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V. K. Unnikrishnan

Bio: V. K. Unnikrishnan is an academic researcher from Manipal University. The author has contributed to research in topics: Laser-induced breakdown spectroscopy & Spectroscopy. The author has an hindex of 15, co-authored 49 publications receiving 663 citations.


Papers
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Journal ArticleDOI
TL;DR: In this paper, the effect of various experimental parameters such as source stability, area of exposure, and angular/distance dependence of a fiber probe, which is used for the fluorescence measurements, from the specimen surface on the spectra.
Abstract: Despite the advances in optical technologies for early detection of cancer, routine clinical applications are still not standardized. Among several optical methods, laser-induced fluorescence is a more matured and well understood technique. Still due care has to be taken about various factors to avoid erroneous results. The authors have carried out a systematic study on the effect of the various experimental parameters such as source stability, area of exposure, and angular/distance dependence of a fiber probe, which is used for the fluorescence measurements, from the specimen surface on the spectra. Investigations are carried out on both idealistic cases as well as on tissue surface. The details of the optimization of the parameters are presented and discussed in this paper.

9 citations

Journal ArticleDOI
TL;DR: In this article, a facile and cost-effective method was developed to create superhydrophobic surfaces onto a super-hydrophilic commercial paper for the application of droplet splitting of microliter droplets into nano and sub-nano liter droplets.

8 citations

Journal ArticleDOI
TL;DR: In this article, a gated time-gated Raman system using a pulsed laser and high-resolution echelle spectrograph was used for spectral band-pass of 0.75 cm�1 for 532 nm at an extremely small slit width of 10 μm.
Abstract: Time-gated Raman system has been assembled using a pulsed laser and high-resolution echelle spectrograph. Echelle spectrograph provides broad spectral band-pass of 0–8500 cm�1 in a single scan with a resolution of 1.75 cm�1 for 532 nm at an extremely small slit width of 10 μm. Advantages of gated mode detection over continuous-wave mode detection are improved signal-to-noise ratio, reduced background signal, and unwanted fluorescent emission. Feasibility of echelle spectrograph for Raman measurements has been tested for both conventional and standoff distance of 5 m with all the external illumination sources on. The echelle system provides high-quality Raman signals with an extremely low inherent bandwidth in solid and liquid samples, (~8 cm�1 ) for 478 cm�1 fundamental band of sulfur. Intensity ratio of e2 fundamental to a1 fundamental of conventional and remote Raman measurements indicates that the spectral features remain the same in both measurements. The advantages of ‘time-gated’ Raman compared with continuous-wave mode detection, like low background even under extraneous illumination and lowered fluorescence, are also illustrated with spectrum of sulfur taken in the two modes.

8 citations

Journal ArticleDOI
TL;DR: In this paper, three optical characterizations, namely, Ultraviolet-Visible-Near Infrared (UV-VIS-NIR), Photoluminescence (PL), and Reflective interference spectra were used to measure NAA thickness.
Abstract: Highly-ordered nanoporous anodic alumina (NAA) with varying thicknesses were prepared by changing the anodization time from 10 min to 10 h, using a two-step electrochemical oxidation in oxalic acid. Three optical characterizations, namely, Ultraviolet–Visible–Near Infrared (UV–VIS–NIR), Photoluminescence (PL), and Reflective interference spectra were used to measure NAA’s thicknesses. All three types of spectra displayed oscillations due to the optical interferences which were used for the extraction of NAA thickness using two approaches (i) Fabry–Perot fringe equation and (ii) Bragg’s interference condition equation. Both these approaches yielded the matching thicknesses. The results are coincident for all three measurement techniques. The obtained thicknesses are in good agreement with the cross-sectional SEM images showcasing the feasibility of such approaches. Measurements were carried out on NAA up to ∼ 10 μ m thickness beyond which no oscillations were observed. Out of the three, reflective interference spectroscopy turns out to be an inexpensive alternative for the NAA thickness measurement. Such nondestructive optical characterization methods are important from the device development point of view for chemical, optical and biosensing applications.

7 citations

Journal ArticleDOI
30 Jun 2020
TL;DR: The potential of optical spectroscopy based techniques for regular screening and early diagnosis of “Killer” diseases (various types of cancers, cardiovascular diseases, etc.) is discussed with focus on routine use under low-resource settings.
Abstract: In this paper the potential of optical spectroscopy based techniques for regular screening and early diagnosis of “Killer” diseases (various types of cancers, cardiovascular diseases, etc.) is discussed with focus on routine use under low-resource settings. A brief account of work carried out in our laboratory to design, assemble and optimize Laser Induced Fluorescence (LIF) based optical devices for routine screening, early diagnosis and discrimination of premalignant/malignant conditions in oral and other cancers is presented. An ultra-sensitive protein profiling system based on highly efficient High Performance Liquid Chromatograpy-Ultrasensitive Laser Induced Fluorescence (HPLC-LIF) detection, and its extensive use in monitoring various cancers, coronary conditions, gynecological problems etc. through protein profile pattern analyses of markers in body fluids is also discussed.

7 citations


Cited by
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Journal ArticleDOI
TL;DR: Basic diagnostics aspects of laser-induced breakdown spectroscopy are focused on and a review of the past and recent LIBS literature pertinent to this topic is presented and previous research on non-laser-based plasma literature, and the resulting knowledge, is emphasized.
Abstract: Laser-induced breakdown spectroscopy (LIBS) has become a very popular analytical method in the last decade in view of some of its unique features such as applicability to any type of sample, practically no sample preparation, remote sensing capability, and speed of analysis The technique has a remarkably wide applicability in many fields, and the number of applications is still growing From an analytical point of view, the quantitative aspects of LIBS may be considered its Achilles' heel, first due to the complex nature of the laser–sample interaction processes, which depend upon both the laser characteristics and the sample material properties, and second due to the plasma–particle interaction processes, which are space and time dependent Together, these may cause undesirable matrix effects Ways of alleviating these problems rely upon the description of the plasma excitation-ionization processes through the use of classical equilibrium relations and therefore on the assumption that the laser-induced

835 citations

01 Jan 1999

643 citations

Book ChapterDOI
01 Jan 2018
TL;DR: Laser induced breakdown spectroscopy (LIBS) as discussed by the authors is a technique where atoms and ions are primarily formed in their excited states as a result of interaction between a tightly focused laser beam and the material sample.
Abstract: Laser induced breakdown spectroscopy (LIBS) is basically an emission spectroscopy technique where atoms and ions are primarily formed in their excited states as a result of interaction between a tightly focused laser beam and the material sample. The interaction between matter and high-density photons generates a plasma plume, which evolves with time and may eventually acquire thermodynamic equilibrium. One of the important features of this technique is that it does not require any sample preparation, unlike conventional spectroscopic analytical techniques. Samples in the form of solids, liquids, gels, gases, plasmas and biological materials (like teeth, leaf or blood) can be studied with almost equal ease.LIBS has rapidly developed into a major analytical technology with the capability of detecting all chemical elements in a sample, of real- time response, and of close-contact or stand-off analysis of targets. The present book has been written by active specialists in this field, it includes the basic principles, the latest developments in instrumentation and the applications of LIBS. It will be useful to analytical chemists and spectroscopists as an important source of information and also to graduate students and researchers engaged in the fields of combustion, environmental science, and planetary and space exploration. It features: recent research work, possible future applications and LIBS Principles.

611 citations

Journal ArticleDOI
TL;DR: This review is focused on recent developments of surface-enhanced Raman scattering (SERS) applications in Analytical Chemistry and covers advances in the fabrication methods of SERS substrates, including nanoparticles immobilization techniques and advanced nanopatterning with metallic features.

276 citations

Journal ArticleDOI
TL;DR: In this article, a review on the analytical results obtained by laser-induced breakdown spectroscopy (LIBS) is presented, including the risk of misclassification, and results on concentration measurement based on calibration are accompanied with significant figures of merit including the concept of accuracy.

236 citations