Enabling the high sensitivity of silver nanoparticles: A ligand-exchange and diblock copolymer templating strategy for high-performance LSPR fiber-optic biosensors

Localized surface plasmon resonance (LSPR) fiber-optic sensors based on silver nanoparticles (AgNPs) offer great potential for label-free biosensing due to their high sensitivity and real-time detection capabilities. However, their application is hindered by susceptibility to oxidation and poor self-assembly caused by surface ligands. In this work, a high-performance LSPR fiber-optic biosensor was constructed based on PS-b-P4VP diblock copolymer (BCP) templated self-assembly combined with a competitive ligand exchange strategy. Compact citrate ligands were used to completely replace bulky tannate ligands on the AgNP surface, which significantly optimized the self-assembled morphology and sensing performance. The effects of self-assembly time, BCP concentration, solution pH and AgNP diameter on the plasmonic sensing performance were systematically investigated and optimized. Finite element simulation was carried out to reveal the regulatory mechanism of interparticle plasmon coupling and near-field enhancement for sensing sensitivity. Under the optimal conditions, the sensor achieved a high refractive index sensitivity of 590   nm/RIU and a nanoparticle surface coverage of 18.3%. The sensor also showed favorable storage stability in aqueous solution. For the label-free detection of human IgG, the sensor presented a linear response in the range of 0–10   μg/mL with a low detection limit of 0.1   μg/mL. This work provides an effective and universal strategy for the fabrication of high-stability and high-sensitivity AgNP-based LSPR fiber sensors, and promotes their application in the field of rapid biochemical detection.