Portrait of Ivan Michel Antolovic
Lives in Lausanne
Scientist, PhD, EPFL
Ivan Michel Antolovic
Michel is from Croatia and enjoyed to live along the beautiful coast of this country. He later moved to Zagreb where he studied Electrical Engineering for the Bachelor and Master degree. Attracted by Switzerland because of well renowned EPFL, he met with Prof. Charbon, who offered him a PhD position in Delft. He worked on super resolution microscopy, trying to understand how to crack the diffraction-limited resolution of 200 nanometers while still using light. In 2014, a Nobel prize was given to 3 scientists also working on super-resolution light microscopy. This advance allowed nanoscale structures – including individual molecules – to be visualized within cells with a higher contrast (labelled with fluorescence molecules) and resolution.
What is the challenge when you have to measure nanometer particles?
Imagine a very small single spot, a molecule for example – with a size under 200 nanometers – looking through a microscope. It would always look like a 200 nanometers spot due to diffraction. Imagine now that you have multiple spots very close to each other: the light emissions overlap and they cannot be distinguished from each other. This is linked to the diffraction: when we observe light as a wave, it’s diffraction properties are linked to a specific wavelength. The simplest example is light transmitted through a small opening. Simplified, the light will exit the opening with a given angular distribution. So the light spot produced could be bigger than the opening. A similar phenomenon happens in microscopes, if two small objects are positioned next to each other, the diffracted light will appear as if the objects (the small spots) are overlapping and it will become difficult to see that there are two objects instead of one.
One way to overcome this is to make these spots blink, so at one point in time, there is only one spot visible. Since the spots have a known light intensity distribution, we estimate where their center is. With this method, we can measure down to 10 nanometers.
How do you use this technology practically ?
Applications are molecular investigations. The key criticism for these techniques is that it is very difficult to use them with live samples which means that you have to usually kill the cells before analyzing them. Because of this important difficulty, recent developments are focusing to enable more sustainable super-resolution imaging techniques for live cells.
The second part of my activities is dedicated to chips and light sensors (SPAD sensors in particular) for all kind of applications. The light signals I try to detect are very weak. Because there is noise in every electrical environment, the signal needs to be amplified. In our sensor, we use avalanche amplification. One or more detected photons (light particles) generate one of more electron-hole pairs, which are then strongly accelerated by a high electric field, subsequently colliding with other atoms of the sensor and ionizing them (impact ionization). This releases additional electrons which accelerate and collide with further atoms, releasing more electrons—a chain reaction. This process is very similar to the classical snow avalanche, hence the name.
What are your other projects ?
We use this sensors in many other field in addition to super-resolution microscopy. A typical and very popular application for the sensors is LiDAR:
There are a lot of companies active in the 3D imaging area, at the moment with the LiDAR technology : Lidar (also called LIDAR, LiDAR, and LADAR) is a surveying method that measures distance to a target by illuminating the target with pulsed laser light and measuring the reflected pulses with a sensor. Differences in laser return times and wavelengths can then be used to make digital 3-D representations of the target. The name lidar, now used as an acronym of light detection and ranging (sometimes light imaging, detection, and ranging), was originally a portmanteau of light and radar. Lidar sometimes is called 3D laser scanning, a special combination of a 3D scanning and laser scanning. It has terrestrial, airborne, and mobile applications.
Lidar is commonly used to make high-resolution maps, with applications in geodesy, geomatics, archaeology, geography, geology, geomorphology, seismology, forestry, atmospheric physics, laser guidance, airborne laser swath mapping (ALSM), and laser altimetry. The technology is also used in control and navigation for some autonomous cars.
You need a 3D environment to have an autonomous car. This is a major, growing market but there are other applications too. For example, this sensors are alos used in positron emission tomography (PET), fluorescence-lifetime imaging microscopy (FLIM), and near infrared optical tomography (NIROT), just to name a few.