Nikolas A. Chaniotakis

Novel carbon materials in biosensor systems.

In this work, novel carbon materials are evaluated as transducers, stabilizers and mediators for the construction of amperometric biosensors. It is shown that materials such as fullerenes and carbon nanotubes are promising materials as electrochemical mediators and enzyme stabilizers. Additionally porous carbon and porous glassy carbon are excellent transducers for amperometric measurements, while they provide cavities adequate for enzyme immobilization. At the same time, the sensitivity to peroxide is shown to depend on the activation procedures. Treatment that introduces oxygen groups increases the sensitivity of the carbon-based sensor to hydrogen peroxide considerably. These materials are used for the construction, mediation and stabilization of glucose biosensor.

Potentiometric phosphate selective electrode based on a multidendate—tin (IV) carrier

Abstract The incorporation of tris(3-chlorodimethylstannyl-propyl) chlorostannane (carrier 1), a novel tin(IV) based carrier, into a liquid polymeric membrane and its potentiometric properties are examined. Membranes doped with 2 wt% of this carrier are shown to display the highest selectivity for phosphate over many anions reported so far, including that of perchlorate. Its response time is in the order of seconds, while its detection limit is 1 × 10−5 M. The ability for a multidentate coordination between the carrier and the phosphate anion is postulated to be the reason for the response, while the observed high selectivity is proposed to be due to the higher tendency for bond formation between the phosphate oxygens and tin(IV) metal centers. On the other hand the lifetime of the electrode is short, due probably to the hydrolysis of the carrier in the membrane phase.

Improved operational stability of biosensors based on enzyme-polyelectrolyte complex adsorbed into a porous carbon electrode

A novel porous active carbon is utilized in order to adsorb the diethylaminoethyl-dextran (DEAE-dextran)-enzyme stabilized complexes, for the construction of highly stable biosensors. The interaction of DEAE-dextran with the examined enzymes increases dramatically the operational stabilization of the sensors, without adverse effects on the enzyme activity. At the same time, the porous active carbon allows for high enzyme loading, good electrical contact and low resistance throughout the sensing element. Glucose oxidase and horseradish peroxidase are used as model enzymes in this study to construct biosensors, with very good reproducibility (less than 5% RSD). As a result, the glucose sensor exhibits very long operational stability (over a period of 5 months), while the hydrogen peroxide sensor retains its initial activity after several weeks.

[60]Fullerene-mediated amperometric biosensors

Abstract In this report the use of [60]fullerene as a novel mediator in amperometric biosensors is presented. Different amounts of the fullerene were immobilized by adsorption into a porous carbon electrode prior the introduction of the enzyme (glucose oxidase). The effects of the amount of fullerene immobilized on the analytical characteristics of the resulting glucose biosensor are shown.

Response to anions of AlGaN∕GaN high-electron-mobility transistors

The response of AlGaN∕GaN electrolyte-gate high-electron-mobility transistors to various concentrations of the potassium salts KCl, KBr, KNO3, and KSCN in an aqueous solution has been investigated. The transistors’ drain-source current decreased with increasing concentration of potassium salts. This indicates that the potential at the gate becomes more negative with respect to the channels’ potential, suggesting a selective anion adsorption onto the GaN gate surface area.

Phosphate‐Binding Characteristics and Selectivity Studies of Bifunctional Organotin Carriers

The selective recognition of the orthophosphate anion by a series of bifunctional Lewis acidic organotin compounds is investigated. The binding affinity of these carriers to anions, as measured by NMR titrations in CH2Cl2 obeyed the potentiometric selectivity order phosphate > sulfate > perchlorate, and provided the corresponding complex-formation constants. More accurate calculations of these values were obtained by the segmented-sandwich-membrane method performed directly inside the liquid polymeric membrane. These carriers were also studied potentiometrically in polymeric liquid membranes. The results indicate that (PhBr2Sn)2CH2 is 2 to 5 orders of magnitude more selective towards phosphate over other oxoanions. These results set the ground for the development of a new series of highly selective anions carriers with a wide range of possible applications.

Tributyl‐ and Triphenyltin Benzoates, Phenylacetates, and Cinnamates as Anion Carriers: an Electrochemical Assessment Coupled to Structural NMR Studies and AM1 Calculations

A series of tributyl and triphenyltin benzoates, phenylacetates, and cinnamates, with different electron-withdrawing substituents, were evaluated for their selectivity as anion carriers and for their application in liquid-membrane potentiometric ion-selective electrodes. The tributyltin carboxylates exhibited good sensitivity and significant chloride selectivities, while the corresponding triphenyltin benzoates were much less active. The observed potentiometric response differences were related to Sn-atom Lewis acidity, as assessed by binding constants of chloride to the tin carriers determined from 117Sn-NMR titration experiments and theoretical simulations of the resulting titration curves. The thermodynamic characteristics as well as the expected chloride-carrier adducts in relation to starting substrates were analyzed theoretically by AM1 calculations.

Solid-contact ion-selective electrode with stable internal electrode

Abstract A new substrate for the construction of solid contact ion-selective electrodes (SC-ISEs) based on a conductive and porous carbon matrix is presented. The conductive characteristics of the substrate, its controlled porosity in combination with the use of a non-aqueous second kind internal reference element offers considerable advantages over the symmetrical configurations. The SC-ISEs presented here are very easy to construct, can be made very small in size, and can be used in high pressure environments. At the same time it is shown that the characteristics of the two electrodes constructed (K + and NO − 3 ) exhibit at least the same performance characteristics as the best commercially available symmetric counterparts. The potentiometric response is monitored over a period of one month with excellent results with regard to drift, base line stability, response time, selectivity, and detection limit.

Polyelectrolyte-stabilized biosensors based on macroporous carbon electrode

Abstract In this work, polyelectrolyte-stabilized enzymes are used for the construction of stable biosensors utilizing a simple manufacture procedure. The stabilized enzyme is immobilized by physical adsorption into activated macroporous and conductive carbon material, which serves as the immobilization matrix and the electrochemical transducer. The amount of polyelectrolyte used is optimized with respect to sensor’s sensitivity and stability. The optimized biosensors exhibit high operational stability and good sensor-to-sensor reproducibility.

Direct Potentiometric Measurement of Nitrate in Seeds and Produce

A highly stable and selective nitrate sensor was utilized for the development of a new methodology for the direct determination of nitrate concentration in dried greens and seeds. The method developed allows for the accurate (100–102% recovery values in lettuce, olive leaves and coffee beans) and fast (4 to 8 minutes) analysis of the samples without the need for filtration or other sample preparation steps. The coefficient of variation (CV) of the proposed method is below 5% for all samples analyzed.