Smartphone-assisted miniature device based on nitrogen and sulfur co-doped carbon dots for point-of-care testing of tetracycline.

A miniature device was design for the point-of-care testing (POCT) of tetracycline (TC) including a ratio fluorescence test strip, a sample slot, a UV lamp and a smartphone. The nitrogen and sulfur co-doped carbon dots (N, S-CDs) and Eu were dropped onto the filter paper to construct the ratio fluorescence test strips for the specific detection of TC. Under the excitation at 390 nm, the fluorescence emission of N, S-CDs at 530 nm decreases through inner filter effect (IEF) after addition of Eu. When the further addition of TC, the emission of N, S-CDs at 530 nm kept unchanged while the emission of Eu at 616 nm was obviously enhanced for the antenna effect (AE) between Eu and TC. The ratio changes of the two-fluorescence emission realized the quantitative detection of TC. In addition, the test strips with different concentrations of TC showed different fluorescence color from green to red under a 365 nm UV lamp. The miniature device was designed as a fluorescence photo reader with the merits of the powerful functions of smartphones and the portability of test strips. The smartphone camera takes a fluorescent color image of the test strips and the photos are recognized by a color recognizer on the smartphone to obtain RGB (red-greenblue) values which reflect the concentrations of the analytes. Therefore, we established a fast, sensitive and efficient POCT of TC. In particular, the proposed nanomaterial-based POCT platform will open a new route towards the development of ratio fluorescence probe for TC analysis for environment samples.