Nano-assembly

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Under Nanoassemblierung refers to the controlled connection of individual nanoparticles to the composite nano- or micro-scale objects. Nanoassembly transfers the principle of building molecular structures by linking atoms to building composite particles by linking nanoparticles. The nano-assembly is therefore part of the so-called “bottom-up strategy” of nanotechnology . It thus makes a contribution to the creation of new materials as well as micro- and nano-scale functional elements. Assembly is both in gas phase and in liquid; H. in colloidal systems, possible. Due to the wide range of materials, sizes and shapes of individual nanoparticles, a large variety of composite micro- and nanoparticles with very different properties and functions is possible. Only a very small part of this abundance is used today.

Assembly to binary nanoparticles

Binary nanoparticles are created when exactly two components are connected to one another. This is achieved either a) by a simple complementary binding function of two types of nanoparticles or b) by triggering the formation of exactly one second particle on a surface region of the initially formed particle or c) by self-regulating physical mechanisms such as e.g. B. a controlled electrostatic repulsion by controlling the electrical surface charge. The bond between the particles can be caused by unspecific interactions such. B. antagonistic surface charges or hydrophobic interactions come about. But it can also be achieved through a highly specific chemical functionality, e.g. B. by functionalizing one type of particle with an antigen and the second type of particle with a complementary antibody . The complementarity of DNA oligonucleotides is used very advantageously for selective addressing in the particle assembly .

Multi-component assembly

Since there are usually several identical chemical binding groups on the surfaces of functionalized nanoparticles, it is easily possible to anchor several bondable nanoparticles of a second type on the surface of the first particle type. The density of the bond can largely be controlled via the concentration ratios or the reaction time. In this type of assembly, smaller nanoparticles are often bound to a larger nanoparticle or a microparticle. The distribution of the smaller particles on the surface of a larger particle can be random, or there are approximately equal distances if an additional control of the distance - z. B. via electrostatic interactions - is present.

Hierarchical assembly of nanoparticles

Complex nanoparticles with several levels of structural organization are formed through a hierarchical assembly. In a second assembly step, a third or further component is attached to assemblies that are primarily formed, or two or more assemblies that are primarily formed are connected to one another. The result is particles with a modular structure, with the modules themselves being composed of nanoparticles.

Nanoparticle assembly using microfluidic techniques

An important prerequisite for a well-defined nano-assembly is a high degree of homogeneity in terms of shape and size of the components used for assembly. Such a high level of homogeneity can be achieved either through thermodynamic control of the particle size during their synthesis, through a subsequent separation process or very homogeneous process conditions. Since the particle homogeneity is often determined by the nucleation phase and this reacts very time-critically to an inhomogeneity in the distribution of the reactants, the temperature and other conditions, conventional nanoparticle syntheses in the liquid phase often result in relatively broad size and shape distributions. The product homogeneity can be significantly improved if very fast mass and heat transfers are realized in the nucleation phase . This is done through microfluidic processes - e.g. B. by the microfluid segment technology - possible. In this way, a “focused nucleation” is achieved, which delivers a high degree of uniformity of the nanoparticles even without subsequent sorting steps and thus creates very good conditions for subsequent assembly steps.

Individual evidence

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