A ratiometric fluorescence/colorimetric dual-mode sensing platform based on CDs@MIL-88-NH₂ for rapid and specific detection of arginine and nitrite.

Arginine and nitrite are widely present in diet and critical determinants of food quality and safety. Herein, CDs@MIL-88-NH₂ integrated fluorescence and peroxidase-like activity was designed for the specific detection of Arg and nitrite. Arg induced structural decomposition of CDs@MIL-88-NH₂ and thereby restored its fluorescence with a blueshift to 430 nm within 1 min. The fluorescence of CDs (λem = 580 nm) remained stable, providing a ratiometric fluorescence (I430/I580) for Arg. Additionally, CDs@MIL-88-NH₂ enzymatically promoted the reaction between 3,3',5,5'-tetramethylbenzidine and nitrite to form a new compound, thereby generating a characteristic absorption at 450 nm within 15 min. By referencing the absorption of CDs at 550 nm, a ratiometric colorimetric method (A450/A550) for nitrite was established using a cyan-magenta-yellow (CMY) multicolour mode. The limits of detection (LODs) were 0.14 μg/mL for Arg and 0.001 μg/mL for nitrite. This method was successfully applied for realizing food safety, food quality, and toxicological intervention.