High-sensitivity determination of heavy metal elements in water with circular grooves and nanoparticle-enhanced LIBS

The highly sensitive detection of heavy metal elements in aqueous solution has been achieved by the combination of circular grooves and nanoparticle-enhanced laser-induced breakdown spectroscopy. The effects of Ag nanoparticles (Ag NPs) and circular grooves on the spectral emission of Cu, Pb and Cr have been investigated. The results show that both Ag NPs and circular grooves can enhance the spectral emission of heavy metal elements, and the circular grooves can improve the spectral reproducibility. The prepared micro/nanostructures can suppress the coffee ring effect and improve the absorption efficiency of light. The average relative standard deviation of the spectral emission can be diminished. By establishing calibration curves for Cu, Pb, and Cr elements, the limits of detection (LODs) for Cu, Pb and Cr elements have been obtained. The results show that by employing Ag NPs and circular grooves the lowest LOD of 0.10 μg mL⁻¹ can be achieved. This improved spectral performance (spectral intensity, stability and detection sensitivity) originates mainly from the collective oscillation of free electrons of Ag NPs excited by the incident laser pulse, which confines the electromagnetic energy with a strongly enhanced electric field. The enhancement in electric field intensity of Ag NPs is calculated and the seed electron is proved to be predominantly excited through a multiphoton photoemission process under the experimental conditions. The results provide an efficient pathway for improving the detection sensitivity of heavy metals in aqueous solution.