Monica Florescu

Development and evaluation of electrochemical glucose enzyme biosensors based on carbon film electrodes

Electrochemical glucose enzyme biosensors have been prepared on carbon film electrodes made from carbon film electrical resistors. Evaluation and characterisation of these electrodes in phosphate buffer saline solution has been carried out with and without pretreatment by cycling in perchloric acid or at fixed applied potential. Both pretreatments led to a reduction in the carbon surface oxidation peak and enabled better detection of hydrogen peroxide in the pH range of 5-7. Glucose oxidase enzyme was immobilised on the carbon surface by mixing with glutaraldehyde, bovine serum albumin and with and without Nafion. The performance of these two types of electrode was similar, that containing Nafion being more physically robust. Linear ranges were up to around 1.5mM, with detection limits 60muM, and pretreatment of the carbon film electrode at a fixed potential of +0.9V versus SCE for 5min was found to be the most beneficial. Michaelis-Menten constants between 5mM and 10mM were found under the different experimental conditions. Coating the immobilised enzyme layer with a thin layer of Nafion was found to give similar results in the determination of glucose to mixing it but with benefits against interferences for the analysis of complex matrices, such as wine. Potentialities, for a short-term-use or disposable sensors, are indicated.

A new self-assembled layer-by-layer glucose biosensor based on chitosan biopolymer entrapped enzyme with nitrogen doped graphene

The layer-by-layer (LbL) technique has been used for the construction of a new enzyme biosensor. Multilayer films containing glucose oxidase, GOx, and nitrogen-doped graphene (NG) dispersed in the biocompatible positively-charged polymer chitosan (chit(+)(NG+GOx)), together with the negatively charged polymer poly(styrene sulfonate), PSS(-), were assembled by alternately immersing a gold electrode substrate in chit(+)(NG+GOx) and PSS(-) solutions. Gravimetric monitoring during LbL assembly by an electrochemical quartz microbalance enabled investigation of the adsorption mechanism and deposited mass for each monolayer. Cyclic voltammetry and electrochemical impedance spectroscopy were used to characterize the LbL modified electrodes, in order to establish the contribution of each monolayer to the overall electrochemical properties of the biosensor. The importance of NG in the biosensor architecture was evaluated by undertaking a comparative study without NG in the chit layer. The GOx biosensors analytical properties were evaluated by fixed potential chronoamperometry and compared with similar reported biosensors. The biosensor operates at a low potential of -0.2V vs., Ag/AgCl, exhibiting a high sensitivity of 10.5 μA cm(-2) mM(-1), and a detection limit of 64 μM. This study shows a simple approach in developing new biosensor architectures, combining the advantages of nitrogen-doped graphene with the LbL technique for enzyme immobilization.

Development and Characterization of Cobalt Hexacyanoferrate Modified Carbon Electrodes for Electrochemical Enzyme Biosensors

Abstract Carbon film electrodes have been modified with films of cobalt hexacyanoferrate by potential cycling from solutions containing cobalt and hexacyanoferrate ions. The voltammetric characteristics of the films have been investigated in different electrolyte solutions and the properties related to insertion reactions within the crystal structure. The application of these modified electrodes as redox mediators in enzyme biosensors has been investigated using the mediated detection of hydrogen peroxide, demonstrated by the determination of glucose using glucose oxidase. Excellent detection limits in the micromolar region have been attained and the principle of measurement in real samples demonstrated by that of glucose in sweet wine.

Development and characterization of a new conducting carbon composite electrode

A new conducting composite flexible material prepared from cellulose acetate (CA) polymer and graphite has been developed and used for the fabrication of electrodes, which were then characterized by cyclic voltammetry and electrochemical impedance spectroscopy. Scanning electron microscopy (SEM) was used to provide information concerning the morphology of the composite electrode surface. The potential window, background currents and capacitance were evaluated by cyclic voltammetry in the pH range from 4.6 to 8.2. The voltammetry of model electroactive species demonstrates a close to reversible electrochemical behaviour, under linear diffusion control. The electroactive area of the composite electrodes increases after appropriate electrode polishing and electrochemical pre-treatment. The electrodes were used as substrate for the electropolymerisation of the phenazine dye neutral red, for future use as redox mediator in electrochemical biosensors. The composite electrodes were also successfully used for the amperometric detection of ascorbate at 0.0 V vs. SCE, and applied to the measurement of ascorbate in Vitamin C tablets; the sensor exhibits high sensitivity and a low detection limit of 7.7 microM. Perspectives for use as a versatile, mechanically flexible and robust composite electrode of easily adaptable dimensions are indicated.

Carbon film electrodes for oxidase-based enzyme sensors in food analysis

Carbon film resistor electrodes have been evaluated as transducers for the development of multiple oxidase-based enzyme electrode biosensors. The resistor electrodes were first modified with Prussian Blue (PB) and then covered by a layer of covalently immobilized enzyme. Electrochemical impedance spectroscopy was used to characterize the interfacial behaviour of the Prussian Blue modified and enzyme electrodes; the spectra demonstrated that the access of the substrates is essentially unaltered by application of the enzyme layer. These enzyme electrodes were used to detect the substrate of the oxidase (glucose, ethanol, lactate, glutamate) via reduction of hydrogen peroxide at +50mV versus Ag/AgCl in the low micromolar range. Response times were 1-2min. Finally, the glucose, ethanol and lactate electrochemical biosensors were used to analyse complex food matrices-must, wine and yoghurt. Data obtained by the single standard addition method were compared with a spectrophotometric reference method and showed good correlation, indicating that the electrodes are suitable for food analysis.

Optimisation of a polymer membrane used in optical oxygen sensing

A method for detection of viable cells utilises a sensor based on the optical measurement of oxygen consuming by cells. Changes in the oxygen level were measured via quenching of the fluorescence of an oxygen-sensitive fluorophor (Ru(dpp) 3Cl2). The fluorescence lifetime changing was measured in accord with Stern–Volmer equation, using a phase-shift method. The fluorophor was embedded into a polysulfone membrane that is in contact with the cell medium. The sensitivity of oxygen sensor depends on behaviour of polysulfone membrane. Manufacturing method, type of polysulfone and concentration of fluorophor can also change this behaviour. These parameters were explored to obtain the optimum analytical performance, and the optimum sensitive membrane was chosen for 3 mmol/l concentration of fluorophor, when a linear plot was obtained with R = 0.99987 for a sensitivity of 12.11 ± 0.11 mV/% O2 (n = 5).

Tyrosinase-Based Biosensors for Selective Dopamine Detection

A novel tyrosinase-based biosensor was developed for the detection of dopamine (DA). For increased selectivity, gold electrodes were previously modified with cobalt (II)-porphyrin (CoP) film with electrocatalytic activity, to act both as an electrochemical mediator and an enzyme support, upon which the enzyme tyrosinase (Tyr) was cross-linked. Differential pulse voltammetry was used for electrochemical detection and the reduction current of dopamine-quinone was measured as a function of dopamine concentration. Our experiments demonstrated that the presence of CoP improves the selectivity of the electrode towards dopamine in the presence of ascorbic acid (AA), with a linear trend of concentration dependence in the range of 2–30 µM. By optimizing the conditioning parameters, a separation of 130 mV between the peak potentials for ascorbic acid AA and DA was obtained, allowing the selective detection of DA. The biosensor had a sensitivity of 1.22 ± 0.02 µA·cm−2·µM−1 and a detection limit of 0.43 µM. Biosensor performances were tested in the presence of dopamine medication, with satisfactory results in terms of recovery (96%), and relative standard deviation values below 5%. These results confirmed the applicability of the biosensors in real samples such as human urine and blood serum.

4th International Conference on Analytical and Nanoanalytical Methods for Biomedical and Environmental Sciences, IC-ANMBES 2016: June 29–July 1 2016, Brasov – Romania (http://icanmbes.unitbv.ro)

It was a pleasure and a great honor to organize the 4th International Conference on Analytical and Nanoanalytical Methods for Biomedical and Environmental Sciences, IC-ANMBES 2016, which was held from June 29th to July 1st, 2016, at Aula of Transilvania University of Brasov, Brasov, Romania (Figure 1). This event was organized by Transilvania University of Brasov in partnership with University of Twente, The Netherlands, University of Perpignan via Domitia, France, University of Wisconsin at Milwaukee, USA and INCDTIM, Cluj-Napoca, Romania, and under the auspices of Romanian Minister of Education and Brasov County Council. The conference was designed as an international forum for effective exchange of knowledge and experience among researchers, active in various theoretical and applied areas of biophysics, medicine, bioengineering, environmental protection, and food safety. The fourth edition of IC-ANMBES 2016 covered different aspects of analytical and nanoanalytical methods for Biomedical and Environmental Sciences, presented in the frame of eight sections, fact which reveals the interdisciplinary nature of the conference: . Atomic and nuclear analytical methods . Analytical methods of medical physics . Medical analysis and diagnosis . Microfluidics and point-of-care microdevices . Nanobiotechnology . Novel materials and biomaterials for analytical methods . Sensors and Biosensors . Spectroscopy These topics were covered by five plenary speakers: . Kalina Hristova, Johns Hopkins University, USA; . André Matagne, University of Liège, Belgium; . Leon WMM Terstappen, University of Twente, The Netherlands; none defined

Characterization of Phenolics in Lavandula angustifolia

ABSTRACT The lavender flowers and their essential oil are widely used in therapy in Romania and the European Community. Since the European Pharmacopoeia only allows the use of Lavandula sp flowers for medicinal purposes, the objective of this study was to investigate the chemical composition of Lavandula angustifolia extracts obtained by ultrasound-assisted extraction, rapid pressurized extraction at 6.7 bar, and subcritical fluid extraction. The solvents used for the first two methods were mixtures of water and alcohol, glycerin, and propylene glycol. These extracts were analyzed by high-performance thin-layer chromatography, infrared spectroscopy with attenuated total reflectance, and Raman spectroscopy. The total phenolics were evaluated using a modified Folin–Ciocalteu method. The primary phenolics were chlorogenic acid, gallic acid, umbelliferone, luteolin 7-O-glucoside, vitexin, and isoquercitroside. The extracts were variable in composition, with the highest yield by subcritical fluid extraction, followed by extraction at 6.7 bar. The infrared and Raman spectroscopy results confirmed the chromatography measurements.

Third International Conference: Analytical and Nanoanalytical Methods for Biomedical and Environmental Sciences (IC-ANMBES 2014) June 13–15, 2014, Brasov, Romania

It was a pleasure and a great honor to organize the Third International Conference on Analytical and Nanoanalytical Methods for Biomedical and Environmental Sciences, IC-ANMBES 2014, which was held from June 13–15, 2014, at Aula of Transylvania University of Brasov, Brasov, Romania. This event was organized by Transylvania University of Brasov in partnership with COST Action TD 1104; the French Institute in Romania; the University of Perpignan via Domitia, France; the University of Wisconsin at Milwaukee, USA; and INCDTIM, Cluj-Napoca, Romania; and under the auspices of the Romanian Minister of Education and Brasov County Council. The conference was designed as an international forum for effective exchange of knowledge and experience among researchers active in various theoretical and applied areas of natural science, medicine, environmental protection, and food safety. The third IC-ANMBES 2014 covered different aspects of analytical and nanoanalytical methods for Biomedical and Environmental Sciences, presented in seven sections demonstrating the interdisciplinary nature of the conference: 1. Analytical and nanoanalytical analysis for medical diagnosis 2. Biosensors for analytical and nanoanalytical analysis 3. Environmental analytical analysis 4. Electroporation in analytical methods 5. Optical methods used in analytical analysis 6. Physical methods for analytical analysis 7. Spectroscopic methods used in analytical analysis These topics were presented by five plenary speakers (Christopher M.A. Brett, University of Coimbra, Portugal; Damijan Miklavčič, University of Ljubljana, Slovenia; Kalina Hristova, Johns Hopkins University, USA; Carmen Socaciu, University of Agricultural Sciences and Veterinary Medicine of Cluj-Napoca, Romania; Jacobus Frederick van Staden, INCEMC, Romania) and keynote speakers (Yves Engelborghs, Katholieke Universiteit Leuven, Belgium; Anca Duta, Transilvania University of Brasov, Romania; Stefana M. Petrescu, Romanian Academy, Institute of Biochemistry, Romania; Ana Maria Oliveira Brett, University of Coimbra, Portugal; Liviu Movileanu, Syracuse University, NY, USA; Tudor Luchian, “Alexandru Ioan Cuza” University, Iasi, Romania; Jean-Louis Marty, University of Perpignan via Domitia, France; Valerică Raicu, University of Wisconsin-Milwaukee, USA) with more than 90 participants from more than thirty countries, (mostly from Europe, but also from USA and Canada) with sixty oral and fifty poster presentations carefully selected by members of the Scientific and Organizing Committees.