A microfluidics-integrated impedance/surface acoustic resonance tandem sensor

We demonstrate a dual sensor concept for lab-on-a-chip in-liquid sensing through integration of surface acoustic wave resonance (SAR) sensing with electrochemical impedance spectroscopy (EIS) in a single device. In this concept, the EIS is integrated within the building blocks of the SAR sensor, but features a separate electrical port. The two-port sensor was designed, fabricated, and embedded in a soft polymer microfluidic delivery system, and subsequently characterized. The SAR-EIS tandem sensor features low cross-talk between SAR and EIS ports, thus promoting non-interfering gravimetric and impedimetric measurements. The EIS was characterized by means of the modified Randle\u27s cell lumped element model. Four sensitive parameters could be established from the tandem sensor readout, and subsequently employed in a proof of principle study of liposome layers and their interaction with Ca2+ ions, leading to transformation into molecular film structures. The associated shift of the sensing quantities is analysed and discussed. The combination of impedimetric and gravimetric sensing quantities provides a unique and detailed description of physicochemical surface phenomena as compared to a single mode sensing routine

Protocells: Milestones and Recent Advances

The origin of life is still one of humankind\u27s great mysteries. At the transition between nonliving and living matter, protocells, initially featureless aggregates of abiotic matter, gain the structure and functions necessary to fulfill the criteria of life. Research addressing protocells as a central element in this transition is diverse and increasingly interdisciplinary. The authors review current protocell concepts and research directions, address milestones, challenges and existing hypotheses in the context of conditions on the early Earth, and provide a concise overview of current protocell research methods

Spontaneous Formation and Rearrangement of Artificial Lipid Nanotube Networks as a Bottom-Up Model for Endoplasmic Reticulum

We present a convenient method to form a bottom-up structural organelle model for the endoplasmic reticulum (ER). The model consists of highly dense lipidic nanotubes that are, in terms of morphology and dynamics, reminiscent of ER. The networks are derived from phospholipid double bilayer membrane patches adhering to a transparent Al2O3 substrate. The adhesion is mediated by Ca2+ in the ambient buffer. Subsequent depletion of Ca2+ by means of BAPTA/EDTA causes retraction of the membrane, resulting in spontaneous lipid nanotube network formation. The method only comprises phospholipids and microfabricated surfaces for simple formation of an ER model and does not require the addition of proteins or chemical energy (e.g., GTP or ATP). In contrast to the 3D morphology of the cellular endoplasmic reticulum, the model is two-dimensional (albeit the nanotube dimensions, geometry, structure, and dynamics are maintained). This unique in vitro ER model consists of only a few components, is easy to construct, and can be observed under a light microscope. The resulting structure can be further decorated for additional functionality, such as the addition of ER-associated proteins or particles to study transport phenomena among the tubes. The artificial networks described here are suitable structural models for the cellular ER, whose unique characteristic morphology has been shown to be related to its biological function, whereas details regarding formation of the tubular domain and rearrangements within are still not completely understood. We note that this method uses Al2O3 thin-film-coated microscopy coverslips, which are commercially available but require special orders. Therefore, it is advisable to have access to a microfabrication facility for preparation

The self-spreading double bilayer/Advances in lipid membrane nanotechnology

In my thesis I describe the generation, characterization and uses of self-spreading double bilayers. This new type of solid-supported model membrane combines features and properties of the 2D lipid bilayer membrane, and the 3D phospholiposome. The double bilayer membrane, i.e., a fully closed, parallel stack of two lipid bilayers, is essentially a surface-adhered flat giant unilamellar vesicle (FGUV) with a very small internal volume. It possesses features of supported membranes, such as flatness, large area coverage and high mechanical stability, and of giant vesicles, such as the ability to encapsulate nanoparticles in its interior volume. In the experimental work towards this thesis, I have probed the response of the FGUV to chemical or physical cues, and studied dynamic features reminiscent of complex cell behavior. A number of examples are discussed, including protrusion formation as a response to a chemical gradient, directed and reversible movement in a temperature gradient, spontaneous nanotube formation in response to the adhesion of virus-like particles, and repair of large area membrane pores. An important outcome of my work is the discovery of two non-trivial pore formation modes in membranes, which links biomembrane materials properties to fundamental properties of thin solid materials. One of the modes displays crackling noise dynamics, featuring sudden intermittent bursts over a broad size range (avalanches), similar to earthquakes. I consider the FGUV to be an experimental model system for studying various aspects of cell like behavior on intact model membranes, as well as a nanotechnological platform, useful to construct mesoscale membrane architectures and networks

The self-spreading double bilayer/Advances in lipid membrane nanotechnology

In my thesis I describe the generation, characterization and uses of self-spreading double bilayers. This new type of solid-supported model membrane combines features and properties of the 2D lipid bilayer membrane, and the 3D phospholiposome. The double bilayer membrane, i.e., a fully closed, parallel stack of two lipid bilayers, is essentially a surface-adhered flat giant unilamellar vesicle (FGUV) with a very small internal volume. It possesses features of supported membranes, such as flatness, large area coverage and high mechanical stability, and of giant vesicles, such as the ability to encapsulate nanoparticles in its interior volume. In the experimental work towards this thesis, I have probed the response of the FGUV to chemical or physical cues, and studied dynamic features reminiscent of complex cell behavior. A number of examples are discussed, including protrusion formation as a response to a chemical gradient, directed and reversible movement in a temperature gradient, spontaneous nanotube formation in response to the adhesion of virus-like particles, and repair of large area membrane pores. An important outcome of my work is the discovery of two non-trivial pore formation modes in membranes, which links biomembrane materials properties to fundamental properties of thin solid materials. One of the modes displays crackling noise dynamics, featuring sudden intermittent bursts over a broad size range (avalanches), similar to earthquakes. I consider the FGUV to be an experimental model system for studying various aspects of cell like behavior on intact model membranes, as well as a nanotechnological platform, useful to construct mesoscale membrane architectures and networks

A Hypothesis for Protocell Division on the Early Earth

I hypothesize that the division of the first protocell might have occurred before genetic polymers were synthesized and redistributed. In the light of recent findings, it is conceivable that the first division event of a primitive protocell might have occurred at the same time as its surface-assisted formation

Formation and dynamics of endoplasmic reticulum-like lipid nanotube networks

We report on the self-organized formation and dynamics of artificial lipid nanotube networks, which, in terms of morphology and behavior, resemble the endoplasmic reticulum(ER) of biological cells. The networks, initially generated from a solid- supported planar phospholipid membrane, undergo a morphological transformation, triggered by the chelation and removal of Ca2+ from the environment surrounding the membrane. Calcium depletion gradually causes de-pinning, thus de-wetting, at the membrane-substrate interface. We observe dynamic re-arrangements very similar to the ones reported for the cellular ER, such as sliding of tubes and formation of new junctions, and quantify these transformations. We also show occurrences of the dynamic replacement of lipidic particles on nanotubes as indicators for the existence of a tension gradient throughout the network, as well as the spontaneous formation of small vesicles from semi-free floating tubes. We propose that these artificial networks are suitable to serve as a bottom-up-generated structural model for the cellular ER, whose fascinating characteristic morphology is suggested to be tied to its biological function, but with respect to formation, dynamics, and functional details still incompletely understood

A cellular automaton for modeling non-trivial biomembrane ruptures

A novel cellular automaton (CA) for simulating biological membrane rupture is proposed. Constructed via simple rules governing deformation, tension, and fracture, the CA incorporates ideas from standard percolation models and bond-based fracture methods. The model is demonstrated by comparing simulations with experimental results of a double bilayer lipid membrane expanding on a solid substrate. Results indicate that the CA can capture non-trivial rupture morphologies such as floral patterns and the saltatory dynamics of fractal avalanches observed in experiments. Moreover, the CA provides insight into the poorly understood role of inter-layer adhesion, supporting the hypothesis that the density of adhesion sites governs rupture morphology