Bacteriophage (phage) are viruses that infect bacteria. It is important to understand how phage move throughout mucosal layers, one of the main entry points for pathogens. To track these small cells (200 nm), we have created a combined optical trapping and fluorescence microscopy system. Optical trapping allows for non-invasive manipulation of objects as well as detection of forces as small as 1 piconewton. Fluorescence microscopy allows us to track individual particles as they move in different environments. Tracking these particles provide valuable information about diffusion characteristics and how they change with particle size or mucus concentration. We will present the results of calibrating this system, as well as the dependence on particle size and height from bottom of slide in various mucus concentrations.