Applied Spectroscopy最新文献

The correlation filter (CF) technique is introduced as a versatile tool for data pretreatment to selectively attenuate interfering or overlapping signals of congested spectra. This technique leverages two-dimensional correlation spectroscopy (2D-COS) to create a filter multiplier that effectively addresses limitations inherent in traditional null-space projection (NSP) methods based on least-squares subtraction. We apply CF to the analysis of a model solution mixture system undergoing spontaneous evaporation, where volatile solvent concentrations change concurrently but at only slightly different rates. Despite the similarity of these parallel processes, CF successfully separates the overlapped dynamics of individual components by attenuating dominant signal contributions. CF also enables streamlined 2D codistribution spectroscopy (2D-CDS) analysis to determine the sequential order of component appearance. Multiple layers of CF can be applied to isolate individual component dynamics. Heterocomponent 2D correlation can then recover lost information by recombining CF-treated spectra. CF is applicable to two-trace two-dimensional (2T2D) correlation for comparative spectral analysis of a pair of spectra. CF treatment is expected to be a useful tool beyond 2D-COS applicable to many areas of spectral analyses, including the environmental and interfacial studies.

The ability to combine microscopy and spectroscopy is beneficial for directly monitoring physical and biological processes. Spectral imaging approaches, where a transmission diffraction grating is placed near an imaging sensor to collect both the spatial image and spectrum for each object in the field of view, provide a relatively simple method to simultaneously collect images and spectroscopic responses on the same sensor. Initially demonstrated with fluorescence spectroscopy, the use of spectral imaging in Raman spectroscopy and surface-enhanced Raman spectroscopy (SERS) can provide a vibrational spectrum containing molecularly specific information that can inform on chemical changes. However, a major complication to this approach is the spectral overlap that occurs when objects are spaced closely together horizontally. In this work, we add a dove prism to a spectral imaging instrument developed for SERS imaging, enabling rotation of the collected SERS image and dispersed spectrum onto the imaging complementary metal-oxide semiconductor (CMOS) sensor. We demonstrate that this effectively reduces spectral overlap for emitters with clear separation between them and emitters with slightly overlapping point spread functions thereby facilitating collection of unambiguous spectra from each emitter.

In this study, Raman spectra (3700-10 cm^-1) and attenuated total reflection infrared-far-infrared (ATR-IR/FIR) spectra (4000-50 cm^-1) including low-frequency region were measured for amorphous rocks, which were five types of obsidians whose formation ages and sources are different and pitchstone to clarify the differences in water content (free and bound water species), their Si-O bonds and possible linkage with a metal ion, and the mean atomic volume. In order to explore these points, we focused on infrared (IR) absorptions of hydroxyl (OH) groups that is observed in the 4000-3000 cm^-1 region, those of Si-O bond that is identified in the 1300-850 cm^-1 region and a Boson peak that appears in a low-frequency region of Raman spectra, respectively. IR absorption of Si-O stretching was detected for all samples and that of OH stretching and H-O-H bending was also detected in some rocks. Therefore, using IR spectroscopy was useful to discriminate each rock based on the water content and the environment of Si-O bonds. On the other hands, a Boson peak could be detected for the low-frequency region below 60 cm^-1 of Raman spectra, which appears in amorphous solids. This study is the first finding that the Raman shift of Boson peak was different among similar natural glassy rocks from multiple sources and it means that the mean atomic volume of samples was different. In addition, sharp bands of Raman scattering which came from inorganic substances such as feldspar helped to identify ingredients in samples. As a results, we made clear that using both IR and Raman including low-frequency regions is effective to identify the same types of natural amorphous rocks.

Hydroxyl-terminated polybutadiene (HTPB) is used in a variety of formulations, particularly for military and aerospace applications as a binder for energetic materials. This work investigates details of its curing process when formulated with isophorone diisocyanate (IPDI). Raman spectroscopy was used as a fast, sensitive, non-destructive technique to monitor the curing process of HTPB-IPDI. A significant feature at 777 cm^-1 was shown to grow over the course of the curing process. Ab initio calculations of the normal modes of the HTPB-IPDI dimer indicate that this feature is most likely connected to the urethane bond, which suggests that the feature at 777 cm^-1 is associated with formation of the urethane linkage as the formulation cures. Raman spectroscopy thus has potential to be used for quality assurance and other material state awareness measurements for HTPB-IPDI materials.

This paper reports on the application of infrared external reflection spectroscopy (IR-ERS) to the characterization of small surface area addresses prepared on smooth gold surfaces after modification for use as capture substrates in sandwich immunoassays based on surface-enhanced Raman scattering (SERS). Most of the past work with IR-ERS on analyzing coatings formed on highly reflective metals utilized relatively large area samples (e.g., 76 × 25  mm glass microscope slides and ∼51  mm diameter silicon wafers) to accommodate the large size of the elliptical IR beam reflected off the metal surface at grazing angles of incidence. Our interest in employing assay-sized (3  mm diameter) addresses for IR-ERS measurements arises from the need to minimize the consumption, and, thereby, the expense of rare biological reagents like the antibodies under development for immunoassays to detect tuberculosis. The obvious approach to achieving this goal would be to utilize the spatial resolution and sample scanning capabilities of Fourier transform infrared (FT-IR) microscopes. We, however, opted to re-examine the physical optics and geometric layout of the measurement through an analysis of the strength of the mean square electric field at the sample/substrate interface as a function of angle of incidence. These findings suggested that, given the high light throughput and low noise levels of today's FT-IR spectrometers, it may be possible to perform these measurements simply by collecting spectra at a lower angle of incidence when using the optical layout of a standard IR-ERS experiment. Herein, we report both the theoretical analysis and experimental results that demonstrate it is possible to obtain useful spectra from much smaller samples than those traditionally used, e.g., those employed in our SERS-based immunoassays, simply by decreasing the angle at which the IR beam is incident on the sample surface. We also demonstrate that these types of samples can be analyzed by constructing a small jig that allows for the careful positioning of the sample in the IR beam, rather than by extensively modifying the optics of the IR-ERS accessory.

Confocal Raman microscopy was applied to detect structural change within individual particles of low-density polyethylene (LDPE) following chemical and electrochemical processing steps that aimed to facilitate material decomposition. A high numerical aperture (NA) oil-immersion objective enabled depth-profiling through the near surface region (20 μm-40 μm) of irregularly shaped particles with an axial spatial resolution < 2 μm estimated from measurements of instrument detection efficiency profiles. Changes in vibrational bands sensitive to polyethylene crystallinity were evident following treatments and linked to the release of low molecular weight compounds present as additives and products of processing. Effects of processing were probed by monitoring the rise of Raman scattering intensity in vibrational modes associated with polyethylene chains in a zig-zag (trans) conformation near 1128 cm^-1, 1294 cm^-1, and 1418 cm^-1, signaling chain clustering and development of organized, crystalline-like assemblies. Pristine LDPE particles displayed a uniform structure across the near surface region, while particles treated initially with chemical extractant and then further processed displayed increasingly enhanced crystallinity up to the maximum depth probed (40 μm). As a step toward measurements on ensembles of particles, least squares modeling was adapted to derive pure component spectra reflecting crystallinity change within spectral datasets. The work demonstrates high spatial resolution Raman depth-profiling for the characterization of processed polymers using a high NA immersion objective to overcome the limitations of air-objectives often used for confocal Raman microscopy.

Presented is a perspective proposing to expand some fragmented spectroscopic modeling and data analysis practices by incorporating multivariate ideologies. For example, through recognizing the theory of analytic chemistry (TAC) by Booksh and Kowalski, it is common to use the multivariate processes (higher orders) of multiple wavelengths for regression and prediction or classification, fusing multiple instruments, or applying multi-way methods such as parallel factor analysis (PARAFAC). Each wavelength, instrument, PARAFAC order deliver different views of underlying sample-wise full matrix effects adding more information per dimension for improved data characterizations. Reasoned here is that model selection, figures of merit, and sample similarity assessments for model prediction reliability, outlier detection, or classification purposes can meaningfully progress by recognizing the multivariate principles of the TAC and additionally, the importance of the Rashomon effect. Applying the Rashomon effect with the TAC removes conventional fragmented data analysis approaches bringing a more wholeness to data analysis. Included in this discussion is that due to the Rashomon effect, interpretation of spectral models is not reasonable. For an uncommon view of these concepts, the perspective ends with drawing parallels between sample-wise matrix effects and the concepts explicate and implicate orders from physicist David Bohm's depiction of our physical and conscious world and universe. It is hoped that this perspective tempts reflection in your particular area of spectroscopy.

Due to the growing interest in high-purity bioplastics for emerging applications, we investigated the solution crystallization of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHx) from a chloroform solution using advanced spectroscopic techniques. Compared to melt crystallization, solution crystallization proved to be a more complex process. Solvent evaporation led to the formation of amorphous PHBHx and less-ordered crystallites. Subsequently, a distinct intermediate species of slightly disordered crystals formed, eventually transforming into more ordered crystalline structures. To analyze the time-dependent attenuated total reflection infrared (ATR-IR) spectra during crystallization, we employed two-dimensional correlation spectroscopy (2D-COS) and codistribution spectroscopy (2D-CDS). To streamline the 2D analysis of this complex dynamic system, we utilized a correlation filter (CF) technique to attenuate interfering contributions from overlapping peaks.

This comprehensive survey review offers the trajectory of research dissemination in the field of two-dimensional correlation spectroscopy (2D-COS) from 1 July 2022 to 17 June 2024. It covers books, reviews, tutorials, innovative concepts and theories, patents applications, and diverse applications that emerged during this period, as well as instances of improper usage or citations of 2D-COS. Innovations in probe integration, data analysis, and technical methodologies highlight the expanding role of 2D-COS in materials science, environmental monitoring, and biological system. This review shows the dynamic growth and diversification of 2D-COS across in many scientific fields.

In attenuated total reflection (ATR) spectroscopy, the presence of an evanescent field penetrating the sample is generally considered crucial. However, according to wave optics, this evanescent field vanishes when the rarer medium is absorbing, and the attenuation of total reflection results from transmission into this medium. While the evanescent field may not play a significant role in this scenario, a closer examination of the relevant relationships reveals that the system's properties vary smoothly with both the angle of incidence and the imaginary part of the dielectric function. This effect can be further illustrated by comparing electric field maps and spectra for semi-infinite rarer media with those for rarer media composed of layers with thicknesses on the order of the wavelength. In the latter case, ATR spectra can be recorded well below the critical angle, where no evanescent field exists. If the layer is vacuum and the underlying semi-infinite medium is assumed to have the same refractive index but is weakly absorbing, tunneling and frustrated total reflection can be observed. Reflecting on our results, we can now define the critical angle in the presence of absorption as the point at which the real and imaginary parts of the perpendicular component of the wavevector become equal. Overall, we conclude that evanescent waves play little to no significant role. Any deviation from total reflection can be attributed to transmission through the ATR crystal-medium interface.