Development of micromarkers with various photoluminescence colors as tracers for shadowing pursuits

Micromarkers with five photoluminescence colors were developed as tracers for shadowing pursuits. The markers are colorless powders with particle diameters of several tens to several hundreds of micrometers, prepared using a cryogenic sample crusher. They were visualized using red, green, yellow, magenta or cyan photoluminescence under ultraviolet light at approximately 365 nm. The markers were composed of photoluminescent compounds dispersed in polyvinyl butyral. The photoluminescent compounds in the polyvinyl butyral were stable under ambient conditions for more than one year after application. The compounds with the red, green, yellow, magenta and cyan photoluminescence contained a europium (Eu(3+)) complex, a terbium (Tb(3+)) complex, a mixture of Tb(3+) and Eu(3+) complexes, a mixture of Eu(3+) complex and o-coumaric acid, and a mixture of Tb(3+) complex and 7-hydroxycoumarin along with a few drops of a sodium bicarbonate aqueous solution, respectively. Neodymium (Nd(3+)) and ytterbium (Yb(3+)) complexes with photoluminescence in the near-IR wavelength region can also be added to these visible photoluminescent compounds as secret markers for discrimination. The markers were non-destructively identified using a microscopic FT-IR spectrometer and a microscopic spectrometer equipped with a fluorescence detector.

5-(4-Nitrophenyl)-2,4-pentadien-1-al (NPPD) used as a tracer by nonscientists at a simulated crime scene

5-(4-Nitrophenyl)-2,4-pentadien-1-al (NPPD) was used as a tracer by nonscientists at a simulated crime scene. A card with both a plastic-coated smooth surface and a porous cellulose matrix paper surface was coated with a methanol solution containing 0.5mg/mL of NPPD. The card was touched with bare fingers and fingers covered by a cotton glove. A color-change protocol was then used to detect the presence of NPPD. The bare fingers or the fingers of gloves were swabbed with a cotton swab, or the parts of the glove that had touched the card were cut out. The swabs or the cloth pieces were dipped in methanol, a 0.1% methanol solution of naphthoresorcinol was added, and then concentrated hydrochloric acid was added. The observation of a red color at this point indicated a positive test. NPPD was easily observed in the experiments involving bare fingers, but no color change was observed from the swabbing of the cotton glove. However, when the cloth pieces cut from the fingers of the glove were subjected to the test, the red color was observed. In an attempt to enhance the sensitivity of the test, the volumes of the reagent solutions were reduced, but no improvement in sensitivity was obtained.