Secondary Structure Analysis of Proteins Embedded in Spherical Polyelectrolyte Brushes by FT-IR Spectroscopy

Polyelectrolyte Brushes with Protein-Like Nanocolloids

Electrostatic interaction of ampholytic nanocolloidal particles (NPs), which mimic globular proteins, with polyelectrolyte brushes is analyzed within mean-field Poisson-Boltzmann approximation. In accordance with experimental findings, the theory predicts that an electrostatic driving force for the particle uptake by the brush may emerge when the net charge of the particle in the buffer and the charge of the brush are of the same sign. The origin of this driving force is change in the ionization state of weak cationic and anionic groups on the NP surface provoked by interaction with the brush. In experimental systems, the ionic interactions are complemented by excluded-volume, hydrophobic, and other types of interactions that all together control NP uptake by or expulsion from the brush. Here, we focus on the NP-brush ionic interactions. It is demonstrated that deviation between the buffer pH and the NP isoelectric point, considered usually as the key control parameter, does not uniquely determine the insertion free energy patterns. The latter depends also on the proportion of cationic and anionic groups in the NPs and their specific ionization constants as well as on salt concentration in the buffer. The analysis of the free energy landscape proves that a local minimum in the free energy inside the brush appears, provided the NP charge reversal occurs upon insertion into the brush. This minimum corresponds either to a thermodynamically stable or to a metastable state, depending on the pH offset from the IEP and salt concentration, and is separated from the bulk of the solution by a free energy barrier. The latter, being fairly independent of salt concentration in height, may strongly impede the NP absorption kinetically even when it is thermodynamically favorable. Hence, change reversal is a necessary but insufficient condition for the uptake of the NPs by similarly charged polyelectrolyte brushes.

Interaction of Polyanionic and Polycationic Brushes with Globular Proteins and Protein-like Nanocolloids

A large number of experimental studies have demonstrated that globular proteins can be absorbed from the solution by both polycationic and polyanionic brushes when the net charge of protein globules is of the same or of the opposite sign with respect to that of brush-forming polyelectrolyte chains. Here, we overview the results of experimental studies on interactions between globular proteins and polycationic or polyanionic brushes, and present a self-consistent field theoretical model that allows us to account for the asymmetry of interactions of protein-like nanocolloid particles comprising weak (pH-sensitive) cationic and anionic groups with a positively or negatively charged polyelectrolyte brush. The position-dependent insertion free energy and the net charge of the particle are calculated. The theoretical model predicts that if the numbers of cationic and anionic ionizable groups of the protein are approximately equal, then the interaction patterns for both cationic and anionic brushes at equal offset on the "wrong side" from the isoelectric point (IEP), i.e., when the particle and the brush charge are of the same sign, are similar. An essential asymmetry in interactions of particles with polycationic and polyanionic brushes is predicted when fractions of cationic and anionic groups differ significantly. That is, at a pH above IEP, the anionic brush better absorbs negatively charged particles with a larger fraction of ionizable cationic groups and vice versa.

Bovine Serum Albumin Interaction with Polyanionic and Polycationic Brushes: The Case Theoretical Study

We apply a coarse-grained self-consistent field Poisson-Boltzmann framework to study interaction between Bovine Serum Albumin (BSA) and a planar polyelectropyte brush. Both cases of negatively (polyanionic) and positively (polycationic) charged brushes are considered. Our theoretical model accounts for (1) re-ionization free energy of the amino acid residues upon protein insertion into the brush; (2) osmotic force repelling the protein globule from the brush; (3) hydrophobic interactions between non-polar areas on the globule surface and the brush-forming chains. We demonstrate that calculated position-dependent insertion free energy exhibits different patterns, corresponding to either thermodynamically favourable BSA absorption in the brush or thermodynamically or kinetically hindered absorption (expulsion) depending on the pH and ionic strength of the solution. The theory predicts that due to the re-ionization of BSA within the brush, a polyanionic brush can efficiently absorb BSA over a wider pH range on the "wrong side" of the isoelectric point (IEP) compared to a polycationic brush. The results of our theoretical analysis correlate with available experimental data and thus validate the developed model for prediction of the interaction patterns for various globular proteins with polyelectrolyte brushes.

Highly sensitive pregnancy test kit via oriented antibody conjugation on brush-type ligand-coated quantum beads

Lateral flow assays (LFA) enable development of portable and rapid diagnostic kits; however, their capacity to detect low levels of disease markers remains poor. Here, we report a highly sensitive pregnancy test kit as a proof of concept, by combining brush-type ligand-coated quantum beads (B-type QBs) and nanobody, which can control the antibody orientation and enhance sensitivity. The brush-type ligand provided excellent dispersion stability and high-binding capacity toward antibody. Fc-binding nanobody increased the antigen-binding capacity of conjugated antibodies on the B-type QBs. To facilitate convenient acquisition of the LFA results, we developed a smartphone-based reader with a 3D-printed optical imaging module, and validated the diagnostic performance of the sensing platform. The pregnancy test kit achieved a 5.1 pg mL^-1 limit of detection, corresponding to the levels for early-stage detection of heart disease and malaria. Our LFA application can potentially be expanded to diagnosis other diseases by simply changing the antibody pair in the kit.

Understanding the Interaction of Polyelectrolyte Architectures with Proteins and Biosystems

The counterions neutralizing the charges on polyelectrolytes such as DNA or heparin may dissociate in water and greatly influence the interaction of such polyelectrolytes with biomolecules, particularly proteins. In this Review we give an overview of studies on the interaction of proteins with polyelectrolytes and how this knowledge can be used for medical applications. Counterion release was identified as the main driving force for the binding of proteins to polyelectrolytes: Patches of positive charge become multivalent counterions of the polyelectrolyte and lead to the release of counterions from the polyelectrolyte and a concomitant increase in entropy. This is shown from investigations on the interaction of proteins with natural and synthetic polyelectrolytes. Special emphasis is paid to sulfated dendritic polyglycerols (dPGS). The Review demonstrates that we are moving to a better understanding of charge-charge interactions in systems of biological relevance. Research along these lines will aid and promote the design of synthetic polyelectrolytes for medical applications.

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.

pH-induced structural transition during complexation and precipitation of sodium caseinate and ε-Poly-l-lysine

ε-Polylysine (EPL) is a food-grade antimicrobial peptide that forms complexes with proteins. Such complexes are potential carriers for targeted delivery of agents. To elucidate the formation of such complexes, the pH-induced phase transition of EPL and sodium caseinate (SC) complexes were characterized in terms of ionic strengths (I) and EPL/SC weight ratios (r). Electrostatic nanocomplexes (e.g. r = 2^-3, I = 2 mM) were formed near the isoelectric point of SC using turbidimetry, dynamic light scattering, and ζ-potential measurements. Phase analyses revealed that the formation of nanocomplexes primarily depends on the I, and saturated binding was recorded above r = 2^-2. Electrostatic potential modelling of EPL was employed to describe the interaction affinity. A three-dimensional phase boundary curve was established which divided the complexation into a nano-scale and phase separation. Atomic force microscopy images confirmed that nanocomplexes were spherical particles with uniform shapes. Morphologic examination using optical and scanning electron microscopy and Fourier transform infrared spectroscopy revealed that the nanocomplexes formed "sponge-like" precipitates at larger length scales. This work reveals the possible mechanism that drives the complexation of sodium caseinate and ε-Poly-l-lysine. This is expected to guide the construction of tailor-made protein complexes in industrial applications.

High-pressure study of magnetic nanoparticles with a polyelectrolyte brush as carrier particles for enzymes

The recovery of enzymes from a reaction medium can be achieved in a convenient way by using magnetic nanoparticles (MNP) as carriers. Here, we present MNP with a polyelectrolyte brush composed of poly(ethylene imine) (PEI) to provide a benign environment for the immobilized enzyme molecules. Yeast alcohol dehydrogenase (ADH) has been tested for enzymatic activity when it is free in solution or adsorbed on the PEI brush-MNP. Furthermore, the effect of pressure on the enzymatic activity has been studied to reveal activation volumes, which are a sensitive probe of the transition state geometry. The results of this study indicate that the secondary structure of ADH is pressure-stable up to 9 kbar. The enzymatic activity of ADH can be analyzed using Michaelis-Menten kinetics free in solution and adsorbed on the PEI brush-MNP. Remarkably, no significant changes of the Michaelis constant and the activation volume are observed upon adsorption. Thus, it can be assumed that the turnover number of ADH is also the same in the free and adsorbed state. However, the maximum enzymatic rate is reduced when ADH is adsorbed, which must be explained by a lower effective enzyme concentration due to steric hindrance of the enzyme inside the PEI brush of the MNP. In this way, the pressure experiments carried out in this study enable a distinction between steric and kinetic effects on the enzymatic rate of adsorbed ADH.

Analyzing protein-ligand and protein-interface interactions using high pressure

All protein function is based on interactions with the environment. Proteins can bind molecules for their transport, their catalytic conversion, or for signal transduction. They can bind to each other, and they adsorb at interfaces, such as lipid membranes or material surfaces. An experimental characterization is needed to understand the underlying mechanisms, but also to make use of proteins in biotechnology or biomedicine. When protein interactions are studied under high pressure, volume changes are revealed that directly describe spatial contributions to these interactions. Moreover, the strength of protein interactions with ligands or interfaces can be tuned in a smooth way by pressure modulation, which can be utilized in the design of drugs and bio-responsive interfaces. In this short review, selected studies of protein-ligand and protein-interface interactions are presented that were carried out under high pressure. Furthermore, a perspective on bio-responsive interfaces is given where protein-ligand binding is applied to create functional interfacial structures.

Interaction of Proteins with Polyelectrolytes: Comparison of Theory to Experiment

We discuss recent investigations of the interaction of polyelectrolytes with proteins. In particular, we review our recent studies on the interaction of simple proteins such as human serum albumin (HSA) and lysozyme with linear polyelectrolytes, charged dendrimers, charged networks, and polyelectrolyte brushes. In all cases discussed here, we combined experimental work with molecular dynamics (MD) simulations and mean-field theories. In particular, isothermal titration calorimetry (ITC) has been employed to obtain the respective binding constants K_b and the Gibbs free energy of binding. MD simulations with explicit counterions but implicit water demonstrate that counterion release is the main driving force for the binding of proteins to strongly charged polyelectrolytes: patches of positive charges located on the surface of the protein become multivalent counterions of the polyelectrolyte, thereby releasing a number of counterions condensed on the polyelectrolyte. The binding Gibbs free energy due to counterion release is predicted to scale with the logarithm of the salt concentration in the system, which is verified by both simulations and experiment. In several cases, namely, for the interaction of proteins with linear polyelectrolytes and highly charged hydrophilic dendrimers, the binding constant could be calculated from simulations to very good approximation. This finding demonstrated that in these cases explicit hydration effects do not contribute to the Gibbs free energy of binding. The Gibbs free energy can also be used to predict the kinetics of protein uptake by microgels for a given system by applying dynamic density functional theory. The entire discussion demonstrates that the direct comparison of theory with experiments can lead to a full understanding of the interaction of proteins with charged polymers. Possible implications for applications, such as drug design, are discussed.

Formation of complexes in aqueous solutions of amphiphilic triblock polyelectrolytes of different topologies and an oppositely charged protein

The complexation of lysozyme with aggregates from two triblock amphiphilic polyelectrolytes of the same blocks but different topologies and block molar masses, namely PS-b-SCPI-b-PEO and SCPI-b-PS-b-PEO, is investigated by scattering and spectroscopy methods. Light scattering reveals that the interaction with lysozyme causes shrinkage of the self-assembled nanoparticles in the case of the hydrophobic-polyelectrolyte-hydrophilic sequence. In the polyelectrolyte-hydrophobic-hydrophilic sequence, the opposite trend is observed. Small angle neutron scattering confirms the existence of micellar and fractal aggregates and the complexation with lysozyme. The pH-dependence of the interactions and the stability of the hybrid protein/polymer nanoparticles upon salt addition are tested. The native conformation of the protein is found to be preserved during complexation. This study reveals that both micellar and fractal aggregates made of amphiphilic triblock polyelectrolytes are capable of loading with oppositely charged proteins in a controllable manner, tuned primarily by the structure of the triblock terpolymer.

Binding of Lysozyme to Spherical Poly(styrenesulfonate) Gels

Polyelectrolyte gels are useful as carriers of proteins and other biomacromolecules in, e.g., drug delivery. The rational design of such systems requires knowledge about how the binding and release are affected by electrostatic and hydrophobic interactions between the components. To this end we have investigated the uptake of lysozyme by weakly crosslinked spherical poly(styrenesulfonate) (PSS) microgels and macrogels by means of micromanipulator assisted light microscopy and small angle X-ray scattering (SAXS) in an aqueous environment. The results show that the binding process is an order of magnitude slower than for cytochrome c and for lysozyme binding to sodium polyacrylate gels under the same conditions. This is attributed to the formation of very dense protein-rich shells in the outer layers of the microgels with low permeability to the protein. The shells in macrogels contain 60 wt % water and nearly charge stoichiometric amounts of lysozyme and PSS in the form of dense complexes of radius 8 nm comprising 30⁻60 lysozyme molecules. With support from kinetic modelling results we propose that the rate of protein binding and the relaxation rate of the microgel are controlled by the protein mass transport through the shell, which is strongly affected by hydrophobic and electrostatic interactions. The mechanism explains, in turn, an observed dependence of the diffusion rate on the apparent degree of crosslinking of the networks.

Protein Immobilization onto Cationic Spherical Polyelectrolyte Brushes Studied by Small Angle X-ray Scattering

The immobilization of bovine serum albumins (BSA) onto cationic spherical polyelectrolyte brushes (SPB) consisting of a solid polystyrene (PS) core and a densely grafted poly(2-aminoethyl methacrylate hydrochloride) (PAEMH) shell was studied by small-angle X-ray scattering (SAXS). The observed dynamics of adsorption of BSA onto SPB by time-resolved SAXS can be divided into two stages. In the first stage (tens of milliseconds), the added proteins as in-between bridge instantaneously caused the aggregation of SPB. Then BSA penetrated into the brush layer driven by electrostatic attractions, and reached equilibrium in the second stage (tens of seconds). The amount of BSA immobilized onto brush layer reached the maximum when pH was increased to about 6.1 and BSA concentration to 10 g/L. The cationic SPB were confirmed to provide stronger adsorption capacity for BSA compared to anionic ones.

Confinement effect on the structure and elasticity of proteins interfacing polymers

The ordered nanostructured surfaces provide confined environments that allow functionalization of proteins. Here, we used the nanopores of poly(methyl methacrylate) films to attach fibrinogen and lysozyme, and discussed the changes in proteins' structures and elasticity upon confinement. Fourier-transform infrared spectroscopic analysis of protein secondary structures reveals that fibrinogen undergoes less structural change and behaves less stiff when the pore size is close to the protein size. Lysozyme, on the other hand, retains its native-like structure, however, it exhibits the highest modulus in 15 nm pores due to the lower macromolecular crowding effect the protein faces compared to lysozyme within larger pores. These findings manifest the effect of confinement and crowding on the conformation and elasticity of different shaped proteins tethered on surfaces.

Volume profile of α-chymotrypsin during adsorption and enzymatic reaction on a poly(acrylic acid) brush

The catalytic rate of α-chymotrypsin that is adsorbed on a poly(acrylic acid) brush can be enhanced by pressure.

Improvement of Protein Immobilization and Bioactivity of Magnetic Carriers Using a Brushed Beads-on-Beads Structure

To achieve higher protein immobilization and bioactivity, as well as automatic manipulation, we prepared a new type of biocarrier based on the brushed beads-on-beads structure. Many poly(acrylic acid) (PAA) brushed nanoparticles were packed onto the surface of amino-functionalized magnetic particles through an efficient carbodiimide-assisted coupling reaction to attain a hierarchical structure, a unique three-dimensional (3D) space and automatic manipulation characteristics. The proposed biocarrier was evaluated in the recognition capability of the immunocomplex and showed a 6.7-fold increase compared with control beads with a hard surface. The results of this study suggest promising applications in targeted capture and high-performance biodetection processes.

Synthesis and Biomedical Applications of Poly((meth)acrylic acid) Brushes

Poly((meth)acrylic acid) (P(M)AA) brushes possess a number of distinctive properties that are particularly attractive for biomedical applications. This minireview summarizes recent advances in the synthesis and biomedical applications of P(M)AA brushes and brushes containing P(M)AA segments. First, we review different surface-initiated polymerization (SIP) methods, with a focus on recent progress in the surface-initiated controlled/living radical polymerization (SI-CLRP) techniques used to generate P(M)AA brushes with a tailored structure. Next, we discuss biomolecule immobilization methods for P(M)AA brushes, including physical adsorption, covalent binding, and affinity interactions. Finally, typical biomedical applications of P(M)AA brushes are reviewed, and their performance is discussed based on their unique properties. We conclude that P(M)AA brushes are promising biomaterials, and more potential biomedical applications are expected to emerge with the further development of synthetic techniques and increased understanding of their interactions with biological systems.

Counterion-Specific Protein Adsorption on Polyelectrolyte Brushes

Protein adsorption is an important issue in biorelated fields. We have investigated the protein adsorption on the poly(ionic liquid) (PIL) brushes in the presence of different types of counterions. The protein adsorption is driven by a decrease in osmotic pressure within the brushes with an increase in entropy via the release of counterions. Our study demonstrates that counterion specificity has a significant influence on protein adsorption on the PIL brushes. There have been two different regimes for counterion-specific protein adsorption. When the released counterions cannot bind to the protein surface, the counterion-specific protein adsorption is dominated by the ion-specific counterion condensation within the PIL brushes. If the released counterions can bind to the protein surface, then counterion-specific protein adsorption is dominated by the ion-specific rebinding of released counterions on the protein surface. This work opens up a new opportunity for controlling protein adsorption on polyelectrolyte brushes.

Enhancement of enzymatic activity by magnetic spherical polyelectrolyte brushes: a potential recycling strategy for enzymes

Interactions between amyloglucosidase and magnetic spherical polyelectrolyte brushes (MSPB) were studied by turbidimetric titration, which reveals reversible and tunable behaviors of pH-dependent enzyme-SPB binding. Quantitative thermodyanmic parameters including binding affinity and stoichiometry between enzyme and SPBs were further measured by isothermal titration calorimetry (ITC). A large amount of enzyme can be loaded in MSPB without loss of MSPB stability. We demonstrated that the enzymatic activity of amyloglucosidase bound in MSPB could be greatly enhanced (catalytic reaction rate, k(bound) = 1.36k(free)) compared to free enzyme acitivity in solution. This is tremendous improvement from other carrier systems that usually lead to a significant decrease of enzymatic activity. Both the high enzyme loading capacity and the enhancement of the catalytic activity probably arise from the Coulombic interactions between the enzyme and MSPB. These findings provide a practical strategy for enhancement of enzyme activity and enzyme recycling by MSPB.

Microcontact-BSA imprinted capacitive biosensor for real-time, sensitive and selective detection of BSA

An analytical method is presented, combining novel microcontact imprinting technique and capacitive biosensor technology for the detection of BSA. Glass cover slips were used for preparation of protein stamps. The microcontact-BSA imprinted gold electrodes were prepared in the presence of methacrylic acid (MAA) and poly-ethylene glycol dimethacrylate (PEGDMA) as the cross-linker by bringing the protein stamp and the gold electrode into contact under UV-polymerization. Real-time BSA detection studies were performed in the concentration range of 1.0 × 10-20-1.0 × 10-8 M with a limit of detection (LOD) of 1.0 × 10-19 M. Cross-reactivity towards HSA and IgG were 5 and 3%, respectively. The electrodes were used for >70 assays during 2 months and retained their binding properties during all that time. The NIP (non-imprinted) electrode was used as a reference. The microcontact imprinting technology combined with the biosensor applications is a promising technology for future applications.

Prevention of thermally induced aggregation of IgG antibodies by noncovalent interaction with poly(acrylate) derivatives

Prevention of thermal aggregation of antibodies in aqueous solutions was achieved by noncovalent association with hydrophobically modified poly(acrylate) copolymers. Using a polyclonal immunoglobin G (IgG) as a model system for antibodies, we have studied the mechanisms by which this multidomain protein interacts with polyanions when incubated at physiological pH and at temperatures below and above the protein unfolding/denaturation temperature, in salt-free solutions and in 0.1 M NaCl solutions. The polyanions selected were sodium poly(acrylates), random copolymers of sodium acrylate and N-n-octadecylacrylamide (3 mol %), and a random copolymer of sodium acrylate, N-n-octylacrylamide (25 mol %), and N-isopropylacrylamide (40 mol %). They were derived from two poly(acrylic acid) parent chains of Mw 5000 and 150000 g·mol(-1). The IgG/polyanion interactions were monitored by static and dynamic light scattering, fluorescence correlation spectroscopy, capillary zone electrophoresis, and high sensitivity differential scanning calorimetry. In salt-free solutions, the hydrophilic PAA chains form complexes with IgG upon thermal unfolding of the protein (1:1 w/w IgG/PAA), but they do not interact with native IgG. The complexes exhibit a remarkable protective effect against IgG aggregation and maintain low aggregation numbers (average degree of oligomerization <12 at a temperature up to 85 °C). These interactions are screened in 0.1 M NaCl and, consequently, PAAs lose their protective effect. Amphiphilic PAA derivatives (1:1 w/w IgG/polymer) are able to prevent thermal aggregation (preserving IgG monomers) or retard aggregation of IgG (formation of oligomers and slow growth), revealing the importance of both hydrophobic interactions and modulation of the Coulomb interactions with or without NaCl present. This study leads the way toward the design of new formulations of therapeutic proteins using noncovalent 1:1 polymer/protein association that are transient and require a markedly lower additive concentration compared to conventional osmolyte protecting agents. They do not modify IgG permanently, which is an asset for applications in therapeutic protein formulations since the in vivo efficacy of the protein should not be affected.

Biosensor utilizing a liquid crystal/water interface functionalized with poly(4-cyanobiphenyl-4'-oxyundecylacrylate-b-((2-dimethyl amino) ethyl methacrylate))

The interface between the nematic liquid crystal, 4-cyano-4'-pentylbiphenyl (5CB) and water within a transmission electron microscopy (TEM) grid cell coated with the pH-dependent weak cationic amphiphilic block copolymer poly((4-cyanobiphenyl-4'-oxyundecylacrylate)-b-((2-dimethyl amino) ethyl methacrylate)) (LCP-b-PDMAEMA) (which was successfully synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization) was subsequently evaluated for protein and deoxyribonucleic acid (DNA) detection. The LCP-b-PDMAEMA monolayer was fabricated using a Langmuir Blodgett trough, transferred to the 5CB-filled TEM grid, and placed on the octadecyltrichlorosilane-coated glass (TEMPDMAEMA) in such a way that the LCP chains were immersed in the 5CB while the PDMAEMA chains were pointed away from the 5CB surface and immersed in water. Several model proteins such as bovine serum albumin (BSA), hemoglobin (Hb), and chymotrypsinogen (ChTg) were tested at pH values ranging from 2 to 12 to determine the role of the charge state of the protein on protein detection by a weak polyelectrolyte such as PDMAEMA. PDMAEMA contains cationic and neutral states below and above the pKa value, respectively, and is thus able to absorb proteins below its pKa threshold through electrostatic interactions. BSA exhibited a homeotropic to planar (H-P) change in orientation within the TEMPDMAEMA grid cell at concentrations greater than 0.02wt% within the pH range between the isoelectric point (pI) of BSA and the pKa of PDMAEMA, where the charge states of BSA and PDMAEMA were negative and positive, respectively. However, this change in orientation did not occur with other proteins that exhibited a pI higher than the pKa of PDMAEMA due to the electrostatic repulsions resulting from their same cationic charges. This result indicates that the electrostatic interactions between proteins and PDMAEMA are a major contributing factor for protein detection by the H-P transformation within the TEMPDMAEMA grid cell. DNA, a pH-independent strong anionic polyelectrolyte, was also tested with the TEMPDMAEMA grid cell, and it exhibited an H-P transformation at the charged state of PDMAEMA below its pKa threshold at concentrations higher than 0.01wt%. Thus, we demonstrated that the TEMPDMAEMA grid cell effectively facilitated the detection of negatively charged biomaterials (i.e.; protein and DNA) through the H-P transformation using the polarized optical microscope. This simple and inexpensive experimental set-up for non-specific biomaterial detection lays the basic groundwork for developing effective biosensors using polyelectrolytes.

Protein-Induced Synthesis of Chiral Conducting Polyaniline Nanospheres

A green and novel method for the synthesis of chiral conducting polyaniline was developed. Chiral polyaniline induced by protein was obtained by using the template-assisted polymerization route. The experimental results demonstrated that proteins such as bovine hemoglobin and bovine serum albumin had the capacity to direct enantio specificity of PANI which may be ascribed to the α-helix structure within the proteins. The achieved chiral conducting polyaniline exhibited nanometered, spherical shape according to scanning electron microscopy and transmission electron microscopy images. Moreover, the high degree of crystallinity and conductivity of chiral polyaniline induced by protein was acquired.

Kinetics of protein unfolding at interfaces

The conformation of protein molecules is determined by a balance of various forces, including van der Waals attraction, electrostatic interaction, hydrogen bonding, and conformational entropy. When protein molecules encounter an interface, they are often adsorbed on the interface. The conformation of an adsorbed protein molecule strongly depends on the interaction between the protein and the interface. Recent time-resolved investigations have revealed that protein conformation changes during the adsorption process due to the protein-protein interaction increasing with increasing interface coverage. External conditions also affect the protein conformation. This review considers recent dynamic observations of protein adsorption at various interfaces and their implications for the kinetics of protein unfolding at interfaces.