Molecular-scale pore structures, called nanopores, can be assembled by protein ion channels through genetic engineering or be artificially fabricated on solid substrates using fashion nanotechnology. When target molecules interact with the functionalized lumen of a nanopore, they characteristically block the ion pathway. The resulting conductance changes allow for identification of single molecules and quantification of target species in the mixture. In this review, we first overview nanopore-based sensory techniques that have been created for the detection of myriad biomedical targets, from metal ions, drug compounds, and cellular second messengers to proteins and DNA. Then we introduce our recent discoveries in nanopore single molecule detection: (1) using the protein nanopore to study folding/unfolding of the G-quadruplex aptamer; (2) creating a portable and durable biochip that is integrated with a single-protein pore sensor (this chip is compared with recently developed protein pore sensors based on stabilized bilayers on glass nanopore membranes and droplet interface bilayer); and (3) creating a glass nanopore-terminated probe for single-molecule DNA detection, chiral enantiomer discrimination, and identification of the bioterrorist agent ricin with an aptamer-encoded nanopore.

Template-driven strategy has been widely used to synthesize inorganic nano/micro materials. Here, we used a bottom-up controlled synthesis route to develop a powerful solution-based method of fabricating three-dimensional (3D), hierarchical, porous-Co₃O₄ superstructures that exhibit the morphology of flower-like microspheres (hereafter, RT-Co₃O₄). The gram-scale RT-Co₃O₄ was facilely prepared using one-pot synthesis with bacterial templating at room temperature. Large-surface-area RT-Co₃O₄ also has a noticeable pseudocapacitive performance because of its high mass loading per area (~10 mg cm⁻²), indicating a high capacitance of 214 F g⁻¹ (2.04 F cm⁻²) at 2 A g⁻¹ (19.02 mA cm⁻²), a Coulombic efficiency averaging over 95%, and an excellent cycling stability that shows a capacitance retention of about 95% after 4,000 cycles.

Guanine-rich nucleic acids can form G-quadruplexes that are important in gene regulation, biosensor design and nano-structure construction. In this article, we report on the development of a nanopore encapsulating single-molecule method for exploring how cations regulate the folding and unfolding of the G-quadruplex formed by the thrombin-binding aptamer (TBA, GGTTGGTGTGGTTGG). The signature blocks in the nanopore revealed that the G-quadruplex formation is cation-selective. The selectivity sequence is K⁺ > NH₄⁺ ∼ Ba²⁺ > Cs⁺ ∼ Na⁺ > Li⁺, and G-quadruplex was not detected in Mg²⁺ and Ca²⁺. Ba²⁺ can form a long-lived G-quadruplex with TBA. However, the capability is affected by the cation–DNA interaction. The cation-selective formation of the G-quadruplex is correlated with the G-quadruplex volume, which varies with cation species. The high formation capability of the K⁺-induced G-quadruplex is contributed largely by the slow unfolding reaction. Although the Na⁺- and Li⁺-quadruplexes feature similar equilibrium properties, they undergo radically different pathways. The Na⁺-quadruplex folds and unfolds most rapidly, while the Li⁺-quadruplex performs both reactions at the slowest rates. Understanding these ion-regulated properties of oligonucleotides is beneficial for constructing fine-tuned biosensors and nano-structures. The methodology in this work can be used for studying other quadruplexes and protein–aptamer interactions.