Water-Soluble Polymeric Probe with Naphthalimide Pendants for Fluorimetric Formaldehyde Sensing

Abstract

Formaldehyde (FA) is a common raw material extensively used in various industrial applications. However, FA is a known carcinogen and poses significant risks to human health. Therefore, developing a sensitive and selective probe for detecting FA is crucial. Herein, a naphthalimide-based water-soluble fluorescent polymeric probe for selective detection of FA in an aqueous medium at physiological pH is presented. The aromatic hydrazine units present in the side chains of the polymer react with FA through an addition-elimination reaction with the formation of hydrazone derivative, which halts the photoelectron transfer (PET) mechanism within the polymer, leading to a “turn-on” in green fluorescence. The formation of hydrazone is confirmed by electrospray ionization mass spectrometry (ESI-MS) analysis for a model reaction of (6-hydrazinyl-2-(2-hydroxyethyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione, SM) with FA. The sensing mechanism through a PET on–off is supported by density functional theory (DFT) calculation. The probe demonstrates remarkable sensitivity, detecting FA concentrations as low as 1.7 µm, and shows a five-fold fluorescence intensity increase within 10 min when exposed to 10 µm formaldehyde. Additionally, the probe offers selective detection of FA over other analytes via fluorometric methods. This study represents a significant advancement in developing sensitive and selective polymeric probes.