Abstract
In this work, we apply Digital Holographic Microscopy (DHM) to track the three-dimensional(3D) motion of bacteria. Measuring bacterial movement and bacterial interaction with solid walls is critical to understand the mechanism of biofilm formation and develop efficient antibiofouling strategies. However, accurately tracking bacteria by DHM remains a challenge since bacteria have a small size and a refractive index very similar to the surrounding medium. Here, we develop new approaches to overcome this challenge. First, we distinguish between real and virtual images in DHM by analyzing the axial intensity distributions of the objects. This allows the hologram plane to be placed within the sample volume and thus maximizes the signal to noise ratio. Second, we detect particle centers based on the local maximum or minimum intensities in the reconstructed field consisting of both the scattered wave and incident wave. We find this approach improves the particle localization accuracy when compared to previous methods. We also examine the impacts of sample concentration, sample thickness, and the iterative phase retrieval method on the quality of reconstructed images. With these improvements, we measure approximately 300 trajectories of Shewanella sp., a type of bacterium isolated from marine biofilm. We find bacterium-wall interactions similar to these reported in the literature. Last, we fabricate micro-textured surfaces which are able to trap gas bubbles when submerged in water. Future study will examine the impact of the entrapped gas bubbles on bacterial motion, as well as the anti-biofouling properties of the textured surfaces.