What is the fine-grained topic of the following text: Nicolas joined Biocartis in 2012 as a scientist after having obtained his PhD in Bioscience Engineering at the Katholieke Universiteit Leuven, Belgium, in collaboration with the École Polytechnique Fédérale de Lausanne (EPFL), Switzerland. Only return the topic.
Nicolas' academic background and joining Biocartis as a scientist.