Analytical Performance Characteristics of Micro-Structured Surfaces for Laser-Induced Breakdown Spectroscopic Analysis of Liquids

Abstract

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-mu m diameter cylinders, CYL-20, has shown the highest signal enhancement for the elements, Cu, Cr, and Pb, compared to 5-mu m diameter cylinders, CYL-5, and 5-mu m 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 drieddroplet 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.