1. Introduction Shiga toxin-producing E. coli (STEC) is a food-borne pathogen of a great public health concern, which can cause severe illness including haemolytic uremic syndrome (HUS), that may even lead to death . Cattle are known to be their main reservoir, and the most typical source of infection is via the consumption of contaminated undercooked beef meat . Since most E. coli are harmless and a part of healthy gut flora in humans and animals, specific detection of STEC is crucial for preventing infections. Since the big multinational STEC O104 outbreak in Germany in 2011, plus an increasingly wide range of STEC serogroups linked to human illness, the targets for detection has shifted off from serogroup based approaches towards targeting the genes coding for Shiga toxin production (stx1 or stx2); which are major virulence factors of STEC . The foremost common technique for DNA based detection is polymerase chain reaction (PCR), in which the specific target sequence from the DNA extracted from the organism is amplified, significantly increasing the sensitivity of the method. Especially real-time PCR (qPCR) found a large application in pathogens during which the number of amplified DNA at the particular time is monitored using fluorescent probes . This approach offers significant advantages like high sensitivity and selectivity, however, it is time-consuming and requires highly trained staff to perform experiments, making it unsuitable for point-of-use detection . A potential alternative is to employ solid-state electrochemical DNA biosensors, comprising a probe DNA as a recognition element and a transducer, which provides a measurable signal following a DNA hybridisation event . Their advantages over traditional techniques include the speed in obtaining results, simplicity of use, and suitability for miniaturisation and portability . The key aspects to consider when developing DNA based electrochemical biosensors are (i) sensor miniaturisation (ii) requirements for robust probe attachment , and (iii) detection methods with low complexity , all of which have enormous impacts on the ultimate performance and use. Miniaturised electrochemical sensors (<10 µm diameter) benefit from enhanced analyte mass transport, reduced background noise, and high current densities making them an ideal choice for point-of-use sensors. Interdigitated microelectrodes (IDEs), comprising two comb-like closely spaced electrodes which are individually electrically connected, have found several applications in point-of-use sensing . For instance, they have recently been applied for the detection of a variety of heavy metals species in water where one comb was used as a working electrode and the other as a generator electrode, allowing electrochemical modification of local pH for improving sensing efficacy . They have also been applied to DNA detection where the probe DNA was either immobilised on both IDEs or the silicon surface between them . Typically, the DNA hybridisation was detected using conductance measured between the two IDEs or impedance, when IDEs were used. Selective modification of only one IDE could enable using the other IDE for other function that sensing as well as using other techniques for DNA detection, such as linear sweep voltammetry. It is a straightforward electrochemical technique that has been applied for DNA detection using redox-active molecules, such as methylene blue (MB) , anthraqinone-2-sulfonic acid monohydrate sodium salt (AQMS) or daunomycin (DNR) . These molecules have different interaction mechanisms to single-stranded (ssDNA) and double-strand DNA (dsDNA). The advantages of such an approach include the short time needed to obtain results and the simplicity of the system. The attachment of probe DNA in a stable and robust manner remains a key challenge in electrochemical sensor development .