An improved ratiometric fluorescent tag based on aggregation-induced emission luminogen for in-situ monitoring of seafood freshness

Volatile basic nitrogens (VBNs) are an important indicator of food freshness. In this work, a novel ratiometric fluorescent sensor was developed. The sensor used blue-green fluorescent N-acetyl-L-cysteine capped silver nanoclusters (NAC-AgNCs) as an indicator and red-orange fluorescent glutathione capped gold nanoclusters (GSH-AuNCs) as an internal reference. With biogenic amines as model targets, results showed that the sensor was sensitive to VBNs with a limit of detection of 3.85 mu M and 6.75 mu M for spermidine and spermine, respectively. Based on these findings, a ratiometric fluorescent tag was further prepared and applied as a gas sensor for ammonia vapour monitoring, which was employed and validated to monitor the freshness of raw shrimp at different storage temperatures (4 and 25 degrees C). For all we know, this is the first ratiometric fluorescent tag based on metal nanoclusters with aggregation-induced emission properties for monitoring seafood freshness.