MOF@Pt-AuPt plasmonic scaffold enables ultrasensitive fiber-optic SPR biosensing of GPNMB toward Parkinson's disease diagnosis.

Glycoprotein non-metastatic melanoma protein B (GPNMB), a biomarker of Parkinson's disease (PD), remains at trace levels in clinical samples, which poses a major obstacle for early diagnosis. Herein, a fiber-optic surface plasmon resonance (FO-SPR) sensor based on MOF@Pt-AuPt plasmonic scaffolds is developed for ultrasensitive detection of GPNMB. In-situ growth of Pt nanoparticles on two-dimensional porphyrinic Cu-TCPP MOF forms a Schottky barrier that narrows the optical band gap from 2.53 eV to 2.38 eV, promoting photogenerated charge separation. Subsequent electrostatic assembly of Au@Pt core-shell satellites generates dense localized surface plasmon resonance "hot spots" that strongly couple with the surface plasmon wave on the Au film, and finite-difference time-domain simulations confirm that the interfacial electric field intensity increases from 3.29 to 11.5 (arbitrary units, a.u.). The sensor exhibits excellent refractive index sensing performance, achieving a sensitivity of 3768.64 nm/RIU, which represents a 131.99% improvement over conventional Au-coated optical fibers. For GPNMB detection, the sensor achieves a limit of detection as low as 0.06 pg/mL, more than sevenfold enhancement. Moreover, the sensor is capable of unambiguously discriminating PD patients from healthy controls while exhibiting superior hydrophilicity, antifouling capability, and selectivity. This method provides a practical and versatile detection strategy for the early diagnosis of Parkinson's disease.