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- N. Asefifeyzabadi, T. Holland, P. Sivakumar , S. Talapatra, I. M. Senanayake, B. M. Goodson, and M. H. Shamsi,
“Sequence-Independent DNA Adsorption on Few-Layered Oxygen-Functionalized Graphene
Electrodes: An Electrochemical Study for Biosensing Application”,
Biosensors (2021), 11 (8), 273 ;
doi.org/10.3390/bios11080273
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Abstract
DNA is strongly adsorbed on oxidized graphene surfaces in the presence of divalent cations. Here, we studied the effect of DNA adsorption on electrochemical charge transfer at few-layered, oxygen-functionalized graphene (GOx) electrodes. DNA adsorption on the inkjet-printed GOx electrodes caused amplified current response from ferro/ferricyanide redox probe at concentration range 1 aM–10 nM in differential pulse voltammetry. We studied a number of variables that may affect the current response of the interface: sequence type, conformation, concentration, length, and ionic strength. Later, we showed a proof-of-concept DNA biosensing application, which is free from chemical immobilization of the probe and sensitive at attomolar concentration regime. We propose that GOx electrodes promise a low-cost solution to fabricate a highly sensitive platform for label-free and chemisorption-free DNA biosensing.
- R. Karunanithy, T. Holland, and P. Sivakumar*,
“Influence of Glutaraldehyde’s Molecular Transformations on Spectroscopic Investigations of
Its Conjugation with Amine-modified Fe3O4 Microparticles in the Reaction Medium”,
Langmuir (2021), 37, 27, 5242-5251 [ Supplementary Cover Art ];
doi.org/10.1021/acs.langmuir.1c00182
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Abstract
Glutaraldehyde (GA) is a widely used cross-linking agent in biological research due to its superior characteristics, such as high reactivity toward proteins, high stability, and cost-effectiveness. In this regard, analyzing spectral changes initiated by various molecular forms and transformations of GA in a reaction medium and its reaction with surface functional-modified solid spheres is vital for a successful bioconjugation process targeting the biomolecules of interest. In this work, we present Fourier transform-infrared (FT-IR), Raman, and UV–visible spectroscopic analyses of glutaraldehyde-modified Fe3O4 microparticles (magnetic beads) to confirm the conjugation between GA and magnetic beads. We also studied the molecular transformations of glutaraldehyde during the reaction with amine-modified magnetic beads via investigating the reaction medium of the glutaraldehyde solution. Our FT-IR and Raman studies confirmed that glutaraldehyde was successfully coupled on the magnetic beads. Furthermore, FT-IR and UV–vis studies on the glutaraldehyde solution revealed the multiple molecular forms of GA in an aqueous medium, and they also confirmed that glutaraldehyde transforms into other molecular forms while the reaction occurs with the magnetic beads.
- T. Holland, A. M. Abdul-Munaim, C. Mandrell, R. Karunanithy, D. Watson, and
P. Sivakumar*, “UV-Visible Spectrophotometer for Distinguishing Oxidation Time of Engine Oil”,
Lubricants (2021),9 (4), 37;
doi.org/10.3390/lubricants9040037
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Abstract
Samples of gasoline engine oil (SAE 5W20) that had been exposed to various oxidation times were inspected with a UV-Visible (UV-Vis) spectrophotometer to select the best wavelengths and wavelength ranges for distinguishing oxidation times. Engine oil samples were subjected to different thermal oxidation periods of 0, 24, 48, 72, 96, 120, and 144 hours, resulting in a range of total base number (TBN) levels. Each wavelength (190.5 – 849.5 nm) and selected wavelength ranges were evaluated to determine the wavelength or wavelength ranges that could best distinguish among all oxidation times. The best wavelengths and wavelength ranges were analyzed with linear regression to determine the best wavelength or range to predict oxidation time.
- C. Mandrell, T. Holland, J. Wheeler, S. Esmaeili, K. Amar, F. Chowdhury, and
P. Sivakumar*, “Machine Learning Approach to Raman Spectrum Analysis
of MIA PaCa-2 Pancreatic Cancer Tumor Repopulating Cells for Classification and Feature Analysis”,
Life (2020),10 (9), 181;
doi.org/10.3390/life10090181
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Abstract
A machine learning approach is applied to Raman spectra of cells from the MIA PaCa-2 human pancreatic cancer cell line to distinguish between tumor repopulating cells (TRCs) and parental control cells, and to aid in the identification of molecular signatures. Fifty-one Raman spectra from the two types of cells are analyzed to determine the best combination of data type, dimension size, and classification technique to differentiate the cell types. An accuracy of 0.98 is obtained from support vector machine (SVM) and k-nearest neighbor (kNN) classifiers with various dimension reduction and feature selection tools. We also identify some possible biomolecules that cause the spectral peaks that led to the best results.
- S. Li, T. De Silva, I. Arsano, D. Gallaba, R.Karunanithy, M. Wasala, X. Zhang, P. Sivakumar ,
A. Migone, M. Tsige, X. Ma, and S. Talapatra, “High Adsorption of Benzoic Acid on Single Walled Carbon Nanotube Bundles”,
Scientific Reports (2020),10, 10013;
doi.org/10.1038/s41598-020-66871-4
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Abstract
Removal of harmful chemicals from water is paramount to environmental cleanliness and safety. As such, need for materials that will serve this purpose is in the forefront of environmental research that pertains to water purification. Here we show that bundles of single walled carbon nanotubes (SWNTs), synthesized by direct thermal decomposition of ferrocene (Fe(C5H5)2), can remove emerging contaminants like benzoic acid from water with high efficiencies. Experimental adsorption isotherm studies indicate that the sorption capacity of benzoic acid on these carbon nanotubes (CNTs) can be as high as 375 mg/g, which is significantly higher (in some cases an order of magnitude) than those reported previously for other adsorbents of benzoic acid such as activated carbon cloth, modified bentonite and commercially available graphitized multiwall carbon nanotubes (MWNTs). Our Molecular Dynamics (MD) simulation studies of experimental scenarios provided major insights related to this process of adsorption. The MD simulations indicate that, high binding energy sites present in SWNT bundles are majorly responsible for their enhanced adsorptive behavior compared to isolated MWNTs. These findings indicate that SWNT materials can be developed as scalable materials for efficient removal of environmental contaminants as well as for other sorption-based applications.
- A. M. Abdul-Munaim, T. Holland, P. Sivakumar, and D. Watson,
“Absorption Wavebands for Discriminating Oxidation Time of Engine Oil as Detected by FT-IR Spectroscopy”,
Lubricants (2019), 7, 24 ;
doi.org/10.3390/lubricants7030024
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Abstract
Fourier Transform-Infrared (FT-IR) spectroscopy was used to analyze gasoline engine oil (SAE 5W20) samples that were exposed to seven different oxidation times (0 h, 24 h, 48 h, 72 h, 96 h, 120 h, and 144 h) to determine the best wavenumbers and wavenumber ranges for the discrimination of the oxidation times. The thermal oxidation process generated oil samples with varying total base number (TBN) levels. Each wavenumber (400–3900 cm−1) and wavenumber ranges identified from the literature and this study were statistically analyzed to determine which wavenumbers and wavenumber ranges could discriminate among all oxidation times. Linear regression was used with the best wavenumbers and wavenumber ranges to predict oxidation time.
- T. Holland, A. M. Abdul-Munaim, D. Watson, and P. Sivakumar*,
“Influence of Sample Mixing Techniques on Engine Oil Contamination Analysis by Infrared Spectroscopy”,
Lubricants (2019), 7(1), 4 [ Invited Paper ];
doi.org/10.3390/lubricants7010004
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Abstract
For the most reliable and reproducible results for calibration or general testing purposes of two immiscible liquids, such as water in engine oil, good emulsification is vital. This study explores the impact of emulsion quality on the Fourier transform infrared (FT-IR) spectroscopy calibration standards for measuring water contamination in used or in-service engine oil, in an attempt to strengthen the specific guidelines of ASTM International standards for sample preparation. By using different emulsification techniques and readily available laboratory equipment, this work is an attempt to establish the ideal sample preparation technique for reliability, repeatability, and reproducibility for FT-IR analysis while still considering the ease and efficiency of the technique. This study demonstrates that a stable emulsion within a sample, which depends heavily upon the method, provides a reliably consistent homogenous sample for quantification purposes with FT-IR analysis. Analysis of variance (ANOVA) modeling and limit of detection calculations demonstrate the stability of the emulsion. The results reveal that setting a mixing time for a calibration standard depends on the emulsification process. Inserting a probe directly into a sample (direct sonication) allows for a rapid, stable emulsion with high reproducibility. Indirect sonication produces relatively non-miscible liquids of different densities. The pan-shaker produces a reasonably stable emulsion, but without the long-term stability or quick production time of direct sonication. Reaction time plays a critical role in the rotary mixing method, which leads to a slow development of emulsification.
- D. D. Pokrajac, P. Sivakumar, Y. Markushin, D. Milovic, G. Holness, J. Liu, N. Melikechi, and M. Rana
“Modeling of Laser Induced Breakdown Spectroscopic Data Analysis by an Automatic Classifier”,
International Journal of Data Science and Analytics (JDSA) 2019, 8, 213-220;
DOI: 10.1007/s41060-018-00172-y
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Abstract
Laser-induced breakdown spectroscopy (LIBS) is a multi-elemental and real-time analytical technique with simultaneous detection of all the elements in any type of sample matrix including solid, liquid, gas, and aerosol. LIBS produces vast amount of data which contains information on elemental composition of the material among others. Classification and discrimination of spectra produced during the LIBS process are crucial to analyze the elements for both qualitative and quantitative analysis. This work reports the design and modeling of optimal classifier for LIBS data classification and discrimination using the apparatus of statistical theory of detection. We analyzed the noise sources associated during the LIBS process and created a linear model of an echelle spectrograph system. We validated our model based on assumptions through statistical analysis of “dark signal” and laser-induced breakdown spectra from the database of National Institute of Science and Technology. The results obtained from our model suggested that the quadratic classifier provides optimal performance if the spectroscopy signal and noise can be considered Gaussian.
- T. Holland, Ali Mazin Abdul-Munaim, Dennis G. Watson, and P. Sivakumar*,
“Importance of Emulsification in Calibrating Infrared Spectroscopes for Analyzing Water Contamination
in Used or In-Service Engine Oil”, Lubricants 2018, 6(2), 35;
doi:10.3390/lubricants6020035
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Abstract
Using Fourier transform infrared (FT-IR) spectroscopy we investigated the water content of SAE 15W–40 diesel engine lubricating oil at various levels of contamination to establish instrument calibration standards for measuring water contamination in used or in-service engine oil by the standards of ASTM International. Since some known additives in consumer grade engine oil possess slightly hydrophilic properties, this experiment avoided changing the sample matrix with supplemental additives, such as adding surfactants, to achieve homogeneity of the original sample. The impact of sampling time after contamination on the spectral absorption signature was examined in an attempt to improve the accuracy of water contamination quantification and determine if water-soluble potassium bromide (KBr) windows were suitable for analyzing water in oil emulsions. Analysis of variance (ANOVA) modeling and limit of detection calculations were used to predict the ability to discriminate contamination levels over time. Our results revealed that the amount of water concentration in engine oil could be misinterpreted depending on the timing of the FT-IR measurement of the calibration standard after initial water contamination. Also, KBr windows are not sufficiently etched due to the limited window interaction with water molecules within micelles of emulsions to alter FT-IR spectral signatures
- Y. Markushin, P. Sivakumar , N. Melikechi, and H. Boukari, “Detection and Identification of Amino Acids in Ficoll Solutions with Femtosecond Laser-induced Breakdown Spectroscopy”, SPIE, Proceedings Article, 10504 (2018).
- A. Fernandez-Bravo, P. Sivakumar , N. Melikechi, A. A Mohamed, "Femtosecond laser synthesis of aryl functional group substituted gold nanoparticles", Journal of Nanoscience and Nanotechnology, 17, 2852-2856 (2017).
- S. Ghosh, P. Patil, M. Wasala, S. Lei, A. Norlander, P. Sivakumar , R. Vaitar, P. M. Ajayan, S. Talapatra. "Fast photoresponse and high detectivity in copper indium selenide", 2D Materials 5 (2017).
- P. Sivakumar , A. Fernández-Bravo, L. Taleh, J.F. Biddle, and N. Melikechi, "Detection and Classification of Live and Dead Escherichia coli by Laser-Induced Breakdown Spectroscopy", Astrobiology 15 (2015) 144-153.
- Y. Markushin, P. Sivakumar , D. Connolly, and N. Melikechi, "Tag-Femtosecond Laser-Induced Breakdown Spectroscopy for the Sensitive Detection of Cancer Antigen 125 in Blood Plasma", Anal Bioanal.Chem 407 (2015) 1849-1855.
- P. Sharma, G. Holness, P. Sivakumar, Y. Markushin, and N. Melikechi, “Investigating Manifold Neighborhood size for Nonlinear analysis of LIBS Amino Acid Spectra.”, 24th International Conference on Software Engineering and Data Engineering (SEDE 2015), California,USA.
- P. Sivakumar , Y. Markushin, E. Jhamba, Z. MRah, L. A.Taleh, A. Fernancdez, N. Melikechi, and H. Houkari, “Detection and Identification of Amino Acids in Ficoll Solutions with Femtosecond Laser-Induced Breakdown Spectroscopy”, Biophysical Journal, 108, 621a, 2015.
- Sams S. Farhana, Poopalasingam Sivakumar , Jebari S. Weekes, Noureddine Melikechi, Sahadat
Hossain, Denial A. Fluman, Mukti M. Rana, “Determination of Metals in Leachate by Laser-Induced
Breakdown Spectroscopy.”, The Journal of Solid Waste Technology and Management 40 (2014) 243-253.
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Abstract
We report on the use of Laser Induced Breakdown Spectroscopy (LIBS) for determining presence of metals in landfill leachate samples from the Delaware Solid Waste Authority’s (DSWA) Sandtown, Delaware landfill. A Q switched Nd:YAG laser along with spectrometer, detector and fiber optics cables were used for analyzing the leachate samples. Presence of each metal in the leachate samples has been uniquely identified from the LIBS emission lines associated with each element. The metals detected in the leachate samples include Al, Ba, Ca, Co, Cr, Fe, Li, Mg, Mn, K, Na, Sr, and Zn. The LIBS results were also compared to results obtained by Inductively Coupled Plasma Mass Spectroscopy (Method SW846 6010C). The results show that LIBS can be an inexpensive and attractive analytical technique for environmental monitoring and analysis.
- David D. Pokrajac, Poopalasingam Sivakumar, Yuri Markushin, Daniela Milovic, Mukti Rana, Gary Holness,
Jinjie Liu, Noureddine Melikechi, "Towards Optimal Classifier of Spectroscopy Data", In proceedings: 1st IcETRAN,
June 2-5 (2014), Serbia.
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Abstract
Laser spectroscopy can produce vast amounts of data, anticipating needs for automatization of tasks such as classification and discrimination of spectra. Using the apparatus of statistical theory of detection, we develop the optimal classifier for spectroscopy data for a linear model of an echelle spectrograph system. We validate model assumptions through statistical analysis of “dark signal” and laser-breakdown induced spectra of standardized NIST glass. The experimental results suggest that the quadratic classifier may provide optimal performance if the spectroscopy signal and noise can be considered Gaussian.
- P.Sivakumar, L. Taleh, Y. Markushin, N. Melikechi, "Packing density effects on the fluctuations of the emission lines in
laser-induced breakdown spectroscopy", Spectrochimica Acta Part B 92, 84–89 (2014).
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Abstract
In an earlier publication, we reported the results of a nanosecond-laser-induced breakdown spectroscopy (LIBS) analysis of pellets of Iron and Carbon and have shown that the shot-to-shot variations of the intensities of iron emission lines measured in iron to be much stronger than thosemeasured in carbon. Here, we present a numerical model based on two-dimensional random close packing of disks in a confined geometry that shows that the fluctuation effects observed in C and Fe are essentially due to the packing density of the samples interrogated.
- S. Farhana, P.Sivakumar, J. Weekes, N. Melikechi, M. S. Hossain, and Fluman, M. Rana, “Laser Induced Breakdown Spectroscopy: A New Technique for Determing Metal in Leachate”, In proceedings: 28th International Conference on Solid Waste technology & Management, March 10-13 (2013), Philadelphia, PA, USA.
- P.Sivakumar, L. Taleh, Y. Markushin, N. Melikechi, J. Lasue, "An experimental observation
of the different behavior of ionic and neutral lines of iron as a function of number density in a binary carbon–iron
mixture", Spectrochimica Acta Part B 82, 76–82 (2013).
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Abstract
We report on the dependence of the intensities of atomic and ionic lines emitted by a nanosecond laser-induced plasma on the atomic number densities of the constituents of a binary mixture formed of carbon and iron. We show that the packing density of the sample greatly affects the relative standard deviation of the emission lines. Furthermore, we show that the variation of the intensities of the C and Fe emission lines depends in a nontrivial way on the relative C–Fe concentration. The intensities of Fe neutral atomic lines behave differently than those of the ionic ones particularly at and above concentrations of 75%–80% Fe embedded in a carbon matrix. Unlike the emission fromneutral Fe, those fromionic Fe yield a very sharp decrease followed by an equally strong increase of the emission lines over a relatively small range of relative concentration of C and Fe. To better investigate this effect, we have compared the results obtainedwith nanosecond-LIBS to thosewith femtosecond-LIBS and found that this phenomenon disappears. The physical interpretation of the sharp decrease followed by an equally sharp increase in the emission intensities from Fe ions as the concentration of Fe is increased requires more studies.
- C. McRaven, P.Sivakumar, N.E. Shafer-Ray, Gregory E. Hall, Trevor J. Sears, "Spectroscopic constants of the known
electronic states of lead monofluoride", Journal of Molecular Spectroscopy 262, 89–92 (2010).
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Abstract
Based on measurements made by mass-resolved 1 + 1' + 1'' resonance-enhanced multiphoton ionization spectroscopy, we have determined new molecular constants describing the rotational and fine structure levels of the B, D, E, and F states of the most abundant isotopic variant 208Pb19F, and we summarize the spectroscopic constants for all the know electronic states of the radical. Many spectroscopic constants for the isotopologues 206Pb19F and 207Pb19F have also been determined. The symmetry of the D-state is found to be 2Π1/2, and the F-state is found to be an Ω = 3/2 state.
- P.Sivakumar, C. McRaven, P.M. Rupasinghe, T.Zh. Yang, N.E. Shafer-Ray, Trevor J. Sears and Gregory E. Hall,
"Pseudo-continuous resonance enhanced multiphoton ionisation: application to the determination of the hyperfine constants of 208Pb19F",
Molecular.Phys 108, 927 (2010).
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Abstract
A highly efficient pseudo continuous resonance enhanced multiphoton ionisation detection scheme is presented that combines the sensitivity of resonance enhanced multiphoton ionisation (REMPI) with high resolution. This detection scheme is employed to obtain the A(v'=1)← X1(v=0) spectra of 208Pb19F with a resolution of 90 MHz. The observed 19F hyperfine splittings are analysed in terms of effective hyperfine parameters that describe the interaction between the fluorine nuclear spin and that of the unpaired electron in the A and X1 states of the molecule.
- C. McRaven, P.Sivakumar, and N.E. Shafer-Ray, "Erratum: Experimental Determination of the Hyperfine Constants of
the X1 and A states of 207Pb19F [Phys. Rev. A 78, 054502 (2008)]", Phys.Rev.A 80, 029902(E) (2009).
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Abstract
The sign of the reported hyperfine constant A⊥,A of the A state of 207Pb19F is in error. Specifically, our measured value is A⊥,A =-1200 ± 300 MHz. We emphasize that this error does not effect the hyperfine constants of the ground state X1 state, the energy level diagram of Fig. 1, or the conclusion that our measurement A⊥,X1 = 7200 ± 150 MHz disagrees with previous predicitions.
- C. McRaven, P.Sivakumar, and N.E. Shafer-Ray, "Experimental Determination of the Hyperfine Constants of
the X1 and A states of 207Pb19F", Phys.Rev.A 78, 054502 (2008).
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Abstract
We have measured the hyperfine energy level structure of the X1 and A states of 207Pb19F and found it to be in disagreement with previous predictions. Specifically, we find our data are reproduced by the hyperfine parameters A⊥,X1 =7200 ±150 MHz, A∥,X1 = 10300 ± 800 MHz, A⊥,A=1200 ±300 MHz, and A∥,A =3000 ± 2500 MHz. The hyperfine structure may also be reproduced with A⊥,X1 =-7200 ± 150 MHz and A⊥,A=-1200 ± 300 MHz. These negative hyperfine constants would, however, require a reinterpretation of the parity assignments of both the X1 and A states of the PbF molecule. - P.Sivakumar, C. McRaven, Dustin Combs, and N.E. Shafer-Ray, "State-selective detection of the PbF
molecule by doubly resonant multiphoton ionization", Phys.Rev.A 77, 062508 (2008).
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Abstract
Doubly resonant multiphoton ionization of PbF has been achieved via the X1→A and A→ D transitions. Excitation of the A to the D state by narrow-bandwidth laser radiation is found to have a cross section of σD=100 ±30 Mb. The ionization potential is found to be 7.55(1) eV, in agreement with our previous result. The lifetime of the D state is found to be 250 ±150 ps and the ionization cross section is found to be σ+ = 90 ± 60 Mb. These characteristics allow for efficient state-selective ionization of the PbF molecule. - C. McRaven, P.Sivakumar, and N.E. Shafer-Ray, "Multiphoton Ionization of Lead Monofluoride
Resonantly Enhanced by the X 1 2Π1/2 → B 2Σ
1/2 Transition Phys.Rev.A 75, 024502 (2007).
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Abstract
Resonance enhanced multiphoton ionization of the X 1 2Π1/2 state of lead monofluoride (208Pb19F) via the B 2Σ 1/2 state is demonstrated. The ionization potential is observed to be 7.54(1) eV. Limits on the lifetime of the B state are found to be consistent with that reported by Chen et al. The transition dipole moment for the X 1→ B transition is found to be 0.005(1) a.u. Limits on the ionization cross section of the B state are found.