Kalle Levon

A potentiometric protein sensor built with surface molecular imprinting method.

Surface molecular imprinting, as compared to molecular imprinted bulk polymers, has the advantages of higher re-occupation percentage of the reception sites, fast response, integration of sensing element and transducer, etc. In this study, a potentiometric protein sensor was developed based on the surface molecular imprinting technique. Using the self-assembled monolayers of alkanethiol with hydroxyl terminal groups as the matrix material, and target protein molecules as the template, the sensing layer was created on the surface of the gold-coated silicon chip-an electrochemical transducer. Potentiometric measurement demonstrated that the sensor could selectively detect myoglobin or hemoglobin molecules, either with or without the presence of other protein molecules in the same solution.

THERMALLY INDUCED PHASE SEPARATION IN TERNARY CRYSTALLIZABLE POLYMER SOLUTIONS

Abstract Microporous membranes were prepared by the thermally induced phase separation (TIPS) process of a ternary solution of HDPE, ditrydecylphthalate and hexadecane. The equilibrium phase diagram calculations were carried out in terms of a pseudo-binary system, considering the solvent mixture to be one component, to show the effect of the interaction parameter on the phase diagram. The experimental results showed that by varying the composition of the solvent pair, i.e., by varying the interaction parameter systematically, the phase diagrams can be controlled successfully. Liquid—liquid phase separation was obtained also below the melting point by controlling the composition of the solvent mixture. It is also shown that the membrane morphology can be controlled with different solvent compositions when the cooling conditions are kept constant.

A polyaniline based ultrasensitive potentiometric immunosensor for cardiac troponin complex detection.

An ultrasensitive immunosensor based on potentiometric ELISA for the detection of a cardiac biomarker, troponin I-T-C (Tn I-T-C) complex, was developed. The sensor fabrication involves typical sandwich ELISA procedures, while the final signal readout was achieved using open circuit potentiometry (OCP). Glassy carbon (GC) working electrodes were first coated with emulsion-polymerized polyaniline/dinonylnaphthalenesulfonic acid (PANI/DNNSA) and the coated surface was utilized as a transducer layer on which sandwich ELISA incubation steps were performed. An enzymatic reaction between o-phenylenediamine (OPD) and hydrogen peroxide (H2O2) was catalyzed by horseradish peroxidase (HRP) labeled on the secondary antibodies. The polymer transducer charged state was mediated through electron (e(-)) and charge transfers between the transducer and charged species generated by the same enzymatic reaction. Such a change in the polymer transducer led to potential variations against an Ag/AgCl reference electrode as a function of Tn I-T-C complex concentration during incubations. The sequence of OPD and H2O2 additions, electrochemical properties of the PANI/DNNSA layer and non-specific binding prevention were all crucial factors for the assay performance. Under optimized conditions, the assay has a low limit of detection (LOD) (< 5 pg/mL or 56 fM), a wide dynamic range (> 6 orders of magnitude), high repeatability (coefficient of variance < 8% for all concentrations higher than 5 pg/mL) and a short detection time (< 10 min).

Solution properties of polyaniline by light scattering measurements: Achieving spatial homogeneity

Abstract Dynamic light scattering has been used to study polyelectrolyte behavior of polyanilines in solution. Comparisons with gel permeation chromatography have confirmed formation of supramolecular structures.

Decontamination of biological warfare agents by a microwave plasma torch

A portable arc-seeded microwave plasma torch running stably with airflow is described and applied for the decontamination of biological warfare agents. Emission spectroscopy of the plasma torch indicated that this torch produced an abundance of reactive atomic oxygen that could effectively oxidize biological agents. Bacillus cereus was chosen as a simulant of Bacillus anthracis spores for biological agent in the decontamination experiments. Decontamination was performed with the airflow rate of 0.393l∕s, corresponding to a maximum concentration of atomic oxygen produced by the torch. The experimental results showed that all spores were killed in less than 8 s at 3 cm distance, 12 s at 4 cm distance, and 16 s at 5 cm distance away from the nozzle of the torch.

Chemical and physical properties of regenerative medicine materials controlling stem cell fate

Abstract Regenerative medicine is a multidisciplinary field utilizing the potential of stem cells and the regenerative capability of the body to restore, maintain, or enhance tissue and organ functions. Stem cells are unspecialized cells that can self-renew but also differentiate into several somatic cells when subjected the appropriate environmental cues. The ability to reliably direct stem cell fate would provide tremendous potential for basic research and clinical therapies. Proper tissue function and regeneration rely on the spatial and temporal control of biophysical and biochemical cues, including soluble molecules, cell–cell contacts, cell–extracellular matrix contacts, and physical forces. The mechanisms involved remain poorly understood. This review focuses on the stem cell–extracellular matrix interactions by summarizing the observations of the effects of material variables (such as overall architecture, surface topography, charge, ζ-potential, surface energy, and elastic modulus) on the stem cell fate. It also deals with the mechanisms underlying the effects of these extrinsic, material variables. Insight in the environmental interactions of the stem cells is crucial for the development of new material-based approaches for cell culture experiments and future experimental and clinical regenerative medicine applications.

Electrically conducting thin films of aniline derivatives

Abstract Electrically conducting thin films of aniline derivatives have been deposited by the Langmuir-Blodgett (LB) technique and vacuum evaporation. Stable LB monolayers of poly(N-alkylanilines) have been formed and subsequently transferred onto substrates without the usual need to mix surface active molecules with the polymer. Problems associated with the LB deposition of polyaniline in the conducting form by use of a functionalized protonic acid, dodecylbenzenesulfonic acid, are also discussed. Thin films of vacuum evaporated tetra-anilinobenzene and an oxidatively polymerized mixture of aniline oligomers exhibit conductivities exceeding 10−3Scm−1 when doped with HCl. The conductivity remains remarkably stable in air in comparison to other doped thin films of conducting polymers or oligomers. Although the oligomers are protonated by HCl, the field-effect mobility, 2.2 × 10−3cm2V−1s−1 for the as-doped polymerized aniline oligomers, appears to be n-type.

Liposome-Nanogel Structures for Future Pharmaceutical Applications

Nanoparticles have been extensively studied as drug delivery systems. In this review, we focus on a relatively new type of nanoparticles--lipobeads--a liposome-hydrogel assembly as a novel drug delivery system. An appropriate assemblage of spherical hydrogel particles and liposomes combines the properties of both classes of materials and may find a variety of biomedical applications. The bi-compartmental structure of lipobeads is a natural configuration. Thus, the technology of their preparation can be a key step of designing more stable and effective vaccines. Biocompatibility and stability, ability to deliver a broad range of bioactive molecules, environmental responsiveness of both inner nanogel core and external lipid bilayer, and individual specificity of both compartments make the liposome-nanogel design a versatile drug delivery system relevant for all known drug administration routes and suitable for different diseases with possibility of efficient targeting to different organs. New findings on reversible and irreversible aggregation of lipobeads can lead to novel combined drug delivery systems regarding lipobeads as multipurpose containers. The research on hydrogel-liposome submicrometer structures has just begun and fundamental studies on interactions between hydrogels and liposomes are in demand.

Conductivity and structure of DBSA-protonated polyaniline

Abstract The discovery of a processable and conducting polyaniline complexes including functionalized sulphonic acids is an important discovery in the field of conjugated polymers. The conductivity, electronic and crystalline structure properties of polyaniline protonated with dodecylbenzenesulphonic acid are proportional to the molar concentration of the acid. The protonation leads to a layer structure evident in X-ray diffraction patterns and the crystallinity follows a growth as a function of the acid concentration similar to the conductivity increase. The electronic structure measured by UV-VIS spectroscopy shows an increase in the polaron concentration up to an acid concentration of 0.35 after which a broadening of the peak indicates the formation of a polaron band.

Potentiometric monitoring DNA hybridization

The usual procedure to monitor the ion exchange of small ions utilizes a potentiometer with a selective membrane as part of the working electrode. As the next step, we have applied polyaniline electrodes to the monitoring the activity macromolecular ions during DNA hybridization. Single-strand oligonucleotide (ssODN) probes were immobilized using a nucleophilic substitution reaction of the thiolated ssODN molecules with polyaniline. The anionic phosphate groups of the probe molecules also interacted with the cationic-doped polyaniline surface. Three useful findings were observed with the potentiometric experiments. First, the binding of the complimentary target molecules with the immobilized probes revealed a substantial potential change. Further, potential change was observed neither with the non-complimentary targets nor with the samples with a mutation in the sequence. The last two experiments were important for the future evaluation of the impact of medium and potential interfering compounds: anionic groups and hydrogen bonding groups in the non-complimentary samples did not cause any interactions.