This new sensor determined exactly how fresh a piece of fish was within two minutes. (Adapted from ACS Sensors 2025, DOI: 10.1021/acssensors.5c01637 via SWNS)
By Stephen Beech
A simple new sensor can determine exactly how fresh fish is in less than two minutes.
To determine the freshness of a piece of fish, cooks traditionally look at its eyes and gills or give it a sniff.
But a far more accurate check for food quality and safety is to look for compounds that form when decomposition starts.
Now, Australian scientists have developed an electronic device the size of a clothes peg that quickly measures one of those compounds.
The prototype sensor can determine how fresh a fish within two minutes, according to a study published in the journal ACS Sensors.
(Photo by Engin Akyurt via Pexels)
Study co-author Professor Nicolas Voelcker said: "For fish, signs of spoilage - cloudy eyes, bruised gills, foul or fishy odors - might take hours or even days to appear.
"In contrast, compounds such as hypoxanthine start forming almost immediately after death because nucleic acids and other molecules begin to break down."
Researchers consider the level of hypoxanthine, or HX, a more reliable “freshness indicator” for both whole fish and individual fillets.
But measuring HX requires time-consuming processes and specialized lab equipment.
To make HX monitoring simpler and portable, Voelcker and his colleagues at Monash University created a micro-needle-based freshness sensor.
While microneedles are normally used in products for drug delivery or skincare, the researchers explained that in this scenario they serve to boost the device’s sensitivity.
To build the sensor, the team created a four-by-four microneedle array and coated it with specialized gold nanoparticles and an enzyme that breaks down HX.
(Photo by cottonbro studio via Pexels)
Voelcker said: "The sensor is pressed into the surface of a piece of fish and anchored by the micro-needles.
"As the enzyme breaks down HX, the electric potential within the fish changes, and the sensor measures and interprets these changes."
The researchers validated the sensor’s performance with salmon steaks cut into small pieces and left to spoil for up to 48 hours at room temperature.
The sensor detected concentrations of HX down to less than 500 parts per billion, which is a level consistent with fish samples considered to be “very fresh.”
The results were returned in around 100 seconds.
Voelcker added: "The new sensor’s sensitivity was comparable to that of a commercially available laboratory-based testing kit."
Although further development is needed before the sensor will be available for use as a portable food safety tool, the research team say that it has already shown its potential for real-time food-quality monitoring.