lvxferre , 4 days ago

If you’re talking about strips that look like this:

https://mander.xyz/pictrs/image/a5bb1633-30e0-43d9-8872-610909400df8.webp

I believe that most brands use Benedict’s reagent: copper sulphate, sodium citrate, sodium carbonate. It interacts with reducing sugars (like glucose) and the colour goes from blue to light green to green to brown-green to brown-red, depending on concentration.