Development of a Single Quantum Dot-Mediated FRET Nanosensor for Sensitive Detection of Single-Nucleotide Polymorphism in Cancer Cells

Single-nucleotide polymorphisms (SNPs) are important hallmarks of human diseases. Herein, we develop a single quantum dot (QD)-mediated fluorescence resonance energy transfer (FRET) nanosensor with the integration of multiple primer generation rolling circle amplification (MPG-RCA) for sensitive detection of SNPs in cancer cells. This assay involves only a linear padlock probe for MPG-RCA. The presence of a mutant target facilitates the circularization of linear padlock probes to initiate RCA, producing three short single-stranded DNAs (ssDNAs) with the assistance of nicking endonuclease. The resulting ssDNAs can function as primers to induce cyclic MPG-RCA, resulting in the exponential amplification and generation of large numbers of linker probes. The linker probes can subsequently hybridize with the Cy5-labeled reporter probes and the biotinylated capture probes to obtain the sandwich hybrids. The assembly of these sandwich hybrids on the 605 nm-emission quantum dot (605QD) generates the 605QD–oligonucleotide–Cy5 nanostructures, resulting in efficient FRET from the 605QD to Cy5. This nanosensor is free from both the complicated probe design and the exogenous primers and has distinct advantages of high amplification efficiency, zero background signal, good specificity, and high sensitivity. It can detect SNPs with a large dynamic range of 8 orders of magnitude and a detection limit of 5.41 × 10–20 M. Moreover, this nanosensor can accurately distinguish as low as 0.001% mutation level from the mixtures, which cannot be achieved by previously reported methods. Furthermore, it can discriminate cancer cells from normal cells and even quantify SNP at the single-cell level.