A ratiometric electrochemiluminescent tetracycline assay based on the combined use of carbon nanodots, Ru(bpy), and magnetic solid phase microextraction.

A method is described for combined magnetic solid phase microextraction and electrochemiluminescent (ECL) detection of the antibiotic tetracycline. A nanocomposite of type FeO@SiO@ZnO was used as the sorbent. Tetracycline has a strong affinity for Zn(II) ion and therefore is well extracted by this sorbent. The loaded sorbent can be magnetically removed. The extraction efficiency at a 1.0 μM tetracycline concentration is around 88%. Detection is based on the use of carbon nanodots that were prepared form urea and ethylenediaminetetraacetic acid as raw materials. The electrochemical probe Ru(bpy) was added to generate double ECL when scanning the potential between -3.5 and + 2 V. The two ECL signals decreased with the increase of tetracycline concentration. Under optimized experimental conditions, the ratio of the two signals is linearly related to the logarithm of the tetracycline concentration in the range from 1.0 nM to 0.1 mM, with a 0.47 nM detection limit. The method was successfully applied to the determination of tetracycline in spiked milk. It exhibited good sensitivity, selectivity and accuracy due to ratiometric read-out and prior preconcentration of analyte. Graphical abstract Tetracycline (TC) has a strong affinity for Zn(II) ion and is well extracted by the FeO@SiO@ZnO nanocomposite. Ru(bpy) can generate double electrochemiluminescence signals based on the use of carbon nanodots (C-dots) as coreactant. The two signals decrease with the increase of tetracycline concentration. [Ru(bpy)]* stands for excited state Ru(bpy).