Afraid your fish is too fishy? Smart sensors might save your nose
A groundbreaking development in food safety technology has emerged from researchers at the American Chemical Society, who have created a new biosensor that could revolutionize how we assess the freshness of fish. Traditionally, consumers have relied on the “smell test” and visible signs of spoilage—such as cloudy eyes and bruised gills—to determine whether fish is safe to eat. However, these methods are not only subjective but also time-consuming, as they often only manifest after significant spoilage has occurred. The new microneedle-based freshness sensor, detailed in the journal *ACS Sensors*, offers a more accurate and rapid alternative by detecting hypoxanthine (HX), a metabolic compound that indicates spoilage at much earlier stages.
The innovative device consists of a 3D-printed array of microneedles coated with gold nanoparticles that release enzymes upon contact with fish. These enzymes interact with HX, allowing the sensor to provide real-time freshness readings within just two minutes. In experiments, the sensor was tested on fish samples left at room temperature for varying durations, demonstrating a direct correlation between the increasing HX levels and the fish’s decay. Notably, the sensor can detect HX concentrations as low as 500 parts per billion, which is indicative of very fresh fish. This technology promises to bring laboratory-level freshness assessments to fish markets, processing facilities, and food safety inspections, potentially sparing consumers from the unpleasant task of sniffing spoiled seafood.
As the food industry increasingly turns to smart sensors for enhanced safety and quality control, this new fish sensor aligns with broader trends in food technology. Other innovations, such as smartphone-controllable sensors for meats and color-changing indicators for contamination, highlight a growing focus on real-time monitoring of food freshness and safety. While the microneedle sensor is not yet commercially available and is currently limited to fish due to species-specific spoilage thresholds, its development marks a significant step forward in food safety. Until it becomes widely accessible, however, home cooks may still have to rely on their noses to judge the freshness of their seafood.
https://www.youtube.com/watch?v=fSw_XROQI0I
A new biosensor made out of needles most commonly seen in dermatology clinics and medspas could make the fresh
fish
“
smell test
” seem antiquated.
For as long as humans have eaten fish, we’ve identified rot or spoilage by looking for a
handful of physical signs
. Cloudy eyes, bruised gills, and the unmistakable “fishy” smell are all signs that a piece of salmon might lead to gastric distress or worse. Though relatively effective, these observable signs take time to develop, time during which the fish may already be decomposing. A far more accurate method involves detecting faint traces of metabolic compounds that appear during the earliest stages of spoilage. While that is possible now, these methods typically require large, controlled laboratory settings.
Researchers at the American Chemical Society believe their new “microneedle based freshness sensors” device could make that process much more efficient. Detailed this week in the
journal
ACS Sensors
, the team describes a small device made from an array of microneedles that inserts into a dead fish (or fillets) and continuously measures
hypoxanthine
(HX), a key compound closely associated with spoilage.
This new sensor determined exactly how fresh a piece of fish was within two minutes.
Image:
Khazaei et al.,
ACS Sensors
, 2025.
In their experiment, the researchers tested fish samples at varying levels of decay and found that the device could deliver a highly accurate freshness reading in under two minutes. They are hopeful the sensor could bring laboratory-level freshness evaluations to more fish markets—and possibly spare some unwilling victims from having to take a whiff of rotting seafood.
“The ability of the biosensor to monitor HX levels directly in fish samples without extensive pretreatment makes it a valuable tool for assessing fish freshness and quality in real-time,”
the researchers write in the paper
. “Its portability, fast response time, and ease of use make it ideal for on-site applications in fish markets, processing facilities, and food safety inspections.”
Scientist poked rancid fish with needles
The device is a four-by-four, 3D-printed microneedle array coated with gold nanoparticles. These particles carry an enzyme that can break down any HX compound present when they come into contact with fish. The sensors then measure the resulting changes in the manipulated molecules, a process the team says corresponds to levels of freshness. Some of those early indicators of decomposition notably appear before any physical signs are noticeable to the human eye (or nose).
Several microneedle sensors attached to the fish immediately begin emitting an enzyme that disturbs molecules associated with rot.
Image: Khazaei et al.,
ACS Sensors
, 2025.
In the testing phase, the sensor was inserted into fish samples that had been left at room temperature for 0, 6, 12, 24, 36, and 48 hours, the last of which is more than enough time for spoilage to occur. Overall, the researchers observed a, “progressive increase in HX levels over time,” with concentrations rising steadily throughout the entire test period. That consistent uptick mirrors already established results from controlled laboratory studies. At the lower end, the microneedle sensors detected HX concentrations below 500 parts per billion, which is considered “very fresh.” In other words, keeping the sensor in the fish allowed the researchers to pinpoint the moment the sample began to deteriorate.
‘Smart sensors’ could reshape industrial-scale food safety
Sensors of various shapes and sizes are becoming common staples in the increasingly industrialized and high-tech world of global food production. Two years ago, engineers at Koç University in Turkey designed a
battery free, smartphone controllable sensor device
that can be applied directly to the surface of protein-rich meats like beef to remotely monitor their spoilage rates. Meanwhile, over at MIT, researchers
developed Velcro-like food sensors
(also made with microneedles) designed to attach to plastic food packaging and detect signs of contamination. In this system, the needles were coated with a bioink that changes color when they encounter fluids with pH levels associated with spoilage. For example, the sensors shift from blue to red when they come into contact with
E. coli
and other harmful bacteria.
Related: [
FDA approves lab-grown salmon
]
More recently, researchers at the University of Connecticut
developed a machine-learning AI model
that analyzes data continuously collected from 12 sensors measuring dairy samples and used it to identify patterns associated with the presence of pathogens. In testing, the model was able to detect eight different pathogens and bacteria that cause spoilage in milk in under two hours, with 98 percent accuracy.
As for the fish sensor, the chemists and engineers developing the device are hopeful it could make a real-world impact in the seafood industry, though it’s not quite ready for commercial use. For now, it is also limited primarily to measuring fish, because the HX spoilage thresholds at the core of its detection method can vary significantly between animal species.
Until then, it looks like the smell test inevitably remains an unpleasant but necessary fallback for most home cooks.
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Afraid your fish is too fishy? Smart sensors might save your nose
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