Asta Kausaite-Minkstimiene

Enzymatically synthesized polyaniline layer for extension of linear detection region of amperometric glucose biosensor.

In this article a new method for fabrication of enzymatic electrodes suitable for design of amperometric glucose biosensor and/or anode of biofuel cell powered by glucose is presented. Glucose oxidase (GOx) E.C. 1.1.3.4. from Penicillium vitale was immobilized on the carbon rod electrode by cross-linking it with glutaraldehyde (GOx-electrode). Catalytic activity of immobilized GOx was exploited for polymerisation of aniline by taking a high concentration of hydrogen peroxide produced during the catalytic action of immobilized GOx and locally lowered pH due to the formation of gluconic acid; it created optimal conditions for the polymerisation of aniline. The GOx layer was self-encapsulated within formed polyaniline (PANI) matrix (GOx/PANI-electrode). Properties of the GOx/PANI-electrode have been studied and results were compared with GOx-electrode. The results show that the upper detection limit of glucose using GOx-electrode was dramatically changed by the formation of PANI layer. An increase in the upper detection limit, optimal pH region for operation and stability of GOx based electrode modified by PANI was detected when comparing that of an unmodified GOx-electrode.

Reagent-less amperometric glucose biosensor based on a graphite rod electrode layer-by-layer modified with 1,10-phenanthroline-5,6-dione and glucose oxidase

A reagent-less amperometric glucose biosensor operating in not-stirred sample solution was developed. A working electrode of the designed biosensor was based on a graphite rod (GR) electrode, which was modified with 1,10-phenanthroline-5,6-dione (PD) and glucose oxidase (GOx). The PD and the GOx were layer-by-layer adsorbed on the GR electrode surface with subsequent drying followed by chemical cross-linking of the adsorbed GOx with glutaraldehyde (GA). Optimal preparation conditions of the working electrode (GR/PD/GOx) were achieved with 12.6μg and 0.24mg loading amount of PD and GOx, respectively and 25min lasting cross-linking of the GOx with GA. A current response to glucose of the GR/PD/GOx electrode was measured at +200mV potential vs Ag/AgCl reference electrode. Maximum current response was registered when the pH of the buffer solution was 6.0. The registered current response to glucose was linear in the concentration range of 0.1-76mmolL-1 (R2=0.9985) and a detection limit was 0.025mmolL-1. The GR/PD/GOx electrode demonstrated good reproducibility and repeatability with the relative standard deviation of 6.2% and 1.8% (at 4.0mmolL-1 of glucose), respectively, high anti-interference ability to uric and ascorbic acids. It was highly selective to glucose and demonstrated good accuracy in the analysis of human serum samples.

A surface plasmon resonance immunosensor for human growth hormone based on fragmented antibodies

An SPR-based immunosensor for human growth hormone (hGH) is reported. It is based on the application of fragments of antibodies against human growth hormone (anti-hGH). The native thiol groups of anti-hGH were liberated by splitting the intact anti-hGH antibody using the reducing agent 2-mercaptoethylamine (2-MEA) into two half-sized fragments (frag-anti-hGH) while retaining active antigen-binding sites. Afterwards frag-anti-hGH were immobilised on the gold film of the SPR-chip by chemisorption. The antibody and 2-MEA concentrations have been optimized with respect to the performance of the immunosensor. The surface morphology of the immunosensor was studied by atomic force microscopy. The binding of hGH to the sensor surface is highly specific, and the respective immunosensor has a limit of detection of 0.0034 μM of hGH. Good repeatability of the analytical signal and selectivity over porcine growth hormone are demonstrated. The sensor has relatively good operational stability, which was satisfactory within 18 days.

Evaluation of poly(pyrrole-2-carboxylic acid) particles synthesized by enzymatic catalysis

In this study an environmentally friendly synthesis of poly(pyrrole-2-carboxylic acid) (PCPy) particles dispersed in water–ethanol medium using enzymatic catalysis is proposed. The polymerization of pyrrole-2-carboxylic acid was initiated by the oxidant hydrogen peroxide resulting from the redox enzyme glucose oxidase (GOx) catalyzed glucose oxidation reaction. The main evidence of the polymerization process was the origin and increase of the absorption peak at 465 nm indicating the presence of PCPy oligomers. The PCPy formation rate in different pH medium was investigated and compared with the formation rate of the PCPy synthesized by chemical oxidative polymerization. The best medium for the enzymatic polymerization was determined at pH 5.0, while for the chemical method it was at pH 2.0. The GOx had a significant positive impact on the outcome of the polymerization reaction and colloidal stability of the formed PCPy particles. The GOx catalyzed polymerization reaction was faster than that based on chemical oxidative polymerization but the precipitation of insoluble precipitate was observed after a longer period of polymerization. The morphology of the PCPy particles was characterized by SEM. Additionally, the presence of carboxylic groups in the formed PCPy particles was confirmed by FTIR spectroscopy and potentiometric back-titration.