A CuO-CeO composite prepared by calcination of a bimetallic metal-organic framework for use in an enzyme-free electrochemical inhibition assay for malathion.

An enzyme-free electrochemical method is described for the determination of trace levels of malathion. It is based on a nanostructured copper-cerium oxide (CuO-CeO) composite prepared by calcination of a Cu(II)/Ce(III) metal-organic framework. The morphology, crystal structure and elemental composition of composite was studied by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction and X-ray photoelectron spectroscopy. The principle for malathion determination is based on the fact that the redox signal of CuO (best measured at around -0.1 V vs. SCE) (at 100 mV/s) is inhibited by malathion due to affinity between CuO and the sulfur groups of malathion. The introduction of CeO into the composite system further improves the analytical performance. This is attributed to the unique microstructure and the synergistic effect between CuO and CeO. Experimental parameters like solution pH value, Cu/Ce molar ratio, accumulation potential, accumulation time, and CuO-CeO volume on the electrode were optimized. The assay has a linear range of 10 fM to 100 nM and a 3.3 fM detection limit (at S/N = 3). The electrode is selectively inhibited by malathion even in the presence of potentially interfering substances. Graphical abstract A sensitive and effective enzyme-free electrochemical sensor has been developed for the detection of malathion based on CuO-CeO composite derived from bimetallic metal-organic frameworks.