Ultrasensitive enhanced Raman spectroscopy by hybrid surface-enhanced and interference-enhanced Raman scattering with metal-insulator-metal structures

High-sensitivity, reproducible, and low-cost substrate has been a major obstacle for practical sensing application of surface-enhancement Raman scattering (SERS). In this work, we report a type of simple SERS substrate which is composed of metal-insulator-metal (MIM) structure of Ag nanoisland (AgNI)-SiO₂-Ag film (AgF). The substrates are fabricated by only evaporation and sputtering processes, which are simple, fast and low-cost. By combining the hotspots and interference-enhanced effects in AgNIs and the plasmonic cavity (SiO₂) between AgNIs and AgF, the proposed SERS substrate shows an enhancement factor (EF) of 1.83 × 10⁸ with limit of detection (LOD) down to 10^-17 mol/L for rhodamine 6 G (R6G) molecules. The EFs are ∼18 times higher than that of conventional AgNIs without MIM structure. In addition, the MIM structure shows excellent reproducibility with relative standard deviation (RSD) less than 9%. The proposed SERS substrate is fabricated only with evaporation and sputtering technique and the conventionally used lithographic methods or chemical synthesis are not required. This work provides a simple way to fabricate ultrasensitive and reproducible SERS substrates which show great promise for developing various biochemical sensors with SERS.