Portable ratiometric probe based on the use of europium(III) coordination polymers doped with carbon dots for visual fluorometric determination of oxytetracycline

A novel ratiometric fluorescent probe for the determination of oxytetracycline (OTC) was developed. The method is based on the use of adenosine monophosphate/Eu(III) nanoscale coordination polymers doped with carbon dots (CDs) (CD@AMP/Eu NCPs). These were fabricated by self-assembly of Eu3+ and AMP on the surface of CDs containing large amounts of hydroxyl and carbonyl groups. Under the excitation at 310 nm wavelength, the doped NCPs display strong pink emission of Eu3+ at 615 nm and blue emission of the CDs at 430 nm on exposure to OTC. The ratio of fluorescence intensity (F615/F430) of such NCPs displays excellent linear relationship with OTC concentration ranging from 0.2 to 60 μM and the limit of detection (LOD) is 25 nM (3σ). The doped NCPs were evenly immobilized on common filter paper to prepare a visual ratiometric probe for the determination of OTC. Assisted by a digital camera with an APP color detector, the paper-based test strip was applied for the quantitative determination of OTC with a LOD of 0.5 μM and a wide linear scope of 1–100 μM. The method was applied to the determination of OTC in milk samples.