Spherical Polyelectrolyte Brushes Research Articles

CO2-Responsive Spherical Polyelectrolyte Brush with Multi-Stimulation for Reversible Protein Immobilization and Release

Multi-responsive materials have received extensive interest in many areas due to their smart characteristics. This paper presents rationally designed multi-responsive spherical polyelectolyte brushes composed of a solid polystyrene (PS) core and a poly (2-(dimethylamino) ethyl methacrylate) (PDMAEMA) shell synthesized by photoemulsion polymerization. Based on dynamic light scattering, Zeta potential, turbidity measurements, isothermal titration calorimetry, and UV-vis spectroscopy, PS-PDMAEMA works as a good potential adsorbent for bovine serum albumin (BSA) for which the maximum adsorption capability could reach up to 5190mg g−1. Moreover, the immobilization and release of protein on the polymer brush could be adjusted with different triggers, including the pH, ionic strength, and temperature. Furthermore, the green gas triggers, CO2 and N2, could be employed in the BSA@ PS-PDMAEMA system by easily bubbling over many cycles without any salt accumulation. The main reason for the observed actions is the brushes could be switched alternately between extended and collapsed states with different stimulations. Upon comparing the circular dichroism spectra of original and released BSA after many cycles of adsorption and release, it’s clear that the protein can retain its initial biological activity after release from the PS-PDMAEMA. This work provides an effective and green way to immobilize and release proteins in biotechnology.

Selective Protein Separation Based on Charge Anisotropy by Spherical Polyelectrolyte Brushes.

Protein purification is of vital importance in the food industry, drug discovery, and other related fields. Among many separation methods, polyelectrolyte (PE)-based phase separation was developed and recognized as a low-cost purification technique. In this work, spherical polyelectrolyte brushes (SPBs) with a high specific surface area were utilized to study the protein accessibility and selective protein binding on highly charged nanoparticles (NPs) as well as the selective phase separation of proteins. The correlation between charge anisotropy, protein binding, and phase separation was investigated on various protein systems including those proteins with similar isoelectric points (pI) such as bovine serum albumin (BSA) and β-lactoglobulin (BLG), proteins with similar molecular weights such as BSA and hemoglobin (HB), and even protein variants (BLG-A and -B) with a tiny difference of amino acids. The nonspecific electrostatic interaction studied by turbidimetric titrations and isothermal calorimetry titration (ITC) indicates a specific binding between proteins and SPBs arising from the charge anisotropy of proteins. An optimized output based on selective protein binding on SPBs could be correlated for efficient protein separation through tuning external conditions including pH and ionic strength. These findings, therefore, proved that phase separation based on selective protein adsorption by SPBs was an efficient alternative for protein separation compared with the traditional practice.

Dual-emission fluorescent probe templated by spherical polyelectrolyte brush for ratiometric detection of copper ions

Dual-emission fluorescent probe templated by spherical polyelectrolyte brush for ratiometric detection of copper ions

Spherical Polyelectrolyte Brushes as Templates to Prepare Hollow Silica Spheres Encapsulating Metal Nanoparticles.

Integrating hollow silica spheres with metal nanoparticles to fabricate multifunctional hybrid materials has attracted increasing attention in catalysis, detection, and drug delivery. Here, we report a simple and general method to prepare hollow silica spheres encapsulating silver nanoparticles (Ag@SiO2) based on spherical polyelectrolyte brushes (SPB), which consist of a polystyrene core and densely grafted poly (acrylic acid) (PAA) chains. SPB were firstly used as nanoreactors to generate silver nanoparticles in situ and then used as sacrificial templates to prepare hybrid hollow silica spheres. The resulted Ag@SiO2 composites exhibit high catalytic activity and good reusability for the reduction of 4-nitrophenol to 4-aminophenol by NaBH4. More importantly, this developed approach can be extended to the encapsulation of other metal nanoparticles such as gold nanoparticles into the hollow silica spheres. This work demonstrates that SPB are promising candidates for the preparation of hollow spheres with encapsulated metal nanoparticles and the resulted hybrid spheres show great potential applications in catalysis.

Application of spherical polyelectrolyte brushes microparticle system in flocculation and retention.

In this paper, a microparticle system consisting of cationic polyacrylamide (CPAM) and anionic spherical polyelectrolyte brushes (ASPB) is proposed to improve the retention of pulp suspension containing bleached reed kraft pulp and precipitated calcium carbonate (PCC). We first describe the preparation of ASPB. The ASPB, consisting of a carbon sphere (CS) core and a shell of sodium polystyrene sulfonate (PSSNa) brushes, was synthesized by surface-initiated polymerization. The structure and morphology of ASPB were characterized by Fourier-transform infrared spectrometry (FTIR), field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). Then, flocculation and retention of pulp suspension by a CPAM/ASPB dual-component system were examined. Our results indicate that more highly effective flocculation and higher retention efficiency could be achieved simultaneously by a CPAM/ASPB dual-component system when compared to the conventional microparticle system. Bridging flocculation and electrostatic attraction might be the main flocculation mechanism for CPAM/ASPB systems.

Interaction among Spherical Polyelectrolyte Brushes in Concentrated Aqueous Solution

Interaction among concentrated spherical polyelectrolyte brushes (SPB) dispersions in water was systematically investigated by means of small-angle X-ray scattering (SAXS), wide-angle X-ray scattering (WAXS), and rheological methods. SPB consist of a core of polystyrene (PS) and a poly(acrylic acid) (PAA) brush shell. The "polyelectrolyte peak" appeared in SAXS spectra and was observed in WAXS curves for the first time. The size of the polyelectrolyte peak and the rheological properties of SPB were found to be strongly effected by SPB concentration, pH, and ionic strength. Combined with SAXS, WAXS, and rheological results, it is confirmed that the polyelectrolyte peak is originated from local ordered structures of polyelectrolyte chains bridged by counterions in the overlapping area among SPB driven by electrostatic interactions.

Preparation of hollow silica nanoparticles using cationic spherical polyelectrolyte brushes as catalytic template

This paper presents a facile procedure to fabricate uniform-sized hollow silica nanoparticles (SNP) under a mild condition by using cationic spherical polyelectrolyte brushes (SPB) with a polystyrene (PS) core and densely grafted poly(2-aminoethyl methacrylate hydrochloride) (PAEMH) brush shell as a catalytic template. By changing the brush layer thickness of SPB, hollow SNP with different silica shell thickness could be easily obtained. This method provides a new way for the preparation of hollow SNP without additional catalyst. The obtained hollow SNP exhibited a high-drug encapsulation efficiency (80%) for doxorubicin hydrochloride (DOX), should be of significance in the fields of drug delivery, cancer therapy, and bioimaging.

Novel Dopant for Conductive Polymers: Spherical Polyelectrolyte Brushes

Conductive polymers with special structure and excellent physical and chemical properties, have become a research focus in materials science since the first discovery in 1977. While a growing body of work in recent years has concentrated on the improvement of the electrical conductivity of conductive polymers by using doping technique. The spherical polyelectrolyte brushes (SPB) consisting of polyelectrolyte chains grafted densely to the surface of the core particles, have shown great promise of novel dopant for conductive polymers due to its spherical structure, high charge density and high grafting density. After summarizing the researches of the general dopant for conductive polymers, this review mainly emphasizes on the preparation, doping mechanism and advance prospect of conductive polymers doped with spherical polyelectrolyte brushes.

Mechanism of the Oxidation of 3,3',5,5'-Tetramethylbenzidine Catalyzed by Peroxidase-Like Pt Nanoparticles Immobilized in Spherical Polyelectrolyte Brushes: A Kinetic Study.

Experimental and kinetic modelling studies are presented to investigate the mechanism of 3,3',5,5'-tetramethylbenzidine (TMB) oxidation by hydrogen peroxide (H2 O2 ) catalyzed by peroxidase-like Pt nanoparticles immobilized in spherical polyelectrolyte brushes (SPB-Pt). Due to the high stability of SPB-Pt colloidal, this reaction can be monitored precisely in situ by UV/VIS spectroscopy. The time-dependent concentration of the blue-colored oxidation product of TMB expressed by different kinetic models was used to simulate the experimental data by a genetic fitting algorithm. After falsifying the models with abundant experimental data, it is found that both H2 O2 and TMB adsorb on the surface of Pt nanoparticles to react, indicating that the reaction follows the Langmuir-Hinshelwood mechanism. A true rate constant k, characterizing the rate-determining step of the reaction and which is independent on the amount of catalysts used, is obtained for the first time. Furthermore, it is found that the product adsorbes strongly on the surface of nanoparticles, thus inhibiting the reaction. The entire analysis provides a new perspective to study the catalytic mechanism and evaluate the catalytic activity of the peroxidase-like nanoparticles.

Thermodynamic Analysis of the Uptake of a Protein in a Spherical Polyelectrolyte Brush.

A thermodynamic study of the adsorption of Human Serum Albumin (HSA) onto spherical polyelectrolyte brushes (SPBs) by isothermal titration calorimetry (ITC) is presented. The SPBs are composed of a solid polystyrene core bearing long chains of poly(acrylic acid). ITC measurements done at different temperatures and ionic strengths lead to a full set of thermodynamicbinding constants together with the enthalpies and entropies of binding. The adsorption of HSA onto SPBs is described with a two-step model. The free energy of binding ΔGb depends only weakly on temperature because of a marked compensation of enthalpy by entropy. Studies of the adsorbed HSA by Fourier transform infrared spectroscopy (FT-IR) demonstrate no significant disturbance in the secondary structure of the protein. The quantitative analysis demonstrates that counterion release is the major driving force for adsorption in a process where proteins become multivalent counterions of the polyelectrolyte chains upon adsorption. A comparison with the analysis of other sets of data related to the binding of HSA to polyelectrolytes demonstrates that the cancellation of enthalpy and entropy is a general phenomenon that always accompanies the binding of proteins to polyelectrolytes dominated by counterion release.

Nanoparticle Capture by Spherical Polyelectrolyte Brushes and Its Grading Separation Assisted by Compressed CO2

Spherical polyelectrolyte brushes (SPBs) could capture some charged nanoparticles, due to the Donnan effect, that have been verified as promising carriers for nanoparticles. However, how to separate the nanoparticles and recycle the expensive polymer brushes is still an obstacle in industrial applications. Compressed carbon dioxide (CO2) could work as a “pressure trigger” to regulate the properties of mixed solvents to accomplish the separation process because of its antisolvent effect. Herein, Ag nanoparticles were in situ synthesized in the spherical poly(acrylic acid) brushes with a polystyrene core (PS–PAA) and recovered easily by a suitable pressure of compressed CO2, while PS–PAA still remained in solution. After temperature quenching and depressurization, Ag nanoparticles could be collected with nearly 100% recovery ratio and narrow distribution. Moreover, further increased pressure could induce the aggregation of PS–PAA later, which could be employed to recycle the polymer brushes without any stru...

Enrichment and distribution of counterions in spherical polyelectrolyte brushes probed by SAXS

ABSTRACTThe spatial correlation of counterions [Li+, Na+, Rb+, Cs+, NH4+, (CH3)4N+] with spherical polyelectrolyte brushes (SPBs), which consist of a PS core and chemically grafted PSS chains, was comprehensively studied through a combination of SAXS, DLS, and Zeta potential. Results show that the SAXS intensity profiles of the brush appears to be “insensitive” to the concentration of Na+. By contrast, introducing salt ions with a density lower than sodium [NH4+, (CH3)4N+ and Li+] into the brush layer will cause a decrease in the scattering intensity while introducing those with a higher density than sodium (Rb+ and Cs+) will cause the opposite result. As verified by the combined results of SAXS, DLS, and Zeta potential, the collapse of the brush and the enrichment of the counterions in the brush layer occur simultaneously. It was further demonstrated that the concentration of counterions enriched in the innermost layer of the brush shell can be enhanced up to hundreds of times compared with the bulk concentration, and the counterion distribution in SPB shell follows a radial attenuation distribution. SAXS is confirmed to be powerful in probing the enrichment and distribution of counterions within SPB. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 738–747

Generation of MnO2 nanozyme in spherical polyelectrolyte brush for colorimetric detection of glutathione

Novel MnO2 nanozymes were prepared as nanosheets in situ using spherical poly[(2-methacryloyloxyethyl) trimethyl ammonium chloride] (PDMC) brushes (SPB) as nanoreactors. The prepared MnO2 nanozymes were immobilized in SPB (SPB-MnO2) showing high stability and excellent oxidase-like property which could oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) into oxidized TMB (oxTMB), accompanied by the change of absorption at 653 nm. The MnO2 nanosheets could be decomposed by trace amount of glutathione (GSH) under acidic environment as validated by small angle X-ray scattering (SAXS). The SPB-MnO2/TMB system, with a detection limit of 450 nM, should be an ideal candidate for colorimetric detection of GSH. This work opens a new way to prepare highly stable nanozymes for the detection of GSH.

Nanostructured switchable pH-responsive membranes prepared via spherical polyelectrolyte brushes

A nano-porous and switchable pH-responsive polymeric membrane was fabricated through filtration technique with the assist of metal hydroxide nanostrands as template. A common used spherical polyelectrolyte brush (SPB), PAA@PS (poly (acrylic acid)) brushes grafted on polystyrene nanospheres, employed in this work as polymeric membrane. It features tunable pore size on line by shrinkage or stretching of PAA brushes under different pH value or ionic strength. Furthermore, both the length of PAA chains and the dimension of PS cores could tailor the pore size of the membrane effectively. These properties of PAA@PS membrane could separate nanoparticles within 10 nm with precise size-selective permeation. Meanwhile, since the membrane was endowed negative charge by PAA brushes, the membrane could adsorb and separate positive charge nanoparticles including dyes though the mixture solution effectively. Herein, this stimuli-responsive membrane is promising in the separation of ultrafine nanoparticles with precise size and charge selectivity.

球型聚电解质刷掺杂导电高分子研究进展

球型聚电解质刷掺杂导电高分子研究进展

Morphological Response of a Spherical Polyelectrolyte Brush to Solvent Quality and Electrostatic Interaction Strength

We study surface morphologies of a spherical polyelectrolyte brush in the presence of trivalent counterions using molecular dynamics simulations. Solvent quality and electrostatic interaction strength are varied to generate a series of structures. Through a careful analysis on snapshots of morphologies, shape factor of tethered chains, and monomer–monomer pair correlation function we find a nonmonotonic dependence of surface morphology on electrostatic strength, which represents clearly the electrostatic correlation effect mediated by the multivalent counterions. Due to the very importance of counterions, we further study the correlation effect by classifying counterions into four states, calculating the monomer–counterion pair correlation function and diffusion coefficient of counterions. Our simulation results clearly demonstrate that ordered patterns can be induced by the electrostatic correlation effect in the presence of trivalent counterions, which is absent in the system with monovalent ions. Also,...

Hollow silica–polyelectrolyte composite nanoparticles for controlled drug delivery

The stimulus-responsive drug delivery system has attracted increasing attention due to its ability to enhance therapeutic efficacy and reduce side effects. Herein, a pH and glutathione (GSH) dually responsive drug carrier, hollow silica–-polyelectrolyte composite nanoparticle, was successfully prepared by using a template of spherical polyelectrolyte brush (SPB) which consists of a polystyrene (PS) core and a densely grafted linear poly(acrylic acid) (PAA) shell. The existence of PAA chains and introduction of disulfide bonds in silica framework endow the composite nanoparticles with pH and GSH dually responsive properties which were confirmed by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS). With doxorubicin hydrochloride (DOX) as the model drug, the loading content and encapsulation efficiency could reach up to 43% and 96%, respectively. The drug release behavior was investigated under various environments, showing that the drug release rate increased with the decrease in pH value and the increase in GSH concentration. The prepared hollow SiO2–PAA composite nanoparticles possess a great potential as carriers for controlled drug delivery.

Facile Fluorescence "Turn on" Sensing of Lead Ions in Water via Carbon Nanodots Immobilized in Spherical Polyelectrolyte Brushes.

Heavy metal detection has become very important for the protection of water resource. In this work, a novel controllable probe is presented for the sensitive detection of Pb2+ in aqueous solutions. The probe was synthesized via the immobilization of surface functionalized carbon dots (named as CAEA-Hs) into the shell of the spherical polyelectrolyte brushes (SPB). The fluorescence of CAEA-H was firstly “turned off” via electrostatic interaction induced quenching. Based on the aggregation induced emission enhancement (AIEE), the fluorescence of the immobilized CAEA-H could be specifically turned on via the aggregation of the SPB particles. This fluorescence “turn on” sensor could selectively detect Pb2+ among five different metal ions with a relatively wide detecting range (0–1.67 mM) and good linear relationship (R2 = 0.9958). Moreover, the aggregating behavior and nano-structure of CAEA-H loaded SPB have been systematically analyzed via small angle X-ray scattering, turbidity titration, and Zeta-potential measurement. Based on a series of control experiments, we finally gain an insight into the sensing mechanism of this novel sensing probe. This contributed a proof of concept demonstration that sensitive and selective chemical detection can be achieved via a C-dot/SPB synergistic platform.

Controllable immobilization of proteins in quenched spherical polyelectrolyte brushes as observed by fluorescence spectroscopy and small angle X‐ray scattering

ABSTRACTThe immobilization of lysozymes (pI = 11) onto anionic spherical polyelectrolyte brushes (SPB) which consist of a solid polystyrene core and a densely grafted poly(styrene sulfonate) (PSS) shell was systematically studied by fluorescence spectroscopy and small angle X‐ray scattering. Results show that the capture of lysozyme by PSS brush is a dynamic process, which involves a quick agglomeration stage and a slow rearrangement one. And lysozyme inclines to immobilize in the inner layer of the brush, and saturation of lysozyme adsorption onto the SPB is gradually reached as the protein concentration increases, proceeding from the inside to the outside of the brush layers. As increasing the pH and ionic strength, the lysozyme previously adsorbed will be partially released and migrate from the inner to the outer layer of SPB. Last competitive adsorption tests between lysozyme and BSA or β‐glucosidase were performed, indicating that besides electrostatic interaction counterion release force also plays an important role in protein adsorption. SPB was proved to be ideal candidate for controllable immobilization of protein, which can be extended into various applications, such as drug delivery and protein separation. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018, 56, 1577–1588

Brownian Dynamics Simulations of Rigid Polyelectrolyte Chains Grafting to Spherical Colloid

Brownian dynamics simulations are employed to explore the effects of chain stiffness and trivalent salt concentration on the conformational behavior of spherical polyelectrolyte brush. The rigid brush adopts bundle-like morphology at a wide range of trivalent salt concentration. The number variation of bundles pinned on the colloid surface shows a non-monotonic profile as a function of the chain stiffness. The radial distributions of monomers and ions and the charge ratio between condensed ions and monomers are calculated. The charge inversion is observed for the high salt concentration regardless of chain rigidity. Furthermore, the pair correlation functions of monomer-monomer and monomer-salt cation are used to elucidate the aggregated mechanism of the bundle-like structure.