Freeze-Fracture Electron Microscopy on Nano- and Microcarrier for Theranostics and Antibiotics

Abstract

Nano- and microparticles are frequently used as carrier systems for delivering therapeutics as well as diagnostics (theranostics) at cellular level. We studied the morphology of a wide variety of such particles suitable as theranostic-carrier by freeze-fracture transmission electron microscopy (ff-TEM). As a cryofixation, replica, and transmission EM method it is a powerful tool to monitor self-assembling of lipid-, polymer-, as well as protein/peptide-based carriers encapsulating drug-, gene-, vaccine, antimicrobial- and imaging molecules [1]. At the resolution limit of 2nm we are able to characterize nano particles such as quantum dots (coupled to drug-loaded immunoliposomes), gold nano-particles, superparamagnetic iron oxide nano-particles loaded in polymeric immunomicelles, micelles (spherical-, disc-, and worm-type micelles), single-wall carbon nano-tubes embedded in hydrated gels, and small unilamellar liposome (targeted and non-targeted) on nano-scale resolution. Furthermore, ff-TEM allows the production of beam-damage-resistant replica from much larger, micrometer-size objects such as multilamellar liposome, niosomes, cationic liposome/DNA complexes, integrin-targeted lipopolyplexes, polymer-, lipid- or surfactant-stabilized gas bubbles, cochleate cylinder [2], depofoam particles, and drug crystals. This way we are able to study nano-scale events in micro-scale biological as well as artificial assemblies. Ff-TEM enables us not only to characterize nano- and microcarriers suitable for theranostics, but is the method of choice as well to study their fate related to their pay load, application milieu, and during cell interaction. Furthermore, we investigated structural modifications within bilayers such as domain-formation [1] but also transformations to non-bilayer structures such as hexagonal and cubic phases. Currently we are focused on cochleate cylinder as macrocarrier for antibiotics combating bacterial multidrug resistance [2].