Polynucleotide differentiation using hybrid solid-state nanopore functionalizing with α-hemolysin

Developing tardigrade-inspired material: Track membranes functionalized with Dsup protein for cell-free DNA isolation

When developing functionalized biomaterials, the proteins from extremophilic organisms, in particular unique tardigrade disordered proteins, are of great value. The damage suppressor protein (Dsup), initially discovered in the tardigrade Ramazzottius varieornatus and found to be an efficient DNA protector under oxidative and irradiation stress, has been hypothesized to possess a good potential for the development of the material, which can isolate cell-free DNA. With this in mind, DNA-nonadsorbing polyethylene terephthalate track membranes have been functionalized using the Dsup protein via covalent bonding with glutaraldehyde. The filtration experiments have verified the ability of track membranes with the immobilized Dsup protein to adsorb cell-free DNA, with an accumulation capacity of 70 ± 19 mg m-2. The resulting track membrane-based biomaterial might be used in various devices for filtration and separation of cell-free DNA molecules from biological solutions and environmental samples, and also for their accumulation, storage, and further manipulation.

Impact of Single-Walled Carbon Nanotube Functionalization on Ion and Water Molecule Transport at the Nanoscale

Nanofluidics has a very promising future owing to its numerous applications in many domains. It remains, however, very difficult to understand the basic physico-chemical principles that control the behavior of solvents confined in nanometric channels. Here, water and ion transport in carbon nanotubes is investigated using classical force field molecular dynamics simulations. By combining one single walled carbon nanotube (uniformly charged or not) with two perforated graphene sheets, we mimic single nanopore devices similar to experimental ones. The graphitic edges delimit two reservoirs of water and ions in the simulation cell from which a voltage is imposed through the application of an external electric field. By analyzing the evolution of the electrolyte conductivity, the role of the carbon nanotube geometric parameters (radius and chirality) and of the functionalization of the carbon nanotube entrances with OH or COO- groups is investigated for different concentrations of group functions.

Nanopore Discrimination of Coagulation Biomarker Derivatives and Characterization of a Post-Translational Modification

One of the most important health challenges is the early and ongoing detection of disease for prevention, as well as personalized treatment management. Development of new sensitive analytical point-of-care tests are, therefore, necessary for direct biomarker detection from biofluids as critical tools to address the healthcare needs of an aging global population. Coagulation disorders associated with stroke, heart attack, or cancer are defined by an increased level of the fibrinopeptide A (FPA) biomarker, among others. This biomarker exists in more than one form: it can be post-translationally modified with a phosphate and also cleaved to form shorter peptides. Current assays are long and have difficulties in discriminating between these derivatives; hence, this is an underutilized biomarker for routine clinical practice. We use nanopore sensing to identify FPA, the phosphorylated FPA, and two derivatives. Each of these peptides is characterized by unique electrical signals for both dwell time and blockade level. We also show that the phosphorylated form of FPA can adopt two different conformations, each of which have different values for each electrical parameter. We were able to use these parameters to discriminate these peptides from a mix, thereby opening the way for the potential development of new point-of-care tests.

Macromolecule sensing and tumor biomarker detection by harnessing terminal size and hydrophobicity of viral DNA packaging motor channels into membranes and flow cells

Biological nanopores for single-pore sensing have the advantage of size homogeneity, structural reproducibility, and channel amenability. In order to translate this to clinical applications, the functional biological nanopore must be inserted into a stable system for high-throughput analysis. Here we report factors that control the rate of pore insertion into polymer membrane and analyte translocation through the channel of viral DNA packaging motors of Phi29, T3 and T7. The hydrophobicity of aminol or carboxyl terminals and their relation to the analyte translocation were investigated. It was found that both the size and the hydrophobicity of the pore terminus are critical factors for direct membrane insertion. An N-terminus or C-terminus hydrophobic mutation is crucial for governing insertion orientation and subsequent macromolecule translocation due to the one-way traffic property. The N- or C-modification led to two different modes of application. The C-terminal insertion permits translocation of analytes such as peptides to enter the channel through the N terminus, while N-terminus insertion prevents translocation but offers the measurement of gating as a sensing parameter, thus generating a tool for detection of markers. A urokinase-type Plasminogen Activator Receptor (uPAR) binding peptide was fused into the C-terminal of Phi29 nanopore to serve as a probe for uPAR protein detection. The uPAR has proven to be a predictive biomarker in several types of cancer, including breast cancer. With an N-terminal insertion, the binding of the uPAR antigen to individual peptide probe induced discretive steps of current reduction due to the induction of channel gating. The distinctive current signatures enabled us to distinguish uPAR positive and negative tumor cell lines. This finding provides a theoretical basis for a robust biological nanopore sensing system for high-throughput macromolecular sensing and tumor biomarker detection.

Atomistic level characterisation of ssDNA translocation through the E. coli proteins CsgG and CsgF for nanopore sequencing

Two proteins of the Escherichia coli membrane protein complex, CsgG and CsgF, are studied as proteinaceous nanopores for DNA sequencing. It is highly desirable to control the DNA as it moves through the pores, this requires characterisation of DNA translocation and subsequent optimization of the pores. In order to inform protein engineering to improve the pores, we have conducted a series of molecular dynamics simulations to characterise the mechanical strength and conformational dynamics of CsgG and the CsgG-CsgF complex and how these impact ssDNA, water and ion movement. We find that the barrel of CsgG is more susceptible to damage from external electric fields compared to the protein vestibule. Furthermore, the presence of CsgF within the CsgG-CsgF complex enables the complex to withstand higher electric fields. We find that the eyelet loops of CsgG play a key role in both slowing the translocation rate of DNA and modulating the conductance of the pore. CsgF also impacts the DNA translocation rate, but to a lesser degree than CsgG.

Selective target protein detection using a decorated nanopore into a microfluidic device

Solid-state nanopores provide a powerful tool to electrically analyze nanoparticles and biomolecules at single-molecule resolution. These biosensors need to have a controlled surface to provide information about the analyte. Specific detection remains limited due to nonspecific interactions between the molecules and the nanopore. Here, a polymer surface modification to passivate the membrane is performed. This functionalization improves nanopore stability and ionic conduction. Moreover, one can control the nanopore diameter and the specific interactions between protein and pore surface. The effect of ionic strength and pH are probed. Which enables control of the electroosmotic driving force and dynamics. Furthermore, a study of polymer chain structure and permeability in the pore are carried out. The nanopore chip is integrated into a microfluidic device to ease its handling. Finally, a discussion of an ionic conductance model through a permeable crown along the nanopore surface is elucidated. The proof of concept is demonstrated by the capture of free streptavidin by the biotins grafted into the nanopore. In the future, this approach could be used for virus diagnostic, nanoparticle or biomarker sensing.

Sensing with Nanopores and Aptamers: A Way Forward

In the 90s, the development of a novel single molecule technique based on nanopore sensing emerged. Preliminary improvements were based on the molecular or biological engineering of protein nanopores along with the use of nanotechnologies developed in the context of microelectronics. Since the last decade, the convergence between those two worlds has allowed for biomimetic approaches. In this respect, the combination of nanopores with aptamers, single-stranded oligonucleotides specifically selected towards molecular or cellular targets from an in vitro method, gained a lot of interest with potential applications for the single molecule detection and recognition in various domains like health, environment or security. The recent developments performed by combining nanopores and aptamers are highlighted in this review and some perspectives are drawn.