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The effect of free space on molecular motion inside the polymer "dead layer" or adsorbed nanolayers on solid surfaces is investigated. Free space is introduced into the nanolayer by choosing a polymer with a relatively big side group, poly

The effect of binding strength of counterions with the polyelectrolyte chain to the swelling of polyelectrolyte brushes is studied, by investigating the swelling of both the polycation and polyanion in response to the variation of the salt concentration under the change of counterion's identity. Two polyelectrolyte brushes grafted on solid substrates are adopted: the cationic poly [2-(methacryloyloxy)ethyltrimethyl ammonium] (PMETA-X, X = F, Cl, Br, and I) and the anionic polystyrene sulfonate (M-PSS, M = Li, Na, K, and Cs). The swelling change with the salt concentration is investigated by ellipsometry, quartz crystal microbalance with dissipation, and dielectric spectroscopy. It is discovered that although the thickness of PMETA-X brushes is larger than that of M-PSS brushes of similar grafting density, the former has much less solvent incorporated than the latter. Such a difference is attributed to the weaker interaction between the PMETA+ chain and its halide counterions than that between the PSS- chain and its alkali counterions, discovered by dielectric spectroscopy. This makes the original charges on the PMETA-X chain less neutralized and therefore have a higher charge density, compared with the M-PSS chain. The results demonstrate that the stronger binding of the counterions to the polyelectrolytes makes the main chains less charged, resulting in the weaker inter-chain electrostatic repulsion and less swelling of the brushes. Investigations into the effect of ion identity show the following order of binding strength: for the cationic PMETA+ chain, F- < Cl- < Br- < I- and for the anionic PSS- chain, Li+ < Na+ < K+ < Cs+.

The dynamics of adsorption and desorption of counterions on a polyelectrolyte chain in aqueous solution is studied at a single molecular level. The investigation is through the process of fluoresce...

A series of Sm3+ ions doped Sr3Al2O6 phosphors was successfully synthesized via hydrothermal method. The crystal structure, morphology and luminescent properties of samples were analyzed by X-ray diffraction, scanning electron microscopy and photoluminescence spectra. All the samples took on cubic structure with Pa-3 space group. The Sr3Al2O6:Sm3+ phosphors could be excited by 405 nm and emit orange-red light peaked at 565, 609 and 660 nm. The effect of hydrothermal reaction time on the morphology and luminescent properties of phosphor was investigated. The influence of molar fraction of Sm3+ ions on the emission intensity of samples was studied and it has been found that the optimal dosage is 0.01. The calculated results by the first principle indicated that the Sm3+ ions will easily occupy the symmetric center site (Sr1). The results indicated that the luminescent intensity of Sr3Al2O6:Sm3+ phosphors could be modulated by reaction conditions of hydrothermal method.

Lateral diffusion of polymer molecules at the interfaces between immiscible oil and water is investigated at the single molecular level. The interfaces between water and alkanes are chosen as the model systems and polyethylene oxide (PEO) is the model polymer. Fluorescence correlation spectroscopy is used to measure the interfacial diffusion of fluorescence-labeled PEO with its molecular weight ranging over more than an order of magnitude. It is discovered that the interfacial diffusion coefficient scales with the molecular weight by the exponent of -0.5. Detailed analysis shows that the PEO chain takes an ideal two-dimensional random coil conformation at these fluidic interfaces and the bigger contribution from water's hydrodynamic friction is discovered.

The activation, by residual stress, of the fast portion of rotational motion of single fluorescent probe molecules inside a polymer thin film near its glass transition temperature is studied at a single molecular level. Spin-casted poly n-butyl methacrylate thin films without thermal annealing are chosen as the model system and single molecule fluorescence defocused microscopy is adopted as the method. The rotational motion of the probes under residual stress is found to be more activated than that under mere thermal activation, and the kinetic energy exhibits a monotonic increase with the stress strength. A rough linear dependence of rotational kinetic energy at low stress is found, yielding the value of characteristic volume for the residual stress to activate the motion of the probes. The values of the volume are close to the van der Waals volume of the probes, indicating that the activation of the fast dynamics by residual stress is localized. The activation effect is weakened and vanishes at or above the glass transition temperature due to stress relaxation. The effect is also absent at temperatures far below T

The physical mechanism of multiple modes in dynamics of polyelectrolyte aqueous solutions has been drawing extensive research attention for decades. This unsolved mystery makes it highly desirable to use new techniques to conduct investigations. In this study, dual-color fluorescence cross-correlation spectroscopy is applied to study the dynamics of individual molecules of a model polyelectrolyte, sodium poly(styrene sulfonate), in aqueous solutions. Anticorrelation in the cross-correlation function is discovered as a result of motion coupling due to interchain electrostatic repulsion. After correction, the self-part of the autocorrelation function is obtained, and the calculated mean square displacement data demonstrate a two-stage diffusion process—a fast one at short time lag and a slow one at long time lag. The two processes are attributed to a faster diffusion inside the cage formed by neighboring chains and a slower diffusion beyond the cage. Effects of the salt level and polyelectrolyte concentrati...

In this study, we modified the well-known photothermal polydopamine nanoparticles with the poly[(2-methacryloyloxy)ethyl phosphorylcholine-b-(2-dimethylamino)ethyl methacrylate] (PMPC-b-PDMAEMA) diblock copolymers, containing both biocompatible cell membrane phosphorylcholine zwitterions segments and pH-responsive dimethylaminoethyl units on the polymer chains, to achieve both the photothermal property and pH-responsive release behavior. The results showed that the obtained nanoparticles had a narrow size distribution with the diameter about 220 nm. Besides, the modified polydopamine nanoparticles showed enhanced colloidal stability, pH-sensitive drug release behavior, excellent biocompatibility and remarkable near-infrared photothermal property. Thus, it is highly anticipated that PMPC-b-PDMAEMA modified polydopamine nanoparticles can serve as a powerful drug delivery system for combined pH-sensitive drug release and near-infrared photothermal therapeutic.

A self-healing hydrogel was synthesized via the multi-component reaction of azobenzene-methacrylamide, β-CD and 3-methacrylamido phenylboronic acid. The orthogonal method was applied to analyze the influence of host–guest inclusion complexation, cross-linker and phenylboronic acid monomers content on mechanical properties and healing efficiency of the hydrogel. The results indicated that hydrogel showed autonomic self-healing behavior. The hydrogel demonstrated light-switchable self-healing ability and pH-sensitive swelling ratio. It was found that hydrogel showed high elongation, excellent resilience and low elastic hysteresis. The design of the combined host–guest interactions and boronate esters on the hydrogel showed advantage for improving the mechanical, self-healing and recovery properties simultaneously.

Extracellular plaque deposits of β-amyloid peptide (Aβ) are one of the main pathological features of Alzheimer's disease (AD). The aggregation of Aβ

Creating densified and stable liquid is a straightforward strategy for the fabrication of strong and ultra-stable amorphous or glassy materials. The current study has discovered that a liquid polymeric thin film is densified under the application of a high frequency surface acoustic wave (SAW). The experimental evidence is the decrease in film thickness and the increase in refractive index, measured by ellipsometry, of polyisobutylene thin films deposited on the solid substrates, when a high frequency SAW (39.5 MHz) is applied to the system. Further investigations by polarization-resolved single molecule fluorescence microscopy have demonstrated that the rotational motion of fluorescent probes doped inside the liquid film is retarded and the dynamical heterogeneity is reduced. The results demonstrate that the application of SAW of high frequency makes the thin polymeric liquid film densified and more dynamically homogeneous.

The correlation between the water content and protein adsorption on the surface of polymer brushes is investigated quantitatively. Using a number of model systems such as poly N-isopropylacrylamide (PNIPAM), polyethylene glycol (PEG), poly(2-(methacryloyloxy)ethyl phosphorylcholine) (PMPC), poly(2-hydroxyethyl methacrylate) (PHEMA), and poly(2,2,3,4,4,4-hexafluorobutyl)methacrylate (PHFBMA) polymer brushes with various grafting densities, the amount of water hydrodynamically coupled inside the brushes and its correlation with protein adsorption (BSA and Fg proteins as model systems) were determined by quartz crystal microbalance with dissipation (QCM-D) and surface plasma resonance (SPR). The results demonstrate the negative correlation between the water content and protein adsorption - the more water is coupled inside the brushes, the more protein adsorption is suppressed. In particular for PNIPAM brushes with a high enough grafting density and with a water content greater than 250 ng cm-2, the protein adsorption is negligible.

It has long been documented that the reduced viscosity of polyelectrolyte has an anomalous dependence on its concentration, i.e., the Fuoss law. To explore the molecular mechanism, the counterion distribution of sodium polystyrenesulfonate (NaPSS) as a function of concentration is investigated at the single-molecule level. By examination of the fluorescence resonance energy transfer (FRET) between a fluorescence donor on NaPSS chain and an acceptor in the counterions using single-molecule fluorescence spectroscopy, an increase of average counterion–chain distance is discovered upon dilution, indicating the expansion of counterion cloud. By photon counting histogram, an increase of effective charge of the NaPSS chain during dilution is exposed. The variation of these parameters agrees well with that of the reduced viscosity, helping to shed light on the molecular mechanism of the Fuoss law: the expansion of the counterion cloud increases hydrodynamic friction, and the increase of effective charges of NaPSS...

Structure and dynamics inside permanently charged polyelectrolyte brushes, sodium polystyrene sulfonate brushes, during their response to the introduction of external ions (NaCl) are investigated by neutron reflectivity and dielectric spectroscopy. Neutron reflectivity measurements show that the segmental density of the inner part of the brushes decreases and that of the outer part increases when the salt level is tuned from the salt-free condition to a moderate level (

Kinetics of the imidization reaction of poly (amic acid) (PAA) film based on pyromellitic anhydride (PMDA) and 4,4′-diaminodiphenyl ether (ODA) was studied by infrared spectroscopy. Attention is paid to the effect of solvent content inside the sample to the reaction kinetics. The results show that the presence of solvent favors the imidization reaction, rendering a much higher reaction kinetics than the case of without solvent. The data indicates that there is almost one NMP solvent molecule lost per imidization reaction. The kinetics of isothermal imidization reaction exhibits huge heterogeneity and is well-fitted by the Kohlraush-Williams-Watts (KWW) equation, from which the characteristic reaction time and the stretching exponent are determined. Both of them decrease with the increasing of the imidization reaction temperature, demonstrating the reaction is retarded with the proceeding of the reaction together with the creation of bigger dynamical heterogeneity.

The effective charge and evolution of single chains of a DNA i-motif during its unfolding process are investigated at the single molecule level. Using fluorescence correlation spectroscopy and photon counting histograms, the single chain dimensions and electrical potential of cytosine-rich human telomeric oligonucleotides are monitored, during their unfolding from the i-motif to the random coil state. It is discovered that the effective charge density of the DNA chain is very sensitive to conformation changes and the results remarkably expose the existence of an intermediate state of the unfolding process. A huge difference in pH value exists in the vicinity of the DNA chain and the bulk solution, depending on the salt concentration, as reflected by a down-shift in the pH value of unfolding. The presence of an external salt in the solution helps to stabilize the i-motif structure at low pH values due to the reduction of the effective charge density. It can also destabilize the folded structure in the pH range of the conformation transition due to the elevation of the local pH value, encouraging the deprotonation of the cytosine groups. These results provide new information for understanding the structure and stability of i-motif DNA, and its biological function, as well as the building blocks for smart nanomaterials.

Polymers doped with photosensitive molecules/nanoparticles are believed to be promising optical data storage media. In this communication, a simple method is reported to incorporate multilayers of photosensitive molecules with controlled concentration and spatial distribution into a polymer matrix. This simple hot pressing-based method makes it compatible with existing polymer processing techniques. It is demonstrated that this approach is effective to fabricate free-standing and multi-layered optical data storage media with commonly available polymers. The formation of a multilayer architecture within the polymer matrix involves no adhesives or polymers of other kinds, thus eliminating the concern of refractive index-mismatch between adjacent layers and making the whole material macroscopically homogeneous in structure. When polymers with good ductility and high glass transition temperature are used as the matrix, the macroscopically homogeneous structure can help the material to endure deformation and heat without losing the recorded information.

The re-entrant phase separation inside an evaporating droplet of poly (N-isopropyl acryl amide) (PNIPAM) solution with the binary solvent of ethanol and water is discovered and monitored continuously by optical microscopy. Because of the higher evaporation rate of ethanol than water, the solvent composition is changed by evaporation. As a result, the cononsolvency of PNIPAM makes the polymer precipitate into the solution and redissolve afterwards along the proceeding of the evaporation. Such a simple strategy enables a continuous observation of the re-entrant phase separation due to cononsolvency. Direct optical microscopic observation is made with quantitative description of the process and the details of the flow patterns during the process. The phase separation is found to occur at the air-liquid interface and the precipitates are brought into the droplet by circulations induced by Marangoni flow, providing a new way of mass transportation during phase separation.

The effect of strengthening of interaction between single fluorescent probes and polymer matrix to the probes' dynamics is investigated using single molecule fluorescence defocus microscopy. By introducing multiple hydroxyl groups to the fluorescent probes (perylene diimide derivatives) which builds up hydrogen bonds between the probe and polymer matrix, the dynamics is discovered to be retarded. This is evidenced by the lowering of the frequency of the vibrational modes in the power spectra of the rotation trajectories of individual fluorescent probes, and also by the decrease in population of rotating probes. The results show that by strengthening the probe-matrix interaction, the local dynamics detected by the probes is equivalent to that detected by a bigger probe, due to the enhanced friction between the probe and the polymer matrix.

Lateral diffusion of diblock copolymer residing on the interfaces between two immiscible liquids is investigated at single molecular level. Fluorescence correlation spectroscopy was used to study the diffusion of fluorescence-labeled diblock copolymer, polystyrene-b-polyisoprene, at the interface formed between two immiscible liquids. The interfaces are formed between N,N-dimethylformamide (DMF) and a few immiscible liquids, n-alkane and polyisoprene. Interfacial diffusion coefficient of the diblock copolymer probe is found to decrease monotonously with the increase of the molecular length of the interface constituting liquids. The decrease of diffusion coefficient follows the prediction by Einstein relation using the viscosity of the constituting liquids as the variables only for interfaces between DMF and very small n-alkanes. For interfaces formed between DMF and bigger alkanes and especially between DMF and polyisoprene, the diffusion coefficient is much higher than the calculated value, indicating that the probe molecule starts to probe the much less viscous interfacial region because the interfacial width gets larger, whose thickness is comparable to the molecule size of the liquids.

This study demonstrates that the conformation transition of single polymer molecules can be adjustable by applying external irradiation. By choosing poly N-isopropylacrylamide as the model system, its coil-to-globule conformation transition temperature is shifted with application of external UV irradiation, due to the photo-isomerization of the azobenzene moiety attached to the chain end. The investigation was conducted at single molecular level by fluorescence correlation spectroscopy, using hydrodynamic radius as the measure of chain dimension. It is discovered that the coil-to-globule transition temperature of the PNIPAM-azo can be controlled up to a difference of 12 °C upon external irradiation, due to the difference in polarity of the azobenzene end group.

As demonstrated previously (X. Chu et al., Soft Matter 2014, 10, 5568), permanently charged polyelectrolyte brushes can experience an enhancement of swelling by exposure to an external monovalent salt solution in moderate concentrations. Beyond the previous static measurements, the kinetics of the swelling enhancement and de-enhancement were investigated in the current study by using a quartz crystal microbalance with dissipation (QCM-D). By developing an effective approach to quantify the response in QCM-D, a vast difference in swelling enhancement and de-enhancement of a model permanently charged polyelectrolyte brush (sodium polystyrene sulfonate, NaPSS) was discovered. The results indicate new physics of the charged brushes: the difference in the attachment and detachment of counterions to the polyelectrolyte chains.

Lateral diffusion of cyclic polystyrene at the interface between fused silica and dichloromethane is investigated at the single-molecular level. Narrowly distributed cyclic polystyrene (c-PS) of high purity with molecular weights spanning nearly an order of magnitude is prepared via atom transfer radical polymerization (ATRP) and Cu-catalyzed azide/alkyne cycloaddition (CuAAC) click reaction. The diffusion coefficients (D) of c-PS and its linear analogue (l-PS) on the surface are measured by fluorescence correlation spectroscopy (FCS). The diffusion coefficient of c-PS is discovered to have an inverse dependence on molecular weight, D ∼ M−1, in contrast to the case of linear polystyrene, which reproduces a stronger molecular weight dependence, D ∼ M−3/2. The slower interfacial motion of cyclic chains is attributed to their stronger binding to the surface and more importantly, the unique surface diffusion mechanism due to the absence of free chain ends.

Rotational motion of single fluorescence probes with different sizes doped inside films of polyvinylacetate is investigated by defocused single molecule fluorescence microscopy. Discrete vibration modes in the rotational motion of individual probes are clearly exposed in the power spectra of the rotation trajectories, reflecting multiple relaxation dynamics and also the difference in dynamics among separate locations. The power spectra show a strong dependence on the probe size and temperature. By sampling the rotation of a large number of probes, the averaged power spectra show that the activated rotation of the probes falls into the frequency range of the α-relaxation and data analysis shows that activation of the vibration modes with all probes corresponds to the maximum population of rotating probes, and this made the comparison between single molecule data and the ensemble data meaningful (differential scanning calorimetry, as an example). Such an analysis shows a coincidence between the temperature of a significant occurrence of glass transition and the activation of rotational motion of all probes with one specific size, indicating that such a dimension correlates with the size of the cooperative rearrangement region - a volume of approximately 1.0 nm(3).

ZnS coating with oleic acid nano-particles have been successfully synthesized through the oil-phase thermal injection method. As-prepared samples are characterized by powder X-ray diffraction, transmission electron microscopy and spectra analysis. The emission color of ZnS NPs changes from blue to cyan with different ratio of Zn/S. ZnS:xEu3+ NPs with different doping concentrations of Eu3+ ions have different emission intensities and CIE coordination. The emission peaks vary with the change of y value of ZnSeyS1-y NPs, and the chromaticity coordinate transit from green to yellow region. The emission color and mechanism of the luminescent properties of ZnS, ZnS:xEu3+ and ZnSeyS1-y NPs are studied in detail. The results indicate that the thermal mixture injection without toxic is an effective and green method for synthesizing metal sulphitde, and the energy level structure, particle size, photoluminescence of ZnS can be achieved by forming different defect or doping of Eu or Se ions.

Fluorescence-based methods are promising for measuring amyloid beta (Aβ) oligomers, given their capacity to analyse a sample at the single-molecule level. As the attachment of fluorescent labels may influence the biochemical properties of the Aβ oligomers, the effects of fluorescent labels on Aβ oligomers must be evaluated. In this paper, we compared the impacts of five different fluorescent dyes on the aggregation of Aβ

The endomembrane system, including the endoplasmic reticulum, Golgi apparatus, lysosomes, and endosomes, is located in the crowded intracellular environment. An understanding of the cellular structure and functions requires knowledge of how macromolecular crowding and confinement affect the activity of membrane and its proteins. Using negatively charged liposome and the peptide K3L8K3 as a model system, we studied the aggregation behavior of liposome in a matrix of polyacrylamide and hyaluronic acid. Without matrix, the liposomes form spherical aggregates in the presence of K3L8K3. However, they orient in one dimension and fuse into a tube up to 40 μm long in the matrix. The growth of the tube is via end-to-end connection. This anisotropic growth is mainly due to the macromolecular confinement provided by the polymer network. The study of the interactions between liposome and peptide in the crowded environment helps to reveal the mechanism of membrane-related processes in vivo.

A study was made of the anti-polyelectrolyte effect of a model polyzwitterion at the single-chain level and from the point of view of comparison with inorganic salts and organic inner salts. A well-defined polymer of sulfobetaine was synthesized and fluorescently labeled. Fluorescence correlation spectroscopy was adopted to probe diffusion and chain size of polyzwitterion single chains in extremely dilute aqueous solutions over a broad concentration range of added salts. By the introduction of inorganic salts and organic inner salts, the single chains of polyzwitterions expanded with an increase of salt concentration. This observation indicates that the break-up of the dipole-dipole attraction between the zwitterion units is the mechanism of the anti-polyelectrolyte effect of polyzwitterions. The difference in the strength of the anti-polyelectrolyte effect induced by inorganic salts and organic inner salts also indicates the partial contribution from the asymmetric adsorption of ions onto polyzwitterion chains. (c) 2015 Society of Chemical Industry

It has been observed previously that when permanently charged polyelectrolyte brushes are exposed to an external salt solution, they shrink when the salt level is high enough. In this study, we observed an enhanced swelling process before the salt concentration reached that limit. We systematically investigated a few strong polyelectrolyte brush systems, including sodium polystyrene sulfonate (PSSNa), poly([2-(methacryloyloxy)ethyl] trimethylammonium chloride) (PMETAC) and potassium poly(3-sulfopropyl methacrylate) (PSPMA) with different molecular weights and grafting density using a combination of methods, including ellipsometry, quartz crystal microbalance with dissipation (QCM-D) and atomic force microscope (AFM). The swelling enhancement is expressed by the thickening of the brush layer at moderate salt concentrations, accompanied by the decrease of refractive index, the increase of the amount of solvent inside the brushes and an increase in retardation time. A scenario is proposed in which the counterions penetrate into the brushes driven by the external salt ions, they disrupt and break up the previously formed multiplets due to the dipole-dipole interaction by the ion-pairs on the polymer chain. This process results in the release of the bound segments and the stretching of the polymer chains.

Graphene-based hydrogels (GH) have exhibited prominent performances in wastewater treatment. Herein, Special-shaped ZnO tetrapods and TiO2 nanosheets were introduced to the preparation of GH via a one-step hydrothermal reduction method. The ZnO-GH and TiO2-GH composite hydrogel with a uniform 3D network structure and good mechanical properties can be used as an adsorbent for printing and dyeing wastewater. The optimum doping amount of ZnO and TiO2 in the composite hydrogel and the adsorption regularity to rhodamine B (RhB) with different concentrations were discussed. The cyclic adsorption performance and adsorption kinetics were briefly discussed. When the doping ratio of ZnO to graphene oxide (GO) is 5:8, ZnO-GH has the best adsorption rate, which is 71.7%. The best degradation rate appears at a ZnO doping ratio of 1:2, which also shows the best total removal rate of RhB of approximately 82.20%. When the doping ratio of TiO2 to GO is 3:4, the photocatalytic degradation rate is 30.3%, and the total removal rate of RhB reaches 99.1%, which indicates that RhB can be almost completely removed by TiO2-GH through adsorption and degradation. After five cycles, the adsorption capacity of ZnO-GH and TiO2-GH for the low RhB concentration is still good. The addition of ZnO and TiO2 improves not only the adsorption and degradation properties of the composite hydrogel but also its recycling performance as a result of the increase in mechanical stability.

There has been recognized that there exist three basic relaxation modes in the molecular dynamics of liquid crystalline side chain polymers (SCLCP) – the α-, β- and δ-relaxation process, and the molecular mechanism of the δ-relaxation has been in controversy, i.e. whether it is a “flip-flop” transition or a continuous rotation. The current study provides the experimental evidence of the multiple steps relaxation by time-resolved emission spectroscopy, taking the intrinsic fluorescence from the model mesogen group of 4-cyanobiphenyl. The temperature dependence of the spectra and its dynamics provides new information on the microscopic picture of the δ-relaxation.

A self-healing hydrogel is prepared by crosslinking acrylamide with a host-guest macro-crosslinker assembled from poly(β-cyclodextrin) nanogel and azobenzeneacrylamide. The photoisomerizable azobenzene moiety can change its binding affinity with β-cyclodextrin, therefore the crosslinking density and rheology property of the hydrogel can be tuned with light stimulus. The hydrogel can repair its wound autonomously through the dynamic host-guest interaction. In addition, the wounded hydrogel will lose its ability of self-healing when exposed to ultraviolet light, and the self-healing behavior can be recovered upon the irradiation of visible light. The utilizing of host-guest macro-crosslinking approach manifests the as-prepared hydrogel reversible and light-switchable self-healing property, which would broaden the potential applications of self-healing polymers.

The molecular conformation of two typical polyelectrolytes, sodium polystyrene sulfonate (NaPSS) and quarternized poly-4-vinylpyridine (QP4VP), was studied in aqueous solutions without salt addition at the single molecular level. By fluorescence correlation spectroscopy, the hydrodynamic radius (Rh) of NaPSS and QP4VP with the molecular weight ranging more than one order of magnitude was measured. The scaling analysis of Rh exhibits scaling exponent of 0.70 and 0.86 for NaPSS and QP4VP in solutions without added salts, respectively, showing the conformation is much more expanded than random coil. Numerical fittings using the model of diffusion of a rod molecule agree with the data well, indicating that the polyelectrolyte chains take the rod-like conformation under the condition without salt addition. Further investigations by determining the electric potential of single PSS- chains using the photon counting histogram technique demonstrate the enhanced counterion adsorption to the charged chain at higher molecular weight.

Although the exact etiology and pathogenesis of Alzheimer's disease (AD) are still unclear, amyloid-β (Aβ) generated by the proteolytic processing of amyloid-β precursor protein (APP) aggregate to form toxic amyloid species. Kinesin-1 is the first identified ATP-dependent axonal transport motor protein that has been proven to affect Aβ generation and deposition. In this paper, we applied dual-color fluorescence cross-correlation spectroscopy (DC-FCCS) to investigate the direct interaction of Aβ with kinesin-1 at the single-molecule fluorescence level in vitro. The results showed that two kinds of enhanced green fluorescent protein (EGFP)-tagged kinesin light-chain subunits of kinesin-1(KLCs), KLC-E and E-KLC inhibited the aggregation of Aβ over a period of time, providing additional insight into the mechanism of axonal transport deficits in AD.

The lateral diffusion of individual polymer chain of polyethylene oxide (PEO) at oil-water interfaces was studied using fluorescence correlation spectroscopy (FCS). The diffusion coefficient of PEO was systematically under variable salt concentration of NaCl in the aqueous phase and it was found that the diffusion coefficient of the adsorbed polymer chain was very much determined by the viscosity of the oil phase. This fact indicates an enhanced hydrophobic interaction of the PEO chain with the oil phase.

Using sodium polystyrene sulfonate (NaPSS) and quarternized poly 4-vinylpyridine (QP4VP) as model systems, the chain conformation of polyelectrolytes under finite salt concentrations is investigated at a single molecular level. By fluorescence correlation spectroscopy (FCS), the hydrodynamic radius (Rh) of the samples with the molecular weight ranging more than one order of magnitude was measured. The variations of Rh as a function of molecular weight reveal the molecular weight dependence: under moderate salt concentrations (such as 10−4 and 0.1M), the shorter chains of both NaPSS and QP4VP take the rod-like conformation, while the longer chains take the coiled conformation (random coil or swelled random coil conformation, respectively). At high enough salt levels, both the charged chains take the coiled conformations. Photon counting histogram (PCH) measurements of the local pH value at the vicinity of the NaPSS chain expose the higher extent of counterion adsorption for longer chains as well as higher salt concentrations, telling that the charge regularization process is the major governing factor.

Fluorescence-based methods are promising for measuring amyloid beta (Aβ) oligomers, given their capacity to analyse a sample at the single-molecule level. As the attachment of fluorescent labels may influence the biochemical properties of the Aβ oligomers, the effects of fluorescent labels on Aβ oligomers must be evaluated. In this paper, we compared the impacts of five different fluorescent dyes on the aggregation of Aβ42 oligomers using fluorescence correlation spectroscopy (FCS). We found that fluorescent labels of BODIPY® FL-C5 (BP), N-hydroxysuccinimide rhodamine B ester (RB) and rhodamine B isothiocyanate (RITC) increased the propensity of labelled Aβ42 oligomers to aggregate, whereas 6-(fluorescein-5-carboxamido) hexanoic acid succinimidyl ester (5-SFX) and fluorescein 5(6)-isothiocyanate (5(6)-FITC) decreased the propensity of labelled Aβ42 oligomers to aggregate. This difference originated from the different electric charges and hydrophobicity of the fluorescent dyes. These results provide valuable information for establishing different aggregation models for Aβ42 oligomers in vitro using FCS.

Thiol-terminated polymers poly(2-methacryloyloxyethyl phosphorylcholine) (PMPC-SH), poly(N,N-isopropylacrylamide) (PNIPAM-SH), and poly(tert-butyl acrylate) (PtBA-SH) were synthesized, and the polymers were grafted on the gold surfaces of quartz crystal microbalance with dissipation (QCM-D) and surface plasmon resonance (SPR) sensor chips to form brushes. The grafting process of the polymer brushes as well as protein adsorption onto the brush layers was monitored by in situ QCM-D and SPR techniques. By examining the changes in frequency and dissipation factor as well as the value of ∂D/∂f from QCM-D measurements, different stages of the polymer grafting and protein adsorption are distinguished. The most interesting discovery is the conformation change of BSA protein adsorption from a weakly adsorbed native state to a strongly immobilized denatured state on the polymer brushes. The corresponding change in BSA adsorption from a reversible state to an irreversible state was confirmed by SPR measurements. The adsorption of protein on the polymer brushes' surface relies largely on interaction between the protein and the polymers, and the stronger hydrophilicity of the surfaces is proved to be more effective to suppress the protein adsorption. Analysis of the D-f plot of QCM-D measurements helps to characterize different binding strength of protein and the underlying polymer surface.

Self-assembly is an efficient strategy of constructing microgel-based intelligent materials. However, it remains a challenge to realize the reversible self-assembly of microgels. Herein, a method to guide the self-assembly of soft colloids with light-stimuli is proposed, utilizing the light-responsive host–guest interaction between an azobenzene functionalized nanogel (the guest colloid) and an α-cyclodextrin functionalized microgel (the host colloid). The two colloids can form a stable colloid cluster when the surface of the host colloid is fully packed with the guest colloids. The colloid cluster can disassemble when irradiated with UV light and reassemble when irradiated with visible light. The reversible colloidal self-assembly can be controlled by the interplay between the supramolecular and covalent crosslinking, and can also be adjusted by the addition of competitive host molecules. Besides the light-sensitivity, the colloid cluster inherits the deformability and temperature-sensitivity from its parent colloids. These features are different from the supramolecular self-assembly of hard colloids or macroscopic gels, and manifest the as-prepared colloid cluster potential building blocks of light-responsive materials.