The Experts below are selected from a list of 5019 Experts worldwide ranked by ideXlab platform
Totaro Imasaka - One of the best experts on this subject based on the ideXlab platform.
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Gas chromatography/multiphoton ionization/time-of-flight mass spectrometry using a femtosecond laser
Analytical and Bioanalytical Chemistry, 2013Co-Authors: Totaro ImasakaAbstract:A laser can be used for the selective excitation and subsequent ionization of a Molecule with an absorption band at the laser wavelength. This technique of multiphoton ionization (MPI), when combined with time-of-flight mass spectrometry (TOF-MS), permits the efficient detection of induced ions in mass analysis. This combination of MPI/TOF-MS can be coupled with gas chromatography (GC) to achieve even more enhanced selectivity. Thus, GC/MPI/TOF-MS can be employed for trace analysis of samples containing numerous chemical species. A variety of laser sources have been used for this purpose. Since Molecules that are classified as environmental pollutants frequently contain chlorine and bromine atoms, the lifetime of the excited state can be decreased by energy transfer from the singlet to triplet levels by spin–orbit interaction. A high-power femtosecond laser with a pulse width shorter than the lifetime of the Analyte Molecule provides femtogram or even subfemtogram detection limits, which have not yet been achieved using the most sensitive high-resolution double-focus sector-type mass spectrometers. Numerous environmental pollutants such as dioxins in soils and pesticides in foods have been successfully quantified using GC/MPI/TOF-MS, and this technique has proven itself to be a useful and practical method for trace analysis. Figure Analytical instrument for laser ionization mass spectrometry
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analysis of dioxins by gas chromatography resonance enhanced multiphoton ionization mass spectrometry using nanosecond and picosecond lasers
Analytical Chemistry, 2011Co-Authors: Tomohiro Uchimura, Yuka Watanabeezoe, Totaro ImasakaAbstract:Dioxins in a soil sample were measured using gas chromatography/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry coupled with different types of laser sources. The fourth-harmonic emission (266 nm) of a nanosecond Nd:YAG laser (1 ns) provided low ionization efficiency, especially for highly chlorinated dioxins/dibenzofurans (CDDs/CDFs). The ionization efficiency was improved using the fourth-harmonic emission (266 nm) of a picosecond Nd:YAG laser (4 ps), due to shorter singlet excited-state lifetimes. It was, however, difficult to efficiently ionize hepta-CDD and octa-CDD/CDF, because of their shorter lifetimes, which were induced by stronger spin−orbit coupling that led to efficient relaxation of the excited Molecule to triplet levels. The ionization efficiency was substantially improved using the fifth-harmonic emission (213 nm) of the picosecond Nd:YAG laser (4 ps), in which the Analyte Molecule that was relaxed to triplet levels was efficiently ionized using a photon with suf...
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selective determination of 2 4 xylenol by gas chromatography supersonic jet resonance enhanced multiphoton ionization time of flight mass spectrometry
Analytica Chimica Acta, 2010Co-Authors: Hiroko Tsukatani, Hiroki Okudaira, Osamu Shitamichi, Tomohiro Uchimura, Totaro ImasakaAbstract:Abstract Gas chromatography/supersonic jet/resonance-enhanced multiphoton ionization/time-of-flight mass spectrometry (GC/SSJ/REMPI/TOF-MS) was employed for isomer-selective determination of 2,4-xylenol in river and seawater samples. The sample containing 2,4-xylenol was measured using argon, rather than helium, as the GC carrier gas to cool the Analyte Molecule sufficiently. The instrumental detection limit (IDL) achieved at a flow rate of 1 mL min −1 was 14 pg. Although this value was comparable to the value (ca. 10 pg) obtained by gas chromatography/electron impact/quadrupole mass spectrometry (GC/EI/QMS). When the flow rate was increased to 8 mL min −1 , interference from the 2,5-xylenol isomer was completely suppressed. The IDL was degraded to 83 or 160 pg at a flow rate of 5 or 8 mL min −1 , respectively. The recovery of 2,4-xylenol from the river and the seawater samples was 85 and 93%, respectively. The time for analysis was only 10 min per one sample in GC/SSJ/REMPI/TOF-MS. These results suggest that GC/SSJ/REMPI/TOF-MS is useful for the selective measurement of 2,4-xylenol, which has been designated a Class I chemical substance in the Pollutant Release and Transfer Register (PRTR).
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online concentration by Analyte adsorption laser desorption for application to gas chromatography resonance enhanced multiphoton ionization time of flight mass spectrometry
Analytical Chemistry, 2010Co-Authors: Yuji Sakoda, Tomohiro Uchimura, Totaro ImasakaAbstract:A novel sample introduction technique, based on online concentration by Analyte adsorption/laser desorption, was applied to resonance-enhanced multiphoton ionization time-of-flight mass spectrometry (REMPI-TOFMS). Signal enhancement and optical selectivity, based on supersonic jet spectrometry, were examined by measuring the REMPI spectra. This sample introduction technique was applied at the interface of a gas chromatograph (GC) and a mass spectrometer (MS). The signal intensity was enhanced ca. 80-fold, compared with that of a conventional technique based on continuous sample introduction. The Analyte Molecule was selectively measured using a tunable laser emitting at a wavelength of the 0-0 transition. With the use of a desorption laser, a linear calibration curve was extended over 4 orders of magnitude. The sensitivity, selectivity, and dynamic range were all superior for this sample introduction system, as were the inherent characteristics, e.g., a near-zero dead volume and thermal durability. This system would provide a useful means for practical trace analysis of aromatic hydrocarbons by GC/REMPI-TOFMS.
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scheme for collinear ionization in supersonic jet multiphoton ionization time of flight mass spectrometry
Analytica Chimica Acta, 2000Co-Authors: Takayuki Onoda, Genta Saito, Totaro ImasakaAbstract:Abstract A new ionization scheme is proposed, in which the Analyte Molecule, ejected from a nozzle into a throat, is expanded from a repeller into a vacuum and immediately ionized and accelerated downstream for time-of-flight mass analysis. The ionization efficiency is improved by a factor of 50, which is in reasonably good agreement with the predicted value of 25, calculated from the distance between the nozzle and the ionization region for the cases of collinear (10 mm) and non-collinear (perpendicular) (50 mm) configurations. This approach has the unique capability for ‘temperature tuning’ of the Analyte Molecule by changing the position of the ionization region, thus permitting control of the spectral linewidth and, thereby, application of supersonic jet spectrometry to samples of unknown composition.
Malini Olivo - One of the best experts on this subject based on the ideXlab platform.
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Optimization and performance analysis of SERS-active suspended core photonic crystal fibers
Optics Express, 2020Co-Authors: Flavien Beffara, Georges Humbert, Jean-louis Auguste, Jayakumar Perumal, U. Dinish, Malini OlivoAbstract:Recently, surface enhanced Raman spectroscopy (SERS)-active photonic crystal fiber (PCFs) probes have gained great interest for biosensing applications due to the tremendous advantages it has over the conventional planar substrate based SERS measurements, with improvements on the detection sensitivity and reliability in measurements. So far, two main approaches were employed to get the Analyte Molecule in the vicinity of nanoparticles (NPs) inside PCFs in order to achieve the SERS effect. In the first case, Analyte and NPs are pre-mixed and injected inside the holes of the PCF prior to the measurement. In the second approach, controlled anchoring of the NPs inside the inner walls of the PCF was achieved prior to the incorporation of the Analyte. Although many studies have been conducted using one configuration or the other, no clear trend is emerging on which one would be the best suited for optimizing the biosensing properties offered by SERS active-PCF. In this paper, we investigate the performances of both configurations along with their interplays with the core size of the PCF probe. We have fabricated several samples of a standard PCF design with different core sizes, and SERS measurements of a standard Raman-active Molecule are realized in the same conditions for enabling direct comparisons of the SERS intensity and measurement reliabilities between each configuration, yielding clear directions on the optimization of the SERS-active PCF probe. We envision that this study will pave the way for next-generation clinical biosensors for body fluid analysis, as it exhibits high sensitivity and excellent reliability.
Regina Ragan - One of the best experts on this subject based on the ideXlab platform.
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quantification of Analyte concentration in the single Molecule regime using convolutional neural networks
Analytical Chemistry, 2019Co-Authors: William John Thrift, Regina RaganAbstract:Single Molecule (SM) detection represents the ultimate limit of chemical detection. Over the years, many experimental techniques have emerged with this capacity. Yet, SM detection and imaging methods produce large spectral data sets that benefit from chemometric methods. In particular, surface enhanced Raman scattering spectroscopy (SERS), with extensive applications in biosensing, is demonstrated to be particularly promising because Raman active Molecules can be identified without recognition elements and is capable of SM detection. Yet quantification at ultralow Analyte concentrations requiring detection of SM events remains an ongoing challenge, with the few existing methods requiring carefully developed calibration curves that must be redeveloped for each Analyte Molecule. In this work, we demonstrate that a convolutional neural network (CNN) model when applied to bundles of SERS spectra yields a robust, facile method for concentration quantification down to 10 fM using SM detection events. We further...
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quantification of Analyte concentration in the single Molecule regime using convolutional neural networks
Analytical Chemistry, 2019Co-Authors: William John Thrift, Regina RaganAbstract:Single Molecule (SM) detection represents the ultimate limit of chemical detection. Over the years, many experimental techniques have emerged with this capacity. Yet, SM detection and imaging methods produce large spectral data sets that benefit from chemometric methods. In particular, surface enhanced Raman scattering spectroscopy (SERS), with extensive applications in biosensing, is demonstrated to be particularly promising because Raman active Molecules can be identified without recognition elements and is capable of SM detection. Yet quantification at ultralow Analyte concentrations requiring detection of SM events remains an ongoing challenge, with the few existing methods requiring carefully developed calibration curves that must be redeveloped for each Analyte Molecule. In this work, we demonstrate that a convolutional neural network (CNN) model when applied to bundles of SERS spectra yields a robust, facile method for concentration quantification down to 10 fM using SM detection events. We further demonstrate that transfer learning, the process of reusing the weights of a trained CNN model, greatly reduces the amount of data required to train CNN models on new Analyte Molecules. These results point the way for unambiguous analysis of large spectral data sets and the use of SERS in important ultra low concentration chemical detection applications such as metabolomic profiling, water quality evaluation, and fundamental research.
C M Galloway - One of the best experts on this subject based on the ideXlab platform.
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polarization dependent effects in surface enhanced raman scattering sers
Physical Chemistry Chemical Physics, 2006Co-Authors: P G Etchegoin, C M GallowayAbstract:A few key examples of polarization effects in surface-enhanced Raman scattering (SERS) are highlighted and discussed. It is argued that the polarization of the local field, which is felt by an Analyte Molecule in a location of high electromagnetic field enhancement (hot-spot), can be very different from that of the incident exciting beam. The polarization dependence of the SERS signal is, therefore, mostly dictated by the coupling of the laser to the plasmons rather than by the symmetry of the Raman tensor of the Analyte. This sets serious restrictions for the interpretation of both single-Molecule SERS polarization studies and for the use of circularly polarized light in techniques like surface-enhanced Raman optical activity.
James Murray - One of the best experts on this subject based on the ideXlab platform.
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Smart SERS Hot Spots: Single Molecules Can Be Positioned in a Plasmonic Nanojunction Using Host–Guest Chemistry
2018Co-Authors: Nam Hoon Kim, Md.rumum Rohman, Wooseup Hwang, Kangkyun Baek, Jeehong Kim, Hyun Woo Kim, Jungho Mun, So Young Lee, Gyeongwon Yun, James MurrayAbstract:Single-Molecule surface-enhanced Raman spectroscopy (SERS) offers new opportunities for exploring the complex chemical and biological processes that cannot be easily probed using ensemble techniques. However, the ability to place the single Molecule of interest reliably within a hot spot, to enable its analysis at the single-Molecule level, remains challenging. Here we describe a novel strategy for locating and securing a single target Analyte in a SERS hot spot at a plasmonic nanojunction. The “smart” hot spot was generated by employing a thiol-functionalized cucurbit[6]uril (CB[6]) as a molecular spacer linking a silver nanoparticle to a metal substrate. This approach also permits one to study Molecules chemically reluctant to enter the hot spot, by conjugating them to a moiety, such as spermine, that has a high affinity for CB[6]. The hot spot can accommodate at most a few, and often only a single, Analyte Molecule. BiAnalyte experiments revealed that one can reproducibly treat the SERS substrate such that 96% of the hot spots contain a single Analyte Molecule. Furthermore, by utilizing a series of Molecules each consisting of spermine bound to perylene bisimide, a bright SERS Molecule, with polymethylene linkers of varying lengths, the SERS intensity as a function of distance from the center of the hot spot could be measured. The SERS enhancement was found to decrease as 1 over the square of the distance from the center of the hot spot, and the single-Molecule SERS cross sections were found to increase with AgNP diameter
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Smart SERS Hot Spots: Single Molecules Can Be Positioned in a Plasmonic Nanojunction Using Host-Guest Chemistry
AMER CHEMICAL SOC, 2018Co-Authors: Nam Hoon Kim, Md.rumum Rohman, Wooseup Hwang, Kangkyun Baek, Jeehong Kim, Hyun Woo Kim, Gyeongwon Yun, Mun J., Lee S.y., James MurrayAbstract:Single-Molecule surface-enhanced Raman spectroscopy (SERS) offers new opportunities for exploring the complex chemical and biological processes that cannot be easily probed using ensemble techniques. However, the ability to place the single Molecule of interest reliably within a hot spot, to enable its analysis at the single-Molecule level, remains challenging. Here we describe a novel strategy for locating and securing a single target Analyte in a SERS hot spot at a plasmonic nanojunction. The smart hot spot was generated by employing a thiol-functionalized cucurbit[6]uril (CB[6]) as a molecular spacer linking a silver nanoparticle to a metal substrate. This approach also permits one to study Molecules chemically reluctant to enter the hot spot, by conjugating them to a moiety, such as spermine, that has a high affinity for CB[6]. The hot spot can accommodate at most a few, and often only a single, Analyte Molecule. BiAnalyte experiments revealed that one can reproducibly treat the SERS substrate such that 96% of the hot spots contain a single Analyte Molecule. Furthermore, by utilizing a series of Molecules each consisting of spermine bound to perylene bisimide, a bright SERS Molecule, with polymethylene linkers of varying lengths, the SERS intensity as a function of distance from the center of the hot spot could be measured. The SERS enhancement was found to decrease as 1 over the square of the distance from the center of the hot spot, and the single-Molecule SERS cross sections were found to increase with AgNP diameter. © 2018 American Chemical Societ
