Graphene liquid cells (GLCs) for transmission electron microscopy (TEM) enable high-resolution, real-time imaging of dynamic processes in water. Large-scale implementation, however, is prevented by... Show moreGraphene liquid cells (GLCs) for transmission electron microscopy (TEM) enable high-resolution, real-time imaging of dynamic processes in water. Large-scale implementation, however, is prevented by major difficulties in reproducing GLC fabrication. Here, a high-yield method is presented to fabricate GLCs under millimeter areas of continuous graphene, facilitating efficient GLC formation on a TEM grid. Additionally, GLCs are located on the grid using correlated light-electron microscopy (CLEM), which reduces beam damage by limiting electron exposure time. CLEM allows the acquisition of reliable statistics and the investigation of the most common shapes of GLCs. In particular, a novel type of liquid cell is found, formed from only a single graphene sheet, greatly simplifying the fabrication process. The methods presented in this work-particularly the reproducibility and simplicity of fabrication-will enable future application of GLCs for high-resolution dynamic imaging of biomolecular systems. Show less
Natural materials, such as collagen, can assemble with multiple levels of organization in solution. Achieving a similar degree of control over morphology, stability and hierarchical organization... Show moreNatural materials, such as collagen, can assemble with multiple levels of organization in solution. Achieving a similar degree of control over morphology, stability and hierarchical organization with equilibrium synthetic materials remains elusive. For the assembly of peptidic materials the process is controlled by a complex interplay between hydrophobic interactions, electrostatics and secondary structure formation. Consequently, fine tuning the thermodynamics and kinetics of assembly remains extremely challenging. Here, we synthesized a set of block co polypeptides with varying hydrophobicity and ability to form secondary structure. From this set we select a sequence with balanced interactions that results in the formation of high-aspect ratio thermodynamically favored nanotubes, stable between pH 2 and 12 and up to 80 °C. This stability permits their hierarchical assembly into bundled nanotube fibers by directing the pH and inducing complementary zwitterionic charge behavior. This block co-polypeptide design strategy, using defined sequences, provides a straightforward approach to creating complex hierarchical peptide-based assemblies with tunable interactions Show less
Inspired by Nature's capacity to synthesize well‐defined inorganic nanostructures, such as the magnetite particles produced by magnetotactic bacteria, genetic algorithms are employed to... Show moreInspired by Nature's capacity to synthesize well‐defined inorganic nanostructures, such as the magnetite particles produced by magnetotactic bacteria, genetic algorithms are employed to combinatorially optimize the aqueous synthesis of magnetite (Fe3O4) nanoparticles through the action of copolypeptide additives. An automated dispensing system is used to prepare and rapidly screen hundreds of mineralization reactions with randomized conditions, varying ferrous iron, base, oxidant, and polypeptide chemistry. Optimization over multiple generations allows identification of conditions under which the copolypeptides promote magnetite formation where this does not occur in their absence. It is found that nanoparticle size, size distribution, and shape can be tuned by the concentrations and compositions of the copolypeptides, and that the reaction pH is the most important factor in controlling the crystalline phase. This approach should be broadly applicable to the syntheses of solid‐state materials and represents a valuable strategy for extending biomimetic mineralization to the production of technological materials. Show less
Tu, J.; Du, G.; Reza Nejadnik, M.; Monkare, J.T.; Maaden, K. van der; Bomans, P.H.H.; ... ; Kros, A. 2017
