Rapid and convenient detection of ascorbic acid using a fluorescent nitroxide switch

► Ascorbic acid is a small-molecule reductant with multiple functions in vivo. ► Nitroxide is reduced to the corresponding hydroxylamine by ascorbic acid. ► Fluorescent nitroxide leads to intramolecular quenching of fluorescence emission. ► The new fluorophore-nitroxide could sensitively and easily detect ascorbic acid.