Development of Aluminum-deposited Sapphire-rod SPR Sensor with Wide Refractive Index Range

Abstract

A miniaturized Surface Plasmon Resonance (SPR) sensing system that uses an aluminum-deposited sapphire rod with a diameter of 2 mm was developed. The response characteristics of various wavelengths of LED as a light source and aluminum thicknesses on the sapphire rod were examined. In addition, sensor responses were simulated using multilayer Fresnel equations and compared with those of experimental results. When the sapphire rod was used as a light-transmitting medium in the SPR phenomenon, it responded to a very wide range of refractive indices. The sensor exhibited optimal performance at an LED wavelength of 402 nm and an aluminum thickness of 30 nm. These results agreed well with theoretical calculations. Furthermore, shading the top of the LED to eliminate irrelevant light increased the SPR response by more than sixfold. This shielding also improved the sensitivity at lower refractive indices compared to the unshielded sensor. Thus, it was confirmed that this sensor is a refractive index sensor that can respond to a wide range of refractive indices. This study provides insights into versatile, and compact SPR sensors that respond to a wide range of refractive indices in samples.