Analyte enrichment and sensitive detection over nanosecond laser textured stainless steel superhydrophobic surfaces

In this report, we have investigated the use of nanosecond laser texturing produced superhydrophobic surfaces for enrichment and sensitive detection of analytes. We have shown that by carefully choosing the laser processing parameters, the superhydrophobic surfaces capable of maintaining a small (5 mu L) aqueous droplet in spherical shape till the last stage of evaporation and hence enabling the droplet to deposit its entire content over similar to 80-100 mu m size residual spot upon complete evaporation, can be prepared. The spot was found to get formed by bridging over the micro structures suggesting that the droplet remained suspended over the structures i.e. did not penetrate the structures till the very end of the evaporation process. By performing fluorescence spectroscopy of the residual spot, Rhodamine 6G could be detected at an ultra-low concentration of 10-18 molL(-1) in a 5 mu L water droplet. When compared with the results obtained on unprocessed stainless steel substrate, these super-hydrophobic steel surfaces were found to provide four orders of magnitude enhancement in the lowest detectable concentration of Rhodamine 6G.