Single 19F Probe for Simultaneous Detection of Multiple Metal Ions Using miCEST MRI

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The local presence and concentration of metal ions in biological systems has been extensively studied ex vivo using fluorescent dyes. However, the detection of multiple metal ions in vivo remains a major challenge. We present a magnetic resonance imaging (MRI)-based method for noninvasive detection of specific ions that may be coexisting, using the tetrafluorinated derivative of the BAPTA (TF-BAPTA) chelate as a (19)F chelate analogue of existing optical dyes. Taking advantage of the difference in the ion-specific (19)F nuclear magnetic resonance (NMR) chemical shift offset (Δω) values between the ion-bound and free TF-BAPTA, we exploited the dynamic exchange between ion-bound and free TF-BAPTA to obtain MRI contrast with multi-ion chemical exchange saturation transfer (miCEST). We demonstrate that TF-BAPTA as a prototype single (19)F probe can be used to separately visualize mixed Zn(2+) and Fe(2+) ions in a specific and simultaneous fashion, without interference from potential competitive ions.