Excitation Laser Line Research Articles

Robot‐assisted crack detection on complex shaped components using constant‐speed scanning infrared thermography with laser line excitation

Robot‐assisted crack detection on complex shaped components using constant‐speed scanning infrared thermography with laser line excitation

Challenges in surface‐enhanced Raman scattering signal for ethephon detection: Theoretical and experimental approaches

AbstractEthephon, a widely used growth regulator in fruits and vegetables, requires careful monitoring because of its toxicity. However, as far as we know, only two works are found in the literature regarding surface‐enhanced Raman scattering (SERS) ethephon detection. Indeed, obtaining the SERS signal revealed to be challenging. Therefore, we have evaluated the SERS signal of ethephon using theoretical (as density functional theory and charge‐assisted fragment interaction) and experimental approaches, addressing this limited literature knowledge. Theoretical Raman spectra with Ag or Au atoms at reactive sites exhibited enhanced ethephon SERS signal via AgCl bonding, consistent with the experimental data. Multiple experimental procedures were employed to obtain the SERS signal, including pH variations, salt addition, excitation laser lines, time dependency, and different SERS substrates (Ag colloid and Ag island films). Salt addition (NaCl) improved SERS signal, correlating with Ag colloid aggregation. Analysis in Ag colloid showed the pH 7.0 as optimal for ethephon detection, using freshly prepared Ag colloid + ethephon dispersion with ethephon powder being directly dissolved into Ag colloid. Only the AgCl band intensity improved with time. Ag colloid (wet medium — 633 nm laser line) outperformed Ag island films (dry medium — 785 nm laser line).

Metal–metal bonding, electronic excitations, and strong resonance Raman effect in 2D layered α-MoCl3

Covalent bonding between transition metal atoms is a common phenomenon in honeycomb lattices of layered materials, which strongly affects their electronic and magnetic properties. This work presents a detailed spectroscopic study of α-MoCl3, 2D van der Waals material with covalently bonded Mo2 dimers, with a particular focus on the Mo–Mo bonding. Raman spectra of α-MoCl3 were studied with multiple excitation laser lines chosen in different parts of the absorption spectrum, while polarization measurements aided in the symmetry assignment of the observed modes. Furthermore, far-IR measurements and (Density Functional Theory) DFT phonon computations were performed to complete vibrational assignment. Polarized absorption, PL, and photoelectron spectroscopy supported by DFT calculations were employed to understand the consequences of the Mo–Mo bonding for the electronic structure and the localization/delocalization balance in d3–d3 interactions. A coupling of dimerization-related structural and electronic properties was revealed in the strong resonance Raman enhancement of the Mo–Mo stretching mode at 153 cm−1 when the excitation laser matched the electronic transition between σ-bonding and antibonding orbitals of the Mo2 dimer (σ → σ*). The deeper understanding of the metal–metal bonding and identification of the vibrational and electronic spectroscopic signatures of the dimerization will be of great use for the studies of electron delocalization in magnetic van der Waals materials.

Silver Nanoparticle Films Obtained by Convective Self-Assembly for Surface-Enhanced Raman Spectroscopy Analyses of the Pesticides Thiabendazole and Endosulfan.

Pesticides pose a great threat to human health and their rapid detection has become an urgent public safety issue engaging the scientific community to search for fast and reliable detection techniques. In this context, Surface Enhanced Raman Spectroscopy (SERS) has emerged as a valuable detection and analysis tool due to its high sensitivity and selectivity, proving its suitability for the food industry and environmental monitoring applications. Here, we report on the fabrication of colloidal silver nanoparticle (AgNP) films by convective self-assembly (CSA) on solid planar substrate and their use for the SERS analyses of two types of pesticides, the fungicide thiabendazole (TBZ) and the insecticide α-endosulfan (α-ES). Electron microscopy shows that these nanoparticle films are dense, highly compact, and uniform across several mm2 areas. The SERS efficiency of the fabricated AgNP films is evaluated using a well-known Raman probe, p-aminothiophenol, for multiple excitation laser lines (532 nm, 633 nm, and 785 nm). The films exhibit the largest SERS enhancement factors for 785 nm excitation, reaching values larger than 105. Thiabendazole could be readily adsorbed on the AgNPs without any sample surface functionalization and detected down to 10−6 M, reaching the sub-ppm range. Endosulfan, a challenging analyte with poor affinity to metal surfaces, was captured near the metal surface by using self-assembled alkane thiol monolayers (hexanethiol and octanethiol), as demonstrated by the thorough vibrational band analysis, and supported by density functional theory (DFT) calculations. In addition, principal component analysis (PCA) based on SERS spectra offers significant leverage in discrimination of the molecules anchored onto the metallic nanostructured surface. This present study demonstrates the utility of self-assembled colloidal nanoparticle films as SERS substrates for a broad range of analytes (para-aminothiophenol, thiabendazole, α-endosulfan, and alkanethiols) and contributes to the development of SERS-based sensors for pesticides detection, identification and monitoring.

Raman spectra of twisted bilayer graphene close to the magic angle

In this work, we study the Raman spectra of twisted bilayer graphene samples as a function of their twist-angles (θ), ranging from 0.03° to 3.40°, where local θ are determined by analysis of their associated moiré superlattices, as imaged by scanning microwave impedance microscopy. Three standard excitation laser lines are used (457, 532, and 633 nm wavelengths), and the main Raman active graphene bands (G and 2D) are considered. Our results reveal that electron–phonon interaction influences the G band’s linewidth close to the magic angle regardless of laser excitation wavelength. Also, the 2D band lineshape in the θ < 1° regime is dictated by crystal lattice and depends on both the Bernal (AB and BA) stacking bilayer graphene and strain soliton regions (SP) (Gadelha et al 2021 Nature 590 405–9). We propose a geometrical model to explain the 2D lineshape variations, and from it, we estimate the SP width when moving towards the magic angle.

Unvailing the spin–phonon coupling in nanocrystalline BiFeO3 by resonant two-phonon Raman active modes

We report on temperature dependence of two-phonon Raman spectra in BiFeO3 nanocrystals, above and below the Néel temperature TN using a resonant laser excitation line (λ=532 nm). Two-phonon modes exhibited anomalous frequency hardening and deviation from the anharmonic decay below TN. Such behavior strongly supported the existence of spin-two-phonon interaction, because these modes are known to be very sensitive to the antiferromagnetic ordering. Within the mean-field theory for the nearest-neighbor interaction, the linear relationship between spin–spin correlation function and observed two-phonon frequency shift below TN was obtained. This approach enabled to quantify the spin–phonon interaction by spin–phonon coupling strength for both two-phonon modes and justified the application of mean-field approach. Magnetic measurements revealed the coexistence of antiferromagnetic and weak ferromagnetic phases below TN, which were found non competitive, additionally supporting the mean-field approach from which we deduced that the two-phonon modes in BiFeO3 are correlated with antiferromagnetic ordering below TN.

Raman scattering and fluorescent behaviors in Ba0.96Nd0.0267Ti(1-x)WxO3 (x = 0.00 and x = 0.05) ceramics

This paper reports on the Raman spectroscopy and the photoluminescence spectra of Nd- and W- doped BaTiO3 (BT) ceramics prepared using the molten-salt method. The samples were subjected to annealing at a temperature of 900 °C. Raman spectroscopy was carried out at room temperature on doped ceramics and pure BT. The incorporation of Nd3+ for Ba2+ in A site and W6+ for Ti4+ in B site into BT lattice was also discussed. Moreover, we controlled the frequency and damping of the main optic modes. No significant change was observed in the frequency and damping. But the only frequency of A1[TO3] mode was slightly sensitive to the Nd and W doping. This could reflect the effect of these ions on the Ti site, since this mode corresponds to a distortion of O octahedron around the central Ti ion.In addition, three different exciting laser lines were used for enlightening the Nd3+ emission effect and the contribution of the luminescence processes in the “abnormal” Raman spectra recorded for 785 nm. These abnormal Raman signals originate from a fluorescent effect corresponding to 4F5/2,3/2 →4I9/2 transitions of Ba-site Nd3+ ions. This behavior is confirmed by photoluminescence data at room temperature under 514.5 nm excitation via the presence of two peaks located at 880 nm and 909 nm corresponding to the 4F5/2,3/2 →4I9/2 transition levels, respectively, which also showed a decrease in the intensity of emission spectra following the incorporation of W6+ ions into the Ti site. The fluorescent signals were so intense that they overwhelmed the traditional Raman spectra of our compounds.

A Modular Fluorescent Probe for Viscosity and Polarity Sensing in DNA Hybrid Mesostructures.

There exists a critical need in biomedical molecular imaging and diagnostics for molecular sensors that report on slight changes to their local microenvironment with high spatial fidelity. Herein, a modular fluorescent probe, termed StyPy, is rationally designed which features i) an enormous and tunable Stokes shift based on twisted intramolecular charge transfer (TICT) processes with no overlap, a broad emission in the far‐red/near‐infrared (NIR) region of light and extraordinary quantum yields of fluorescence, ii) a modular applicability via facile para‐fluoro‐thiol reaction (PFTR), and iii) a polarity‐ and viscosity‐dependent emission. This renders StyPy as a particularly promising molecular sensor. Based on the thorough characterization on the molecular level, StyPy reports on the viscosity change in all‐DNA microspheres and indicates the hydrophilic and hydrophobic compartments of hybrid DNA‐based mesostructures consisting of latex beads embedded in DNA microspheres. Moreover, the enormous Stokes shift of StyPy enables one to detect multiple fluorophores, while using only a single laser line for excitation in DNA protocells. The authors anticipate that the presented results for multiplexing information are of direct importance for advanced imaging in complex soft matter and biological systems.

Surface-enhanced Raman scattering for the diagnosis of ulcerative colitis: will it change the rules of the game?

Ulcerative colitis (UC) is a relapsing-remitting inflammatory bowel disease that requires numerous costly invasive investigations which lead to physical and psychological patient discomfort. We need a non-invasive technological approach that would significantly improve its diagnosis. Surface-enhanced Raman scattering (SERS) is a growing technique that can provide a molecular diagnostic fingerprint in just a few minutes, without the need for prior sample preparation. The aim of this pilot in vivo study was to prove that multivariate analysis of SER spectra collected on plasma samples could be employed for non-invasive diagnosis of UC. Plasma samples were collected from healthy subjects (n = 35) and patients with UC (n = 28). SERS spectra were acquired using a 785-nm excitation laser line and a solid plasmonic substrate developed in our laboratory using an original procedure described in the literature. The classification accuracy yielded by SERS was assessed by principal component analysis-linear discriminant analysis (PCA-LDA) and partial least squares discriminant analysis (PLS-DA). PCA-LDA differentiated UC samples from those of healthy subjects with a sensitivity of 86%, a specificity of 92%, and an accuracy of 89%, the AUC being 0.96. The PLS-DA analysis resulted in a sensitivity of 89%, a specificity of 94%, an accuracy of 92%, and an AUC value of 0.92. Several spectral bands were associated with UC: 376-420, 440-513, 686-715, 919-939, 1035-1062, 1083-1093, 1120-1132, 1148-1156, 1191-1211, 1234-1262, 1275-1294, 1382-1405, 1511-1526, and 1693-1702cm-1. Changes in plasma levels of amino acids, proteins, lipids, and other compounds were noted using SERS in patients with UC. Multivariate analysis of SER spectra collected on a solid plasmonic substrate represents a promising alternative to diagnosing UC, as it is non-invasive, easy to use, and fast.

Raman scattering detection of high explosives on human hair

High explosives (HE) represent a high risk to the safety and health of the general population. Therefore, there is an ongoing demand for methods of analysis with limits of detection at trace levels for these hazardous chemicals. Since human hair is one of the main physical attributes of our bodies, the interaction of hair surfaces with HE can be of critical importance in forensic and security applications. Noninvasive in situ approaches such as spectroscopic methods are preferred for elucidating these interactions. Among the spectroscopy-based methodologies, those based on Raman scattering are often favored because the sharpness of the vibrational signals facilitates the precise location of the peak maxima and enables more precise determination of the band shifts due to intermolecular interactions. This preliminary study is based on the detection of the HEs 2,4,6-trinitrotoluene (TNT), 1,3,5-trinitroperhydro-1,3,5-triazine (RDX), and pentaerythritol tetranitrate (PETN) on human hair strands by RS. Raman spectral libraries obtained with a 660-nm laser excitation line were generated for black, bleached, and natural gray hair using direct deposition of PETN, TNT, and RDX. Results obtained were confirmed using portable systems operating at 785 and 1064 nm. Spectral data were preprocessed to correct a high fluorescence background exhibited by the samples due to the indole groups and melanin present in hair. Despite the high fluorescence levels that characterized all the samples, the vibrational signatures that identify the presence of the HEs studied could be detected once the optimum acquisition parameters were established. Among the three hair types studied, gray hair was the best substrate to observe the vibrations of HE crystals on hair. A method limit of detection of 2 ± 1 ng was estimated from image analysis of the HE crystals observed and confirmed as ∼3 ± 1 ng using spectroscopic analysis.

Raman spectra of MXenes Zr2X(X=C and N)

We investigate a polarized Raman characterization of Zr2X (X = C, N), excited by two commonly used laser lines with wavelenghts of 532 nm and 633 nm, based on first principle calculations. The Raman spectra of Zr2X has two Raman shift peaks which correspond to the degenerate in-plane vibration mode (Eg) and out-of-plane vibration mode (A1g). Furthermore, we study the polarization angle dependent Raman intensity for both Eg and A1g modes in parallel and perpendicular configurations for these two materials. We found that the polarization angle dependent Raman intensity is isotropic when the laser line is perpendicular to the Zr2X plane. There are either only two maxima, or two maxima larger than the other maxima, in the parallel configuration when the laser line is parallel to the Zr2X plane, which might be useful in identifying the orientation of Zr2X in experiment. The results show that the locations of the maxima of the polarization angle dependent Raman intensity rarely depend on the exciting laser line, except that of the Eg mode of Zr2N.

Broadband unidirectional scattering in visible ranges and controllable hot-spot spatial transfer via a single nanoparticle

The manipulation of optical fields plays an essential role in various areas including physics, chemistry, surface science, materials science, and nanophotonics. Herein, for the first time, we have demonstrated that a single core–shell nanoparticle features the broadband zero-backward scattering, which spans as broadly as 140 nm in the visible range. This result is acquired by tuning both the electric-dipole mode of the core and the magnetic-dipole mode of the shell, such that an effective modes coupling is achieved. By choosing special modes (or via the specific excitation laser lines), “hot spots” can be controllably transferred among the Au core surface, the shell surface, or both. This work may provide guidance for designing structures with broadband directional scattering characteristics and controllable spatial transfer of “hot spots”.

Probing the structure-function relationship of hemoglobin in living human red blood cells.

Hemoglobin (Hb) is a key component of respiratory system and as such plays important role in human physiology. The studies of Hb's structure and functions are usually performed on cell-free protein; however, it has been shown that there are functionally relevant differences between isolated Hb and Hb present inside red blood cells (RBCs). It is clear that new experimental approaches are needed to understand the origin of these differences and to gain insight into the structure-function relationship of Hb within intact living cells. In this work we present a novel application of Resonance Raman spectroscopy to study heme active site of different forms of human Hb within living RBCs using laser excitation lines in resonance with their Soret absorption bands. These studies revealed that there are no significant changes in the disposition of the Fe-O-O fragment or the Fe-NHis linkage for Hb molecules enclosed in RBCs and these in free isolated states. However, some changes in the orientation of the heme vinyl groups were observed which might account for the differences in the protein activity and ligand affinity. This work highlights importance of protein-based studies and presents a new opportunity to translate these results to physiological cell systems.

Effective SERS substrate obtained by Au deposition at silica surfaces through a top down method

Background: In the last years some of us developed methods for preparing, through simple synthesis protocols, gold nanoparticles supported on silica surfaces: in that cases, bottom-up approaches has been adopted (i.e. starting from HAuCl4 precursor) and high surface area silica (Aerosil 300) was chosen as support (together with controlled pH conditions), to facilitate Au dispersion. The obtained substrates showed the ability to enhance Raman signals of dosed molecules pyridine and bi-pyridine and/or of silanols species populating the silica surface. Following this idea, in this paper we will present results concerning surface-enhanced Raman spectroscopy (SERS) activity of substrates obtained by a top-down technique (i.e. gold sputtering) which allowed depositing gold nanoparticles at surfaces of silica nanoparticles. Pyridine molecule has been then used as a probe molecule to estimate the SERS activity of the obtained substrates. Objectives: The purpose of the work was to study the SERS activity of the prepared substrates through the estimation of limit of detection (LoD) of pyridine molecule dosed from solutions (benzene was used as solvent) with decreasing pyridine concentration. Materials and methods: For the preparation of the samples AOX50 silica (Evonik Industries, surface area of 50 m2/g) in form of pressed disk, a gold target and a K575X Turbo Sputter Coater (Quorum Technologies) were used. Methods applied: UV-Vis-NIR spectroscopy; HR-TEM microscopy; Raman spectroscopy. Results: Prepared Au/AOX50 substrates with nominal Au thickness 10 nm were characterized by the UV-Vis spectroscopy and HR-TEM microscopy. They showed a relatively complex absorption profile extending to the NIR region. The substrates contained gold nanoparticles with diameter in the range of 2.0–3.5 nm. By using the 785 nm exciting laser line (suggested by the results coming from UV-Vis spectroscopy) for recording Raman spectra, it was possible to observe characteristic pyridine Raman signals by contacting Au/AOX50 substrates with vapour phase of benzene solutions with pyridine concentration as low as 10-7 M comprising LoD. This allowed us to estimate roughly an enhancement factor of 108, as compared with 12.4 M pyridine dosed at naked AOX50 silica surface. Conclusion: Through a top-down technique it was possible to prepare effective SERS substrates composed by Au nanoparticles dispersed at AOX50 silica surfaces. LoD for pyridine dosed from the vapour of its benzene solution appeared to be 10-7 M and the SERS enhancement factor, using as a reference Raman spectra of 12.4 M pyridine interacting with naked AOX50 silica, has been estimated to be approximately 108.

Intramolecular and Metal-to-Molecule Charge Transfer Electronic Resonances in the Surface-Enhanced Raman Scattering of 1,4-Bis((E)-2-(pyridin-4-yl)vinyl)naphthalene.

Electrochemical surface-enhanced Raman scattering (SERS) of the cruciform system 1,4-bis((E)-2-(pyridin-4-yl)vinyl)naphthalene (bpyvn) was recorded on nanostructured silver surfaces at different electrode potentials by using excitation laser lines of 785 and 514.5 nm. SERS relative intensities were analyzed on the basis of the resonance Raman vibronic theory with the help of DFT calculations. The comparison between the experimental and the computed resonance Raman spectra calculated for the first five electronic states of the Ag2-bpyvn surface complex model points out that the selective enhancement of the SERS band recorded at about 1600 cm−1, under 785 nm excitation, is due to a resonant Raman process involving a photoexcited metal-to-molecule charge transfer state of the complex, while the enhancement of the 1570 cm−1 band using 514.5 nm excitation is due to an intramolecular π→π* electronic transition localized in the naphthalenyl framework, resulting in a case of surface-enhanced resonance Raman spectrum (SERRS). Thus, the enhancement of the SERS bands of bpyvn is controlled by a general chemical enhancement mechanism in which different resonance processes of the overall electronic structure of the metal-molecule system are involved.

Study of deprotonation processes of polyaniline by differential multiwavelength Raman spectroscopy in an electrochemical system

A layer of polyaniline has been deposited at a gold electrode and studied by differential multiwavelength Raman spectroelectrochemistry. A set of laser line excitation wavelengths was used, including blue (442 nm), green (532 nm), red (633 nm) and far red (785 nm). From the results obtained, the difference spectra between deprotonated (pH 9.0) and protonated (pH 1.0) forms of oxidized and reduced polyaniline were derived and analysed. The characteristic features for different forms of polyaniline were identified, and their dependence on the excitation wavelength was shown. In addition to the usual Raman spectroscopy, the differential spectroscopy enables one to analyse the increase or decrease of intensity for selected Raman bands upon a reversible deprotonation of this polymer.

Structural and optical study of alternating layers of In and GaAs prepared by magnetron sputtering

Currently, the obtention of nano-structures based on III-V materials is expensive. This calls for novel and inexpensive nanostructure manufacturing approaches. In this work we report on the manufacture of a nanostructures consisting of alternating layers of In and GaAs on a silicon substrate by magnetron sputtering. Furthermore, we characterized the produced nanostructures using secondary ion mass spectroscopy (SIMS), X-ray diffraction analysis, and Raman spectroscopy. SIMS revealed variation in the concentration of In atoms across In/GaAs/In interphases, and X-ray diffraction revealed planes corresponding to phases associated with GaAs and InAs due to In interfacial diffusion across GaAs layers. Finally, in order to study the composition and crystalquality of the manufactured nanostaructures, Raman spectra were taken using laser excitation lines of 452 nm, 532 nm, and 562 nm at different points across the nanostructures.This allowed to determine the transverse and longitudinal optical modes of GaAs and InAs,characteristic of a two-mode behavior. An acoustic longitudinal vibrational mode LA(Γ) of GaAs and an acoustic longitudinal mode activated by disorder (DALA) were observed. These resulted from the substitution of Ga atoms for In atoms in high concentrations due to the generation of Ga(VGa) and/or Arsenic(VAs) vacancies.This set of analyses show that magnetron sputtering can be aviable and relatively low-cost technique to obtain this type of semiconductors.

Quantification of fluorescence emission from extraterrestrial materials and its significance for planetary Raman spectroscopy

AbstractFluorescence emission has been a serious impediment in the application of Raman spectroscopy to terrestrial geologic samples. It is largely unknown how significant the fluorescence problem would affect Raman analyses during a planetary surface exploration mission. We have completed a set of two experimental studies to quantitatively evaluate the fluorescence emission excited by multiple wavelengths from a set of 21 stony meteorites that represent 98.9% (by types) of all stony meteorites collected, named, and classified worldwide. Our data revealed a general trend, that is, the non‐Raman emission intensities of extraterrestrial materials are two to three orders of magnitude lower than those of typical terrestrial clays and the soils from hyperarid Mars‐analog region (Atacama Desert). Based on &gt;4,500 Raman spectra (excited by continuous wave [continuous wave] 532‐nm laser line) obtained by auto‐scans on these 21 meteorites, we found that the average percentage of informative Raman spectra is nearly 98%, with a standard deviation of 2% and the lowest value of 93%. We also found that the information on major and minor mineral phases revealed by our multispots Raman measurements are consistent with those published in Meteoritic Bulletin database for the examined meteorites. In conclusion, our experimental results demonstrated that the fluorescence interference that sometimes concealed the Raman signals of terrestrial samples would not be a threat to planetary Raman spectroscopy that uses CW 532‐nm laser line for excitation. This conclusion is consistent with the in situ fluorescence observations made during two missions on Mars and with many Raman spectroscopic studies of lunar rocks and soils returned by Apollo missions.

Raman spectroelectrochemical study of redox dye Nile blue adsorbed or electropolymerised at a gold electrode

The redox dye Nile blue has been adsorbed and electrochemically polymerised at a roughened gold electrode. The resulting modified electrodes were subjected to Raman spectroelectrochemical study with 785 nm laser line excitation. For both types of electrodes, well-expressed and rich in features Raman spectra were obtained. The spectra are closely related to those of another oxazine type redox dye Meldola blue. At solution pH 7.0, the overall intensity of the Raman spectra for both types of modified electrodes appears higher than in a pH 1.0 solution. Probably, this is caused by different light absorbance properties of this dye in two solutions. In a pH-neutral solution, the dye possess light absorbance in the red range of the visible spectrum, thus, resonance enhancement is possible. The intensity of the Raman spectra also increases by the shift of the electrode potential to higher positive values. This effect could be understood taking into account an intensifying colouration of the dye at a stepwise increase of the electrode potential due to a continuous growth of the content of oxidised forms within the electrode-bound layer.

SERS, XPS and DFT Study of Xanthine Adsorbed on Citrate-Stabilized Gold Nanoparticles.

We have studied the adsorption of xanthine, a nucleobase present in human tissue and fluids that is involved in important metabolic processes, on citrate-reduced gold colloidal nanoparticles by means of surface-enhanced Raman scattering (SERS), absorption, and X-ray photoelectron spectroscopy (XPS) measurements, along with density functional theory (DFT) calculations. The citrate anions stabilize the colloidal suspensions by strongly binding the gold nanoparticles. However, these anions do not impair the adsorption of xanthine on positively-charged active sites present on the metal surface. We have obtained the Fourier transform (FT)-SERS spectra of adsorbed xanthine by laser excitation in the near infrared spectral region, where interference due to fluorescence emission does not usually occur. In fact, the addition of chloride ions to the Au/xanthine colloid induces the aggregation of the gold nanoparticles, whose plasmonic band is shifted to the near infrared region where there is the exciting laser line of the FT–Raman instrument. Hence, this analytical approach is potentially suitable for spectroscopic determination of xanthine directly in body fluids, avoiding fluorescence phenomena induced by visible laser irradiation.