A novel dual-mode sensor based on green-synthesized AuNPs and natural nitrogen-doped CQDs for tobramycin detection: enhanced sensitivity and specificity.

A novel and environmentally sustainable dual-mode sensing platform was developed for highly sensitive and selective detection of TOB, offering a portable and visually interpretable analytical system. This approach was realized through the synthesis of nanomaterials from natural waste resources (crude beehives and silkworm cocoons) and their integration with smartphone-based technology. Comprehensive characterization revealed that the synthesized gold nanoparticles (AuNPs) were spherical, with an average diameter of 9.71 ± 1.43 nm, and surface-enriched with oxygen-containing functional groups. The nitrogen-doped carbon (N-CQDs) exhibited a spherical morphology with an average size of 3.07 nm and were abundant in oxygen- and nitrogen-containing functional groups, particularly pyrrolic nitrogen, which contributed to their stronger fluorescence emission. The proposed sensor demonstrated excellent analytical performance as follows: the fluorescence-based method achieved a limit of detection (LOD) of 39.18 ng·mL and a limit of quantification (LOQ) of 130.58 ng·mL, while the smartphone-integrated colorimetric method yielded an LOD of 50.41 ng·mL and an LOQ of 168.04 ng·mL. The platform was successfully applied to detect TOB in real milk and water samples, achieving recovery rates ranging from 82.28% to 110.40%, with relative standard deviation (RSD) values below 8.77%, thereby confirming its accuracy and precision. Overall, the newly developed dual-mode sensor based on AuNPs/N-CQDs coupled with a smartphone interface, provides a rapid, user-friendly, and robust solution for on-site monitoring of TOB, demonstrating great potential for applications in food safety and environmental surveillance.