A comprehensive review on the use of rare earth-based luminophores for latent fingerprint detection

Latent prints are pivotal in forensic science and criminal investigations. These hidden human impressions formed on various substrates can provide invaluable evidence to link suspects to crime scenes and identify criminals. The use of rare earth based upconversion nanoparticles (UCNPs) and downconversion nanoparticles (DCNPs) in developing latent fingerprints (LFPs) to explore their unique characteristics has significantly advanced forensic science. UCNPs are characterized by high photostability with minimal background fluorescence, making them ideal materials for enhancing the contrast and clarity of LFPs on various surfaces. DCNPs, which emit visible light upon UV excitation also provide distinct fingermark signatures with several advantages over traditional methods, including enhanced sensitivity and accuracy. These nano-fluorophores have the potential to transform forensic techniques, by offering robust, reliable, and non-destructive methods underscoring the exclusive integration of science and art in the collection, enhancement, and interpretation of unique ridge patterns in LFPs. The field of LFP detection has advanced significantly from early basic UCNPs with green and red emissions to the development of multifunctional nanophosphors with improved luminescent efficiency, morphology control, miniaturization, multi-color imaging, and AI-driven enhancements, making fingerprint analysis more sensitive, precise, and adaptable to complex forensic scenarios. The initial section of the article introduces the types of fingerprints and the different development methods to visualise these marks left on various kinds of substrates. Further, the recent progresses reported on the use of different UC and DC rare earth nanoparticles for visualising the LFPs are compared. Moreover, the scope for prospective research advances is discussed based on the challenges related to consistency, cost, toxicity, stability, safety, and procedural complexity that needs to be addressed for the broader application of these nanophosphors in LFP development and visualisation.