Dual-signal biosensor based on G-quadruplex/hemin DNAzyme and zinc-doped molybdenum disulfide quantum dots for ultrasensitive detection of tumor biomarker

Herein, a dual-mode fluorometric and colorimetric biosensor for Pax-5a gene was developed based on zinc-doped molybdenum disulfide quantum dots (Zn-MoS2 QDs) by coupling exonuclease-assisted recycling amplification and peroxidase-mimic DNAzyme. In the presence of Pax-5a gene, the exonuclease III can cleave the duplexes formed by Pax-5a gene and the hairpin DNA (HP), releasing the output DNA (oDNA). G-rich DNA and magnetic beads (MBs) labeled with capture DNA (cDNA) can hybridize with oDNA to form the MBs-cDNA/oDNA/G-rich DNA sandwich complex. The remaining G-rich DNA in the supernatant through magnetic separation could bind hemin to produce G-quadruplex/hemin peroxidase-mimicking DNAzyme, which catalyzed the oxidization of 3,3 ' diaminobenzidine (DAB) by H2O2. The generated brown oxidation product (oxDAB) had a distinct absorption peak at 464 nm and could quench the fluorescence of Zn-MoS2 QDs at 406 nm. The high peroxidase activity of DNAzyme, recycling amplification strategy and magnetic separation technique led to excellent sensitivity and specificity of this detection platform. The detection limits of Pax-5a gene by fluorometric and colorimetric methods were 0.52 pM and 1.12 pM, respectively. Furthermore, this sensing system was successfully applied to Pax-5a gene determination in human serum samples, which had promising potential in biochemical analysis and clinical diagnosis.