Abstract
Cerium oxide (ceria) nanoparticles (NPs) have been proved to be an efficient optical fluorescent material through generating visible emission (~530 nm) under violet excitation. This feature allowed ceria NPs to be used as an optical sensor via the fluorescence quenching Technique. In this paper, the impact of in-situ embedded gold nanoparticles (Au NPs) inside ceria nanoparticles was studied. Then, gold–ceria NPs were used for sensing dissolved oxygen (DO) in aqueous media. It was observed that both fluorescence intensity and lifetime were changed due to increased concentration of DO. Added gold was found to enhance the sensitivity of ceria to DO quencher detection. This enhancement was due to optical coupling between the fluorescence emission spectrum of ceria with the surface plasmonic resonance of gold nanoparticles. In addition, gold caused the decrease of ceria nanoparticles’ bandgap, which indicates the formation of more oxygen vacancies inside the non-stoichiometric crystalline structure of ceria. The Stern–Volmer constant, which indicates the sensitivity of optical sensing material, of ceria–gold NPs with added DO was found to be 893.7 M−1, compared to 184.6 M−1 to in case of ceria nanoparticles only, which indicates a superior optical sensitivity to DO compared to other optical sensing materials used in the literature to detect DO. Moreover, the fluorescence lifetime was found to be changed according to the variation of added DO concentration. The optically-sensitivity-enhanced ceria nanoparticles due to embedded gold nanoparticles can be a promising sensing host for dissolved oxygen in a wide variety of applications including biomedicine and water quality monitoring.
Highlights
Fluorescence quenching mechanisms are widely used for optical sensing, depending on fluorescent nanostructures
There is still a need to raise the optical sensitivity of ceria nanoparticles to quench some elements such as dissolved oxygen, which is important for water quality monitoring, fishery, and biomedical applications [13,14,15,16]
Gold-ceria nanoparticles were used as an optical sensing material for dissolved oxygen (DO)
Summary
Fluorescence quenching mechanisms are widely used for optical sensing, depending on fluorescent nanostructures. The formed tri-valent cerium ions are associated with the formation of oxygen vacancies which can adsorb some quenchers such as dissolved oxygen (DO) and radicals [10,11]. This adsorption can lead to fluorescence intensity quenching the visible emission of ceria nanoparticles. Plasmonic nanostructures, such as gold nanoparticles (Au NPs), can enhance the emission intensity of fluorescence nanostructures. There are previous research studies that used ceria nanoparticles or lanthanide-doped-ceria nanoparticles as optical nanosensors for dissolved oxygen [11], but the addition of plasmonic nanostructures within ceria is still lacking
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