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

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^-1 and a limit of quantification (LOQ) of 130.58 ng·mL^-1, while the smartphone-integrated colorimetric method yielded an LOD of 50.41 ng·mL^-1 and an LOQ of 168.04 ng·mL^-1. 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.