A Universal Developing Strategy for Fingermark Detection and Enhancement Based on Disodium Iminodiacetate-Functionalized Conjugated Polymer

Abstract

Finding a universal fingermark developing strategy effective for all types of fingermarks may improve the efficiency of forensic investigation. Here, we synthesized a fluorescent conjugated polymer (PTPEPE-IDA) with poly[p-(tetraphenylethene)-alt-(phenylene ethylene)] as the backbone and carrying pendant disodium iminodiacetate and monocarboxylate groups to interact with sweat, which is commonly present in fingermarks. PTPEPE-IDA was dissolved in ethanol to form the developing reagent, which was demonstrated to be effective in visualizing and enhancing sweat-containing sebaceous and blood fingermarks on various substrates with the same developing protocol. With the increase of the sweat content in fingermarks, the fluorescence intensity and clarity of patterns of the developed fingermarks increased. This strategy was effective for sweat-containing fingermarks aged for up to 100 days. The developed fingerprint has high stability, being recognizable after storage for 100 days or immersion in water (or ethanol). Mechanism investigation suggests that PTPEPE-IDA can bind some components in sweat and blood through synergistic effects of multiple interactions, and the aggregation-induced emission enhancement (AIEE) upon sweat was demonstrated by the macroscopic view and emission/absorption spectra, which is beneficial to detect the fingermark quickly and then enhance the legibility of the pattern. This universal strategy is expected to make fingermark development more efficient.