Polyelectrolyte-Enhanced Localized Surface Plasmon Resonance Optical Fiber Sensors: Properties Interrogation and Bioapplication

Localized surface plasmon resonance (LSPR) and lossy mode resonance (LMR) are excited simultaneously by the gold nanoparticle (AuNP) arrays and the top-coated polyelectrolyte layer on optical fibers. The well-dispersed and dense AuNP arrays ordered by the diblock copolymer-template have LSPR sensing characteristics, whereas the layer-by-layer coated polyelectrolyte film carries LMR-based sensitivity enhancement. Both the experimental and simulation results illustrated that the thickness of the polyelectrolyte layer is the key factor affecting the optical properties of the proposed polyelectrolyte-enhanced LSPR sensor, and the sensor with a thicker polyelectrolyte layer presents a higher refractive index (RI) sensitivity because the lossy mode of the polyelectrolyte layer enhances the plasmonic resonance of AuNP arrays. The optimal sensor, which self-assembles with 50 nm AuNPs and 20 PAH/PSS bilayers, shows higher sensitivity and stability, with an RI sensitivity of 1312 nm/RIU and a detection limit for human IgG of 32.1 μg/mL. In addition, we observed an abnormally enhanced peak with an invariable wavelength, which has great potential to eliminate interference as a self-reference signal.