Heteroatom-Tuned Carbon Dots for Multimode High-Resolution Fluorescence Imaging of Latent Imprints

Fingerprints are recognized as one of the most reliable biometric features in forensic science. High-quality fingerprint imaging facilitates the extraction of essential personal information during examination and analysis. Here, we utilized the transfer mechanism between precursors and carbon dots (CDs) to synthesize wavelength-tunable fluorescent nanoparticles for developing latent fingerprints (LFPs). Experimental and theoretical results revealed that the precise design of the heteroatom-doped structure of carbon sources enabled the sequential introduction of heteroatoms to CDs, from oxygen alone, to bromine, chlorine, and finally nitrogen, which induced a gradual reduction of energy level gaps, thereby realizing adjustable fluorescence from green to red (538-612 nm). By combining CDs with diatomite, the resulting composite powders, available as multicolor fluorescence and daylight developers, demonstrated high sensitivity and selectivity for detecting both fresh and aging LFPs. Using a typical powdering method with CDs/diatomite stored for 30 days, level 1-3 fingerprint details were visualized with high contrast, and diversified latent imprints deposited on various substrates, including knuckle prints, palmprints, and footprints, were clearly developed. Furthermore, the developed multicolor enhancement technique ensured high-resolution details and overcame the challenges of poorly developed fingerprints. Thus, the proposed multimode framework establishes a viable platform for practical imprint imaging.