Underwater atomic force microscope

Abstract

We developed a novel underwater atomic force microscopy (UAFM) system that is mountable on underwater vehicles or submersible seafloor platforms. This system is intended for in situ observation of microorganisms and microparticulates suspended and dispersed in deepwater near hydrothermally active features, with nanometer-scale spatial resolution. The system is composed of several technological elements: the main unit of the UAFM system, fluidic devices for sample collection from deepwater (e.g., pumps and a filtration unit equipped with membrane filters), and robust mounting mechanisms for the underwater vehicles or submersible seafloor platforms. We also use a commercially available self-sensitive cantilever as the AFM probe to detect cantilever deflection. To insulate the integrated piezoresistive gauges on the cantilever surface from the seawater under high pressure in deep sea, we applied thin coatings of poly(p-xylylene) polymer (Parylene) onto the cantilever surface. We successfully balanced the imaging quality and insulation performance by optimizing the conditions of the layer formation, i.e., the Parylene dimer type, temperature, and final layer thickness. Moreover, we invented a novel UAFM sample stage equipped with a sample filtration system based on membrane filters. To demonstrate the effectiveness of the sample stage with membrane filters in deep sea exploration, microorganisms suspended and dispersed in deepwater were successfully collected and fixed on the membrane filter. The developed UAFM system would be a useful tool for in situ observation of living microorganisms and microparticulates at nanoscale spatial resolution, possibly leading to new findings in deep sea.