The selective capture of Pb2+ in rice phloem sap using glutathione-functionalized gold nanoparticles/multi-walled carbon nanotubes: enhancing anti-interference electrochemical detection

Abstract

The monitoring of heavy metal ions (HMIs) in rice phloem sap is of great significance for studying the migration and accumulation of HMIs in rice plants and, ultimately, for human health. However, achieving sensitive and selective electroanalysis of HMIs in such complex real samples is a huge challenge due to severe interference. In this work, a sensitive anti-interference sensing interface for the analysis of Pb²⁺ in rice phloem sap is fabricated based on glutathione-functionalized gold/multi-walled carbon nanotubes (MWCNTs-GSH-Au-GSH). Combining the selective capturing abilities of glutathione and the electrocatalytic abilities of small sized gold nanoparticles (mean diameter: 3.1 nm) toward Pb²⁺, the sensitivity of MWCNTs-GSH-Au-GSH is as high as 1122.8 μA μM⁻¹ cm⁻² without interference from other small ions, sucrose, ATP, amino acids, plant hormones, and so on. The limit of detection (0.01 μM) satisfactorily meets the requirements for sensing trace Pb²⁺. Importantly, a MWCNTs-GSH-Au-GSH electrode exhibited excellent stability over a test period of 6 months. In addition, the developed sensor shows high reproducibility, which is checked using ten different MWCNTs-GSH-Au-GSH electrodes. Based on the above advantages, the MWCNTs-GSH-Au-GSH electrode can be suitably applied to the detection of Pb²⁺ in rice phloem sap. The mechanism behind the high selectivity and sensitivity of the MWCNTs-GSH-Au-GSH electrode toward Pb²⁺ is clearly investigated via X-ray photoelectron spectroscopy (XPS) and extended X-ray absorption fine structure (EXAFS) studies.