Paper-based sap enrichment device combined with laser-induced breakdown spectroscopy for the minimally invasive detection of Cd(Ⅱ) and Pb(Ⅱ) in plants

Abstract

Detecting heavy metals in plants is highly important for diagnosing plant health and understanding the stress mechanisms induced by heavy metals. However, the minimally invasive detection of heavy metals in plants remains a challenge. A novel paper-based sap enrichment device (PBSED), combined with laser-induced breakdown spectroscopy (LIBS) was proposed for the minimally invasive detection of Cd(Ⅱ) and Pb(Ⅱ) in plants. The PBSED included a stainless-steel capillary and heavy metal ion enrichment filter paper (HMIE-FP). The stainless-steel capillary was inserted into the plant stem, where plant sap was transported onto the paper substrate through capillary action. The heavy metal ions (HMIs) in the plants were enriched on the HMIE-FP, and LIBS was used to detect Cd(Ⅱ) and Pb(Ⅱ) on the HMIE-FP to determine the Cd(Ⅱ) and Pb(Ⅱ) concentration within the plant. COMSOL simulations were employed to analyse the flow dynamics of plant sap within the PBSED. To increase the heavy metal enrichment amount, the HMIE-FP was modified with AuAg bimetallic nanoparticles (AuAgBNPs). The PBSED–LIBS method was applied to detect Cd(Ⅱ) and Pb(Ⅱ) in cucumber plants, and the results were strongly correlated with the inductively coupled plasma mass spectrometry (ICP–MS) results (R² = 0.99 for Cd(Ⅱ) and 0.96 for Pb(Ⅱ)). The proposed PBSED–LIBS method demonstrated high sensitivity and minimal invasiveness; thus, it is suitable for rapid, in vivo detection of HMIs in plants. These findings provide valuable insights for the development of efficient, nondestructive tools for environmental applications.