Plasmon-Induced Charge Transfer-Enhanced Raman Scattering on a Semiconductor: Toward Amplification-Free Quantification of SARS-CoV-2

Semiconductors demonstrate great potentials as chemical mechanism-based surface-enhanced Raman scattering (SERS) substrates in determination of biological species in complex living systems with high selectivity. However, low sensitivity is the bottleneck for their practical applications, compared with that of noble metal-based Raman enhancement ascribed to electromagnetic mechanism. Herein, a novel Cu₂O nanoarray with free carrier density of 1.78×10²¹ cm⁻³ comparable to that of noble metals was self-assembled, creating a record in enhancement factor (EF) of 3.19×10¹⁰ among semiconductor substrates. The significant EF was mainly attributed to plasmon-induced hot electron transfer (PIHET) in semiconductor which was never reported before. This Cu₂O nanoarray was subsequently developed as a highly sensitive and selective SERS chip for non-enzyme and amplification-free SARS-CoV-2 RNA quantification with a detection limit down to 60 copies/mL within 5 min. This unique Cu₂O nanoarray demonstrated the significant Raman enhancement through PIHET process, enabling rapid and sensitive point-of-care testing of emerging virus variants.