Solid-state Membrane Research Articles

Novel creatine biosensors based on all solid-state contact ammonium-selective membrane electrodes

Novel creatine bienzymatic potentiometric biosensors were prepared by immobilizing urease and creatinase on all solid-state contact PVC-containing palmitic acid and carboxylated PVC matrix membrane ammonium-selective electrodes without inner reference solution. Potentiometric characteristics of biosensors were examined in physiological model solutions at different creatine concentrations. The linear working range and long-term sensitivity of the biosensors were also determined. The creatine biosensors prepared by using the carboxylated PVC membrane electrodes showed more effective performance than those of the PVC containing palmitic acid membrane electrodes. Creatine assay in serum samples was successfully carried out by using the standard addition method.

Solid-State Water Electrolysis with an Alkaline Membrane

We report high-performance, durable alkaline membrane water electrolysis in a solid-state cell. An anion exchange membrane (AEM) and catalyst layer ionomer for hydroxide ion conduction were used without the addition of liquid electrolyte. At 50 °C, an AEM electrolysis cell using iridium oxide as the anode catalyst and Pt black as the cathode catalyst exhibited a current density of 399 mA/cm(2) at 1.80 V. We found that the durability of the AEM-based electrolysis cell could be improved by incorporating a highly durable ionomer in the catalyst layer and optimizing the water feed configuration. We demonstrated an AEM-based electrolysis cell with a lifetime of >535 h. These first-time results of water electrolysis in a solid-state membrane cell are promising for low-cost, scalable hydrogen production.

DNA Origami Gatekeepers for Solid‐State Nanopores

DNA has it covered: DNA origami gatekeeper nanoplates convert nanopores in solid-state membranes into versatile devices for label-free macromolecular sensing applications. The custom apertures in the nanoplates can be chemically addressed for sequence-specific detection of DNA.

Montagem de uma célula universal para ensaios de permeação em membranas semipermeáveis sólidas em escala laboratorial

This technical note describes the assembly of a glass-made universal cell that was designed for solid-state membrane permeation or electrodiffusion experiments. It can be used to measure the permeation rates of practically any molecule or ion in solution and even in gas phase through solid membranes. The experiments, driven by concentration gradients or electric fields, may be followed and recorded in real time over long periods of time using serial data acquisition programs. The cell itself allows the utilization of a wide range of different chemical sensors and up to eight of them simultaneously.

Effects of the Focused Ion Beam Parameters on Nanopore Milling in Solid State Membranes

Abstract This work describes a reliable nanofabrication technology of solid state nanopore arrays. The geometric parameters of pores are achieved and optimized according to the requirements of bioanalytical applications regarding conformation and size of the characteristic proteins in clinical diagnostics. Different structural configurations and material compositions of the nanopore structures were developed and characterised according to the variable biofunctionalisation strategies. The geometry of the fabricated pores were analysed as the statistical function of the focused ion beam milling parameters.

Electrokinetic ion and fluid transport in nanopores functionalized by polyelectrolyte brushes

Chemically functionalized nanopores in solid-state membranes have recently emerged as versatile tools for regulating ion transport and sensing single biomolecules. This study theoretically investigated the importance of the bulk salt concentration, the geometries of the nanopore, and both the thickness and the grafting density of the polyelectrolyte (PE) brushes on the electrokinetic ion and fluid transport in two types of PE brush functionalized nanopore: PE brushes are end-grafted to the entire membrane surface (system I), and to its inner surface only (nanopore wall) (system II). Due to a more significant ion concentration polarization (CP), the enhanced local electric field inside the nanopore, the conductance, and the electroosmotic flow (EOF) velocity in system II are remarkably smaller than those in system I. In addition to a significantly enhanced EOF inside the nanopore, the direction of the flow field near both nanopore openings in system I is opposite to that of EOF inside the nanopore. This feature can be applied to regulate the electrokinetic translocation of biomolecules through a nanopore in the nanopore-based DNA sequencing platform.

A novel conductometric creatinine biosensor based on solid-state contact ammonium sensitive PVC–NH2 membrane

A novel, highly sensitive and stable conductometric biosensor for creatinine determination is developed. The biosensor is based on solid-state contact ammonium-sensitive sensor. Creatininase is chemically immobilized on the surface of the solid-state contact ammonium-sensitive membrane via glutaraldehyde covalent attachment method. The developed conductometric creatinine biosensors demonstrate high sensitivity and short response time toward creatinine. The detection limit of the biosensor was about 2×10−6M and the response time was shorter than 10s in phophate buffer solution at pH 7.20. The linear dynamic range of the biosensor was between 1×10−1 and 9×10−6M creatinine concentration in phosphate buffer solution at pH 7.20. The biosensor exhibited good operational and storage stability for at least 4 weeks kept in dry at 4–6°C. It had a reproducible and stable response during continuous work at least for 10h with the relative standard deviation of 0.5% (n=48) for creatinine of 1×10−3M in phosphate buffer solution.

Solid Character of Membrane Ceramides: A Surface Rheology Study of Their Mixtures with Sphingomyelin

The compression and shear viscoelasticities of egg-ceramide and its mixtures with sphingomyelin were investigated using oscillatory surface rheology performed on Langmuir monolayers. We found high values for the compression and shear moduli for ceramide, compatible with a solid-state membrane, and extremely high surface viscosities when compared to typical fluid lipids. A fluidlike rheological behavior was found for sphingomyelin. Lateral mobilities, measured from particle tracking experiments, were correlated with the monolayer viscosities through the usual hydrodynamic relationships. In conclusion, ceramide increases the solid character of sphingomyelin-based membranes and decreases their fluidity, thus drastically decreasing the lateral mobilities of embedded objects. This mechanical behavior may involve important physiological consequences in biological membranes containing ceramides.

Nanopore Analysis of Individual RNA/Antibiotic Complexes

Nanopores in thin solid-state membranes are used to rapidly analyze individual RNA/drug complexes. The interactions of a truncated A-site RNA model of the prokaryotic ribosome with aminoglycoside antibiotics are characterized by passing individual molecules through a 3-3.5 nm diameter pore fabricated in a 8-10 nm thick silicon nitride membrane. Complexes of the A-site RNA with aminoglycosides can be distinguished from unbound A-site based on the ion current signatures produced as they pass through the nanopores. Counting the fraction of free and drug-bound molecules affords label-free drug-RNA binding isotherms consistent with literature reports and with data generated using independent fluorescence-based assays. Our measurements are supported by molecular dynamics simulations, which illustrate the relationship between the ionic current and complexation of the A-site RNA with paramomycin, a prototypical aminoglycoside antibiotic.

Tuned galvanostatic polarization of solid-state lead-selective electrodes for lowering of the detection limit

Lowering of the detection limit of solid-state lead-selective electrodes was achieved by using the tuned galvanostatic polarization method. A Nernstian response was obtained down to nanomolar concentrations (low detection limit 10 −9 mol dm −3 Pb 2+). Good repeatability of the calibration curves was achieved by using a well established measuring procedure. Relatively high cathodic current densities were applied to the solid-state membrane in order to shorten the measurement time. Successful determination of lead in a synthetic sample (pPb 2+ = 7.97 ± 0.08) was achieved by introducing an analytical protocol and favourably compared to inductively coupled plasma mass spectrometry (pPb = 7.93). By applying this method, a significant improvement in the detection limit of solid-state lead-selective electrodes was attained.

Hybrid Biological/Solid-State Nanopores

Biomolecular translocation through the bacterial nanopore α hemolysin (αHL) has been suggested as a possible platform for next generation sequencing technology. In this method, a single protein pore is inserted in an otherwise impermeable lipid membrane and an applied electric field is used to drive charged biomolecules like DNA through it. Information like nucleotide sequence could then conceivably be read from the molecule as it translocates linearly to the other side. One challenge to the incorporation of this system into wafer-scale device architectures, however, is its reliance on a delicate lipid bilayer for mechanical support. The solid-state (SS) nanopore- composed of a single, fabricated aperture in a thin, solid-state membrane- offers a potential solution with demonstrated durability and integration potential. But, this system lacks the atomically resolved interior structure and genetic engineering ability of the protein pore. Here we present a potential solution that consists of a combination of the two systems, wherein a single αHL protein pore is inserted directly into a SS nanopore with orientation control, yielding a robust hybrid system.

Study on the Size Shrinking and Shape Changing of Solid-State Nanopores

Nanopores etched in the solid-state membranes have become the hotpot of nanotechnology research. Various methods for fabricating solid-state nanopores have been developed and reported, but the fabrication of nanopore is also a difficult challenge. In this paper, we milled nanopores of different sizes in the free-stand and low-stress solid-state membranes. And then the area around nanopores were scanned with the diffused ion beam, we found that the sediment around will melt and the shape of the nanopore becomes circular.

Stochastic Sensing of His-Tagged Proteins with a NTA-Functionalized Solid-State Nanopore

Artificial nanopores in solid-state membranes have emerged as a versatile tool to study single biomolecules. Employing nanopores as stochastic sensors offers the attractive prospect of detecting and quantifying molecular interactions and bindings on a single-molecule level. Individual interactions between analyte molecules and receptor sites within the pore can be observed as transient modulations of the trans-pore current.Here we demonstrate the stochastic sensing of single proteins in a solid-state nanopore functionalized with nitrilotriacetic acid (NTA) chelator groups as specific binding sites for histidine-tagged proteins. The non-covalent yet selective His-tag/NTA interaction is well suited as a model system, since the binding strength depends on NTA valency and presence of competitive binders.NTA affinity groups are tethered within the nanopores by first coating the walls of pores in SiN membranes with gold, and subsequently adsorbing NTA-functionalized alkane-thiol self-assembled monolayers.Individual binding events of His-tagged proteins were successfully detected in real-time. Analysis of the binding times provide kinetic information and corroborate the occurrence of bimolecular interactions. The binding is shown to be reversible and specific, as the kinetics can be significantly altered by the addition of imidazole as a competitive binding agent and is completely inhibited by removal of the chelated metal ions. In concentration dependent studies we elucidate the influence of the competitive binder on the single-molecule binding times.We systematically studied the influence of the NTA valency on the binding strength, comparing mono-, bis-, and tris-NTA receptors and present a ranking of single-molecule binding times. Our results indicate that multivalent interactions are strong enough to stably immobilize His-tagged proteins within the pore, so their interactions with third-party proteins can be studied. This paves the way for the use of NTA functionalized metal nanopores as generic tools to study protein-protein interactions one-on-one.

Micro- and Nanoparticle Translocation through a Solid-State Membrane Pore Thinner than their Diameters

Micron-sized particles have been detected by the resistive-pulse or Coulter counting technique since the 1950's (Coulter, US Pat. 2656508) with 90 nm particle detection reported in 1970 (DeBlois and Bean, Rev. Sci. Inst. 41, 909). Due to the challenges of fabricating submicron pores in those times, the pores used were all several microns in length. Nanofabrication has advanced significantly since then, and in this poster we examine the interesting case of particles translocating through a membrane pore thinner than those particles.With micron-long, high aspect ratio pores, a spherical particle will be entirely contained within the pore for the majority of the time it translocates. Thus, all but the beginning and end of the observed signal is due to the entire particle. In addition, pore resistance dominates over access resistance. In contrast, with low-aspect ratio pores thinner than the particle, the signal reflects the interactions of the particle with both the access resistance volumes and the pore volume. The signal is a complex combination of these interactions, that changes as the particle moves through the pore. Another advantage of shorter pores is that identical particles passing through longer pores give smaller modulations in current, because the proportional change in resistance due to the particle is smaller.We use a focused ion beam to drill nanopores tens to hundreds of nanometers in diameter in silicon nitride membranes, with thicknesses in the same range. Polystyrene microspheres are driven through these pores by an applied electric field. As they pass through, they modulate the flux of ions through the pore, and thus the current flowing between the electrodes. We present experimental and simulated studies of particle translocation, aimed at determining the optimum system for analyzing virus particles using this method.

Elucidation of Abnormal Potential Responses of Cation-Selective Electrodes with Solid-State Membranes to Aqueous Solutions of CuCl2 and CdI2

An empirical solution to abnormal potential responses, showing peaks of emf, of commercial Cu2+- and Cd2+-selective electrodes with solid-state membranes was proposed for aqueous solutions of CuCl2 and CdI2. The two-step processes of Mn+ + Yn? (s: solid phase) MY(s) and MY(s) + 2X? X2MY2?(s) (n = 1, 2) at a test solution/electrode-interface were considered as a model. Here, Mn+, Yn?, and X? refer to a divalent or univalent cation, functional groups of electrode materials, and a halide ion (X? = Cl?, Br?, I?), respectively. By applying electrochemical potentials to these processes at n = 2, we derived an equation. Regression analyses based on the equation reproduced well the plots of emf versus log 2(*[M]t) for the Cd(II) and Cu(II) systems: *[M]t denotes a total concentration of species relevant to M2+ in a bulk of the aqueous solution. Also, we obtained log Ks(CdBr2) = 4.28 ? 0.22, log Ks(CdI2) = 6.98 ? 0.05, log Ks(CuCl2) = 3.96 ? 0.09, and log Ks(CuBr2) = 11.4 at 25?C. The magnitude in ?log Ks reflected that in the logarithmic solubility product, log {*[M2+](*[X?])2}, for bulk water, where *[M2+] or *[X?] denotes a molar concentration of the bulk solu-tion of M2+ or X? at equilibrium, respectively. Moreover, a mixture of CuSO4 with NaCl at the molar ratio of 1:1 yielded a plot similar to that of CuCl2.

Self-assembled organic nanotubes embedding hydrophobic molecules within solid bilayer membranes

We have carried out co-assembly of N-(11-cis-octadecenoyl)-β-D-glucopyranosylamine 1 with hydrophobic molecules, 8-anilinonaphthalene-1-sulfonate (1,8-ANS) 2 or Zn-phthalocyanine 3 in a mixed solvent of organic solvents and water to form nanotubes embedding the hydrophobic molecules. Transmission electron microscopic (TEM), fluorescence microscopic observations, and X-ray diffraction (XRD) analysis revealed the formation of nanotubes where the interdigitated bilayer membranes of 1 function as an embedded matrix for the hydrophobic molecules. We have compared the release behavior of 2 embedded in the bilayer membranes with that of 2 encapsulated inside the nanotube hollow cylinder of 60-nm inner diameter. Although the encapsulated molecules 2 proved to be slowly released from both open ends of the hollow cylinder at room temperature, the embedded ones kept staying in the bilayer membranes. Similarly, the embedded molecules 3 kept staying in the interdigitated bilayer membranes at temperatures below a thermal phase transition temperature (Tg-l = 59 °C) of the nanotubes. However, when the solid-state bilayer membranes of the nanotubes converted into a fluid bilayer membrane at temperatures above the Tg-l, the molecules 3 was instantly released. Such self-assembled nanotubes embedding hydrophobic molecules are applicable to medical diagnosis systems containing deliveries of drugs, photosensitizers, fluorescence- and spin-probes.

Synthesis, characterization of poly(4, 4’-diaminophenylethanepyromellitimide) and its use as immobilized enzyme polyimide membrane

A novel polyimide prepared from pyromellitic dianhydride (PMDA) and 1,2-bis(4-aminophenyl)ethane was characterized by Fourier transform infrared spectrometer and gel permeation chromatography. Thermal properties of the poly(4,4’-diaminophenylethane-pyromellitimide) (PDP) were evaluated by differential scanning calorimetry, differential thermal analysis and thermogravimetry. The PDP exhibited high decomposition temperature Td (°C), good thermal stability and good adhesive properties. Moreover, that the possibility of whether the chemically-prepared polyimide film could be used as a membrane for immobilization of glucose oxidase (GOx) was investigated. The amperometric response of the PDP/GOx/Pt electrode to hydrogen peroxide, formed as the product of enzymatic reaction, was measured at a potential of 700 mV (vs. SCE) in phosphate buffer solution by means of the TB technique. The amperometric glucose sensor was very high R-value (0.9995). The structure of the GOx micelles contained in polyimide membrane was observed by scanning electron microscopy. From the amperometric responses, it was also demonstrated that PDP film could be used as a solid-state immobilized enzyme polyimide membrane for biosensor design because of its strong adherence to electrode surface and chemical stability.

A study on lowering the detection limit with solid-state lead-selective electrodes

The detection limit of a Pb 2+ ion-selective electrode with a solid state (PbS/Ag 2S) membrane was successfully lowered to the nanomolar range. The electrode was applied in direct potentiometric determination of Pb 2+ in aqueous solutions. Hydrodynamics, redox reaction at the solid-state surface as well as time dependency were investigated and found as key factors affecting the low detection limit. By optimizing these parameters improving detection limit by ca. three orders of magnitude was achieved.

Recent trends in potentiometric sensor arrays—A review

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed.

Anisotropic etching of diamond by molten Ni particles

Nanopores in insulating solid state membranes have recently attracted much interest in the field of probing, characterizing, and manipulating single linear polymers such as DNA/RNA and proteins in their native environment. Here a low cost, fast, and effective way to produce nanostructures such as pyramidal shaped nanopores and nanochannels with dimensions down to about 15 nm in diamond membranes without any need for electron-beam lithography is demonstrated. By use of a catalytic process, anisotropic etching of diamond with self-organized Ni nanoparticles in hydrogen atmosphere at 900 °C is achieved and possible etching mechanisms are discussed. It is shown that diamond planes with the crystallographic orientation of [111] are etched slowest with this method.