Xenon biosensors have an outstanding potential to increase the significance of magnetic resonance imaging (MRI) in molecular imaging and to combine the advantages of MRI with the high sensitivity of hyperpolarized Xe-129 and the specificity of a functionalized contrast agent. Based on new detection schemes (Hyper-CEST method) in Xe MRI, this novel concept in molecular diagnostics will be made available for biomedical applications. The advancement focuses on high-sensitivity in vitro diagnostics for localization of tumour cells in cell cultures and first demonstrations on animal models based on a transferrin-functionalized biosensor. Such a sensor will enable detection of subcutaneous tumours at high sensitivity without any background signal. More detailed work on the different available Hyper-CEST contrast parameters focuses on an absolute quantification of new molecular markers that will improve non-invasive tumour diagnostics significantly. NMR detection of functionalized Xe biosensors have the potential to close the sensitivity gap between modalities of nuclear medicine like PET/SPECT and MRI without using ionizing radiation or making compromises in penetration depth like in optical methods.