MnO2 nanosheets based fluorescent sensing platform with organic dyes as a probe with excellent analytical properties

Manganese dioxide (MnO2) nanosheets have recently been demonstrated to be particularly attractive for fluorescent sensing and imaging; however, almost all MnO2 nanosheets-based fluorescent assays have been developed with emissive nanoparticles as the probes. In this study, we developed a novel strategy to use organic dyes, instead of emissive nanoparticles, as the probe to construct a platform for biosensing with excellent analytical properties. With 5-carboxyfluorescein (FAM) as a model organic dye, we firstly investigate the effect of MnO2 nanosheets on the fluorescence of FAM and find that the fluorescence intensity of FAM is considerably suppressed by MnO2 nanosheets based on the inner filter effect (IFE). To demonstrate that the MnO2 nanosheets-based fluorescence sensing platform can easily achieve a high selectivity with organic dyes as the probe, we use single-stranded DNA (ssDNA) oligonucleotide as a typical biorecognition unit, which is labeled with the FAM probe to form FAM-ssDNA. The fluorescent intensity of FAM-ssDNA is first suppressed by MnO2 nanosheets through the combination of IFE and Förster resonant energy transfer (FRET), and then recovered with subsequent hybridization with the complementary DNA oligonucleotide. To demonstrate the potential applications of the MnO2 nanosheets-based fluorescence sensing platform with organic dyes as the probes, we developed methods for simple but effective microRNA and thrombin assays. With the platform demonstrated here, the limits of detection for miR124a and thrombin are 0.8 nM and 11 nM, respectively. Moreover, the fluorescent sensing assay for thrombin exhibits high selectivity. This study essentially demonstrates a new 2D nanostructure-based fluorescent sensing platform that is robust, technically simple, and easily manipulated to achieve high selectivity and sensitivity for practical applications.