NaYF₄ Upconversion Nanoparticles Coated with Zinc Bzimpy for High-Resolution Dual-Mode Visualization of Latent Fingerprints

The high-resolution, anti-interference visualization of latent fingerprints (LFPs) is of vital importance in the fields of individual identification, security, and forensic analysis. Here, zinc(II) bzimpy complex K[Zn{(O3SCH2CH2CH2)2bzimpy}OAc] (ZnB)-modified NaYF4:Yb/Er upconversion nanoparticles (ZnB-UCNPs) were designed. The specific coordination between the Zn center of ZnB and the oleic acid (OA) molecules within LFP secretions greatly enhances the binding of ZnB-UCNPs onto the LFPs and thus the corresponding visualizing quality of LFPs. The LFP images developed by the NIR-to-VIS/UV-to-VIS dual-mode visualization on various substrates are found to be evident and intact enough, enabling even level 3 details such as sweat pores to be well-displayed. This work is expected to provide a guide for the exploration of nanoscale materials for high-contrast visualization of LFPs and to shine light on techniques for criminal investigation and individual identification.