Significance The field of xenon magnetic resonance imaging (MRI) is moving closer to the development of targeted xenon biosensors for in vivo applications. It is motivated by a ca. 10 8 -fold improved sensitivity compared with conventional proton MRI. This has been enabled by significant improvements to hardware (xenon polarizer design) and sensitivity (through the hyperpolarized 129 Xe chemical exchange saturation transfer technique). In this paper, we capitalize on these improvements by demonstrating targeted xenon imaging on cells using a modular xenon biosensor. With this method, we can detect target cells with as little as 20 nM of our xenon contrast agent. Imaging of such low levels of cell-specific xenon hosts is unprecedented and reinforces the potential of xenon–cryptophane biosensors for molecular imaging applications.

The targeting of metabolically labeled glycans with conventional MRI contrast agents has proved elusive. In this work, which further expands the utility of xenon Hyper-CEST biosensors in cell experiments, we present the first successful molecular imaging of such glycans using MRI. Xenon Hyper-CEST biosensors are a novel class of MRI contrast agents with very high sensitivity. We designed a multimodal biosensor for both fluorescent and xenon MRI detection that is targeted to metabolically labeled sialic acid through bioorthogonal chemistry. Through the use of a state of the art live-cell bioreactor, it was demonstrated that xenon MRI biosensors can be used to image cell-surface glycans at nanomolar concentrations.

Caged xenon has great potential in overcoming sensitivity limitations for solution-state NMR detection of dilute molecules. However, no application of such a system as a magnetic resonance imaging (MRI) contrast agent has yet been performed with live cells. We demonstrate MRI localization of cells labeled with caged xenon in a packed-bed bioreactor working under perfusion with hyperpolarized-xenon-saturated medium. Xenon hosts enable NMR/MRI experiments with switchable contrast and selectivity for cell-associated versus unbound cages. We present MR images with 10(3) -fold sensitivity enhancement for cell-internalized, dual-mode (fluorescence/MRI) xenon hosts at low micromolar concentrations. Our results illustrate the capability of functionalized xenon to act as a highly sensitive cell tracer for MRI detection even without signal averaging. The method will bridge the challenging gap for translation to in vivo studies for the optimization of targeted biosensors and their multiplexing applications.