Heterojunction-Enhanced Interfacial Evanescent-Tunable Fiber Optic Probe for Amplification-free CRISPR/Cas12a-Based Rapid and Ultrasensitive Detection of MPXV.

Conventional polymerase chain reaction (PCR)-based detection methods suffer from time-consuming procedures, reliance on specialized equipment, and difficulty in achieving early viral diagnosis. In this study, interferometric fiber-optic sensing is integrated with the CRISPR/Cas12a system for the first time. With sensitivity further enhanced by immobilizing ZnO@Au on the fiber surface, the platform enables rapid, amplification-free detection of monkeypox virus (MPXV) at the single-molecule level. Whispering-gallery modes (WGMs) excited in the fiber probe provide high sensitivity to ambient refractive-index changes, while the ZnO@Au layer induces localized surface plasmon resonance (LSPR) and coupled plasmon-waveguide resonance (CPWR) on the fiber surface. By controlling the AuNPs occupancy on ZnO, the LSPR and CPWR absorption peaks can be tuned to match the demodulation spectral band. Moreover, the ZnO-Au heterojunction further strengthens the LSPR, thereby improving the sensitivity of the fiber probe. The resulting sensing probe achieves amplification-free detection of plasmid targets from both MPXV subtypes down to 10° copies/μL, with the entire assay completed within 9 min. The detection capability was validated using real clinical MPXV samples, showing complete agreement with qPCR results. The strategy proposed in this work offers a feasible approach for early and rapid viral detection.