Sensitivity enhancement of localized SPR sensor towards Pb(II) ion detection using natural bio-polymer based carrageenan

This work demonstrates the employment of a natural biopolymer-based kappa-carrageenan (κCarr) and chitosan (CS) for Pb(II) ion detection using LSPR sensor. κCarr and CS are utilized as active layers on top of gold nanoparticle (AuNP) in LSPR sensor. The characterization of these materials is carried out using Fourier transform infrared spectroscopy (FTIR), atomic force microscopy (AFM), field emission scanning electron microscopy (FESEM) and X-ray diffractions (XRD) analysis. FTIR analysis exhibits that, κCarr has OS = O, OH and C-O functional groups, meanwhile CS has OH, NH and C-O functional groups. This shows that κCarr possesses more oxygen atom in its structure. AFM measurement further proves this result whereas a high surface roughness is observed for AuNP-κCarr compared to AuNP-CS due to the plenty of oxygen atoms on the surface of AuNP-κCarr, therefore AuNP-κCarr is able to provide more active sites for adsorption of Pb(II) ion. In LSPR sensing, the shift in reflectance for κCarr exhibits a linearity response of R2 = 0.9722 and a sensitivity of 1.3535 nm ppm−1, meanwhile CS exhibits a linearity response of R2 = 0.6086 and a sensitivity of 0.8165 nm ppm-1 upon exposure to Pb(II) ion. Based on these results, κCarr shows a better linearity response and a higher sensitivity in comparison to CS when it is exposed to Pb(II) ion, hence proves that κCarr is the best sensing material in this study.