DNAzyme-mediated fluorescence sensor based on covalent organic framework for Pb2+ detection

DNA-Functionalized Covalent Organic Framework for Colorimetric Detection and Adsorption Removal of Uranyl Ions.

Inspired by the modulatable nanozymatic activity of covalent organic frameworks (COFs) by single-stranded DNA (ssDNA), herein, we developed a versatile platform for sensitive/specific colorimetric detection and efficient adsorption of UO22+ based on DNA aptamer-functionalized COFs. Three COFs with varying alkyne contents (Py-BDA, Py-BDA-BPTA, and Py-BPTA) were synthesized, followed by precisely covalent immobilization of UO22+-specific DNA aptamers via click chemistry. These COFs possess intrinsic oxidase-mimicking activity capable of catalyzing TMB oxidation to oxTMB, and the DNA aptamer covalent modification can regulate the enzymatic activity of COFs, with the most suppressing effect for Py-BDA-BPTA. The subsequent UO22+ binding can significantly restore the nanozymatic activity of Py-BDA-BPTA by charge neutralization. This "off-on" switching mechanism enabled sensitive and selective UO22+ detection with a low limit of detection (LOD) about 10 nM (3σ). Moreover, the DNA aptamer-functionalized COFs can be applied for efficient adsorption and removal of UO22+ with rapid kinetics and excellent cycling stability. This study provides novel insights into the postmodification of COFs by biomacromolecules to modulate their mimic enzymatic activity for sensing and adsorption applications.

A Label-free Simple Biosensor for Pb2+ Detection Based on G-quadruplex DNA and Exonuclease III.

A Label-Free Fluorescence Detection Strategy for Cd2⁺ Based on an Aptamer, Exonuclease I, and SYBR Gold

A Schiff base-functionalized europium metal-organic framework for turn-off fluorescence sensing of Cu2.

Developing a low-cost, highly sensitive, and accurate fluorescence-based approach for Cu2+ detection is crucial for reducing heavy metal pollution in industrial effluent. Here, we report a newly synthesized Schiff base europium metal-organic framework (Eu-MOF) and demonstrate its use for turn-off fluorescent detection of Cu2+. A Schiff base ligand derived from 2-aminoterephthalic acid and 2-hydroxynicotinaldehyde was coordinated with Eu3+ to construct the framework, enabling a simple and rapid sample pretreatment procedure. The material exhibited pH-dependent fluorescence behavior. With the concentration range of 2.5 to 500 mg L-1, a linear response to Cu2+ was observed. The limit of quantification (LOQ) was 2.5 mg L-1, while the limit of detection (LOD) was 0.83 mg L-1. The method was effectively performed on vinegar, tea, fruit juice, and water samples, yielding spike recoveries of 84.5%-100.9% and relative standard deviations (RSDs) of 1.7%-4.8%. This method can be used to determine Cu2+ in various matrices.

Preparation of a versatile fluorescence sensor for co-detecting ions in aqueous solution.

Label-free and enzyme-free fluorescent biosensor for ultrasensitive detection of tobramycin via cascade signal amplification.

Uncontrolled use of tobramycin (TOB) raises serious health concerns, including nephrotoxicity and ototoxicity, making it imperative to develop simple and sensitive detection methods. This study introduces a novel enzyme-free and label-free fluorescent biosensor based on a cascade signal amplification strategy, integrating an entropy-driven DNA circuit (EDC) with catalytic hairpin assembly (CHA). The mechanism is initiated by the specific binding of TOB to its aptamer, which induces a conformational change and exposes a priming sequence. This sequence triggers a strand displacement reaction to release an initiator strand, subsequently activating the CHA process to generate fuel strands. These fuel strands drive the EDC, resulting in the liberation of numerous G-quadruplex sequences from the stem of hairpin probes. The released G-quadruplexes bind to thioflavin T (ThT), yielding a significantly enhanced fluorescence signal proportional to the TOB concentration. The proposed biosensor exhibits outstanding analytical performance with a detection limit of 92 fM and a wide linear range from 3 pM to 30 nM. Furthermore, the method effectively distinguishes TOB from other interfering antibiotics, highlighting its high specificity. It also demonstrates practical applicability by achieving satisfactory recovery rates in milk sample assays. With its high sensitivity, cost-effectiveness, and operational simplicity without the need for complex enzymes or labels, the proposed strategy offers a promising platform for food safety supervision and clinical diagnostics.