Morphology controlled NiO nanostructures as fluorescent quenchers for highly sensitive aptamer-based FRET detection of ochratoxin A

Herein, we presented a comprehensive investigation of structural properties of nickel oxide (NiO) nanomaterials prepared by rationally designed temperature-controlled synthesis. A series of eight types (A-H) of nickel oxide nanomaterials were synthesized by hydrothermal approach at different calcination temperatures (40–180) °C. Depending on temperature, different sizes and shapes were obtained including spherical nanoparticles, nanoclusters and flower-like morphologies, as characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM) and Raman spectroscopy. The best fluorescence quenching properties were obtained with spherical NiO-B nanoparticles 18 nm, prepared at 60 °C. The optimized NiO was used to develop an apta-assay for the detection of a food-relevant toxin, ochratoxin-A (OTA). In the presence of OTA, the biomolecular binding induced changes in the FAM labelled-aptamer structure and preferential formation of an aptamer-OTA complex. The method exhibited a limit of detection of 0.49 ng.L⁻¹ with a wide linear range from 0.5 to 200 ng.L⁻¹. The results demonstrate not only that rationally designed NiO nanostructures of varying shapes and sizes can be obtained by temperature-controlled synthesis, but they are also powerful fluorescent quenchers.