Trichromatic fluorescent diatomite-based carbon dot composites for dual-mode high-resolution imaging of latent fingerprints

Fluorescence-based imaging has emerged as a powerful tool for detecting latent fingerprints (LFPs). However, existing fluorescent developers face challenges in differentiating friction ridges from backgrounds with intractable fluorescence, and to date, post-processing techniques fail to effectively enhance poorly visualized fingerprints. Herein, trichromatic-emitting carbon dots (CDs) were synthesized via a one-step solvothermal method using dyes and ethylene glycol as precursors. Experimental and theoretical results revealed that the high photostability and photobleaching resistance of the synthesized CDs originated from the hydrogen-bond interactions between the carbonaceous matrix and dye-related functional groups and fragments, which served as the fluorophore of these Dye-CDs. By combining CDs with diatomite, the resulting composite powders demonstrated high sensitivity and selectivity in fluorescence visualization of both fresh and aging LFPs. Using a typical powdering method with Dye-CDs/diatomite stored for 30 days, levels 1–3 detailed features of LFPs deposited on various porous or non-porous substrates were identified with high contrast. The developed tunable multicolor post-processing technique, achieved by separating ridge patterns from background noise, ensured high-resolution details and overcame the challenges of weakly developed fingerprints. Thus, the proposed dual-mode strategy provides a promising solution for practical fingerprint imaging.