A selective multi-emission chemiluminescence system using hollow Eu3+/Gd2O3@SiO2 spheres modified by naphthalene derived molecules for the quantification of Cr6+ ions

Abstract

We developed a multi-emission fluorescence sensor based on hybridizing two different fluorescent centers, which provides a built-in correction to remove environmental effects. Eu³⁺ doped Gd₂O₃ nanoparticles were embedded in the silica hollow spheres while the fluorophore naphthalene derived molecules were covalently linked to the surface of silica to form multi-emission fluorescence sensors (Eu³⁺/Gd₂O₃@HSiO₂/NCO). With a detection limit of 3.8 nM, the nanosensor offers an effective platform for reliable Cr⁶⁺ detection. The obtained accuracy is considerably lower than the maximum level of Cr⁶⁺ in drinking water permitted by the U.S. Environmental Protection Agency (EPA). The prepared Eu³⁺/Gd₂O₃@HSiO₂/NCO inherited simultaneously the excellent luminescence performance of Eu³⁺/Gd₂O₃ and the fluorophore group and exhibited interesting structural and fluorescence stability in aqueous solution. A higher enhancement of fluorescence emission stemming from an intrinsic structure of Eu³⁺/Gd₂O₃ nanoparticles was observed by adding Cr⁶⁺ ions as opposed to naphthalene molecules. There was a good linear relationship between the sum of fluorescence intensity changes (ΔI₃₃₀ + ΔI₆₁₀) and the Cr⁶⁺ concentration in the range of 0.1–1.0 ppm. The nanosensor fabricated by this method showed good reversibility, enabling the rapid detection of Cr⁶⁺ in real water samples. As a result of this groundbreaking study, we are able to develop an idea for building a multifunctional fluorescent probe, with potential applications in biotechnology, food analysis, and environmental analysis.