When you're checking the freshness of a piece of fish that you plan on eating, you want results right away. That's where a new microneedle-based sensor comes in, as it delivers a yay or nay in less than two minutes.
Almost as soon as a fish dies, nucleic acids and other molecules in its flesh begin breaking down, triggering the formation of a compound known as hypoxanthine (HX). The longer the elapsed time since death, the higher the HX concentrations in the flesh.
For that reason, hypoxanthine levels are considered a good objective measure of fish freshness. Unfortunately, however, assessing those levels is typically a time-consuming procedure that requires specialized lab-based equipment. If you're testing a piece of fish in a home or restaurant kitchen, that just won't do.
With that limitation in mind, scientists from Australia's Deakin and Monash universities have developed a small sensor with a 4x4 grid of microneedles at one end. Microneedles are essentially tiny, sharp studs, which we've previously seen utilized for applications such as delivering medication through the top layer of the skin.
In this particular case, however, the microneedles are coated with gold nanoparticles along with xanthine oxidase, which is an enzyme that breaks down HX. When the needles are pressed down into a piece of fish flesh and the enzyme goes to work on the HX, it causes a change in the electrical potential of the flesh. The sensor measures that change, thus providing an objective measurement of freshness.
The technology was tested on pieces of salmon that were left at room temperature for anywhere up to 48 hours, and it successfully detected HX concentrations down to less than 500 parts per billion (which is considered to be "very fresh") within 100 seconds. Its readings also fell in line with those obtained by a commercially available laboratory-based testing kit.
A paper on the research – which was led by Nicolas Voelcker, Azadeh Nilghaz and Muamer Dervisevic – was recently published in the journal ACS Sensors.
Source: American Chemical Society
