The goal of this communication is to present new electrochemical biosensors devoted to the quantification of compounds of clinical, environmental and pharmacological interest. Different biosensing schemes involving enzymes and DNA and diverse electrode materials will be discussed.
We will show enzymatic biosensors based on the use of glassy carbon paste electrode containing polyphenol oxidase as biorecognition element. The electrode was successfully used for the determination of phenolic compounds and neurotransmitters in different real samples. Another interesting and very innovative application of this biosensor was the detection of 2,4-dinitrotoluene (2,4-DNT) derivatives. We demonstrate for the first time that 4-methyl-5-nitrocatechol (4M5NC) and 2,4,5-trihydroxytoluene (2,4,5-THT), two compounds obtained from the 2,4-DNT biodegradation, are recognized by polyphenol oxidase as substrates. The biosensor was used for the detection of these compounds and for evaluating the efficiency of the 2,4-DNT conversion into 4M5NC in the presence of bacteria able to produce the 2,4-DNT-biotransformation. Under the experimental conditions, it was possible the selective quantification of 4M5NC even in the presence of a large excess of 2,4-DNT. The usefulness of the biosensor for detecting the biotransformation of 2,4-DNT into 4M5NC in comparison with HPLC-spectrophotometric detection, demonstrated an excellent correlation.
Another important strategy was the use of a new electrode material to improve the electron transfer of compounds involved in enzymatic reactions of interest. In this sense, the use of carbon nanotubes (CNT) represents an advantageous and very promising alternative as electrode material. Our group proposed for the first time a new composite based on the dispersion of multi-walled carbon nanotubes with mineral oil. Due to their properties, carbon nanotubes have allowed the facilitated charge transfer of different analytes of interest like phenols, hydrogen peroxide, neurotransmitters and NADH. The inclusion of enzymes within the composite material has allowed to obtain highly sensitive and selective enzymatic electrodes for the detection of alcohols, glucose, lactate, phenols and catechols.
CNTs were also dispersed in polymeric matrices and then deposited on glassy carbon electrodes. Two polymers were used, Nafion and polyethyleneimine (PEI). The Nafion/multi-wall carbon nanotubes dispersion deposited on glassy carbon electrodes (GCE) was used as a new platform for developing enzymatic biosensors based on the self-assembling of a chitosan derivative as polycation and glucose oxidase, L-aminoacid oxidase or polyphenol oxidase, as polyanions and biorecognition elements. The analytical performance of GCE modified with a dispersion of multi-wall carbon nanotubes in polyethylenimine showed an excellent electrocatalytic activity toward different bioanalytes like ascorbic acid, dopamine, 3,4-dihydroxyphenylacetic acid and hydrogen peroxide. The currents are higher than those obtained with other dispersant agents like Nafion, concentrated acids or
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chitosan, evidencing the high efficiency of the dispersion in PEI. The CNT/PEI layer immobilized on GCE has been also used as a platform for building supramolecular architectures based on the self-assembling of polyelectrolytes without any pretreatment of the electrode surface, oxidation or derivatization of CNTs, just taking advantages of the polycationic nature of the dispersant agent. The self-assemblying of glucose oxidase has allowed us to obtain a supramolecular architecture for glucose biosensing, with detection limits of 0.6 µM (0.11 g/L). Such an excellent performance of CNTPE toward hydrogen peroxide and the effectiveness of the use of CNT/PEI as a platform for obtaining supramolecular multistructures, represents a very good alternative for developing other enzymatic biosensors.
The use of DNA as biorecognition layer will be also discussed, either in connection with the incorporation of DNA within a composite matrix or by self-assembling of multilayers. DNA is an important enzymatic tool due to its unique properties of biorecognition. Therefore, it is possible to develop biosensors for detecting the hybridization event or to study the interaction of drugs and pollutants with the confined DNA layer. In this sense, our group was pioneer in Argentina in the development of biorecognition layers based on the use of single and double stranded DNA. In this presentation we will discussed some interesting applications of these biosensors.
In summary, we will show different alternatives for developing electrochemical biosensors that allows the highly sensitive and selective detection of different analytes of pharmacological, clinical and environmental interest.
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