Optimization of gold-nanoparticle-based optical fibre surface plasmon resonance (SPR)-based sensors

This paper discusses a systematic optimization process for the fabrication of better surface plasmon resonance (SPR)-based optical fibre sensors in order to enhance their performance when used for refractive index measurement. A set of key optimization parameters has been investigated, including the size of the gold-nanoparticles (AuNPs), the pH of the gold-nanoparticle solutions prior to the coating, the coating time of the gold-nanoparticles on the fibre substrate and the coating temperature used. A series of tests undertaken has confirmed that the increase of the gold nanoparticles size (within the limits of the experiment carried out) makes the device more sensitive. The variation of the pH of the gold solutions within the range investigated appears not significantly to affect the sensitivities of the devices created. Under the circumstances considered, the longer coating time results in a higher surface density which therefore allows a stronger SPR effect, creating a higher level of sensitivity of the device. In addition, the coating temperature has been investigated in this paper for 60 nm AuNP solutions and it has been concluded that the sensor fabricated at a temperature of 25 °C has demonstrated a better performance compared to others, evaluated when the surrounding refractive index of the sensors was varied over the range from 1.333 to 1.424.