Applied Spectroscopy

An approach binary spectronephelometry (BSN) to perform real-time simultaneous noninvasive in situ physical and chemical analysis of bacterial cultures in fluid media is described. We choose to characterize cultures of Escherichia coli (NC), Pseudomonas aeruginosa (PA), and Shewanella oneidensis (SO) in the specific case of complex media whose Raman spectrum cannot be unambiguously assigned. Nevertheless, organism number density and a measure of the chemical makeup of the fluid medium can be monitored noninvasively, simultaneously, and continuously, despite changing turbidity and medium chemistry. The method involves irradiating a culture in fluid medium in an appropriate vessel (in this case a standard 1 cm cuvette) using a near infrared laser and collecting all the backscattered light from the cuvette, i.e., the Rayleigh–Mie line and the inelastically emitted light which includes unresolved Raman scattered light and fluorescence. Complex “legacy” media contain materials of biological origin whose chemical composition cannot be fully delineated. We independently calibrate this approach to a commonly used reference, optical density at 600 nm (OD600) for characterizing the number density of organisms. We suggest that the total inelastically emitted light could be a measure of the chemical state of a biologically based medium, e.g., lysogeny broth (LB). This approach may be useful in a broad range of basic and applied studies and enterprises that utilize bacterial cultures in any medium or container that permits optical probing in the single scattering limit.

Ascorbic acid (AA), or vitamin C, is an important reactive biological molecule in vivo, and an abnormal level of AA is associated with many diseases. Therefore, the rapid, sensitive, and selective detection of AA levels is of significance in cases of medical assay and diagnosis. Compared with other nanoparticles, lanthanide coordination polymer nanoparticles (Ln-CPs) have been demonstrated as the excellent biomolecule sensing platforms due to their unique optical properties and intrinsic porosities. In this work, the cerium coordination polymer nanoparticles ATP-Ce-Tris were synthesized in a simple and quick way. The synthesized ATP-Ce-Tris nanoparticle shows the characteristic peak of Ce³⁺ located at 365 nm, which is corresponding to the 4f→5d transition of Ce³⁺. In the presence of Fe³⁺, the fluorescence of ATP-Ce-Tris quenched, and the following added ascorbic acid (AA) makes it restoring effectively. Based on this, we constructed a fluorescence probe with excellent sensitivity for AA sensing in a wide linear relationship from 0.05 to 500 μM. The detection limit was as low as 18 nM (signal-to-noise ratio of three), which is one or two orders of magnitude lower than those of reported sensors. The proposed sensing systems also exhibits excellent sensitivity for AA detection in human serum sample, exploiting a valuable platform for AA analysis in clinic diagnostic and drug screening.

In this study, the performance of a thermoelectric cooler (TEC) as a simple and easy-to-assemble freezing instrument has been evaluated. Experiments were carried out using samples with different viscosity ranging from 44.07 to 16 965.80 MPa. The analysis of sodium component of the samples by direct laser irradiation of frozen samples showed emission enhancement and higher signal-to-noise ratio compared to that of liquids. This work also focused on using chemometrics methods such as principal component analysis (PCA) to compare the principal component score separation and clustering pattern between frozen and liquid samples. The PCA was constructed by dividing the samples into two different categories: (i) type (paste, cream, gel, and oil) and (ii) viscosity (more than and less than 10 000 MPa). The frozen samples showed a more established separation and clustering compared to that acquired from the liquid samples. However, poorer clustering pattern of some frozen samples could be due to the heat transfer during laser–sample interaction inducing surface melting and splashing. The average laser-induced breakdown spectroscopy (LIBS) spectra were taken at as many different surface areas as possible to ensure the sample surface always maintain similar freezing temperature. This work showed that the TEC pre-treatment method had improved the LIBS measurement of the liquid samples.

Little is known concerning Phoenician and Punic cosmetics, and pertinent studies and analyses on archaeological finds are particularly scanty. The present study has taken into account 22 archaeological red and pink Punic make-up samples collected in several Sicilian museums. The samples were analyzed by infrared spectroscopy, Raman microscopy, and surface-enhanced Raman spectroscopy (SERS). The analyses revealed an interesting and unusual variability in the use of raw materials, ranging from the mineral to the organic world. Not only traditional dye-based pigments were identified, but also rare ones never reported previously for this use. We show also an occurrence unusual in antiquity of a lead chromate block presumably intended to be ground just before its use in cosmetics.

This article presents a method for extracting the optical constants of homogeneous isotropic materials using the infrared spectra of that material. The method is based on using the harmonic oscillator model of molecular polarizability to obtain optical constants, then calculating the spectrum, comparing the calculated spectrum to an experimental spectrum of the material, and adjusting the model parameters until a close fit between the spectra is obtained. Corrections that need to be made to the experimental spectra in order to remove instrumental distortions are also briefly described. The remainder of the article centers on describing how the optical constants can be used to simulate spectra of that material in different experimental arrangements and the benefits that spectral simulations afford to experimentalists.

Almost all archaeometric studies on Chinese ceramics are carried out on the excavation materials. Therefore, a detailed, comparable database that defines different workshops and production periods already exists. But the masterpieces preserved at museums, art galleries, and/or private collections, which are artistically considered as genuine artifacts, also require similar scientific investigations to define their provenance and authenticity. The research on artworks is only possible with the use of portable, noninvasive techniques that are developing daily concerning their capability of detection limits, rate of measurement, and ease of use. In this study, the results obtained with a handheld X-ray fluorescence (XRF) (also called portable XRF) and wavelength dispersive XRF instrument were compared to evidence the efficiency and drawbacks of the portable model. To achieve this goal, 12 sherds, which represent blue-and-white porcelains of Yuan and Ming Dynasties (China), were analyzed and the chemical composition of the body, glaze, and blue decor were identified. The comparison of the results with the measurements carried out on the excavation materials, which are produced in both southern and northern China, revealed the authenticity of the artifacts. Even sodium cannot be detected with portable XRF, the distinction of different production centers is possible with the detection of major (Mg, Al, Si, K, Ca), minor (Fe, Ti), and trace elements (Zr, Sr, Rb).

Distribution of substandard and falsified (SF) medicines is on the rise, and its impact on public health, particularly in low-resource countries, is becoming increasingly significant. Portable, nondestructive screening devices can support regulatory authorities in their defense against the spread of SF medicines. Vibrational spectroscopy is an ideal candidate due to its sampling ease and speed. In this work, five portable, among which four are considered low-cost, spectroscopic devices based on near-infrared (NIR), Raman, and mid-infrared (MIR) were evaluated to quantify active pharmaceutical ingredients (APIs) and formulation accuracy within simulated authentic, falsified, and substandard medicines. Binary sample mixtures containing a typical API in antimalarial, antiretroviral, or anti-tuberculosis medicines were assessed. In both univariate and multivariate analyses, the API quantification performance of the digital light processing (DLP) NIR spectrometer and a handheld Raman device consistently matched or exceeded that of the other NIR spectrometers and a scientific grade MIR spectrometer. In the formulation accuracy tests, data from all devices, other than the silicon photodiode array NIR spectrometer, were able to create regression models with less than 6% error. From this exploratory study, we conclude that certain portable NIR devices hold significant promise as cost-effective screening tools for falsified and potentially substandard medicines, and they warrant further investigation and development.

Studies on the reflectance spectra of different mixtures of sand and silt were performed in the infrared spectral region of 7–25 µm to explore the behavior of a second reststrahlen band occurring between 17 and 25 µm with respect to different mixtures of sand and silt. The reflectance spectrum of all samples exhibited reststrahlen bands within both the long wavelength infrared (LWIR) and the very long wavelength infrared (VLWIR) regions of the reflectance spectrum. Results demonstrate that both LWIR and VLWIR reststrahlen bands increase in area as the fraction of sand increases to 80%. More importantly, the data demonstrate that the VLWIR reststrahlen band, like that in LWIR, exhibits a significant and reproducible decrease in reflectivity for mixed soil versus weathered soil.

Time-gated picosecond laser-induced breakdown spectroscopy (ps-LIBS) for the determination of local equivalence ratios in atmospheric-pressure adiabatic methane–air flames is demonstrated. Traditional LIBS for equivalence-ratio measurements employ nanosecond (ns)-laser pulses, which generate excessive amounts of continuum, reducing measurement accuracy and precision. Shorter pulse durations reduce the continuum emission by limiting avalanche ionization. Furthermore, by contrast the use of femtosecond lasers, plasma emission using picosecond-laser excitation has a high signal-to-noise ratio (S/N), allowing single-shot measurements suitable for equivalence-ratio determination in turbulent reacting flows. We carried out an analysis of the dependence of the plasma emission ratio H_α (656 nm)/N_II (568 nm) on laser energy and time-delay for optimization of S/N and minimization of measurement uncertainties in the equivalence ratios. Our finding shows that higher laser energy and shorter time delay reduces measurement uncertainty while maintaining high S/N. In addition to atmospheric-pressure flame studies, we also examine the stability of the ps-LIBS signal in a high-pressure nitrogen cell. The results indicate that the plasma emission and spatial position could be stable, shot-to-shot, at elevated pressure (up to 40 bar) using a lower excitation energy. Our work shows the potential of using ps-duration pulses to improve LIBS-based equivalence-ratio measurements, both in atmospheric and high-pressure combustion environments.

We demonstrate the performance of a dual frequency comb quantum cascade laser (QCL) spectrometer for the application of vibrational Stark spectroscopy. Measurements performed on fluorobenzene with the dual-comb spectrometer (DCS) were compared to results obtained using a conventional Fourier transform infrared (FT-IR) instrument in terms of spectral response, parameter estimation, and signal-to-noise ratio (S/N). The dual-comb spectrometer provided similar qualitative and quantitative data as the FT-IR setup in 250 times shorter acquisition time. For fluorobenzene, the DCS measurement resulted in a more precise estimation of the fluorobenzene Stark tuning rate ((0.81 ± 0.09) cm⁻¹/(MV/cm)) than with the FT-IR system ((0.89 ± 0.15) cm⁻¹/(MV/cm)). Both values are in accordance with the previously reported value of 0.84 cm⁻¹/(MV/cm). We also point to an improvement of signal-to-noise ratio in the DCS configuration. Additional characteristics of the dual-comb spectrometer applicable to vibrational Stark spectroscopy and their scaling properties for future applications are discussed.

This study expresses our results on surface-enhanced Raman spectroscopy (SERS) analyses of neonicotinoid insecticide thiacloprid, i.e., Calypso 480 SC, in quantities much smaller than usually applied in the agricultural medicine. Advanced Ag and Au nanostructures created by the thermal deposition technique on Al₂O₃ ceramic were applied as active substrates for SERS analyses. The minimum concentration of thiacloprid detected was 380 µM and the enhancement factor was estimated to be about 3 × 10³. The intensity of the SERS peaks increased by an order of magnitude after pulsed laser annealing of the films and formation of nanoparticle arrays and the enhancement factor reached ≈10⁴, respectively. The proposed study has direct bearing on the environment and human health by detection of small amounts or residue of harmful pollutants using a relatively cheap and easy method to produce active SERS substrates.

Eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) are commercially important omega-3 fatty acids found in fish oils. Here we demonstrate that a handheld Raman spectrometer can be used to quantitate these compounds in intact fish oil capsules, avoiding oxidizing risk. Partial least squares regression models were prepared by relating Raman spectral variance to EPA and DHA concentrations determined using gas chromatography–mass spectrometry (GC-MS) analysis of fatty acid methyl esters in 15 commercial samples containing 145–473 mg g⁻¹ EPA and 101–260 mg·g⁻¹ DHA. Handheld Fourier transform (FT)-Raman models had root mean square errors of cross-validation of 38 mg g⁻¹, 24 mg g⁻¹, and 32 mg·g⁻¹ for EPA, DHA, and EPA+DHA, respectively. Models generated from a benchtop FT-Raman spectrometer had corresponding errors of 32 mg·g⁻¹, 22 mg·g⁻¹, and 26 mg·g⁻¹. By comparison, average standard deviations from triplicate GC-MS analyses were 11 mg·g⁻¹ for EPA and 9 mg·g⁻¹ for DHA.