The authors would like to acknowledge the Union College Faculty Research Fund, Student Research Grant program, and the summer undergraduate research program for financial support of the project. The authors would also like to acknowledge Joana Santos for the design of the three-piece mold, Chris Avanessian for SEM imaging, Ronald Tocci for etching onto the curved aerogel surface, and Dr. Ioannis Michaloudis for inspiration and initial work on the etching project as well as for providing the Kouros image and cylindrical aerogel.

<ol>
	<li>Aegerter, M. A., Leventis, N., Koebel, M. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Aerogels Handbook. , (2011).</li><li>Pierre, A. C., Pajonk, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemistry+of+aerogels+and+their+applications.">Chemistry of aerogels and their applications.</a> Chemical Reviews. 102 (11), 4243-4266 (2002).</li><li>Zinzi, M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+and+visual+experimental+characterization+of+a+glazing+system+with+monolithic+silica+aerogel.">Optical and visual experimental characterization of a glazing system with monolithic silica aerogel.</a> Solar Energy. 183, 30-39 (2019).</li><li>Bhuiya, M. M. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparation+of+monolithic+silica+aerogel+for+fenestration+applications:+scaling+up,+reducing+cycle+time,+and+improving+performance.">Preparation of monolithic silica aerogel for fenestration applications: scaling up, reducing cycle time, and improving performance.</a> Industrial &amp; Engineering Chemistry Research. 55 (25), 6971-6981 (2016).</li><li>Jelle, B. P., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fenestration+of+today+and+tomorrow:+A+state-of-the-art+review+and+future+research+opportunities.">Fenestration of today and tomorrow: A state-of-the-art review and future research opportunities.</a> Solar Energy Materials and Solar Cells. 96, 1-28 (2012).</li><li>Michalous, I., Carroll, M. K., Kupiec, S., Cook, K., Anderson, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Facile+method+for+surface+etching+of+silica+aerogel+monoliths.">Facile method for surface etching of silica aerogel monoliths.</a> Journal of Sol-Gel Science and Technology. 87 (1), 22-26 (2018).</li><li>Stanec, A. M., Anderson, A. M., Avanessian, C., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+and+characterization+of+etched+silica+aerogels.">Analysis and characterization of etched silica aerogels.</a> Journal of Sol-Gel Science and Technology. 94, 406-415 (2020).</li><li>Sun, J., Longtin, J. P., Norris, P. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ultrafast+laser+micromachining+of+silica+aerogels.">Ultrafast laser micromachining of silica aerogels.</a> Journal of Non-Crystalline Solids. 281 (1-3), 39-47 (2001).</li><li>Bian, Q., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Micromachining+of+polyurea+aerogel+using+femtosecond+laser+pulses.">Micromachining of polyurea aerogel using femtosecond laser pulses.</a> Journal of Non-Crystalline Solids. 357 (1), 186-193 (2011).</li><li>Yalizay, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Versatile+liquid-core+optofluidic+waveguides+fabricated+in+hydrophobic+silica+aerogels+by+femtosecond-laser+ablation.">Versatile liquid-core optofluidic waveguides fabricated in hydrophobic silica aerogels by femtosecond-laser ablation.</a> Optical Materials. 47, 478-483 (2015).</li><li>Vainos, N. A., Karoutsos, V., Mills, B., Eason, R. W., Prassas, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Isotropic+contractive+scaling+of+laser+written+microstructures+in+vitrified+aerogels.">Isotropic contractive scaling of laser written microstructures in vitrified aerogels.</a> Optical Materials Express. 6 (12), 3814-3825 (2016).</li><li>Plata, D. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aerogel-platform+optical+sensors+for+oxygen+gas.">Aerogel-platform optical sensors for oxygen gas.</a> Journal of Non- Crystalline Solids. 350, 326-335 (2004).</li><li>Carroll, M. K., Anderson, A. 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A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preparing+silica+aerogel+monoliths+via+a+rapid+supercritical+extraction+method.">Preparing silica aerogel monoliths via a rapid supercritical extraction method.</a> Journal of Visualized Experiments: JoVE. (84), e51421 (2014).</li><li>Gauthier, B. M., Bakrania, S. D., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+fast+supercritical+extraction+technique+for+aerogel+fabrication.">A fast supercritical extraction technique for aerogel fabrication.</a> Journal of Non-Crystalline Solids. 350, 238-243 (2004).</li><li>Gauthier, B. M., Anderson, A. M., Bakrania, S. D., Mahony, M. K., Bucinell, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+and+device+for+fabricating+aerogels+and+aerogel+monoliths+obtained+thereby.">Method and device for fabricating aerogels and aerogel monoliths obtained thereby.</a> U.S. Patent. , (2011).</li><li>Gauthier, B. M., Anderson, A. M., Bakrania, S. D., Mahony, M. K., Bucinell, R. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Method+and+device+for+fabricating+aerogels+and+aerogel+monoliths+obtained+thereby.">Method and device for fabricating aerogels and aerogel monoliths obtained thereby.</a> U.S. Patent. , (2008).</li><li>Estok, S. K., Hughes, T. A., Carroll, M. K., Anderson, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fabrication+and+characterization+of+TEOS-based+silica+aerogels+prepared+using+rapid+supercritical+extraction.">Fabrication and characterization of TEOS-based silica aerogels prepared using rapid supercritical extraction.</a> Journal of Sol-gel Science and Technology. 70 (3), 371-377 (2014).</li><li>Roth, T. B., Anderson, A. M., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Analysis+of+a+rapid+supercritical+extraction+aerogel+fabrication+process:+Prediction+of+thermodynamic+conditions+during+processing.">Analysis of a rapid supercritical extraction aerogel fabrication process: Prediction of thermodynamic conditions during processing.</a> Journal of Non-Crystalline Solids. 354 (31), 3685-3693 (2008).</li><li>Bouck, R. M., Anderson, A. M., Prasad, C., Hagerman, M. E., Carroll, M. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cobalt-alumina+sol+gels:+Effects+of+heat+treatment+on+structure+and+catalytic+ability.">Cobalt-alumina sol gels: Effects of heat treatment on structure and catalytic ability.</a> Journal of Non-Crystalline Solids. 453, 94-102 (2016).</li><li>Dunn, N. J. H., Carroll, M. K., Anderson, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Characterization+of+alumina+and+nickel-alumina+aerogels+prepared+via+rapid+supercritical+extraction.">Characterization of alumina and nickel-alumina aerogels prepared via rapid supercritical extraction.</a> Polymer Preprints. 52 (1), 250-251 (2011).</li><li>Tobin, Z. 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The authors have nothing to disclose.

This protocol demonstrates how laser etching and the inclusion of dyes can be employed to prepare aesthetically pleasing aerogel materials.
Making large (10 cm x 11 cm x 1.5 cm) aerogel monoliths requires proper mold preparation through sanding, cleaning, and grease application to prevent the aerogel from sticking to the mold and major cracks from forming. The parts of the mold in direct contact with the precursor solution/soon to be formed aerogel are the most critical. Reducing the surface roughness of the mold via machine polishing will improve performance. It is important to apply grease only to the outer perimeter (13 mm) of the top part of the mold so that when the hot press force is applied to the mold, grease does not seep into the cavity of the mold. If grease gets into the cavity, major cracks will form in the aerogel.
When using the laser engraver, the aerogel needs to be properly placed in the top-left corner of the laser engraver and the dimensions of the aerogel need to correspond with those of the drawing program document. The image to be etched must be properly prepared by removing the non-white background, adjusting contrast to get definition and highlight features in the image. Although it is possible to print dense patterns (see Figure 8b), if the pattern is too dense, the ablated material can separate from the bulk of the aerogel. When cutting through an aerogel the laser parameters should be adjusted to avoid discoloration6,7. High frequency, high power, and low speed settings will cause more damage. These settings will also affect the quality of the cut and the amount of damage at the cut surface. The guidelines provided here for laser power level, frequency and speed are for a typical silica aerogel of density 0.09 g/mL. Adjustments to these parameters may be needed for aerogels of different densities.
It is important to select dyes that can survive the RSCE aerogel fabrication process. They need to be thermally stable at 290 &#176;C (550 &#176;F) and they must not react with methanol. However, even if a dye meets these requirements, it may not work. In addition to the dyes described above, we tested Bismarck Brown, Indigo, Brilliant Blue and Congo Red (in an effort to satisfy Victorian Gothic aesthetics in the mosaic designs). These dyes did not survive the RSCE process and resulted in opaque cloudy white aerogels. The concentration level of dye affected the opacity of the aerogel but not the expected color. If aerogels produced from a precursor solution that includes dye show no color (indicating decomposition of the dye), the maximum processing temperature can be lowered to 260&#160;&#176;C, which is still above the supercritical temperature of methanol. Or an alternative aerogel preparation method (CO2 supercritical extraction, ambient pressure drying, or freeze drying) can be used, although solvent exchange steps are likely to wash away a significant fraction of the dye. Another method for making colored aerogels is to incorporate metal salts into the precursor mixture. For example, cobalt, nickel, and copper salts can be used to produce blue21, green22 and red-brown aerogels23, respectively, via the RSCE method; however, the resulting aerogels are opaque.
We are not aware of any other methods for etching or writing onto an aerogel surface. There are other methods for cutting aerogels including the use of mechanical saws24. Diamond saws can cut aerogel, but it is difficult to avoid cracking and excessive saw kerf. In applications to remove space dust from aerogels Ishii et al.25,26 demonstrate the use of ultrasonic microblades to cut aerogel and minimize these issues.
The ability to dye and etch onto silica aerogels can be used to enhance the aesthetics of aerogel monoliths, which in native un-etched form often exhibit imperfections due to haze and light scattering. We are incorporating the resulting aesthetically enhanced aerogels into window prototypes and sculpture; however, it would be possible to use the methods described here in other applications, including printing inventory information and precise target patterns onto aerogel monoliths. The cutting and etching procedures also offer methods for machining silica aerogels into specific shapes.

Silica aerogel is a nanoporous, high surface area, acoustically insulating material with low thermal conductivity that can be used in a range of applications from collecting space dust to building insulation material1,2. When manufactured in monolithic form, silica aerogels are translucent and can be used to make highly insulating windows3,4,5.
Recently, we have demonstrated that it is possible to alter the appearance of a silica aerogel by etching onto or cutting through the surface using a laser engraving system6,7 without causing bulk structural damage to the aerogel. This could be useful for making aesthetic enhancements, printing inventory information and machining aerogel monoliths into various forms. Femtosecond lasers have been shown to work for crude &#34;micro-machining&#34; of aerogels8,9,10,11; however, the current protocol demonstrates the ability to alter the surface of aerogels with a simple laser engraving system. As a result, this protocol is broadly applicable to the artistic and technical communities.
It is also possible to incorporate dyes into the aerogel chemical precursor mixture and thereby make dye-doped aerogels with a range of hues. This method has been used to fabricate chemical sensors12,13, to enhance Cerenkov detection14, and for purely aesthetic reasons. Here, we demonstrate the use of dyes and laser etching to prepare aesthetically pleasing aerogels.
In the section that follows, we describe procedures for making large silica aerogel monoliths, altering the monolith preparation procedure to incorporate dyes, etching text, patterns and images onto the surface of an aerogel monolith, and cutting shapes from large dyed monoliths to be assembled into mosaics.

<table><tbody><tr><td>2000 grit sandpaper</td><td>Various</td><td></td><td></td></tr><tr><td>50W Laser Engraver</td><td>Epilog Laser</td><td></td><td>Any laser cutter is suitable</td></tr><tr><td>Acetone</td><td>Fisher Scientific www.fishersci.com</td><td>A18-20</td><td>Certified ACS Reagent Grade&amp;nbsp;</td></tr><tr><td>Ammonium Hydroxide (aqueous ammonia)</td><td>Fisher Scientific www.fishersci.com</td><td>A669S212</td><td>Certified ACS Plus, about 14.8N, 28.0-20.0 w/w%</td></tr><tr><td>Beakers</td><td>Purchased from Fisher Scientific</td><td></td><td>Any glass beaker is suitable.</td></tr><tr><td>Deionized Water</td><td>On tap in house</td><td></td><td></td></tr><tr><td>Digital balance</td><td>OHaus Explorer Pro</td><td></td><td>Any digital balance is suitable.</td></tr><tr><td>Disposable cleaning wipes</td><td>Fisher Scientific www.fishersci.com</td><td>06-666</td><td>KimWipe</td></tr><tr><td>Drawing Software</td><td>CorelDraw Graphics Suite</td><td></td><td>CorelDraw</td></tr><tr><td>Flexible Graphite Sheet</td><td>Phelps Industrial Products</td><td>7500.062.3</td><td>1/16&quot; thick</td></tr><tr><td>Fluorescein</td><td>Sigma Aldrich www.sigmaaldrich.com</td><td>F2456</td><td>Dye content ~95%</td></tr><tr><td>Foam paint brush&amp;nbsp;</td><td>Various&amp;nbsp;</td><td></td><td>1-2 cm size</td></tr><tr><td>High Vacuum Grease</td><td>Dow Corning</td><td></td><td></td></tr><tr><td>Hydraulic Hot Press</td><td>Tetrahedron www.tetrahedronassociates.com</td><td>MTP-14</td><td>Any hot press with temperature and force control will work. Needs maximum temperature of ~550 F and maximum force of 24 tons.</td></tr><tr><td>Laser Engraver</td><td>Epilogue Laser</td><td>Helix - 24</td><td>50 W</td></tr><tr><td>Methanol (MeOH)</td><td>Fisher Scientific www.fishersci.com</td><td>A412-20</td><td>Certified ACS Reagent Grade, &amp;ge;99.8%</td></tr><tr><td>Mold</td><td>Fabricated in House</td><td></td><td>Fabricate from cold-rolled steel or stainless steel.</td></tr><tr><td>Paraffin Film</td><td>Fisher Scientific www.fishersci.com</td><td>S37441</td><td>Parafilm M Laboratory Film</td></tr><tr><td>Rhodamine-6G&lt;br/&gt; Rhodamine-6g&lt;br/&gt; FlouresceinRhodamine-6g</td><td>Sigma Aldrich www.sigmaaldrich.com</td><td>20,132-4</td><td>Dye content ~95%</td></tr><tr><td>Rhodamine-B&lt;br/&gt; Rhodamine-6g&lt;br/&gt; FlouresceinRhodamine-6g</td><td>Sigma Aldrich www.sigmaaldrich.com</td><td>R-953</td><td>Dye content ~80%</td></tr><tr><td>Soap to clean mold</td><td>Various</td><td></td><td></td></tr><tr><td>Stainless Steel Foil</td><td>Various</td><td></td><td>.0005&quot; thick, 304 Stainless Steel</td></tr><tr><td>Tetramethylorthosilicate (TMOS)</td><td>Sigma Aldrich www.sigmaaldrich.com</td><td>218472-500G</td><td>98% purity, CAS 681-84-5</td></tr><tr><td>Ultrasonic Cleaner</td><td>FisherScientific FS6</td><td>153356</td><td>Any sonicator is suitable.</td></tr><tr><td>Vacuum Exhaust system</td><td>Purex</td><td>800i</td><td>Any exhaust system is suitable.</td></tr><tr><td>Variable micropipettor, 100-1000 &amp;micro;L</td><td>Manufactured by Eppendorf, purchased from Fisher Scientific www.fishersci.com</td><td>S304665</td><td>Any 100-1000 &amp;micro;L pipettor is suitable.</td></tr></tbody></table>

aesthetically enhanced silica aerogel via incorporation of laser etching and dyes

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid supercritical extraction method, large silica aerogel monolith (10 cm x 11 cm x 1.5 cm) can be fabricated in about 10 h. Dyes incorporated into the precursor mixture result in yellow-, pink- and orange-tinged aerogels. Text, patterns, and images can be etched onto the surface (or surfaces) of the aerogel monolith without damaging the bulk structure. The laser engraver can be used to cut shapes from the aerogel and form colorful mosaics.

This protocol can be employed to prepare a wide variety of aesthetically pleasing aerogel monoliths for applications including, but not limited to, art and sustainable building design. Inclusion in the precursor mixture of the small amounts of dye employed here is only observed to impact the color of the resulting aerogel monolith; changes in other optical or structural properties are not observed.
Figure 8&#160;shows an approach to preparing an aerogel mosaic from large silica monoliths. The same pattern (shown in Figure 3) is cut into three different dyed aerogel monoliths (Figure 8a-c). Aerogel pieces are then reassembled into a mosaic pattern (Figure 8d-e). To prepare a mosaic window, the aerogel mosaic can be sandwiched between two panes of glass or transparent plastic within a frame assembly. Use of a compression frame will eliminate gaps between the re-assembled pieces in the final mosaic assembly.
It is possible to etch designs on smaller monolithic pieces, following the same procedure outlined in section 3, in order to obtain visually interesting arrangements. Figure 9 presents images of dyed, etched aerogel pieces under natural lighting conditions (Figure 9a) and under UV light (Figure 9b), highlighting the fluorescent nature of the dyes used here. Note that small monoliths of irregular size and shape were used to illustrate the feasibility of etching onto smaller pieces; the etching process did not cause them to break.
Figure 10&#160;presents a montage of etched aerogels that illustrate different aesthetic effects that can be achieved using this protocol: native aerogels etched with patterns of various density (Figure 10a-c), aerogels with photographs printed onto the front surface of a planar surface (Figure 10d) and front and back of a curved surface (Figure 10e) as well as an etched fluorescein-dyed aerogel (Figure 10f). The montage illustrates the versatility of the etching and dying processes.
Etching results in changes to the surface of the aerogel, but visual observation, imaging and BET analysis demonstrates that it leaves the bulk structure intact6,7. Photographs in Figure 5, Figure 6, Figure 7, Figure 8,&#160;Figure 9 illustrate that the unetched portions of the monolith are unscathed. The localized damage caused by etching can be imaged. Figure 11 shows scanning electron microscope (SEM) images of etched silica aerogel. Figure 11a shows the interface between etched &#34;lines&#34; (upper right portion of image, with features in a venation pattern) and the un-etched nanoporous aerogel (which appears almost smooth at this magnification). Etching causes ablation of material from the surface and melting of some of the silica into filament-like structures hundreds of &#181;m in length7. Figure 11b shows the effect of a single laser pulse in the aerogel.
<table border="1" fo:keep-together.within-page="always" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Dye&#160; &#38; Structure</td>
			<td>Melting Point (&#176;C)</td>
			<td>Mass ratio (Dye/Methanol) in stock solution</td>
			<td>Images of Resulting Aerogels</td>
		</tr>
		<tr>
			<td> 
			Fluorescein 
			<img alt="Image 1" src="/files/ftp_upload/61986/61986img1v2.png" /></td>
			<td>315</td>
			<td>0.05% g /g</td>
			<td><img alt="Image 3" src="/files/ftp_upload/61986/61986img03.jpg" /></td>
		</tr>
		<tr>
			<td> 
			Rhodamine B 
			<img alt="Image 2" src="/files/ftp_upload/61986/61986img2v2.png" /></td>
			<td>165</td>
			<td>0.075% g/g</td>
			<td><img alt="Image 4" src="/files/ftp_upload/61986/61986img04.jpg" /></td>
		</tr>
		<tr>
			<td> 
			Rhodamine 6G 
			<img alt="Image 3" src="/files/ftp_upload/61986/61986img3v2.png" /></td>
			<td>290</td>
			<td>0.16% g/g</td>
			<td><img alt="Image 5" src="/files/ftp_upload/61986/61986img05.jpg" /></td>
		</tr>
	</tbody>
</table>
Table 1: Information on the dyes. Information on dyes used for making yellow-, pink-, and orange-tinged aerogels and representative images. Different shades are achieved by diluting the methanol/dye stock mixture with additional methanol (as described in step 1.2.2.4.) prior to use in the precursor mixture. Images are shown for materials prepared with 0x dilution (stock solution, shown to the left), 2x dilution (50% methanol/dye + 50% methanol, shown in the center), and 6.67x dilution (15% methanol/dye + 85% methanol, shown to the right).
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Step</td>
			<td>Temperature (&#176;F, &#176;C)</td>
			<td>T-Rate (&#176;F/min, &#176;C/min)</td>
			<td>Force (Kip, kN)</td>
			<td>F-Rate(Kip/min, kN/min)</td>
			<td>Dwell (min)</td>
			<td>Step Duration (min)</td>
		</tr>
		<tr>
			<td>1</td>
			<td>90, 32</td>
			<td>200, 111</td>
			<td>55, 245</td>
			<td>600, 2700</td>
			<td>30</td>
			<td>30</td>
		</tr>
		<tr>
			<td>2</td>
			<td>550, 288</td>
			<td>2, 1.1</td>
			<td>55, 245</td>
			<td>--</td>
			<td>55</td>
			<td>285</td>
		</tr>
		<tr>
			<td>3</td>
			<td>550, 288</td>
			<td>--</td>
			<td>1, 4.5</td>
			<td>1, 4.5</td>
			<td>15</td>
			<td>70</td>
		</tr>
		<tr>
			<td>4</td>
			<td>90, 32</td>
			<td>2, 1.1</td>
			<td>1, 4.5</td>
			<td>--</td>
			<td>0</td>
			<td>230</td>
		</tr>
	</tbody>
</table>
Table 2: Hot press parameters.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Parameter</td>
			<td>Values</td>
		</tr>
		<tr>
			<td colspan="1" rowspan="2">Maximum Speed</td>
			<td>8.9 cm/s (vector mode)</td>
		</tr>
		<tr>
			<td>208 cm/s (raster mode)</td>
		</tr>
		<tr>
			<td>Maximum Power</td>
			<td>50 W</td>
		</tr>
		<tr>
			<td>Frequency Range</td>
			<td>1 - 5000 Hz</td>
		</tr>
		<tr>
			<td>Print Resolution</td>
			<td>75 - 1200 DPI</td>
		</tr>
	</tbody>
</table>
Table 3: Laser engraver properties.
<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>Speed (cm/s)</td>
			<td>Cut Depth (mm)</td>
		</tr>
		<tr>
			<td>0.27</td>
			<td>12.8</td>
		</tr>
		<tr>
			<td>0.45</td>
			<td>12.2</td>
		</tr>
		<tr>
			<td>0.71</td>
			<td>10.4</td>
		</tr>
		<tr>
			<td>0.89</td>
			<td>10.2</td>
		</tr>
		<tr>
			<td>1.78</td>
			<td>7</td>
		</tr>
		<tr>
			<td>2.67</td>
			<td>6.2</td>
		</tr>
		<tr>
			<td>3.56</td>
			<td>5.2</td>
		</tr>
		<tr>
			<td>4.45</td>
			<td>4.6</td>
		</tr>
		<tr>
			<td>5.34</td>
			<td>4.3</td>
		</tr>
		<tr>
			<td>6.23</td>
			<td>3.7</td>
		</tr>
		<tr>
			<td>7.12</td>
			<td>3.4</td>
		</tr>
		<tr>
			<td>8.01</td>
			<td>2.8</td>
		</tr>
		<tr>
			<td>8.9</td>
			<td>3</td>
		</tr>
	</tbody>
</table>
Table 4: Laser cut depth as a function of laser head speed for a laser power of 100% (50 W) and frequency of 500 Hz cutting through a 12.7 mm thick aerogel sample.
<img alt="Figure 1" class="xfigimg" src="/files/ftp_upload/61986/61986fig01.jpg" /> 
Figure 1:&#160;Mold Assembly. Schematics of the (a) top (with fourteen vent holes), (b) middle, and (c) bottom mold assembly. The blue surface (d) indicates the connecting surface of the bottom part (a similar one exists on the top surface) and the off-white surfaces (e) indicate the inside surfaces of the middle and bottom mold (a similar one exists on the top surface). A three-part mold is used to facilitate removal of the aerogel, if needed. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig01large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 2" class="xfigimg" src="/files/ftp_upload/61986/61986fig02.jpg" /> 
Figure 2: Schematic showing mold placement in hot press. (a) Hot press platens, (b) graphite gasket, (c) stainless steel foil, (d) 3-part mold. NOTE: A piece of stainless steel foil can be placed between the platen and the graphite gasket to prevent sticking to the platen, as described in step 1.1.12.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig02large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" class="xfigimg" src="/files/ftp_upload/61986/61986fig03.jpg" /> 
Figure 3:&#160;Example construction of a mosaic design. (a) square outline created, (b) diagonal lines added, (c) circle added, (d) inner diagonal lines removed, (e) hexagon added, and (f) final design. See Figure 8 for aerogel mosaic constructed from this design. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig03large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" class="xfigimg" src="/files/ftp_upload/61986/61986fig04.jpg" /> 
Figure 4: Example adjustment of a cloud image. (a) Original image. (b) Inverted image with off-white background. (c) Original image with background removed and contrast adjusted to 40% to highlight features. (d) Photograph of aerogel etched with image shown in panel a. The low contrast level in the original image results in an indistinct etched pattern. (e) Photograph of aerogel etched with image shown in panel b. Here, the cloud is more visible but the off-white background results in less distinction. Note that the cracks observed were present on the monolith prior to etching and are not due to the etching process. (f) Photograph of aerogel etched with image shown in panel c. The adjusted contrast and removal of the background results in a more distinct cloud. In all the images, the cloud is approximately 2 cm high. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig04large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" class="xfigimg" src="/files/ftp_upload/61986/61986fig05.jpg" /> 
Figure 5: Laser engraver. (a) manual focus gauge, (b) laser and lens assembly, (c) aerogel and (d) platform. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig05large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 6" class="xfigimg" src="/files/ftp_upload/61986/61986fig06.jpg" /> 
Figure 6:&#160;Cut depth versus laser speed. Cut depth versus laser speed (100% leftmost cut, 3% rightmost cut) for a power of 100% (50 W) and a frequency of 500 Hz (see accompanying data in Table 4) for a 12.7 mm thick aerogel sample. This figure has been modified from Stanec et al.7&#160;The arrow indicates the cut that penetrated the full depth of the aerogel. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig06large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 7" class="xfigimg" src="/files/ftp_upload/61986/61986fig07.jpg" /> 
Figure 7:&#160;Photograph of cut aerogel edge. Pieces of ablated aerogel can be seen on the leftmost surface. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig07large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 8" class="xfigimg" src="/files/ftp_upload/61986/61986fig08.jpg" /> 
Figure 8: Example of aerogel mosaic. The final pattern of Figure 3 cut into (a) rhodamine-6G-dyed aerogel (orange), (b) fluorescein-dyed (yellow) aerogel, and (c) rhodamine-B-dyed (pink) aerogel (d,e) individual cut pieces reassembled to form tri-color mosaics. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig08large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 9" class="xfigimg" src="/files/ftp_upload/61986/61986fig09.jpg" /> 
Figure 9: Etched dyed aerogel samples. Etched dyed aerogel samples (a) under natural lighting conditions and (b) under UV light. Notes: the size of the largest aerogel piece (left side, middle) is approximately 3 cm x 3 cm x 1 cm. Dark spots observed are due to staining from the laser engraver platform or are loose particles, rather than an indication of inhomogeneity in dye distribution. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig09large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 10" class="xfigimg" src="/files/ftp_upload/61986/61986fig10.jpg" /> 
Figure 10: Photographs of etched aerogels. (a) view of geometric pattern etched on front and back of aerogel, (b) a dense etching pattern leaves the bulk structure intact, (c) flower pattern etching, (d) photograph (top) etched onto silica aerogel (bottom), (This figure has been modified from Michaloudis et al.6) (e) photograph (top) of Kouros statue etched onto front and back of cylindrical aerogel of diameter 2.5 cm (note the original photo was inverted to create a white background before etching), and (f) image etched onto fluorescein-dyed silica aerogel of height 9 cm. <a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig10large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 11" class="xfigimg" src="/files/ftp_upload/61986/61986fig11.jpg" /> 
Figure 11: SEM images of a silica aerogel showing the effect of (a) etching lines on the upper-right side of the image and (b) a single laser pulse. (This figure has been modified from Stanec et al.7) The images show structural changes caused by the laser. The scale bar is 20 &#181;m.&#160;<a href="https://www-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/61986/61986fig11large.jpg" style="font-size: 14px;" target="_blank">Please click here to view a larger version of this figure.</a>

Watch this Scientific Journal Video about Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes at JoVE.com

Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

This protocol describes a method for etching text, patterns, and images onto the surface of silica aerogel monoliths in native and dyed form and assembling the aerogels into mosaic designs.

A procedure for aesthetically enhancing silica aerogel monoliths by laser etching and incorporation of dyes is described in this manuscript. Using a rapid ...

aesthetically-enhanced-silica-aerogel-via-incorporation-laser-etching

Nanyang Technological University

Research

JoVE Journal

Engineering

2.8K Views.  Union College. Dit protocol presenteert de eerste visuele methodologie voor het etsen en snijden van effen en geverfde Aerogel met behulp van een lasergraveersysteem. Het belangrijkste voordeel van deze techniek is de eenvoud, omdat aerogelmonolieten van elke vorm, grootte of kleur kunnen worden geëtst. Videopresentatie maakt het mogelijk om de praktische overwegingen van het protocol te demonstreren, inclusief plaatsing van de Aerogel en uitlijning van de lasersnijder.Om een mal voor te bereiden vo...

Video: Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

Fabrication of Silica Ultra High Quality Factor Microresonators

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the quality factor (Q) of the cavity, can be in excess of 500ns for cavities with Q factors above 100 million. As a result of their low material losses, silica microcavities have demonstrated some of the longest photon lifetimes to date1-2. Since a portion of the circulating light extends outside the resonator, these devices can also be used to probe the surroundings. This interaction has enabled numerous experiments in biology, such as single molecule biodetection and antibody-antigen kinetics, as well as discoveries in other fields, such as development of ultra-low-threshold microlasers, characterization of thin films, and cavity quantum electrodynamics studies.3-7
The two primary silica resonant cavity geometries are the microsphere and the microtoroid. Both devices rely on a carbon dioxide laser reflow step to achieve their ultra-high-Q factors (Q&gt;100 million).1-2,8-9 However, there are several notable differences between the two structures. Silica microspheres are free-standing, supported by a single optical fiber, whereas silica microtoroids can be fabricated on a silicon wafer in large arrays using a combination of lithography and etching steps. These differences influence which device is optimal for a given experiment.
Here, we present detailed fabrication protocols for both types of resonant cavities. While the fabrication of microsphere resonant cavities is fairly straightforward, the fabrication of microtoroid resonant cavities requires additional specialized equipment and facilities (cleanroom). Therefore, this additional requirement may also influence which device is selected for a given experiment.
Introduction
An optical resonator efficiently confines light at specific wavelengths, known as the resonant wavelengths of the device. 1-2 The common figure of merit for these optical resonators is the quality factor or Q. This term describes the photon lifetime (&tau;o) within the resonator, which is directly related to the resonator's optical losses. Therefore, an optical resonator with a high Q factor has low optical losses, long photon lifetimes, and very low photon decay rates (1/&tau;o). As a result of the long photon lifetimes, it is possible to build-up extremely large circulating optical field intensities in these devices. This very unique property has allowed these devices to be used as laser sources and integrated biosensors.10
A unique sub-class of resonators is the whispering gallery mode optical microcavity. In these devices, the light is confined in circular orbits at the periphery. Therefore, the field is not completely confined within the device, but evanesces into the environment. Whispering gallery mode optical cavities have demonstrated some of the highest quality factors of any optical resonant cavity to date.9,11 Therefore, these devices are used throughout science and engineering, including in fundamental physics studies and in telecommunications as well as in biodetection experiments. 3-7,12
Optical microcavities can be fabricated from a wide range of materials and in a wide variety of geometries. A few examples include silica and silicon microtoroids, silicon, silicon nitride, and silica microdisks, micropillars, and silica and polymer microrings.13-17 The range in quality factor (Q) varies as dramatically as the geometry. Although both geometry and high Q are important considerations in any field, in many applications, there is far greater leverage in boosting device performance through Q enhancement. Among the numerous options detailed previously, the silica microsphere and the silica microtoroid resonator have achieved some of the highest Q factors to date.1,9 Additionally, as a result of the extremely low optical loss of silica from the visible through the near-IR, both microspheres and microtoroids are able to maintain their Q factors over a wide range of testing wavelengths.18 Finally, because silica is inherently biocompatible, it is routinely used in biodetection experiments.
In addition to high material absorption, there are several other potential loss mechanisms, including surface roughness, radiation loss, and contamination loss.2 Through an optimization of the device size, it is possible to eliminate radiation losses, which arise from poor optical field confinement within the device. Similarly, by storing a device in an appropriately clean environment, contamination of the surface can be minimized. Therefore, in addition to material loss, surface scattering is the primary loss mechanism of concern.2,8
In silica devices, surface scattering is minimized by using a laser reflow technique, which melts the silica through surface tension induced reflow. While spherical optical resonators have been studied for many years, it is only with recent advances in fabrication technologies that researchers been able to fabricate high quality silica optical toroidal microresonators (Q&gt;100 million) on a silicon substrate, thus paving the way for integration with microfluidics.1
The present series of protocols details how to fabricate both silica microsphere and microtoroid resonant cavities. While silica microsphere resonant cavities are well-established, microtoroid resonant cavities were only recently invented.1 As many of the fundamental methods used to fabricate the microsphere are also used in the more complex microtoroid fabrication procedure, by including both in a single protocol it will enable researchers to more easily trouble-shoot their experiments.

We describe the use of a carbon dioxide laser reflow technique to fabricate silica resonant cavities, including free-standing microspheres and on-chip microtoroids. The reflow method removes surface imperfections, allowing long photon lifetimes within both devices. The resulting devices have ultra high quality factors, enabling applications ranging from telecommunications to biodetection.

Whispering gallery resonant cavities confine light in circular orbits at their periphery.1-2 The photon storage lifetime in the cavity, quantified by the ...

A Method of Targeted Cell Isolation via Glass Surface Functionalization

One of the limiting factors to the adoption and advancement of personalized medicine is the inability to develop diagnostic tools to probe individual nuances in expression from patient to patient. Current methodologies that try to separate cells to fill this niche result in disruption of physiological expression, making the separation technique useless as a diagnostic tool. In this protocol, we describe the functionalization and optimization of a surface for the cellular capture and release. This functionalized surface integrates biotinylated antibodies with a glass surface functionalized with an aminosilane (APTES), desthiobiotin and streptavidin. Cell release is facilitated through the introduction of biotin, allowing the recollection and purification of cells captured by the surface. This release is done through the targeting of the secondary moiety desthiobiotin, which results in a much more gentle release paradigm. This reduction in harsh reagents and shear forces reduces changes in cellular expression. The functionalized surface captures up to 80% of cells in a single cell mixture and has demonstrated 50% capture in a dual-cell mixture. Applications of this technology to xenografts and cancer separation studies are investigated. Quantification techniques for surface verification such as plate reader and ImageJ analyses are described as well.

This protocol describes customizable surface functionalization of the desthiobiotin, streptavidin, and APTES system in order to isolate specific cell types of interest. In addition, this manuscript covers the applications, optimization, and verification of this process.

One of the limiting factors to the adoption and advancement of personalized medicine is the inability to develop diagnostic tools to probe individual ...

Cancer Research

Preparing Silica Aerogel Monoliths via a Rapid Supercritical Extraction Method

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The procedure requires 15-20 min of preparation time, during which a liquid precursor mixture is prepared and poured into wells of a metal mold that is placed between the platens of a hydraulic hot press, followed by several hours of processing within the hot press. The precursor solution consists of a 1.0:12.0:3.6:3.5 x 10-3 molar ratio of tetramethylorthosilicate (TMOS):methanol:water:ammonia. In each well of the mold, a porous silica sol-gel matrix forms. As the temperature of the mold and its contents is increased, the pressure within the mold rises. After the temperature/pressure conditions surpass the supercritical point for the solvent within the pores of the matrix (in this case, a methanol/water mixture), the supercritical fluid is released, and monolithic aerogel remains within the wells of the mold. With the mold used in this procedure, cylindrical monoliths of 2.2 cm diameter and 1.9 cm height are produced. Aerogels formed by this rapid method have comparable properties (low bulk and skeletal density, high surface area, mesoporous morphology) to those prepared by other methods that involve either additional reaction steps or solvent extractions (lengthier processes that generate more chemical waste).The rapid supercritical extraction method can also be applied to the fabrication of aerogels based on other precursor recipes.

This article describes a rapid supercritical extraction method for fabricating silica aerogels. By utilizing a confined mold and hydraulic hot press, monolithic aerogels can be made in eight hours or less.

A procedure for the fabrication of monolithic silica aerogels in eight hours or less via a rapid supercritical extraction process is described. The ...

Chemistry

Spatial Separation of Molecular Conformers and Clusters

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold molecular beams. However, these beams often contain multiple conformers and clusters, even at low rotational temperatures. We present an experimental methodology that allows the spatial separation of these constituent parts of a molecular beam expansion. Using an electric deflector the beam is separated by its mass-to-dipole moment ratio, analogous to a bender or an electric sector mass spectrometer spatially dispersing charged molecules on the basis of their mass-to-charge ratio. This deflector exploits the Stark effect in an inhomogeneous electric field and allows the separation of individual species of polar neutral molecules and clusters. It furthermore allows the selection of the coldest part of a molecular beam, as low-energy rotational quantum states generally experience the largest deflection. Different structural isomers (conformers) of a species can be separated due to the different arrangement of functional groups, which leads to distinct dipole moments. These are exploited by the electrostatic deflector for the production of a conformationally pure sample from a molecular beam. Similarly, specific cluster stoichiometries can be selected, as the mass and dipole moment of a given cluster depends on the degree of solvation around the parent molecule. This allows experiments on specific cluster sizes and structures, enabling the systematic study of solvation of neutral molecules.

We present a technique that allows the spatial separation of different conformers or clusters present in a molecular beam. An electrostatic deflector is used to separate species by their mass-to-dipole moment ratio, leading to the production of gas-phase ensembles of a single conformer or cluster stoichiometry.

Gas-phase molecular physics and physical chemistry experiments commonly use supersonic expansions through pulsed valves for the production of cold ...

Attaching Biological Probes to Silica Optical Biosensors Using Silane Coupling Agents

In order to interface with biological environments, biosensor platforms, such as the popular Biacore system (based on the Surface Plasmon Resonance (SPR) technique), make use of various surface modification techniques, that can, for example, prevent surface fouling, tune the hydrophobicity / hydrophilicity of the surface, adapt to a variety of electronic environments, and most frequently, induce specificity towards a target of interest.1-5 These techniques extend the functionality of otherwise highly sensitive biosensors to real-world applications in complex environments, such as blood, urine, and wastewater analysis.2,6-7 While commercial biosensing platforms, such as Biacore, have well-understood, standard techniques for performing such surface modifications, these techniques have not been translated in a standardized fashion to other label-free biosensing platforms, such as Whispering Gallery Mode (WGM) optical resonators.8-9
WGM optical resonators represent a promising technology for performing label-free detection of a wide variety of species at ultra-low concentrations.6,10-12 The high sensitivity of these platforms is a result of their unique geometric optics: WGM optical resonators confine circulating light at specific, integral resonance frequencies.13 Like the SPR platforms, the optical field is not totally confined to the sensor device, but evanesces; this "evanescent tail" can then interact with species in the surrounding environment. This interaction causes the effective refractive index of the optical field to change, resulting in a slight, but detectable, shift in the resonance frequency of the device. Because the optical field circulates, it can interact many times with the environment, resulting in an inherent amplification of the signal, and very high sensitivities to minor changes in the environment.2,14-15
To perform targeted detection in complex environments, these platforms must be paired with a probe molecule (usually one half of a binding pair, e.g. antibodies / antigens) through surface modification.2 Although WGM optical resonators can be fabricated in several geometries from a variety of material systems, the silica microsphere is the most common. These microspheres are generally fabricated on the end of an optical fiber, which provides a "stem" by which the microspheres can be handled during functionalization and detection experiments. Silica surface chemistries may be applied to attach probe molecules to their surfaces; however, traditional techniques generated for planar substrates are often not adequate for these three-dimensional structures, as any changes to the surface of the microspheres (dust, contamination, surface defects, and uneven coatings) can have severe, negative consequences on their detection capabilities. Here, we demonstrate a facile approach for the surface functionalization of silica microsphere WGM optical resonators using silane coupling agents to bridge the inorganic surface and the biological environment, by attaching biotin to the silica surface.8,16 Although we use silica microsphere WGM resonators as the sensor system in this report, the protocols are general and can be used to functionalize the surface of any silica device with biotin.

Biosensors interface with complex, biological environments and perform targeted detection by combining highly sensitive sensors with highly specific probes attached to the sensor via surface modification. Here, we demonstrate the surface functionalization of silica optical sensors with biotin using silane coupling agents to bridge the sensor and the biological environment.

In order to interface with biological environments, biosensor platforms, such as the popular Biacore system (based on the Surface Plasmon Resonance (SPR) ...

Bioengineering

Fabrication and Testing of Catalytic Aerogels Prepared Via Rapid Supercritical Extraction

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three preparation methods are described: (a) the incorporation of metal salts into silica or alumina wet gels using an impregnation method; (b) the incorporation of metal salts into alumina wet gels using a co-precursor method; and (c) the addition of metal nanoparticles directly into a silica aerogel precursor mixture. The methods utilize a hydraulic hot press, which allows for rapid (&#60;6 h) supercritical extraction and results in aerogels of low density (0.10 g/mL) and high surface area (200-800 m2/g). While the work presented here focuses on the use of copper salts and copper nanoparticles, the approach can be implemented using other metal salts and nanoparticles. A protocol for testing the three-way catalytic ability of these aerogels for automotive pollution mitigation is also presented. This technique uses custom-built equipment, the Union Catalytic Testbed (UCAT), in which a simulated exhaust mixture is passed over an aerogel sample at a controlled temperature and flow rate. The system is capable of measuring the ability of the catalytic aerogels, under both oxidizing and reducing conditions, to convert CO, NO and unburned hydrocarbons (HCs) to less harmful species (CO2, H2O and N2). Example catalytic results are presented for the aerogels described.

Here we present protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms. Methods for preparing materials using copper salts and copper-containing nanoparticles are featured. Catalytic testing protocols demonstrate the effectiveness of these aerogels for three-way catalysis applications.

Protocols for preparing and testing catalytic aerogels by incorporating metal species into silica and alumina aerogel platforms are presented. Three ...

Preparation of Functional Silica Using a Bioinspired Method

The goal of the protocols described herein is to synthesize bioinspired silica materials, perform enzyme encapsulation therein, and partially or totally purify the same by acid elution. By combining sodium silicate with a polyfunctional bioinspired additive, silica is rapidly formed at ambient conditions upon neutralization. 
The effect of neutralization rate and biomolecule addition point on silica yield are investigated, and biomolecule immobilization efficiency is reported for varying addition point. In contrast to other porous silica synthesis methods, it is shown that the mild conditions required for bioinspired silica synthesis are fully compatible with the encapsulation of delicate biomolecules. Additionally, mild conditions are used across all synthesis and modification steps, making bioinspired silica a promising target for the scale-up and commercialization as both a bare material and active support medium.
The synthesis is shown to be highly sensitive to conditions, i.e., the neutralization rate and final synthesis pH, however tight control over these parameters is demonstrated through the use of auto titration methods, leading to high reproducibility in reaction progression pathway and yield. 
Therefore, bioinspired silica is an excellent active material support choice, showing versatility towards many current applications, not limited to those demonstrated here, and potency in future applications.

Here, we present a protocol to synthesize bioinspired silica materials and immobilize enzymes therein. Silica is synthesized by combining sodium silicate and an amine &#39;additive&#39;, which neutralize at a controlled rate. Material properties and function can be altered either by in situ enzyme immobilization or post-synthetic acid elution of encapsulated additives.

The goal of the protocols described herein is to synthesize bioinspired silica materials, perform enzyme encapsulation therein, and partially or totally ...

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping microtextures (GEMs) on them comprising cavities and pillars with reentrant and doubly reentrant features. Specifically, we use SiO2/Si as the model system and share protocols for two-dimensional (2D) designing, photolithography, isotropic/anisotropic etching techniques, thermal oxide growth, piranha cleaning, and storage towards achieving those microtextures. Even though the conventional wisdom indicates that roughening intrinsically wetting surfaces (&#952;o &#60; 90&#176;) renders them even more wetting (&#952;r &#60; &#952;o &#60; 90&#176;), GEMs demonstrate liquid repellence despite the intrinsic wettability of the substrate. For instance, despite the intrinsic wettability of silica &#952;o &#8776; 40&#176; for the water/air system, and &#952;o &#8776; 20&#176; for the hexadecane/air system, GEMs comprising cavities entrap air robustly on immersion in those liquids, and the apparent contact angles for the droplets are &#952;r &#62; 90&#176;. The reentrant and doubly reentrant features in the GEMs stabilize the intruding liquid meniscus thereby trapping the liquid-solid-vapor system in metastable air-filled states (Cassie states) and delaying wetting transitions to the thermodynamically-stable fully-filled state (Wenzel state) by, for instance, hours to months. Similarly, SiO2/Si surfaces with arrays of reentrant and doubly reentrant micropillars demonstrate extremely high contact angles (&#952;r &#8776; 150&#176;&#8211;160&#176;) and low contact angle hysteresis for the probe liquids, thus characterized as superomniphobic. However, on immersion in the same liquids, those surfaces dramatically lose their superomniphobicity and get fully-filled within &#60;1 s. To address this challenge, we present protocols for hybrid designs that comprise arrays of doubly reentrant pillars surrounded by walls with doubly reentrant profiles. Indeed, hybrid microtextures entrap air on immersion in the probe liquids. To summarize, the protocols described here should enable the investigation of GEMs in the context of achieving omniphobicity without chemical coatings, such as perfluorocarbons, which might unlock the scope of inexpensive common materials for applications as omniphobic materials. Silica microtextures could also serve as templates for soft materials.

Rendering SiO2/Si Surfaces Omniphobic by Carving Gas-Entrapping Microtextures Comprising Reentrant and Doubly Reentrant Cavities or Pillars

This work presents microfabrication protocols for achieving cavities and pillars with reentrant and doubly reentrant profiles on SiO2/Si wafers using photolithography and dry etching. Resulting microtextured surfaces demonstrate remarkable liquid repellence, characterized by robust long-term entrapment of air under wetting liquids, despite the intrinsic wettability of silica.

We present microfabrication protocols for rendering intrinsically wetting materials repellent to liquids (omniphobic) by creating gas-entrapping ...

Encapsulating Cytochrome c in Silica Aerogel Nanoarchitectures without Metal Nanoparticles while Retaining Gas-phase Bioactivity

Applications such as sensors, batteries, and fuel cells have been improved through the use of highly porous aerogels when functional compounds are encapsulated within the aerogels. However, few reports on encapsulating proteins within sol&#8211;gels that are processed to form aerogels exist. A procedure for encapsulating cytochrome c (cyt. c) in silica (SiO2) sol-gels that are supercritically processed to form bioaerogels with gas-phase activity for nitric oxide (NO) is presented. Cyt. c is added to a mixed silica sol under controlled protein concentration and buffer strength conditions. The sol mixture is then gelled and the liquid filling the gel pores is replaced through a series of solvent exchanges with liquid carbon dioxide. The carbon dioxide is brought to its critical point and vented off to form dry aerogels with cyt. c encapsulated inside. These bioaerogels are characterized with UV-visible spectroscopy and circular dichroism spectroscopy and can be used to detect the presence of gas-phase nitric oxide. The success of this procedure depends on regulating the cyt. c concentration and the buffer concentration and does not require other components such as metal nanoparticles. It may be possible to encapsulate other proteins using a similar approach making this procedure important for potential future bioanalytical device development.

Encapsulating Cytochrome c in Silica Aerogel Nanoarchitectures without Metal Nanoparticles while Retaining Gas-phase Bioactivity

This procedure describes how to encapsulate cytochrome c (cyt. c) in silica (SiO2) sol-gels, process these gels to form bioaerogels, and use these bioaerogels to rapidly recognize nitric oxide (NO) through a gas-phase reaction. This type of protocol may aid in the future development of biosensors or other bioanalytical devices.

Applications such as sensors, batteries, and fuel cells have been improved through the use of highly porous aerogels when functional compounds are ...

Impregnation and Grafting of Aminated Compounds onto Silica Substrates

A Synthetic Methodology for Preparing Impregnated and Grafted Amine-Based Silica Composites for Carbon Capture

Recently, there has been a significant effort towards reducing or mitigating CO2 emissions through the use of carbon capture materials for point source or direct air capture (DAC) methods. This work focuses on amine-functionalized CO2 adsorbents for DAC. These materials show promise for CO2 removal because they have low regeneration energy consumption and high adsorption capacity. The incorporation of amine species into a porous substrate combines the advantages of the amine species&#39; affinity to CO2 with the large pore volumes and surface areas of the porous substrate. There are three methods commonly used to prepare amine-based CO2 sorbents, depending on the selection of the amine species, material support, and preparation method. These methods are impregnation, grafting, or chemical synthesis. Silica is a prevalent choice of substrate material because of its adjustable pore size, moisture tolerance, temperature stability, and ability to adsorb CO2 in low concentrations for DAC applications. Typical synthetic procedures and primary attributes of both impregnated and grafted amine-silica composites are described herein.

Author Spotlight: Standardizing the Development of Amine-Based Silica Composites as CO2 Adsorbents for Direct Air Capture 

This work aims to facilitate the development of standardized techniques for impregnating or grafting aminated compounds onto silica substrates, which are often broadly described in the literature. Specific amounts of solvent, substrate, amines, and the values of other important experimental parameters will be discussed in detail.

Recently, there has been a significant effort towards reducing or mitigating CO2 emissions through the use of carbon capture materials for point source or ...

Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

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