A ratiometric nanoprobe based on carboxylated graphitic carbon nitride nanosheets and Eu3+ for the detection of tetracyclines.

A ratiometric fluorescence method based on carboxylated graphitic carbon nitride nanosheets (C-g-C3N4) and Eu3+ (C-g-C3N4-Eu3+) is described for the detection of tetracyclines (TCs), a broad-spectrum antibiotic. C-g-C3N4, which was used as a fluorescence enhancer of Eu3+, was prepared by direct pyrolysis of melamine and post-functionalization. In the presence of TCs, the fluorescence intensity of Eu3+ at 616 nm increased, accompanied by a decrease of fluorescence intensity of C-g-C3N4 at 435 nm. Under the optimal conditions, the ratio of fluorescence intensity at 616 nm to the one at 435 nm (I616/I415) increases linearly in the 10 nM to 40 μM TC concentration range with a detection limit of 7.7 nM (S/N = 3). It has been successfully applied in the detection of TCs in spiked tap water and soil samples with satisfactory recovery (96.6-107.2%) and high precision. Furthermore, a test paper and smartphone can assist in rapidly detecting TCs due to the emission color change from blue to red with the addition of TCs. This shows that the proposed method has great potential for the rapid detection TCs in real samples.