Chemisorbed gold Nanorods on optical fibers for refractive index sensing

The applicability of gold nanoparticles with optical fibers has emerged as a promising approach for developing compact and sensitive biosensors. Among these nanostructures, gold nanorods (AuNRs) offer distinct advantages due to their localized surface plasmon resonance properties. While previous studies have demonstrated immobilization of AuNRs on optical fibers for sensing applications, challenges remain in achieving stable, consistent, and aggregation-free attachment of AuNRs. In this work, we present a systematic study to synthesize, functionalize, and chemisorb AuNRs onto amine-functionalized U-bent optical fibers.

To address the issue of particle aggregation and inconsistent attachment, we performed an extensive study on the effect of varying concentrations of EDC/NHS coupling agents. The optimized conditions significantly improved chemisorption consistency and minimized aggregation. The plasmonic behaviour of the immobilized AuNRs was characterized under varying refractive indices. The transverse surface plasmon resonance (TSPR) exhibited a bulk refractive index sensitivity of 7 ∆Abs/RIU. The measurement was performed at a particle concentration of 0.2 OD. In contrast, the longitudinal surface plasmon resonance (LSPR) peak position showed sensitivity to the microenvironment, demonstrated a consistent shift with increasing concentrations of Polymyxin B, reaching a maximum shift of 1.4 % at 20 μM. These results bridge the gap between AuNRs functionalization and reliable sensor chemisorption and highlight the potential of this platform for biosensing applications in medical diagnostics and environmental monitoring.