Gold electrode modified by self-assembled monolayers of thiols to determine DNA sequences hybridization

The process of immobilization of biological molecules is one of the most important steps in the construction of a biosensor. In the case of DNA, the way it exposes its bases can result in electrochemical signals to acceptable levels. The use of self-assembled monolayer that allows a connection to the gold thiol group and DNA binding to an aldehydic ligand resulted in the possibility of determining DNA hybridization. Immobilized single strand of DNA (ssDNA) from calf thymus pre-formed from alkanethiol film was formed by incubating a solution of 2-aminoethanothiol (Cys) followed by glutaraldehyde (Glu). Cyclic voltammetry (CV) was used to characterize the self-assembled monolayer on the gold electrode and, also, to study the immobilization of ssDNA probe and hybridization with the complementary sequence (target ssDNA). The ssDNA probe presents a well-defined oxidation peak at +0.158 V. When the hybridization occurs, this peak disappears which confirms the efficacy of the annealing and the DNA double helix performing without the presence of electroactive indicators. The use of SAM resulted in a stable immobilization of the ssDNA probe, enabling the hybridization detection without labels. This study represents a promising approach for molecular biosensor with sensible and reproducible results

Electrochemical detection of dengue virus NS1 protein with a poly(allylamine)/carbon nanotube layered immunoelectrode

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)BACKGROUNDA sensitive nanostructured immunoelectrode based on poly(allylamine) (PAH) sandwich is developed for non-structural 1 (NS1) of dengue virus. NS1 is a secretory protein abundant in the acute phase of disease associated to hemorrhagic fever. Anti-NS1 antibodies are immobilized on the electrode surface by a thin layer of PAH assembled on carboxylated carbon nanotubes (CNTs). PAH is cationic polymer acting as bi-functional agent to tightly attach CNTs to the electrode surface and anti-NS1 antibodies through their Fc terminal, avoiding random immobilization. Electrochemical responses of immunoassay are generated at a controlled potential by a reaction between H2O2 and peroxidase enzyme conjugated to anti-NS1 antibodies. RESULTSThe immunosensor developed exhibited a linear range to NS1 varying between 0.1 mu g mL(-1) and 2.5 mu g mL(-1), with clinical range for early diagnostic of acute dengue and a limit of detection of 0.035 mu g mL(-1) that is much lower than the concentration observed from the first day after the onset of fever up to the 9th day. Serum samples are also tested showing good accuracy and specificity. CONCLUSIONSAn immunosensor for NS1 protein of dengue virus was developed. This versatile and reproducible PAH-sandwich platform can be applied to other immunoassays to give reliable and highly sensitive responses. (c) 2014 Society of Chemical IndustryA sensitive nanostructured immunoelectrode based on poly(allylamine) (PAH ) sandwich is developed for non‐structural 1 (NS1 ) of dengue virus. NS1 is a secretory protein abundant in the acute phase of disease associated to hemorrhagic fever. Anti‐NS1 anti901194200CNPQ - CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICOConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)sem informaçãoThe authors thank the National Council for Scientific and Technological Development ‐ CNPq for supporting this work and Physics Department of Federal University of Pernambuco for performing the SEM image