Femtosecond laser-induced surface nanostructures for enhanced trace metal element detection in water

As societal concern for environmental and public health issues intensifies, precisely monitoring harmful heavy metal concentrations in aquatic systems has become a critical scientific endeavor. Although laser-induced breakdown spectroscopy (LIBS) allows for the simultaneous detection of multiple elements, its sensitivity for tracing metal in water remains inadequate. This work investigates the enhancement of LIBS signals for chromium (Cr) and lead (Pb) detection of micro/nanostructures on aluminum surfaces, generated by femtosecond laser irradiation. These structures effectively reduce the coffee-ring effect, increasing plasma temperature and electron density. At a concentration of 100 µg/L, the spectral intensities of Cr and Pb increased by 378% and 307%, respectively. Consequently, this reduced the detection limits to 6.33 µg/L for Cr and 2.53 µg/L for Pb. Additionally, a partial least squares regression (PLSR) model was employed to quantitatively analyze the concentrations of Cr and Pb in water, achieving correlation coefficients (R²) of 0.997, 0.981 for Cr, and 0.995, 0.977 for Pb, in the training and prediction sets, respectively. This work demonstrates that integrating micro/nanostructures induced by femtosecond lasers on aluminum surfaces with the PLSR model substantially improves the detection sensitivity for trace amounts of Cr and Pb in water, offering new avenues for environmental monitoring and research.