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 selfassembling
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.