Floating assembly of diatom Coscinodiscus sp. microshells

Diatoms have silica frustules with transparent and delicate micro/nano scale structures, two dimensional pore arrays, and large surface areas. Although, the diatom cells of Coscinodiscus sp. live underwater, we found that their valves can float on water and assemble together. Experiments show that the convex shape and the 40 nm sieve pores of the valves allow them to float on water, and that the buoyancy and the micro-range attractive forces cause the valves to assemble together at the highest point of water. As measured by AFM calibrated glass needles fixed in manipulator, the buoyancy force on a single floating valve may reach up to 10 μN in water. Turning the valves over, enlarging the sieve pores, reducing the surface tension of water, or vacuum pumping may cause the floating valves to sink. After the water has evaporated, the floating valves remained in their assembled state and formed a monolayer film. The bonded diatom monolayer may be valuable in studies on diatom based optical devices, biosensors, solar cells, and batteries, to better use the optical and adsorption properties of frustules. The floating assembly phenomenon can also be used as a self-assembly method for fabricating monolayer of circular plates.

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► Coscinodiscus valves can float on water because of their convex shape and 40 nm sieve pores.
► Buoyancy and the micro-range attractive force cause the valves to assemble together.
► Turning the valves over, enlarging the sieve pores, reducing the liquid surface tension, or vacuum pumping cause valves to sink.
► AFM calibrated glass needles are used to test the buoyancy of floating micro scale shells.
► Compact monolayer film of valves fixed on glass/PDMS can be obtained by floating self-assembly.