A framework for generating highly modular genetic sensors for deep-tissue imaging

Biosensors typically use fluorescence as a measurable output. Despite its prevalence in cellular imaging, fluorescence is limited in its application within mammalian vertebrate models due to light scattering and absorption. Conversely, magnetic resonance imaging (MRI) is uniquely suited for noninvasively capturing high-resolution images regardless of tissue depth. However, detecting molecular-level changes via MRI is constrained by a lack of biosensors. We address this challenge by modifying Organic Anion Transporting Polypeptide 1B3 (OATP1B3), a gadolinium-based T1-weighted MRI reporter, to create highly modular genetic sensors. The fusion of a destabilizing domain to OATP1B3 leads to rapid degradation (MRI off-state). MRI signal can be rescued (MRI on-state) by inserting protease cleavage sites between the degron and OATP1B3 and inducing protease expression. By reconfiguring the protease, multiple different analytes can be imaged without the need to design completely new MRI sensors.