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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. Source

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. Source

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. Source

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. Source

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. Source

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