In the present study we generated a single chain antibody (scFv) against a novel cancer biomarker (i.e. the hERG1 potassium channel) and provide a preliminary proof of concept that it has the appropriate features (easy production protocols, good stability and immunoreactivity, favourable pharmacokinetic and tumor-to-organ ratios in vivo) to be exploited for in vivo cancer diagnostics in the near future. Here, KCNA3 is linked to cancer.