Applied Spectroscopy最新文献

The development of non-contact in situ techniques for monitoring cure kinetics has the potential to greatly improve both resin formulation and processing. We have recently shown that low-frequency Raman spectroscopy is a viable method for assessing resin structural cure kinetics and complements the traditional chemical conversion determined from the fingerprint region of the spectrum. In this work, we further evaluate the relationship between structural and chemical conversion by investigating two chemically identical yet rheologically different interpenetrating polymer network resin formulations. Rheological analysis demonstrates a relationship between structural conversion and storage modulus, which is not observed in the chemical conversion data. We show that one can produce master cure kinetics curves with comparable kinetic constants using both the chemical and structural conversion methodologies. Parametric analysis of the structural conversion, chemical conversion, and photorheological conversion was combined with a semi-empirical model for the storage shear modulus as a function of the extent of cure.

We demonstrate single-shot standoff hyperspectral Raman imaging of liquid diisopropyl methylphosphonate at a standoff distance of 1 m using two different techniques: multi-bandpass filter imaging (MBFI) and fiber-bundle imaging spectroscopy (FBIS). We find that MBFI has good spatial resolution, but poor spectral resolution, due to the limitations of commercially available bandpass filters. On the other hand, we find FBIS to have excellent spectral resolution, but limited spatial resolution due to the relatively small number of fibers in a bundle. For FBIS, we also determine, for a 1 m standoff distance, a minimum pump fluence of 10 mJ/cm² to obtain good single-shot spectra.

This study investigates the combined effects of nanoscale surface roughness and electron-phonon interaction on the vibrational modes of cadmium telluride (CdTe) using resonant Raman spectroscopy. Raman spectra simulations aided in identifying the active phonon modes and their dependence on roughness. Our results reveal that increasing surface roughness leads to an asymmetric line shape in the first-order longitudinal optical (1LO) phonon mode, attributed to an increase in the electron-phonon interaction. This asymmetry broadens the entire Raman spectrum. Conversely, the overtone (second-order longitudinal optical, or 2LO. mode exhibits a symmetrical line shape that intensifies with roughness. Additionally, we identify and discuss the contributions of surface optical phonon mode and multiphonon modes to the Raman spectra, highlighting their dependence on roughness. This work offers a deeper understanding of how surface roughness and electron-phonon scattering influence the line shape of CdTe resonant Raman spectra, providing valuable insights into its vibrational properties.

This study developed a dual-readout system utilizing fluorescence and colorimetry based on iron oxide quantum dots (IO-QDs) for detecting tetracycline (TCy). IO-QDs were synthesized within 6 h using L-leucine as a surface modifier, achieving a more efficient route. Upon interaction with TCy, IO-QDs exhibited a significant decrease in fluorescence response and observable color changes, while fluorescence lifetime remained consistent regardless of TCy presence. Moreover, IO-QDs' fluorescence response remained stable across various temperatures. The Förster resonance energy transfer distance of less than 2 nm and a quenching constant of 2.90 × 10¹² M^-1s^-1 indicated static quenching in the presence of TCy. Additionally, significant changes in observed and corrected fluorescence efficiency suggested the involvement of the inner filter effect in the fluorescence quenching of IO-QDs. The synthesized IO-QDs were then utilized for selective and rapid fluorescence-based TCy detection, showing a linear range of 0.5 to 80 μM. Simultaneously, a colorimetric method for TCy detection was established, demonstrating a good linear relationship within the range of 0.5 to 20 μM. The detection limits for TCy were determined as 0.539 and 0.329 μM using fluorescence and colorimetric approaches, respectively. Furthermore, IO-QDs were applied to detect real samples, and the dual-readout probe exhibited satisfactory recoveries, confirming the practical reliability of the developed method for analyzing milk and drinking water samples.

We have demonstrated high-speed, super-resolution infrared (IR) spectroscopy and chemical imaging of autofluorescent biomaterials and organisms using camera-based widefield photothermal detection that takes advantage of temperature-dependent modulations of autofluorescent emission. A variety of biological materials and photosynthetic organisms exhibit strong autofluorescence emission under ultraviolet excitation and the autofluorescent emission has a very strong temperature dependence, of order 1%/K. Illuminating a sample with pulses of IR light from a wavelength-tunable laser source causes periodic localized sample temperature increases that result in a corresponding transient decrease in autofluorescent emission. A low-cost light-emitting diode-based fluorescence excitation source was used in combination with a conventional fluorescence microscopy camera to detect localized variations in autofluorescent emission over a wide area as an indicator of localized IR absorption. IR absorption image stacks were acquired over a range of IR wavelengths, including the fingerprint spectral range, enabling extraction of localized IR absorption spectra. We have applied widefield fluorescence detected photothermal IR (FL-PTIR) to an analysis of autofluorescent biological materials including collagen, leaf tissue, and photosynthetic organisms including diatoms and green microalgae cells. We have also demonstrated the FL-PTIR on live microalgae in water, demonstrating the potential for label-free dynamic chemical imaging of autofluorescent cells.

Artemisinin (ART) is a most promising antimalarial agent. However, its low aqueous solubility limits its oral absorption, resulting in low bioavailability. In this study, we have successfully discovered a novel cocrystal with 2-methyl resorcinol (ART-2MRE) providing improved solubility compared with a previously reported cocrystal with resorcinol (ART-RES). Single crystal X-ray structure analysis revealed that the ART-2MRE cocrystal was composed of ART and 2MRE in a molar ratio of 2 : 1. Though the ART-2MRE and ART-RES cocrystals were found to have similarities in their crystal structures, with one layer of a cocrystal former and two layers of ART arranged in alternating rows, the ART-2MRE cocrystal showed higher dissolution rate than ART-RES cocrystal. In situ real-time low-frequency (LF) Raman monitoring and powder X-ray diffraction (PXRD) measurements of the crystals during the dissolution test proved useful to investigate the dissolution behavior of the cocrystals. Low-frequency Raman monitoring revealed that as dissolution progressed, there was a continuous shift from the peak unique to the ART-2MRE cocrystal to the peak unique to the ART stable form. Similar observations were obtained in PXRD measurements as well. Furthermore, experiments were conducted by adding a polymer to the dissolution test solution to investigate the dissolution behavior under supersaturation, indicating the possibility of differences in the dissolution behavior between the ART-2MRE cocrystal and ART-RES cocrystal. Understanding the dissolution behavior from cocrystals is essential in developing cocrystals.

Azurite, a historical blue mineral pigment, has previously been described to contain certain elemental impurities. These may originate from host rocks, vein fillings, or the primary copper ore mineralization. In this study, azurites (and also green malachites) from three important Central European deposits with a potential of being exploited for pigment usage already in the Middle Ages have been studied, together with azurite from Chessy, France, with a different geological setting. Using electron probe microanalysis and, more importantly, laser ablation inductively coupled plasma mass spectroscopy for trace elemental analysis, several indicators were pinpointed as important for provenance: characteristic elemental fingerprint of the deposit, e.g., elevated lead (Pb) in combination with rare earth elements, may be combined with zinc (Zn)/arsenic (As) ratio (indicating sources of excess Zn in the primary deposit) and the overall amount of metal impurities (suggesting the source mineral of copper for azurite formation). In addition, malachites from the same deposits were found to preferentially incorporate primary ore metal elements as well as Cd, Mg, Mn, or U. Therefore, if azurite pigment contains an elevated amount of malachite as an impurity, it may significantly influence the overall elemental composition. The results obtained on geological samples were applied to two micro-samples of works of art containing azurite-rich layers originating from the 13th-14th and 16th centuries. It was shown that it is highly beneficial to focus on the overall trace elemental composition of the paint layer and not on the admixed mineral grains, as their presence, especially in minute micro-samples, is largely accidental and thus not representative. Although a higher number of samples need to be studied in the future, the newly described criteria made it possible to exclude some of the localities of the employed azurite pigment. This confirmed the key importance of trace elements analysis of mineral pigments for the provenance studies of fine arts.

Diabetes mellitus is a prevalent chronic disease necessitating timely identification for effective management. This paper introduces a reliable, straightforward, and efficient method for the minimally invasive identification of diabetes mellitus through nanosecond pulsed laser-induced breakdown spectroscopy (LIBS) by integrating a state-of-the-art machine learning approach. LIBS spectra were collected from urine samples of diabetic and healthy individuals. Principal component analysis and an ensemble learning classification model were used to identify significant changes in LIBS peak intensity between the diseased and normal urine samples. The model, integrating six distinct classifiers and cross-validation techniques, exhibited high accuracy (96.5%) in predicting diabetes mellitus. Our findings emphasize the potential of LIBS for diabetes mellitus identification in urine samples. This technique may hold potential for future applications in diagnosing other health conditions.

Exposure of polytetrafluoroethylene (PTFE) to argon plasma results in chemical modification of the polymer near the surface. Interestingly, PTFE modification can be induced by the sub-band gap ultraviolet (UV) irradiation. In the latter case, the changes in the chemical structure are very subtle, and they are practically invisible to conventional experimental techniques. Raman spectra of irradiated and raw samples show practically identical peaks. However, the baseline that is commonly considered as an unwanted spectral component contains an important information that reflects the minor structural changes. With the proper data analysis, this allows us to visualize the effects of the argon plasma and sub-band gap UV irradiation on the polymer.