Zinc analysis in human skin by laser induced-breakdown spectroscopy

The feasibility of using laser induced-breakdown spectroscopy (LIBS) as a quick and simple method to analyze trace elemental concentrations in the stratum corneum of human skin was investigated. A 60 mJ pulse−1 Nd:YAG laser operating at 1064 nm was used to form the laser induced plasma. Zinc was chosen for this study. By using poly-(methyl methacrylate) (PMMA) solution to coat the slides, zinc standard solutions were dispersed on the slides with the help of a centrifuge. The percent of R.S.D. of the dispersed area size obtained from 17 measurements was 6%. The precision from intra-measurements (precision on one slide) and inter-measurements (precision between slides) was 4–8% and less than 1%, respectively. A calibration curve with a linear correlation coefficient of 0.998 and a detection limit of 0.3 ng cm−2 were obtained. An aqueous zinc solution or zinc ointment was deposited on the biceps area of the forearms of several volunteers for a time period of 30 min and 2.75 h. Six skin layers of 2–3 μm each in thickness were then removed using cyanoacrylate glue without causing any pain for the volunteers. The results indicated that Zn was absorbed through the skin and the concentration decreased exponentially with depth into the skin. The results indicate that LIBS is a useful tool for trace elemental analysis in human skin.