A Submersible Digital Holographic Microscope for In Situ Microbial Imaging

Abstract:

A microscope for life detection is a top candidate for inclusion in biological instrument packages for potential ocean world missions. Holographic microscopy offers several advantages over traditional light microscopy including image reconstructions over a 3D volume and phase information retrieval. This approach enables non-destructive detection of microbes based on morphology, motility, and physical properties such as density and index of refraction. Here we present a submersible Digital Holographic Microscope (DHM) developed for in situ operation and microbe detection in terrestrial oceans, including under-ice polar and deep-sea environments. This microscope uses an optical design being developed for potential planetary missions and offers a means for testing instrumentation as well as for conducting biological studies in analog terrestrial settings.

The submersible DHM achieves micron scale resolution underwater using a twin-beam off-axis holographic imaging setup. An integrated pump cycles water through a flow cell for imaging and onboard control electronics enable completely self-contained and autonomous microscope operations. The system achieves a compact form factor and is enclosed in a housing designed for 1500 m deep ocean deployments. It has been developed for deployment both aboard the underwater robot “Icefin” as well as for independent operations. Here we overview the instrument’s design including optical, mechanical, fluidic, and control systems. We additionally demonstrate preliminary biological imaging results and discuss automated image processing.