A study of the stability and repeatability of U-shaped plastic optical fibers functionalized with gold nanoparticles for refractive index measurement

The development of sensors based on the concept of Localized Surface Plasmon Resonance (LSPR) has increased significantly in the last years. This study is focused on the stability and repeatability of an optical sensor based on U-shaped plastic optical fibers (POF) functionalized with gold nanoparticles (AuNP) to measure the refractive index (RI). The AuNP were produced by two methodologies and were characterized by transmission electron microscopy (TEM) and ultraviolet–visible spectroscopy (UV–Vis). The repeatability and stability of the sensors were evaluated using air and ultrapure water as media to measure absorbance. The results showed a maximum absorption peak of AuNP from 517.49 nm to 520.34 nm. The TEM showed an AuNP average diameter from 10.9 ± 1.5 to 31.7 ± 5.2. The UV–Vis showed constant results for the U-shaped POFs functionalized with AuNP in both media, and ultrapure water was considered the best medium for measurement. The homogenous AuNP showed better results than the heterogenous AuNP for binding to the U-shaped POF surface in terms of repeatability and stability. The best sensor presented the R2 of 0.9871 and 4.3541 of sensitivity. The results qualify the U-shaped POF functionalized with AuNP to become a sensor.