Selective self-assembly of biogenic silica assisted by Layer-by-Layer deposition and Inkjet printingWei Wang, Doo-Hyoung Lee, Clayton Jeffryes, Debra Gale, Gregory L. Rorrer, Timothy Gutu, Jun Jiao, and Chih-hung ChangOregon State University, Department of Chemical Engineering, Corvallis, OR 97330Portland State University, Department of Physics, Portland, OR 97201

AbstractNature is an inspirational source of silica structures that possess unique optical properties. A few classes of organisms fabricate metal oxides with nanoscale features by a bottom-up self assembly process. In particular, diatoms are a prolific class of single-celled algae that possess silica shells or “frustules” with intricate submicron scale features, including two-dimensional pore arrays. During frustule development, membrane-bound transporters actively take actively up the soluble silicon in the form of Si(OH) 4. Once inside the cell, Si(OH)4 is converted to nanostructured silica by protein-mediated condensation reaction within the silicon deposition vesicle, an organelle which serves as the mold for frustule development. Recently, it has been shown that intact diatom frustules can act as 2D photonic crystals and optical sensor platforms for the detection of organic vapors. Techniques to assemble and pattern these microorganisms at large scale is needed to take advantage of these nanostructured silica for device applications such as sensors, photonic crystals and electroluminescence devices, Herein, biogenic silica fabricated from marine diatom whose cell walls possess intricate nano- and microstructures was selectively adsorbed on polyelectrolyte layers which was patterned by inkjet printing. In addition, we will also describe a new technique to fabricate patterned nanostructured silicate-based luminescent materials by inkjet printing.

Using Layer-by-Layer deposition, positively charged Poly(sodium 4-stryrene sulfonate) (PSS) and negatively charged Poly(allylamine hydrochloride) (PAH) were alternatively deposited on glass followed by inkjet-printing a PAH layer which attracted frustules on them, resulting in a frustule-matrix.

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Doped with Rhodamine-123, printed PAH layers can be visualized in fluorescence images. Based on intensity of green, one can observe that the PAH films are uniform across the printed area. The size of PAH dots is about 250µm which is similar to the dimension of cosco sp. diatom frustules.

2-Dimensional diatom shell matrix

Biogenic silica based phosphor materials patterned by inkjet printing

Future work

After deposition diatom silica shells (cosco sp. ~200µm in diameter) were arranged in a 2-dimentsion matrix with preservation of submicron structure. Only one diatom shell seats on a PAH dot controlled by the area of printed PAH dots.

Using smaller diatom shells (cyclotella sp. ~10µm ) uniform frustules monolayers were formed on printed PAH dots. Due to strong Brownian motion, Cyclotella frustules are easier to pattern compared to larger species.

This research was supported by the National Science Foundation (NSF) under Nanoscale Interdisciplinary Research Team (NIRT) award number BES-0400648.

TEM images and EDX analysis on frustules show the crystalline of Y2SiO5:Eu3+ which was formed by printing yttrium precursor solution on deposited frustule layers.

Zn2SiO4:Mn2+ and Y2SiO5:Eu3+ had

photoluminescence emission spectra in green and orange. The words ‘green’ and ‘OSU’ in the image are made from frustules and precursor inks via inkjet printing.

Idea sketch of gas sensor matrix with diatom shells which are selectively converted to sensing materials by inkjet- printing various precursor inks on each diatom shell. The large surface/volume ratio of frustules enables them to be a good candidate for the device of sensors.

Diatom sensorsConductive lines

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Positively charged polyelectrolyte layer

OH groups on the diatom shells surface endow frustules with negative charges which are attracted by positive charges on PAH layer and expelled by negative charges on PSS via electrostatic force. That results in the selective adsorption of biogenic silica.

The adsorption of biogenic silica is controllable in aspect of patterning. One can adjust the assembly via varying the pH and ionic strength of suspension of frustules and also the area of printed PAH dots. The attractive point in this research is the potential application of 2-dimensional diatom shell matrix into gas sensor and 2-dimensional photonic crystals.

Sketch of Gas sensor matrix