Dual-mode detection of KRAS gene by target recycling amplification based on molybdenum disulfide quantum dots and the catalytic reduction of rhodamine B

In this work, a novel dual-mode ratiometric fluorometric and colorimetric system was proposed based on molybdenum disulfide quantum dots (MoS2 QDs) and rhodamine B (RhB) by combining the Exo III-assisted target recycling approach with the magnetic separation method. KRAS (Kirsten rat sarcoma viral oncogene homolog) gene as the target DNA could hybridize with the hairpin DNA to generate the output DNA through exonuclease III-assisted recycling amplification. The output DNA served as a bridge to link magnetic beads labeled with ssDNA1 (MBs-ssDNA1) to gold nanoparticles modified with ssDNA2 (AuNPs-ssDNA2). After magnetic separation, the remaining AuNPs could catalyze the reduction of RhB with the aid of sodium borohydride (NaBH4). When the KRAS gene concentration increased, the AuNPs in the solution decreased and thus less RhB was reduced. In this process, the fluorescence of RhB at 582 nm enhanced while the fluorescence of MoS2 QDs at 420 nm as a reference signal kept unchanged. Meanwhile, the absorbance of the MoS2 QDs/RhB sensing platform at 554 nm gradually increased. The dual-mode fluorometric and colorimetric sensing methods displayed excellent selectivity for KRAS gene determination with limits of detection (LOD) of 0.22 and 0.41 pM, respectively. By combining signal amplification and magnetic separation technology, this method effectively eliminated background interference and improved the sensitivity of the results. The two detection modes were successfully applied to detect the KRAS gene in real samples.