Position-sensitive photodetector for plasmonic detection in a random metasurface

In this work, we have developed a refractive index change sensing system utilizing localized surface plasmon resonance (LSPR) transduction, combined with a position-sensitive photodetector (PSPD). As the transducers, we utilized gold nano-islands formed through thermal annealing of an Au film with a nominal thickness of 13 nm. The LSPR was excited by evanescent wave in an attenuated total reflectance configuration. Refractive index changes result in modifications across the angular spectrum of LSPR, giving rise to variations in the differential signal detected between the two quadrants of the photodetector. We determined the refractive index resolution of our sensing system at different wavelengths and performed a comparative analysis with traditional surface plasmon resonance (SPR) transducers and available literature data. While LSPR transducers demonstrate a lower refractive index resolution (RIR) compared to SPR, the approach presented in this work stands out when compared to other LSPR sensing methods. Notably, at a wavelength of 785 nm, it achieves a remarkable RIR of 1.4 × 10−6 RIU.