the colour change under UV light in acidic (yellow-green) and basic to neutral (blue) medium. The above results pave the way for multiutility fluorescent probes for environmental purposes along with a deep understanding of the underlying photophysical processes which bestow the probes with such outstanding utilities.

Fluorescence Anisotropy in Radachlorin and Chlorin e6 in Water–Methanol Solutions under One- and Two-Photon Excitation

The fluorescence anisotropy of photosensitizers Radachlorin and chlorin e6 was studied using the time-resolved single photon-counting technique under one- and two-photon excitation within the Soret absorption band. A very small negative anisotropy was observed in both photosensitizers under one-photon excitation in the vicinity of the absorption maximum within the wavelength range of 395–405 nm. Meanwhile, two-photon excitation of the photosensitizers in the same spectral range demonstrated high fluorescence anisotropy with the maximum value of about 0.43. The drastic difference of the fluorescence anisotropy parameters at one- and two-photon excitation modes was suggested to be due to the different symmetries of one- and two-photon absorption tensors when two-photon absorption tensor components have comparable values. The variation of excitation wavelengths in the spectral range of 375–425 nm demonstrated nonlinear wavelength dependence of anisotropy of both Radachlorin and chlorin e6, with opposite tendencies at one- and two-photon excitation. The data obtained suggest that one-photon excitation at about 405 nm often utilized in FLIM experiments is not sensitive to fluorescence anisotropy in Radachlorin and chlorin e6 and therefore cannot be used for the determination of anisotropy/rotational diffusion time in these molecules. Meanwhile, two-photon excitation can provide high fluorescence anisotropy and accurate determination of the rotational diffusion time. At the same time, one-photon excitation at about 405 nm can be used for the accurate evaluation of fluorescence lifetimes within the standard FLIM schematic where fluorescence polarization is not taken into account.

Assessing the impact of increase in the number of hydroxyl groups on the microscopic behaviors of ammonium-based room temperature ionic liquids: A combined fluorescence up-conversion, fluorescence correlation and NMR spectroscopic study

The current study aims to understand the impact of variation of number of hydroxyl groups on the cationic head of ammonium-based room temperature ionic liquids (RTILs) towards inter/intra molecular hydrogen bonding interaction, local structural organization and dynamics of the solvent systems. For this purpose, three hydroxyl functionalized ammonium based RTILs (HFILs) bearing different numbers of hydroxyl groups on the cationic head as well as a non-hydroxyl ammonium based RTIL have been examined using both ensembled average and single-molecule spectroscopy techniques. Investigation of solvent relaxation dynamics of all the concerned RTILs by the combination of femto-second fluorescence up-conversion techniques and time corelated single photon counting techniques reveals a bimodal solvent relaxation behaviour having a very fast sub-picosecond and a relatively slower picosecond to nanosecond solvation time component for all the RTILs. Interestingly, analysis of the rotational and translational diffusion dynamics of a few particular solutes shows that the solvent–solvent interaction in the poly-hydroxyl-based HFILs is substantially stronger than the solute–solvent interaction. Additionally, analysis of the rotational diffusion data reveals that all RTILs exhibit significant dynamic heterogeneity, which increases with increase the number of hydroxyl groups on the cationic head of HFILs. Moreover, PFG-NMR study have shown that the HFILs had considerably greater hydrodynamic radii than the non-hydroxyl RTILs, which is likely due to the result of stronger hydrogen bonding interaction between the hydroxyl groups and the constituent of the HFILs. The outcomes of all these investigations have essentially demonstrated that subsequent addition of hydroxyl functionalities to the cationic head of the RTILs significantly alter the intra/inter molecular interaction, local structural organisation and heterogeneity of the medium.

Effect of Zn2+ on emodin molecules studied by time-resolved fluorescence spectroscopy and quantum chemical calculations

Emodin is a natural drug for treating neurodegenerative diseases and plays a vital role in the mitigation of nerve damage. Metal ions can modify the drug properties of emodin, where Zn2+ can synergize with the emodin molecule and enhance the drug effect of emodin. Besides, complex changes can be observed in the fluorescence intensity and fluorescence lifetime of the emodin molecule as the concentration of Zn2+ increases. Herein, the synergistic effects of ligand structural in Zn(II)-Emodin complexes and the electronic effects of metal elements on the antioxidant properties of the complexes are discussed in detail based on UV–vis absorption spectroscopy, fluorescence spectroscopy, time-correlated single photon counting (TCSPC) technique and quantum chemical calculations at the B3LYP/6-31G(d) level. The experimental results confirm that Zn2+ can coordinate with the hydroxyl groups on the emodin to make the molecule structure more rigid, thus inhibiting the non-radiative processes such as high-frequency vibrations of the emodin molecule in solution. The suppression of non-radiative processes leads to an increase in the average fluorescence lifetime of the emodin molecule, and finally results in the enhanced fluorescence intensity. The chemical softness of Zn(II)-Emodin is then confirmed to be higher than that of emodin by Gaussian calculations, indicating its higher chemical reactivity and lower stability. The stronger electron donating ability of Zn(II)-Emodin compared to emodin may explain the higher antioxidant activity of Zn(II)-Emodin, which gives it a stronger pharmacological activity. The results of this study show that emodin can well complex with Zn2+ to remove excess Zn2+ in human body and the resulting complex has better antioxidant properties, which helps to understand the role of Zn2+ in drug-metal coordination and provides guidance for the design of new drugs.

Spectral and kinetic properties of silver sulfide quantum dots in an external electric field

The effect of an external electric field on the luminescence characteristics of silver sulfide nanoparticles embedded in a film based on an optically passive dielectric matrix has been studied. The luminescence characteristics were studied using methods of optical and time-resolved spectroscopy involving the time-correlated single-photon counting technique. The morphology of the nanoparticles was studied using transmission electron microscopy. It was shown that in an external electric field, an increase in the intensity of the recombination luminescence band is observed for silver sulfide nanoparticles, together with an increase in the electronic relaxation rate. This effect is explained by the fact that the electric field enhances the transport of free holes to electron traps which are radiative recombination centers. The observed effects indicate that silver sulfide nanoparticles can be effectively used as active layers of organic light-emitting diodes, where an external field of the order of 500 kV/cm will not lead to a deterioration in their operating luminescence characteristics.

Temperature-dependent ultrafast solvation dynamics of choline chloride-based deep eutectic solvent (DES) and hydroxyl functionalized room temperature ionic liquids (RTILs): Exploring the difference in solvent response between DES and RTILs

The present study aims to provide a comprehensive understanding of the difference in solvent relaxation behavior between DESs and RTILs. For this purpose, dynamics of solvation have been investigated in a choline chloride-based DES and three hydroxyls functionalized ILs, keeping the hydroxyl functionalities same in both classes of media, so that the role of various inter/intra molecular interactions, including hydrogen bonding interaction on the solvent relaxation behavior can be understood. Fluorescence up-conversion spectroscopy (FLUPS) techniques coupled with time-correlated single-photon counting (TCSPC) techniques have been exploited to study the complete Stokes shift dynamics of a dipolar probe, coumarin 153 (C153) dissolved in these media. The solvent response functions generated from the complete dynamic Stokes shift data reveal a bimodal solvent relaxation behaviour having a very fast sub-picosecond and a relatively slower picosecond to sub-nanosecond solvation time component for both DES and hydroxyl ILs. The relatively slower solvation time component, which correlates with bulk viscosity of the concerned medium, is found to arise due to the diffusional motion of the constituents of both DES and hydroxyl ILs. However, temperature-dependent solvent relaxation measurements have revealed that at nearly isoviscous conditions, the solvent relaxation is much faster in the DES as compared to that in hydroxyl IL indicating the differences in solvent relaxation behaviour at the later part of the solvent response. Interestingly, when the early part of the dynamics is monitored, the amplitude associated with the ultrafast component for the DES increases significantly with the increase in temperature, whereas the same remains almost unchanged for the hydroxyl IL. This essentially indicates that even at shorter time scale, the process of solvent relaxation is considerably different for both DES and hydroxyl ILs. All these investigations have essentially demonstrated that despite having similar functionalities, different motions related to the solvent relaxation, operating at microscopic level in both these classes of solvents, are significantly different from each other.

Spectroscopic analysis to identify the binding site for Rifampicin on Bovine Serum Albumin

This article reports the interaction of rifampicin, one of the important antituberculosis drugs, with Bovine Serum Albumin (BSA). Herein, we have monitored the fluorescence properties of tryptophan (Trp) residue in BSA to understand the interactions between protein and rifampicin. Fluorescence intensity of BSA was quenched tremendously upon interacting with the drug. Using steady state and time-resolved spectroscopic tools the static and dynamic nature of quenching have been characterised. Time correlated single photon counting technique confirmed that out of two lifetime components ∼6.2 ns and ∼2.8 ns of BSA, the rifampicin has affected only the shorter lifetime component a lot that was assigned to Trp-213 residue. Hence, it was thought that the drug must have been located near to the amino acid residue. Molecular docking studies have revealed the structural information of drug-protein complex which supported the above conjecture, confirming the nearest tryptophan as Trp-213 to the complexing rifampicin molecule.