Spectroscopy Journal

19 pages, 6192 KiB

Open AccessArticle

Dynamic FTIR Spectroscopy for Assessing the Changing Biomolecular Composition of Bacterial Cells During Growth

by Gary Hastings, Michael Nelson, Caroline Taylor, Alex Marchesani, Wilbur Hudson, Yi Jiang and Eric Gilbert

Spectrosc. J. 2025, 3(2), 15; https://doi.org/10.3390/spectroscj3020015 - 14 Apr 2025

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Abstract

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

(This article belongs to the Special Issue Feature Papers in Spectroscopy Journal)

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18 pages, 3200 KiB

Open AccessArticle

Influence of Tissue Curvature on the Absolute Quantification in Frequency-Domain Diffuse Optical Spectroscopy

by Giovani G. Martins, Rodrigo M. Forti and Rickson C. Mesquita

Spectrosc. J. 2025, 3(2), 14; https://doi.org/10.3390/spectroscj3020014 - 13 Apr 2025

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Abstract

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

(This article belongs to the Special Issue Feature Papers in Spectroscopy Journal)

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16 pages, 5391 KiB

Open AccessArticle

Mid-Infrared Spectrometer for Black Plastics Sorting Using a Broadband Uncooled Micro-Bolometer Array

by Gabriel Jobert and Xavier Brenière

Spectrosc. J. 2025, 3(2), 13; https://doi.org/10.3390/spectroscj3020013 - 3 Apr 2025

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Abstract

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

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24 pages, 1224 KiB

Open AccessReview

Spectroscopic Advances in Real Time Monitoring of Pharmaceutical Bioprocesses: A Review of Vibrational and Fluorescence Techniques

by Abhishek Mishra, Mohammad Aghaee, Ibrahim M. Tamer and Hector Budman

Spectrosc. J. 2025, 3(2), 12; https://doi.org/10.3390/spectroscj3020012 - 1 Apr 2025

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Abstract

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 article belongs to the Special Issue Feature Papers in Spectroscopy Journal)

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18 pages, 5740 KiB

Open AccessArticle

The Presence of Excitons in Short Single-Stranded DNA Revealed by Absorption and Circular Dichroism Spectroscopy

by Alessandra Picchiotti, Amy L. Stevens, Valentyn I. Prokhorenko and R. J. Dwayne Miller

Spectrosc. J. 2025, 3(2), 11; https://doi.org/10.3390/spectroscj3020011 - 28 Mar 2025

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Abstract

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

(This article belongs to the Special Issue Feature Papers in Spectroscopy Journal)

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Spectrosc. J., Volume 3, Issue 2 (June 2025) – 5 articles

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