SPR sensor for detection of heavy metal ions: Manipulating the EM waves polarization modes

Abstract

Water contamination by heavy metals is a common issue encountered in many countries due to industrial and urban wastes in water resources which give health and socio-economic impacts. This work is carried out to investigate the effect of EM wave polarization modes on the sensing properties of surface plasmon resonance (SPR) sensor in detecting heavy metal ions namely mercury (Hg) and plumbum (Pb). Three types of polarization modes such as p-polarized, s-polarized and circular-polarized light were introduced. Gold and silver thin films with thicknesses of 50nm were deposited on top of SPR layer system to excite surface plasmon polaritons (SPPs). The SPR curves were analyzed by studying the FWHM, Q-factor and angle shifting characteristics. We manage to prove theoretically that the SPR phenomena able to be created by using not only the p-polarized light, yet by employing a circular-polarized light. The sensor shows positive respond for both polarization modes, where the troughs were red-shifted about 23.78% as Pb was introduced on the top of the gold-coated SPR sensor. The SPR angles were shifted about 24.45% as the sensor was exposed with Hg metal ions. Different response due to the presence of different analytes exhibits an excellent criteria of high selectivity sensor. In conclusion, the combination of p-polarized light or circular-polarized light and gold thin film able to accentuate the significant role of SPR sensor in detecting heavy metal ions.