Contractible Plasmonic Nanospheres Array with Dynamically Tailorable Gap Size for Molecule Trapping and Sensitive SERS Detection

Surface-enhanced Raman spectroscopy (SERS) is a powerful analysis technique, and the SERS sensitivity is strongly dependent on metallic nanogaps with a greatly enhanced local electromagnetic field (i.e., hot spots). Once the analytes are located in the hot spot region, their Raman signals are enormously amplified. However, delivering analytes into such tiny hot spots remains a great challenge, particularly for molecules with small Raman scattering cross-sections and no metal affinity. Here, by employing the isotropic contraction characteristics of polyvinyl chloride (PVC) when heated, a molecule trapping and SERS sensing strategy is demonstrated based on a large-area ordered gold-coated polystyrene nanospheres (PS@Au NSs) array with well-controlled gap size assembled on PVC sheet. Compared with the traditional contraction-adsorption mode, the developed adsorption-contraction mode enables efficient delivery of analytes with or without metal affinity into the hot spots between the PS@Au NSs, leading to a significantly improved SERS performance with a large SERS enhancement factor of approximate to 3.57 x 107. The contractible SERS substrate exhibits a high sensitivity of 10-12 m for rhodamine 6G (R6G), 10-10 m for thiram, and 5 x 10-6 m for 2,3,4-trichlorobiphenyl, as well as good signal reproducibility with relative standard deviations of 2.81% and 4.25% for R6G and thiram, respectively. An efficient strategy for precisely controlling the gap size between the orderly-arranged plasmonic nanospheres and actively delivering molecules with or without metal affinity into the hot spot region is developed, leading to a significant improvement in SERS performance. The strategy opens up numerous possibilities for the future development of SERS substrates, with the potential to push detection capability to its limit.image