Biomedical subjects

Vasilis G Gavalas

Publications and source records attributed to Vasilis G Gavalas.

9 recordsLinked to original sources

PubMed2006

Microfabrication of screen-printed nanoliter vials with embedded surface-modified electrodes.

A self-contained ion-selective sensing system within a nanoliter-volume vial has been developed by integrating screen printing, laser ablation, and molecular imprinting techniques. Screen printing and laser ablation are used in tandem to fabricate nanoliter-volume vials with carbon and Ag/AgCl ring electrodes embedded in the sidewalls. Using multisweep cyclic voltammetry, the surface of the carbon electrode can be modified with a polypyrrole film. By polymerizing pyrrole in the presence of nitrate, pores complementary to the nitrate anion in size, shape, and charge distribution are formed in the resulting film. Electrochemical cells modified with this nitrate-imprinted polypyrrole film show a near-Nernstian response to nitrate, and excellent reproducibility. The integration of molecular recognition and electrochemical response in the nanoliter vials is demonstrated by the detection of as little as 0.36 ng nitrate in nanoliter-volume samples. The integration of tailored molecular recognition within nanoliter vials via established fabrication and imprinting protocols should result in a number of nanosensor devices with applications in BioMEMS and micro total analysis systems.

Electrochemistry↗

PubMed2006

Decyl methacrylate-based microspot optodes.

Optode sensing membranes employing decyl methacrylate cross-linked with 1,6-hexanediol dimethacrylate as the polymer support were fabricated by a direct microspotting method on several surfaces. Photopolymerization was used to attach the microspots to the substrate. Using this method, diameters in the micrometer domain were obtained. Silanized glass, poly(methyl methacrylate) (PMMA), polycarbonate, and poly(dimethylsiloxane) were tested as possible substrates. Both polypropylene tips and the steel tips of drafting pens were used for spotting. It was determined that both silanized glass and PMMA gave working optodes, but the ones on PMMA did not fit the theoretical model. Diameters of 994 +/- 80 and 1279 +/- 85 microm were obtained on silanized glass and PMMA, respectively, using the polypropylene tips for spotting. Different size optodes were fabricated using 0.35- and 0.50-mm steel drafting pen tips. The 0.35-mm tips produced diameters of 895 +/- 26 and 688 +/- 54 microm on silanized glass and PMMA, respectively, and the 0.50-mm tips produced diameters of 1274 +/- 94 microm on silanized glass and 839 +/- 28 microm on PMMA. Thus, the microspot size can be controlled based on the hydrophobicity of the surface and the size of the tip used for spotting. Calibration plots of potassium optode microspots indicated that miniaturization does not alter response characteristics, such as selectivity, response time, and dynamic range, of the optodes.

Journal Article↗

PubMed2006

Poly(amino acid)-facilitated electrochemical growth of metal nanoparticles.

Poly(amino acids) are natural chelating agents for various metal ions. Zinc ions were encapsulated in situ in a conductive polypyrrole film using polyglutamic acid as a localized complexing agent within the film. The subsequent electrochemical reduction of the metal ions to zero-valent metal leads to the formation of the nanoparticles. The electrochemical approach demonstrated in this report provides facile regeneration of the particles and also prevents aggregation of nanoparticles in the conductive polymeric film. The correlation of the amount of zinc with the thickness of the film indicates that the zinc resides largely in the outer layer of the film. TEM and EDS data show that the nanoparticles formed are composed of zinc and are 18 +/- 7 nm in diameter. The nanoparticle/ polymer composite was used to reduce halogenated organics, indicating its potential usefulness in remediation applications.

Amino Acids↗

PubMed2005

Enhancing the blood compatibility of ion-selective electrodes.

In vivo monitoring of various analytes is important for many bioanalytical and biomedical applications. The crucial challenge in this type of applications is the interaction of the sensor with the host environment, which is qualitatively described by the term biocompatibility. This review discusses recent advances in methods and materials used for the improvement of the biocompatibility of ion-selective electrodes especially as it relates to their interaction with blood components.

Biocompatible Materials↗

PubMed2004

Carbon nanotube aqueous sol-gel composites: enzyme-friendly platforms for the development of stable biosensors.

A new type of composite material based on carbon nanotubes and an aqueous sol-gel process has been developed. The electrochemical characteristics of these composites were investigated and compared to composites made with an alkoxy silane sol-gel process. The use of carbon nanotubes, as the conductive part of the composite, facilitated fast electron transfer rates. The feasibility of this type of composite for the development of biosensors was demonstrated using l-amino acid oxidase. The stability of the enzyme was increased when it was encapsulated in the aqueous sol-gel, and the sensor retained more that 50% of its response after 1 month of testing.

Biosensing Techniques↗

PubMed2004

Protein immobilization on carbon nanotubes through a molecular adapter.

A new approach to the modification of carbon nanotubes with biomolecules for the development of nanoscale biosensors is presented. Alkaline phosphatase was immobilized on the surface of multi-wall carbon nanotubes utilizing a layer-by-layer methodology. Carbon nanotubes were incubated with streptavidin, resulting in the formation of a protein layer on the surface of the nanotubes. Biotinylated alkaline phosphatase was then allowed to bind to streptavidin, anchoring the sensing protein onto the surface. Electrochemical biosensors were constructed by using carbon nanotubes compacted into pellets. 1-Naphthyl phosphate, which is hydrolyzed by alkaline phosphatase to the electroactive 1-naphthol, was used as a substrate. Electrodes constructed in this manner were observed to generate an electrochemical signal that was a function of substrate concentration.

Adsorption↗

PubMed2002

Potentiometric behavior of electrodes based on overoxidized polypyrrole films.

Electrodes based on oxidized polypyrrole films have potentiometric selectivity toward anions. When the films are overoxidized, however, electron-rich groups are introduced on to the polymer chains, reversing the selectivity of the electrodes from anionic to cationic. In this study, electrochemically overoxidized polypyrrole film electrodes were prepared, and the conditions for film formation that lead to near-Nernstian potentiometric response were investigated. It was found that the doping ion, overoxidation solution, and pH affect the response of these electrodes. Redox interference is significantly lower for the overoxidized polypyrrole films than for polypyrrole electrodes.

Journal Article↗

PubMedDate not supplied

Hybrid nanoparticles based on organized protein immobilization on fullerenes.

Nanoscale carbon materials (i.e., fullerenes and nanotubes) are an attractive platform for applications in biotransformations and biosensors. The interesting properties displayed by nanoparticles demand new strategies for the manipulation of these materials on the nanoscale. Controlled modification of their surface with biomolecules is required to fully realize their potential in bionanotechnology. In this work, immobilization of a fullerene derivative with a mutant subtilisin is demonstrated, and the effect of the fullerene on the protein activity is determined. The fullerene-conjugated enzyme had improved catalytic properties in comparison to subtilisin immobilized on nonporous silica. Further, the pH profile of free and fullerene-conjugated subtilisin were almost identical.

Enzymes, Immobilized↗

PubMedDate not supplied

Coupling biomolecules to fullerenes through a molecular adapter.

A novel biotinylated fullerene has been synthesized to facilitate the attachment of biotin-conjugated proteins to C(60) through the use of streptavidin as a molecular adapter. The strong biotin-streptavidin interaction enables the attachment of fullerenes to streptavidin and, because of the availability of four biotin-binding sites on streptavidin, to biotinylated biomolecules. The feasibility of this approach is demonstrated by using biotinylated alkaline phosphatase. Due to the insolubility of fullerenes in aqueous media, the immobilized enzyme can be eventually recovered by simple centrifugation with no significant loss in activity.

Alkaline Phosphatase↗