Hyperpolarized Xenon-Based Molecular Sensors for Label-Free Detection of analytes

Abstract

Nuclear magnetic resonance (NMR) can reveal the chemical constituents of a complex mixture without resorting to chemical modification, separation, or other perturbation. Recently, we and others have developed magnetic resonance agents that report on the presence of dilute analytes by proportionately altering the response of a more abundant or easily detected species, a form of amplification. One example of such a sensing medium is xenon gas, which is chemically inert and can be optically hyperpolarized, a process that enhances its NMR signal by up to 5 orders of magnitude. Here, we use a combinatorial synthetic approach to produce xenon magnetic resonance sensors that respond to small molecule analytes. The sensor responds to the ligand by producing a small chemical shift change in the Xe NMR spectrum. We demonstrate this technique for the dye, Rhodamine 6G, for which we have an independent optical assay to verify binding. We thus demonstrate that specific binding of a small molecule can produce a xenon chemical shift change, suggesting a general approach to the production of xenon sensors targeted to small molecule analytes for in vitro assays or molecular imaging in vivo.

Development of an antibody-based, modular biosensor for129Xe NMR molecular imaging of cells at nanomolar concentrations

“…Xenon can be hyperpolarized, enhancing its signal by up to five orders of magnitude and enabling it to be detected at extremely low concentrations (5). In addition, the exquisite sensitivity of xenon to its local chemical environment, as indicated by wellresolved chemical shift changes, brings with it the potential to distinguish not only localization but also specific functional events (6)(7)(8)(9)(10). This sensitivity may also be exploited in the development of different xenon MRI contrast agents which could be used to perform multiplexed molecular imaging (11), especially useful as clusters of biomarkers are often more informative than a single indicator.…”

“…In response to these developments, there have been a number of recent studies describing the development of new xenon contrast agents (17)(18)(19) and biosensors (10,(20)(21)(22)(23) for xenon NMR applications. Critically however, only recently have images of cells been achieved with xenon MRI, with a nontargeted approach using the contrast agent CrA (24).…”

NMR-Based Chemosensing via p-H2 Hyperpolarization: Application to Natural Extracts

“…Notably, nuclear spin hyperpolarization was used for the 129 Xe NMRbased chemosensor to maximize the sensitivity. 20 However, the small 129 Xe chemical shift changes observed upon binding of the target analytes to the receptor has so far determined a detection limit in the submillimolar range, despite the high signal-to-noise ratio of the NMR spectrum.…”

“…Recent implementations of NMR chemosensing for chemical analysis report such limit in the submillimolar range. 20,22 Here, interaction with the receptor, an iridium complex, in the presence of p-H 2 , results in approximately 1000-fold amplification of the NMR response. As a consequence, a …”

Rotaxane probes for protease detection by 129Xe hyperCEST NMR

“…14 Since the development of the 129 Xe hyperCEST approach, 129 Xe hosts have been conjugated to targeting groups and chemical shift agents for applications in cancer marker imaging and detection of other analytes. [15][16][17] Typically, cryptophane-A (CryA) has been the 129 Xe host of choice for these applications; however, the low solubility of CryA creates difficult procedures for conjugate synthesis, and has low synthetic yields. Cucurbit [6]uril (CB6) was also reported as a promising 129 Xe host for hyperCEST NMR.…”