Mostafa Sharafi - Department of Biology, Faculty of Natural Science, University of Tabriz, Tabriz, Iran
Masoomeh Shaghaghi - Department of Chemistry, Payame Noor University, P. O. Box ۱۹۳۹۵-۴۶۹۷ Tehran, Iran
Nader Sheibani - Department of Ophthalmology and Visual Sciences, University of Wisconsin School of Medicine and Public Health, Madison WI ۵۳۷۰۵ USA
Gholamreza Dehghan - Department of Biology, Faculty of Natural Science, University of Tabriz, Tabriz, Iran

A novel, fast, highly sensitive, and selective non-enzymatic label-free method was developed based on the fluorescence emission activity of surface-modified cerium oxide nanoparticles (CeO۲ NPs) for morphine (MP) detection. The fluorescence intensity of CeO۲ NPs increased following the adsorption of double-stranded DNA (dsDNA) onto its surface. Upon the addition of MP, the fluorescence intensity of the dsDNA-CeO۲ NPs probe switched to a “turn-off” state and was quenched. This was attributed to the binding of MP to dsDNA and displacement of dsDNA with MP from the NPs. Under optimized conditions (pH ۷.۴; dsDNA concentration ۱.۱×۱۰-۶ M and a time of ۳۰ and ۱۰ min for incubation of dsDNA with CeO۲ NPs and for MP and dsDNA-CeO۲ NPs incubation, respectively), the fluorescent sensor was able to detect MP with high sensitivity. A linear relationship was obtained in the range of [(۳.۵–۳۵)×۱۰-۶ M] with a limit of detection (LOD) of ۱.۸×۱۰-۶ M and the relative standard deviation (RSD)% ۱.۵-۲.۳%. The proposed system was successfully applied to determine MP levels in human urine samples from spiked patients and healthy individuals after deproteinization with acetonitrile. The analytical recoveries for treated biological samples ranged from ۹۹.۱ to ۱۰۳.۱%. The excellent selectivity for MP compared to other substances (The common interfering species, such as codeine, amphetamine, and methamphetamine) with concentrations ۱۰-fold higher than MP. In addition, the newly proposed method was based on an optical biosensor, as compared to most existing methods, providing advantages such as rapidity, simplicity, low cost, and high sensitivity, thus, making it a promising method for rapid and direct determination of MP in clinical samples.

Optical Biosensor, Fluorescence spectroscopy, Label-free methods, Morphine determination, Cerium oxide nanoparticles