Synthesis of starch-based F/N-doped carbon dots for enhanced detection of latent fingerprint tertiary structures

Fluorine and nitrogen co-doped carbon dots (FNCDs) were synthesized using a one-step pyrolysis method with citric acid, urea, and triethylamine hydrogen fluoride as precursors. A series of FNCDs/starch nanocomposites were then prepared by forming hydrogen bonds between FNCDs and starch. The morphology of both FNCDs and FNCDs/starch nanocomposites was analyzed using transmission electron microscopy (TEM), while their chemical composition and structure were characterized using Fourier-transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The optimal FNCDs/starch nanocomposite had a mass ratio of 1 : 40 and exhibited the highest fluorescence quantum yield of 26.7%. These nanocomposites demonstrated strong solid-state green light emission under 365 nm ultraviolet irradiation. The small particle size of FNCDs/starch nanocomposites allows for effective adsorption onto latent fingerprints (LFPs) and facilitates hydrogen bond formation with sweat components, enabling high-contrast LFP detection and imaging with minimal background interference. Employing a classic powder-dusting method with these nanocomposites effectively reduced background fluorescence interference, resulting in high-resolution, visually distinct fingerprint patterns on various surfaces. In conclusion, FNCDs/starch nanocomposites present a promising and reliable solution for LFP imaging in real-world forensic applications.