Bimodal single-atom iron nanozyme biosensor for volatile amine and food freshness detection

Volatile amines (VAs) play a critical role in detecting the freshness of meat. However, the development of nondestructive, real-time, and portable techniques for monitoring VAs remains a challenge. Here, we successfully created a colorimetric-fluorescent dual-signal biosensor for meat freshness detection by using a single-atom iron nanozyme (SAFe-N-C nanozyme) and carbon quantum dots (CDs). The SAFe-N-C nanozyme with high peroxidase-like (POD-like) activity (40.22 U/mg) acts as a catalyst by facilitating the conversion of the colourless reduced state 3,3′,5,5′-tetramethylbenzidine (redTMB) to its oxidized product (oxTMB). Subsequently, the fluorescence signal of the CDs is quenched due to the inner filtering effect (IFE) between oxTMB and CDs. During food spoilage, the generation of VAs results in the reduction of oxTMB, which subsequently recovers the fluorescence of the CDs. As a result, the limits of detection (LOD) for ammonia detection are 0.9840 ppm and 0.0838 ppm within a linear range of 0.5–50 ppm. This colorimetric-fluorescent dual-signal biosensor effectively detects VAs during the spoilage of livestock and poultry meat in a nondestructive and real-time manner. This innovative work overcomes the limitation of single signal output and provides a portable and reliable method for VAs detection, proving to be a significant advancement in meat freshness assessment.