The present invention concerns an improved optical method and optical sensing device for determining the levels of polyhydroxyl-substituted organic molecules in vitro and/or in vivo in aqueous media. The range of detection is between about 400 and 800 nm. In particular, a sensory devise is implemented in a mammal to determine sugar levels. Specifically, a dye is combined with a conjugated nitrogen-containing heterocyclic aromatic boronic acid-substituted bis-onium compound in the presence of a sugar, such as fructose or glucose. The viologens are preferred as the aromatic conjugated nitrogen-containing boronic acid substituted compounds. The method is useful to determine sugar levels in a human being.