Abstract
We present the first cryptophane-based "turn-on" (129)Xe NMR biosensor, employing a peptide-functionalized cryptophane to monitor the activation of calmodulin (CaM) protein in solution. In the absence of CaM binding, interaction between the peptide and cryptophane completely suppresses the hyperpolarized (129)Xe-cryptophane NMR signal. Biosensor binding to Ca(2+)-activated CaM produces the expected (129)Xe-cryptophane NMR signal.