Colocalization of β-Sheets and Carotenoids in Aβ Plaques Revealed with Multimodal Spatially Resolved Vibrational Spectroscopy

The aggregation of amyloid β(Aβ) peptides is at the heart of Alzheimer's disease development and progression. As a result, amyloid aggregates have been studied extensively in vitro, and detailed structural information on fibrillar amyloid aggregates is available. However, forwarding these structural models to amyloid plaques in the human brain is still a major challenge. The chemistry of amyloid plaques, particularly in terms of the protein secondary structure and associated chemical moieties, remains poorly understood. In this report, we use Raman microspectroscopy to identify the presence of carotenoids in amyloid plaques and demonstrate that the abundance of carotenoids is correlated with the overall protein secondary structure of plaques, specifically to the population of β-sheets. While the association of carotenoids with plaques has been previously identified, their correlation with the β structure has never been identified. To further validate these findings, we have used optical photothermal infrared (O-PTIR) spectroscopy, which is a spatially resolved technique that yields complementary infrared contrast to Raman. O-PTIR unequivocally demonstrates the presence of elevated β-sheets in carotenoid-containing plaques and the lack of β structure in noncarotenoid plaques. Our findings underscore the potential link between anti-inflammatory species as carotenoids to specific secondary structural motifs within Aβ plaques and highlight the possible role of chemically distinct plaques in neuroinflammation, which can uncover new mechanistic insights and lead to new therapeutic strategies for AD.

Probing Individual Particles Generated at the Freshwater-Seawater Interface through Combined Raman, Photothermal Infrared, and X-ray Spectroscopic Characterization

Sea spray aerosol (SSA) is one of the largest global sources of atmospheric aerosol, but little is known about SSA generated in coastal regions with salinity gradients near estuaries and river outflows. SSA particles are chemically complex with substantial particle-to-particle variability due to changes in water temperature, salinity, and biological activity. In previous studies, the ability to resolve the aerosol composition to the level of individual particles has proven necessary for the accurate parameterization of the direct and indirect aerosol effects; therefore, measurements of individual SSA particles are needed for the characterization of this large source of atmospheric aerosol. An integrated analytical measurement approach is required to probe the chemical composition of individual SSA particles. By combining complementary vibrational microspectroscopic (Raman and optical photothermal infrared, O-PTIR) measurements with elemental information from computer-controlled scanning electron microscopy with energy-dispersive X-ray analysis (CCSEM-EDX), we gained unique insights into the individual particle chemical composition and morphology. Herein, we analyzed particles from four experiments on laboratory-based SSA production using coastal seawater collected in January 2018 from the Gulf of Maine. Individual salt particles were enriched in organics compared to that in natural seawater, both with and without added microalgal filtrate, with greater enrichment observed for smaller particle sizes, as evidenced by higher carbon/sodium ratios. Functional group analysis was carried out using the Raman and infrared spectra collected from individual SSA particles. Additionally, the Raman spectra were compared with a library of Raman spectra consisting of marine-derived organic compounds. Saccharides, followed by fatty acids, were the dominant components of the organic coatings surrounding the salt cores of these particles. This combined Raman, infrared, and X-ray spectroscopic approach will enable further understanding of the factors determining the individual particle composition, which is important for understanding the impacts of SSA produced within estuaries and river outflows, as well as areas of snow and ice melt.

Transparent soil microcosms for live-cell imaging and non-destructive stable isotope probing of soil microorganisms

Microscale processes are critically important to soil ecology and biogeochemistry yet are difficult to study due to soil's opacity and complexity. To advance the study of soil processes, we constructed transparent soil microcosms that enable the visualization of microbes via fluorescence microscopy and the non-destructive measurement of microbial activity and carbon uptake in situ via Raman microspectroscopy. We assessed the polymer Nafion and the crystal cryolite as optically transparent soil substrates. We demonstrated that both substrates enable the growth, maintenance, and visualization of microbial cells in three dimensions over time, and are compatible with stable isotope probing using Raman. We applied this system to ascertain that after a dry-down/rewetting cycle, bacteria on and near dead fungal hyphae were more metabolically active than those far from hyphae. These data underscore the impact fungi have facilitating bacterial survival in fluctuating conditions and how these microcosms can yield insights into microscale microbial activities.

Wear Simulation of Ceramic-on-Crosslinked Polyethylene Hip Prostheses: A New Non-Oxide Silicon Nitride versus the Gold Standard Composite Oxide Ceramic Femoral Heads

The purpose of the present study was to compare the wear behavior of ceramic-on-vitamin-E-diffused crosslinked polyethylene (Vit-E XLPE) hip bearings employing the gold standard oxide ceramic, zirconia (ZrO₂)-toughened alumina (Al₂O₃) (ZTA, BIOLOX^®delta) and a new non-oxide ceramic, silicon nitride (Si₃N₄, MC^2®). In vitro wear test was performed using a 12-station hip joint simulator. The test was carried out by applying the kinematic inputs and outputs as recommended by ISO 14242-1:2012. Vitamin-E-diffused crosslinked polyethylene (Vit-E XLPE) acetabular liners (E1^®) were coupled with Ø28-mm ZTA and Si₃N₄ femoral heads. XLPE liner weight loss over 5 million cycles (Mc) of testing was compared between the two different bearing couples. Surface topography, phase contents, and residual stresses were analyzed by contact profilometer and Raman microspectroscopy. Vit-E XLPE liners coupled with Si₃N₄ heads produced slightly lower wear rates than identical liners with ZTA heads. The mean wear rates (corrected for fluid absorption) of liners coupled with ZTA and Si₃N₄ heads were 0.53 ± 0.24 and 0.49 ± 0.23 mg/Mc after 5 Mc of simulated gait, respectively. However, after wear testing, the ZTA heads retained a smoother topography and showed fewer surface stresses than the Si₃N₄ ones. Note that no statistically significant differences were found in the above comparisons. This study suggests that the tribochemically formed soft silica layer on the Si₃N₄ heads may have reduced friction and slightly lowered the wear of the Vit-E XLPE liners. Considering also that the toughness of Si₃N₄ is superior to ZTA, the present wear data represent positive news in the future development of long-lasting hip components.

Screening of Astaxanthin-Hyperproducing Haematococcus pluvialis Using Fourier Transform Infrared (FT-IR) and Raman Microspectroscopy

Haematococcus pluvialis has promising applications owing to its ability to accumulate astaxanthin under stress conditions. In order to acquire higher astaxanthin productivity from H. pluvialis, it is critical not only to develop efficient mutagenesis techniques, but also to establish rapid and effective screening methods which are highly demanded in current research and application practice. In this work, we therefore attempted to develop a new approach to screening the astaxanthin-hyperproducing strains based on spectroscopic tools. Using Fourier transform infrared (FT-IR) and Raman microspectroscopy, we have achieved rapid and quantitative analysis of the algal cells in terms of astaxanthin, β-carotene, proteins, lipids, and carbohydrates. In particular, we have found that the ratio of the IR absorption band at 1740 cm^-1 to the band at 1156 cm^-1 can be utilized for identifying astaxanthin-hyperproducing strains. This work may therefore open a new avenue for developing high-throughput screening methods necessary for the microbial mutant breeding industry.

Toxicity effects of short term diesel exhaust particles exposure to human small airway epithelial cells (SAECs) and human lung carcinoma epithelial cells (A549)

In this study, confocal Raman spectroscopy, atomic force microscope (AFM) and multiplex ELISA were applied to analyze the biophysical responses (biomechanics and biospectroscopy) of normal human primary small airway epithelial cells (SAECs) and human lung carcinoma epithelial A549 cells to in vitro short term DEP exposure (up to 2h). Raman spectra revealed the specific cellular biomolecular changes in cells induced by DEP compared to unexposed control cells. Principal component analysis was successfully applied to analyze spectral differences between control and treated groups from multiple individual cells, and indicated that cell nuclei are more sensitive than other cell locations. AFM measurements indicated that 2h of DEP exposure induced a significant decrease in cell elasticity and a dramatic change in membrane surface adhesion force. Cytokine and chemokine production measured by multiplex ELISA demonstrated DEP-induced inflammatory responses in both cell types.

Looking inside the box: using Raman microspectroscopy to deconstruct microbial biomass stoichiometry one cell at a time

Stoichiometry of microbial biomass is a key determinant of nutrient recycling in a wide variety of ecosystems. However, little is known about the underlying causes of variance in microbial biomass stoichiometry. This is primarily because of technological constraints limiting the analysis of macromolecular composition to large quantities of microbial biomass. Here, we use Raman microspectroscopy (MS), to analyze the macromolecular composition of single cells of two species of bacteria grown on minimal media over a wide range of resource stoichiometry. We show that macromolecular composition, determined from a subset of identified peaks within the Raman spectra, was consistent with macromolecular composition determined using traditional analytical methods. In addition, macromolecular composition determined by Raman MS correlated with total biomass stoichiometry, indicating that analysis with Raman MS included a large proportion of a cell's total macromolecular composition. Growth phase (logarithmic or stationary), resource stoichiometry and species identity each influenced each organism's macromolecular composition and thus biomass stoichiometry. Interestingly, the least variable peaks in the Raman spectra were those responsible for differentiation between species, suggesting a phylogenetically specific cellular architecture. As Raman MS has been previously shown to be applicable to cells sampled directly from complex environments, our results suggest Raman MS is an extremely useful application for evaluating the biomass stoichiometry of environmental microorganisms. This includes the ability to partition microbial biomass into its constituent macromolecules and increase our understanding of how microorganisms in the environment respond to resource heterogeneity.

Raman and infrared microspectral imaging of mitotic cells

We report the first ever Raman and infrared microspectroscopic images of human cells at different stages of mitosis. These spectroscopic methods monitor the distribution of condensed nuclear chromatin, and other biochemical components, utilizing inherent protein and DNA spectral markers, and, therefore, do not require the use of any stains. In conjunction with previously reported data from the G1, S, and G2 phases of the cell cycle, the complete cell division cycle has now been mapped by spectroscopic methods. Although the results reported here do not offer new insights into the distribution of biochemical components during mitosis, the recognition of cell division without the use of stains, and the possibility of doing so on living cells, may be useful for an automatic, spectroscopic determination of the proliferation rates of cells and tissues. Spectral images were constructed by plotting spectral intensities of DNA or protein versus the coordinates from which spectra were recorded. We found that both Raman and infrared intensities depend on the overall chromatin density variation among the individual subphases of mitosis.