The coexisting phase behavior of thermo-responsive copolymer solutions

Hydrogen Bond Network Disruption by Hydration Layers in Water Solutions with Salt and Hydrogen-Bonding Polymers (PEO)

A mean field theory model describing the interaction of ion hydration layers with the network of hydrogen bonds of both water and the nonionic polymer poly(ethylene oxide) (PEO) is presented. The predictions of the model for types and statistics of hydrogen bonds, the number of water molecules bound to PEO, or their dependence on temperature are successfully verified from all-atom simulations at different NaCl and PEO concentrations. Furthermore, our simulations show that the binding of cations to PEO increases monotonically with salt concentration, in agreement with recent experimental results, through a mechanism in which the sum of the number of bound water and cations is independent of salt concentration. The model introduced is general and can describe any salt or hydrogen-bond-forming polymer.

Phase Behavior and Aggregate Transition Based on Co-assembly of Negatively Charged Carbon Dots and a pH-Responsive Tertiary Amine Cationic Surfactant

We studied the co-assembly of an oppositely changed binary mixture of selenium-doped carbon quantum dots (Se-CQDs) and N,N-dimethyl octylamide-propyl tertiary amine (DOAPA) through turbidity, ζ potential measurement, and cryogenic transmission electron microscopy (cryo-TEM) with the aim of fabricating supramolecular assemblies with multiple dimensions and novel morphologies. The Se-CQD/DOAPA binary mixture exhibited abundant phase behavior, in which an isotropic phase (I₁) was first observed, followed by turbidity (T), precipitation (P), and a second isotropic phase (I₂), as the DOAPA concentration increased. Then we focused on investigating the morphologies of samples. In cryo-TEM observations, spherical aggregates were observed in all phase sequences, whereas the aggregates have different ζ potentials and sizes. In the I₂ phase, interesting nanocapsule-like aggregates and spindle-like aggregates can be identified in addition to spherical aggregates. In combination with the rheological behaviors of the I₂ phase solution and the detailed structure of the aggregates from enlarged cryo-TEM images, it is possible that the Se-CQDs and DOAPA co-assemble with novel network-like building blocks. The turbid solutions were found to be responsive to pH in phase P, and spherical aggregates were obtained at pH 6.5 but turned into vesicles when the pH reached 5.0. On the basis of these findings, CQDs and surfactants can be good structural building blocks for supramolecular structures, and the diverse morphologies of aggregates offer the prospect of multiple applications in the future.

The responsive behaviors of bilayer membrane under uniaxial mechanical probe

In experiments, atomic force microscopy technology was used to measure the modulus of the membrane. However, these studies mainly focus on the linear responsive behavior. In the present work, a theoretical study is performed to show the nonlinear responsive behavior, which includes the stretching induced structural transitions. It demonstrates that the structural transition of the bilayer membrane takes place during the stretching process of the mechanical probe. A vertical cylindrical micelle can be obtained by stretching the membrane under deep compression conditions, and the cylindrical micelle can grow continuously along the axial direction. Moreover, under shallow compression conditions, the probe pulls a spherical micelle from the membrane, and then, the membrane returns to flatness. A comprehensive study is performed to show the mechanism of the responsive behaviors of the structural transition during the compression and stretching processes. When the probe acts on the B-rich layer, it is more likely to pull out a regular micelle. However, when the probe acts on the bottom A-rich layer, complex vesicles are more likely to be pulled out from the bilayer membrane. This study provides a comprehensive diagram of the mechanical responsive behavior of the membrane, which would be a guide for an experiment of biomembranes and the design of new self-assembled structures.

Temperature-regulated protein adsorption on a PNIPAm layer

In immunosensors, antibody orientation is a key factor that determines the sensitivity of a device. To date much effort has been devoted to exploring strategies for the direct control of the orientation of antibodies immobilized on a bioactive surface, but less attention has been paid to controlling the orientation of intermediate proteins (though usually used when immobilizing antibodies), which may greatly limit the sensitivity of immunological activities. Therefore, it is of great significance to seek novel methods for controlling protein orientation. Here, we design a new strategy for controlling protein orientation. The main idea is to bind proteins to a ligand-functionalized poly(N-isopropylacrylamide) (PNIPAm) layer, and then the protein orientation can be mediated by environmental temperature. The theory predicts that the protein orientation can show unexpected triple-thermo-responsive behavior. Based on the fraction of ligand adsorbed by the protein, the reponsive behavior can be either complete adsorption or partial adsorption, which is determind by the polymer's surface coverage and the protein's properties. We expect that the present strategy can enrich the methods for controlling intermediate protein orientation and can guide the design of novel immunosensors with superior sensitivity.

Designing new strategy for controlling DNA orientation in biosensors

Orientation controllable DNA biosensors hold great application potentials in recognizing small molecules and detecting DNA hybridization. Though electric field is usually used to control the orientation of DNA molecules, it is also of great importance and significance to seek for other triggered methods to control the DNA orientation. Here, we design a new strategy for controlling DNA orientation in biosensors. The main idea is to copolymerize DNA molecules with responsive polymers that can show swelling/deswelling transitions due to the change of external stimuli, and then graft the copolymers onto an uncharged substrate. In order to highlight the responsive characteristic, we take thermo-responsive polymers as an example, and reveal multi-responsive behavior and the underlying molecular mechanism of the DNA orientation by combining dissipative particle dynamics simulation and molecular theory. Since swelling/deswelling transitions can be also realized by using other stimuli-responsive (like pH and light) polymers, the present strategy is universal, which can enrich the methods of controlling DNA orientation and may assist with the design of the next generation of biosensors.

Selective ion-permeable membranes by insertion of biopores into polymersomes

Biomimetic polymersomes with an ion-selective membrane were successfully engineered by insertion of ionomycin, without affecting their final architecture.