In this report, we present sequence-specific DNA detection by means of a competitive hybridization assay with osmium tetroxide-labelled signalling strands. The labelling of the signalling strands has been performed using protective strands to preserve the recognition site of these single strands for hybridization with the immobilized capture probes. At optimized measuring conditions and especially assay temperature, we could detect the presence of 25 nM target DNA within 30 minutes, whereas the non-complementary target sequence did not yield any signal. The latter was observed as a decrease in square-wave voltammetric response of the signalling probes. Single base mismatches could be detected at a stringent 35 degrees C electrolyte temperature. Moreover, the concentration dependency of the signal was investigated. A time-consuming labelling procedure of the target, as typically used before, is not necessary. Upon application of the new protocol, there is no need for handling osmium(VIII) compounds during sample treatment. The signalling strands containing Os(VI) are prepared separately and can be stored over several months.

As a nontoxic substitute for mercury electrodes, bismuth electrodes attained a lot of attention during the last years. In this report we describe for the first time the preparation of two different directly heatable bismuth-modified microwire electrodes. We characterized the electrochemical behaviour using cyclic voltammetry in acetate buffer and alkaline tartrate solution. The bismuth electrodes show a significantly wider potential window compared with bare gold wires. In the presence of picric acid as one example for the detection of explosives, the bismuth electrodes deliver higher signals. By applying heat during the measurements, the signals can be enhanced further. We used the temperature pulse amperometry (TPA) technique to improve the electrochemical response at the different types of electrodes. In this preliminary study, we were able to detect 3 ppm traces of picric acid.

This communication reports on electrochemical detection of thrombin based on labeling with osmium tetroxide bipyridine [OsO4(bipy)]. Tryptophan amino acids can be labeled at the C−C‐double bond, and at least some tryptophan moieties are accessible for labeling in thrombin. Using the catalytic hydrogen signal from adsorptive stripping voltammetry performed on hanging mercury drop electrode, we could detect as little as 1.47 nM [OsO4(bipy)]‐modified thrombin. We also tested the binding of [OsO4(bipy)]‐modified thrombin with the classic thrombin binding aptamer (TBA) on gold electrodes. This preliminary study revealed that even after modification, a major part of the affinity was conserved, and that the aptamer self‐assembled monolayer (SAM) could be regenerated several times. Molecular simulations confirm that [OsO4(bipy)]‐modified thrombin largely preserves the high binding affinity also of the alternative HD22 aptamer to thrombin, albeit at slightly reduced affinities due to steric hindrance when tryptophans 96 and 237 are labelled. Based on these simulations, compensatory modifications in the aptamer should result in significantly improved binding with labelled thrombin. This combined experimental‐computational approach lays the groundwork for the rational design of improved aptamer sensors for analytical applications.

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We report about hybridization detection of different nucleic acids on capture probe‐modified heated gold wire electrodes. We have compared three kinds of nucleic acid targets: DNA, uracil‐conjugated DNA, and RNA. All three sorts of nucleic acids targets could be labeled with osmium tetroxide bipyridine, hybridized with immobilized DNA capture probes and then detected by square‐wave voltammetry. Heating the gold electrode instead of the entire bulk hybridization solution leads to improved hybridization efficiency in most cases. The reason could be found in a thermal micro‐stirring effect around the heated wire electrode. Also selectivity was improved. Mismatches could be discriminated for DNA and uracil‐conjugated DNA targets. Mismatches in RNA strands, however, are more difficult to detect due to relatively stable secondary structures.