Adsorption independent silver colloids index measurement with metal-cladding optical waveguide

The refractive index measurements of silver nanoparticles colloids can provide chemical composition and nanostructure details. Although the standard surface plasmon resonance (SPR) approach improves index measurement precision, it is restricted by silver nanoparticles adsorption and incapable of detecting the colloid index due to the evanescent nature of the surface wave. Herein, a method utilizing metal-cladding optical waveguide (MCOW) was proposed to measure the volume refractive index of silver nanoparticles colloids, importantly, which is independent of particle adsorption. The experimental results show that the sensitivity of the refractive index measurement using the MCOW approach is at least 10−6 RIU (Refractive Index Unit) owing to the oscillating ultrahigh-order modes, this work not only presents a high-sensitivity, high-yield, simple-to-process, and effective refractive index measuring technique, but also recommends a more practical and adaptable colloidal particle characterization approach.