Ultra-long-range hot electron tunneling: Plasmonic nanoengineering enhanced self-powered photoelectrochemical immunoassay

Constructing ultra-long-range nanogaps for enabling significant plasmonic tunneling phenomena represents a long-standing goal of the research on localized surface plasmon resonance effect. However, such electric field-enhanced tunneling effect is frequently limited by the gap size and band structure configurations between plasmonic nanoparticles and semiconductors. Here, we designed six distinct morphologies of gold nanoparticles and dual Z-scheme substrate with matchable tunneling barriers, which successfully achieved the ultrasensitive PEC immunoassay by utilizing bioconjugates as an ultra-long-range dielectric layer. First, Au stars demonstrated the optimal performances in both finite element method simulations and surface-enhanced Raman spectroscopy experiments among the six gold nanoparticles. Furthermore, the density functional theory calculations and experimental results revealed the dual Z-scheme heterojunction configuration (TiO₂@TpPa-2@CdS) as the most efficient substrate for facilitating ultra-long-range hot electron tunneling. The plasmonic tunneling enhanced immunoassay exhibited an ultrasensitive detection of carcinoembryonic antigen (CEA) with the limit of detection as low as 0.012 pg·mL⁻¹. These results provide compelling evidence for ultra-long-range tunneling effect in plasmonic systems, thereby enabling more potential applications in plasmonic technology.