Ultra‐Sensitive Reconfigurable SERS Platform Enabled by Tunable Plasmonic Nanogaps

Plasmonic nanogaps that generate intense electromagnetic hot spots are crucial for surface‐enhanced Raman scattering (SERS) sensing, particularly at the single‐molecule level. However, plasmonic nanogaps in conventional SERS platforms are usually fixed, posing significant challenges for precise and ultra‐sensitive molecular detection. Here, we propose a stretchable SERS platform, on which plasmonic nanogaps can be modulated stepwise, to sequentially control the trapping and deposition of target molecules, which are subsequently detected by significantly enhanced Raman signals. Functionalized with monodisperse silver nanoparticles, the platform enables reversible and precise bidirectional tuning of plasmonic nanogaps from nearly 400 nm down to sub‐5 nm, endowing the SERS sensor with excellent sensitivity, robust reconfigurability, and broad detection versatility. SERS measurements on various small‐molecule analytes achieve the lowest detectable concentrations of 10 −14 m (rhodamine 6G, R6G), 10 −12 m (4‐Mercaptopyridine, 4‐MPY), and 10 −5 m (urea and sodium lactate). The dual‐analyte measurement confirms the single‐molecule SERS detection capability. Meanwhile, large biomolecules (hemoglobin, Hb) detection down to a limit of 10 pg/mL further validates the reliability and universality of the developed SERS sensor. Our scheme paves the road for ultrasensitive detection of arbitrary molecules with robust reconfigurability.