Ashok Kumar Mishra
Other affiliations: University of California, San Diego, Dr. Shakuntala Misra National Rehabilitation University, Gunma University ...read more
Bio: Ashok Kumar Mishra is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Quenching (fluorescence) & Excited state. The author has an hindex of 33, co-authored 220 publications receiving 3915 citations. Previous affiliations of Ashok Kumar Mishra include University of California, San Diego & Dr. Shakuntala Misra National Rehabilitation University.
Papers published on a yearly basis
TL;DR: A review of synchronous fluorescence scan (SFS) methods for analysis of multi-component systems can be found in this paper, where the authors discuss the use of SFS in the analysis of complex multichannel mixtures.
Abstract: The ability to analyse complex multi-component mixtures without resorting to tedious separation procedures is extremely useful for routine analysis. Single-wavelength fluorescence measurement is limited in its ability to analyse complicated multi-component samples when they have severely overlapping emission and/or excitation spectra. This can be overcome by using synchronous fluorescence scan (SFS), where overlapping of spectra can be minimized. The selectivity of SFS can still be increased by taking derivative spectrum, applying different multivariate methods, selective fluorescence quenching, three-dimensional synchronous measurement or using some of these procedures in combination. Recent developments in various synchronous fluorescence methods for analysis of multi-component systems are discussed in this review.
TL;DR: In this paper, three aspects of inner filter effect (IFE) in fluorescence spectroscopy are discussed, and the strategy for exclusive inclusion of IFE and IFE induced CDRS as characteristics of the system for development of fluorescence based assay, towards maximizing fluorescence sensitivity of optically dense multi-fluorophoric systems, have been discussed.
Abstract: This article discusses three aspects of inner filter effect (IFE) in fluorescence spectroscopy. (i) First, IFE as undesirable in fluorescence measurements: IFE results in non-linear fluorescence response of the analyte under study and it has been verified that IFE cannot be eliminated; it can either be minimized or corrected for intensity loss. Over the years, researchers have proposed many intensity correction methods to avoid IFE related issues. Often analysts using fluorescence spectroscopy, knowingly or unknowingly, ignore IFE or use an inappropriate intensity correction method. Herein, we have highlighted the basis and significances of various correction models that are proposed since 1970s to till date. (ii) Second, IFE mediated concentration dependent red shift (CDRS) as an analytical tool: the conventional fluorescence measurements and IFE correction strategies cannot be applied in analysis of optically dense multi-fluorophoric samples like oils, petrochemicals, biological samples and food samples etc. The strategy for exclusive inclusion of IFE and IFE induced CDRS as characteristics of the system for development of fluorescence based assay, towards maximizing fluorescence sensitivity of optically dense multi-fluorophoric systems, have been discussed. (iii) Third, IFE based sensing: when the sample contains chromophores, which absorb either at the excitation or at the emission wavelength range of the fluorophore, then the chromophores act as a filter. Thus tuning either the absorber or fluorophore concentration will lead to development of fluorescence based assay for a selective analyte. Principles and protocols are described to identify whether a sensing event is due to IFE or any other fluorescence mechanism. Additionally, a brief description is given on advanced findings and progresses made in sensing of for various classes of analytes in the recent past, using IFE concept. The second and third aspect combined together serve as a tool towards enhancing sensitivity of fluorescence measurement.
TL;DR: A new method involving SA as fluorescence-enhancing reagent for estimation of BRD in aqueous samples has been suggested, and selective excitation of tryptophan residue results in emission from bromadiolone, thereby indicating a Förster type energy transfer from Trp to BRD.
Abstract: Bromadiolone (BRD), a substituted 4-hydroxycoumarin derivative, is known to possess anti-coagulant activity with acute toxicity. In this paper, we report a study on the interaction of bromadiolone with the plasma proteins bovine serum albumin (BSA) and human serum albumin (HSA), using the intrinsic fluorescence emission properties of bromadiolone. Bromadiolone is weakly fluorescent in aqueous buffer medium, with an emission at 397 nm. Binding of bromadiolone with serum albumins (SA) leads to a marked enhancement in the fluorescence emission intensity and steady state fluorescence anisotropy ( r ss ), accompanied by a blueshift of 10 nm. In the serum albumin–bromadiolone complex, selective excitation of tryptophan (Trp) residue results in emission from bromadiolone, thereby indicating a Forster type energy transfer from Trp to BRD. This quenching of Trp fluorescence by BRD was used to estimate the binding constant of the SA–BRD complex. The binding constants for BRD with BSA and HSA were 7.5 × 10 4 and 3.7 × 10 5 L mol −1 , respectively. Based on this, a new method involving SA as fluorescence-enhancing reagent for estimation of BRD in aqueous samples has been suggested. The detection limits of bromadiolone under the optimum conditions were 0.77 and 0.19 μg mL −1 in presence of BSA and HSA, respectively.
TL;DR: TSFS can provide an alternative way of presenting the fluorescence response of concentrated multifluorophoric samples and make it easy to obtain the optimized Δλ of an unknown sample of analytical interest.
Abstract: 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 (Δλ), 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 Δλ 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.
TL;DR: In this article, the interaction of 7-aminocoumarins with human serum albumin (HSA) was studied by using fluorescence spectroscopic technique and modeling studies.
Abstract: Interactions of several 7-aminocoumarins with human serum albumin (HSA) were studied by using fluorescence spectroscopic technique and modeling studies. There is a large change in fluorescence spectral parameters like intensity, emission maxima and anisotropy for all aminocoumarins. There were two binding sites for cou-1, 311 and a single binding site for other coumarins. The binding constant(s) are large for all coumarins reflective of a strong binding. These spectral studies show that structural variants at the third, fourth and seventh position affects binding. The probable location of these coumarins in domain Ii has been predicted based on modeling. The effect of structural modification on the efficiency of binding was obtained for various other coumarins, using modeling.
01 Jan 2015
01 Jan 2016
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TL;DR: This review focuses on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators.
Abstract: In this review we intend to provide a relatively comprehensive summary of the work of supramolecular hydrogelators after 2004 and to put emphasis particularly on the applications of supramolecular hydrogels/hydrogelators as molecular biomaterials. After a brief introduction of methods for generating supramolecular hydrogels, we discuss supramolecular hydrogelators on the basis of their categories, such as small organic molecules, coordination complexes, peptides, nucleobases, and saccharides. Following molecular design, we focus on various potential applications of supramolecular hydrogels as molecular biomaterials, classified by their applications in cell cultures, tissue engineering, cell behavior, imaging, and unique applications of hydrogelators. Particularly, we discuss the applications of supramolecular hydrogelators after they form supramolecular assemblies but prior to reaching the critical gelation concentration because this subject is less explored but may hold equally great promise for helping ...