A polylysine-based fluorescent probe for sulfite anion detection in aqueous media via analyte-induced charge generation and complexation

Abstract

Sulfite is widely used as a preservative in food and beverages; and human exposure to SO₂ (which is easily transformed into sulfite) has become increasingly widespread. Overdose or inhalation of sulfite may induce many respiratory responses and a number of diseases. Hence, it is important to achieve rapid, sensitive and selective detection of sulfites. Herein, we report a robust fluorescent turn-on probe for sulfite anions via the analyte-induced charge generation and AIE effect (the aggregation induced emission effect). The two-component sensing system comprises a modified polylysine with benzoic aldehyde side groups and a positively charged tetraphenylethene bearing two quaternary ammonium groups. In the presence of sulfite anions, the benzoic aldehyde groups on polylysine side chains react with sulfite and turn into negatively charged groups, leading to the complexation between the polymer chains and the positively charged fluorophores (TPE-2N⁺) and eventually achieving the fluorescence enhancement of the system as a result of the AIE effect. The integration of the water-soluble biopolymer and AIE-active fluorophore ensures that the system is operable in totally aqueous media (100% water), which is beneficial for applications in food quality control, environmental pollution monitoring and biological assays. Furthermore the system exhibits highly selective and sensitive fluorescent turn-on detection for sulfite, with the detection limit of 3.6 μM. Moreover, it can be used in real samples such as red wine, beer and rainwater, and there is no need for special sample pretreatment.