Tetracyclines are a widely used group of antibiotics, many of which are currently only used in veterinary medicine and animal husbandry due to their adverse side effects. For the detection of tetracyclines, we previously reported a DNA aptamer named OTC5 that binds to tetracycline, oxytetracycline, and doxycycline with similar KD’s of ~100 nM. Tetracyclines have an intrinsic fluorescence that is enhanced upon binding to OTC5, which can be used as a label-free and dye-free sensor. In this work, the effect of pH and metal ions on the sensor was studied. Mg2+ ions are required for the binding of OTC5 to its target with an optimal concentration of 2 mM. Other metal ions including Ca2+ and Zn2+ can also support aptamer binding. Although Mn2+ barely supported binding, the binding can be rescued by Mg2+. ITC studies confirmed that OTC5 had a KD of 0.2 μM at a pH of 6.0 and 0.03 μM at a pH of 8.3. Lower pH (pH 6) showed better fluorescence enhancement than higher pH (pH 8.3), although a pH of 6.0 had slightly higher KD values. Under optimized sensing conditions, sensors with limit of detections (LODs) of 0.1–0.7 nM were achieved for tetracycline, oxytetracycline, and doxycycline, which are up to 50-fold lower than previously reported. Milk samples were also tested yielding an LOD of 16 nM oxytetracycline at a pH of 6.0.

Recent advances of the tandem difunctionalization of alkynes in decade (2010-2020) were summarized via five categories by triggered mechanisms: (1) radical addition and coupling for the synthesis of polysubstituted ketones and alkenes; (2) electrophilic addition of alkynes; (3) haloalkyne or copper acetylide-mediated reactions; (4) preparation of cyclic compounds via radical process, palladium-catalyzed reactions or conjugate addition; (5) cyclic compounds as intermediates in ring openings. Herein, radical, electrophilic and nucleophilic reactions were well discussed. We hope this review will promote future research in this area.

Tetracyclines are a class of antibiotics with a similar four-ringed structure. Due to this structural similarity, they are not easily differentiated from each other. We recently selected aptamers using oxytetracycline...