Mn2+-mediated magnetic relaxation switching for direct assay of ctDNA in whole blood via exonuclease III assisted amplification

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.