Afraid your fish is too fishy? Smart sensors might save your nose
A new biosensor made from needles most commonly found in dermatology clinics and medical centers could make the fresh fish “smell test” seem outdated.
For as long as humans have been eating fish, we have identified rotting or spoilage by looking for a handful of physical signs. Blurry eyes, bruised gills and the distinctive “fishy” smell are all signs that a piece of salmon could cause stomach upset or worse. Although relatively effective, these observable signs take time to develop, during which time the fish may already be decomposing. A much more precise method is to detect faint traces of metabolic compounds that appear in the early stages of deterioration. Although this is now possible, these methods generally require large, controlled laboratories.
Researchers at the American Chemical Society believe their new “microneedle-based freshness sensors” device could make this process much more efficient. Detailed this week in the newspaper ACS sensorsThe 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.
Khazaei et al., ACS sensors2025.
In their experiment, the researchers tested fish samples at different levels of decomposition and found that the device could provide a highly accurate reading of freshness in less than two minutes. They hope the sensor can bring lab-level freshness assessments to more fish markets and possibly save some reluctant victims from having to breathe in rotten seafood.
“The biosensor’s ability to monitor HX levels directly in fish samples without extensive preprocessing 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. »
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The device is an array of four-by-four microneedles, printed in 3D, coated with gold nanoparticles. These particles carry an enzyme capable of breaking down any HX compound present when they come into contact with the fish. The sensors then measure the resulting changes in the manipulated molecules, a process that the team believes corresponds to freshness levels. Some of these early indicators of decomposition appear before physical signs are perceptible to the human eye (or nose).
During the testing phase, the sensor was inserted into fish samples left at room temperature for 0, 6, 12, 24, 36 and 48 hours, the last being more than enough for deterioration to occur. Overall, the researchers observed a “gradual increase in HX levels over time,” with concentrations steadily increasing throughout the testing period. This steady increase reflects already established results from controlled laboratory studies. At the lower end, microneedle sensors detected HX concentrations below 500 parts per billion, which is considered “very cool.” In other words, keeping the sensor in the fish allowed the researchers to determine the precise moment when the sample began to deteriorate.
‘Smart sensors’ could reshape food safety on an industrial scale
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 sensor, controllable by smartphone, that can be applied directly to the surface of protein-rich meats like beef to remotely monitor their spoilage rate. Meanwhile, at MIT, researchers have developed Velcro-style 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 bio-ink that changes color when they encounter fluids whose pH is associated with deterioration. For example, sensors change 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 analyzed data collected continuously 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 responsible for milk spoilage in less than two hours, with 98% accuracy.
As for the fish sensor, the chemists and engineers who developed the device hope it can have a real impact on the seafood industry, even if it’s not quite ready for commercial use. For now, it is also primarily limited to measuring fish, as the HX alteration thresholds at the heart of its detection method can vary significantly between animal species.
In the meantime, it seems that the smell test inevitably remains an unpleasant but necessary alternative for most home cooks.
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