7 research outputs found
Ultrasensitive Fiber Enhanced UV Resonance Raman Sensing of Drugs
Fiber
enhanced UV resonance Raman spectroscopy is introduced for
chemical selective and ultrasensitive analysis of drugs in aqueous
media. The application of hollow-core optical fibers provides a miniaturized
sample container for analyte flow and efficient light-guiding, thus
leading to strong light–analyte interactions and highly improved
analytical sensitivity with the lowest sample demand. The Raman signals
of the important antimalaria drugs chloroquine and mefloquine were
strongly enhanced utilizing deep UV and electronic resonant excitation
augmented by fiber enhancement. An experimental design was developed
and realized for reproducible and quantitative Raman fiber sensing,
thus the enhanced Raman signals of the pharmaceuticals show excellent
linear relationship with sample concentration. A thorough model accounts
for the different effects on signal performance in resonance Raman
fiber sensing, and conclusions are drawn how to improve fiber enhanced
Raman spectroscopy (FERS) for chemical selective analysis with picomolar
sensitivity
Isotopomeric Peak Assignment for N<sub>2</sub>O in Cross-Labeling Experiments by Fiber-Enhanced Raman Multigas Spectroscopy
Human intervention in nature, especially fertilization,
greatly
increased the amount of N2O emission. While nitrogen fertilizer
is used to improve nitrogen availability and thus plant growth, one
negative side effect is the increased emission of N2O.
Successful regulation and optimization strategies require detailed
knowledge of the processes producing N2O in soil. Nitrification
and denitrification, the main processes responsible for N2O emissions, can be differentiated using isotopic analysis of N2O. The interplay between these processes is complex, and studies
to unravel the different contributions require isotopic cross-labeling
and analytical techniques that enable tracking of the labeled compounds.
Fiber-enhanced Raman spectroscopy (FERS) was exploited for sensitive
quantification of N2O isotopomers alongside N2, O2, and CO2 in multigas compositions and
in cross-labeling experiments. FERS enabled the selective and sensitive
detection of specific molecular vibrations that could be assigned
to various isotopomer peaks. The isotopomers 14N15N16O (2177 cm–1) and 15N14N16O (2202 cm–1) could be clearly
distinguished, allowing site-specific measurements. Also, isotopomers
containing different oxygen isotopes, such as 14N14N17O, 14N14N18O, 15N15N16O, and 15N14N18O could be identified. A cross-labeling showed the
capability of FERS to disentangle the contributions of nitrification
and denitrification to the total N2O fluxes while quantifying
the total sample headspace composition. Overall, the presented results
indicate the potential of FERS for isotopic studies of N2O, which could provide a deeper understanding of the different pathways
of the nitrogen cycle
Analysis of Fiber-Enhanced Raman Gas Sensing Based on Raman Chemical Imaging
Fiber enhanced Raman spectroscopy
(FERS) is an arising new technique
for versatile highly sensitive and selective multigas analysis in
various applications, such as environmental monitoring and medical
breath diagnosis. In this study, the performance of FERS was thoroughly
studied with the help of a specially designed multichannel Raman chemical
imaging. Several types of hollow core photonic crystal fibers were
thoroughly analyzed in terms of their performance in light confinement
and sensitive gas sensing. The optimal fiber length for Raman gas
sensing was found to be 15 cm in our spectroscopic system. To separate
the Raman scattering of the target gas molecules from the background
generated by the silica microstructure of the fiber, the optimal diameter
of a spatial filter was analyzed and quantified as Ø3.9 μm,
which balances the suppression of the silica background and the attenuation
of the gas signal, originating from different regions in the plane
of the fiber end-face. To achieve an easy-to-use gas monitoring system
with stable performance, an automated coupling-method was developed,
to simplify the alignment of the FERS setup. The optimized design
of the FERS setup has remarkable potential for highly sensitive, miniaturized,
easy-to-use, and versatile gas sensing
Fast and Highly Sensitive Fiber-Enhanced Raman Spectroscopic Monitoring of Molecular H<sub>2</sub> and CH<sub>4</sub> for Point-of-Care Diagnosis of Malabsorption Disorders in Exhaled Human Breath
Breath gas analysis is a novel powerful
technique for noninvasive, early-stage diagnosis of metabolic disorders
or diseases. Molecular hydrogen and methane are biomarkers for colonic
fermentation, because of malabsorption of oligosaccharides (e.g.,
lactose or fructose) and for small intestinal bacterial overgrowth.
Recently, the presence of these gases in exhaled breath was also correlated
with obesity. Here, we report on the highly selective and sensitive
detection of molecular hydrogen and methane within a complex gas mixture
(consisting of H<sub>2</sub>, CH<sub>4</sub>, N<sub>2</sub>, O<sub>2</sub>, and CO<sub>2</sub>) by means of fiber-enhanced Raman spectroscopy
(FERS). An elaborate FERS setup with a microstructured hollow core
photonic crystal fiber (HCPCF) provided a highly improved analytical
sensitivity. The simultaneous monitoring of H<sub>2</sub> with all
other gases was achieved by a combination of rotational (H<sub>2</sub>) and vibrational (other gases) Raman spectroscopy within the limited
spectral transmission range of the HCPCF. The HCPCF was combined with
an adjustable image-plane aperture pinhole, in order to separate the
H<sub>2</sub> rotational Raman bands from the silica background signal
and improve the sensitivity down to a limit of detection (LOD) of
4.7 ppm (for only 26 fmol H<sub>2</sub>). The ability to monitor the
levels of H<sub>2</sub> and CH<sub>4</sub> in a positive hydrogen
breath test (HBT) was demonstrated. The FERS sensor possesses a high
dynamic range (∼5 orders of magnitude) with a fast response
time of few seconds and provides great potential for miniaturization.
We foresee that this technique will pave the way for fast, noninvasive,
and painless point-of-care diagnosis of metabolic diseases in exhaled
human breath
Fiber-Enhanced Raman Multigas Spectroscopy: A Versatile Tool for Environmental Gas Sensing and Breath Analysis
Versatile
multigas analysis bears high potential for environmental
sensing of climate relevant gases and noninvasive early stage diagnosis
of disease states in human breath. In this contribution, a fiber-enhanced
Raman spectroscopic (FERS) analysis of a suite of climate relevant
atmospheric gases is presented, which allowed for reliable quantification
of CH<sub>4</sub>, CO<sub>2</sub>, and N<sub>2</sub>O alongside N<sub>2</sub> and O<sub>2</sub> with just one single measurement. A highly
improved analytical sensitivity was achieved, down to a sub-parts
per million limit of detection with a high dynamic range of 6 orders
of magnitude and within a second measurement time. The high potential
of FERS for the detection of disease markers was demonstrated with
the analysis of 27 nL of exhaled human breath. The natural isotopes <sup>13</sup>CO<sub>2</sub> and <sup>14</sup>N<sup>15</sup>N were quantified
at low levels, simultaneously with the major breath components N<sub>2</sub>, O<sub>2</sub>, and <sup>12</sup>CO<sub>2</sub>. The natural
abundances of <sup>13</sup>CO<sub>2</sub> and <sup>14</sup>N<sup>15</sup>N were experimentally quantified in very good agreement to theoretical
values. A fiber adapter assembly and gas filling setup was designed
for rapid and automated analysis of multigas compositions and their
fluctuations within seconds and without the need for optical readjustment
of the sensor arrangement. On the basis of the abilities of such miniaturized
FERS system, we expect high potential for the diagnosis of clinically
administered <sup>13</sup>C-labeled CO<sub>2</sub> in human breath
and also foresee high impact for disease detection via biologically
vital nitrogen compounds
Ultrasensitive Detection of Antiseptic Antibiotics in Aqueous Media and Human Urine Using Deep UV Resonance Raman Spectroscopy
Deep
UV resonance Raman spectroscopy is introduced as an analytical
tool for ultrasensitive analysis of antibiotics used for empirical
treatment of patients with sepsis and septic shock, that is, moxifloxacin,
meropenem, and piperacillin in aqueous solution and human urine. By
employing the resonant excitation wavelengths λ<sub>exc</sub> = 244 nm and λ<sub>exc</sub> = 257 nm, only a small sample
volume and short acquisition times are needed. For a better characterization
of the matrix urine, the main ingredients were investigated. The capability
of detecting the antibiotics in clinically relevant concentrations
in aqueous media (LODs: 13.0 ± 1.4 μM for moxifloxacin,
43.6 ± 10.7 μM for meropenem, and 7.1 ± 0.6 μM
for piperacillin) and in urine (LODs: 36.6 ± 11.0 μM for
moxifloxacin, and 114.8 ± 3.1 μM for piperacillin) points
toward the potential of UV Raman spectroscopy as point-of-care method
for therapeutic drug monitoring (TDM). This procedure enables physicians
to achieve fast adequate dosing of antibiotics to improve the outcome
of patients with sepsis
Direct Raman Spectroscopic Measurements of Biological Nitrogen Fixation under Natural Conditions: An Analytical Approach for Studying Nitrogenase Activity
Biological
N<sub>2</sub> fixation is a major input of bioavailable
nitrogen, which represents the most frequent factor limiting the agricultural
production throughout the world. Especially, the symbiotic association
between legumes and Rhizobium bacteria
can provide substantial amounts of nitrogen (N) and reduce the need
for industrial fertilizers. Despite its importance in the global N
cycle, rates of biological nitrogen fixation have proven difficult
to quantify. In this work, we propose and demonstrate a simple analytical
approach to measure biological N<sub>2</sub> fixation rates directly
without a proxy or isotopic labeling. We determined a mean N<sub>2</sub> fixation rate of 78 ± 5 μmol N<sub>2</sub> (g dry weight
nodule)<sup>−1</sup> h<sup>–1</sup> of a Medicago sativa–Rhizobium consortium by continuously analyzing the amount of atmospheric N<sub>2</sub> in static environmental chambers with Raman gas spectroscopy.
By simultaneously analyzing the CO<sub>2</sub> uptake and photosynthetic
plant activity, we think that a minimum CO<sub>2</sub> mixing ratio
might be needed for natural N<sub>2</sub> fixation and only used the
time interval above this minimum CO<sub>2</sub> mixing ratio for N<sub>2</sub> fixation rate calculations. The proposed approach relies
only on noninvasive measurements of the gas phase and, given its simplicity,
indicates the potential to estimate biological nitrogen fixation of
legume symbioses not only in laboratory experiments. The same methods
can presumably also be used to detect N<sub>2</sub> fluxes by denitrification
from ecosystems to the atmosphere