Impedimetric detection of influenza A (H1N1) DNA sequence using carbon nanotubes platform and gold nanoparticles amplification.

In this work we report the use of an impedimetric genosensor for the model detection of H1N1 swine flu correlated DNA sequence. An oligonucleotide DNA probe, complementary to the target H1N1 virus sequence, was immobilized onto the electrode surface by covalent binding. Two different protocols, i.e. direct hybridization with the DNA target and a sandwich scheme, were employed and compared. In both cases the resulting hybrid was biotin-labelled to allow the additional conjugation with streptavidin gold nanoparticles (strept-AuNPs). The latter were used with the aim of enhancing the impedimetric signal, thus improving the sensitivity of the technique. The best limit of detection, obtained with the sandwich scheme after signal amplification step was 7.5 fmol (corresponding to 577 pmol L(-1)). Furthermore, a gold enhancement treatment was performed in order to compare the presence and distribution of gold nanoparticles onto the electrode surface. As an alternative way of visualization, streptavidin conjugate quantum dots (strept-QD) were employed to obtain fluorescence images of the DNA-biotin-strept-QD electrode surface. Finally, a comparison between impedance and microscopy was performed in terms of viability and feasibility of the techniques.

Immunoassay for folic acid detection in vitamin-fortified milk based on electrochemical magneto sensors.

An immunoassay-based strategy for folic acid in vitamin-fortified milk with electrochemical detection using magneto sensors is described for the first time. Among direct and indirect competitive formats, best performance was achieved with an indirect competitive immunoassay. The immunological reaction for folic acid (FA) detection was performed, for the first time on the magnetic bead as solid support by the covalent immobilization of a protein conjugate BSA-FA on tosyl-activated magnetic bead. Further competition for the specific antibody between FA in the food sample and FA immobilized on the magnetic bead was achieved, followed by the reaction with a secondary antibody conjugated with HRP (AntiIgG-HRP). Then, the modified magnetic beads were easily captured by a magneto sensor made of graphite-epoxy composite (m-GEC) which was also used as the transducer for the electrochemical detection. The performance of the immunoassay-based strategy with electrochemical detection using magneto sensors was successfully evaluated using spiked-milk samples and compared with a novel magneto-ELISA based on optical detection. The detection limit was found to be of the order of microgl(-1) (13.1 nmoll(-1), 5.8 microgl(-1)) for skimmed milk. Commercial vitamin-fortified milk samples were also evaluated obtaining good accuracy in the results. This novel strategy offers great promise for rapid, simple, cost-effective and on-site analysis of biological and food samples.