X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR) and atomic force microscopy (AF... more X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR) and atomic force microscopy (AFM) specialize in nano-scale characterizations of, respectively, the composition, structure and surface topography of multiphase polymer systems but offer limited specialization overlap. This article presents dielectric spectroscopic (DS) studies of organic and polystyrene structures on silicon that demonstrate the ability of DS to perform comparable characterizations to XPS, XRR and AFM as well as in situ characterizations of the interfacial electrochemistry that enhances thermodynamic properties of environments in contact with these systems.
, our Managing Editor P. C. Huang (Pien-Chien Huang) passed away. The Editorial Board of Biophysi... more , our Managing Editor P. C. Huang (Pien-Chien Huang) passed away. The Editorial Board of Biophysical Reviews and Letters is deeply saddened by the loss of a colleague and a pre-eminent scientist. Born on July 13, 1931 in Shanghai, China, Huang received a BS in genetics from National Taiwan University, an MS in genetics from Virginia Polytechnic Institute, and a PhD in genetics and biochemistry from Ohio State University. He held a
Hans G. L. Coster, School of Chemical and Biomolecular Engineering, University of Sydney, Sydney,... more Hans G. L. Coster, School of Chemical and Biomolecular Engineering, University of Sydney, Sydney, Australia [email protected] Jia Shin Ho, Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences ; Singapore Membrane Technology Centre, Nanyang Technological University, Singapore Lee Nuang Sim, Singapore Membrane Technology Centre, Nanyang Technological University, Singapore. Anthony G. Fane, Singapore Membrane Technology Centre ; School of Civil and Environmental Engineering, Nanyang Technological University, Singapore.
A linker and label free biosensing method is proposed, which utilizes nitrogen doped plasma polym... more A linker and label free biosensing method is proposed, which utilizes nitrogen doped plasma polymer to achieve linker free covalent binding of biorecognition molecules and the label free ellipsometric diagnosis technique. The high coverage of covalent binding of the link free plasma polymer surfaces is confirmed using different proteins. The highly sensitive and simplified biosensing diagnosis approach is demonstrated using three pairs of different antigen-antibodies.
Model lipid bilayers tethered to a gold substrate with molecular tethers are constructed. The con... more Model lipid bilayers tethered to a gold substrate with molecular tethers are constructed. The conductance versus temperature dependence curve is then obtained. Here, a method to measure the activation energy for translocation of an ion through existing transmembrane pores in a sparsely tethered bilayer lipid membranes is presented.
Solution-phase photocatalytic reduction of graphene oxide (GO) to reduced graphene oxide (RGO) by... more Solution-phase photocatalytic reduction of graphene oxide (GO) to reduced graphene oxide (RGO) by titanium dioxide (TiO 2) nanoparticles produces an RGO-TiO 2 composite that possesses enhanced charge transport properties beyond those of pure TiO 2 nanoparticle films. These composite films exhibit electron lifetimes up to four times longer than that of intrinsic TiO 2 films due to RGO acting as a highly conducting intra-particle charge transport network within the film. The intrinsic UV-active charge generation (photocurrent) of pure TiO 2 was enhanced by a factor of ten by incorporating RGO; we attribute this to both the highly conductive nature of the RGO and to improved charge collection facilitated by the intimate contact between RGO and the TiO 2-uniquely afforded by the solutionphase photocatalytic reduction method. Integrating RGO into nanoparticle films using this technique should improve the performance of photovoltaic devices that utilize nanoparticle films, such as dye sensitized and quantum-dot sensitized solar cells.
ABSTRACT Piezoelectric membranes were produced by “poling” prefabricated polyvinylidene fluoride ... more ABSTRACT Piezoelectric membranes were produced by “poling” prefabricated polyvinylidene fluoride (PVDF) membranes in an electric field. Scanning electron microscopy (SEM) studies revealed that electrical poling changed the microstructure of membranes significantly. Infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) measurements confirmed the formation of β-phase crystals in PVDF membranes as a result of poling in an intense electric field. Dynamic mechanical analysis (DMA) and measurement the surface displacement when the membranes were energized by AC signals, confirmed that the poled membranes were piezoelectric. Piezo-response force microscopy (PFM) analysis showed that the piezoelectric domains were not uniformly distributed over the sample.
Electric breakdown studies using a range of membranes made of various polymers showed that, in pr... more Electric breakdown studies using a range of membranes made of various polymers showed that, in principle, electrical poling can be applied to most membranes types. The results showed that the electric breakdown behavior of membranes was affected by their material type. The microstructure of the membranes was the most important factor in determining their dielectric strength. It was found that anisotropic membranes with layered structures had the lowest electric breakdown strength. The sample size and temperature also affected the electric breakdown of membranes. The former is probably due to a probabilistic presence of defects.
An analysis has been made of the dielectrophoretic ͑DEP͒ forces acting on a spheroidal particle i... more An analysis has been made of the dielectrophoretic ͑DEP͒ forces acting on a spheroidal particle in a traveling alternating electric field. The traveling field can be generated by application of alternating current signals to an octapair electrode array arranged in phase quadrature sequence. The frequency dependent force can be resolved into two orthogonal forces that are determined by the real and the imaginary parts of the Clausius-Mossotti factor. The former is determined by the gradient in the electric field and directs the particle either toward or away from the tip of the electrodes in the electrode array. The force determined by the imaginary component is in a direction along the track of the octapair interdigitated electrode array. The DEP forces are related to the dielectric properties of the particle. Experiments were conducted to determine the DEP forces in such an electrode arrangement using yeast cells ͑Saccharomyces cervisiate TISTR 5088͒ with media of various conductivities. Experimental data are presented for both viable and nonviable cells. The dielectric properties so obtained were similar to those previously reported in literature using other DEP techniques.
It is shown that if the membrane potential of cells of Valonia utricularis was increased rapidly ... more It is shown that if the membrane potential of cells of Valonia utricularis was increased rapidly by applying ~500 μs current pulses, dielectric breakdown of the membrane occured when the potential reached a value of ~0.85 V. The breakdown phenomenon observed was not associated with global damage to the cell or its membrane. The process could be repeated after a short resealing time (~ 10s), many times on a single cell. The rapidity of the breakdown process (~1 μs) rules out the possibility that dielectric breakdown occurs by a mechanism similar to that of punch-through, which involves changes in ionic profiles.
Voltage-clamp experiments were made to determine the effect of temperature on the Hodgkin-Huxley ... more Voltage-clamp experiments were made to determine the effect of temperature on the Hodgkin-Huxley parameters describing the excitation of the plasmalemma of C. covallina. In these cells two activated and inactivated transients in addition to a potential-dependent leak conductance occur during excitation. The activation and inactivation time constants for both the Cl- and X (� Ca�+?) channels decreased with increasing temperature. The relative changes with temperature, however, were the same at all potentials. That is, the thermodynamic activation enthalpies for activation and inactivation were independent of membrane potential. This suggests that these parts of the gating processes do not involve movement, normal to the membrane, of charged moieties (other than the ions carrying the clamp currents). For clamps beyond the threshold, both gated current transients occur only after a delay, the latter being strongly dependent on the clamp potential. The delays �*Cl and �*x in the Cl- tra...
At the punchthrough, the current required to maintain the hyperpolarized potential difference (p.... more At the punchthrough, the current required to maintain the hyperpolarized potential difference (p.d.) of the plasmalemma increases very rapidly with increasing hyperpolarization so that, in the steady state, the membrane cannot be hyperpolarized beyond a certain level. It was found that punchthrough in the plasmalemma of C. corallina occurred at more negative (i.e. at greater hyperpolarizing) potentials as the temperature was decreased, from a value of ~ -310mV at T = 32�C to ~ -420 mV at T = 5�C. Some considerations are given to the compressive stress induced in the plasmalemma due to the electric field. These stresses at the p.d. values required for punchthrough are very considerable (~ 3 x 10*6 Nm*-�), and could lead to significant strains in the membrane. The degree of electromechanical compression of the membrane would increase with increasing temperature if, as the evidence cited suggests, the elastic modulus of the membrane decreases with increasing temperature. This would acc...
Voltage-clamp experiments over a wide range of clamp potentials were made with cells of C. corall... more Voltage-clamp experiments over a wide range of clamp potentials were made with cells of C. corallina using a fast voltage-clamp apparatus. Clamps of the plasmalemma potential in the range - 170 mV to - 70 mV revealed a large transient inward current which followed the usual chloride current transient hitherto described in the literature. This additional component decreased in amplitude and occurred earlier in the clamp as the clamp potentials were made more positive up to ~ -70 mV. For clamp potentials > - 50 mV, a large, prompt, outward current appeared. The additional current transients could not be observed in vacuolar potential clamp experiments, except at clamps � - 10 mV. The effects of changes in the external Cl- and Ca�+ concentrations with plasmalemma clamps at various potentials suggest that the additional transient here reported consists of a flow of Ca�+ ions and also reaffirms the identification of the other transient with a flow of Cl- ions. Reversal of the addition...
Simultaneous measurements of the separate plasmalemma and tonoplast capacitance and conductance (... more Simultaneous measurements of the separate plasmalemma and tonoplast capacitance and conductance (as a function of frequency) are described. For frequencies > 1 Hz, the capacitance of both membranes increased with decreasing frequency. Below 1 Hz, two distinctly different types of behaviour were observed: either the membrane capacitances continued to increase, reaching values of 0.5 F/m� (50 �F/cm�) at 0.07 Hz, or the membranes became inductive at very low frequencies. At frequencies > 10 Hz, the tonoplast capacitance was 1.5-3 times higher than that of the plasmalemma and increased more rapidly with decreasing frequency. Notwithstanding this, in each case the frequency dependence of the capacitance determined from vacuolar measurements (i.e. tonoplast, cytoplasm and plasmalemma in series) was nearly the same as that of the plasmalemma alone. The conductance of the tonoplast at all frequencies was 4-10 times higher than that of the plasmalemma.
An analysis is given of the effects of electromechanical compression (electrostriction) on the el... more An analysis is given of the effects of electromechanical compression (electrostriction) on the electrical characteristics of double-fixed-charge membranes. It is shown that the voltage-current characteristics of Chaua couallina, and in particular the punchthrough potential, as a function of temperature can be accounted for on the basis of the double-fixed-charge membrane model when electrostrictive effects are taken into account.
An analysis, based on the Hodgkin-Huxley (H-H) equations is given of excitation processes in the ... more An analysis, based on the Hodgkin-Huxley (H-H) equations is given of excitation processes in the plasmalemma of cells of C. corallina. Voltage clamp data for the plasmalemma show the presence of two activation and two inactivation processes and both of these transients are modelled in a manner analagous to the gated Na+ current in squid axons. Separation of the various ionic components of the experimental clamp currents was achieved by fitting the experimental data over a wide range of potentials to the model equations. The potential dependencies of the various H-H parameters for C. corallina, determined from the analysis of experimental results, are presented. A reconstruction is also given of the action potential and it is shown to be in satisfactory agreement with the experimental data. Comparisons are made of the experimental and predicted threshold potential, refractory period and the effects of the external Cl- and Ca�+ ion concentrations on the action potential. From the H-H ...
Influx and efflux of chloride ions in Ohara australis have been measured under a variety of condi... more Influx and efflux of chloride ions in Ohara australis have been measured under a variety of conditions in an attempt to relate the active transport inwards to a particular aspect of metabolism. Influx across the plasmalemma in single cells was 1-4 p-equiv_ cm-2 sec-I. The rate constant for exchange of cytoplasmic chloride was of the order of 10-3 sec-1 and the content of chloride in the cytoplasm was found to be about 100 n-equiv. cm-2? From these values the influx across the tonoplast was inferred to be ~ 100 p-equiv. cm-2 sec-I. Most of the cytoplasmic chloride was probably in the chloroplasts.
The ion-exchange properties of the cytoplasm are of fundamental importance in determining the ove... more The ion-exchange properties of the cytoplasm are of fundamental importance in determining the overall ionic relations of the cell.
X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR) and atomic force microscopy (AF... more X-ray photoelectron spectroscopy (XPS), X-ray reflectometry (XRR) and atomic force microscopy (AFM) specialize in nano-scale characterizations of, respectively, the composition, structure and surface topography of multiphase polymer systems but offer limited specialization overlap. This article presents dielectric spectroscopic (DS) studies of organic and polystyrene structures on silicon that demonstrate the ability of DS to perform comparable characterizations to XPS, XRR and AFM as well as in situ characterizations of the interfacial electrochemistry that enhances thermodynamic properties of environments in contact with these systems.
, our Managing Editor P. C. Huang (Pien-Chien Huang) passed away. The Editorial Board of Biophysi... more , our Managing Editor P. C. Huang (Pien-Chien Huang) passed away. The Editorial Board of Biophysical Reviews and Letters is deeply saddened by the loss of a colleague and a pre-eminent scientist. Born on July 13, 1931 in Shanghai, China, Huang received a BS in genetics from National Taiwan University, an MS in genetics from Virginia Polytechnic Institute, and a PhD in genetics and biochemistry from Ohio State University. He held a
Hans G. L. Coster, School of Chemical and Biomolecular Engineering, University of Sydney, Sydney,... more Hans G. L. Coster, School of Chemical and Biomolecular Engineering, University of Sydney, Sydney, Australia [email protected] Jia Shin Ho, Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences ; Singapore Membrane Technology Centre, Nanyang Technological University, Singapore Lee Nuang Sim, Singapore Membrane Technology Centre, Nanyang Technological University, Singapore. Anthony G. Fane, Singapore Membrane Technology Centre ; School of Civil and Environmental Engineering, Nanyang Technological University, Singapore.
A linker and label free biosensing method is proposed, which utilizes nitrogen doped plasma polym... more A linker and label free biosensing method is proposed, which utilizes nitrogen doped plasma polymer to achieve linker free covalent binding of biorecognition molecules and the label free ellipsometric diagnosis technique. The high coverage of covalent binding of the link free plasma polymer surfaces is confirmed using different proteins. The highly sensitive and simplified biosensing diagnosis approach is demonstrated using three pairs of different antigen-antibodies.
Model lipid bilayers tethered to a gold substrate with molecular tethers are constructed. The con... more Model lipid bilayers tethered to a gold substrate with molecular tethers are constructed. The conductance versus temperature dependence curve is then obtained. Here, a method to measure the activation energy for translocation of an ion through existing transmembrane pores in a sparsely tethered bilayer lipid membranes is presented.
Solution-phase photocatalytic reduction of graphene oxide (GO) to reduced graphene oxide (RGO) by... more Solution-phase photocatalytic reduction of graphene oxide (GO) to reduced graphene oxide (RGO) by titanium dioxide (TiO 2) nanoparticles produces an RGO-TiO 2 composite that possesses enhanced charge transport properties beyond those of pure TiO 2 nanoparticle films. These composite films exhibit electron lifetimes up to four times longer than that of intrinsic TiO 2 films due to RGO acting as a highly conducting intra-particle charge transport network within the film. The intrinsic UV-active charge generation (photocurrent) of pure TiO 2 was enhanced by a factor of ten by incorporating RGO; we attribute this to both the highly conductive nature of the RGO and to improved charge collection facilitated by the intimate contact between RGO and the TiO 2-uniquely afforded by the solutionphase photocatalytic reduction method. Integrating RGO into nanoparticle films using this technique should improve the performance of photovoltaic devices that utilize nanoparticle films, such as dye sensitized and quantum-dot sensitized solar cells.
ABSTRACT Piezoelectric membranes were produced by “poling” prefabricated polyvinylidene fluoride ... more ABSTRACT Piezoelectric membranes were produced by “poling” prefabricated polyvinylidene fluoride (PVDF) membranes in an electric field. Scanning electron microscopy (SEM) studies revealed that electrical poling changed the microstructure of membranes significantly. Infrared spectroscopy (FTIR) and differential scanning calorimetry (DSC) measurements confirmed the formation of β-phase crystals in PVDF membranes as a result of poling in an intense electric field. Dynamic mechanical analysis (DMA) and measurement the surface displacement when the membranes were energized by AC signals, confirmed that the poled membranes were piezoelectric. Piezo-response force microscopy (PFM) analysis showed that the piezoelectric domains were not uniformly distributed over the sample.
Electric breakdown studies using a range of membranes made of various polymers showed that, in pr... more Electric breakdown studies using a range of membranes made of various polymers showed that, in principle, electrical poling can be applied to most membranes types. The results showed that the electric breakdown behavior of membranes was affected by their material type. The microstructure of the membranes was the most important factor in determining their dielectric strength. It was found that anisotropic membranes with layered structures had the lowest electric breakdown strength. The sample size and temperature also affected the electric breakdown of membranes. The former is probably due to a probabilistic presence of defects.
An analysis has been made of the dielectrophoretic ͑DEP͒ forces acting on a spheroidal particle i... more An analysis has been made of the dielectrophoretic ͑DEP͒ forces acting on a spheroidal particle in a traveling alternating electric field. The traveling field can be generated by application of alternating current signals to an octapair electrode array arranged in phase quadrature sequence. The frequency dependent force can be resolved into two orthogonal forces that are determined by the real and the imaginary parts of the Clausius-Mossotti factor. The former is determined by the gradient in the electric field and directs the particle either toward or away from the tip of the electrodes in the electrode array. The force determined by the imaginary component is in a direction along the track of the octapair interdigitated electrode array. The DEP forces are related to the dielectric properties of the particle. Experiments were conducted to determine the DEP forces in such an electrode arrangement using yeast cells ͑Saccharomyces cervisiate TISTR 5088͒ with media of various conductivities. Experimental data are presented for both viable and nonviable cells. The dielectric properties so obtained were similar to those previously reported in literature using other DEP techniques.
It is shown that if the membrane potential of cells of Valonia utricularis was increased rapidly ... more It is shown that if the membrane potential of cells of Valonia utricularis was increased rapidly by applying ~500 μs current pulses, dielectric breakdown of the membrane occured when the potential reached a value of ~0.85 V. The breakdown phenomenon observed was not associated with global damage to the cell or its membrane. The process could be repeated after a short resealing time (~ 10s), many times on a single cell. The rapidity of the breakdown process (~1 μs) rules out the possibility that dielectric breakdown occurs by a mechanism similar to that of punch-through, which involves changes in ionic profiles.
Voltage-clamp experiments were made to determine the effect of temperature on the Hodgkin-Huxley ... more Voltage-clamp experiments were made to determine the effect of temperature on the Hodgkin-Huxley parameters describing the excitation of the plasmalemma of C. covallina. In these cells two activated and inactivated transients in addition to a potential-dependent leak conductance occur during excitation. The activation and inactivation time constants for both the Cl- and X (� Ca�+?) channels decreased with increasing temperature. The relative changes with temperature, however, were the same at all potentials. That is, the thermodynamic activation enthalpies for activation and inactivation were independent of membrane potential. This suggests that these parts of the gating processes do not involve movement, normal to the membrane, of charged moieties (other than the ions carrying the clamp currents). For clamps beyond the threshold, both gated current transients occur only after a delay, the latter being strongly dependent on the clamp potential. The delays �*Cl and �*x in the Cl- tra...
At the punchthrough, the current required to maintain the hyperpolarized potential difference (p.... more At the punchthrough, the current required to maintain the hyperpolarized potential difference (p.d.) of the plasmalemma increases very rapidly with increasing hyperpolarization so that, in the steady state, the membrane cannot be hyperpolarized beyond a certain level. It was found that punchthrough in the plasmalemma of C. corallina occurred at more negative (i.e. at greater hyperpolarizing) potentials as the temperature was decreased, from a value of ~ -310mV at T = 32�C to ~ -420 mV at T = 5�C. Some considerations are given to the compressive stress induced in the plasmalemma due to the electric field. These stresses at the p.d. values required for punchthrough are very considerable (~ 3 x 10*6 Nm*-�), and could lead to significant strains in the membrane. The degree of electromechanical compression of the membrane would increase with increasing temperature if, as the evidence cited suggests, the elastic modulus of the membrane decreases with increasing temperature. This would acc...
Voltage-clamp experiments over a wide range of clamp potentials were made with cells of C. corall... more Voltage-clamp experiments over a wide range of clamp potentials were made with cells of C. corallina using a fast voltage-clamp apparatus. Clamps of the plasmalemma potential in the range - 170 mV to - 70 mV revealed a large transient inward current which followed the usual chloride current transient hitherto described in the literature. This additional component decreased in amplitude and occurred earlier in the clamp as the clamp potentials were made more positive up to ~ -70 mV. For clamp potentials > - 50 mV, a large, prompt, outward current appeared. The additional current transients could not be observed in vacuolar potential clamp experiments, except at clamps � - 10 mV. The effects of changes in the external Cl- and Ca�+ concentrations with plasmalemma clamps at various potentials suggest that the additional transient here reported consists of a flow of Ca�+ ions and also reaffirms the identification of the other transient with a flow of Cl- ions. Reversal of the addition...
Simultaneous measurements of the separate plasmalemma and tonoplast capacitance and conductance (... more Simultaneous measurements of the separate plasmalemma and tonoplast capacitance and conductance (as a function of frequency) are described. For frequencies > 1 Hz, the capacitance of both membranes increased with decreasing frequency. Below 1 Hz, two distinctly different types of behaviour were observed: either the membrane capacitances continued to increase, reaching values of 0.5 F/m� (50 �F/cm�) at 0.07 Hz, or the membranes became inductive at very low frequencies. At frequencies > 10 Hz, the tonoplast capacitance was 1.5-3 times higher than that of the plasmalemma and increased more rapidly with decreasing frequency. Notwithstanding this, in each case the frequency dependence of the capacitance determined from vacuolar measurements (i.e. tonoplast, cytoplasm and plasmalemma in series) was nearly the same as that of the plasmalemma alone. The conductance of the tonoplast at all frequencies was 4-10 times higher than that of the plasmalemma.
An analysis is given of the effects of electromechanical compression (electrostriction) on the el... more An analysis is given of the effects of electromechanical compression (electrostriction) on the electrical characteristics of double-fixed-charge membranes. It is shown that the voltage-current characteristics of Chaua couallina, and in particular the punchthrough potential, as a function of temperature can be accounted for on the basis of the double-fixed-charge membrane model when electrostrictive effects are taken into account.
An analysis, based on the Hodgkin-Huxley (H-H) equations is given of excitation processes in the ... more An analysis, based on the Hodgkin-Huxley (H-H) equations is given of excitation processes in the plasmalemma of cells of C. corallina. Voltage clamp data for the plasmalemma show the presence of two activation and two inactivation processes and both of these transients are modelled in a manner analagous to the gated Na+ current in squid axons. Separation of the various ionic components of the experimental clamp currents was achieved by fitting the experimental data over a wide range of potentials to the model equations. The potential dependencies of the various H-H parameters for C. corallina, determined from the analysis of experimental results, are presented. A reconstruction is also given of the action potential and it is shown to be in satisfactory agreement with the experimental data. Comparisons are made of the experimental and predicted threshold potential, refractory period and the effects of the external Cl- and Ca�+ ion concentrations on the action potential. From the H-H ...
Influx and efflux of chloride ions in Ohara australis have been measured under a variety of condi... more Influx and efflux of chloride ions in Ohara australis have been measured under a variety of conditions in an attempt to relate the active transport inwards to a particular aspect of metabolism. Influx across the plasmalemma in single cells was 1-4 p-equiv_ cm-2 sec-I. The rate constant for exchange of cytoplasmic chloride was of the order of 10-3 sec-1 and the content of chloride in the cytoplasm was found to be about 100 n-equiv. cm-2? From these values the influx across the tonoplast was inferred to be ~ 100 p-equiv. cm-2 sec-I. Most of the cytoplasmic chloride was probably in the chloroplasts.
The ion-exchange properties of the cytoplasm are of fundamental importance in determining the ove... more The ion-exchange properties of the cytoplasm are of fundamental importance in determining the overall ionic relations of the cell.
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