1Department of Radiology, Johns Hopkins University, Baltimore, MD, United States; 2Institute for Cell Engineering, Johns Hopkins University, Baltimore, MD, United States; 3F.M. Kirby Research Center, Kennedy Krieger Institute, Baltimore, MD, United States
Although Ca2+ ions are involved in a myriad of biological signaling processes, a non-invasive means of detecting micromolar Ca2+ levels remains a formidable challenge. We present an approach for specifically sensing the presence of Ca2+ ions through its substrate binding kinetics by exploiting the chemical shift change of 19F upon binding of Ca2+ to the fluorinated chelator 1,2-Bis-[2-bis(carboxymethyl)amino-5-19fluorophenoxy]ethane (5-19FBAPTA). Using RF labeling at the bound-19F frequency and detection of label transfer to the free-19F frequency (Δω=5.8ppm) in millimolar concentration substrate, we were able to amplify the signal of Ca2+ with supreme specificity over other divalent cations.