Analytical performance characteristics of Micro-structured surfaces for laser-induced breakdown spectroscopic analysis of liquids

We have previously shown the design and fabrication studies of 3-D micro-structured surfaces, to be used as a sample loading substrate for liquids analysis via dried-droplet LIBS methodology. Among the three designs, the substrate structured with 20-μm diameter cylinders, CYL-20, has shown the highest signal enhancement for the elements, Cu, Cr, and Pb, compared to 5-μm diameter cylinders, CYL-5, and 5-μm side-length triangular prisms, TAP-5, surfaces. Here, in this study, the analytical performance characteristics (LOD, accuracy, and precision) of these micro-structured Si-wafer surfaces are presented in comparison with unstructured surfaces. The dried-droplet residue of aqueous heavy metal solutions of Pb, Cr, and Cu were analyzed at their respective emission wavelengths under optimized experimental conditions. The results obtained from CYL-20 structured surfaces in comparison to 300 nm thin-film coated surfaces indicate up to 17, 11, and 7-fold increases in LIBS signal strength for Cu, Cr, and Pb, respectively. The experiments were performed using single and multi-element standards, and certified reference water samples. Sub-picogram absolute detection limits, 0.8 pg Pb, 0.5 pg Cu, and 0.45 pg Cr were obtained from the analysis of 500 nanoliters standard solutions, via dried-droplet methodology. Results with 70–75% accuracy and 95% precision were obtained from the repeated measurements. Though the results are promising, more extensive fabrication and application studies are required to find optimum structures of different sizes and shapes.