Controlling Chemistry in Dynamic Nanoscale Systems

Spatial organization and shape dynamics are inherent properties of biological cells and cell interiors. There are strong indications that these features are important for the in vivo control of reaction parameters in biochemical transformations. Nanofluidic model devices founded on surfactant systems, such as phospholipids or phospholipid mixtures, that can be assembled and manipulated through a combination of self-assembly and forced shape transformations, offer numerous practical benefits since they closely resemble their biological counterparts both in function and in structure. To date, these systems belong to a rare group of techniques that are used to model shape and volume changes on the micrometer and nanometer-scale on relevant time scales. Diffusion is an efficient means of materials transport in natural and artificial nanoscale systems and can be readily employed in the study of enzymatic reactions in fluid membrane reactors of static or of changing geometries and morphologies. Other means of transport, e.g. electrophoretic or tension-driven modes are also available. Most importantly, reaction rates in nanofluidic systems can be controlled both by shape and volume changes. The important interplay between chemical reactions and geometry has been conceptualized within a theoretical framework for ultra-small volumes and tested on a number of experimental systems, opening pathways to more complex, dynamically compartmentalized ultra-small volume reactors, or artificial model cells, that offer more detailed understanding of cellular kinetics and biophysical phenomena, such as macromolecular crowding. A projection of nanotube vesicle networks onto surfaces is a viable strategy to overcome challenging difficulties with respect to stability, portability, and ease of fabrication. The negative photoresist SU-8 has been utilized as a hydrophobic, structured support with feature sizes in the “μm” and “nm” range, accommodating hydrophobic or hydrophobized molecularly thin films. A unique feature of such structures is the controlled and stoichiometrically well-defined mixing of dynamically flowing surface coatings, for example, through the formation of spreading and mixing lipid monolayers. Moreover, other immobilization strategies based on hydrophobic interactions have been explored and established, such as the surface attachment of cholesterol-modified DNA, serving as anchors for complementary DNA recognition. Immobilized chol-TEG-DNA shows robust and efficient attachment, high surface coverage, and is well accessible for complementary strands. dsDNA disassociation and hybridization on chip via surface printed thin film heaters or infrared laser light is a possible extension of the concept. Controlled release of chol-DNA molecules from SU-8 surfaces gives the possibility to dynamically change surface and/or solution properties in micro and nanoreactor applications, opening access to stable 2D chemistry on surface-based devices with potential for easy interfacing with conventional microfluidic devices.