Lead pollution presents a significant threat to ecological systems and human health, underscoring the urgent need for highly sensitive detection methods. Herein, we introduce a novel DNA concatemer-encoded CRISPR/Cas12a fluorescence sensor (MDD-Cas12a) for sensitive detection of Pb2+ based on DNAzymes. To accomplish this, we designed a substrate strand containing a long DNA concatemer encoding multiple protospacer adjacent motifs (PAMs) and protospacer sequences for activation of the CRISPR/Cas12a system. The DNA concatemer was subsequently anchored to the surface of magnetic beads (MBs) to fabricate a MBs-DNA concatemer nanoprobe. In the presence of Pb2+, the DNAzyme structure catalyzes the cleavage of the substrate strand, leading to the release of DNA concatemers. Following magnetic separation, the released DNA concatemers significantly activate the non-specific trans-cleavage activity of the Cas12a/crRNA complex. The fluorescence reporter DNA is then completely cleaved by the activated Cas12a/crRNA complex, and the Pb2+ concentration in the sample can be quantified by measuring the fluorescence signal. By harnessing the specific recognition capability of DNAzymes for Pb2+, the programmability of DNA concatemers, and the self-amplification features of the CRISPR/Cas12a system, the MDD-Cas12a platform demonstrates high sensitivity and specificity for detecting Pb2+ in milk and lake water samples.
In this study, we report a metallobioassay for ultrasensitive electrochemical detection of prostate-specific antigen (PSA) based on DNA hybridization chain reaction (HCR) for amplifying the signal, which is derived from silver nanoparticles (Ag NPs) on DNA concatemers. The assay mainly consists of primary antibody (Ab1), secondary antibody (Ab2) with primer, and a signal probe. In the presence of PSA, a sandwich structure with DNA concatemers was formed, and numerous Ag NPs were loaded on the DNA concatemers, resulting in a strong signal, which appeared within the applied potential (−0.2 V to 0.3 V) in the phosphate-buffered saline (PBS). Differential pulse voltammetry (DPV) was employed to evaluate the analytical performance. Under optimal conditions, the DPV peak current of Ag NPs at about +0.09 V (vs. SCE) increased linearly as the logarithm of PSA concentration increased from 0.1 pg mL−1 to 75 ng mL−1, and the detection limit of PSA was estimated to be 0.033 pg mL−1 at the signal to noise ratio of 3. In addition, the assay was evaluated with human serum samples, and satisfying results were obtained, indicating that the assay can achieve PSA detection in the serum sample.
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