Solid-state fluorescence from carbon dots through surface-ligand modification for latent fingerprint visualization

Abstract

Latent fingerprints (LFPs) imaging is the most important approach to identify individuals, and there is a persisting need for the development of simple, rapid, accurate, and universal LFPs recognition methods. As the Carbon dots (CDs), being quasi-spherical in shape, exhibit unique physical, chemical, and optical properties, making them propitious for multifaceted usage. The nitrogen-doped CDs were synthesised from potassium humate as a carbon precursor and oPD as a nitrogen dopant via a one-step hydrothermal method. The obtained CDs have a particle size in the range of 2-9 nm with a quantum yield (QY) of 8.9%. However, obtaining CDs with multicolor emission in the solid state remains a great challenge, as typical aggregation-induced fluorescence quenching occurs in powder forms. Moreover, the construction of CDs with color-tunable solid-state fluorescence (SSF) has limited reports. Herein, through a surface ligand modification strategy, SSF CDs were prepared. Their emission wavelengths range from the yellow to the pink region were obtained. The multicolor SSF CDs are potentially utilized in the field of latent fingerprint visualization. The LFPs are detected with high resolution through the powder method on various substrates such as glass slide, cover slip, amber color glass bottle, aluminium foil, and steel. Also, their second and third-level substructures are clearly identified. The method is validated for LFPs visualization on different substrates and can also be stable up to around 30 days. The results demonstrate that the SSF CDs as a developer have great potential in LFP imaging for forensic investigation.