Fluorescent probe based on EDOT derivative EDOT-EN: Highly selective detection of biogenic amine Cadaverine and its application in food freshness monitoring

Food spoilage is a silent process, often beginning long before a smell becomes obvious to the human nose. As meat, fish, and dairy products break down, microscopic organisms convert amino acids into small nitrogen-based molecules known as biogenic amines. Among these, a specific compound called cadaverine acts as a reliable warning sign. When fresh protein-rich foods begin to rot, cadaverine levels rise, signaling that the product is no longer safe to eat. While laboratories can measure these chemicals with heavy, complex machinery, such tools are impractical for a home cook or a market vendor. The challenge for scientists has been to create a method that is simple, fast, and sensitive enough to spot these warning signs before they become a health hazard.

A team of researchers at Qilu University of Technology and the 960th Hospital of the People's Liberation Army in China has developed a new tool to meet this need. They created a special chemical probe, a molecule designed to act like a light switch that changes color when it encounters cadaverine. The researchers started by building four different versions of this probe, all based on a core structure called EDOT, which is known for its ability to conduct electricity and emit light. They attached different chemical groups to the end of each probe to see which one would react most effectively. After testing them in various liquid environments, they found that one specific version, which they named EDOT-EN1, was far superior to the others. This molecule glows with a bright red light when it is alone, but when it meets cadaverine, the light shifts to a pale blue, providing a clear visual signal that the spoilage chemical is present.

The science behind this change relies on how the molecule is built. The probe is constructed with a part that pushes electrons and a part that pulls them, creating a flow of energy that produces the red glow. When cadaverine enters the scene, it chemically attaches itself to the probe, breaking the pull on the electrons. This disruption stops the flow of energy in its original form and forces the molecule to release light at a different, higher energy level, which our eyes see as blue. The researchers confirmed this process by observing the molecule under a microscope and using computer simulations to map out how the electrons moved before and after the reaction. They found that the change was not just a temporary flicker but a permanent chemical transformation, meaning the probe could reliably record the presence of the spoilage marker.

To prove this concept works in the real world, the team turned the chemical solution into practical tools. First, they soaked small pieces of filter paper in the probe solution and let them dry, creating simple test strips. When they placed a drop of liquid containing cadaverine onto these strips, the red fluorescence vanished, replaced by a faint blue glow, while drops of other common chemicals caused no change. They then took these strips to the kitchen, placing them on fresh shrimp and fish. One group of seafood was kept in a refrigerator at a cold temperature, while another group sat out at room temperature. Over the course of four days, the researchers watched the strips under a special ultraviolet lamp. The strips on the room-temperature food, which was rotting, changed color from red to blue as the cadaverine levels rose. The strips on the refrigerated food, which stayed fresh, remained red. This demonstrated that the strips could visually track the freshness of food over time without any electronic equipment.

The researchers also explored a more advanced application by embedding the probe into a thin, fibrous film using a process called electrospinning. This created a lightweight mesh that could detect cadaverine not just in liquids, but in the air as a vapor. When they exposed this film to the smell of cadaverine rising from a solution, the film changed color just as the paper strips did. This suggests that the technology could eventually be used to monitor the air inside a refrigerator or a shipping container, alerting people to spoilage before the food is even opened. The study showed that the probe could detect cadaverine at very low concentrations, down to less than one micromole, and could do so within about fifty minutes. By turning a complex chemical reaction into a simple color change, this work offers a promising path toward safer food monitoring, allowing anyone to see the invisible signs of spoilage with their own eyes.