Hyperpolarized 129Xe NMR spectra of biosensor 5 alone, binding αIIbβ3 integrin, and blocked by c[RGDyK], all studies in Tris buffer (1 mM, pH 7.2) (a) 5 gave 129Xe NMR chemical shift at 65.8 ppm. (b) 5 and αIIbβ3 integrin in Tris buffer with 30% glycerol and 0.1% Triton X-100. “Free” biosensor gave 129Xe NMR chemical shift at 67.1 ppm, which was shifted 1.3 ppm downfield from “free” biosensor in (a) due to addition of glycerol. “Bound” biosensor appeared at 71.2 ppm, representing a 4.1 ppm downfield shift. (c) c[RGDyK] added to solution of 5 and αIIbβ3 integrin gave “free” biosensor at the same 129Xe NMR chemical shift, but no “bound” biosensor was detected.