Laser Spectroscopic Techniques Research Articles

New Aspects Regarding the Fluorescence Spectra of Melanin and Neuromelanin in Pigmented Human Tissue Concerning Hypoxia.

Melanin is a crucial pigment in melanomagenesis. Its fluorescence in human tissue is exceedingly weak but can be detected through advanced laser spectroscopy techniques. The spectral profile of melanin fluorescence distinctively varies among melanocytes, nevomelanocytes, and melanoma cells, with melanoma cells exhibiting a notably "red" fluorescence spectrum. This characteristic enables the diagnosis of melanoma both in vivo and in histological samples. Neuromelanin, a brain pigment akin to melanin, shares similar fluorescence properties. Its fluorescence can also be quantified with high spectral resolution using the same laser spectroscopic methods. Documented fluorescence spectra of neuromelanin in histological samples from the substantia nigra substantiate these findings. Our research reveals that the spectral behavior of neuromelanin fluorescence mirrors that of melanin in melanomas. This indicates that the typical red fluorescence is likely influenced by the microenvironment around (neuro)melanin, rather than by direct pigment interactions. Our ongoing studies aim to further explore this distinctive "red" fluorescence. We have observed this red fluorescence spectrum in post-mortem measurements of melanin in benign nevus. The characteristic red spectrum is also evident here (unlike the benign nevus in vivo), suggesting that hypoxia may contribute to this phenomenon. Given the central role of hypoxia in both melanoma development and treatment, as well as in fundamental Parkinson's disease mechanisms, this study discusses strategies aimed at reinforcing the hypothesis that red fluorescence from (neuro)melanin serves as an indicator of hypoxia.

Shear Coaxial Methane–Oxygen Injector Mixing and Combustion Examined by Laser Absorption Tomography

Mixing length scales for methane–oxygen shear-coaxial single-element rocket injectors were experimentally assessed using laser absorption tomography. The laser spectroscopy technique enables quantitative and spatially resolved measurements of carbon monoxide (CO) and temperature within the near-field region, probing rovibrational absorption lines of CO near 5 μm. Multiple injector designs were examined with differing oxidizer post recess depths to compare mixing characteristics. All tests were performed at an oxidizer-to-fuel ratio of 3 with a total propellant flow rate of 0.350 g/s. Planar measurements were taken at 16 axial positions, which collectively captured the first 57 mm of each flame. A tomographic inversion method was applied to obtain radially resolved distributions of temperature and CO mole fraction for each axial position, from which two-dimensional images of the thermochemical structure were generated. Characteristic mixing parameters are defined and extracted from features within the species and temperature profiles to visualize the spatial evolution of CO production. Increasing oxidizer post recess improved mixing due to enhanced shear-induced turbulence and associated radial diffusion of species and temperature; however, the enhancement was nonlinear. This work establishes the first use of laser absorption tomography to directly measure mixing length scales associated with temperature and species profiles in coaxial flames.

Case study of fluorite mineralization using traditional and laser spectroscopic techniques, homret akarem area south eastern desert, Egypt

Green fluorite samples from Homret Akarem, eastern desert Egypt, were investigated by laser-based Raman spectroscopy to study the effect of rare earth elements (REEs) and natural radiation from the surrounding environment on their physico-chemical properties, taking into consideration the geological setting. Geochemical data of trace elements display fluorite enrichment with Y, Pb, Sr, Sn, and other REEs. XRD showed lattice parameters with values higher than those for synthetic fluorite due to the substitution of Ca by Sr and less likely by radiation from U. A considerable shift in the binding energy (BE) for Ca and F obtained from the XPS spectrum indicates that U carried by the hydrothermal solutions formed a discontinuous thin film on the surface of fluorite. Laser-Raman spectroscopy showed strong peaks below 500 cm−1 and both shallow and weak peaks above 500 cm−1. The strong peaks indicate that the substitution of Ca by Sr, point defects, and natural radiation caused by U have a stronger effect on the crystal structure than REEs. Raman spectroscopy supported the initial reports of uranium minerals like Rutherfordine, Kasolite, Soddyite, and Uranophane-alpha.

Site-selective time resolved laser spectroscopy and DFT studies of Nd3+ optical centers in BaF2 doped crystals

Site-selective time-resolved laser spectroscopy techniques, which provide high spectral resolution at low temperatures (4.2 K and 6.5 K), were used to clarify the formation mechanism, spectral and kinetic properties of the Nd3+ ion single-site optical centers formed in the fluorite-type BaF2 single crystals doped with Nd3+. This formation occurs by heterovalent substitution of Ba2+ host cations with additional charge compensation by F− anions. To determine the lifetimes of the Stark 4F3/2(1) levels of the Nd3+ impurity centers, the fluorescence decay kinetics was measured using the gated photon counting technique. The data from spectroscopic experiments were combined with density functional theory (DFT) calculations to identify and analyze the local structure of Nd3+ cations in the Nd3+ ions doped BaF2 crystal. Our studies have shown that several types of single-site Nd3+ optical centers can be distinguished in BaF2:Nd3+. We confirmed the existence of an optical center with high C4v site symmetry and a long radiative lifetime of the 4F3/2(1) state τ = 14.3 ms. We also describe two other configurations of centers with local structure characterized by low site symmetry of Cs, which were identified and described for the first time. The decrease in the tetragonal site symmetry from C4v to Cs was explained by the fact that the Nd3+ dopants, distributed over the equivalent cationic positions of the fluorite-type crystal lattice, coordinate to anionic motifs that essentially differ in the position of the additional charge compensator F−. This structural variability induced in the local coordination environment of the optical center affects its spectroscopic properties through a shift in the energy of the 4F3/2(1) Stark level of the Nd3+ ion and results in a different radiative lifetime τ.

Exploration of the impact of graphene oxide, acetylenic gemini, and CTAT on the photophysical and aggregation properties of dipolar coumarin 153.

Advanced spectroscopic techniques have been utilized to study the interaction between the laser dye coumarin 153 (C153) and graphene oxide (GO) nanoparticles. GO was synthesized using a modified Hummers' method and characterized by UV-vis spectroscopy, Raman laser spectroscopy, FTIR-ATR spectroscopy, FESEM, HR-TEM, and XRD techniques. The GO@C153 composite was formed by mixing two aqueous solutions of GO and C153 due to their strong interaction through stacking and hydrophobic interactions. In this case, GO acts as an effective fluorescence quencher for C153 molecules, which undergo H-type aggregation in the presence of GO. The Stern-Volmer equation and time-dependent fluorescence studies were utilized to analyse the mechanism of fluorescence quenching. According to the findings, both static and dynamic quenching processes are responsible for the reduction in fluorescence intensity. The effect of surfactants (both cetyltrimethylammonium p-toluenesulfonate (CTAT) and synthesized N,N'-dihexadecyl-N,N,N',N'-tetramethyl-N,N'-but-2-ynediyl-di-ammonium chloride (16-4-16)) on the aggregation and photophysical properties of the dye was investigated using surface tensiometry, conductometry, UV-vis absorption spectroscopy, steady-state fluorescence measurements, DLS, and time-dependent fluorescence spectroscopy. Surfactants change the microenvironment of the C153 dye, leading to spectrum shifting and a higher quantum yield, which causes a rapid rise in fluorescence intensity in the micellar medium. It has been noted that in a micellar medium rather than in an aqueous one, the luminous intramolecular charge transfer (ICT) state of C153 stabilises. Lastly, we investigated the photophysical behavior of the GO-C153-micelle ternary system and discovered that, in the presence of a micellar medium, the quenched and blue-shifted (H-type aggregation) fluorescence peak of C153 (in the presence of GO) began to intensify once more. The main goal of this work is to create an effective and fairly cost powerful fluorescence sensor. Additionally, the ternary system (GO-C153-micelle) analytical idea can be employed to identify the onset of micelle formation. In wastewater treatment analysis, the GO-C153-surfactant ternary system concept can also be used to regenerate the adsorbent (in this case, GO) from dye molecules by allowing the dye molecules to exit the adsorbent and enter the micellar medium.

Exploration of carvacrol aggregation by laser spectroscopy.

Carvacrol is an aromatic monoterpenoid found in thyme oil. Due to its implications for human health, it is important to elucidate its structure and its intramolecular interactions. We have characterised the carvacrol monomer, its complex with water, its dimer, and even its trimer in a supersonic expansion using mass-resolved laser spectroscopy techniques complemented by quantum-chemical computations. The resonance-enhanced multiphoton ionisation spectrum of the monomer features several transitions, which were assigned to the same conformer, confirmed by ion-dip infrared spectroscopy. However, a conclusive assignment of the infrared bands to one of the four conformations of carvacrol remains elusive. The experimental spectra for the monohydrated, the homodimer, and the homotrimer point to the detection of the lowest energy isomer in each case. Their structures are governed by a balance of intramolecular interactions, specifically hydrogen bonding and dispersion forces. Comparison with other similar systems demonstrates that dispersion interactions are key to the stabilisation of the aggregates, being present in all the structures. However, the hydrogen bonding is the dominant force as observed in the lowest-energy conformations.

Deformation versus Sphericity in the Ground States of the Lightest Gold Isotopes.

The changes in mean-squared charge radii of neutron-deficient gold nuclei have been determined using the in-source, resonance-ionization laser spectroscopy technique, at the ISOLDE facility (CERN). From these new data, nuclear deformations are inferred, revealing a competition between deformed and spherical configurations. The isotopes ^{180,181,182}Au are observed to possess well-deformed ground states and, when moving to lighter masses, a sudden transition to near-spherical shapes is seen in the extremely neutron-deficient nuclides, ^{176,177,179}Au. A case of shape coexistence and shape staggering is identified in ^{178}Au which has a ground and isomeric state with different deformations. These new data reveal a pattern in ground-state deformation unique to the gold isotopes, whereby, when moving from the heavy to light masses, a plateau of well-deformed isotopes exists around the neutron midshell, flanked by near-spherical shapes in the heavier and lighter isotopes-a trend hitherto unseen elsewhere in the nuclear chart. The experimental charge radii are compared to those from Hartree-Fock-Bogoliubov calculations using the D1M Gogny interaction and configuration mixing between states of different deformation. The calculations are constrained by the known spins, parities, and magnetic moments of the ground states in gold nuclei and show a good agreement with the experimental results.

Characterization of a multi-stage focusing nozzle for collection of spot samples for aerosol chemical analysis

Concentrated collection of aerosol particles on a substrate is essential for their chemical analysis using various microscopy and laser spectroscopic techniques. An impaction-based aerosol concentration system was developed for focused collection of particles using a multi-stage nozzle that consists of a succession of multiple smooth converging stages. Converging sections of the nozzle were designed to focus and concentrate a particle diameter range of 900–2500 nm into a relatively narrower particle beam to obtain particulate deposits with spot diameters of 0.5–1.56 mm. A slightly diverging section before the last contractions was included to allow for better focusing of particles at the lower end of the collectable diameter range. The characterization of this multi-stage nozzle and the impaction-based aerosol concentration system was accomplished both numerically and experimentally. The numerical and experimental trends in collection efficiency and spot diameters agreed well qualitatively; however, the quantitative agreement between numerical and experimental results for wall losses was poor, particularly for larger particle diameters. The resulting concentrated particulate deposit, a spot sample, was analysed using Raman spectroscopy to probe the effect of spot size on analytical sensitivity of measurement. The method's sensitivity was compared against other conventional techniques, such as filtration and aerosol focused impaction, implementing condensational growth. Impaction encompassing the multi-stage focusing nozzle is the only method that can ensure high sensitivity at Reynolds numbers greater than 2000, that can be supported by small pumps which renders such method suitable for portable instrumentation.

White Lasing and White Fluorescence from the Simplified Two‐Dyes Organic System

AbstractThe invention of lasers, which took place a few decades ago, marks a milestone in the past, present, and future technologies in optoelectronics. In particular, the colorful and white tones produced by lasers are appealing from a utilization standpoint and align well with human eye perception. In this paper, an idea for a white laser based on the attractive perylene family of luminescent dyes is introduced. This concept provides multicolor emission and brilliant photostability upon external optical pumping. The main advantage of the approach is the construction of a fully organic and two‐component white laser. The versatility of the system is demonstrated by assembling multicolor, tunable, and efficient fluorescent systems using a liquid crystalline matrix, which is supported by comprehensive experimental studies. Additionally, by utilizing laser spectroscopy techniques, it is able to narrow the emission bandwidth and enhance the light in a typical synthetic polymeric matrix. This leads to the realization of white lasing emission with just two luminescent dyes: perylene blue and perylene orange.

Laser spectroscopy imaging technique coupled with nanomaterials for cancer diagnosis: A review

Laser spectroscopic imaging techniques have received tremendous attention in the field of cancer diagnosis due to their high sensitivity, high temporal resolution, and short acquisition time. However, the limited tissue penetration of the laser is still a challenge for the in vivo diagnosis of deep-seated lesions. Nanomaterials have been universally integrated with spectroscopic imaging techniques for deeper cancer diagnosis in vivo. The components, morphology, and sizes of nanomaterials are delicately designed, which could realize cancer diagnosis in vivo or in situ. Considering the enhanced signal emitting from the nanomaterials, we emphasized their combination with spectroscopic imaging techniques for cancer diagnosis, like the surface-enhanced Raman scattering (SERS), photoacoustic, fluorescence, and laser-induced breakdown spectroscopy (LIBS). Applications of the above spectroscopic techniques offer new prospects for cancer diagnosis.

Laser ionization scheme development for in-gas-jet spectroscopy studies of Th+

The in-gas laser ionization and spectroscopy (IGLIS) technique has been a cornerstone in the study of heavy elements. The addition of a convergent–divergent (de Laval) nozzle to perform laser ionization in a cold hypersonic gas jet greatly improves the achievable resolution. Recent efforts have focused on preparing the in-gas-jet method for the study of the low-lying 229Th isomer. Tailor-made recoil sources of 233U are installed inside a fast extraction gas cell to provide the (isomeric) thorium ions. A level search above the second ionization potential (IP) uncovered several auto-ionizing states, greatly improving the laser ionization efficiency of singly charged thorium ions.

Breath analysis by ultra-sensitive broadband laser spectroscopy detects SARS-CoV-2 infection

Rapid testing is essential to fighting pandemics such as coronavirus disease 2019 (COVID-19), the disease caused by the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Exhaled human breath contains multiple volatile molecules providing powerful potential for non-invasive diagnosis of diverse medical conditions. We investigated breath detection of SARS-CoV-2 infection using cavity-enhanced direct frequency comb spectroscopy (CE-DFCS), a state-of-the-art laser spectroscopic technique capable of a real-time massive collection of broadband molecular absorption features at ro-vibrational quantum state resolution and at parts-per-trillion volume detection sensitivity. Using a total of 170 individual breath samples (83 positive and 87 negative with SARS-CoV-2 based on reverse transcription polymerase chain reaction tests), we report excellent discrimination capability for SARS-CoV-2 infection with an area under the receiver-operating-characteristics curve of 0.849(4). Our results support the development of CE-DFCS as an alternative, rapid, non-invasive test for COVID-19 and highlight its remarkable potential for optical diagnoses of diverse biological conditions and disease states.

Abstract 6526: Investigation levels of trace elements in breast cancer types using laser spectroscopic techniques

Abstract Breast cancer (BC) is the 2nd leading cause of death from cancer in women. Women have a lifetime risk of breast cancer of around 31%, which makes it the first most common malignancy in women. Diagnosing cancer and classifying its types is a complex process that relies heavily on sample analysis. Early detection of cancer diseases is one of the important and main factors in determining treatment and saving many patients before the disease worsens and reaches dangerous stages. Alterations in the levels of trace elements have been observed in breast cancer (BC) patients. However, the relationships between these alterations and the metabolic and clinical consequences of BC are unknown. The aim of the present work is to study in vitro possibilities and the effectiveness of introducing an efficient optical spectroscopic technique such as LIBS for the identification types of breast cancer, as well as determining the disease grade and severity. The ultimate goal of this work is to investigate the concentrations of several trace elements in BC patients, and their relationships with the molecular subtypes of tumors. The atomic transition of the neutral element lines of Fe, Al, Na, Ca, K, V, Co and Pb was chosen to determine the trace element levels of four breast cancer types. We found that the measured average level of trace elements can differentiate between different types of breast cancer. Citation Format: Ola Sayed Ahmed, hisham imam. Investigation levels of trace elements in breast cancer types using laser spectroscopic techniques [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 6526.

High-precision measurements of the hyperfine structure of cobalt ions in the deep ultraviolet range

High-precision hyperfine structure measurements were performed on stable, singly-charged ^{59}Co ions at the IGISOL facility in Jyväskylä, Finland using the collinear laser spectroscopy technique. A newly installed light collection setup enabled the study of transitions in the 230 nm wavelength range from low-lying states below 6000 cm^{-1}. We report a 100-fold improvement on the precision of the hyperfine A parameters, and furthermore present newly measured hyperfine B paramaters.

Quantification of Elevated Hydrogen Cyanide (HCN) Concentration Typical in a Residential Fire Environment Using Mid-IR Tunable Diode Laser.

A versatile portable tunable diode laser based measurement system for measuring elevated concentrations of hydrogen cyanide (HCN) in a time-resolved manner is developed for application in the fire environment. The direct absorption tunable diode laser spectroscopy (DA-TDLAS) technique is employed using the R11 absorption line centered at 3345.3 cm-1 (2989.27 nm) in the fundamental C-H stretching band (ν1) of the HCN absorption spectrum. The measurement system is validated using calibration gas of known HCN concentration and the relative uncertainty in measurement of HCN concentration is 4.1% at 1500 ppm. HCN concentration is measured with a sampling frequency of 1 Hz, in gas sampled from 1.5 m, 0.9 m, and 0.3 m heights in the Fireground Exposure Simulator (FES) prop at the University of Illinois Fire Service Institute, Champaign, Illinois. The immediately dangerous to life and health (IDLH) concentration of 50 parts per million (ppm) is exceeded at all the three sampling heights. A maximum concentration of 295 ppm is measured at the 1.5 m height. The HCN measurement system, expanded to measure HCN simultaneously from two sampling locations, is then deployed in two full-scale experiments designed to simulate a realistic residential fire environment at the Delaware County Emergency Services Training Center, Sharon Hill, Pennsylvania.

Final report of CCQM-P204, comparison on CO2 isotope ratios in pure CO2

Final report of CCQM-P204, comparison on CO2 isotope ratios in pure CO2

The Influence of Temperature on Frequency Modulation Spectroscopy in Atom Gravimeter.

Atom gravimeters use locked lasers to manipulate atoms to achieve high-precision gravity measurements. Frequency modulation spectroscopy (FMS) is an accurate method of optical heterodyne spectroscopy, capable of the sensitive and rapid frequency locking of the laser. Because of the effective absorption coefficient, Doppler broadening and susceptibility depend on temperature, and the signal-to-noise ratio (SNR) of the spectroscopy could be affected by temperature. We present a detailed study of the influence of the temperature on FMS in atom gravimeters, and the experimental results show that the SNR of the spectroscopy is dependent on temperature. In this paper, the frequency of the reference laser is locked by tracking the set point of the fringe slope of FMS. The influence of the frequency-locking noise of the reference laser on the sensitivity of the atom gravimeter is investigated by changing the temperature of the Rb cell without extra operations. The method presented here could be useful for improving the sensitivity of quantum sensors that require laser spectroscopic techniques.

Investigation of ion-ion (Nd–Nd) interaction mechanisms in Sr3LaNb3O12:Nd3+ crystals

The spectral-kinetic characteristics of Nd3+ optical centers (A, B, C centers) in Sr3LaNb3O12 crystals are studied by selective laser spectroscopy technique. It is found that the luminescence decay of A centers (donors) at the first stage is quenched by an ordered ensemble of acceptors (B centers) while the second stage is disordered and follows the Förster law.The macro-(γ(N1) = 55 cm−1/2, γ(N2) = 95 cm−1/2) and microparameters (CDA = 4.5⋅10−40 cm6/s) of the ion–ion (Nd3+–Nd3+) interaction are calculated using the static quenching theory. The closest distance between neodymium ions involved into the ion–ion (A and B optical centers) interaction is calculated to be Rmin. = 0.45 nm, and the boundary time at which the ordered luminescence quenching stage changes for disordered one is determined as tbound. ∼19 μs. It is shown that the A centers luminescence quenching mechanism is the dipole–dipole (S = 6) one.The Nd3+ luminescence build-up and decay kinetics in ensemble of acceptor centers (B centers) in case of unequal donor and acceptor lifetimes (τD <τA) are determined.

Quantum Cascade Laser Based Infrared Spectroscopy: A New Paradigm for Protein Secondary Structure Measurement.

Mid-infrared spectroscopy is one of the major analytical techniques employed for measurements of protein structure in solution. Traditional Fourier Transform-Infrared (FT-IR) measurement is limited by its blackbody light source that is inherently spatially incoherent and has low optical power output. This limitation is pronounced when working with proteins in aqueous solutions. Strong absorbance of water in protein amide I region 1600-1700cm-1 restricts light path length to <10μm and imposes significant experimental challenges in sample and flow cell handling. Emerging laser spectroscopic techniques use high-power coherent laser as light source that overcomes the limitation in FT-IR measurement. In this study, we employed an innovative infrared spectrometer that uses quantum cascade laser (QCL) as light source. Continuous infrared radiation from this laser source can be swiftly swept within the amide I region (1600-1700cm-1) and amide II region (1500-1600cm-1), which makes this technique ideal for protein secondary structure study. Protein solutions as low as 0.5mg/mL were measured rapidly without any sample preparation. Infrared spectra of model proteins were thus collected, and a chemometric model based on partial least squares regression was developed to quantify α-helix and β-strand motifs in protein secondary structure. The model was applied to measurement of the native secondary structure of commercial therapeutic proteins and bovine serum albumin (BSA) and in thermal degradation studies.

Identification and differentiation between olive oil from different Al Jouf olive field areas by optical spectroscopic techniques

Identification and determination of the authenticity of the produced oliveoil by potential spectroscopic techniques have become of nutritional importance to human diet. The study of olive oil is significantly important in trade and business due to the commercial fraud that occurs in the associated business. Al Jouf city, which lies in the northern part of the Kingdom of Saudi Arabia, is famous for its production of the finest quality of olive oil in the kingdom. There is a need to develop feasible in situ identification techniques for the recognition of and discrimination between different olive oil products. One main laser spectroscopic technique known for its superiority over other conventional techniques as an elemental analytical tool is laser induced breakdown spectroscopy (LIBS). Inductive couple plasma mass spectrometry is also a well-known conventional technique with very high sensitivity to most of the elements to the range of parts per billion. However, it requires extensive sample preparation and consumes a lot of time. It has been used as a reference technique to validate the results of the LIBS technique. Moreover, phenolic compounds, which are essential in various types of functional food and folk medicine, were investigated using conventional vibrational analytical tools such as Fourier transform infrared spectroscopy.