Introduction. Ca2+ is an important second messenger in the brain. Tracking the significant changes in its concentration during neuronal activity, may increase our understanding of basic aspects of neuronal regulation as well as highlight abnormalities in diseased state1. The excellent spatial resolution and the noninvasive nature of Magnetic Resonance Imaging (MRI) combined with the use of ‘smart’ contrast agents reflecting Ca2+ dynamics are likely to provide invaluable information about normal and diseased brains states. To accomplish our goal of tracking neuronal activity using ‘smart’ contrast agents, two bismacrocyclic contrast agents (Ln2L1 and Ln2L2) were synthesized. Gd3+ loaded DO3A was used as MR detectable part while BAPTA (Ca2+ chelating part) was used as the core structure to link two DO3A units via amide bonds (Fig). Results. The relaxivity increased upon Ca2+ addition was 15% for Gd2L1 and 10% for Gd2L2 respectively which was selective for Ca2+over Mg2+. High resolution UV-Vis measurements of Eu2L1 at different temperatures indicated the presence of two distinct species with absorption maxima at 579.8 nm and 579.3 nm. Their intensities were temperatur