Integrated Experimental–Numerical PCF-LSPR Sensor for Dopamine Monitoring

Precise and real-time detection of dopamine (DA) is essential for biomedical diagnostics and for understanding its role in neurological and metabolic disorders. This study presents a high-performance photonic crystal fiber-based localized surface plasmon resonance (PCF-LSPR) biosensor for refractive index-based dopamine sensing, integrating experimentally measured refractive index data with detailed numerical simulations. The proposed sensor employs a D-shaped photonic crystal fiber geometry to enhance the interaction between the guided core mode and localized surface plasmons supported by gold (Au), silver (Ag), and bimetallic Au-Ag nanoparticles. The refractive index of dopamine solutions was experimentally measured over the concentration range of 25-150 mM using an Abbe refractometer and directly incorporated into the numerical model to ensure realistic and application-oriented performance evaluation. Finite element method (FEM) simulations were carried out to analyze the coupling between the fundamental core-guided mode and the surface plasmon polariton mode through confinement loss spectra. The results show that all three plasmonic configurations achieve a high wavelength sensitivity of 5000 nm/RIU with excellent linearity (R2= 1) and a resolution of 2 × 10-6RIU. While the wavelength sensitivity and resolution are identical, variations in full width at half maximum (FWHM), figure of merit (FOM), and amplitude sensitivity reveal the influence of plasmonic material selection. Silver nanoparticles exhibit the narrowest resonance peaks and highest FOM, whereas the bimetallic Au-Ag configuration provides an optimal balance between sensitivity, resonance stability, and chemical robustness. All configurations demonstrate a low limit of detection of 4 × 10-10RIU2/nm. These findings highlight the strong potential of the proposed PCF-LSPR biosensor for real-time dopamine monitoring in biomedical and neurochemical applications.