Ultrasensitive fluorescence detection of microRNA through DNA-induced assembly of carbon dots on gold nanoparticles with no signal amplification strategy.

An ultrasensitive fluorescence assay strategy on the basis of carbon dots (CDs) and cDNA-modified gold nanoparticles (AuNP-cDNA) was developed for the determination of microRNA-21 (miRNA-21) via internal filtering effect (IFE). Positively charged CDs (PEI-CDs), the fluorophores in IFE, were synthesized via a hydrothermal method using polyethyleneimine (PEI) as surface ligand. The maximum emission wavelength is located at 500 nm under the excitation of 410 nm. AuNPs, the absorbers, were modified with single-stranded DNA (cDNA), which is completely complementary to miRNA-21. The fluorescence of PEI-CDs is quenched due to the assembly of PEI-CDs and AuNPs-cDNA. In the presence of miRNA-21, the hybridization between miRNA-21 and cDNA causes the release of PEI-CDs and the recovery of fluorescence intensity.The fluorescence recovery degree is linearly correlated with the logarithm of miRNA-21 concentration in the range of 1-1000 fM. This method can be applied to determine miRNA-21 in real serum samples, and the detection results are in well agreement with those of qRT-PCR. The determination of miRNA-21 spiked into diluted human serum samples displays satisfactory recovery within the range 88.44-112.7%, which confirmed the reliability for miRNAs detection in real samples.

An ultrasensitive colorimetric and fluorescence dual-readout assay for glutathione with a carbon dot-MnO2 nanosheet platform based on the inner filter effect.

An ultrasensitive colorimetric and fluorescence dual-readout assay based on the inner filter effect (IFE) was developed for glutathione (GSH) determination, in which carbon dots (C-dots) were used as a fluorophore and MnO2 nanosheets as an absorber. Due to the excellent optical absorption properties of MnO2 nanosheets and the good spectral overlap between the fluorophore and absorber, MnO2 nanosheets could effectively quench the fluorescence of C-dots via the IFE. As the target, GSH could reduce MnO2 nanosheets to Mn2+ ions, which inhibited the IFE and resulted in the fading of solution color and the recovery of the fluorescence signal. And these two kinds of signals were respectively used for qualitative and quantitative detection of GSH. The results showed that this proposed assay could distinguish 10 µM GSH with the naked eye and quantitatively detect GSH within the concentration range of 0.1-400 µM. The limit of detection was 6.6 nM. Moreover, this assay showed sensitive responses in human serum and urine samples, which indicated that this IFE-based assay has great potential in GSH-related clinical and bioanalytical applications.