During the spoilage process, a lot of bacteria are produced, which can significantly impact our health. As these bacteria grow, they secrete small molecules called AHL. We thought that by testing the concentration of these small molecules, we could determine the bacterial content in the corresponding milk sample and ultimately assess the degree of spoilage.

We designed a sensor for AHL molecules to test the concentration of AHL in milk, thereby determining the spoilage level of the milk in hand. This is mainly achieved using a dual-plasmid system to implement this function.

First plasmid system: J23119 directly initiates the transcription and translation of the LuxR protein, resulting in the production of a large amount of LuxR protein within the bacteria. AHL small molecules can diffuse through the bacterial cell membrane and encounter LuxR protein, forming a protein-small molecule complex.

Second plasmid system: When the LuxR protein and AHL small molecule complex bind to the Lux promoter region, transcription and translation are activated, producing a corresponding amount of VenusNB protein, which generates a fluorescent signal.

This establishes a relationship between specific fluorescence intensity, AHL concentration, and the bacterial content within the sample, allowing us to infer whether the milk in hand has spoiled.

With our sensor systems, we can create compact home devices that quickly and conveniently detect whether milk has spoiled. We aim to assist and support people in accessing healthy milk in their daily lives. We hope everyone can enjoy fresh, healthy, and safe milk.