Electropolymerization of pyrrole and phenylenediamine over an organic conducting salt based amperometric sensor of increased selectivity for glucose determination

Comparative study on aptamers as recognition elements for antibiotics in a label-free all-polymer biosensor

We present an all-polymer electrochemical microfluidic biosensor using Topas(®) as substrate and a conductive polymer bilayer as electrode material. The conductive bilayer consists of tosylate doped poly(3,4-ethylenedioxythiophene) (PEDOT:TsO) and the hydroxymethyl derivative PEDOT-OH:TsO, which was covalently functionalized with two aptamer probes with affinity to ampicillin or kanamycin A, respectively. Using electrochemical impedance spectroscopy (EIS) we were able to detect ampicillin in a concentration range from 100pM to 1μM and kanamycin A from 10nM to 1mM. The obtained EIS spectra were fitted with an equivalent circuit model successfully explaining the impedance signal. Real samples from regular ultra-high temperature treated low-fat milk spiked with ampicillin were successfully tested to assess the functionality of the sensor with real samples. In conclusion, we have demonstrated the applicability of the newly developed platform for real time, label-free and selective impedimetric detection of commonly used antibiotics. Additionally it was possible to detect ampicillin in a milk sample at a concentration below the allowed maximum residue limit (MRL) in the European Union.

Amperometric cholesterol biosensors based on the electropolymerization of pyrrole and aniline in sulphuric Acid for the determination of cholesterol in serum

A new amperometric cholesterol biosensor was prepared by immobilizing cholesterol oxidase by a glutaraldehyde crosslinking procedure on polypyrrole-polyaniline (ppy-pani) composite film on the surface of a platinum electrode. In order to prepare a biosensor for the determination of cholesterol, electropolymerization of pyrrole and aniline on Pt surface was performed with an electrochemical cell containing pyrrole and aniline in sulphuric acid by cyclic voltammetry between 0.0 and 0,7 V (vs.Ag/AgCl) at a scan rate of 50 mV upon Pt electrode. The amperometric determination is based on the electrochemical detection of H(2)O(2), which is generated in enzymatic reaction of cholesterol. The cholesterol determined by the oxidation of enzymatically generated H(2)O(2) at 0.7 V vs. Ag/AgCl. The optimized cholesterol oxidase biosensor displayed linear working range and a response time of 300 s. The effects of pH and temperature were investigated and optimum parameters were found to be 7.0, 25 degrees C, respectively. In addition to this, the stability and reproducibility of biosensor were tried. Operational stability of the proposed cholesterol biosensor was obtained by periodical measurements of the biosensor response. Biosensor at optimum activity conditions was used in 30 activity assays in one day to determine the operational stability. The results show that 82% of the response current was retained after 30 activity assays. The electrode was stored in a refrigerator at 4 degrees C after the measurements. The storage stability of the biosensor was determined by performing activity assays within 23 days. The results demonstrate that 60% of the response current was retained after 23 days. Preparing biosensor is used for the analysis of cholesterol in serum.

Polyvinylferrocenium modified Pt electrode for anaerobic glucose monitoring

An amperometric enzyme electrode for the determination of glucose under anaerobic solution conditions was developed by immobilizing glucose oxidase and then by adsorbing ferrocene in polyvinylferrocenium matrix coated on a Pt electrode surface. The amperometric response due to the electrooxidation of ferrocene that the reduced flavin adenine dinucleotide centers of glucose oxidase was measured at a constant potential. The response characteristics of the enzyme electrode were investigated. The effects of the thickness of the polymeric film, the amount of the enzyme immobilized, the amount of the mediator, the glucose concentration, the applied potential, operating pH and temperature on the response of the enzyme electrode were studied. The response time and the optimum pH were found to be 30-40 s and pH 7.4 at 25 degrees C, respectively. The linear response was observed up to 5.0 mM glucose concentration that the produced detectable current was 0.0075 mM glucose concentration. The activation energy (E(a)) of immobilized enzyme reaction was calculated to be 41.3 kJ mol(-1) from the Arrhenius plot. The apparent Michaelis-Menten constant (K(Mapp)) was found to be 6.05 mM glucose according to the Lineweaver-Burk graph of the Michaelis-Menten equation under the optimum conditions. The interference signal due to the most common electrochemical interfering species was also evaluated.

Cholesterol biosensors prepared by layer-by-layer technique

The analysis of formation, deposition and characterization of cholesterol oxidase (COX) layer-by-layer films were performed. Initially, a layer of polyanion, poly(styrene sulfonate) (PSS) was adsorbed followed by a layer of polycation, poly(ethylene imine) (PEI) on each solid substrate from aqueous solutions. The alternating layers were formed by consecutive adsorption of polycations (PEI) and negatively charged proteins (COX) and cholesterol esterase (CE). A strong interaction between protein and polyelectrolyte improves the stability of the alternating multilayer; however, it can change a native protein conformation and impair the protein activity. The PSS/PEI/COX, PSS/PEI/COX/PEI/CE, PSS/PEI/COX-CE/PEI etc. layered structures were prepared on the surface of a platinum electrode, ITO coated glass plate, quartz crystal microbalance, quartz plates, mica and silicon substrates. Optical and gravimetric measurements based on an ultraviolet-visible absorption spectroscopy and a quartz crystal microbalance revealed that the enzyme multilayers thus prepared consist of molecular layered of the proteins. The surface morphology of such bilayer films was investigated by using atomic force microscopy. The electrochemical redox processes of the enzyme-layered films deposited either on platinum or ITO coated glass plate were investigated. The response current of cholesterol oxidase electrode with concentration of cholesterol was investigated at length.

Strategies for the improvement of an amperometric cholesterol biosensor based on electropolymerization in flow systems: use of charge-transfer mediators and platinization of the electrode

Different configurations based on an amperometric biosensor with cholesterol oxidase entrapped in a polypyrrole film have been developed with a view to improving the analytical properties of this biosensor. The alternatives considered involve the simultaneous entrapment of the enzyme and a charge-transfer mediator as well as previous platinization of the surface of the Pt electrode. Both artificial (a ferrocene derivative) and natural (flavin nucleotides) mediators were studied as constituents of the charge-transfer process between the enzyme and the electrode. The comparative study of these biosensors, which were prepared in situ in a continuous flow system, made it possible to determine the advantages and disadvantages of each configuration when applied to flow-injection determination of cholesterol.