Ultrasensitive and light erasable surface-enhanced Raman scattering substrates based on Au-MoO₂ heterostructures

Metal nanostructures are commonly utilized as surface-enhanced Raman scattering (SERS) substrates due to their strong localized surface plasmon resonance (LSPR) effects. However, these substrates are typically single-use because the analytes tend to remain on them. Molybdenum dioxide (MoO₂), a metalloid oxide with excellent photothermal properties, allows for removal of residues through photothermolysis. Nevertheless, its inherent SERS performance is relatively limited, with a detection threshold around 10^-7 M, approximately two orders of magnitude less sensitive than metal-based substrates. Here, we harnessed the synergistic interaction between Au and MoO₂ to develop reusable and highly sensitive SERS substrates. Au nanoparticles (NPs) were selectively deposited onto MoO₂ through a light-induced reduction method. The resulting Au-MoO₂ heterostructures exhibit an excellent electric field at interstitial sites due to LSPR coupling and present remarkable SERS sensitivity towards rhodamine 6G (R6G), methyl blue (MB), rhodamine B (RhB), and crystal violet (CV). The limit of detection can be improved down to 10^-9 M, achieving a maximum enhancement factor of 4.9 × 10⁶. Additionally, when exposed to an 808 nm laser beam, the surface temperature of the Au-MoO₂ nanocomposites can reach up to 529 °C, exceeding the decomposition temperatures of most organic compounds. Therefore, the residues can be entirely eliminated from the substrate under irradiation within 12 min, without sacrificing the SERS reproducibility and sensitivity. We expect our work to provide beneficial insights into the construction of ultrasensitive and recyclable SERS substrates.