Dual-mode visual imaging of latent fingerprints based on organic fluorescent probe with enhanced TICT emission

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Fluorescence-based imaging has emerged as a promising technique for high-resolution visualization of latent fingerprints (LFPs), but detecting LFPs by fluorescent probes remains challenging at present. Herein, a water-soluble fluorescent dye (DEPN) with red emission and twisted intramolecular charge transfer (TICT) properties was synthesized, which function as a dual-mode in-situ imaging probe for LFPs. The desired solid composite fluorescent fingerprint powder DEPN@MMT can be obtained by milling with montmorillonite (MMT) to realize the imaging of LFPs with 1–3 levels of details, which has the advantages of simple preparation, low doping ratio, good photostability, and is not limited by the substrate. Comparison with the actual fingerprint details extracted by fingerprint reader revealed a good match between the both, indicating that the fingerprint powder has high application value. The permanent preservation of LFPs with different curvatures was also realized by making rubbings. In addition, DEPN was able to image LFPs in aqueous solution with a concentration of 50 μM over a wide pH range, and it took only 20 s to obtain high-quality images that met the NFIQ2 detection standard. This dual-mode imaging probe of LFPs is highly practical, offering adaptable detection patterns for a range of complicated situations. It provides a valuable method for rapid and convenient visualization of LFPs, as well as their subsequent preservation and analysis.