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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 2 - CSI.interface (A molecular interface science approach: Decoding single molecular reactions and interactions at dynamic solid/liquid interfaces)

Teaser

Summary

Generating a detailed molecular understanding of complex, simultaneous interactions at reactive/dynamic solid/fluid interfaces is one of the biggest contemporary scientific challenges across disciplines. Whether it is during corrosive coating degradation, in biological adhesion, or during adaptive interfacial redox-cycle feedback in strongly adhesive seawater organisms: It is a large numbers of similar or dissimilar molecule/molecule, molecule/surface and competing interactions with ions/water that mediate complex macroscopic properties at crowded solid/liquid interfaces. How do single molecular interactions at dynamic, reactive or steady state interfaces translate into a macroscopically observable outcome?
After decades of truly transformative advancements in single molecule (bio)physics and surface science, it is still no more than a vision to predict and control macroscopic phenomena such as adhesion or electrochemical reaction rates at solid/liquid interfaces based on well-characterized single molecular interactions. How exactly do inherently dynamic and simultaneous interactions of a countless number of interacting â€œcrowdedâ€ molecules lead to a concerted outcome/property at the macroscopic scale?
In CSI.interface, we aim to unravel the scaling of single molecule interactions towards macroscopic properties at adhesive and redox-active solid/liquid interfaces. Combining Atomic Force Microscopy (AFM) based single molecule force spectroscopy and macroscopic Surface Forces Apparatus (SFA) experiments CSI.interface

(1) derives rules for describing complex chemically diverse adhesive solid/liquid interfaces, and
(2) we build a novel apparatus in order to measure single-molecule steady-state dynamics of both redox cycles as well as binding unbinding cycles of specific interactions, and how these react to environmental triggers.

With this, CSI.interface goes well beyond present applications of AFM and SFA and has the long-term potential to revolutionize our understanding of interfacial interaction under steady state, responsive and dynamic conditions. This work will pave the road for knowledge-based designing of next-generation technologies in gluing, coating, bio-adhesion, materials design and much beyond. Specifically, applications of this fundamental research can range from propelling the development of novel medical adhesives, to understanding delamination and corrosion protection by coatings in automotive and aviation industry, or materials design for electrochemical reactivity and transformation of materials. A spin of company for commercializing the proposed unique apparatus and other transformative new technology is anticipated, aiming at boosting competitiveness and innovation leadership of Europe.

Work performed

The work performed from the beginning of the project to the current status is organized around the two major objectives, which are (1) to provide a general scheme for predicting macroscopic properties such as adhesion and redox/reactivity at crowded solid/liquid interfaces, including understanding the scaling of nonlinearities from the single molecular to the macroscopic scale. The aim is to ultimately derive macroscopic properties directly from single molecule measurements together with a comprehensive scaling approach, i.e. and understanding of time and dimensionality of a system emerging from molecular units (Objective 1), and to (2) setup a novel scientific equipment â€“ the Molecular Forces Apparatus (MFA) â€“ that will transform how we can measure and manipulate molecules at dynamic/ reactive solid/liquid interfaces, and in particular under steady state conditions. This will allow to â€œfeelâ€ a steady state condition and how it reacts to environmental triggers. (Objective 2).
Work towards objective 1: Due to low stability of the conventional model systems, first a new supported lipid bilayer model system, using polymer-cushioned molecular thiol anchors, on ultra-smooth gold, was established and tested for SFA measurements under highly adhesive conditions. In comparison to conventional lipid bilayers supported on muscovite mica, the stability of the newly established model surfaces under high loads (up to 200 mN/m tested) is exceptional, and now provides the basis for all scaling studies in this work.
Model surfaces (muscovite mica, lipid bilayers) and model electrolytes were characterized using high resolution AFM imaging. Here, we managed to achieve molecular level resolution at solid liquid interfaces, and we are now able to correlate measured force versus distance characteristics and resulting adhesion forces to the molecular hydration behavior of the interfaces.
First unexpected time and size effects were already discovered. We find that hydration has a strong influence on the time scale of bond formation at extended interfaces. By now we can unambiguously show that dehydration precedes adhesive bond formation at the macroscopic scale. This is a major step forward and will help to understand adhesive interactions in aqueous electrolytes at an unprecedented level.
Work towards objective 2: In the current reporting period we uniquely established reflection mode multiple beam interferometry (rMBI) and provide a commercial tool (SFAexplorer) to analyze the resulting data with sub-nm accuracy. The unique proposed detection principle is now implemented in a novel and newly designed apparatus that can provide real time absolute distance feedback for single molecule experiments in 3D. The apparatus is by now constructed, its stability is tested and programming is of the machine is in its final stage. Proof-of-principle measurements were performed and active research with the novel tool will start with the expected commissioning within in the next 6-8 months.

Final results

During the first 30 months the project achieved two major results beyond state of the art, and we were able to develop and commercialize a new software code for analysis of multiple beam interferometry in reflection mode.
(1) Proof-of-principle for novel force probe technique achieved: The novel apparatus was designed, constructed and its performance was benchmarked. It is by now clear, that the proposed principle indeed provides the possibility to enable superior drift stability and real-time compensation with sub-nm precision in 3D.
(2) We were able to develop new and ultra-stable model systems for deriving scaling at complex chemically diverse adhesive solid/liquid interfaces. This is a first major scientific achievement towards achieving the overall aim of this this project, i.e. to unravel the scaling of single molecule interactions towards macroscopic properties at adhesive and redox-active solid/liquid interfaces.
(3) A new software tool, the SFAexplorer, was developed, tested and commercialized during the first 30 months of this project. This new tool allows the analysis of reflection mode multiple beam interference and provides a simple user interface, making this a tool that will be useful for many other purposes and in many other fields. This software is now commercially available via the HI and it will be one foundation for starting a spin-off company.

As anticipated, the expected results can be summarized as transformative outcome towards three major directions: First, until the end of this project we will be able to progress to measuring single molecular interactions at constant distance at solid/liquid interfaces. The unique scientific tool that we are constructing for this unique experiment is by now past the proof of principle, and we are close to starting active research. This work will be absolutely new and beyond state of the art, as there is currently no other equipment that can perform a similar experiment.
Second, since stable model systems for probing scaling relations are now established by unique techniques developed by this team, we are absolutely confident that the other major aim of this action will be achieved within the timeline of this project. In this direction we expect to be able to (a) fully correlate how hydration of interfaces influences molecular interactions and reactions, (b) how patterning and time dependencies are related to hydration effects and interaction forces on the macroscale, and (c) how reactive (electrochemical) interactions, and hydration effects can trigger changes in the interaction of molecules in real time. Third, the developed equipment and software will be the basis for founding a highly competitive and cutting-edge spin-off company with a unique portfolio at the end, or even during this project.