"Rapid visual screening" and precise quantification: A colorimetric-ratiometric fluorescent dual-mode sensing platform based on DT-Cu nanozymes for rapid detection of kasugamycin.

Rapid screening and quantitative confirmation of kasugamycin (KSM) residues in foods remain challenging without chromatographic instruments. Herein, a low-cost colorimetric/dual-excitation ratiometric fluorescent platform was developed using 3,5-diamino-1,2,4-triazole-coordinated copper nanozymes (DT-Cu). Characterization verified Cu-N-associated active sites and homogeneous elemental distribution. DT-Cu catalyzed H2O2-mediated oxidation of Ampliflu Red to resorufin, whereas KSM inhibited its peroxidase-like activity through coordination/hydrogen-bonding-associated interactions, causing color fading and red fluorescence attenuation. Blue carbon dots were introduced as an internal reference to construct an I435/I584 readout, improving resistance to matrix and instrumental fluctuations. Under optimized conditions, KSM was detected over 0.001-50 μg mL-1 with a detection limit of 2.31 pg mL-1 within 40 min. The probe showed good 7-day storage stability. Recoveries of 90.0%-103.6% with RSDs of 0.11%-5.89% were obtained in real samples, demonstrating its potential for rapid on-site screening.