Interview: An entire laboratory on a chip?

Interview with Dr. Rico Huhnstock, head of the "Functional Thin Films" subgroup at the Institute of Physics under Prof. Dr. Arno Ehresmann, "Functional Thin Films and Physics with Synchrotron Radiation".

• Dr. Huhnstock, what do you mean by "functional thin films"?

Dr. Rico Huhnstock: We are primarily concerned with magnetic thin films applied to flat chips. A concrete application example from the past would be a computer memory chip. Early PCs usually had hard disks on which magnetic thin films were applied. The information, which typically consisted of logical 0s and 1s, was written there by specifying a magnetization state. As with our everyday magnets, magnetization refers to the north and south pole orientation. On the thin layer in the hard disk, these poles were defined in such a way that a 1 is produced in one direction and a 0 in another. In this way, the 0s and 1s could be written into the layer. However, these earlier hard disks had the disadvantage that the fast writing and reading of the logical states was carried out using a mechanical process. As a result, access speeds were limited and wear could occur quickly. For this reason, magnetic hard disks were replaced by SSD technology at the turn of the millennium, which does not have this problem. However, they are still relevant in this area, e.g. in large storage centers, as the storage capacity is generally somewhat higher than that of SSD hard drives and they are cheaper on average.

• What are you currently researching in your group?

Dr. Rico Huhnstock: We are mainly conducting basic research. In a DFG-funded project, we are producing magnetic thin films and placing spherical magnetic particles in the nanometer and micrometer size range on them. These spheres essentially consist of iron nanoparticles, which are enclosed in a polymer layer in the particle. We use special magnetization states in the underlying layer to set the particles in motion. It is precisely this movement or the transport of the particles initiated by us that interests us. A wide variety of measurement techniques are used for the investigations, including AI-supported methods. The aim is to be able to control these particles in a targeted manner.

• How do you do that?

Dr. Rico Huhnstock: You may remember this from your school lessons: if you put metal shavings around a horseshoe magnet, you can make the field lines of the magnet visible. Similarly, the small particles we use are attracted to the magnetic layers we create, as these generate defined microscale magnetic fields. Using a special technique, we can determine the distribution of the magnetic fields and thus define where particles accumulate above the layer. In our experiments, we also install additional magnetic fields on a macroscopic scale using larger coils. In combination with the microscopic fields originating from the layer, we are then able to move the particles above the layer back and forth in a controlled manner.

• What is the aim of your investigations?

Dr. Rico Huhnstock: We want to use these particle movements to create what are known as "pocket laboratories" or "lab-on-a-chip" systems. Here I can use the example of hard disks again. There is a drive to miniaturize things further and further so that less space and less material is required. This would also be an advantage in medical diagnostics. At some point in the future, if you go to your GP and you don't feel well, you won't have to send a blood sample from your GP to a laboratory where laboratory staff use expensive machines and instruments to carry out complex and cost-intensive tests that then take several days. All this could be made more efficient and cost-effective if there were rapid tests that work just as reliably as laboratory tests. Perhaps these rapid tests would initially be more likely to be used by GPs, but the aim is eventually for them to be available in pharmacies or drugstores and for the diagnosis to even take place at home, as with the Covid19 rapid tests during the coronavirus pandemic. For this to happen, however, the next step is for engineers to package this technology with magnetic chips in a miniaturized design so that ultimately only a small, handy device is needed.

• What method do you want to use to realize the "lab-on-a-chip" systems you mentioned?

Dr. Rico Huhnstock: Our approach is based on using the particles on the magnetic layer to "capture" viruses or other bio-substances that are characteristic of a disease, such as certain proteins, and thus detect them. The advantage of magnetic particles for us is that we can move them via magnetic fields and measure their jumps. If viruses or other bio-substances settle on the particles, for example, they become heavier and slower, which we want to measure in future studies. In addition, the magnetic fields used are harmless to biological materials. Finally, particles have a surface that we can cover with so-called scavenger molecules. Capturing molecules are able to capture only the one substance we are interested in. In biology, this is known as the lock and key principle. In other words, there is a key that only fits into one lock, such as a virus or a protein, and the lock is the capture molecule.

The magnetic particles (blue spheres) have a capture group (yellow "cap") that allows the particles to bind the substance of interest (e.g. a virus). The particles are moved across the chip due to the magnetic stripes in the chip substrate (tiny magnets with different north/south pole orientations). In the first step, the particles are guided through a channel through which the liquid to be examined (body sample) flows. All kinds of substances float in this fluid, symbolized by pyramids, cubes and spheres. However, the particles should only capture the red spheres with the yellow capture groups (specific binding). However, some of the other substances from the sample liquid also bind non-specifically at first. These are washed off in the next channel by a flowing liquid in which nothing else is present. In the third and final channel, so-called fluorescent proteins are bound to the particles, which are intended to make the particle glow at the end. Finally, the particles are physically concentrated by channel walls, similar to a funnel, in order to obtain the largest possible luminous signal.

• Has this technique been used for the Covid19 tests that you are investigating?

Dr. Rico Huhnstock: No, these Covid19 rapid tests are not magnetic. Particles, which are usually made of gold or silver, are actually applied to a chip. These are then able to capture viruses, in this case the Covid19 viruses, which are applied to the chip through the liquid. The movement of the viruses or particles then takes place via the spread of the liquid in a paper-like membrane. The particles can only bind to the test strip if the virus is attached to it, which then causes the strip to change color. Typically, however, quite high virus concentrations are required for this to happen. This is where we want to start and significantly lower the detection threshold for such rapid tests by using magnetic particles as "virus scavengers". It also gives us the opportunity to quantify the quantity of viruses present using an appropriate detection method. This is generally not possible with current rapid tests.

• The BiTWerk research cluster, of which your boss, Prof. Dr. Arno Ehresmann, is a member, aims to consider different materials such as plastic, metal or concrete and their properties as an inseparable unit, starting with the production processes through to use and recycling, in order to establish a fully biologized process chain. By increasing efficiency and thus saving natural resources, this has a direct impact on the ecological footprint of both industry and individuals. The scientists and engineers involved want to learn from nature or copy how these processes take place there and make them usable for humans. One focus here is the integration of functions into materials. This allows materials to be used more efficiently and some of them can be saved. How do you see your research in this context?

Dr. Rico Huhnstock: One principle that characterizes our immune system is the body's immune response when, for example, malignant viruses enter the body. Antibodies are immediately released that are able to capture these foreign organisms. They do this very specifically via corresponding bindings. We want to use this binding principle, i.e. key and lock as described above, to realize our project with the "Lab-on-the-Chip". Of course, the aim here is also to work more efficiently and save on materials through the desired miniaturization and integration of "lab functions" on a single tiny chip.

• You work together with the departments of Prof. Dr. Bernhard Sick, "Intelligent Embedded Systems", and Prof. Dr. Peter Lehmann, "Measurement Technology", which are also part of BiTWerk. What is the intersection of your research?

Dr. Rico Huhnstock: We apply the AI methods developed in the "Intelligent Embedded Systems" department. For example, this enables us to better evaluate the videos we record of the particle movement. The collaboration with metrology also involves using evaluation methods, in this case measurement techniques developed there, to investigate the vertical position of the particles. We can already evaluate very well under the microscope how the particles move in the plane, but we are also interested in how they behave vertically over several planes. For example, how does the interaction between the surface of the particle and the chip take place when viruses have bound to the particles and how does this influence the vertical distance? This would be another tool to demonstrate the binding of biosubstances to particles.

• What interests you in your research?

Dr. Rico Huhnstock: There are always new ideas and approaches, if only for particle transport, that I would like to pursue. In addition, the intersections with other specialist areas in this field are very pronounced. It's fun to find these and to strive for interdisciplinary collaboration. So for me, it's not about hardcore physics that remains vague in its applicability, but pursuing a concrete goal through this interdisciplinarity is what appeals to me. It starts with the fact that the particles move in liquids, so we have to take chemical parameters into account. When viruses come into play, the biology behind them is of course also very important. I like being part of this joint research and would like to develop it further. For example, we are currently establishing a collaboration with the Department of Pathology at Freiburg University Hospital, which aims to apply our research. It's very exciting and nice to see when you can achieve such synergy effects.

• Did you study physics?

Dr. Rico Huhnstock: No, nanostructure sciences in Kassel. Even this degree course focuses on interdisciplinarity, as you are taught knowledge from all the natural sciences and can still find your own focus during your studies. As a result, you also learn the specialist vocabulary of all subjects, which is very useful in later research. In fact, before I started my studies, I had no idea which direction I wanted to take. Over time, however, it became clear to me that I wanted to study experimental physics.

• Why did you study in Kassel?

Dr. Rico Huhnstock: Because, as far as I know, it was the only university at the time that offered such an interdisciplinary course. I originally come from near Hamburg, but this course brought me to Kassel.

• What are your next research projects?

Dr. Rico Huhnstock: I am currently in the process of applying to the DFG for a research project for a device that we want to build ourselves, i.e. not just buy, but actually develop ourselves. It is also based on the investigation of particles and should be able to determine the vertical position of as many particles as possible using AI methods. As described above, the focus here is on the vertical distance between the particles and the surface of the chip. With this apparatus, we will hopefully also be able to intensively investigate the interaction between the surface of the particle and the chip. However, this device will also be used not only by us, but also by other research groups. We may therefore be contributing to research progress in several specialist areas and thus to interdisciplinarity.

• Dr. Huhnstock, thank you for this interview.

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