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Abstract

Magnetic resonance imaging (MRI) has become one of the essential noninvasive diagnostic techniques for soft tissues and diseases. Contrast agents (CAs) are used to produce additional contrast and increase the signal intensity for MRI [1]. The commonly available monomeric CAs have disadvantages such as non-specificity, fast renal excretion, low contrast efficiency and therefore they require higher dosage. To overcome this problem, we use multivalent, highly-branched dendrimeric molecules that are capable of carrying large number of CAs and hence the amplification of MRI signal [2]. Here we report the development of a new type of target-specific contrast agents (TCA). We took advantage of the highly specific interaction of the protein avidin with its ligand biotin and synthesized biotinylated monomeric and dendrimeric TCAs. These TCAs are additionally labeled with a fluorescent dye to achieve their multimodal detection by means of optical and MR-based techniques. The affinity assay showed that TCAs bind specifically to avidin-coated beads. The MRI phantom experiments exhibited approximately 5-fold better efficiency of the dendrimeric TCA when compared to the monomeric CA. In parallel, commercially available, non-targeted CA Dotarem did not show the specific binding to avidin since no significant increase in the T1-weighted MRI signal was observed in samples treated with this CA.