Forensic soil source identification: comparing matching by color, vis-NIR spectroscopy and easily-measured physio-chemical properties

This study evaluates to what degree soil samples associated in characteristic space are also close in geographical space, i.e., the possible location from which an unknown sample was obtained in a forensic investigation. The study compares similarity computed from Munsell colors, RGB colors, and full visible-near infrared (vis-NIR) spectra by the spectral angle mapper with similarity based on six easily-measured physio-chemical properties. The reference area is Anhui Province, China with three scales of datasets: provincial, county, and field. Ten diverse "unknown" samples were selected by the Kennard-Stone algorithm from the field-scale dataset and their matches in characteristic space from the several datasets were found by the different methods. The geographic distances of the matches to the "unknowns" were used to evaluate the source identification ability. When a detailed library with local samples is present, a limited set of physio-chemical properties achieved higher geographic accuracy than the color and spectral methods. However, with a regional library the spectral and color methods are superior. Distances in RGB space reveal finer differences than exact matching in Munsell space, but whole-spectra matching outperforms both, because of the rich information influenced by more soil properties than influencing color. We recommend the use of soil vis-NIR spectra as a priority indicator for forensic soil analysis because of its success in this study and its ability to work non-destructively on small quantities of soil.

Microfluidic Paper-based Analytical Device for the Determination of Hexavalent Chromium by Photolithographic Fabrication Using a Photomask Printed with 3D Printer

This article describes a simple and inexpensive microfluidic paper-based analytical device (μPAD) for the determination of hexavalent chromium (Cr^VI) in water samples. The μPADs were fabricated on paper by photolithography using a photomask printed with a 3D printer and functionalized with reagents for a colorimetric assay. In the μPAD, Cr^VI reacts with 1,5-diphenylcarbazide to form a violet-colored complex. Images of μPADs were captured with a digital camera; then the red, green, and blue color intensity of each detection zone were measured using images processing software. The green intensity analysis was the best sensitive among the RGB color. A linear working range (40 - 400 ppm; R² = 0.981) between the Cr^VI and green intensity was obtained with a detection limit of 30 ppm. All of the recoveries were between 94 and 109% in recovery studies on water samples, and good results were obtained.

Temporal and Remote Tuning of Piezophotonic-Effect-Induced Luminescence and Color Gamut via Modulating Magnetic Field

Light-emitting materials have been extensively investigated because of their widespread applications in solid-state lighting, displays, sensors, and bioimaging. In these applications, it is highly desirable to achieve tunable luminescence in terms of luminescent intensity and wavelength. Here, a convenient physical approach of temporal and remote tuning of light-emitting wavelength and color is demonstrated, which is greatly different from conventional methods. It is shown that by modulating the frequency of magnetic-field excitation at room temperature, luminescence from the flexible composites of ZnS:Al, Cu phosphors induced by the piezophotonic effect can be tuned in real time and in situ. The mechanistic investigation suggests that the observed tunable piezophotonic emission is ascribed to the tilting band structure of the ZnS phosphor induced by magnetostrictive strain under a high frequency of magnetic-field excitation. Furthermore, some proof-of concept devices, including red-green-blue full-color displays and tunable white-light sources are demonstrated simply by frequency modulation. A new understanding of the fundamentals of both luminescence and magnetic-optics coupling is thus provided, while offering opportunities in magnetic-optical sensing, piezophotonics, energy harvesting, novel light sources, and displays.