Dual-mode fluorescent development of latent fingerprints using NaYbF4:Tm upconversion nanomaterials

Latent fingerprint development plays an important role in forensic sciences. In the last two decades, various fluorescent nanomaterials have been used to develop latent fingerprints, of which rare earth ion edoped upconversion nanomaterials (UCNMs) are outstanding examples. The use of UCNMs is advantageous for several reasons, including high contrast due to the strong fluorescence signal and negligible background interference, high sensitivity owing to the tunable nanoparticle size, and high selectivity arising from the proper particle morphology with suitable absorbability. In most cases, NaYF4:Yb,Er UCNM-based development involves a single near-infrared (NIR)-to-visible (VIS) process, enabling the observation of fingerprints by detecting VIS light under NIR light excitation. Inspiringly, other infrequently used UCNMs, such as NaYbF4:Tm, can irradiate both NIR and VIS emissions under NIR excitation, making it possible to develop latent fingerprints in dual modes, namely, through both NIR-to-NIR and NIR-to-VIS process. In this work, we synthesized high-quality NaYbF4:Tm UCNMs as fluorescent markers for dual-mode development of latent fingerprints. We found that our NaYbF4:Tm UCNMebased method exhibited high contrast, high sensitivity, high selectivity, and extensive applicability in fingerprint development under both NIR-to-VIS and NIR-to-NIR modes. We expect that this work will open up a new avenue in the application of UCNMs to develop latent fingerprints under dual modes in forensic sciences. (C) 2020 The Author(s). Published by Elsevier Ltd.