Analysis of trace gold in sub-microliter samples by surface-enhanced laser-induced breakdown spectroscopy using porous silicon with a single laser shot.

Surface-enhanced laser-induced breakdown spectroscopy (SELIBS) using porous silicon (Si) is an attractive technique for liquid analysis in terms of requiring only microvolume samples, simple pretreatment, and a low plasma generation threshold. These features make SELIBS particularly suitable for industrial process monitoring, such as wet metal recovery processes. In our previous studies, we have analyzed sample solutions with volumes of approximately 10 µL by accumulating multiple spectra measured over the spread area of the sample. Reducing the volume of sample solutions and enabling rapid analysis remain important challenges for practical applications. In this study, we demonstrate single-shot analysis of trace gold (Au) in sub-microliter solution samples by SELIBS using porous Si, representing a step toward practical use. The emission line of Au was successfully observed using only 0.5 µL of sample and a single laser shot with an energy of 2.0 mJ. A calibration curve for Au was built using the Au intensity normalized by the Si intensity in the Au concentration range of 0.5-5.0 ppm (mg/L). From this calibration curve, a coefficient of determination of 0.997 was obtained. The limit of detection was estimated to be 0.48 ppm based on the Au intensity. The relative errors of predicted Au concentrations in additionally analyzed samples using the Au/Si calibration curve were approximately 10%. The proposed method has a potential for in-situ monitoring of wet metal recovery processes.