Formula omitted]-Carrageenan-capped core–shell gold@silver nanoparticles: Optical device for hydrogen peroxide detection

Abstract

Metallic nanoparticles have outstanding properties that can be used to design optical detection devices, such as their high surface area and localized surface plasmon resonance (LSPR) effect. Despite these properties, metallic nanoparticles have low stabilities against aggregation and silver nanoparticles are quickly oxidized even in aqueous suspensions. To overcome these disadvantages, this study reports a new κ-carrageenan-stabilized core–shell gold@silver nanoparticles (κ-CAR-Au@AgNPs) composite. The κ-carrageenan (κ-CAR) was used as a reducing and stabilizing agent toward Au(III)/Ag(I) and Au0/Ag0, respectively. A pre-synthesized κ-CAR-capped gold nanoparticle (κ-CAR-AuNPs) suspension was mixed with Ag(I) ions and ascorbic acid to produce the κ-CAR-Au@AgNPs composite. The as-synthetized composite had an average hydrodynamic radius of 122 nm and a Zeta potential of −24 mV. The composite suspension had an LSPR band with high intensity after 15 days of storage. The κ-CAR stabilized the nanoparticles against aggregation and environmental oxidation. The physiochemical properties of κ-CAR-Au@AgNPs were compared to the properties of κ-CAR-capped silver nanoparticles (κ-CAR-AgNPs). The core–shell nanoparticle LSPR intensity was higher (10-fold) than that of the monometallic sample. Therefore, its optical response is improved for sensing applications. Thus, core–shell nanoparticles were used to detect hydrogen peroxide (H2O2). The H2O2 can almost completely oxidize the Ag shell of the Au@AgNPs after 4 h, altering the optical absorption intensity of the nanoparticles. Therefore, the κ-CAR-Au@AgNPs LSPR intensity can be used as an optical signal to assess H2O2 concentration in aqueous solutions.