**2.1 General**

Biologically essential d-block metal ions such as zinc (Zn2+), copper (Cu2+), manganese (Mn2+), and iron (Fe2+) are involved in a variety of physiological processes in living systems as cofactors for various enzymes, intracellular second messengers, and related processes [10]. It was reported that a metal imbalance in cells and tissues causes a number of disorders such as Alzheimer's disease, Parkinson's disease, Willson's disease, etc. [10]. Therefore, the development of fluorescence-based probes for the detection of these intracellular metal ions has contributed to our understanding of their functions and metabolism in living cells, while some limitations to detecting their emission from tissues remain due to their impermeability [10–12].

It is well known that MRI is one of the useful noninvasive methods for *in vivo* visualization and that it permits three-dimensional images of organisms and drug distributions to be obtained [13]. Although MRI is powerful method, there are only a few examples of MRI probes such as Gd3+-based contrast agents [14, 15].
