Spectroscopy Journal

Unsaturated fatty acids have cis and trans isomers. The naturally stable isomer is the cis isomer, which is changed to the trans isomer by a thermal reaction. The reaction order, reaction constant, and activation energy are required to confirm the reaction mechanism. Therefore, the concentrations of the cis and trans isomers must be determined simultaneously. In the present study, oleic acid (cis isomer) and elaidic acid (trans isomer) were measured using Raman spectroscopy and partial least squares regression. The thermal reaction of oleic acid was performed at several temperatures. The reaction was determined as a first-order reaction. The reaction rate constants at several temperatures were determined as 1.3 × 10⁻³ to 5.2 × 10⁻³/h at 100 °C to 160 °C by plotting the logarithm of the oleic acid concentration against reaction time. The activation energy obtained by the Arrhenius plot was 31 kJ/mol. Full article

Time-resolved fluorescence techniques, such as fluorescence lifetime imaging microscopy (FLIM), fluorescence correlation spectroscopy (FCS), and time-resolved fluorescence spectroscopy, are ideally suited for investigating molecular dynamics and interactions in biological and chemical systems. However, the analysis and interpretation of these datasets require advanced computational tools capable of handling diverse models and datasets. This paper presents a comprehensive software solution designed for model generation and analysis of time-resolved fluorescence data with a strong focus on fluorescence for quantitative structural analysis and biophysics. The software supports the integration of multiple fluorescence techniques and provides users with robust tools for performing complex model analysis across diverse experimental data. By enabling global analysis, model generation, data visualization, and sampling over model parameters, the software enhances the interpretability of intricate fluorescence phenomena. By providing flexible modeling capabilities, this solution offers a versatile platform for researchers to extract meaningful insights from time-resolved fluorescence data, aiding in the understanding of dynamic biomolecular processes. Full article

Fourier-transform infrared (FTIR) spectroscopy can detect biomolecular changes in bacterial cells in response to drugs or other stimuli. Fully developing this area requires an understanding of IR spectral changes associated with the growth of unperturbed cells. Such an understanding is still lacking, however. To address this issue, attenuated total reflectance (ATR) FTIR spectroscopy has been used to probe changes in the composition of Staphylococcus aureus ATCC 6538 cells during exponential growth, with a 30 min time resolution. We find prominent spectral changes in proteins, nucleic acids, and carbohydrates evolving from the early (30–120 min) to the late (240–360 min) log phase of growth. Principal component analysis (PCA) shows that spectra obtained for cells during the early and late log phases of growth can be discriminated against with 100% accuracy. Protein-related spectral features are most significant in spectra collected at 30- and 90-min post-inoculation and provide a robust basis for temporal differentiation. Spectral changes that occur during the first 30 min after inoculation are shown to reverse over the next 30–120 min, indicating dynamic adaptations during cellular growth. Overall, we demonstrate a band assignment strategy based on time resolution, underscoring the utility of FTIR spectroscopy in dynamic studies of bacterial cells. Full article

Accurate estimation of optical properties and hemodynamic parameters is critical for advancing frequency-domain diffuse optical spectroscopy (FD-DOS) techniques in clinical neuroscience. However, conventional FD-DOS models often assume planar air–tissue interfaces, introducing errors in anatomically curved regions such as the forehead or infant heads. This study evaluates the impact of incorporating tissue curvature into forward models for FD-DOS analysis. Using simulations and optical phantoms, we demonstrate that curved models reduce errors in absorption coefficient estimation from 20% to less than 10% in high-curvature scenarios. Within the curvatures tested, even minor curvature mismatches resulted in errors significantly lower than those observed from planar approximations (p < 0.001). In low-curvature regions, curved models yielded errors comparable to planar models (<5% in both cases). When applied to human data, our proposed curved model increased absorption and hemoglobin concentration estimates by 10–15% compared to standard semi-infinite models, closer to physiological expectations. Overall, these results quantitatively demonstrate that accounting for tissue curvature in FD-DOS forward models significantly improves the accuracy of optical property estimation. We propose a numerical framework that achieves this in a fast and reliable manner, advancing FD-DOS as a robust tool for clinical and research applications in anatomically complex regions. Full article

We report the design, implementation and test of a Mid-Infrared spectrometer proof-of-concept that utilizes an uncooled micro-bolometer array, sensitive in the 3–14 µm spectral range, integrated in a conventional optical dispersive spectrometry setup. Such a spectrometer enables instantaneous measurements across this broad spectral range, comparable to that of a FTIR but with a more compact design and without moving parts. This makes it ideal for integration into portable, battery-powered devices such as handheld scanners. The Mid-IR range offers significant advantages over NIR-SWIR spectrometers, especially for organic compound analysis. A notable application for this instrument: plastic waste sorting—including black plastics—was tested with significant accuracy and effectiveness of plastic classification (on PP, PET and PE samples) with a very simple machine learning algorithm. Full article

The pharmaceutical industry has witnessed exponential growth in production volumes, driven by factors such as an aging global population and the COVID-19 pandemic. To meet the demand for high product quality alongside increased productivity, there is a growing emphasis on developing innovative Fermentation Analytical Technology (FAT) and Process Analytical Technology (PAT) tools for real-time performance monitoring, modeling, measurement, and control. Building on our earlier work involving in-line monitoring of Bordetella pertussis fermentations using fluorescence spectroscopy, this review explores and compares the applications of vibrational and fluorescence spectroscopy for real-time bioprocess monitoring. We examine recent technological advancements and ongoing challenges in the field. Various spectroscopic techniques are evaluated in terms of cost-effectiveness and practical applicability, with a particular focus on in-line spectroscopy as a promising, low-cost solution for effective bioprocess monitoring. Full article

This paper presents a systematic absorption and circular dichroism spectroscopy study of short single strands of DNA, from 2 to 20 bases. They are composed of a sequence-specific nucleobase composition, either adenine (A), thymine (T), or AT repeats. The absorption spectra hypochromism and the circular dichroism one show butterfly-shaped spectra. Data analysis conducted on the spectra of these oligomers provides evidence for the formation of excitons and their delocalization length along the strand of DNA in relation to how many bases are involved in the excitonic coupling. In particular, the extent of this coupling is limited to adjacent nucleobases in the case of pure adenine strands but spans multiple nucleobases in the case of pure thymine strands. Predictably, AT repeats show a mixed behavior between the two. Full article

Mössbauer spectroscopy can be advantageous for studying catalysts. In particular, its use in in situ studies can provide unique access to structural features. However, special attention must be paid to the interpretation of data, since in most studies, the samples are not perfectly homogeneous. Balance and compromise should be found between the refinement of evaluations by extracting and interpreting data from spectra, while also considering the presence of possible inhomogeneities in samples. In this review, examples of studies on two types of catalysts are presented, from which, despite possible inhomogeneities, clear statements can be derived. The first example pertains to selected iron-containing microporous zeolites (with ⁵⁷Fe Mössbauer spectroscopy), from which unique information is collected on the coordination of iron ions. The second example is related to studies on supported PtSn alloy particles (with ¹¹⁹Sn probe nuclei), from which reversible modifications of the tin component due to interactions with the reaction partners are revealed. Full article

In this review, we demonstrate that the carotenoids–retinoids–cytochromes c triangle is an important cancer factor controlling most aspects of the development, proliferation, and progression of cancer. Cancer is a multidimensional disease that needs a balance between the enzymes controlling the amount of carotenoids, the production of retinoids (particularly retinoic acid), and the concentration of cytochromes (particularly cytochrome c). The proper balance between these enzymes will help in overcoming the bottleneck in cancer therapeutics using drugs. First, we discuss the impact of carotenoids on cancer. In the next section, we show how carotenoid cleavage products, including retinal, retinol, and retinoic acid, induce positive and negative effects on cancer development. Then, we discuss the impact of cytochrome c on cancer. We have demonstrated that an alteration in the cellular redox status of cytochrome c is a crucial factor in cancer, influencing numerous aspects of malignant progression. The results obtained by Raman imaging showed significant differences between normal and cancerous human cells. First, a significant redox imbalance in the hem group of cytochrome c with the upregulation of the reduced form of hem is observed. Cancer tissue has a higher concentration of reduced cytochrome c than normal tissue. Secondly, both breast and brain tumors exhibit enhanced de novo lipogenesis in comparison to normal cells. Third, this research illustrates the essential function of the extracellular matrix in oxidative phosphorylation and apoptosis pathways. Full article

Fourier transform infrared (FTIR) spectroscopy, coupled with machine learning (ML) analysis can be used for disease monitoring with high speed and accuracy, including the classification of mosquito samples by species, age and malaria detection. However, current FTIR instruments use low-brightness thermal light sources to generate infrared light, which limits their ability to measure complex biological samples, especially where high spatial resolution is necessary, such as for specific mosquito tissues. Moreover, these systems lack portability, which is essential for field applications. To overcome these issues, spectrometers using quantum cascade lasers (QCLs) have become an attractive alternative for building fast, and portable systems due to their high electrical-to-optical efficiency, small size, and potential for low-cost. Here, we present a QCL-based spectrometer prototype designed for large scale, low-cost, environmental field-based disease surveillance. Full article

Optical spectroscopic methods such as Raman spectroscopy offer several advantages for the analysis of water-soluble polymers (WSPs). There is often no need for complex sample preparation, and measurements are usually rapid, mostly non-destructive and no harmful chemicals are required. In this work, we investigated WSPs and their interaction with bacteria using Raman spectroscopic methods. We analyzed four different WSPs, each with three different molar masses, in solid form using Raman microscopy, and in aqueous solutions using another Raman system designed for measurements in cuvettes, to train predictive models for concentration determination. Thus, we were able to show both the high potential of these approaches, especially for fast and easy investigations both qualitatively and quantitatively, as well as their limitations. Furthermore, we chose one of the molar masses of each tested polymer to carry out extensive Raman spectroscopic investigations with Escherichia coli and Enterococcus faecium, and revealed that bacterial cells exposed to polymers exhibited distinguishable spectral characteristics compared to those not in contact with polymers. Using Raman microscopy combined with partial least squares discriminant analysis (PLS-DA), we effectively distinguished between these groups. Further chemometric analysis indicated potential polymer-induced modifications to the bacterial cell membranes. While this differentiation may partly reflect polymer interactions at the membrane level, it could also correspond to shifts in bacterial growth phases. Together, these findings suggest a complex interplay between polymer exposure and bacterial physiological states. Full article

Significance: We describe a novel, specimen-free diagnostic platform that can immediately detect both a metabolite (glucose) or an infection (COVID-19) by non-invasively using Raman spectroscopy and machine learning. Aim: Current diagnostic testing for infections and glucose monitoring requires specimens, disease-specific reagents and processing, and it increases environmental waste. We propose a new hardware–software paradigm by designing and constructing a finger-scanning hardware device to acquire Raman spectroscopy readouts which, by varying the machine learning algorithm to interpret the data, allows for diverse diagnoses. Approach: A total of 455 patients were enrolled prospectively in the COVID-19 study; 148 tested positive and 307 tested negative through nasal PCR testing conducted concurrently with testing using our viral detector. The tests were performed on both outpatients (N = 382) and inpatients (N = 73) at Holy Name Medical Center in Teaneck, NJ, between June 2021 and August 2022. Patients’ fingers were scanned using an 830 nm Raman System and then, using machine learning, processed to provide an immediate result. In a separate study between April 2023 and August 2023, measurements using the same device and scanning a finger were used to detect blood glucose levels. Using a Dexcom sensor and an Accu-Chek device as references, a cross-validation-based regression of 205 observations of blood glucose was performed with a machine learning algorithm. Results: In a five-fold cross-validation analysis (including asymptomatic patients), a machine learning classifier using the Raman spectra as input achieved a specificity for COVID-19 of 0.837 at a sensitivity of 0.80 and an area under receiver operating curve (AUROC) of 0.896. However, when the data were split by time, with training data consisting of observations before 1 July 2022 and test data consisting of observations after it, the model achieved an AUROC of 0.67, with 0.863 sensitivity at a specificity of 0.517. This decrease in AUROC may be due to substantial domain shift as the virus evolves. A similar five-fold cross-validation analysis of Raman glucose detection produces an area under precision–recall curve (AUPR) of 0.58. Conclusions: The combination of Raman spectroscopy, AI/ML, and our patient interface admitting only a patient’s finger and using no specimen offers unprecedented flexibility in introducing new diagnostic tests or adapting existing ones. As the ML algorithm can be iteratively re-trained with new data and the software deployed to field devices remotely, it promises to be a valuable tool for detecting rapidly emerging infectious outbreaks and disease-specific biomarkers, such as glucose. Full article

Dehydration is known to affect the rate of electron transfer backreaction from the light-induced charge separation state P⁺Q_A⁻ to the neutral ground state PQ_A in photosynthetic bacterial Reaction Centers. On the other hand, a 20 s continuous illumination period has been demonstrated to induce (at 297 K) formation of one or more light-adapted states at different levels of dehydration; these light-adapted states are believed to be related to peculiar response(s) from the protein. In this work, we applied time-resolved rapid-scan FTIR difference spectroscopy to investigate the protein response under dehydrated conditions (RH = 11%) at 281 K both after a flash and under prolonged continuous illumination. Time-resolved FTIR difference spectra recorded after a laser flash show a protein recovery almost synchronous to the electron transfer backreaction P⁺Q_A⁻ → PQ_A. Time-resolved FTIR difference spectra recorded after 20.5 s of continuous illumination (RH = 11%, T = 281 K) surprisingly show almost the same kinetics of electron transfer back reaction compared to spectra recorded after a laser flash. This means that the mechanism of formation of a light-adapted stabilized state is less effective compared to the same hydration level at 297 K and to the RH = 76% hydration level (both at 281 K and 297 K). Time-resolved FTIR difference spectra after continuous illumination also suggest that the 1666 cm⁻¹ protein backbone band decays faster than marker bands for the electron transfer back reaction P⁺Q_A⁻ → PQ_A. Finally, FTIR double-difference spectra (FTIR difference spectrum recorded after 18.4 s illumination minus flash-induced FTIR difference spectrum) suggest that at RH = 11%, a light-adapted state different from the one observed at RH = 76% is formed. A possible interpretation is that at RH = 11%, the protein response is modified by the fact that only protons can move easily, differently from water molecules, as instead observed for RH = 76%. This probably makes the formation of a real light-adapted P⁺Q_A⁻ stabilized state at RH = 11% unfeasible. Full article

The change in the geometry of 1,3-dicyanobenzene upon electronic excitation to the lowest excited singlet state has been elucidated by simultaneous Franck–Condon (FC) fits of the fluorescence emission spectra originating from the vibrationless origin and from four vibronic bands. The geometry changes obtained from the FC fits were compared to the results of ab initio calculations at the SCS-CC2/cc-pVTZ level of theory. We found close agreement between the spectral determination and the theoretical prediction of the geometry changes upon excitation. The aromatic ring opens upon excitation, resulting in a symmetrically distorted structure in the excited state. Full article

Rare-earth doped transparent glass-ceramic waveguides are playing a very crucial role in integrated optics. We fabricated ZnO-HfO₂ hybrid nanocrystals embedded with 70 SiO₂–(30-x) HfO₂–x ZnO (x = 0, 2, 5 and 7 mol %) ternary transparent glass-ceramic waveguides doped with 1 mol % Eu-ions. The formation and size of the nanocrystals evolved with an increase in ZnO concentration in the glass-ceramic waveguides. In this context, key factors of such nanocrystals embedded active glass-ceramic waveguides were optical losses and transparency. A lab-built m-line experimental set-up was used for the characterization of the waveguides. On the other hand, optical gain measurements of the Eu-doped hybrid nanocrystals embedded glass-ceramic waveguides were performed using the variable stripe length method. The optical amplification of the waveguides was investigated on the red emission line (⁵D₀ → ⁷F₂) of Eu-ions pumped by a 532 nm laser in a stripe-like geometry generated by a cylindrical lens. Here, we report, the optical gain in rare-earth activated glass-ceramic waveguides with nanocrystals of varying sizes formed in the waveguides with increasing ZnO concentration. Full article

In this paper, methods for the determination of clopidogrel bisulphate and metamizole sodium in rinse waters from industrial equipment, using multiwavelength UV spectrometry and the calculation of areas under curves, are proposed. Spectra were recorded in an aqueous medium without preliminary pH adjustment. A numerical integration of the spectra was performed in the wavelength range of 210 to 290 nm for clopidogrel bisulphate, and 220 to 320 nm for metamizole sodium. The methods enable the determination of clopidogrel bisulphate and metamizole sodium in solution in the concentration range of 1–100 mg/L, do not require lengthy sample preparation and complex analytical equipment, and are suitable for the routine determination of these drugs in rinse waters from industrial equipment. Full article

Bulk 2D electronic–vibrational (2D-EV) and 2D vibrational–electronic spectroscopies (2D-VE) were previously developed to correlate the electronic and vibrational degrees of freedom simultaneously, which allow for the study of couplings between electronic and vibrational transitions in photo-chemical systems. Such bulk-dominated methods have been used to extensively study molecular systems, providing unique information such as coherence sensitivity, molecular configurations, enhanced resolution, and correlated states and their dynamics. However, the analogy of interfacial 2D spectroscopy has fallen behind. Our recent work presented interface-specific 2D-EV spectroscopy (i2D-EV). In this work, we develop interface-specific two-dimensional vibrational–electronic spectroscopy (i2D-VE). The fourth-order spectroscopy is based on a Mach–Zehnder IR interferometer that accurately controls the time delay of an IR pump pulse pair for vibrational transitions, followed by broadband interface second-harmonic generation to probe electronic transitions. We demonstrate step-by-step how a fourth-order i2D-VE spectrum of AP3 molecules at the air/water interface was collected and analyzed. The line shape and signatures of i2D-VE peaks reveal solvent correlations and the spectral nature of vibronic couplings. Together, i2D-VE and i2D-EV spectroscopy provide coupling of different behaviors of the vibrational ground state or excited states with electronic states of molecules at interfaces and surfaces. The methodology presented here could also probe dynamic couplings of electronic and vibrational motions at interfaces and surfaces, extending the usefulness of the rich data that are obtained. Full article

Local heating was performed on a thermoplastic polymer film by contact with the tip of a soldering iron heated above the glass-transition temperature. The locally heated area was measured using microscopic Raman scattering spectroscopy, and the spatial distribution of the crystallinity was obtained from the low-frequency peak. The crystallinity distribution can be evaluated using the microscale spatial resolution. The temperature distribution around the locally heated area was calculated by applying the heat conduction equation, and good correspondence was obtained with the obtained crystallinity. Full article

Industrial agriculture, while necessary to meet current food production needs, can have damaging effects on the environment and local water supply. For monitoring purposes, Raman spectra of common fertilizers in solution are measured and presented. Raman spectra of the fertilizer species combined with data from Inductively Coupled Plasma Emission Spectrometry (ICP-AES) is used to construct an empirical model of contaminant concentration. This work expands upon the authors’ prior work in Raman Spectroscopy of Common Fertilizers in Bulk and in Aqueous Solution, which was presented during the virtual sessions at OSA Optical Sensors and Sensing Congress in 2021 (AIS, FTS, HISE, SENSORS, ES). Full article