Optical Contrast Agents by Molecular Self-Assembly
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Abstract
Development of new contrast agents is a complex task that involves combinatorial screening of different constructs for their targeting ability, reporting properties and biocompatibility. In the traditional approach each such construct is obtained by the means of covalent synthesis to form a conjugate of desired properties. Molecular self-assembly emerges as an alternative approach to the synthesis of complex structures. Here, individual molecular entities are joined by non-covalent interactions to form a new supramolecular unit whose properties are defined by the participating molecules. The science of molecular self-assemblies has progressed to the point where such structures can be generated with good reproducibility and control of their size and shape. Among many self-assembling molecules lipids are of particular interest because of their excellent biological compatibility and their ability to form assemblies of various shapes and sizes, often referred to as polymorphism. Such assemblies include spherical liposomes, nanotubes of the hexagonal phase, and tortuous channels of the cubic phase. Liposomes and similarly sized nanoparticles are specially well studied as carriers for therapeutic and contrast agents. Examples from our research will be used to discuss encapsulation of molecules, improved circulatory concentration, and passive targeting of pathological sites. These concepts are then applied in the development of liposomes as templates to support near-infrared fluorescent molecules and gold nanostructures for the use as optical contrast agents. Building on these principles we will briefly discuss lipid templates for manufacturing of other nanostructures.