Ari Ivaska

Direct Electrochemistry of Glucose Oxidase and Biosensing for Glucose Based on Graphene

We first reported that polyvinylpyrrolidone-protected graphene was dispersed well in water and had good electrochemical reduction toward O(2) and H(2)O(2). With glucose oxidase (GOD) as an enzyme model, we constructed a novel polyvinylpyrrolidone-protected graphene/polyethylenimine-functionalized ionic liquid/GOD electrochemical biosensor, which achieved the direct electron transfer of GOD, maintained its bioactivity and showed potential application for the fabrication of novel glucose biosensors with linear glucose response up to 14 mM.

Graphene/AuNPs/chitosan nanocomposites film for glucose biosensing

A novel glucose biosensor based on immobilization of glucose oxidase in thin films of chitosan containing nanocomposites of graphene and gold nanoparticles (AuNPs) at a gold electrode was developed. The resulting graphene/AuNPs/chitosan composites film exhibited good electrocatalytical activity toward H(2)O(2) and O(2). The wide linear response to H(2)O(2) ranging from 0.2 to 4.2 mM (R=0.998) at -0.2V, high sensitivity of 99.5 microA mM(-1) cm(-2) and good reproducibility were obtained. The good electrocatalytical activity might be attributed to the synergistic effect of graphene and AuNPs. With glucose oxidase (GOD) as a model, the graphene/AuNPs/GOD/chitosan composite-modified electrode was constructed through a simple casting method. The resulting biosensor exhibited good amperometric response to glucose with linear range from 2 to 10 mM (R=0.999) at -0.2V and from 2 to 14 mM (R=0.999) at 0.5 V, good reproducibility and detection limit of 180 microM. Glucose concentration in human blood was studied preliminarily. From 2.5 to 7.5 mM, the cathodic peak currents of the biosensor decrease linearly with increasing the glucose concentrations. The graphene/AuNPs/GOD/chitosan composites film shows prominent electrochemical response to glucose, which makes a promising application for electrochemical detection of glucose.

Applications of ionic liquids in electrochemical sensors.

Ionic liquids (ILs) are molten salts with the melting point close to or below room temperature. They are composed of two asymmetrical ions of opposite charges that only loosely fit together (usually bulky organic cations and smaller anions). The good solvating properties, high conductivity, non-volatility, low toxicity, large electrochemical window (i.e. the electrochemical potential range over which the electrolyte is neither reduced nor oxidized on electrodes) and good electrochemical stability, make ILs suitable for many applications. Recently, novel ion selective sensors, gas sensors and biosensors based on ILs have been developed. IL gels were found to have good biocompatibility with enzymes, proteins and even living cells. Besides a brief discussion of the properties of ILs and their general applications based on these properties, this review focuses on the application of ILs in electroanalytical sensors.

Water-Soluble Graphene Covalently Functionalized by Biocompatible Poly-l-lysine

Graphene sheets functionalized covalently with biocompatible poly-l-lysine (PLL) were first synthesized in an alkaline solution. PLL-functionalized graphene is water-soluble and biocompatible, which makes it a novel material promising for biological applications. Graphene sheets played an important role as connectors to assemble these active amino groups of poly-l-lysine, which provided a very biocompatible environment for further functionalization, such as attaching bioactive molecules. As an example, an amplified biosensor toward H(2)O(2) based on linking peroxidase onto PLL-functionalized graphene was investigated.

Covalent functionalization of chemically converted graphene sheets via silane and its reinforcement

Polydisperse, functionalized, chemically converted graphene (f-CCG) nanosheets, which can be homogeneously distributed into water, ethanol, DMF, DMSO and 3-aminopropyltriethoxysilane (APTS), were obtained via facile covalent functionalization with APTS. The resulting f-CCG nanosheets were characterized by FTIR, XPS, TGA, EDX, AFM, SEM, and TEM. Furthermore, the f-CCG nanosheets as reinforcing components were extended into silica monoliths. Compressive tests revealed that the compressive failure strength and the toughness of f-CCG-reinforced APTS monoliths at 0.1 wt% functionalized, chemically converted graphene sheets compared with the neat APTS monolith were greatly improved by 19.9% and 92%, respectively.

One-step synthesis of graphene/SnO2 nanocomposites and its application in electrochemical supercapacitors

A one-step method was developed to fabricate conductive graphene/SnO2 (GS) nanocomposites in acidic solution. Graphite oxides were reduced by SnCl2 to graphene sheets in the presence of HCl and urea. The reducing process was accompanied by generation of SnO2 nanoparticles. The structure and composition of GS nanocomposites were confirmed by means of transmission electron microscopy, x-ray photoelectron and Raman spectroscopy. Moreover, the ultracapacitor characteristics of GS nanocomposites were studied by cyclic voltammograms (CVs) and electrical impedance spectroscopy (EIS). The CVs of GS nanocomposites are nearly rectangular in shape and the specific capacitance degrades slightly as the voltage scan rate is increased. The EIS of GS nanocomposites presents a phase angle close to pi/2 at low frequency, indicating a good capacitive behavior. In addition, the GS nanocomposites could be promisingly applied in many fields such as nanoelectronics, ultracapacitors, sensors, nanocomposites, batteries and gas storage.

Electrochemical impedance spectroscopy of oxidized poly(3,4-ethylenedioxythiophene) film electrodes in aqueous solutions

The electrochemical properties of oxidized (p-doped) poly(3,4-ethylenedioxythiophene) (PEDOT) film electrodes in aqueous solutions were investigated by electrochemical impedance spectroscopy (EIS). PEDOT was electrochemically deposited on platinum from aqueous solutions containing 0.01 M 3,4-ethylenedioxythiophene (EDOT) and 0.1 M supporting electrolyte: KCl, NaCl or poly(sodium 4-styrenesulfonate) (NaPSS). Impedance spectra were obtained for Pt/PEDOT electrodes at dc potentials where PEDOT is in the oxidized (p-doped) state. Electrodes with PEDOT films of different thickness, containing different doping ions, were investigated in contact with different aqueous supporting electrolyte solutions. The EIS data were fitted to an equivalent electrical circuit in order to characterize the electrochemical properties of the Pt/PEDOT film electrodes. Best fits to the experimental impedance data were obtained for an equivalent circuit where the total bulk (redox) capacitance of the polymer film is composed of the diffusional pseudocapacitance in series with a second bulk capacitance. The results imply that the PEDOT film contains an excess of supporting electrolyte, which facilitates ion diffusion and gives rise to a large diffusional pseudocapacitance.

In situ spectroelectrochemical characterization of poly(3,4-ethylenedioxythiophene)

The electrochemical polymerization of 3,4-ethylenedioxythiophene (EDOT), in diAerent electrolyte‐solvent media was studied with cyclic voltammetry, in situ UV‐VIS-spectroelectrochemistry, electrochemical quartz crystal microbalance technique (EQCM) and with in situ Fourier transform infrared (FTIR) spectroscopy using external and internal reflection techniques. The eAect of polymerization current density and monomer concentration on the formation of the film structure was studied. The redox reactions and the stability of charged films of diAerent thickness were studied with cyclic voltammetry and open circuit potentiometric measurements. FTIR spectra were recorded in situ during step-wise and continuous potential cycling of the polymer films in diAerent electrolytes. A characterization of the doping induced IR-bands has been made. # 1999 Elsevier Science Ltd. All rights reserved.

Electrochemical determination of NADH and ethanol based on ionic liquid-functionalized graphene.

It is firstly reported that low-potential NADH detection and biosensing for ethanol are achieved at an ionic liquid-functionalized graphene (IL-graphene) modified electrode. A substantial decrease (440 mV) in the overvoltage of the NADH oxidation was observed using IL-graphene/chitosan coating, with oxidation starting at ca. 0 V (vs. Ag|AgCl). And the NADH amperometric response at such a modified electrode is more stable (95.4% and 90% of the initial activity remaining after 10 min and 30 min at 1 mM NADH solution) than that at bare electrode (68% and 46%). Furthermore, the IL-graphene/chitosan-modified electrode exhibited a good linearity from 0.25 to 2 mM and high sensitivity of 37.43 microA mM(-1)cm(-2). The ability of IL-graphene to promote the electron transfer between NADH and the electrode exhibited a novel and promising biocompatible platform for development of dehydrogenase-based amperometric biosensors. With alcohol dehydrogenase (ADH) as a model, the ADH/IL-graphene/chitosan-modified electrode was constructed through a simple casting method. The resulting biosensor showed rapid and highly sensitive amperometric response to ethanol with a low detection limit (5 microM). Moreover, the proposed biosensor has been used to determine ethanol in real samples and the results were in good agreement with those certified by the supplier.

pH sensitivity of polyaniline and its substituted derivatives

Abstract The pH sensitivity of electrically conducting polyaniline (PANI) and its derivatives poly( o -methylaniline) (P o MeANI), poly( o -ethylaniline) (P o EtANI), poly( o -propylaniline) (P o PrANI) and poly( N -methylaniline) (PNMeANI) have been studied with potentiometry and UV–vis spectroscopy. The electropolymerisation of PANI was carried out either in hydrochloric acid (HCl), methanesulphonic acid (MSA), benzenesulphonic acid (BSA) or dodecylbenzenesulphonic acid (DBSA). It is shown that the pH sensitivity of PANI and its derivatives depend on the substituent and the size of the acid anion that is used in the electropolymerisation. PANI membranes prepared in HCl show a selective and slightly super-Nernstian potentiometric pH response (62.4±0.9 mV per pH; pH 2–9), while PNMeANI, P o PrANI and PANI prepared with DBSA have a strongly suppressed pH response. The hysteresis effect observed in the UV–vis measurements for all membrane types studied restrict the use of PANI-based optical pH sensors to the pH range of only 5–8.