Structure-function decoupled water-soluble fluorescent probes for high-contrast imaging of latent fingerprints with Level-3 details

Designed two water-soluble D–π–A fluorescent probes for LFP visualization. • Inert ammonium groups grant high water solubility and LFP enrichment ability. • Probes show weak aqueous emission (TICT) and strong solid-state RIR fluorescence. • Achieved high-contrast imaging of level-3 LFP features on diverse substrates. • Electrostatic adsorption to LFP lipids drives the high-contrast development. High-sensitivity, high-contrast and eco-friendly visualization of latent fingerprints (LFPs) remains a key demand in forensic analysis. Most organic fluorescent developers suffer from poor water solubility and rely on organic solvents, while hydrophilic modifications often lead to fluorescence quenching. Herein, we designed and synthesized two D-π-A fluorescent molecules ( TPA-Q and DMPA-Q ) functionalized with spectroscopically inert alkyl quaternary ammonium groups for LFP development. The alkyl quaternary ammonium groups confer mg/mL-level water solubility and electrostatic enrichment for fingerprint residues without perturbing the intrinsic luminescence. Both compounds exhibit weak fluorescence in aqueous solution due to twisted intramolecular charge transfer (TICT), but intense emission in solid (Φ> 62%) and film states. Using an aqueous atomization method, clear LFPs were successfully developed on various substrates with well-resolved level-3 details (e.g., pores and ridge contours). Notably, TPA-Q excelled on green backgrounds (e.g., Snow beer cans), while DMPA-Q performed better on blue ones (e.g., Pepsi cans, G/G 0  = 3.0), respectively avoiding blue/green substrate interference. These water-soluble fluorescent developers exhibit low background interference, high contrast, and broad applicability when combined with aqueous nebulization and powder-dusting protocols, offering a promising strategy for efficient and nondestructive LFP visualization in practical forensic applications. Download: Download high-res image (298KB) Download: Download full-size image