Hualin Yang

Lead ions (Pb²⁺), as heavy metal ions, pose significant hazards to human health. Therefore, it is of great significance to establish a simple and effective method for detecting Pb²⁺. In this study, a label-free Pb²⁺ biosensor was established based on G-quadruplex DNA (G4-DNA) and Exonuclease III (Exo III). In the absence of Pb²⁺, the double-stranded DNA formed by G4-DNA and its complementary strand can be cleaved by Exo III. When Pb²⁺ was present, G4-DNA can form a cage-like structure with the assistance of Pb²⁺, thereby disrupting the formation of double-stranded structures and blocking the cleavage of DNA by Exo III. Subsequently, the fluorescence signal was released upon the addition of the DNA dye (SG I). This biosensor possessed a broad linear detection range of 10 nM – 20 µM and a low limit of detection (LOD) of 7.3 nM. Moreover, the proposed biosensor exhibited excellent specificity for Pb²⁺ and achieved satisfactory recovery rates (91.4%-109.7%) in pond water.

A dual-mode ALP biosensor was designed. ALP catalyzed the dephosphorylation of AAP to form AA and PO ₄ ³⁻ . Then, AA reduced DCIP from blue to colorless, while PO ₄ ³⁻ chelates with Eu ³⁺ to restore Eu ³⁺ -calcein fluorescence.

A sensitive fluorescence and colorimetric dual-mode detection method based on Eu³⁺ and Fe₃O₄@MoS₂ nanocomposites was constructed. In this technique, tetracycline antibiotics (TCs) chelated with Eu³⁺ to form a Eu³⁺-TCs complex which emits red fluorescence at 620 nm through the antenna effect. At the same time, Eu³⁺-TCs complex enhances the peroxidase-like activity of Fe₃O₄@MoS₂ to catalyze the oxidation of 3,3’,5,5’-tetramethylbenzidine (TMB) that can produce a colorimetric signal. This proposed strategy has been used to detect three antibiotics including oxytetracycline (OTC), tetracycline (TC), and chlortetracycline hydrochloride (HCl-CTC). The linear ranges of the new assay for OTC, TC, and HCl-CTC were 0.1–25 μM, 0.5–25 μM, and 0.05–5 μM with the detection limits of 0.016 μM, 0.039 μM, and 0.036 μM, respectively. Meanwhile, this new method was fast and convenient which can complete the detection in 22 min. The assay has been effectively applied to TCs detection in tap water, lake water and honey with satisfactory recoveries of 90.55–109.86%. Graphical Abstract