Abstract: The present disclosure generally relates to various articles, systems, and methods for trapping cells, e.g., within a microfluidic device. Some aspects describe microfluidic channels that prevent certain entities such as microbial cells from flowing through the channels, while allowing certain cells (e.g., blood cells) to pass. In one set of embodiments, for example, a sample (e.g., a blood sample) having a plurality of mammalian cells and a plurality of microbial cells is flowed through the microfluidic devices described herein, resulting in retention of the microbial cells.