LONDON (WPVI) -- British researchers have developed a simple paper-based sensor that indicates when meat and fish have gone bad.
The sensor traces amounts of ammonia and another chemical released by food as it spoils.
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And it can be read by your smartphone - if there's no ammonia, it responds.
But if there is ammonia, no response.
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The sensors could be placed on food wrappers, replacing expiration dates.
The U.S. wastes nearly a third of its food supply every year.