Sven Krabbenborg

Surface gradients under electrochemical control

Promotion date: January 24.

Promotor: Jurriaan Huskens

The work described in this thesis aims at the development and application of electrochemical methods for the fabrication of covalent and non-covalent surface gradients on the micron scale.

Gradients are systems in which the physicochemical properties of a solution and/or surface change gradually in space and/or time. They are used for a myriad of technological and biological applications, for example high-throughput screening, or the investigation of biological systems, in which gradients in solution (chemotaxis) and on surfaces (haptotaxis) play an important role.

An electrochemical system to generate solution and surface gradients on the micron scale has been developed. Also have non-covalent surface gradients been fabricated on the micron scale, in a supramolecular system and in lipid bilayers.

We envision that gradient fabrication methods in the future will be developed in the direction of dynamic gradients, the properties of which can be controlled at will in space and time. When combining dynamic gradients both in solution and on a surface, such a system could be used for the investigation of unique, dynamic systems. It can provide, for example, the possibility of electrochemical control over droplet and molecular motion which will play an important role in the field of nanochemistry, or over out-of-equilibrium systems, which opens the possibility of inferring interesting properties to technological systems and devices such as adaptability, self-healing and defect-tolerant structures. Dynamic gradients can also be used for studies of dynamic cell behavior.

Was your research fundamental in nature or more application driven?

The research was a mixture of both. Several projects were fundamental, to see if we could get control on the nanoscale, and fabricate the gradients on the micron-scale. After this initial period we went on and tried to apply the obtained results in a more application oriented way, for example for the high-throughput screening of surface reactions.

The gradient theme is present in all the different projects upon which this PhD thesis is built. Fabricating dynamic gradients on the micrometer scale and proving the switch mechanisms - by making these gradients active or inactive at will - is an important first step towards new investigation methods on dynamic cell level. Continuing in this direction, static and dynamic gradients were fabricated in artificial cell membranes (lipid membranes).

Were there some memorable moments during your PhD period?

The generation of pH gradients proved to be more difficult as expected. Together with a colleague, who used a completely different chemistry, we started to see consistency and understanding. At last the various ends began to fall into place. We were able to finish this pH gradient project incorporating this specific knowledge. This finally led to the publication about the fabrication of micron-scale surface chemical gradients for the high-throughput investigation of the reactivity of chemical surface reactions. This was highlighted on the Mesa+ webpage:

Were your results published?

Seven publications appeared, or are about to appear, in various magazines including high-impact journals like Advanced Functional Materials, Nature Communications, the Journal of the American Chemical Society (JACS) and Angewandte Chemie. I was a speaker on a Dutch micro and nano technology conference in Switzerland as well as in and Singapore, regarding supramolecular self assembly and molecular materials respectively.

In what way did you develop as a researcher and scientist?

I worked on many different multidisciplinary projects and problems. I had many synergistic collaborations with talented people, especially from the Molecular Nanofabrication Group. Coming into contact with all of these different aspects and backgrounds in physics, chemistry and biology, I became an independent and all round researcher with a vast amount of knowledge on various fields. I learned that collaboration is at the heart of scientific research. Working with organic chemists, for example, brought me a great deal further building new molecules. This expertise I could not have done without.

In my bachelor period, in advanced technology, I still had not chosen an expertise field of research. Also my master period was rather general and broadly orientated, on nanotechnology. Though the PhD was multidisciplinary in nature still, I am very glad to have gained in-depth knowledge on surface chemistry. In nanotechnology as well as in lots of modern devices, chemistry is an inescapable part of research and production technology.

Collaborating with master students - guiding them at first and watching them to gain their own vision and making great contributions – I perceived as very rewarding. The collaboration was very fruitful, leading to new publications.

What are your future plans?

I would like to stay close to research and development, more focused on practical application. Both, a large multinational or a small spin-off company, could be interesting, as long as I can proceed performing multidisciplinary research.

After completing the PhD thesis work I feel I really can contribute to the company’s needs, confidently expressing the expertise in fields in which I am good at. I value this greatly, as I feel the choice now between academics versus industry, is one of the more important moments one encounters in his lifetime. It is a good thing to feel able to make this choice in a self-conscious way.

What is important for Mesa+ to stay successful in future, you believe?

I guess, it is important for Mesa+ to find a way to preserve the practical knowledge obtained in a more efficient and effective way. PhD’s and post-docs are the most experimentally productive members of research groups, but they are only staying for limited periods of time. A lot of knowledge on apparatus and machines leaves MESA+ with them.

A good example is the initiative of the cleanroom, collecting ‘working recipes’ in a database, while each machine has an experienced operator.

If more practical knowledge would be freely available and categorized, the capacity of the machines would be better used, and the collaboration between researchers and groups would benefit from this a lot.