Fig. 1. (a) Schematic diagram of the anionic Au₂₅(SG)₁₈ cluster-enhanced nanopore detection and (b) it′s corresponding current traces^[18]

Fig. 2. Various material framework of zero-mode waveguide (ZMW) plasma nanopore^[20]. (a)The autofluorescence of Al ZMW monoprotein was enhanced by deep ultraviolet plasma. (b) Au-Si zero-mode hybrid waveguides for enhanced single-molecule detection. (c)The plasma nanopore device structure enhances single-molecule fluorescence detection, which consists of nanopore prepared by gold film and nanopore prepared by independent silicon nitride film.

Fig. 3. Transporting C-A₃ and mC-A₃ through a wild-type aerolysin membrane channel^[33]. (a) All-atom model of the full-length aerolysin nanopore system. Aerolysin (gray) was inserted into a lipid bilayer membrane (dark blue), while nucleotides (red) were placed at the entrance of the pore. (b) Structure of methylated and unmethylated oligonucleotides containing methylcytosine and cytosine, respectively. The only difference between them was the addition of a methyl group which is marked in red

Fig. 4. Magnetic bead seeding^[35]. (a) Schematic of the magnetic bead seeding on HIH microwell arrays. (b) The bead distribution in arrays with varying well diameters, array pitches and well depths, for multiple-seeding cycles. (c,d) ×40 magnification bright field microscopy image of a microwell array before and after magnetic bead seeding, respectively. (e) ×100 magnification bright field microscopy image of a microwell array after seeding

Fig. 5. Schematic representation of digital ELISA^[37]. (a) Antibody-coated beads captures the single target biomolecules, which are then detected by another antibody conjugated with a labeled antibody. Loading of beads into femtoliter well arrays for isolation and detection of single molecules. (b) Fluorescence image of a small section of the femtoliter well array after signals from single molecules are generated. While the majority of femtoliter chambers contain a bead from the assay, only a fraction of those beads possesses catalytic enzyme activity, indicative of a single, bound protein. (c) The concentration of protein in the bulk solution is correlated to the percentage of beads that have bound a protein molecule

Fig. 6. MicroRNA detection with digital single molecule detection technology^[43]. (a) Individual miRNA molecules are captured by hybridization to probecoated paramagnetic beads, along with biotinylated detector probe. The streptavidin-conjugated enzyme is subsequently added to label the captured miRNA complex, to allow generation of a fluorescent signal upon incubation with a fluorogenic enzyme substrate. (b) Individual beads are loaded along with fluorogenic substrate into a femtoliter microwell array, which is subsequently sealed with oil. The number of fluorescent “on” wells is then counted as a digital readout of the target miRNA concentration

Fig. 7. Illustration of a WGM cavity excited by frustrated total internal reflection at a prism surface^[51]

Fig. 8. Detection of virus particles of aptamer on solid substrates^[79]

Fig. 9. Two CRISPR methods for detecting viral RNA^[89]. (a) SHERLOCK assay; (b) DETECTR assay