Silver or gold? A comparison of nanoparticle modified electrochemical genosensors based on cobalt porphyrin-DNA

•Genosensors based on AgNPs functionalized with DNA–Co-porphyrin have been made.•Sensitivity in attomolar range close to single molecule detection has been achieved.•AgNP sensor was directly compared to an analogous AuNP system.•AgNP and AuNP nanospheres are not involved in electron transfer.•AgNP systems are more cost-effective, whereas AuNP systems are easier to handle. We applied a cobalt-porphyrin modified DNA as electrochemical marker, which was attached to nanoparticles, to detect specific DNA sequences. We compare the performance of gold and silver NPs in oligonucleotide sensors to determine if a change in metal will lead to either higher sensitivity or different selectivity, based on the redox behaviour of silver vs. gold. Surprisingly, we find that using either gold or silver NPs yields very similar overall performance. The electrochemical measurements of both types of sensors show the same redox behaviour which is dominated by the cobalt porphyrin, indicating that the electron pathway does not include the NP, but there is direct electron transfer between the porphyrin and the electrode. Both sensors show a linear response in the range of 5 × 10–17–1 × 10–16 M; the limit of detection (LOD) is 3.8 × 10–18 M for the AuNP sensor, and 5.0 × 10–18 M for the AgNP sensor, respectively, which corresponds to the detection of about 20–50 DNA molecules in the analyte. Overall, the silver system results in a better DNA economy and using cheaper starting materials for the NPs, thus shows better cost-effectivness and could be more suitable for the mass-production of highly sensitive DNA sensors.