Shape-controlled Synthesis and Bulk Refractive Index Sensitivity Studies of Gold Nanoparticles for LSPR-based Sensing

The localized surface plasmon resonance (LSPR) is an optical phenomenon observed in noble metal nanoparticles such as gold, silver, copper, and platinum. In LSPR, the metal nanoparticles show strong electric field enhancement and extinction. The LSPR peaks of metal nanoparticles are sensitive to their size, shape and refractive index (RI) of the medium. Any changes in these parameters can be observed as the shift in the LSPR peaks of nanoparticles and used for sensing applications. Among different plasmonic metal nanoparticles, gold nanoparticles are the most suitable candidates for fabricating LSPR-based biosensors due to their exceptional long-term stability and biocompatibility. In this paper, we synthesized different shapes and sizes of gold nanoparticles, such as nanospheres, nanorods, nanostars, and nanoprisms, using simple chemical methods and compared their bulk refractive index sensitivities (RIS). The sensitivity of nanoparticles increases with the size of nanoparticles, and a maximum sensitivity in gold nanoprisms was observed. The comparison of bulk RIS of different sizes and shapes of gold nanoparticles helps in selecting the most suitable nanoparticle to achieve high sensitivity in LSPR-based sensing.