Dark-Field Hyperspectral Microscopy for Carbon Nanotubes Bioimaging

Carbon nanotubes have emerged as a versatile and ubiquitous nanomaterial, finding applications in industry and biomedicine. As a result, biosafety concerns that stimulated the research focused on evaluation of carbon nanotube toxicity. In addition, biomedical applications of carbon nanotubes require their imaging and identification in biological specimens. Among other methods, dark-field microscopy has become a potent tool to visualise and identify carbon nanotubes in cells, tissues, and organisms. Based on the Tyndall effect, dark-field optical microscopy at higher magnification is capable of imaging nanoscale particles in live objects. If reinforced with spectral identification, this technology can be utilised for chemical identification and mapping of carbon nanotubes. In this article we overview the recent advances in dark-field/hyperspectral microscopy for the bioimaging of carbon nanotubes.

Mapping Pigments in a Painting with Low Frequency Electron Paramagnetic Resonance Spectroscopy

An electron paramagnetic resonance (EPR) mobile universal surface explorer (MOUSE) was recently introduced for noninvasively studying paramagnetic pigments in paintings. This study determined that the EPR MOUSE could map the spatial locations of four pigments in a simple impasto painting. Results from three spectral identification algorithms were examined to assess their ability to identify the pigments using an unsupervised approach. Resulting pigment maps are displayed as colorized images of the spatial distribution of the pigments. All three algorithms produced reasonable representations of the painting. The algorithms achieved excellent true positive, true negative, false positive, and false negative rates of ≥0.95, ≥0.98, ≤0.02, and ≤0.05, respectively, for the identification of the pigments. We conclude that the EPR MOUSE is suitable for accurately mapping the location of paramagnetic pigments in a painting.

Estimation of the Relative Abundance of Quartz to Clay Minerals Using the Visible–Near-Infrared–Shortwave-Infrared Spectral Region

Quartz is the most abundant mineral on the earth’s surface. It is spectrally active in the longwave infrared (LWIR) region with no significant spectral features in the optical domain, i.e., visible–near-infrared–shortwave-infrared (Vis–NIR–SWIR) region. Several space agencies are planning to mount optical image spectrometers in space, with one of their missions being to map raw materials. However, these sensors are active across the optical region, making the spectral identification of quartz mineral problematic. This study demonstrates that indirect relationships between the optical and LWIR regions (where quartz is spectrally dominant) can be used to assess quartz content spectrally using solely the optical region. To achieve this, we made use of the legacy Israeli soil spectral library, which characterizes arid and semiarid soils through comprehensive chemical and mineral analyses along with spectral measurements across the Vis–NIR–SWIR region (reflectance) and LWIR region (emissivity). Recently, a Soil Quartz Clay Mineral Index (SQCMI) was developed using mineral-related emissivity features to determine the content of quartz, relative to clay minerals, in the soil. The SQCMI was highly and significantly correlated with the Vis–NIR–SWIR spectral region (R2 = 0.82, root mean square error (RMSE) = 0.01, ratio of performance to deviation (RPD) = 2.34), whereas direct estimation of the quartz content using a gradient-boosting algorithm against the Vis–NIR–SWIR region provided poor results (R2 = 0.45, RMSE = 15.63, RPD = 1.32). Moreover, estimation of the SQCMI value was even more accurate when only the 2000–2450 nm spectral range (atmospheric window) was used (R2 = 0.9, RMSE = 0.005, RPD = 1.95). These results suggest that reflectance data across the 2000–2450 nm spectral region can be used to estimate quartz content, relative to clay minerals in the soil satisfactorily using hyperspectral remote sensing means.

Using matrix-assisted ionization method for mass spectral identification of fullerene-dye conjugates

Traditional soft ionization methods are not always suitable for mass spectral analysis of complex compounds. Factors such as laser radiation and heating resulting in fragmentations of sample molecules in the case of matrix-assisted laser desorption/ionization and difficulties in preparing suitable sample solutions in the case of electrospray ionization make it impossible to use these methods in some cases. Matrix-assisted ionization was used to analyze products of chemical synthesis involving pyropheophorbide and fullerene. Mass spectra were acquired using a simple effective modification of the Exactive Orbitrap mass spectrometer electrospray interface. Reliable identification of pyropheophorbide-fullerene dyad ions and its derivatives was carried out. An experimental comparison of a matrix-assisted ionization and an electrospray ionization technique demonstrated the significant advantage in sensitivity to the ions under study (approximately 20 times higher) of the matrix-assisted ionization method in this particular study.