A highly specific fluorescent probe with facile pretreatment for rapid and accurate detection of sulfur dioxide residues in Wolfberry (Lycium barbarum L.)

Abstract

Sulfur fumigation is a traditional technique for drying, pest control and mildew prevention in traditional Chinese medicine (TCM). However, excessive sulfur fumigation significantly impairs drug safety and clinical efficacy, rendering sulfur dioxide (SO₂) residues in sulfur-fumigated TCM a growing concern. Conventional detection methods exhibit drawbacks in practical operation, such as complex procedures, long time consumption, low sensitivity and expensive instruments. Herein, a fluorescent probe-based method was established for the rapid and accurate detection of SO₂ residues in wolfberry, leveraging the nucleophilic addition-elimination reaction between the probe and sulfite. The detection limit (LOD) was 1.5 μM, and the limit of quantification (LOQ) was 5 μM. Considering the practical application requirements for the quality testing of TCM, the pretreatment parameters including sample forms, extraction modes, extraction times with extraction solvent were optimized. The detection protocol was finalized as follows: samples were soaked for 15 minutes in HEPES buffer (20 mM, pH 7.4), and the extract was reacted with the fluorescent probe at 35 °C for 15 minutes, followed by detection on a microplate reader. The average recovery rates at low, medium, and high spiked concentrations ranged from 89.5% to 100.8%, the corresponding detection method was further applied to actual samples. Accordingly, this method features facile pretreatment, rapid operation and detection, high accuracy and sensitivity, enabling rapid and reliable determination of SO2 residues in wolfberry. It provides a novel technical tool for TCM quality supervision and offers technical support for safeguarding public health.