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Digambara Patra

Publications and source records attributed to Digambara Patra.

9 recordsLinked to original sources
PubMed2005

Performance of fluorescence correlation spectroscopy for measuring diffusion and concentration.

Fluorescence correlation spectroscopy (FCS) has become an important tool for measuring diffusion, concentration, and molecular interactions of cellular components. The interpretation of FCS data critically depends on the measurement set-up. Here, we present a rigorous theory of FCS based on exact wave-optical calculations. Six of the most important optical and photophysical factors that influence FCS are studied: fluorescence anisotropy, cover-slide thickness, refractive index of the sample, laser-beam geometry, optical saturation, and pinhole adjustment. Our theoretical framework represents a general attempt to link all relevant parameters of the experimental set-up with the measured correlation function.

Diffusion↗
PubMed2005

Optical saturation in fluorescence correlation spectroscopy under continuous-wave and pulsed excitation.

A detailed theoretical and experimental study of the dependence of fluorescence correlation measurements on optical excitation power due to optical saturation effects is presented. It is shown that the sensitivity of a fluorescence correlation measurement on excitation power becomes increasingly stronger for decreasing excitation power. This makes exact measurements or diffusion coefficients with fluorescence correlation spectroscopy rather difficult. A strong difference of this behavior for continuous-wave and pulsed excitation is found.

Journal Article↗
PubMed2005

Statistical analysis of diffusion coefficient determination by fluorescence correlation spectroscopy.

Fluorescence correlation spectroscopy (FCS) has become an important and widely used technique for many applications in physics, chemistry, and biology. The parameter most frequently addressed by FCS is the diffusion of molecules in solution. Due to the highly non-linear connection between the diffusion coefficient and a measured autocorrelation function, it is extremely difficult to analyse the accuracy of the diffusion-coefficient determination in a FCS experiment. Here, we present a simplified analysis based on some general maximum-likelihood considerations, and numerical result are given for the dependence of the accuracy of the diffusion-coefficient determination on sample concentration, brightness, and measurement time. Optimal concentration values for performing FCS are found.

Journal Article↗
PubMed2004

Fluorescence lifetimes and emission patterns probe the 3D orientation of the emitting chromophore in a multichromophoric system.

In this Communication, we report on the fluorescence behavior of an individual first generation multichromophoric dendrimer. The fact that each of the chromophores in time acts as a fluorescent trap is demonstrated by directly probing the dipole orientation of the emitting chromophore by means of defocused wide-field imaging and comparing experimental and calculated emission patterns. It is shown that in such cases the electromagnetic boundary condition effect results in discrete changes in the fluorescence lifetime as a function of time for individual dendrimers.

Journal Article↗
PubMed2004

Art and artefacts of fluorescence correlation spectroscopy.

Fluorescence correlation spectroscopy (FCS) is an important technique for studying low concentrations of analyte molecules in solution. The core molecular characteristic that can be addressed by FCS is the translational diffusion coefficient of the analyte molecules, which can be used for i.e. studying molecular binding and reactions, or conformational changes of macromolecules. The present paper discusses several possible optical and photophysical effects that can influence the outcome of a FCS measurement and thus can bias the value of the derived diffusion coefficient.

Artifacts↗
PubMed2002

Total synchronous fluorescence scan spectra of petroleum products.

Extending the two-dimensional synchronous fluorescence scan to a three-dimensional total synchronous fluorescence scan (TSFS) spectral measurement gives the total synchronous fluorescence characteristics of a multifluorophoric sample at various possible wavelength intervals (Deltalambda), which could help to characterize multifluorophoric systems better. TSFS spectra of petroleum products such as diesel, kerosene, petrol, engine oil etc., available in the Indian market, are reported. Fluorescence in these samples is due to the presence of polycyclic aromatic hydrocarbons (PAHs) of various ring sizes. The TSFS contour plot profiles of the neat samples measured at right-angle geometry is a result of various energy-degrading photophysical processes such as inner filter effect, light attenuation, resonance energy transfer, collisional quenching etc. TSFS plots make it easy to obtain the optimized Deltalambda of an unknown sample of analytical interest. TSFS and the excitation-emission matrix (EEM) techniques are similar, but the contour profiles generated are different. The response of the TSFS contour profiles to dilution is different from that in the EEM contour profiles. Thus, TSFS can provide an alternative way of presenting the fluorescence response of concentrated multifluorophoric samples.

Fuel Oils↗
PubMedDate not supplied

Simple luminescence method for estimation of benzo[a]pyrene in a complex mixture of polycyclic aromatic hydrocarbons without a pre-separation procedure.

Benzo[a]pyrene causes cancer at cellular level and is widely present in the environment. Conventional spectroscopic methods for analysis of this compound need a pre-separation procedure due to severe spectral overlap from other polycyclic aromatic hydrocarbons. We report a simple method that avoids spectral overlap of benzo[a]pyrene from other impurities or polycyclic aromatic hydrocarbons (PAHs), thus it can easily identify benzo[a]pyrene in a complex PAH mixture. The method could easily identify benzo[a]pyrene in an 18-component PAH mixture. Calibration plots in methanol solution and in micellar media show a good linearity (R > 0.9997) in the benzo[a]pyrene concentration range generally found in the environment. The method gives a detection limit of 1.52 x 10(-9) mol/L in CTAB micellar medium and 2.55 x 10(-9) mol/L in methanol solution. The proposed method is selective, sensitive and fast. The fluorescence response of benzo[a]pyrene is found to be a potential candidate to sense the critical micellar concentration (CMC) of CTAB micelles.

Algorithms↗
PubMedDate not supplied

Investigation of polar and stereoelectronic effects on pure excited-state hydrogen atom abstractions from phenols and alkylbenzenes.

The fluorescence quenching of singlet-excited 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) by 22 phenols and 12 alkylbenzenes has been investigated. Quenching rate constants in acetonitrile are in the range of 10(8)-10(9) M(-1)s(-1) for phenols and 10(5)-10(6) M(-1)s(-1) for alkylbenzenes. In contrast to the quenching of triplet-excited benzophenone, no exciplexes are involved, so that a pure hydrogen atom transfer is proposed as quenching mechanism. This is supported by (1) pronounced deuterium isotope effects (kH/kD ca 4-6), which were observed for phenols and alkylbenzenes, and (2) a strongly endergonic thermodynamics for charge transfer processes (electron transfer, exciplex formation). In the case of phenols, linear free energy relationships applied, which led to a reaction constant of rho = -0.40, suggesting a lower electrophilicity of singlet-excited DBO than that of triplet-excited ketones and alkoxyl radicals. The reactivity of singlet-excited DBO exposes statistical, steric, polar and stereoelectronic effects on the hydrogen atom abstraction process in the absence of complications because of competitive exciplex formation.

Journal Article↗