Gheorghe Mihailescu

Free Base Porphyrins as Ionophores for Heavy Metal Sensors

Two functionalized porphyrins: 5,10,15,20-tetrakis(3,4-dimethoxyphenyl) porphyrin (A) and 5,10,15,20-tetrakis(3-hydroxyphenyl)porphyrin (B) obtained and characterized by us were used as ionophores (I) for preparing PVC-based membrane sensors selective to Ag+, Pb2+ and Cu2+. The membranes were prepared using three different plasticizers: (bis(2-ethylhexyl)sebacate (DOS), dioctylphtalate (DOP), o-nitro-phenyl octyl ether (NPOE) and potassium tetrakis(4-chlorophenyl)borate (KTClPB) as additive. The functional parameters (linear concentration range, slope and selectivity) of the sensors with membrane composition: (I:PVC:KTClPB:Plasticizer) in different ratios were investigated. The best results were obtained for the membranes in the ratio I:PVC:KTClPB:Plasticizer 10:165:5:330. The influence of pH on the sensors response was studied. The sensors were used for a period of four months and their utility has been tested on synthetic and real samples.

Investigation of carbon nanofibers as support for bioactive substances

In this paper we have studied the adsorption properties of various bio-active systems onto the surface of carbon nanofibers (CNF) synthesized by chemical vapor deposition (CVD). Amino acids (alanine, aspartic acid, glutamic acid) and glucose oxidase (GOx) were adsorbed on CNF and the results were compared with those obtained when activated carbon (AC) was used as support. CNF and AC properties (hydrophilic or hydrophobic properties) were characterized by the pH value, the concentration of acidic/basic sites and by naphthalene adsorption. CNF with immobilized GOx was additionally investigated as a highly sensitive glucose biosensor. An amperometric method was used in an original manner to detect the changes in the specific activity of GOx, immobilized longer time on CNF. The method demonstrates that not the whole enzyme adsorbed onto CNF can catalyze the oxidation of glucose from the solution.

Investigation of Electrochemical Properties of Carbon Nanofibers Prepared by CCVD Method

Carbon nanofibers, with diameters between 80 and 290 nm and specific area of 242 m2g−1, have been prepared by the catalytic chemical vapor deposition method. After preparation, the powder was mixed with silicon oil in order to create a paste electrode. The electrochemical behavior of this type of electrode was investigated by cyclic voltammetry, using a solution of 10−3 M ferrocenecarboxylic acid as mediator. The redox process is quasi-reversible, and it involves the transfer of electrons between Fe(II) and Fe(III). The same mediator was used for the construction of a second-generation glucose biosensor. The mediator was co-immobilized with the enzyme in the carbon nanofibers paste. The sensor linearly responded to glucose, in the concentration range of 1.7 to 7 mM. A time of around 30 seconds was required to reach 95% of the maximum steady-state current. Also, the oxidation of calf thymus DNA at the carbon nanofiber paste electrode was investigated by differential pulse voltammetry (DPV). A clear signal, due to guanine oxidation, was obtained in the case of single-stranded DNA.

Nanoparticles from a gold complex with sulfite ion as ligand: preparation and characterization

ABSTRACT Gold colloidal nanoparticles (GNPs) were prepared by reducing a complex of Au+. Na3Au(SO3)2 with sodium citrate. The procedure provides control of the dimension of nanoparticles produced, which is a function of reaction time and concentration of reactants. The nanoparticles were separated by centrifugation and their characteristics and dimensions were studied using UV-Vis and IR spectroscopy and transmission electronic microscopy (TEM).

Gold nanoparticles bind to porphyrins. A potential dye-sensitized solar cell

Porphyrins could be used for designing dye sensitized solar cells. The correlation between their band gap HOMO-LUMO and the conduction band of the semiconductor (TiO2) allows the electron transfer from the dye to the electrode, through the semiconductor. Our work reported here has revealed that a strong and large absorption band is obtained when a complex between gold nanoparticles (GNP) and porphyrin dye is formed.

Applications of nanoporous alumina membranes

Nanoporous alumina membranes were electrochemically prepared in sulfuric or phosphoric acid. After preparation they were used for microfiltration of biological media, such as human red blood cells and bovine serum albumin. The filtration efficiency was studied by UV-Vis absorption spectroscopy. Additionally, nanoporus alumina substrate was filled by cobalt and used as catalyst for nanocarbon growth.

Spectroscopic investigation of hemoglobin adsorbed onto gold nanoparticles

The adsorption of horse hemoglobin onto the surface of gold nanoparticles was studied using fluorescence spectroscopy. Gold nanoparticles quench the fluorescence emission of tryptophan residues in the structure of hemoglobin. By representing the dependence of log[(F0-F)/(F-Fsat)] on the logarithm of the concentration of gold nanoparticles in the solution, we obtained the binding parameters of hemoglobin onto the surface of gold nanoparticles. The number of binding sites was calculated to be 1.181 and the binding constant 7.935*109 M−1.

Characterization of nanoporous alumina membranes filled by gold particles

In this paper, we describe a method for chemical deposition of gold particles into nanoporous alumina membranes. After deposition, the membranes were investigated by several methods. X-ray diffraction studies have evidenced the presence of gold crystallites in the nanoporous membranes. The size of these crystallites depends on the deposition time. UV-vis absorption spectra of gold-filled membranes reveal a shift of the absorption peak from 520 nm to 580 nm, after deposition in solution with various pH values. Cyclic voltammetric experiments, performed on macro and nanoelectrodes, evidenced a lower detection limit of the redox species, for the nanoelectrode.