DNA nanotechnology allows for the rational construction of synthetic nanoscale structures including nanorobots, motors and devices, via highly specific and programmable base-pairing interactions. We exploit this capacity to design and build a DNA-based biosensor with tunable detection limits. The detection limits of the biosensor are controlled by the linker that connects its two recognition elements, as the linker’s properties determine the kinetics of those recognition elements binding a biomarker from solution. The biosensor can in principle be customized for the detection of a range of biomarkers via the chemical attachment of proteins like antibodies as recognition elements using conjugation chemistry. This biosensor could provide a new platform for the development of quantitative point-of-care diagnostics of diseases like HIV or cancer as there are no amplification steps involved in the detection of the biomarker. This preserves curtail information about the initial concentration of the biomarker which can be used in concentrations dependent diagnoses. The DNA linkers used for these biosensors could eventually replace peptide linkers as DNA nanotechnology techniques give greater control over the behaviour of the linker, and hence the spatial arrangements of the biomolecules attached to its ends, than peptide linkers.