Circulating tumor cells (CTCs) are shed from cancerous tumors even in the initial phase of malignant progression, enter the circulatory system, and migrate to distant organs to form metastases which lead to the death of most patients with cancer. Identification and characterization of CTCs provides a great opportunity to study, monitor, and potentially interfere with the metastatic process. The efficient entrapment of CTCs from whole blood means dealing with rare events and is still a challenging research field even nowadays. Using microfluidic devices, the efficiency of cell entrapment can be increased significantly. For this purpose we have developed a microfluidic device capable of isolation of microparticles and/or cells based on size exclusion technique. In the present work, we show our results on filtration of fluorescent microbeads as model particles in PBS and in human EDTA-blood as well, to determine the capturing efficiency of our microfluidic device with a novel geometric structure.