Although metal ions are involved in a myriad of biological processes, noninvasive detection of free metal ions in deep tissue remains a formidable challenge. We present an approach for specific sensing of the presence of Ca2+ in which the amplification strategy of chemical exchange saturation transfer (CEST) is combined with the broad range of chemical shifts found in 19F NMR spectroscopy to obtain magnetic resonance images of Ca2+. We exploited the chemical shift change (Δω) of 19F upon binding of Ca2+ to the 5,5′-difluoro derivative of 1,2-bis(o-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid (5F-BAPTA) by radiofrequency labeling at the Ca2+-bound 19F frequency and detection of the label transfer to the Ca 2+-free 19F frequency. Through the substrate binding kinetics we were able to amplify the signal of Ca2+ onto free 5F-BAPTA and thus indirectly detect low Ca2+ concentrations with high sensitivity.
ASJC Scopus subject areas
- Colloid and Surface Chemistry