Abstract
A novel nanostructure with silver nanoparticles assembled in silver nanoholes array was fabricated and developed as a novel metal ion sensor in this work. It has been demonstrated to fabricate nanoholes array by nanosphere lithography (NSL). Silver nanoparticles were synthesized by sodium citrate through the chemical reduction method, and then were surface modified by tiopronin. The tiopronin-modified silver nanoparticles were immobilized into the nanoholes array, so that the sensing substrate with novel nanostructure, nanoparticle-in-nanohole array, was fabricated and used as nickel (II) ion sensing. In addition, the sensitivity of the novel metal ion sensor was characterized under different media with varying refractive indices. The sensing substrate was composed of 2 components, the nanoholes array and the tiopronin-modified silver nanoparticles (Tio-Ag NPs). The nanohole array was fabricated on glass substrates with surface modification of polydiallyldimethylammonium chloride (PDDA), which is an ionic polymer with positive charge. The NSL was then utilized to arrange polystyrene (PS) mask on the substrates, and PS nanospheres were etched by O2 plasma treatment. Following above, silver was deposited by E-gun and the PS mask was lifted off by common tapes. The Tio-Ag NPs were synthesized through chemical reduction method and followed by the surface modification of tiopronin. Finally, the Tio-Ag NPs were then immobilized into the nanohole array to form a novel nanostructure, nanoparticle-in-nanohole array. The sensing substrates with nanoparticle-in-nanohole array were placed in nickel ion solution by increasing the concentration from 1 × 10-4 to 1 mM step by step and from 1 × 10-9 to 1 mM step by step, and then characterized by ultraviolet-visible spectroscopy (UV-Vis) at each step. The absorbance enhancement was observed as concentration elevation of nickel ion. The sensitivity was also identified as 21.23 nm/RIU through measuring the absorbance peak shift of the sensing substrates in the media with different refractive indices, such as air, water, ethanol, and isopropyl alcohol (IPA).