Synthesizing fluorescent europium oxide nanosheets for the detection of ampicillin using a photoluminescence-based assay

Abstract

In this study, we synthesized fluorescent europium oxide (Eu2O3) nanosheets (EuNSs) using different approaches such as chemical-based methods and green synthesis, using Dedleya brittonii (DB) extract as an effective chelating agent for biological preparation. A modified hydrothermal method was used to synthesize chemical Eu2O3 nanosheets (CH-EuNS) and DB extract-based Eu2O3 nanosheets (DB-EuNS). Field emission scanning electron microscopy and HR-TEM analyses revealed that both EuNS had a sheet-like morphology, with an average thickness of 5–8 nm. The UV–Vis absorbance spectra of CH-EuNS and DB-EuNS showed clear bands at 320 and 325 nm, respectively; the band at approximately 320 nm corresponded to the absorbance of the Eu nanomaterial. The luminescence spectra of CH-EuNS and DB-EuNS showed strong red emission peaks centered at 616 and 612 nm, respectively, which were attributed to (5D0→7F3) and (5D0→7F2), respectively. Pure CH-EuNS and DB-EuNS showed no cytotoxicity against NIH 3 T3 fibroblasts and HeLa cancer cells at a high concentration (2 mg/mL) after 24 hr of exposure. Based on this outcome, unmodified CH-EuNS and DB-EuNS were used to detect ampicillin (AMP) antibiotics. The effectiveness of pure EuNS in detecting the presence of AMP was evaluated in various media, i.e., water, ethanol, and citrate buffer. Depending on the concentration of the different media, CH-EuNS with citrate buffer and ethanol exhibited maximum emission intensity variations of the 5D0 → 7F3 transition in the EuNS and AMP complexes at 618 nm. The luminescence of CH-EuNS and DB-EuNS was quenched in the presence of AMP at different concentrations (50 – 1 µM) in citrate buffer, whereas the luminescence intensity of pure EuNS was significantly higher than that of the EuNS-AMP mixture. The optimal linear concentration range for AMP was assessed under photoluminescence intensities of 0 to 50 µM, and the detection limit was determined to be 5 µM. This study suggests that CH-EuNS and DB-EuNS in a citrate buffer medium could effectively bind with AMP without ligand modification and significantly reduce the emission intensity due to the presence of AMP in the solution. Therefore, unmodified EuNS could be applied to detect AMP in a solution; however, for it to be used to detect AMP in real samples, it had to be optimized using a fluorescent nanomaterial.