Fingermarks Development Using Dry Powder Alizarin Red Lake (1,2-Dihydroxyanthraquinone) and Its Nanosecond Transient Absorption Measurement in Isopropyl Alcohol

Alizarin red lake (1,2-dihydroxyanthraquinone) was utilized to develop latent fingermarks and palm marks on porous substrates. In addition, nanosecond transient absorption spectroscopy was employed to investigate its excited-state dynamics in isopropyl alcohol. Alizarin was used in its solid form (via the powdering method), marking it the first time dry powder alizarin that has been reported for fingermarks development. The palm marks and fingermarks exhibited distinctive, visible friction ridges under the light sources used in this study. In daylight and under yellow-filtered LED (395 - 405 nm) light, the marks were apparent. However, under unfiltered LED, they appear blurry, perhaps due to LED interference with the mark’s background. Three substrates were used, including printmaking papers, event tickets, and thermal papers. The marks on printmaking paper (commonly used in the arts) were visible in daylight and under yellow-filtered LED. Under unfiltered LED light, the visibility of the friction ridges appears blurry. Similar visibility was observed with the event tickets and thermal papers, where the friction ridges under unfiltered light showed reduced visibility, whereas they were clearly visible in daylight and under yellow filtered LED. The transient absorption spectra revealed the formation of excited-state species upon nanosecond laser excitation, providing insights into the photophysical properties of the dye. Kinetic analysis indicated a rapid decay of the excited-state absorption, suggesting efficient non-radiative relaxation pathways. The findings demonstrate the suitability of Alizarin red lake for enhancing fingermarks visualization under visible light, attributed to its distinct transient absorption characteristics and solvent interactions. This study contributes to the optimization of dye-based forensic techniques, thereby improving latent fingermarks detection on various substrates. The fast decay dynamics of the dye suggest possible picosecond decay dynamics.