Designs of enterobacteriaceae lac Z gene DNA gold screen printed biosensors

This paper describes specific electrochemical enterobacteriaceae lac Z gene DNA sensors based on immobilization of a thiolated 25 base single stranded probe onto disposable screen printed gold electrodes (gold SPEs). Two configurations have been evaluated. In the first one, the capture probe was attached to the electrode surface through its -SH moiety, while mercaptohexanol (MCH) was used as spacer for the displacement of nonspecifically adsorbed oligonucleotide molecules. The hybridization event between the probe and target DNA sequences was detected at -0.20 V by square-wave voltammetry (SWV), using methylene blue (MB) as electrochemical indicator. The second genosensor configuration involved modification of gold high temperature SPEs with a 3,3'-dithiodipropionic acid di(N-succinimidyl ester) (DTSP) self-assembled monolayer (SAM). Moreover, 2-aminoethanol was used as blocking agent, and further modification with avidin allowed binding of the biotinylated enterobacteriaceae lac Z gene DNA probe. An enzyme amplified detection scheme was applied, based on the coupling of streptavidin-peroxidase to the biotinylated complementary target, after the hybridization process, and immobilization of tetrathiafulvalene (TTF) as redox mediator atop the modified electrode. The amperometric response obtained at -0.15 V after the addition of hydrogen peroxide was used to detect the hybridization process. Experimental variables concerning sensors composition and electrochemical transduction were evaluated in both cases. A better precision and reproducibility in the fabrication process, as well as a higher sensitivity were achieved using the biotinylated probe-based sensor configuration. A limit of detection of 0.002 ng/mu L was obtained without any preconcentration step.