Solid-state nanopore: chemical modifications, interactions, and functionalities

Improving the Performance of Selective Solid-State Nanopore Sensing Using a Polyhistidine-Tagged Monovalent Streptavidin

Solid-state (SS-) nanopore sensing has gained tremendous attention in recent years, but it has been constrained by its intrinsic lack of selectivity. To address this, we previously established a novel SS-nanopore assay that produces translocation signals only when a target biotinylated nucleic acid fragment binds to monovalent streptavidin (MS), a protein variant with a single high-affinity biotin-binding domain. While this approach has enabled selective quantification of diverse nucleic acid biomarkers, sensitivity enhancements are needed to improve the detection of low-abundance translational targets. Because the translocation dynamics that determine assay efficacy are largely governed by constituent charge characteristics, we here incorporate a polyhistidine-tagged MS (hMS) to alter the component detectability. We investigate the effects of buffer pH, salt concentration, and SS-nanopore diameter on the performance with the alternate reagent, achieve significant improvements in measurement sensitivity and selectivity, and expand the range of device dimensions viable for the assay. We used this improvement to detect as little as 1 nM miRNA spiked into human plasma. Overall, our findings improve the potential for broader applications of SS-nanopores in the quantitative analyses of molecular biomarkers.

Solid-State Nanopore/Nanochannel Sensors with Enhanced Selectivity through Pore-in Modification

Nanopore sensing technology, as an emerging analytical method, has the advantages of simple operation, fast output, and label-free and has been widely used in fields such as protein analysis, gene sequencing, and biomarker detection. Inspired by biological ion channels, scientists have prepared various artificial solid-state nanopores/nanochannels. Biological ion channels have extremely high ion transport selectivity, while solid-state nanopores/nanochannels have poor selectivity. The selectivity of solid-state nanopores and nanochannels can be enhanced by modifying channel charge, varying pore size, incorporating specific chemical functionality, and adjusting operating (or solution) conditions. This Perspective highlights pore-in modification strategies for enhancing the selectivity of solid-state nanopore/nanochannel sensors by summarizing the articles published in the last 10 years. The future development prospects and challenges of pore-in modification in solid-state nanopore and nanochannel sensors are discussed. This Perspective helps readers better understand nanopore sensing technology, especially the importance of detection selectivity. We believe that solid-state nanopore/nanochannel sensors will soon enter our homes after various challenges.

Confirming Silent Translocation through Nanopores with Simultaneous Single-Molecule Fluorescence and Single-Channel Electrical Recordings

Most of what is known concerning the luminal passage of materials through nanopores arises from electrical measurements. Whether nanopores are biological, solid-state, synthetic, hybrid, glass-capillary-based, or protein ion channels in cells and tissues, characteristic signatures embedded in the flow of ionic current are foundational to understanding functional behavior. In contrast, this work describes passage through a nanopore that occurs without producing an electrical signature. We refer to the phenomenon as "silent translocation." By definition, silent translocations are invisible to the standard tools of electrophysiology and fundamentally require a simultaneous ancillary measurement technique for positive identification. As a result, this phenomenon has been largely unexplored in the literature. Here, we report on a derivative of Cyanine 5 (sCy5a) that passes through the α-hemolysin (αHL) nanopore silently. Simultaneously acquired single-molecule fluorescence and single-channel electrical recordings from bilayers formed over a closed microcavity demonstrate that translocation does indeed take place, albeit infrequently. We report observations of silent translocation as a function of time, dye concentration, and nanopore population in the bilayer. Lastly, measurement of the translocation rate as a function of applied potential permits estimation of an effective energy barrier for transport through the pore as well as the effective charge on the dye, all in the absence of an information-containing electrical signature.

Solid-State Nanopore Sensors with Enhanced Sensitivity through Nucleic Acid Amplification

Solid-state nanopores have wide applications in DNA sequencing, energy conversion and storage, seawater desalination, sensors, and reactors due to their high stability, controllable geometry, and a variety of pore-forming materials. Solid-state nanopore sensors can be used for qualitative and quantitative analyses of ions, small molecules, proteins, and nucleic acids. The combination of nucleic acid amplification and solid-state nanopores to achieve trace detection of analytes is gradually attracting attention. This review outlines nucleic acid amplification strategies for enhancing the sensitivity of solid-state nanopore sensors by summarizing the articles published in the past 10 years. The future development prospects and challenges of nucleic acid amplification in solid-state nanopore sensors are discussed. This review helps readers better understand the field of solid-state nanopore sensors. We believe that solid-state nanopore sensors will break through the bottleneck of traditional detection and become a powerful single-molecule detection platform.

Mapping the Acetylamino and Carboxyl Groups on Glycans by Engineered α-Hemolysin Nanopores

Glycan is a crucial class of biological macromolecules with important biological functions. Functional groups determine the chemical properties of glycans, which further affect their biological activities. However, the structural complexity of glycans has set a technical hurdle for their direct identification. Nanopores have emerged as highly sensitive biosensors that are capable of detecting and characterizing various analytes. Here, we identified the functional groups on glycans with a designed α-hemolysin nanopore containing arginine mutations (M113R), which is specifically sensitive to glycans with acetamido and carboxyl groups. Molecular dynamics simulations indicated that the acetamido and carboxyl groups of the glycans produce unique electrical signatures by forming polar and electrostatic interactions with the M113R nanopores. Using these electrical features as the fingerprints, we mapped the length of the glycans containing acetamido and carboxyl groups at the monosaccharide, disaccharide, and trisaccharide levels. This proof-of-concept study provides a promising foundation for developing single-molecule glycan fingerprinting libraries and demonstrates the capability of biological nanopores in glycan sequencing.

Functional Nanopores Enabled with DNA

Membrane-spanning nanopores are used in label-free single-molecule sensing and next-generation portable nucleic acid sequencing, and as powerful research tools in biology, biophysics, and synthetic biology. Naturally occurring protein and peptide pores, as well as synthetic inorganic nanopores, are used in these applications, with their limitations. The structural and functional repertoire of nanopores can be considerably expanded by functionalising existing pores with DNA strands and by creating an entirely new class of nanopores with DNA nanotechnology. This review outlines progress in this area of functional DNA nanopores and outlines developments to open up new applications.