Biological nanopores are emerging as powerful and low-cost sensors for real-time analysis of biological samples. Proteins can be incorporated inside the nanopore, and ligand binding to the protein adaptor yields changes in nanopore conductance. In order to understand the origin of these conductance changes and develop sensors for detecting metabolites, we tested the signal originating from 13 different protein adaptors. We found that the quality of the protein signal depended on both the size and charge of the protein. The engineering of a dipole within the surface of the adaptor reduced the current noise by slowing the protein dynamics within the nanopore. Further, the charge of the ligand and the induced conformational changes of the adaptor defined the conductance changes upon metabolite binding, suggesting that the protein resides in an electrokinetic minimum within the nanopore, the position of which is altered by the ligand. These results represent an important step toward understanding the dynamics of the electrophoretic trapping of proteins inside nanopores and will allow developing next-generation sensors for metabolome analysis.

The detection of analytes and the sequencing of DNA using biological nanopores have seen major advances over recent years. The analysis of proteins and peptides with nanopores, however, is complicated by the complex physicochemical structure of polypeptides and the lack of understanding of the mechanism of capture and recognition of polypeptides by nanopores. In this work, we show that introducing aromatic amino acids at precise positions within the lumen of α-helical fragaceatoxin C (FraC) nanopores increased the capture frequency of peptides and largely improved the discrimination among peptides of similar size. Molecular dynamics simulations determined the sensing region of the nanopore, elucidated the microscopic mechanism enabling accurate characterization of the peptides via ionic current blockades in FraC, and characterized the effect of the pore modification on peptide discrimination. This work provides insights to improve the recognition and to augment the capture of peptides by nanopores, which is important for developing a real-time and single-molecule size analyzer for peptide recognition and identification.

The ability to measure the concentration of metabolites in biological samples is important, both in the clinic and for home diagnostics.H ere we present an anopore-based biosensor and automated data analysis for quantification of thiamine in urine in less than am inute,w ithout the need for recalibration. Fort his we use the Cytolysin An anopore and equip it with an engineered periplasmic thiamine binding protein (TbpA). To allow fast measurements we tuned the affinity of TbpA for thiamine by redesigning the p-p stacking interactions between the thiazole group of thiamine and TbpA. This substitution resulted furthermore in am arked difference between unbound and bound state,a llowing the reliable discrimination of thiamine from its two phosphorylated forms by residual current only.Using an arrayofnanopores,this will allowt he quantification within seconds,p aving the way for next-generation single-molecule metabolite detection systems.

The real-time identification of protein biomarkers is crucial for the development of point-of-care and portable devices. Here, we use a PlyAB biological nanopore to detect haemoglobin (Hb) variants. Adult haemoglobin (HbA) and sickle cell anaemia haemoglobin (HbS), which differ by just one amino acid, were distinguished in a mixture with more than 97 % accuracy based on individual blockades. Foetal Hb, which shows a larger sequence variation, was distinguished with near 100 % accuracy. Continuum and Brownian dynamics simulations revealed that Hb occupies two energy minima, one near the inner constriction and one at the trans entry of the nanopore. Thermal fluctuations, the charge of the protein, and the external bias influence the dynamics of Hb within the nanopore, which in turn generates the unique ionic current signal in the Hb variants. Finally, Hb was counted from blood samples, demonstrating that direct discrimination and quantification of Hb from blood using nanopores, is feasible.

Nanopores are label-free single-molecule analytical tools that show great potential for stochastic sensing of proteins. Here, we described a ClyA nanopore functionalized with different nanobodies through a 5–6 nm DNA linker at its periphery. Ty1, 2Rs15d, 2Rb17c, and nb22 nanobodies were employed to specifically recognize the large protein SARS-CoV-2 Spike, a medium-sized HER2 receptor, and the small protein murine urokinase-type plasminogen activator (muPA), respectively. The pores modified with Ty1, 2Rs15d, and 2Rb17c were capable of stochastic sensing of Spike protein and HER2 receptor, respectively, following a model where unbound nanobodies, facilitated by a DNA linker, move inside the nanopore and provoke reversible blockade events, whereas engagement with the large- and medium-sized proteins outside of the pore leads to a reduced dynamic movement of the nanobodies and an increased current through the open pore. Exploiting the multivalent interaction between trimeric Spike protein and multimerized Ty1 nanobodies enabled the detection of picomolar concentrations of Spike protein. In comparison, detection of the smaller muPA proteins follows a different model where muPA, complexing with the nb22, moves into the pore, generating larger blockage signals. Importantly, the components in blood did not affect the sensing performance of the nanobody-functionalized nanopore, which endows the pore with great potential for clinical detection of protein biomarkers.

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Nanopores are promising single-molecule tools for the electrical identification and sequencing of biomolecules. However, the characterization of proteins, especially in real-time and in complex biological samples, is complicated by the sheer variety of sizes and shapes in the proteome. Here, we introduce a large biological nanopore, YaxAB for folded protein analysis. The 15 nm cis-opening and a 3.5 nm trans-constriction describe a conical shape that allows the characterization of a wide range of proteins. Molecular dynamics showed proteins are captured by the electroosmotic flow, and the overall resistance is largely dominated by the narrow trans constriction region of the nanopore. Conveniently, proteins in the 35−125 kDa range remain trapped within the conical lumen of the nanopore for a time that can be tuned by the external bias. Contrary to cylindrical nanopores, in YaxAB, the current blockade decreases with the size of the trapped protein, as smaller proteins penetrate deeper into the constriction region than larger proteins do. These characteristics are especially useful for characterizing large proteins, as shown for pentameric C-reactive protein (125 kDa), a widely used health indicator, which showed a signal that could be identified in the background of other serum proteins.