J. Song, W. Cheng, M. Nie, W. Nam, X. He, J. Cheng, W Zhou
Keywords: surface-enhanced Raman scattering, Hierarchical plasmonic micro/nanostructures, Leidenfrost evaporation
Summary:By concentrating and localizing analyte molecules within a small footprint on a hydrophobic surface, surface-enhanced Raman spectroscopy (SERS) sensing can achieve high-resolution detection of analytes in highly diluted solutions. However, the majority of the current SERS substrates heavily relies on various chemical coatings on the platform surfaces, which can deteriorate the SERS enhancement factor (EF) as the coating materials may block hot spots. With nanolaminated plasmonic nanostructures patterned on a hierarchical micro/nanostructured surface, i.e., carbon nanotubes (CNTs) decorated on Si micropillar arrays, we report a new type of high-performance SERS substrate, which demonstrates SERS enhancement factor as high as 1.8 x 10^7. By utilizing a heating-assisted evaporation approach, we can extremely localize Rhodamine 6G (R6G) molecules contained in a water droplet within a significantly reduced footprint of 450 micrometer^2, which is over three orders of magnitude lower than that of 3 mm^2 without heating assistance. For a solution with an initial R6G concentration as low as 10^-9 M, we can remarkably increase the density of Rhodamine 6G molecules on the hot spots of the SERS surface after carefully controlling solution evaporation, and those condensed molecules lead to practical detection time of 0.1 s and a low excitation power of 1.3 mW.