Porphyrin-based Sensors for Fluorescence and MRI

The present invention generally relates to agents and compositions having MRI and/or optical signals, and methods for their use in the determination of an analyte. In some cases, an optical, MRI, or other signal produced by the agent or composition may be affected by the presence of an analyte. Some embodiments of the present invention may provide agents or compositions which are cell permeable. Examples of analytes that may be determined by the present invention include zinc ions, calcium ions, and other biological analytes.