Strongly fluorescent conjugated polymer nanoparticles in aqueous colloidal solution for universal, efficient and effective development of sebaceous and blood fingerprints.

Taking the same developing strategy for different types of latent fingerprints is helpful in improving the efficiency of criminal investigation. Here we advanced a new strategy based on amino-functionalized poly(p-phenylenevinylene) nanoparticles (PPV-brPEI NPs) in aqueous colloidal solution as the developing reagent. The desirable amino functionality and strong emission of NPs were simultaneously realized by adding branched polyethyleneimine (brPEI) during the process of thermal elimination of the PPV polymer precursor. The NPs were demonstrated to have negligible effects on the extraction of biological information from DNA. Using the PPV-brPEI NPs-soaked cotton pad, both latent sebaceous fingerprints (LSFPs) and latent blood fingerprints (LBFPs) can be effectively developed on different nonporous substrates. This strategy was highly sensitive and effective for aged, contaminated and moldy fingerprints. Additionally, the developed fingerprints could tolerate humidity environment and the alcohol atmosphere. The mechanism investigation suggests that interaction between PPV-brPEI NPs and sebum ingredients contributes to the development of LSFPs and interaction between PPV-brPEI NPs and proteins in blood contributes to the development of LBFPs, but the former is not as stable as the latter. This work provides a simple, environment/operator-friendly strategy for efficient fingerprint development, which is very promising for practical criminal investigations.