Ultrasensitive Sensing of Volatile Organic Compounds Using a Cu-Doped SnO₂-NiO p-n Heterostructure That Shows Significant Raman Enhancement**

Surface enhanced Raman scattering (SERS) based on chemical mechanism (CM) attracts tremendous attention for great selectivity and stability. However, low enhancement factor (EF) limits its practical applications for trace detection. Here, a novel sponge-like Cu-doping SnO₂-NiO p-n semiconductor heterostructure (SnO₂-NiO_x/Cu), was first created as a CM-based SERS substrate with a significant EF of 1.46×10¹⁰. This remarkable EF was mainly attributed to the enhanced charge-separation efficacy of p-n heterojunction and charge transfer resonance resulted from Cu doping. Moreover, the porous structure enriched the probe molecules, resulting in further SERS signals magnification. By immobilizing CuPc as an inner-reference element, SnO₂-NiO_x/Cu was developed as a SERS nose for selective recognition of multiple lung cancer related VOCs down to ppb level. The information of VOCs was recorded in a barcode, demonstrating practical potential of a desktop SERS device for biomarker screening.