Abstract
Nanopore membranes exhibit tremendous potential for applications such as molecular filtration and DNA sequencng studies. However, the large-scale manufacturing of these nanopore membranes using MEMS technology is challenging, requiring slow serial electron or ion-beam patterning. Marine diatoms on the other hand feature biomineralized silica shells with the smallest pore diameters being 40 nm. Their hierarchical pore architecture makes these nanomembranes exceptionally mechanically stable. Moreover, the nanopores are homogeneous in size and have a low aspect ratio, enabling fast diffusion-driven transport. The drawback of the biomineralized structures is that they are single entities, which have to be combined with a support structure to integrate them into a microsystem. Our solution consists of immobilizing the biomineralized structures on silicon substrates. With the diatom shells growing up to 200 μm in diameter, they are easy to manipulate on the oxidized silicon surface. Through-wafer via holes with diameters between 5 μm and 30 μm were etched using a dry etching technique to allow free access to the bottom of the immobilized diatom shell. Two pathways towards immobilization of the diatom shells were used, one being a chemical linkage approach using poly-L-lysine and the other involving UV-polymerizable epoxy. Controlled etching of the silica structure has been employed to manipulate both the dimensions of the nanopores as well as the pore hierarchy. Studies of transport phenomena were carried out after mounting the silicon chip in a fluidic chamber with reservoirs for aqueous solution on either side of the chip. Electrical contact was made via Ag/AgCl electrodes and the transmembrane current was measured by a transimpedance amplifier. Results on our transport studies based on size and chemical considerations will be presented for ions, such as potassium and sodium, present in physiologically relevant isotonic buffers, polystyrene nanobeads and gold nanoparticles.
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