Soft and wrap-like nanofibers@plasmonic SERS sensors for high-fidelity visualized Raman imaging of micro-curved targets

As for surface-enhanced Raman scattering spectroscopy (SERS), a challenge is how to achieve conformally attachable substrates that can get close enough to micro-curved samples, promoting Raman imaging of specific targets. Herein, we propose a simple yet efficient approach to produce soft and wrap-like SERS sensors by anisotropic in-site overgrowth of 2D plasmonic Ag nanosheets (NSs) on 1D bacterial nanocelluloses (BNCs). The optimal BNCs@Ag NSs with exhibit broadband and high SERS activities under broadened laser wavelengths, facilitating the limit of detection (LOD) at ~10^-15 M femtomole level. Besides, the excellent spatial SERS uniformity with relative standard deviation (RSD) < 5.1% throughout whole platform is also confirmed here. By virtue of the fibrous scaffolds, the free-standing flexible BNCs@Ag NSs films at dry state can be very easily softened into adhesive membranes after appropriately wetting process. It endows BNCs@Ag NSs with conformal adaptability and distinctive adhesive fixation on microscopic curvilinear surfaces of arbitrary-shaped targets, enabling them to fully wrap and intimately capture 3D polystyrene (PS) microspheres. Notably, the smart SERS sensors are capable of high-fidelity Raman imaging of individual or multiple-isolated PS microspheres, demonstrating robust and precise SERS visualization of micro-curved samples. So, the exceptional double-merits are then highlighted: 1) affording a complementary feature to the field of routine flexible SERS substrates that are impossible or difficult to conformally contact or firmly integrate with micro-warped targets; 2) compensating the inherent deficiency of colloidal nanoparticles used in quantitative SERS visualization that suffer from the ubiquitous aggregation-induced poor spatial SERS uniformity on complex curvy objects.