Water-soluble polymeric probe with tryptophan pendants for formaldehyde sensing

Formaldehyde (FA) is a grade-I carcinogen and the most reactive aldehyde in the carbonyl family, posing substantial health hazards. Herein, a water-soluble polymeric probe with side-chain tryptophan pendants is proposed that relies on an FA-induced Pictet-Spengler reaction for FA sensing in an aqueous medium. The polymeric probe shows cyan fluorescence in an aqueous medium after the interaction with FA due to the formation of a β-carboline derivative, confirmed by high-resolution mass spectrum analysis of the product from the model reaction between tryptophan methyl ester and FA. The copolymer's sensitivity to FA in aqueous solutions at the nanomolar level is estimated using the fluorescence titration method, where ∼20-fold enhancement in fluorescence intensity is observed within 2 min when 200 µM FA is added to the aqueous solution of the copolymer. The probe can selectively detect FA using colorimetric and fluorometric methods with a detection limit as low as 25 nM. The FA-sensing mechanism is studied from the model reaction of tryptophan methyl ester (TME) with FA, and density functional theory (DFT).