Biomass derived L-Histidine functionalized N-doped carbon dots from Spatholobus littoralis for detection of Cr6+ and latent fingerprint on non-porous surfaces

Biomass-derived nitrogen doped carbon dots (NCDs) were successfully synthesized using Spatholobus littoralis via a hydrothermal method and functionalized with L-histidine to enhance their fluorescence properties for dual applications in heavy metal ion detection and forensic fingerprint visualization. Structural and morphological characterization confirmed the formation of quasi-spherical carbon dots with an average particle size of approximately 6 nm and abundant surface functional groups, which contribute to strong photoluminescence behavior. The synthesized NCDs exhibited excellent fluorescence response and selectivity toward Cr⁶⁺ ions through a fluorescence quenching mechanism. The sensing system demonstrated good analytical performance with a LOD of 145.4 ppb and LOQ of 440.55 ppb for Cr⁶⁺. In addition, the practical applicability of the sensing platform was evaluated using spiked drinking water and tap water samples, where satisfactory recovery values ranging from 94.98% to 110.81% were obtained, confirming good accuracy and reliability for real sample analysis. Furthermore, the NCDs combined with tapioca powder demonstrated strong fluorescence and high contrast for latent fingerprint detection on non-porous surfaces under UV illumination. The developed multifunctional fluorescent material offers a promising, ecofriendly platform for simultaneous applications in environmental monitoring and forensic science.