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Electrical transduction of DNA hybridization events is a major challenge in genoelectronics. Here we report on a new strategy for amplifying electrical DNA sensing based on the use of microsphere tags loaded internally with a redox marker. The resulting “electroactive beads” are capable of carrying a huge number of the ferrocenecarboxaldehyde marker molecules and hence offer a remarkable amplification of single hybridization events. This allows chronopotentiometric detection of target DNA down to the 5.1 × 10^-21 mol level (~31 000 molecules) in connection to 20 min of hybridization and “release” of the marker in an organic medium. The dramatic signal amplification advantage is combined with a remarkable discrimination against a huge excess (10⁷) of noncomplementary nucleic acids. Such electroactive beads hold great promise for multitarget detection (in connection to spheres loaded with different redox markers) and for enhancing the sensitivity of other bioassays.

We report on a novel method for detecting DNA hybridization, based on the precipitation of silver on gold nanoparticle tags and a subsequent electrochemical stripping detection of the dissolved silver. Such coupling of a nanoparticle-promoted silver precipitation with the remarkable sensitivity of stripping metal analysis offers a dramatic enhancement of the hybridization response. An efficient magnetic isolation of the duplex is used for discriminating against nonhybridized DNA, including an excess of mismatched oligonucleotides. The new silver-enhanced colloidal gold stripping detection strategy holds great promise for the detection of DNA hybridization and represents an attractive alternative to indirect optical affinity assays of nucleic acids and other biomolecules.

We report on an electrochemical protocol for the selective formation of self-assembled alkanethiol monolayers on a given microelectrode in the presence of a nearby second one. The procedure relies on the accelerated self-assembly of alkanethiols in ethanolic solutions under a cathodic polarization. Voltammetric “blocking” and electrochemical quartz crystal microbalance experiments, along with optical surface imaging, are used for demonstrating the selective electrochemisorption process. Using closely spaced electrodes (with 6 μm gaps), we demonstrate that only electrodes kept at negative potentials have been coated. Such attractive behavior is attributed to the simultaneous cathodic removal of an inhibitory surface layer. The high spatial resolution opens the way for localizing different reactive chemistries onto predetermined locations of sensor arrays.