Dual function platinum nanoparticles (PtNPs) incorporating two functions, i.e., DNA capture and electrocatalysis that are physically separated, are described. The physical separation of the two functions significantly enhances the sensitivity of DNA detection giving attomolar limits of detection. The regio-selective functionalisation has been achieved using defects within a dodecanethiol (C12) monolayer deposited on a gold electrode. These defects–nucleation sites allow for the electrodeposition of electrocatalytic, mushroom shaped PtNPs. The monolayer allows one side of the nanoparticle to be functionalised with a 20-base oligonucleotide with a C3 spacer thiol (probe) that selectively captures a sequence specifically associated with the strain of Staphylococcus aureus associated with mastitis. Once functionalised with capture strand DNA, the particles are released by sonication which maintains the structural integrity of the DNA. Thus, the desorbed nanoparticles are capable of biorecognition on the top curved side and electrocatalytic reduction of hydrogen peroxide on the non-functionalised lower surface. A second gold disc electrode was modified with a 15-base oligonucleotide with a C3 spacer thiol (capture). The presence of a 41-base target oligonucleotide, S. Aureus, which hybridized with both capture and probe oligonucleotides, brings the PtNP close to the electrode surface facilitating the electrocatalytic reduction of hydrogen peroxide generating a significant current for each hybridisation event. This highly sensitive detection approach opens up the possibility of avoiding polymerase chain reaction (PCR) or nucleic acid sequence-based amplification (NASBA) based amplification of the target.