Enhancing the sensitivity of a surface plasmon resonance-based optical sensor for zinc ion detection by the modification of a gold thin film

Abstract

Surface plasmon resonance (SPR) sensors as novel optical sensors for the detection of a variety of analytes have been receiving increasing attention and their sensitivity has become the research hotspot recently. In this study, the sensitivity of an SPR optical sensor was enhanced by modifying a gold thin film with a nanocrystalline cellulose (NCC)-based material for zinc ion (Zn²⁺) detection that exists in the environment due to industrial processing. By replacing the gold thin film with a novel modified-gold thin film, Zn²⁺ can be detected from the range of 0 to 10 ppm using SPR. It is believed that the Zn²⁺ may interact with the negative charge molecules that exist on the modified-gold thin film, and this was confirmed via X-ray photoelectron spectroscopy (XPS). Moreover, this modified-gold-SPR has a high sensitivity of 1.892° ppm⁻¹ up to 0.1 ppm with an enhanced detection of Zn²⁺ as low as 0.01 ppm. The SPR results also followed the Langmuir isotherm model with a binding affinity of 1.927 × 10³ M⁻¹, which further confirmed the sensitivity of the SPR sensor. In addition, using the modified-gold thin film, SPR has a higher affinity towards Zn²⁺ compared to other metal ions, i.e. Ni²⁺, Fe²⁺, Cr²⁺, Mn²⁺, and Co²⁺.