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Oztekin Y.,Selcuk University | Oztekin Y.,Vilnius University | Yazicigil Z.,Selcuk University | Ramanaviciene A.,Vilnius University | And 2 more authors.
Talanta | Year: 2011

Applicability of square wave voltammetry for the determination of Cu(II) ions by PolyLut/GC and PolyKae/GC electrodes was evaluated in this study. For this luteolin and kaempferol were electrochemically polymerized on glassy carbon (GC) electrode surface in order to get polyluteolin and polykaempferol-modified glassy carbon electrodes (PolyLut/GC and PolyKae/GC, correspondingly). The formation of polyphenol layer on the GC electrode surface was evidenced by atomic force microscopy. Square wave voltammetry was found to be more sensitive in comparison with differential pulse voltammetry. It was determined that PolyLut/GC and PolyKae/GC electrodes offered great sensitivity towards Cu(II) ions with very low limit of detection, good reproducibility, sufficient stability and excellent selectivity of analytical signal. © 2011 Elsevier B.V.

Ramanavicius A.,Vilnius University | Ramanavicius A.,Institute of Semiconductor Physics | Genys P.,Vilnius University | Ramanaviciene A.,Vilnius University
Electrochimica Acta | Year: 2014

1,10-Phenanthroline-5,6-dione and glucose oxidase modified and unmodified graphite electrodes were analysed in buffer/glucose media by the electrochemical impedance spectroscopy (EIS) method. The EIS analysis was carried out under potentiostatic conditions. The gathered impedimetric data was evaluated applying estimated equivalent circuits. It was determined that equivalent circuit RΩ(RF2C2)(C[RFW]) most optimally describes this electrochemical system. The study revealed redox mediating properties of 1,10-phenanthroline-5,6-dione deposited on graphite electrodes. © 2014 Elsevier Ltd. All rights reserved.

Leonavicius K.,Vilnius University | Ramanaviciene A.,Vilnius University | Ramanavicius A.,Vilnius University | Ramanavicius A.,Institute of Semiconductor Physics
Langmuir | Year: 2011

A very simple, environmentally friendly, one-step oxidative polymerization route to fabricate polypyrrole (Ppy) nanoparticles of fixed size and morphology was developed and investigated. The herein proposed method is based on the application of sodium dodecyl sulfate and hydrogen peroxide, both easily degradable and cheap materials. The polymerization reaction is performed on 24 h time scale under standard conditions. We monitored a polaronic peak at 465 nm and estimated nanoparticle concentration during various stages of the reaction. Using this data we proposed a mechanism for Ppy nanoparticle formation in accordance with earlier emulsion polymerization mechanisms. Rates of various steps in the polymerization mechanism were accounted for and the resulting particles identified using atomic force microscopy. Application of Ppy nanoparticles prepared by the route presented here seems very promising for biomedical applications where biocompatibility is paramount. In addition, this kind of synthesis could be suitable for the development of solar cells, where very pure and low-cost conducting polymers are required. © 2011 American Chemical Society.

German N.,State Research Institute Center for Innovative Medicine | German N.,Institute of Semiconductor Physics | Ramanavicius A.,Vilnius University | Ramanavicius A.,Institute of Semiconductor Physics | Ramanaviciene A.,Vilnius University
Sensors and Actuators, B: Chemical | Year: 2014

A biosensor based on glucose oxidase (GOx) immobilized on gold nanoparticles (Au-NPs) electrochemically predeposited on the surface of graphite rod (GR) electrode was developed (GOx/Au-NPs/GR). Main analytical characteristics of this biosensor were determined and compared with those determined using a biosensor setup without Au-NP modification (GOx/GR). The highest analytical signal of GOx/Au-NPs/GR electrode was observed after 13 nm Au-NP deposition on the electrode from 0.8 nmol L-1 solution lasting 20 min, when cyclic voltammetry was performed in the range from 0.0 to +1.0 V vs Ag/AgCl. The best analytical characteristics of the developed biosensor were obtained after 25 mg mL-1 GOx immobilization on the Au-NPs/GR electrode. Analytical signal registered using GOx/Au-NPs/GR electrode was 2.08 times higher in comparison to GOx/GR electrode. The registered currents of both electrodes were linearly dependent on glucose concentration in the range of 0.1-10 mmol L-1. The developed GOx/Au-NPs/GR electrode was characterized by high sensitivity, which was equal to 101.02 μA mM -1 cm-2 in the linear glucose detection range. The limit of detection was 0.083 mmol L-1 with relative standard deviation of 6% for GOx/Au-NPs/GR electrode. This study demonstrates a successful practical exploitation of the developed biosensor in a human serum sample. © 2014 Elsevier B.V.

German N.,State Research Institute Center for Innovative Medicine | Ramanavicius A.,Vilnius University | Ramanavicius A.,Institute of Semiconductor Physics | Voronovic J.,Vilnius University | And 2 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2012

Different glucose biosensors based on glucose oxidase (GOx) immobilised on bare carbon rod electrode (CR) modified with gold nanoparticles (Au-NPs) of (i) 3.5. nm (GOx/3.5Au-NPs/CR), (ii) 6. nm (GOx/6Au-NPs/CR) and (iii) 13. nm (GOx/13Au-NPs/CR) were investigated and compared with biosensors based on GOx immobilised on bare CR (GOx/CR). Enzymatic polymerisation of pyrrole was applied to increase linear detection range of biosensors. The influence of the formed polypyrrole layer on sensitivity and Michaelis-Menten kinetics of designed electrochemical biosensors was investigated. The linear glucose detection interval for GOx/CR and GOx/Au-NPs/CR electrodes was dependent on the duration of polymerisation. © 2012 Elsevier B.V.

Kausaite-Minkstimiene A.,Vilnius University | Mazeiko V.,Vilnius University | Ramanaviciene A.,Vilnius University | Ramanaviciene A.,Institute of Semiconductor Physics | And 2 more authors.
Colloids and Surfaces A: Physicochemical and Engineering Aspects | Year: 2015

π-π conjugated polymer polypyrrole (PPy) particles were synthesized by chemical oxidative polymerization of pyrrole (Py) monomers using H2O2 as an oxidant. No surfactants were added to the polymerization solution, therefore pure PPy particles were formed. UV-vis molecular absorption spectroscopy (UV-vis MAS) was used to monitor the Py polymerization process. The spectral properties and morphology of formed PPy particles were studied using Fourier-transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The influence of H2O2 and Py concentration, temperature and pH of media on the PPy particles formation rate was investigated. It was found that the polymerization solutions were unstable colloidal suspensions consisting of the PPy particles. SEM analysis revealed that PPy particles were 50-100nm in diameter, which aggregated into larger structures of 600-1000nm in diameter with irregular granular morphology. FTIR data showed that the molecular structure of the synthesized particles was identical to that of PPy produced by conventional methods. © 2015 Elsevier B.V.

Baniukevic J.,Vilnius University | Kirlyte J.,Vilnius University | Ramanavicius A.,Vilnius University | Ramanavicius A.,Institute of Semiconductor Physics | Ramanaviciene A.,Vilnius University
Sensors and Actuators, B: Chemical | Year: 2013

An immunosensor for the determination of bovine leukemia virus (BLV) antigen (gp51) using surface plasmon resonance (SPR) equipment and SPR-chip modified by oriented and randomly immobilized antibodies (anti-gp51) was developed. Different conditions of anti-gp51 reduction by 2-mercaptoethanol (2-ME) and dithiothreitol (DTT) solutions were compared and explored. The best gp51 detection sensitivity was monitored using SPR-chip modified with oriented antibody fragments (frag-anti-gp51) obtained after reduction with DTT at 50 mM concentration. The SPR sensor could detect gp51 antigen in a range from 0.01 to 0.5 mg/mL. The developed SPR sensor offered the limit of detection (LOD) as low as 0.0028 mg/mL, while the limit of quantification was as low as 0.0092 mg/mL with very good repeatability during the three detection-regeneration cycles (1-4%). Oriented immobilization of frag-anti-gp51 was found to be more suitable for the design of SPR-immunosensor for the detection of gp51 if compared with random immobilization of anti-gp51. This method was successfully applied for the detection of gp51 in blood serum samples in a rapid, reliable and selective manner. © 2013 Elsevier B.V.

Vaitkuviene A.,Vilnius University | Vaitkuviene A.,State Research Institute Center for Innovative Medicine | Kaseta V.,State Research Institute Center for Innovative Medicine | Voronovic J.,Vilnius University | And 5 more authors.
Journal of Hazardous Materials | Year: 2013

Polypyrrole (Ppy) is known as biocompatible material, which is used in some diverse biomedical applications and seeming to be a very promising for advanced biotechnological applications. In order to increase our understanding about biocompatibility of Ppy, in this study pure Ppy nanoparticles (Ppy-NPs) of fixed size and morphology were prepared by one-step oxidative polymerization and their cyto-compatibility was evaluated. The impact of different concentration of Ppy nanoparticles on primary mouse embryonic fibroblasts (MEF), mouse hepatoma cell line (MH-22A), and human T lymphocyte Jurkat cell line was investigated. Cell morphology, viability/proliferation after the treatment by Ppy nanoparticles was evaluated. Obtained results showed that Ppy nanoparticles at low concentrations are biocompatible, while at high concentrations they became cytotoxic for Jurkat, MEF and MH-22A cells, and it was found that cytotoxic effect is dose-dependent. © 2013 Elsevier B.V.

Balevicius Z.,Vilnius University | Balevicius Z.,Lithuanian Academy of Sciences | Ramanaviciene A.,Vilnius University | Ramanaviciene A.,State Research Institute Center for Innovative Medicine | And 5 more authors.
Sensors and Actuators, B: Chemical | Year: 2011

Total internal reflection ellipsometry (TIRE) technique was used to investigate biological recognition layers of immunosensors in order to estimate orientation of immobilized intact- and fragmented-antibodies. Two differently prepared biological recognition layers formed on gold-substrate were investigated: one layer was based on intact-antibodies (intact-Ab), second layer was based on chemically fragmented specific-antibodies (frag-Ab), which were obtained by reduction of intact-Ab. It was shown that TIRE enables to resolve differences in nanostructures of intact-Ab and frag-Ab layers. A multilayer model applied in our calculations shows that the distance between fragmented-antibody active sites and gold-surface after the immobilization process is lower than theoretical dimension of fragmented-antibodies. Moreover, it was calculated that analytical sensitivity of the Δ(λ) parameter of TIRE was 5.89 times better if compared to the sensitivity of the Ψ(λ) parameter, which is in fact similar to the sensitivity of surface plasmon resonance (SPR) based immunosensors. © 2011 Elsevier B.V. All rights reserved.

Kausaite-Minkstimiene A.,Vilnius University | Mazeiko V.,Vilnius University | Ramanaviciene A.,Vilnius University | Ramanavicius A.,Vilnius University | Ramanavicius A.,Institute of Semiconductor Physics
Sensors and Actuators, B: Chemical | Year: 2011

In this article potential and suitability of enzymatically synthesized conducting polymers polyaniline (PANI) and polypyrrole (PPY) for fabrication of enzymatic amperometric glucose biosensors were evaluated. The polymerisation of these polymers was induced by catalytic activity of glucose oxidase (GOx) from Penicillium vitale cross-linked by glutaraldehyde (GA) on the graphite rod electrode (GOx-electrode) surface. The main precursors for initiation of polymerisation reactions were hydrogen peroxide as an initiator of polymerisation reaction and β-d-gluconic acid as a medium, which reduced the pH towards acidic one is the most suitable for the formation of PANI and PPY. During the polymerisation reactions the immobilized GOx was self-encapsulated within formed PANI or PPY layers in order to form GOx/PANI- and GOx/PPY-modified electrodes (GOx/PANI-electrode and GOx/PPY-electrode, respectively). Kinetic properties of GOx, which is acting as a biocatalyst in GOx/PANI- and GOx/PPY-electrodes, were studied and results were compared with GOx-electrode. The results show that in both GOx/PANI- and GOx/PPY-electrodes self-encapsulated GOx exhibited different parameters of catalysed reaction kinetics due to increasing diffusion limitations if compared with that of the GOx-electrode and it allowed the detection of glucose in a wider concentration interval. Moreover, both GOx/PANI- and GOx/PPY-electrodes exhibited good operational stability and reproducibility of analytical signal. The electrochemical characteristics of formed PANI and PPY in the GOx/PANI- and GOx/PPY-electrodes were also determined. In addition, the influence of temperature, pH and common interfering compounds on the steady-state current response of modified electrodes were investigated and discussed. © 2011 Elsevier B.V. Al rights reserved.

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