Daniel Casals i Martorell

Amperometric determination of pesticides using a biosensor based on a polishable graphie-epoxy biocomposite

Abstract The determination of organophosphorus and carbamate pesticides was carried out using an amperometric transducer based on a robust, polishable and easily mechinable biocomposite. The biocomposite material contains graphite powder, a non-conducting epoxy resin and acetylcholinesterase. The enzyme retains its bioactivity in the rigid epoxy-graphite matric. Measurements were carried out with acetylhiocholine as a substrate. Thiocholine produced by enzymatic hydrolysis was oxidized electrochemically at 70 mV (vs. Ag/AgCl in pH 7.0 buffered solution with 0.1 M phosphate and 0.1 m KCl). The decrease rate of substrate steady-state current after the addition of pesticide was used for evaluation. The method of construction allows for the repetitive use of the electrode. Simple polishing procedures are used to regenerate the bioactive transducer surface.

Determination of organophosphorus and carbamate pesticides using a biosensor based on a polishable, 7,7,8,8-tetracyanoquino-dimethane-modified, graphite—epoxy biocomposite

Abstract An amperometric biosensor for the determination of organophosphorus and carbamate pesticides is described. The biosensor is based on robust, polishable and easily machinable biocomposites containing graphite powder, a non-conducting epoxy resin, the electronic mediator 7,7,8,8-tetracyanoquinodimethane (TCNQ) and the enzyme acetylcholinesterase (AChE) or butyrylcholinesterase (BChE) immobilized on aminated silica particles. Determinations were done with acetylthiocholine (ATCh) or butyrylthiocholine (BTCh) as substrate. Thiocholine produced by enzymatic hydrolysis is oxidized electrocatalytically. The biosensor operates at a potential of 300 mV vs. Ag/AgCl in a pH buffered solution with 0.1 M phosphate and 0.1 M KCl. The decrease rate of the steady-state current after the addition of pesticides was used for the determination. The materials employed in the construction of the reported biosensors allow for a prolonged use of the device if a slight polish of the surface is performed from time to time.

Carbon-polymer biocomposites for amperometric sensing☆

Abstract New electrochemical sensing biocomposite materials are reported. These materials are based on polymer technology and are prepared mixing graphite powder, a non-conducting polymer resin and a lyophilized enzyme. The resulting biosensing material is inexpensive, robust, polishable and easy to machine. A survey of potentially suitable polymeric matrices was carried out. Epoxy, silicone, methacrylate and polyester polymers have been used to prepare rigid conducting composite materials of the graphite-polymer type. For each material, an optimal graphite content was determined. Amperometric transducers built with these materials were characterized electrochemically using cyclic voltammetry and linear-sweep voltammetry. Their linear response to hydrogen peroxide was evaluated. The applicability of these conducting polymer-graphite composites has been extended to the construction of conventional glucose biosensors. In these devices the conducting composite is bulk-modified with the addition of glucose oxidase. The amperometric detection of hydrogen peroxide serves as the analytical signal. Following the same construction method, it is also possible to obtain other biosensing systems. New biocomposites have been prepared, using a different enzyme in each case, i.e. acetylcholinesterase and peroxidase.

ISFET-based urea biosensor

A new construction method of a PVC-matrix membrane ISFET-based urea sensor is described and compared with a pH ISFET-based urea sensor which uses a classical immobilization procedure on a nylon net. The response slope obtained with data from the pH ISFET-urea sensor is 57 mV/decade over a linear working range of 10−4−3 × 10−3 M urea with a lifetime over 20 days. This sensor, applied in a flow-injection system, presents a sensitivity of 60 mV/decade and shows an acceptable sampling rate of 35 samples/h. Although its lifetime is shorter under dynamic conditions the membrane is easily changeable in the flow system. The new sensor reported is based on an ammonium ISFET with the PVC-matrix membrane cast on a graphite/epoxy composite. The enzyme is deposited and covalently fixed onto the PVC membrane by means of a fine spraying of glutaraldehyde. This sensor shows a sensitivity of 42 mV/decade over a linear working range between 4 × 10−5 and 10−2 M urea and a long-term stability of one week.

urea potentiometric biosensor based on all-solid-state technology

Abstract A new urea potentiometric biosensor based on all-solid-state (without inner liquid contacts) technology has been developed. Potentiometric transducers consisting of selective poly(vinyl chloride) (PVC) membranes directly applied onto electrically-conducting composite materials ([0–3] graphite/epoxy composites) has been previously developed in our laboratory. This all-solid-state construction procedure has been extended to the preparation of urea potentiometric biosensors using a new enzyme-immobilization technique based on the deposition of the biocatalyst layer onto the active transducer surface by spraying a diluted solution of glutaraldehyde. The combination of these new simple technologies provides a wide range of adaptability and multifunctional designs for the resulting sensing devices. Furthermore, by using a PVC-matrix membrane as the support of the enzymatic layer, the detachment of the enzyme (urease) is considerably reduced since a better adsorption on the enzyme layer is achieved. The results obtained with this new type of urea potentiometric biosensor show a low response time (10 s) and a wide linear range (10 −5 to 10 −3 M) with a sensitivity of 55 mV per urea decade. A great gain is achieved in terms of stability with a lifetime of about 40 days in periodical calibration use. Additionally, a flow-through urea biosensor using the same type of potentiometric transducer and immobilization procedure has been constructed for the use in flow-injection analysis systems.

Use of mathematical models to describe dynamic behaviour of potentiometric biosensors: Comparison of deterministic and empirical approaches to an urea flow-through biosensor

Abstract The response of a flow-through biosensor is the consequence of complex interrelations between the dilution of the sample in a continuous stream (governed by physical variables) and the phenomena involved in the reactions between enzyme and substrate (governed by diffusion and kinetic processes). These interrelations make it difficult to know in advance the influence of manifold parameters in the biosensor response. If a reliable model of these processes is attainable, it will be possible to test rapidly, by computer, the effect of the variation of different operating variables on the response of the biosensor. This paper presents the results obtained when two models are applied to describe dynamic behaviour of a potentiometric flow-through urea biosensor. One of these models uses an empirical approach based on neural networks, while the other proposes a deterministic approach that takes into account reaction-diffusion equations.

Contribució de Josep Ibàñez i Senserrich a la difusió i a la reivindicació del català durant el Franquisme a la premsa: la primera etapa (1966-1967) de la secció "Aclariments lingüístics" de Tele/Estel

L’objectiu d’aquest article es, en primer lloc, estudiar les seixanta-dues contribucions de Josep Ibanez i Senserrich durant la primera etapa (1966-1967) de la seccio «Aclariments linguistics», publicada al setmanari escrit en catala Tele/estel (1966-1970). La finalitat d’aquesta columna era difondre la normativa linguistica fixada per l’Institut d’Estudis Catalans i reivindicar l’us public de la llengua catalana. La reconstruccio d’aquest episodi ha permes incorporar-lo a la tradicio de la premsa de Catalunya de divulgar la normativa linguistica des de les seves pagines. El segon objectiu d’aquest treball es la reconstruccio biografica de Josep Ibanez (1929-2004), un activista cultural i linguistic que va desenvolupar la seva accio durant el tardofranquisme, sobretot en el camp de l’ensenyament de la llengua. Aixo ho ha fet possible el fet d’haver pogut accedir a documentacio inedita, escrita i grafica, procedent de fons privats i publics.

BASSOLS, Margarida (2007): El llenguatge dels polítics. Anàlisi del cas català, Vic, Eumo Editorial («Llengua i text», núm. 10).

Obra ressenyada: Margarida BASSOLS, El llenguatge dels politics. Analisi del cas catala. Vic: Eumo Editorial, 2007.

2.75 – Use of Mathematical Models to Desribe Dynamic Behaviour of Potentiometric Biosensors: Comparison of Deterministic and Empirical Approaches to an Urea Biosensor Flow-Through/Biosensor

Publisher Summary This chapter focuses on the use of mathematical models to describe dynamic behavior of potentiometric biosensors. Analysis of urea is important in several fields that require the development of optimal analytical procedures and devices for each one. Mathematical models for the whole process may be useful to optimize the working conditions for suitable analytical signal. If a reliable model is attainable it will be possible to test, by computer in a fast way, the effect of the variation of different operating variables on the response of the biosensor. The chapter also presents results obtained when two models (one based on neural networks and the other one on reaction–diffusion equations), are applied to describe dynamic behavior of the previously developed urea biosensor. A procedure to use these models to obtain different optimal manifolds reducing the experimental effort required nowadays using trial and error procedures is also presented.

2.16 – Carbon-Polymer Biocomposites for Amperometric Sensing

Publisher Summary This chapter describes carbon–polymer biocomposites for amperometric sensing. A survey of potentially suitable polymeric matrices was carried out. Epoxy resins, silicones, methacrylates, polyesters and polyurethanes were tested. For each material, optimal graphite content was determined. The criteria for this evaluation were maximal electrical conductivity without loss of material stability. Atypical ohmic resistance was 1 kΩ, but the optimal graphite content was not constant, even for the same type of polymer. The transducers were characterized electrochemically using cyclic voltammetry and linear-sweep voltammetry. The linear response for hydrogen peroxide was evaluated. They were also studied spectroscopically using FTIR, and microscopically by SEM. The applicability of these conducting polymer composites has been extended to the construction of glucose biosensors where the composite is bulk-modified by glucose oxidase, and where the amperometric detection of hydrogen peroxide serves as the analytical signal. Glucose biosensors have been prepared mixing a redox mediator, enzyme, graphite powder and a polymer. The resulting material modulates electron transfer between the enzyme and the transducer.