Paper sensor detects when meat and fish go bad

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.

And it can be read by your smartphone - if there's no ammonia, it responds.

But if there is ammonia, no response.

The sensors could be placed on food wrappers, replacing expiration dates.

The U.S. wastes nearly a third of its food supply every year.