New sensor uses microneedles to confirm fish freshness in just two minutes

Checking whether fish is fresh has traditionally meant relying on appearance and smell. Clear eyes, bright gills, and a clean scent usually signal freshness, while cloudy eyes or a foul odor are seen as warnings. But these visible and sensory signs often appear late in the spoilage process. Chemical changes begin long before the fish looks or smells bad.

Now, researchers have developed a portable device that can measure freshness in under two minutes by detecting those early changes. The prototype sensor could eventually make seafood evaluation faster, easier, and far more accurate. Detecting freshness at the molecular level Fish begin decomposing almost immediately after death. One of the earliest chemical markers of this process is hypoxanthine (HX).

It forms as nucleic acids and other molecules start breaking down. Because HX levels rise quickly, scientists recognize it as a reliable freshness indicator. It works for both whole fish and packaged fillets. However, testing for HX currently requires skilled technicians, laboratory equipment, and long analysis times.

These factors make routine testing unrealistic in markets, cold storage, or kitchens. The research team, including Nicolas Voelcker, Azadeh Nilghaz, and Muamer Dervisevic, set out to design a tool that could be used almost anywhere without complicated preparation or machines.

Simple Test With Microneedles The device uses a small four-by-four microneedle array coated with gold nanoparticles and an enzyme that reacts specifically to HX. Microneedles are often found in skincare and medical patches, but here they play a different role. They help the device make contact with chemical activity below the surface of the fish, where spoilage starts. To perform a measurement, the sensor is gently pressed against the fish.

The tiny needles anchor it in place. As the enzyme reacts with hypoxanthine, electrical signals shift inside the flesh. The sensor reads those shifts and interprets them to determine freshness. The researchers tested the prototype on fresh salmon cut into pieces and left out at room temperature for up to 48 hours.

The sensor detected hypoxanthine levels as low as 500 parts per billion, which corresponds to what experts classify as very fresh fish. Results appeared in roughly 100 seconds. The accuracy and sensitivity matched those of an existing lab-based testing kit. Although more work is needed before it becomes widely available, the demonstration shows strong potential.

The researchers say the device could be used for real-time food quality monitoring. If developed commercially, the tool could benefit seafood distributors, grocery stores, restaurants, and home cooks. Consumers often rely on trust and guesswork when buying fish. A sensor that quickly and objectively confirms freshness could reduce waste, cut the risk of foodborne illness, and increase confidence in seafood products.

The study suggests that in the future, testing fish for freshness might become as simple as pressing a small device onto its surface and waiting a minute. Instead of judging by smell or guessing based on appearance, users could get a measurable answer backed by chemistry. The study is published in the journal ACS Sensors.