Programmable strand displacement-driven assembly of single quantum dot nanosensor for accurately monitoring human SMUG1 uracil-DNA glycosylase at single-cell level

Abstract

Human single-stranded selective monofunctional uracil glycosylase (hSMUG1) is an important uracil-DNA glycosylase (UDG) subfamily responsible for repair of uracil and oxidized pyrimidine derivatives as well as maintenance of genomic integrity. The abnormal hSMUG1 level is closely associated with various human diseases and cancers. Herein, we demonstrate for the first time the programmable strand displacement-driven assembly of single quantum-dot (QD) nanosensor for accurately monitoring hSMUG1 at single-cell level. We used an oxidation marker 5-hydroxymethyluracil (5hmU) as a novel specific catalysis site for hSMUG1. The presence of hSMUG1 catalyzes 5hmU excision to activate exponential strand-displacement cascades for producing abundant primer probes. Subsequently, primer probes induce the self-assembly of 605QD-dsDNA-Cy5 nanostructures and fluorescence resonance energy transfer (FRET) between 605QD and Cy5. The FRET signal can be quantified via single-molecule imaging. This single QD nanosensor exhibits a detection limit of 7.08 × 10−11 U/μL over a wide dynamic range of 8 orders of magnitude. Importantly, it can measure enzymatic kinetics, screen potential inhibitors, discriminate hSMUG1 expression between cancer cells and normal cells, and quantify hSMUG1 activity in various cancer cells at single-cell level, promising a new avenue for hSMUG1-related biomedical studies and clinical diagnostics.