One sensor for different liquids

It is small but mighty. We are talking about a sensor that was developed at the Vienna University of Technology by Dr. Georg Pfusterschmied. Its use is not limited to medical technology but also includes applications in the automotive industry and winemaking.

Dr. Pfusterschmied, how does the sensor measure viscosity?

Georg Pfusterschmied: We develop sensors based on so-called micro-electro-mechanical systems, or MEMS. We use microelectronic technology to produce chips and combine electrical and mechanical components in this setting. The principle of our sensor system is a small microscopic plate that can be electrically actuated to vibrate. The vibrating plate then interacts with the surrounding liquid. The liquid subsequently dampens the plate’s vibration behavior. This change can be used to calculate viscosity and density.

What makes it different from already available sensors?

Pfusterschmied: The required sample volume is probably the biggest difference. Normally, you measure viscosity by using rotational viscometers. These are devices used in laboratories and thus facilitate measurements on a more macroscopic scale. In contrast, we use a microsensor that is as thick as aluminum foil and measures about 1 mm x 2 mm. What’s more, we only need one sample drop to fully characterize the liquid in just a few seconds. Those are the biggest advantages. Another benefit is the fact that the sensor can be integrated. You can’t do that with conventional lab equipment. Our sensor could also be installed in cars to monitor the condition of the engine oil. This makes the sensor far more flexible in use than traditional measurement devices.

What are some potential applications of your sensor in medical technology?

Pfusterschmied: The fact that we only need a small sample size makes the sensor very interesting for medical technology applications. Having said that, many body fluids are so-called non-Newtonian fluids. That means the viscosity changes with the shear rate at which the plate moves through the liquid. Take honey for example. It is quite easy to move a spoon through the medium as long as you do it slowly. But if you try to remove the spoon quickly, you scoop up the jar with it because the resistance is high. Body fluids present a challenge that way. The red blood cells are the reason blood behaves as a non-Newtonian fluid. The red blood cells have many functions, one of them is the transport of oxygen. You can measure this via a hematocrit test. We are confident that our sensor can measure this value. This makes it interesting for a potential use in doping for example. Many sports have a 50 percent cut-off value for hematocrit. The test is carried out by taking a vial of blood and adding anticoagulants to it. Lab technicians then use a centrifuge to separate the red blood cells and determine their mass. If our sensor were used in this case, it would resemble the way you check blood sugar levels - a drop of blood is sufficient for a quick test. If the test is suspicious, you could collect a B sample and check it in the lab.

Another fact that makes the sensor exciting for medical technology: the sensors can be produced at low cost, making them ideal for single use. The sensor can simply be disposed of as residual waste, since it is mostly made of silicon and aluminum nitrite.

When do you expect the sensor to be ready for the marketplace?

Pfusterschmied: We are still in the early stages of development. We will develop a broad concept to incorporate many aspects. In addition to engine oil and blood, we are presently also studying sensor use in wine fermentation. We welcome collaboration and partnership opportunities to explore potential applications in medical technology and to ultimately put them into practice.