Yunyun Hu,Xin Guo,Peilin Gu,Qin Luo,Yang Song,Erqun Song
Since circulating tumor DNA (ctDNA) has been regarded as a promising noninvasive biomarker for early cancer screening, cancer condition monitoring, and prognosis evaluation, the accurate and simple detection of ctDNA has been extensive explored. Up to now, there is still a lot of space for following-up the assay of ctDNA, especially simply direct analysis ctDNA in complex biological samples such as blood sample. In this work, we develop a Mn 2+ -mediated magnetic relaxation switching (MRS) assay for direct and simple detection of ctDNA via exonuclease III-assisted signal amplification. In the presence of target ctDNA, exonuclease III selectively cleaves the hybridization complex of between ctDNA and its complementary DNA labeled with magnetic beads and alkaline phosphatase (MB 1000 -DNA 1 -ALP) to release ALP and ctDNA, the former further generating Mn 2+ and causing transverse relaxation time signal change while the later recycling to amplify the signal. The combination of efficient recognition of ctDNA, enzyme-assisted amplification, and the MRS assay could achieve direct and specific detection of ctDNA with a detection limit of 340 pM. In our opinion, this is the first successful direct detection of ctDNA in whole blood sample without ctDNA extraction from biospecimen, which make the assay for ctDNA much accurate and timely since a short half-life (2 h) of ctDNA in blood. The as-proposed method for ctDNA assay in this study shows potential tracking the evolution of tumor timely and serving as a liquid biopsy for diagnosis.
Long Wu,Wei Zeng,Bing Hu,Ting Wu,Min Zhou,Weihong Xie
Since pesticide residues in food have attracted increasing concern worldwide, it is crucial to develop rapid and sensitive analytical methods to detect pesticide residues and ensure food safety. In this work, via the biotin-streptavidin (SA) recognition system, we constructed a magnetic relaxation switching (MRS) immunosensor for sensitive detection of chlorpyrifos (CPF). With a competitive immunoassay mode, H 2 O 2 and Fe 2+ were firstly optimized as the reaction substrates. Wherein, horseradish peroxidase (HRP) acted as enzyme label to catalyze H 2 O 2 and mediated the conversion of Fe 2+ /Fe 3+ . By introducing Fe 2+ /Fe 3+ interconversion as MRS signal output, CPF was detected by the immunoreaction induced variations of the transverse relaxation time (ΔT 2 ). The proposed MRS immunosensor exhibited a detection linear range from 0.01 to 1000 ng mL −1 (R 2 = 0.9916), with the limit of detection (LOD) of 6 pg mL −1 (3S/M, n = 3). As a proof-of-concept, CPF was easily detected among five different pesticides at a low concentration level (0.1 ng mL −1 ), as well as in real samples (apple, tea, and lettuce) with recoveries of 80.70–115.30%. Besides, the sensor can realize one step of “separation and detection” towards CPF with the aid of magnetic nanoparticles , which demonstrate its promising potential for pesticide residue detection in food samples and environment.
Chlorpyrifos (CPF) is the most frequently found organophosphate pesticide residue in solid food samples and can cause increasing public concerns about potential risks to human health. Traditional detection signals of such small molecules are mostly generated by target-mediated indirect conversion, which tends to be detrimental to sensitivity and accuracy. Herein, a novel magnetic relaxation switching detection platform was developed for target-mediated direct and sensitive detection of CPF with a controllable aggregation strategy based on a bioorthogonal ligation reaction between tetrazine (Tz) and trans-cyclooctene (TCO) ligands. Under optimal conditions, this sensor can achieve a detection limit of 37 pg/mL with a broad linear range of 0.1–500 ng/mL in 45 min, which is approximately 51-fold lower than that of the gas chromatography analysis and 13-fold lower than that of the enzyme-linked immunosorbent assay. The proposed click chemistry-mediated controllable aggregation strategy is direct, rapid, and sensitive, indicating great potential for residue screening in food matrices.
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