Circular dichroism (CD) spectroscopy is a powerful optical technique for the study of chiral materials and molecules. It gives access to an enantioselective signal based on the differential... Show moreCircular dichroism (CD) spectroscopy is a powerful optical technique for the study of chiral materials and molecules. It gives access to an enantioselective signal based on the differential absorption of right and left circularly polarized light, usually obtained through polarization analysis of the light transmitted through a sample of interest. CD is routinely used to determine the secondary structure of proteins and their conformational state. However, CD signals are weak, limiting the use of this powerful technique to ensembles of many molecules. Here, we experimentally realize the concept of photothermal circular dichroism, a technique that combines the enantioselective signal from circular dichroism with the high sensitivity of photothermal microscopy, achieving a superior signal-to-noise ratio to detect chiral nano-objects. As a proof of principle, we studied the chiral response of single plasmonic nanostructures with CD in the visible range, demonstrating a signal-to-noise ratio better than 40 with only 30 ms integration time for these nanostructures. The high signal-to-noise ratio allows us to quantify the CD signal for individual nanoparticles. We show that we can distinguish relative absorption differences for right circularly and left circularly polarized light as small as gmin = 4 × 10–3 for a 30 ms integration time with our current experimental settings. The enhanced sensitivity of our technique extends CD studies to individual nano-objects and opens CD spectroscopy to numbers of molecules much lower than those in conventional experiments. Show less
Steinborn, B.; Hirschle, P.; Hohn, M.; Bauer, T.; Barz, M.; Wuttke, S.; ... ; Lachelt, U. 2019
Selected drug molecules with Lewis base functions can be assembled into coordinative nanoparticles (NPs) by linking them with suitable metal ions. Such nanomaterials exhibit a high material economy... Show moreSelected drug molecules with Lewis base functions can be assembled into coordinative nanoparticles (NPs) by linking them with suitable metal ions. Such nanomaterials exhibit a high material economy due to high drug contents and minor amounts of inactive additives. The antifolate pemetrexed (PMX) which is used for the treatment of lung cancers contains two carboxy functions that are able to undergo coordinative binding of metal ions. This study presents the development of a multilayer PMX NP system where each layer serves a distinct purpose. The metal-drug NP core is assembled in a bottom-up approach by coordinative interactions between zirconium (IV) ions and PMX molecules. Since the NP core is generated from drug molecules as essential units, it features a very high drug content of almost 80%. The NP core is stabilized against serum with a shell of a polymerized oligoamine-modified trimethoxysilane derivative (TMSP). As external layer, a polyglutamate-block-polysarcosine-N-3 (pGlu-b-pSar) coating mediates efficient colloidal stabilization and enables introduction of targeting functionalities by click chemistry. Attaching folate or transferrin ligands to the polymer layer enhances NP uptake into target receptor positive KB and L1210 cells. This study illustrates the development and characterization of metal-drug coordination NPs with high drug content and variable external functionalizations. Show less
Zimpel, A.; Danaf, N. Al; Steinborn, B.; Kuhn, J.; Hohn, M.; Bauer, T.; ... ; Wuttke, S. 2019
Metal-organic framework nanoparticles (MOF NPs) are of growing interest in diagnostic and therapeutic applications, and due to their hybrid nature, they display enhanced properties compared to more... Show moreMetal-organic framework nanoparticles (MOF NPs) are of growing interest in diagnostic and therapeutic applications, and due to their hybrid nature, they display enhanced properties compared to more established nanomaterials. The effective application of MOF NPs, however, is often hampered by limited control of their surface chemistry and understanding of their interactions at the biointerface. Using a surface coating approach, we found that coordinative polymer binding to Zr-fum NPs is a convenient way for peripheral surface functionalization. Different polymers with biomedical relevance were assessed for the ability to bind to the MOF surface. Carboxylic acid and amine containing polymers turned out to be potent surface coatings and a modulator replacement reaction was identified as the underlying mechanism. The strong binding of polycarboxylates was then used to shield the MOF surface with a double amphiphilic polyglutamate-polysarcosine block copolymer, which resulted in an exceptional high colloidal stability of the nanoparticles. The effect of polymer coating on interactions at the biointerface was tested with regard to cellular association and protein binding, which has, to the best of our knowledge, never been discussed in literature for functionalized MOF NPs. We conclude that the applied approach enables a high degree of chemical surface confinement, which could be used as a universal strategy for MOF NP functionalization. In this way, the physicochemical properties of MOF NPs could be tuned, which allows for control over their behavior in biological systems. Show less
Holm, R.; Douverne, M.; Weber, B.; Bauer, T.; Best, A.; Ahlers, P.; ... ; Barz, M. 2019
The size control of nanomedicines for tumor diagnosis and therapy is of high importance, since it enables or disables deep and sufficient tumor penetration. Amphiphilic star-shaped block copolypept... Show moreThe size control of nanomedicines for tumor diagnosis and therapy is of high importance, since it enables or disables deep and sufficient tumor penetration. Amphiphilic star-shaped block copolypept(o)ides offer substantial promise to precisely adjust the hydrophobic core and the hydrophilic corona, independent of each other, and therefore simultaneously control the size dimension in the interesting size range from 10 to 30 nm. To gain access to core-shell structures of such sizes, 3-arm and 6-arm PeptoStars, based on poly(gamma-tert-butyloxycarbonyl-L-glutamate)-b-polysarcosine (pGlu(OtBu)-b-pSar), were prepared via controlled living ring-opening polymerization (ROP) of the corresponding N-carboxyanhydrides. Moreover, size exclusion chromatography (SEC) proves the presence of well-defined star shaped polymers with molecular weights from 38 to 88 kg/mol with low polymer dispersities of 1.16 to 1.23. By varying the alpha-helical peptide core and maintain a constant polysarcosine corona, hydrodynamic size analyses revealed the importance of using a sufficiently large and dense hydrophilic shielding corona to prevent aggregation of the hydrophobic core and obtain uniform-sized spherical-shaped particles with hydrodynamic diameters below 24 nm. Fluorescence correlation spectroscopy (FCS) additionally demonstrates the absence of protein adsorption in human plasma for 6-arm polypept(o)ide stars and thus confirms polysarcosine as stealthlike material. Show less
Otter, R.; Henke, N.A.; Berac, C.; Bauer, T.; Barz, M.; Seiffert, S.; Besenius, P. 2018
Achieving precise control over the morphology and function of polymeric nanostructures during self-assembly remains a challenge in materials as well as biomedical science, especially when... Show moreAchieving precise control over the morphology and function of polymeric nanostructures during self-assembly remains a challenge in materials as well as biomedical science, especially when independent control over particle properties is desired. Herein, we report on nanostructures derived from amphiphilic block copolypept(o)ides by secondary-structure-directed self-assembly, presenting a strategy to adjust core polarity and function separately from particle preparation in a bioreversible manner. The peptide-inherent process of secondary-structure formation allows for the synthesis of spherical and worm-like core-cross-linked architectures from the same block copolymer, introducing a simple yet powerful approach to versatile peptide-based core-shell nanostructures. Show less
