Non-uniform droplet deposition on femtosecond laser patterned superhydrophobic/superhydrophilic SERS substrates for high-sensitive detection

Surface-enhanced Raman scattering (SERS) sensors combined with superhydrophobic/superhydrophilic (SH/SHL) surfaces have shown the ability to detect ultra-low concentrations. In this study, femtosecond laser fabricated hybrid SH/SHL surfaces with designed patterns are successfully applied to improve the SERS performances. The shape of SHL patterns can be regulated to determine the droplet evaporation process and deposition characteristics. The experimental results show that the uneven droplet evaporation along the edges of non-circular SHL patterns facilitates the enrichment of analyte molecules, thereby enhancing the SERS performance. The highly identifiable corners of SHL patterns are beneficial for capturing the enrichment area during Raman tests. The optimized 3-pointed star SH/SHL SERS substrate shows a detection limit concentration as low as 10-15 M by using only 5 & mu;L R6G solutions, corresponding to an enhancement factor of 9.73 x 1011. Meanwhile, a relative standard deviation of 8.20% can be achieved at a concentration of 10-7 M. The research results suggest that the SH/SHL surfaces with designed patterns could be a practical approach in ultratrace molecular detections.