Carbon Nanodot–Based Fluorescent Method for Virus DNA Analysis with Isothermal Strand Displacement Amplification

In this work, a fluorescent method is developed for ultrasensitive detection of virus DNA, coupling DNA‐modified carbon nanodots (CDs) and an isothermal amplification technology. The sensitivity is significantly improved with cyclic strand displacement polymerization and highly luminescent CDs. Taking the hemagglutinin7 (H7) gene and neuraminidase 9 (N9) gene as examples, the limits of detection are 4.6 × 10^?15 and 3.4 × 10^?15 m , respectively. Furthermore, the proposed method is highly selective and capable of detecting target sequences in biological samples, indicating great potential for applications in life science research and clinical diagnosis.     

Fluorescence Turn-On Analysis of Trace Protein Based on Carbon Nanodots and Hybridization Chain Reaction

In this work, an ultrasensitive method for trace protein detection based on fluorescent carbon nanodots and hybridization chain reaction (HCR) is designed. Generally, the synthesized bright carbon nanodots are conjugated with two hairpin-structured DNA probes, respectively, which act as subsequent HCR fuel strands. Since single-stranded parts of DNA probes could be easily absorbed on graphene oxide (GO) nanosheets, fluorescence emission of carbon nanodots is effectively quenched via fluorescence resonance energy transfer. However, in the presence of target protein, the aptamer sequence in another hairpin-structured DNA probe specially interacts with target and the hairpin is opened. A single-stranded region is thus exposed, which initiates HCR by coupling with the DNA fuel strands on carbon nanodots. The formed HCR product displays a rigid, long double-stranded structure, which facilitates the release of carbon nanodots from GO surface. As a result, fluorescence of carbon nanodots is recovered and initial concentration of target protein can be estimated. This protein detection method shows a favorable linear response with a low limit of detection (2.3 fg mL⁻¹). Furthermore, it is highly selective and capable of detecting target in biological fluids like serum samples, which demonstrates the promising applications of this method.