Aptamer-functionalized lipid-core micelles loaded with rhenium tricarbonyl complex

Due to its distinctive physicochemical properties, diimine rhenium(I) tricarbonyl complexes are one of the most common type of complexes used in cellular imaging. The reasonably simple synthesis and modification of rhenium complexes in addition to their stability and remarkable luminescent properties provide a robust method to perform this goal. In general, organometallic complexes must be biocompatible to development imaging agents. Consequently, modification and bio-functionalization of the transition complexes is crucial to enhance biocompatibility. Here, we synthesize and characterize the luminescent tricarbonyl rhenium complex, [(bpy)(H₂O)Re(CO)₃]⁺, and propose a reasonably simple preparation of an aptamer-functionalized lipid core micelle (LCM), loaded with this complex, to endow it with suitable properties to be used in cellular imaging. The [(bpy)(H₂O)Re(CO)₃]⁺ exhibit a broad emission band centered around 550 nm at room temperature after excitation at 360 nm. The luminescent intensity is higher in nonpolar solvents such as chloroform. The complex was loaded into LCMs and, at the same time, the carrier was functionalized in situ with the nucleolin aptamer, AS1411, to improve the complex delivery and uptake to target cells. After physicochemical and spectroscopic characterization of the aptamer-functionalized vehicle, cellular studies were performed to evaluate its toxicity and its efficiency as cellular imaging agent. The combined AS1411 aptamer-functionalized lipid core micelle system effectively encapsulated the [(bpy)(H₂O)Re(CO)₃]⁺ complex, maintained its luminescent properties, and showed potential features to be used in cellular imaging experiments.