One-step solvothermal synthesis of red emissive carbonized polymer dots for latent fingerprint imaging

Photoluminescent carbon-based nanomaterials (CNMs) have attracted much attention over the past decade due to their unique optical characteristics and negligible toxicity. However, it is very difficult to obtain red emission of CNMs. Bright red fluorescent carbonized polymer dots (CPDs) were prepared by facilely adjusting the reaction temperature through a one-step solvothermal route, using p-phenylenediamine (PPD) as precursor. The as-synthesized CPDs exhibit excitation-independent emission at about 608 nm under excitation from 365 to 550 nm. Loading CPDs in starch to form CPDs-starch powder, the resultant powder exhibits strong red emission and the typical aggregation-induced fluorescence quenching was effectively suppressed, thus allowing the CPDs to be used in solid state form. More importantly, latent fingerprints (LFPs) on surfaces of various substrates, including glass, stainless steel, marble, adhesive tape, aluminum foil, painted wood, compact disc (CD), and coin, are developed by CPDs-starch powder and exhibit clear patterns and satisfactory ridge details under a 365 nm UV lamp. Furthermore, fingerprints on surfaces with multicolored background and strong florescent properties could also be clearly observed. These results suggest that CPDs-starch powder can be used as a fluorescent labeling agent for the visualization of LFPs in forensic science.