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The structure of unconventional complex coacervates, such as polymer–nonpolymer complex coacervates, remains less investigated than that of the conventional coacervates formed between oppositely ch...

The phase behavior and chain conformational structure of biphasic polyzwitterion–polyelectrolyte coacervates in salted aqueous solution are investigated with a model weak cationic polyelectrolyte, poly(2-vinylpyridine) (P2VP), whose charge fraction can be effectively tuned by pH. It is observed that increasing the pH leads to the increase of the yielding volume fraction and the water content of dense coacervates formed between net neutral polybetaine and cationic P2VP in contrast to the decrease of critical salt concentration for the onset of coacervation, where the P2VP charge fraction is reduced correspondingly. Surprisingly, a single-molecule fluorescence spectroscopic study suggests that P2VP chains upon coacervation seem to adopt a swollen or an even more expanded conformational structure at higher pH. As the hydrophobicity of P2VP chains is accompanied by a reduced charge fraction by increasing the pH, a strong pH-dependent phase and conformational behaviors suggest the shift of entropic and enthalpic contribution to the underlying thermodynamic energy landscape and chain structural dynamics of polyelectrolyte coacervation involving weak polyelectrolytes in aqueous solution.

Effluent wastewater containing dyes from textile, paint, and various other industrial wastes have long posed environmental damage. Functional nanomaterials offer new opportunities to treat these effluent wastes in an unprecedentedly rapid and efficient fashion due to their large surface area-to-volume ratio. In this work, we explore a new approach of wastewater treatment using macroionic coacervate complexes formed with zwitterionic polyampholytes and anionic inorganic polyoxometalate (POM) nanoclusters to extract methylene blue (MB) dye as well as other cationic industrial dyes from model wastewater. Biphasic organic-inorganic macroion complexes are designed to produce a small volume of coacervate adsorbents of high density and viscoelasticity, in contrast to a large volume of supernatant solution for rapid and efficient dye removal. The efficiency of coacervate extraction is characterized by the adsorption isotherm and maximum MB uptake capacity against the concentrations of polyampholyte, POM, and LiCl salt using UV-vis spectrophotometry to optimize the coacervate formation conditions. Our macroionic coacervate complexes could reach nearly 99% removal efficiency for the model wastewater samples of varied MB concentration in

The mitochondria have emerged as a novel target for cancer chemotherapy primarily due to their central roles in energy metabolism and apoptosis regulation. Here, we report a new molecular approach to achieve high levels of tumor- and mitochondria-selective deliveries of the anticancer drug doxorubicin. This is achieved by molecular engineering, which functionalizes doxorubicin with a hydrophobic lipid tail conjugated by a solubility-promoting poly(ethylene glycol) polymer (amphiphilic doxorubicin or amph-DOX). In vivo, the amphiphile conjugated to doxorubicin exhibits a dual function: (i) it binds avidly to serum albumin and hijacks albumin's circulating and transporting pathways, resulting in prolonged circulation in blood, increased accumulation in tumor, and reduced exposure to the heart; (ii) it also redirects doxorubicin to mitochondria by altering the drug molecule's intracellular sorting and transportation routes. Efficient mitochondrial targeting with amph-DOX causes a significant increase of reactive oxygen species levels in tumor cells, resulting in markedly improved antitumor efficacy than the unmodified doxorubicin. Amphiphilic modification provides a simple strategy to simultaneously increase the efficacy and safety of doxorubicin in cancer chemotherapy.

Macromolecular coacervate complexation via spontaneous liquid–liquid separation has become a facile supramolecular assembly approach to produce new functional nanomaterials in aqueous media. Distin...

Multiblock poly(arylene ether sulfone) copolymers are attractive for polyelectrolyte membrane fuel cell applications due to their reportedly improved proton conductivity under partially hydrated conditions and better mechanical/thermal stability compared to Nafion. However, the long hydrophilic sequences required to achieve high conductivity usually lead to excessive water uptake and swelling, which degrade membrane dimensional stability. Herein, we report a fundamentally new approach to address this grand challenge by introducing shape-persistent triptycene units into the hydrophobic sequences of multiblock copolymers, which induce strong supramolecular chain-threading and interlocking interactions that effectively suppress water swelling. Consequently, unlike previously reported multiblock copolymer systems, the water swelling of the triptycene-containing multiblock copolymers did not increase proportionally with water uptake. This combination of high water uptake and low swelling behavior of these copolymers resulted in excellent proton conductivity and membrane dimensional stability under fully hydrated conditions. In particular, the triptycene-containing multiblock copolymer film with the longest hydrophilic block length (i.e., BPSH100-TRP0-15k-15k) had a water uptake of 105%, an excellent proton conductivity of 0.150 S/cm, and a volume swelling ratio of just 29% (more than 42% reduction compared to Nafion 212).

Coacervate complexes that are liquid-liquid separated complex materials are often formed by stoichiometrically mixing oppositely charged polyelectrolytes in salted aqueous solution. Entropy-driven ion pairing, resulting from the release of counterions near polyelectrolytes, has been identified as the primary driving force for coacervate formation between oppositely charged polyelectrolytes, including proteins and DNA, in aqueous solution. In this work we have examined the complexation between net neutral zwitterionic poly(sulfobetaine methacrylate) (PSBMA) and inorganic polyoxometalate (POM) polyanions in LiCl aqueous solutions. Biphasic liquid-like coacervate complexes can be formed over a much broader range of POM-to-PSBMA molar ratio and LiCl concentration than that for conventional polyelectrolyte coacervate complexation. Composition analysis of the dried supernatant and dense coacervate has confirmed that both PSBMA and POM macroions are primarily present in the dense coacervate as the macroion-rich phase in contrast to the presence of LiCl solely in the supernatant as the macroion-poor phase. The increase of net charge negativity of PSBMA and supernatant conductivity suggests stronger binding of PSBMA with POM anions than monovalent Cl-, resulting in the release of bound Cl- anions to the aqueous solution for the formation of PSBMA-POM coacervates in LiCl solution. All experimental evidence has demonstrated the generality of ion-pairing induced coacervate complexation with net neutral zwitterionic polymers and multivalent inorganic nanomaterials. The complexation between organic and inorganic macroions could give insights into many supramolecular assembly processes in nature and also lead to a new paradigm in developing hybrid macroionic materials for emerging applications from green catalysis to nanomedicine.

A method was developed to synthesize molecular brushes with polymethacrylate backbone and ultrahigh density of grafted side chains (SCs), i.e., 1.34 SCs per backbone carbon atom, using accelerated copper-catalyzed azide–alkyne cycloaddition (CuAAC) grafting-onto strategy. This acceleration effect that benefits from the complexation of triazole with Cu was first confirmed in two model CuAAC reactions of (a) 1:1 molar ratio of a diazide compound and an alkynyl-terminated poly(ethylene oxide) (ay-PEO18 with average degree of polymerization DP = 18) and (b) 1:1 molar ratio of a dialkyne compound and an azido-terminated N3-PEO18. It was found that both model reactions produced ditriazoles as major products, although the former reaction exhibited a higher yield of PEO–PEO dimers, demonstrating better CuAAC acceleration effect. Following this principle, polymethacrylate backbones with multiazido dangling groups were subsequently used for grafting-onto reaction with ay-SCs to prepare an array of molecular brushes...

Ionic liquids (ILs) have been widely considered and used as "green solvents" for more than two decades. However, their ecotoxicity results have contradicted this view, as ILs, particularly hydrophobic ones, are reported to exhibit high toxicity. Yet the origin of their toxicology remains unclear. In this work, we have investigated the interaction of amphiphilic ILs with a lipid bilayer as a model cell membrane to understand their cytotoxicity at a molecular level. By employing fluorescence imaging and light and X-ray scattering techniques, we have found that amphiphilic ILs could disrupt the lipid bilayer by IL insertion, end-capping the hydrophobic edge of the lipid bilayer, and eventually disintegrating the lipid bilayer at high IL concentration. The insertion of ILs to cause the swelling of the lipid bilayer shows strong dependence on the hydrophobicity of IL cationic alky chain and anions and is strongly correlated with the reported IL cytotoxicity.

The conformational structure of a polyelectrolyte chain in dilute aqueous solution is strongly coupled with its surrounding electrostatic environment. With the introduction of branched topology, the distribution of counterions in the vicinity of a polyelectrolyte chain becomes highly inhomogeneous, giving rise to complex structures of branched polyelectrolytes in dilute aqueous solution. To directly probe the local electrostatic conditions near a branched polyelectrolyte in aqueous solutions, star-shaped poly(2-vinylpyridine) (P2VP) polymers with precise labeling of one single fluorophore at different locations, for example, the star center or the terminal group of one arm, were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization of vinyl-terminated P2VP macromonomers. Using fluorescence correlation spectroscopy (FCS) combined with photon counting histogram (PCH) analysis, the conformational structures and local electric potential of P2VP star polyelectrolytes were investigated in dilute aqueous solutions of varied pH at a single molecule level. Despite the same hydrodynamic radius of P2VP stars, pH-sensitive fluorophores labeled at different locations sensitively differentiated the higher electric potential at the star center from the lower electric potential at the periphery in dilute aqueous solutions.

Adding ionic species can critically affect the structure of weak polyelectrolyte (PE) chains, whose charge density in aqueous solution can be greatly regulated by bathing solution conditions such as pH and added ions. Distinct from simple ions that can be treated as point charges, multivalent macroions of finite size, including many charged nanoparticles and biopolymers, could show strong electrostatic coupling with PEs and effectively modify the conformation and assembly of PEs in aqueous solution. In this work, we have compared the effects of hydrophilic multivalent macroion of finite size and simple divalent ion on the conformational transition of a model weak polybase, poly(2-vinylpyridine) (P2VP), in dilute aqueous solution. By using fluorescence correlation spectroscopy combined with photon counting histogram analysis, we have examined the swollen-to-collapsed conformational transition and local electric potential of a P2VP chain in ionic aqueous solution at a single-molecule level. Adding inorganic polytungstate ([W

Polymersomes are self-assembled vesicles of amphiphilic block copolymers and have been explored for wide applications from drug delivery to micro/nanoreactors. As polymersomes are soft and highly deformable, their shape instability due to osmolarity difference across polymer membranes and low elasticity could conversely limit their practical use. Instead of selecting particular polymer chemical reactions to enhance the mechanical properties, we have employed inorganic polyoxometalate (POM) clusters as simple physical cross-linkers to control the shape and mechanical stability of polymersomes in aqueous suspensions. Robust spherical shape with enhanced elastic and bending moduli of POM-dressed poly(ethylene oxide) (PEO) based polymersomes is achieved. We have accounted for the hydrogen bonding between POM and PEO blocks for the adsorption and stabilization of POMS on polymersomes, whose interaction strength could also be tuned by mixing solvents of hydrogen bond donors or receptors with water. The stimuli-responsive properties of POMs are introduced in POM-dressed polymersomes upon the interaction of POMs with PEO blocks in aqueous media. As POM can be used as nanomedicines, catalysts, and other functional nanomaterials, POM-dressed polymersomes with significant shape and mechanical reinforcement could broaden the applications of PEO-based polymersomes and other PEO-tethered nanocolloids.

The interaction of nanoparticles with cell membranes is critical to understand and control the structural change and molecular transport of cell membranes for medicines and medical diagnostics, in which hydrophobic interaction is often involved. We examine the specific ion effect on the interaction of semihydrophobic nanoparticle with zwitterionic phospholipid bilayer in aqueous media added with different types of salts. Specifically, we compare the effect of different anions or cations on the adsorption of carboxyl-functionalized polystyrene nanoparticle on supported lipid bilayer and its induced bilayer disruption. By adding different anions at the same ionic concentration to the nanoparticle-lipid bilayer interface, we observe that the growth rate of nanoparticle-induced lipid-poor regions follows the exact Hofmeister anion order of CH3COO(-) > Cl(-) > NO3(-) ≫ SCN(-), suggesting the regulated hydrophobic interaction by anions. In contrast, the specific cation effect on nanoparticle-induced disruption rate of lipid bilayer does not follow the Hofmeister cation order and instead exhibits a trend of Cs(+) ∼ Rb(+) > Na(+) ≫ N(CH3)4(+). It is suggested that the effect of specific ions can be exploited as a simple and efficient approach to modify the nanoparticles-biomembrane interactions with the implication from drug delivery to nontoxic nanomaterial design.

Membranes derived from self-assembled block polymers have shown promise as highly selective and highly permeable filters, but the complex synthetic routes and limited pore functionalities of existing systems need to be improved if these materials are to serve as a platform for the next generation of nanostructured membranes. Here, the facile synthesis of a polyisoprene- b -polystyrene- b -poly( N,N -dimethylacrylamide) (PI–PS–PDMA) triblock polymer using a controlled reversible addition-fragmentation chain transfer (RAFT) polymerization mechanism is reported. This material is then processed into a membrane using a self-assembly and non-solvent induced phase separation (SNIPS) technique, which creates an asymmetric, porous structure consisting of a selective layer that contains a high density of PDMA-lined pores (9.4×10 13 pores m −2 ) with an average diameter of 8.1 nm, as determined using solute rejection tests. Solvent flow experiments demonstrate that the PI–PS–PDMA membrane has a pH-independent permeability of 6 L m −2 h −1 bar −1 . The PDMA moiety lining the pore walls is converted, through simple hydrolysis in the solid state, to yield a poly(acrylic acid)-lined (PAA-lined) structure. The permeability of the PI–PS–PAA membrane is pH-dependent, and ranges from 0.6 L m −2 h −1 bar −1 for solutions with a pH greater than 4 to 16 L m −2 h −1 bar −1 for a solution at pH 1. Solute rejection tests demonstrated a pore size of 3.4 nm for the PI–PS–PAA membrane, which is the smallest pore size reported to date for membranes fabricated from self-assembled block polymers. The facile synthesis of the PI–PS–PDMA material, the scalable SNIPS membrane fabrication protocol, and the simple conversion chemistry of the pore functionality demonstrate that these nanostructured membranes are a strong platform for applications within the range of water purification, pharmaceutical separations, sensors, and drug delivery.

Polymer brushes have been widely used as functional surface coatings for broad applications including antifouling, energy storage, and lubrications. Understanding the molecule dynamics at polymer brush interfaces is important in unraveling the structure–property relationships in these materials and establishing a new materials design paradigm of novel functional polymer thin films with efficient interfacial transport. By applying modern fluorescence-based single-molecule spectroscopic and microscopic techniques, molecule dynamics at varied polymer brush interfaces have been experimentally investigated in recent years. New insights are given to the understandings of some unique and unusual materials properties of polymer brush thin films. This review summarizes some recent studies of molecular diffusion at polymer brush interfaces, highlights some new understandings of the interfacial properties of polymer brushes, and discusses future research opportunities in this field. © 2013 Wiley Periodicals, Inc. J. Polym. Sci. Part B: Polym. Phys. 2014, 52, 85–103

A facile and low-cost method is developed to functionalize engineering metal membrane supports, such as stainless steel (SS), with epoxy-containing polymer poly(glycidyl methacrylate) (PGMA) to produce a versatile and universal platform for subsequent surface modification. With a PGMA anchoring layer, we have demonstrated that hydrogel particles, such as polyacrylamide-co-poly(acrylic acid) (PAM-co-PAA), can be subsequently grafted to form functional polymer membranes for rapid and efficient oilewater separation. By contact angle and AFM measurement, we have confirmed that PAM-co-PAA hydrogel particle layer grafted on a PGMA-modified SS surface exhibits excellent selectivity as required for liquid eliquid separation, showing high affinity to water but not to oils as an ideal membrane for oilewater separation. To evaluate the separation efficiency, a simple flow-through device is employed to separate free-floating oil from water in the mixture of varied initial oil volume fraction and oil composition. Under substantially high pump flow rate up to 1.3 L/min, PAM-co-PAA hydrogel treated SS mesh can achieve excellent separation efficiency with less than 5% oil or water in the respective filtrate at the flux of as high as 540 m 3 /(m 2 $h) and retentate at the flux of 1.95 m 3 /(m 2 $h). This separation efficiency is better than, or comparable to, the maximal performance achieved using conventional gravity methods at much lower flow rate. Similar approach could be also adapted to graft superhydrophobic and superoleophilic polymer membranes with PGMA-treated engineering support to separate water from oil.

The structure of a hydrated poly(N-isopropylacrylamide) brush loaded with 5 vol % Isoniazid is studied as a function of temperature using neutron reflectometry (NR) and atomic force microscopy (AFM). NR measurements show that Isoniazid increases the thickness of the brush before, during and after the polymer collapse, and it is retained inside the brush at all measured temperatures. The Isoniazid concentration in the expanded brush is ~14% higher than in the bulk solution, and the concentration nearly doubles in the collapsed polymer, suggesting stronger binding between Isoniazid and the polymer compared to water, even at temperatures below the lower critical solution temperature (LCST) where the polymer is hydrophilic. Typically, additives that bind strongly to the polymer backbone and increase the hydrophilicity of the polymer will delay the onset of the LCST, which is suggested by AFM and NR measurements. The extent of small-molecule loading and distribution throughout a thermo-responsive polymer brush, such as pNIPAAm, will have important consequences for applications such as drug delivery and gating.

Ionic liquids (ILs) are salts that remain liquid down to low temperatures and sometimes well below room temperature. ILs have been called “green solvents” because of their extraordinarily low vapor pressure and excellent solvation power, but ecotoxicology studies have shown that some ILs exhibit greater toxicity than traditional solvents. A fundamental understanding of the molecular mechanisms responsible for IL toxicity remains elusive. Here we show that one mode of IL toxicity on unicellular organisms is driven by swelling of the cell membrane. Cytotoxicity assays, confocal laser scanning microscopy and molecular simulations reveal that IL cations nucleate morphological defects in the microbial cell membrane at concentrations near the half maximal effective concentration (EC50) of several microorganisms. Cytotoxicity increases with increasing alkyl chain length of the cation due to the ability of the longer alkyl chain to more easily embed in and ultimately disrupt, the cell membrane.

Giant vesicles of larger than 5 microm, which have been of intense interest for their potential as drug delivery vehicles and as a model system for cell membranes, can be rapidly formed from a spin-coated lipid thin film under an electric field. In this work, we explore the AC-field dependent electroformation of giant lipid vesicles in aqueous media over a wide range of AC-frequency from 1 Hz to 1 MHz and peak-to-peak field strength from 0.212 V/mm to 40 V/mm between two parallel conducting electrode surfaces. By using fluorescence microscopy, we perform in-situ microscopic observations of the structural evolution of giant vesicles formed from spin-coated lipid films under varied uniform AC-electric fields. The real-time observation of bilayer bulging from the lipid film, vesicle growth and fusing further examine the critical role of AC-induced electroosmotic flow of surrounding fluids for giant vesicle formation. A rich AC-frequency and field strength phase diagram is obtained experimentally to predict the AC-electroformation of giant unilamellar vesicles (GUVs) of l-alpha-phosphatidylcholine, where a weak dependence of vesicle size on AC-frequency is observed at low AC-field voltages, showing decreased vesicle size with a narrowed size distribution with increased AC-frequency. Formation of vesicles was shown to be constrained by an upper field strength of 10 V/mm and an upper AC-frequency of 10 kHz. Within these parameters, giant lipid vesicles were formed predominantly unilamellar and prevalent across the entire electrode surfaces.

The instability of supported poly(methyl methacrylate) (PMMA) thin films in water has been investigated. It is found that PMMA films partially detach from the solid substrate, resulting in the formation of bubbles under water. The process is reversible. Surface morphology analysis shows that the radius of curvature of the bubbles is dependent on the thickness of the PMMA films and is independent of the treatment of the films, such as the annealing temperature and the annealing time. Theoretical analysis based on a two-layer model (the swollen layer and the interior layer) shows that the partial swelling of PMMA in water is the physical origin of bubble formation.

The motion of DNA chain under electric field when it is in transient contact with the solid surfaces in aqueous solution was studied by single molecule fluorescence microscopy at the total internal reflection geometry (TIRFM). In situ observation discovered that single λ-DNA chains driven by electric field made transient contact with the solid surface and made hitting–sliding–leaving-like motion along the surface. By varying the surface chemistry, from the negative-charged silanol group-rich surface to positive-charged amino group-rich surface, as well as hydrophobic surfaces, the dependence of DNA mobility on the surface–DNA interaction was studied. The results show that a dependence of the mobility of DNA on the surface polarity with respect to DNA itself. The study on different surfaces rich of silanol, amide, amino, and methyl groups show a sequence of DNA mobility of silanol > amide > amino. The mobility of DNA on methyl terminated surface was found to be similar to that on amino surface. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 2541–2546, 2009

We report on studies of lipid transfer rates between different morphology nanoparticles and lipids with different length acyl chains. The lipid transfer rate of dimyristoylphosphatidylcholine (di-C14, DMPC) in discoidal "bicelles" (0.156 h(-1)) is 2 orders of magnitude greater than that of DMPC vesicles (ULVs) (1.1 × 10(-3) h(-1)). For both bicellar and ULV morphologies, increasing the acyl chain length by two carbons [going from di-C14 DMPC to di-C16, dipalmitoylphosphatidylcholine (DPPC)] causes lipid transfer rates to decrease by more than 2 orders of magnitude. Results from small angle neutron scattering (SANS), differential scanning calorimetry (DSC), and fluorescence correlation spectroscopy (FCS) are in good agreement. The present studies highlight the importance of lipid dynamic processes taking place in different morphology biomimetic membranes.

Particle-stabilized Pickering emulsions have shown unusual behaviours such as the formation of non-spherical droplets and the sudden halt of coalescence between individual droplets. Here we report another unusual behaviour of Pickering emulsions-the simultaneous coalescence of multiple droplets in a single event. Using latex particles, silica particles and carbon nanotubes as model stabilizers, we show that multi-body coalescence can occur in both water-in-oil and oil-in-water emulsions. The number of droplets involved in the nth coalscence event equals four times the corresponding number of the tetrahedral sequence in close packing. Furthermore, coalescence is promoted by repulsive latex and silica particles but inhibited by attractive carbon nanotubes. The revelation of multi-body coalescence is expected to help better understand Pickering emulsions in natural systems and improve their designs in engineering applications.

Water contaminated by oil and gas production poses challenges to the management of America's water resources. Here we report the design, fabrication, and laboratory evaluation of multi-walled carbon nanotubes decorated with superparamagnetic iron-oxide nanoparticles (SPIONs) for oil-water separation. As revealed by confocal laser-scanning fluorescence microscopy, the magnetic carbon nanotubes (MCNTs) remove oil droplets through a two-step mechanism, in which MCNTs are first dispersed at the oil-water interface and then drag the droplets with them out of water by a magnet. Measurements of removal efficiency with different initial oil concentration, MCNT dose, and mixing time show that kinetics and equilibrium of the separation process can be described by the Langmuir model. Separation capacity qt is a function of MCNT dose m, mixing time t, and residual oil concentration Ce at equilibrium: 1 q t = 1 q max 2 k w m ( 1 K C e + 1 ) 2 1 t + 1 q max ( 1 K C e + 1 ) where qmax, kw, and K are maximum separation capacity, wrapping rate constant, and equilibrium constant, respectively. Least-square regressions using experimental data estimate qmax = 6.6(±0.6) g-diesel g-MCNT−1, kw = 3.36(±0.03) L g-diesel−1 min−1, and K = 2.4(±0.2) L g-diesel−1. For used MCNTs, we further show that over 80% of the separation capacity can be restored by a 10 min wash with 1 mL ethanol for every 6 mg MCNTs. The separation by reusable MCNTs provides a promising alternative strategy for water treatment design complementary to existing ones such as coagulation, adsorption, filtration, and membrane processes.

Understanding the interaction between functional nanoparticles and cell membranes is critical to use nanomaterials for broad biomedical applications with minimal cytotoxicity. In this work, we have investigated the effect of adsorbed semihydrophobic nanoparticles (NPs) on the dynamics and morphology of model cell membranes. We have systematically varied the degree of surface hydrophobicity of carboxyl end-functionalized polystyrene NPs of varied size in buffer solutions with varied ionic strength. It is observed that semihydrophobic NPs can readily adsorb on neutral SLBs and drag lipids from SLBs to NP surfaces. Above a critical NP concentration, the disruption of SLBs is observed, accompanied with the formation and rapid growth of lipid-poor regions on NP-adsorbed SLBs. In the study of the effect of solution ionic strength on NP surface hydrophobic degree and the growth of lipid-poor regions, we have concluded that the hydrophobic interaction enhanced by screened electrostatic interaction underlies the envelopment of NPs by lipids that are attracted from SLBs to the surface of NPs or their aggregates. Hence, the formation and growth of lipid-poor regions, or vaguely referred as "pores" or "holes" in the literature, can be controlled by NP concentration, size, and surface hydrophobicity, which is critical to design functional nanomaterials for effective nanomedicine while minimizing possible cytotoxicity.

The time-dependent nucleation phase is critical to amyloid fibrillation and related to many pathologies, in which the conversion from natively folded amyloidogenic proteins to oligomers via nucleation is often hypothesized as a possible underlying mechanism. In this work, non-uniform AC-electric fields across two asymmetric electrodes were explored to control and examine the aggregation of insulin, a model amyloid protein, in aqueous buffer solution at constant temperature (20 °C) by fluorescence correlation spectroscopy and fluorescence microscopy. Insulin was rapidly concentrated in a strong AC-field by imposed AC-electroosmosis flow over an optimal frequency range of 0.5–2 kHz. In the presence of an AC-field, direct fibrillation from insulin monomers without the formation of oligomer precursors was observed. Once the insulin concentration had nearly doubled its initial concentration, insulin aggregates were observed in solution. The measured lag time for the onset of insulin aggregation, determined from the abrupt reduction in insulin concentration in solution, was significantly shortened from months or years in the absence of AC-fields to 1 min–3 h under AC-fields. The ability of external fields to alter amyloid nucleation kinetics provides insights into the onset of amyloid fibrillation.

The interaction of multivalent macroions with cell membrane can have a profound and significant impact on the functionality and viability of the cell membrane, and this is also critically related to drug and gene delivery as well as nanomaterial cytotoxicity. Using AFM, calorimetry, and light scattering techniques, we have investigated the effect of an anionic polyoxometalate (POM) nanocluster as a model macroion on the phase and structural stability of a lipid bilayer. A POM is distinct from commonly used nanoparticles, in this case comprising a stoichiometric and ordered crystalline nanocluster of typically

Molecular diffusion on a surface is often considered as a thermal energy-activated process of molecular hopping between adjacent adsorption sites on a surface and simply determined by molecule–surface interaction. In this work, we report distinct diffusive dynamics of probe molecules on methyl-terminated self-assembled monolayer (SAM), polymer brush layer and lipid bilayer by using fluorescence correlation spectroscopy (FCS) at a single-molecule level. We have observed that despite weaker molecule–surface interaction, the surface diffusion of probe molecules on soft polymer brush surface and fluid lipid bilayer can be much slower than that on hard SAM surface, suggesting a strong impact of interfacial dynamics of the underlying coating on molecular surface diffusion. To further examine the coupling of thermal activated molecular hopping and soft surface dynamics, we have investigated the diffusion of probe molecules on polymer brushes of varied grafting density and thickness, where the molecule–surface interaction remains nearly the same, yet the adopted conformations and dynamics of surface-grafted PNIPAM chains vary considerably; it is striking to observe that the diffusion of probe molecules could be further retarded on PNIPAM brush surfaces of lower grafting density or higher brush thickness, thereby exhibiting the presence of an optimal brush thickness range to facilitate fast surface diffusion of adsorbed probe molecules. All the observations combined lead to a general model by taking the dynamics of underlying surface layers into account to elucidate the molecular diffusion mechanism on varied surfaces.