Development of latent fingerprints by degradable highly-adhering powder——a long-term strategy for the fading of fingerprint residues

The development of highly efficient and harmless reagent for visualization of latent fingerprints (LFPs) on variety substrates is of great importance for criminal investigations. Herein, a kind of “green” and cost-effective fingerprint development powder (polydopamine nanospheres, PDA NSs) is facilely synthesized via self-polymerization of dopamine under mild condition. Due to the abundant functional groups (catechol and amine), PDA-based powder can firmly adhere to the fingerprint residues via supermolecule interactions on various substrates (permeable or not) rapidly. The apparent LFPs from male or female were successfully obtained and analyzed. The fingerprint images exhibited clear first level (fingerprint patterns) and second level (detail features) fingerprint information on the challenging substrates (colored lid, cambered cup, paper, wood, and leather). Even fingerprint aged for more than 90 days on the non-permeable substrate surface can be recognized obviously with extremely lower detection limit. In addition, the gray value analysis further verified the advantage of PDA-based fingerprint development with good contrast, resolution and selectivity. Moreover, the excellent properties of the novel PDA NSs powder endow it highly competitiveness to the commercial low hazard black magnetic powder, which may be expected to make it become an attractive nanomaterial in crime scenes and forensic investigations.