Ultrafiltration of single-chain polymer nanoparticles through nanopores and nanoslits

Why Single-Chain Nanoparticles from Weak Polyelectrolytes Can Be Synthesized at Large Scale in Concentrated Solution?

Here, the unresolved question of why single-chain nanoparticles (SCNPs) prepared from a weak polyelectrolyte (PE) precursor can be synthesized on a large is addresses, unlike SCNPs obtained from an equivalent neutral (nonamphiphilic) polymer precursor. The combination of the standard elastic single-chain nanoparticles (ESN) model -developed for neutral chains- with the classical scaling theory of PE solutions provides the key. Essentially, the long-range repulsion between electrostatic blobs in a weak PE precursor restricts the cross-linking process during SCNPs formation to the interior of each blob. Consequently, the maximum concentration at which PE-SCNPs can be prepared without interchain cross-linking is not determined by the full size of the PE precursor but, instead, by the smaller size of its electrostatic blobs. Therefore, PE-SCNPs can be synthesized up to a critical concentration where electrostatic blobs from different chains touch each other. This concentration can be 30 times higher than that for non-PE polymer precursors. Upon progressive dilution, the size of PE-SCNPs synthesized in concentrated solution increases until it reaches the bigger size of PE-SCNPs prepared under highly diluted conditions. PE-SCNPs do not adopt a globular conformation either in concentrated or in diluted solution. It shows that the main model predictions agree with experimental results.

Ionic current magnetic fields in 3D finite-length nanopores and nanoslits

Deoxyribonucleic acid (DNA) encodes all genetic information, and in genetic disorders, DNA sequencing is used as an effective diagnosis. Nanopore/slit is one of the recent and successful tools for DNA sequencing. Passage of DNA along the pores creates non-uniform ionic currents which creates non-uniform electric and magnetic fields, accordingly. Sensing the electric field is usually used for sequencing application. We suggest to use the magnetic field induced by pressure-driven ionic currents as a secondary signal. We systematically compared the induced magnetic field of nanopores and nanoslits with equal cross-sectional area. The 3D magnetic field is numerically obtained by solving the Poisson-Nernst-Planck, Ampere, and Navier-Stokes equations. As expected, the maximum value of the maximum magnetic flux occurs near the wall and inside the channel, and increasing the pressure gradient along the pore/slit increases the flowrate and magnetic field, consequently. At a given pressure difference across the pore/slit, nanopores are better than nanoslits in sensing the magnetic flux. For example, by applying 2 MPa across the pore/slit, the maximum magnetic flux density for nanopore, nanoslit A R = 1 and nanoslit A R = 5 are 1.10 pT, 1.08 pT and 0.45 pT, accordingly. Also, at a given flowrate across the pore/slit, nanoslits are the better choice. It should be noted the external magnetic fields as small as pico-Tesla are detectable and measurable in voltage/pressure driven electrokinetic flow slits.

Graphical abstract

A method to estimate the size of single-chain nanoparticles under severe crowding conditions

Single-chain nanoparticles (SCNPs) result from the folding of isolated polymer chains via intramolecular interactions. Currently, there is no theory able to rationalize the astonishing conformational behaviour of SCNPs under severe crowding conditions (e.g., highly concentrated solutions, all-polymer nanocomposites) and, specifically, the significant size reduction observed in highly crowded solutions of covalent-bonded SCNPs and all-polymer nanocomposites containing SCNPs. Herein, we propose a valuable method to estimate the size of SCNPs under crowding. The method - which is based on combining MD simulations results with scaling concepts - is also useful for ring polymers and nanostructured Janus-shaped SCNPs.

Valuable structure-size relationships for tadpole-shaped single-chain nanoparticles with long and short flexible tails unveiled

Tadpole-shaped single-chain nanoparticles (TSCNPs) are useful soft building blocks for nanotechnology composed of a flexible polymer chain tethered to an intramolecularly folded single-chain nanoparticle.

Local Domain Size in Single-Chain Polymer Nanoparticles

Single-chain polymer nanoparticles (SCNPs) obtained through chain collapse via intramolecular cross-linking are attracting significant interest for nanomedicine and biomimetic catalysis applications, among other fields. This interest arises from the possibility to bind active species (e.g., drugs and catalysts)-either temporally or permanently-to the SCNP local pockets formed upon chain collapse. However, direct quantification of the size and number of such local domains in solution-even if highly desirable-is currently highly demanding from an experimental point of view because of the small size involved (<5 nm). On the basis of a scaling analysis, we establish herein a connection between the global compaction degree (R/R 0) and the size (ξ) and number (n) of the "collapsed domains" generated upon SCNP formation at high dilution from a linear semiflexible precursor polymer. Results from molecular dynamics simulations and experimental data are used to validate this scaling analysis and to estimate the size and number of local domains in polystyrene SCNPs synthesized through a "click" chemistry procedure, as a representative system, as well as for relevant catalytic SCNPs containing Cu, Pt, and Ni atoms. Remarkably, the present work is a first step toward tuning the local domain size of the next generation of SCNPs for nanomedicine and bioinspired catalysis applications.