Optimised surface modification strategy for TNF-α detection using localised surface plasmon resonance

• Optical fibre LSPR sensor optimised by comparing AuNP deposition times. • Maximum sensitivity (257 nm/RIU) and strong linearity (R 2 = 0.99) achieved with 1-hour AuNP immersion. • Sensor demonstrated excellent reproducibility, repeatability, and stability. • Findings support the rational design of low-cost fibre-tip biosensors for detection of TNF-α with LoD of 5.86 pg/mL. This research explores the development and refinement of a localised surface plasmon resonance (LSPR) biosensor using gold nanoparticles (AuNPs) for enhanced biomarker detection. The study aims to address the challenge of cost-effective fabrication while achieving high sensitivity, with a focus on optimising the AuNP deposition process on an optical fibre’s end face. The biosensor was constructed using a silane-based method, particularly aminosilanisation, allowing AuNPs to attach to the fibre’s tip surface. Different deposition times were tested, ranging from 1 to 6 h, to determine their impact on the sensor’s sensitivity to refractive index changes. The findings revealed that the 1-hour deposition time yielded the optimal balance of sensitivity (257.05 nm/RIU) and linearity (R2 = 0.9917). In contrast, longer deposition times led to reduced effectiveness due to excessive binding of AuNPs and reduced spatial separation between them. The sensor demonstrated excellent reproducibility, repeatability and stability. Beyond refractive index sensing, we further functionalised the sensor and successfully demonstrated its ability to detect tumour necrosis factor-alpha (TNF-α), a key inflammatory biomarker, with a clinically relevant limit of detection (LoD) of 5.86 pg/ml. This optimised LSPR biosensor platform demonstrates strong potential for future development towards cytokine detection in clinical settings.