Interfacial Sensitivity Enhancement in Optical Microfiber Functionalized With Gold Nanorods Through Tunable LSPR Coupling Strategy

The nanointerface-sensitized optical microfiber is shown with ultrahigh sensing sensitivity to the small variation of the external refractive index. By optimizing localized surface plasmon resonance (LSPR), we theoretically and experimentally investigated the extinction characteristics of three gold nanorods with different aspect ratios. A simple self-assembly method through electrostatic attraction was used to immobilize gold nanorods with different aspect ratios on optical microfiber. By tuning the LSPR to be consistent with operation wavelengths of the microfiber, the optimized nanointerface-sensitized optical microfiber shows the highest sensing sensitivity of 3146 nm/RIU, which is about 2-fold better than that of the silica optical microfiber, and about 3-fold and 4-fold better than that of the nanointerface-sensitized plastic-clad silica multimode optical fiber. For better understanding of the enhancement mechanism, a FDTD method was used to simulate the near-field mapping of the different nanointerfaces for comparison, and a first order perturbation theory was employed to detailed illustrate the interacting between the electric field overlap integral and the shift of the wavelength. Thus, this work can open up a significant way for developing the ultrasensitive optical microfiber sensing probe.