This work is supported by National Institutes of Health through contract # R01 AI132413-01.

1. Synthesis of porous silicon nanoparticles (pSINPs)
CAUTION: Always use caution when working with hydrofluoric acid (HF). Follow all safety guides according to its safety data sheet (SDS), handle any HF-containing chemicals in a fume hood, and wear appropriate personal protective equipment (PPE; double gloves with butyl gloves on the outside, butyl apron with lab coat underneath, face shield with safety goggles underneath). All universities and R&#38;D labs require specific training on HF safety prior to usage. Do not attempt to work with HF without pre-approval of your local lab safety coordinator, as additional safety measures not described here are required.
<ol>
	<li>Preparation of the etching solutions
	<ol>
		<li>To make the 3:1 HF solution for etching (used in Steps 1.3 and 1.4), fill a plastic graduated cylinder with 30 mL of aqueous 48% HF and 10 mL of absolute ethanol (EtOH). The solution must be contained in high density plastics (e.g., HDPE), as the HF dissolves glass.</li>
		<li>To make a 1:29 HF solution for lift-off (used in Step 1.5), fill a plastic graduated cylinder with 1 mL of aqueous 48% HF and 29 mL of absolute ethanol. The solution must be contained in high density plastics (e.g., HDPE), as the HF dissolves glass.</li>
		<li>Make the 1 M KOH solution in 10% EtOH for excess pSi dissolution (used in Steps 1.3 and 1.5).</li>
	</ol>
	</li>
	<li>Setting up the etch cell 
	<ol>
		<li>In a Teflon etch cell with a 8.6 cm2 etch well (area is calculated by measuring the diameter of the silicon surface available for etching within the O-ring, and calculating the area by A = &#960;r2), place in descending order (Figure 2a): (1) the Teflon cell top; (2) an O-ring; (3) a quarter piece of the single crystal (1 0 0)-oriented p++-type silicon wafer cut into quarters (using a diamond cutter); (4) aluminum foil; and (5) the Teflon cell base with screws gently tightened to prevent leakage.</li>
		<li>Fill the well with EtOH. Take a wipe and insert into the crevice between the Teflon cell top and base. If the wipe is dry upon removal, the etch cell is sealed. If wet, the cell is leaking, and tighten the screws further until sealed.</li>
	</ol>
	</li>
	<li>Electropolishing the silicon wafer
	<ol>
		<li>Bring the assembled etch cell into a fume hood.</li>
		<li>Fill the well with 10 mL of 3:1 HF solution.</li>
		<li>Connect the positive lead to the aluminum foil (electrode) from the etch cell and connect the negative lead to the platinum coil (counter-electrode) immersed in the 3:1 HF solution of the etch cell to complete the circuit (Figure 2b).</li>
		<li>Run a constant current at 50 mA cm-2 for 60 s. Once etch is finished, remove the cell from the circuit, and rinse out the 3:1 HF carefully using a syringe. Rinse with EtOH three times.</li>
		<li>Dissolve away the etched layer by filling the well slowly with 10 mL of 1 M KOH. Wait until the bubbling subsides.</li>
		<li>Rinse out the KOH with water three times, and then with EtOH three times.</li>
	</ol>
	</li>
	<li>Electrochemically etching porous layers into silicon wafer
	<ol>
		<li>Run an alternating current of a square waveform, with lower current density of 50 mA/cm2 for 0.6 s and high current density of 400 mA/cm2 for 0.36 s repeated for 500 cycles.</li>
		<li>Once etch is finished, remove the cell from the circuit, and rinse out the 3:1 HF carefully using a syringe. Rinse with EtOH three times.</li>
	</ol>
	</li>
	<li>Lifting-off the porous layer from the silicon wafer
	<ol>
		<li>Fill the well with 10 mL of 1:29 HF solution.</li>
		<li>Run a constant of 3.7 mA/cm2 for 250 s. Once etch is finished, remove the cell from the circuit. The pSi layer may have visible ripples indicating detachment from the crystalline silicon wafer. Gently wash out the 1:29 HF solution and rinse with EtOH three times, then with water three times.</li>
		<li>Using a pipette tip, firmly crack the circumference of the pSi layer for complete detachment. Using EtOH, collect the pSi fragments (chips) from the Teflon etch cell into a weighing boat. Transfer the chips to a glass vial. The pSi chips may be kept at room temperature in EtOH for over 6 months for storage.</li>
		<li>Dissolve away any remaining porous silicon on the wafer by filling the well slowly with 10 mL of 1 M KOH. Wait until the bubbling subsides.</li>
		<li>Rinse out the KOH with water three times, and then with EtOH three times.</li>
		<li>Repeat Steps 1.3-1.5 until the entire wafer thickness has been etched.</li>
	</ol>
	</li>
	<li>Sonicating porous layers for nanoparticle formation 
	<ol>
		<li>Replace the solvent of the glass vial containing pSi chips from EtOH to 2 mL of DI water.</li>
		<li>Firmly close the cap, and seal using parafilm.</li>
		<li>Place the glass vial in a sonicator bath and suspended such that the volume of pSi chips is completely submerged below the surface.</li>
		<li>Sonicate for 12 h at 35 kHz and RF power of 48W. To prevent significant water loss during sonication, place a volumetric flask filled with water, inverted so that the opening of the flask touches the surface of the water bath.</li>
		<li>Place the glass vial on a flat surface for 1 h to allow larger particles to settle at the bottom. Collect the supernatant using a pipette; the suspension contains sub-100 nm pSiNPs.</li>
	</ol>
	</li>
</ol>
2. Preparation of fusogenic lipid film
<ol>
	<li>Preparation of the lipid stock solutions
	<ol>
		<li>In a fume hood, make 10 mg/mL stocks of lipids by hydrating DMPC, DSPE-PEG-MAL and DOTAP lipids in chloroform. These stock solutions may be kept at -20 &#176;C for up to 6 months under tight parafilm seal.</li>
	</ol>
	</li>
	<li>Making the fusogenic lipid film 
	NOTE: The fusogenic composition is made of the lipids, DMPC, DSPE-PEG, and DOTAP, at the molar ratio of 76.2:3.8:20 and 96.2:3.8:0, respectively.
	<ol>
		<li>In a glass vial, mix 72.55 &#956;L of DMPC, 15.16 &#956;L of DSPE-PEG, and 19.63 &#956;L of DOTAP by pipetting.</li>
		<li>Optional: For fluorescent labelling of the lipid coating, additionally add 20 &#181;L of DiI dissolved in EtOH at a concentration of 1 mg/mL.</li>
		<li>Place the vial in a fume hood with a loose cap to allow the chloroform to evaporate overnight. The dried film will be a cloudy hard gel-like substance at the bottom of the vial.</li>
	</ol>
	</li>
</ol>
3. Loading and sealing of siRNA in pSiNPs
<ol>
	<li>Preparation of the calcium chloride loading stock
	<ol>
		<li>Dissolve 1.11 g of CaCl&#173;2 in 10 mL of RNAse-free water to make a 2 M CaCl2 solution.</li>
		<li>Centrifuge the solution at &#62; 10,000 x g for 1 min to settle the aggregates and collect the supernatant using a pipette. Alternatively, filter the solution through a 0.22 &#181;m filter.</li>
	</ol>
	</li>
	<li>Preparation of the siRNA loading stock
	<ol>
		<li>Hydrate or dilute the siRNA to 150 &#181;M in RNAse-free water. This stock solution may be aliquoted and kept frozen at -20 &#176;C for at least 30 days given that it does not undergo frequent freeze-thaw cycles.</li>
	</ol>
	</li>
	<li>Loading the siRNA in pSiNPs with calcium chloride
	<ol>
		<li>Prepare an iced sonication bath.</li>
		<li>Under 15 min ultrasonication, gently pipette 150 &#181;L of siRNA and 700 &#181;L of 2 M CaCl2 into 150 &#181;L of pSiNP. Make sure to leave the lid of the microcentrifuge tube open for gas generation.</li>
		<li>Remove the tube containing 1 mL of siRNA-loaded calcium coated pSiNPs from the sonicator.</li>
	</ol>
	</li>
</ol>
4. Coating siRNA-loaded pSiNPs with fusogenic lipids
<ol>
	<li>Preparation of the liposome extrusion kit
	<ol>
		<li>Fill a wide beaker with DI water. Soak 1 polycarbonate membrane (200 nm pores), and 4 filter supports by floating them on water surface. Assemble the liposome extrusion kit by following manufacturer&#8217;s instructions</li>
	</ol>
	</li>
	<li>Hydrating the lipid film with siRNA-loaded pSiNps
	<ol>
		<li>Hydrate the dried lipid film in the glass vial with 1 mL of of siRNA-loaded calcium coated pSiNPs obtained from step 3.3.3. Pipette until all lipids film have lifted from the bottom of the vial and have mixed into a cloudy homogenous solution.</li>
		<li>Place a magnetic stirring bar in the glass vial, and place the vial onto a hot plate to heat the particles to 40 &#176;C (or high enough above the lipids&#8217; phase transformation temperature to maintain the lipids in the more fluidic liquid crystal phase) while magnetically stirring the solution for 20 min.</li>
	</ol>
	</li>
	<li>Extruding the lipid-coated pSiNPs for size control
	<ol>
		<li>Aspirate the 1 mL of lipid-coated pSiNP-siRNA solution in the extrusion syringe. Insert an empty syringe on one side of the extruder, and the filled syringe on the other end.</li>
		<li>Begin extrusion by pushing the piston in slowly to push the particles from one syringe, through the polycarbonate membrane, and into the other. Repeat 20 times. If the piston is stuck, the filter and membrane may be clogged. Disassemble the extruder and replace the membrane and filter supports. If the problem persists, dilute the particles until clogging is manageable.</li>
		<li>Collect the extruded particles into a microcentrifuge tube.</li>
	</ol>
	</li>
</ol>
5. Conjugation of targeting peptides
<ol>
	<li>Conjugating targeting peptide to lipid coating
	<ol>
		<li>Prepare the peptide stock with a 1 mg/mL peptide concentration in RNAse-free water.</li>
		<li>In the microcentrifuge tube containing fusogenic lipid-coated pSiNPs, add 100 &#181;L of the 1 mg/mL peptide stock and pipet gently. Keep the tube static at room temperature for 20 min (alternatively, &#62; 2 h at 4 &#176;C).</li>
		<li>To remove excess peptide or siRNA and other excipients, wash in a 30 kDa centrifugal filter by spinning at 5,000 x g at 25 &#176;C for 1 h. Centrifuge twice more with 1 mL of PBS under the same setting.</li>
		<li>Resuspend the final peptide-conjugated fusogenic lipid-coated pSiNPs in PBS at the desired concentration. The particles can now be aliquoted and frozen at -80 &#176;C for storage of at least 30 days.</li>
	</ol>
	</li>
</ol>

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MJS is a scientific founder of Spinnaker Biosciences, Inc., and has an equity interest in the company.&#160; Although this grant has been identified for conflict of interest management based on the overall scope of the project and its potential benefit to Spinnaker Biosciences, Inc., the research findings included in this particular publication may not necessarily relate to the interests of Spinnaker Biosciences, Inc. The terms of this arrangement have been reviewed and approved by the University of California, San Diego in accordance with its conflict of interest policies. Other authors have nothing to disclose.

Synthesis of porous silicon nanoparticles is shown in Figure 5. The critical step in the synthesis of fusogenic pSiNPs is in the loading step (step 3). If the fusogenic nanoparticles are aggregating post-synthesis (Figure 3), the reason may be due to the following: (1) calcium chloride stock was not homogenously prepared, thus step 3.1.2 must be carefully followed or refined; or (2) the ratio of pSiNP : siRNA : CaCl2 or the concentration of one or mor...

Gene therapy modulates specific gene expression to obtain a therapeutic outcome. Numerous tools for gene modulation have been discovered and studied, including ribonucleic acid interference (RNAi) using oligonucleotides (e.g., short interfering RNA (siRNA)1,2, microRNA (miRNA)3,4), DNA plasmids5,6, nucleases (e.g., zinc finger, TALENS)7,8, and CRISPR/Cas9 systems9,10. While each tool&#8217;s mechanism of action differs, all of the tools must reach the cell&#8217;s cytoplasm or the nucleus to be active. As such, while these tools have proven to induce significant effect in modulating gene expression in vitro, the in vivo efficacy suffers from extracellular and intracellular obstacles. Due to the fact that the tools are of biological origin, many enzymes and clearance systems exist in our body that have the ability to degrade or remove the foreign molecules11. Even in the case that the tools reach the target cell, they suffer from endocytosis; a mode of cellular uptake that encapsulates and traps the tools in acidic stomach-like vesicles that degrade or expel the tools out of the cell. In fact, studies have shown that lipid nanoparticles are endocytosed via macropinocytosis, from which approximately 70% of the siRNA are exocytosed from the cells within 24h of uptake12,13. The majority of the remaining siRNA are degraded through the lysosomal pathway, and ultimately only 1-2% of the siRNA that initially enters the cell with the nanoparticles achieve endosomal escape to potentially undergo RNAi13,14.
We have recently developed fusogenic porous silicon nanoparticles (F-pSiNPs) that have an siRNA-loaded core composed of porous silicon nanoparticles, and a fusogenic lipid shell15. The F-pSiNPs present three major advantages over other conventional oligonucleotide delivery systems: (1) a fusogenic lipid coating which enables the particles to bypass endocytosis and deliver the entire payload directly in the cell cytoplasm (versus the 1-2% achieved by endocytosed particles13,14) (Figure 1); (2) high mass loading of siRNA in the pSiNPs (&#62;20 wt% compared to 1-15 wt% by conventional systems)15, which rapidly degrade in the cytoplasm (once the core particles shed the lipid coating via fusogenic uptake) to release the siRNA; and (3) targeting peptide conjugation for selective homing to desired cell types in vivo. &#160;
The F-pSiNP system has demonstrated significant gene silencing efficacy (&#62;95% in vitro; &#62;80% in vivo) and subsequent therapeutic effect in a fatal mouse model of S. aureus pneumonia; the results of which were published previously15. However, the complex structure of the F-pSiNP system requires delicate handling and fine-tuned optimization to generate uniform and stable nanoparticles. Thus, the purpose of this work is to present a thorough protocol, as well as optimization strategies for the synthesis, functionalization, and characterization of F-pSiNPs to be used in targeted delivery of siRNAs for potent gene silencing effect.

<table border="0" cellpadding="0" cellspacing="0" style="width:1192px;" width="1191">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC)</td>
			<td style="width:163px;">Avanti Polar Lipids</td>
			<td style="width:119px;">850345P</td>
			<td style="width:512px;">Powder</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:399px;">1,2-dioleoyl-3-trimethylammonium-propane (chloride salt) (DOTAP)</td>
			<td style="width:163px;">Avanti Polar Lipids</td>
			<td style="width:119px;">890890P</td>
			<td style="width:512px;">Powder</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:399px;">1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[maleimide(polyethylene glycol)-2000] (ammonium salt) (DSPE-PEG(2000) Maleimide)</td>
			<td style="width:163px;">Avanti Polar Lipids</td>
			<td style="width:119px;">880126P</td>
			<td style="width:512px;">Powder</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">Aluminum foil</td>
			<td style="width:163px;">VWR International, LLC</td>
			<td style="width:119px;">12175-001</td>
			<td style="width:512px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">Calcium chloride (CaCl2)</td>
			<td style="width:163px;">Spectrum</td>
			<td style="width:119px;">C1977</td>
			<td style="width:512px;">Anhydrous, Pellets</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">Chloroform</td>
			<td style="width:163px;">Fisher Scientific</td>
			<td style="width:119px;">C6061</td>
			<td style="width:512px;"></td>
		</tr>
		<tr height="24">
			<td height="24" style="height:25px;width:399px;">Computer</td>
			<td style="width:163px;">Dell</td>
			<td style="width:119px;">Dimension 9200</td>
			<td style="width:512px;">Any computer with PCI card slot is acceptable</td>
		</tr>
		<tr height="63">
			<td height="63" style="height:63px;width:399px;">Dil Stain (1,1&#39;-Dioctadecyl-3,3,3&#39;,3&#39;-Tetramethylindocarbocyanine Perchlorate (&#39;DiI&#39;; DiIC18(3)))</td>
			<td style="width:163px;">Life Technologies</td>
			<td style="width:119px;">D3911</td>
			<td style="width:512px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">Ethanol (EtOH)</td>
			<td style="width:163px;">UCSD Store</td>
			<td style="width:119px;">111</td>
			<td style="width:512px;">200 Proof</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">Hydrofluric acid (HF)</td>
			<td style="width:163px;">VWR International, LLC</td>
			<td style="width:119px;">MK264008&#160;</td>
			<td style="width:512px;">Purity: 48%</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">Keithley 2651a Sourcemeter</td>
			<td style="width:163px;">Keithley</td>
			<td style="width:119px;">2651A</td>
			<td style="width:512px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">LabVIEW</td>
			<td style="width:163px;">National Instruments</td>
			<td style="width:119px;"></td>
			<td style="width:512px;">Sample program available at: http://sailorgroup.ucsd.edu/sofware/</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:399px;">LysoTracker Green DND-26</td>
			<td style="width:163px;">Thermo Fisher Scientific</td>
			<td style="width:119px;">L7526</td>
			<td style="width:512px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">Liposome extrusion set with heating block</td>
			<td style="width:163px;">Avanti Polar Lipids</td>
			<td style="width:119px;">610000</td>
			<td style="width:512px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:399px;">Microcon-30kDa Centrifugal Filter Unit</td>
			<td style="width:163px;">EMD Millipore</td>
			<td style="width:119px;">MRCF0R030</td>
			<td style="width:512px;"></td>
		</tr>
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synthesis, functionalization, and characterization of fusogenic porous silicon nanoparticles for oligonucleotide delivery

With the advent of gene therapy, the development of an effective in vivo nucleotide-payload delivery system has become of parallel import. Fusogenic porous silicon nanoparticles (F-pSiNPs) have recently demonstrated high in vivo gene silencing efficacy due to its high oligonucleotide loading capacity and unique cellular uptake pathway that avoids endocytosis. The synthesis of F-pSiNPs is a multi-step process that includes: (1) loading and sealing of oligonucleotide payloads in the silicon pores; (2) simultaneous coating and sizing of fusogenic lipids around the porous silicon cores; and (3) conjugation of targeting peptides and washing to remove excess oligonucleotide, silicon debris, and peptide. The particle&#8217;s size uniformity is characterized by dynamic light scattering, and its core-shell structure may be verified by transmission electron microscopy. The fusogenic uptake is validated by loading a lipophilic dye, 1,1&#39;-dioctadecyl-3,3,3&#39;,3&#39;-tetramethylindocarbocyanine perchlorate (DiI), into the fusogenic lipid bilayer and treating it to cells in vitro to observe for plasma membrane staining versus endocytic localizations. The targeting and in vivo gene silencing efficacies were previously quantified in a mouse model of Staphylococcus aureus pneumonia, in which the targeting peptide is expected to help the F-pSiNPs to home to the site of infection. Beyond its application in S. aureus infection, the F-pSiNP system may be used to deliver any oligonucleotide for gene therapy of a wide range of diseases, including viral infections, cancer, and autoimmune diseases.

A successful synthesis of fusogenic pSiNPs should produce a homogenous, slightly opaque solution (Figure 3a). Failure to optimize the ratio and concentration of pSiNPs : siRNA : CaCl2 may lead to aggregation upon loading (Figure 3b). As the particles are extruded through 200 nm membranes, the average hydrodynamic diameter of the fusogenic pSiNPs measured by DLS should be approximately 200 nm, and the average zeta-poten...

Watch this Scientific Journal Video about Synthesis, Functionalization, and Characterization of Fusogenic Porous Silicon Nanoparticles for Oligonucleotide Delivery at JoVE.com

Synthesis, Functionalization, and Characterization of Fusogenic Porous Silicon Nanoparticles for Oligonucleotide Delivery

We demonstrate the synthesis of fusogenic porous silicon nanoparticles for effective in vitro and in vivo oligonucleotide delivery. Porous silicon nanoparticles are loaded with siRNA to form the core, which is coated by fusogenic lipids through extrusion to form the shell. Targeting moiety functionalization and particle characterization are included.

With the advent of gene therapy, the development of an effective in vivo nucleotide-payload delivery system has become of parallel import. Fusogenic ...

synthesis-functionalization-characterization-fusogenic-porous-silicon

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JoVE Journal

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7.5K Views.  University of California, San Diego. We demonstrate the synthesis of fusogenic porous silicon nanoparticles for effective in vitro and in vivo oligonucleotide delivery. Porous silicon nanoparticles are loaded with siRNA to form the core, which is coated by fusogenic lipids through extrusion to form the shell. Targeting moiety functionalization and particle characterization are included.

Video: Synthesis, Functionalization, and Characterization of Fusogenic Porous Silicon Nanoparticles for Oligonucleotide Delivery

Optical Trapping of Nanoparticles

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping and manipulating small biological particles. Ashkin and co-workers first demonstrated optical tweezers using a single focused beam1. The single beam trap can be described accurately using the perturbative gradient force formulation in the case of small Rayleigh regime particles1. In the perturbative regime, the optical power required for trapping a particle scales as the inverse fourth power of the particle size. High optical powers can damage dielectric particles and cause heating. For instance, trapped latex spheres of 109 nm in diameter were destroyed by a 15 mW beam in 25 sec1, which has serious implications for biological matter2,3.
A self-induced back-action (SIBA) optical trapping was proposed to trap 50 nm polystyrene spheres in the non-perturbative regime4. In a non-perturbative regime, even a small particle with little permittivity contrast to the background can influence significantly the ambient electromagnetic field and induce a large optical force. As a particle enters an illuminated aperture, light transmission increases dramatically because of dielectric loading. If the particle attempts to leave the aperture, decreased transmission causes a change in momentum outwards from the hole and, by Newton's Third Law, results in a force on the particle inwards into the hole, trapping the particle. The light transmission can be monitored; hence, the trap can become a sensor. The SIBA trapping technique can be further improved by using a double-nanohole structure.
The double-nanohole structure has been shown to give a strong local field enhancement5,6. Between the two sharp tips of the double-nanohole, a small particle can cause a large change in optical transmission, thereby inducing a large optical force. As a result, smaller nanoparticles can be trapped, such as 12 nm silicate spheres7 and 3.4 nm hydrodynamic radius bovine serum albumin proteins8. In this work, the experimental configuration used for nanoparticle trapping is outlined. First, we detail the assembly of the trapping setup which is based on a Thorlabs Optical Tweezer Kit. Next, we explain the nanofabrication procedure of the double-nanohole in a metal film, the fabrication of the microfluidic chamber and the sample preparation. Finally, we detail the data acquisition procedure and provide typical results for trapping 20 nm polystyrene nanospheres.

The following setup approach details low power optical trapping of dielectric nanoparticles using a double-nanohole in metal film.

Optical trapping is a technique for immobilizing and manipulating small objects in a gentle way using light, and it has been widely applied in trapping ...

Synthesis and Functionalization of Nitrogen-doped Carbon Nanotube Cups with Gold Nanoparticles as Cork Stoppers

Nitrogen-doped carbon nanotubes consist of many cup-shaped graphitic compartments termed as nitrogen-doped carbon nanotube cups (NCNCs). These as-synthesized graphitic nanocups from chemical vapor deposition (CVD) method were stacked in a head-to-tail fashion held only through noncovalent interactions. Individual NCNCs can be isolated out of their stacking structure through a series of chemical and physical separation processes. First, as-synthesized NCNCs were oxidized in a mixture of strong acids to introduce oxygen-containing defects on the graphitic walls. The oxidized NCNCs were then processed using high-intensity probe-tip sonication which effectively separated the stacked NCNCs into individual graphitic nanocups. Owing to their abundant oxygen and nitrogen surface functionalities, the resulted individual NCNCs are highly hydrophilic and can be effectively functionalized with gold nanoparticles (GNPs), which preferentially fit in the opening of the cups as cork stoppers. These graphitic nanocups corked with GNPs may find promising applications as nanoscale containers and drug carriers.

We discussed the synthesis of individual graphitic nanocups using a series of techniques including chemical vapor deposition, acid oxidation and probe-tip sonication. By citrate reduction of HAuCl4, the graphitic nanocups were effectively corked with gold nanoparticles due to the chemically reactive edges of the cups.

Nitrogen-doped carbon  nanotubes consist of many cup-shaped graphitic compartments termed as  nitrogen-doped carbon nanotube cups (NCNCs).  These ...

Monolayer Contact Doping of Silicon Surfaces and Nanowires Using Organophosphorus Compounds

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra shallow and sharp doping profiles at the nanometer scale. In MLCD process the dopant source is a monolayer containing dopant atoms.
In this article a detailed procedure for surface doping of silicon substrate as well as silicon nanowires is demonstrated. Phosphorus dopant source was formed using tetraethyl methylenediphosphonate monolayer on a silicon substrate. This monolayer containing substrate was brought to contact with a pristine intrinsic silicon target substrate and annealed while in contact. Sheet resistance of the target substrate was measured using 4 point probe. Intrinsic silicon nanowires were synthesized by chemical vapor deposition (CVD) process using a vapor-liquid-solid (VLS) mechanism; gold nanoparticles were used as catalyst for nanowire growth. The nanowires were suspended in ethanol by mild sonication. This suspension was used to dropcast the nanowires on silicon substrate with a silicon nitride dielectric top layer. These nanowires were doped with phosphorus in similar manner as used for the intrinsic silicon wafer. Standard photolithography process was used to fabricate metal electrodes for the formation of nanowire based field effect transistor (NW-FET). The electrical properties of a representative nanowire device were measured by a semiconductor device analyzer and a probe station.

A detailed procedure for surface doping of Silicon interfaces is provided. The ultra-shallow surface doping is demonstrated by using phosphorus containing monolayers and rapid annealing process. The method can be used for doping of macroscopic area surfaces as well as nanostructures.

Monolayer Contact Doping (MLCD) is a simple method for doping of surfaces and nanostructures1. MLCD results in the formation of highly controlled, ultra ...

Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of biosensing devices. We report on a protocol of using KrF and ArF lasers irradiating Si (001) samples immersed in a liquid environment with low number of pulses and operating at moderately low pulse fluences to induce Si wettability modification. Wafers immersed for up to 4 hr in a 0.01% H2O2/H2O solution did not show measurable change in their initial contact angle (CA) ~75&#176;. However, the 500-pulse KrF and ArF lasers irradiation of such wafers in a microchamber filled with 0.01% H2O2/H2O solution at 250 and 65 mJ/cm2, respectively, has decreased the CA to near 15&#176;, indicating the formation of a superhydrophilic surface. The formation of OH-terminated Si (001), with no measurable change of the wafer&#8217;s surface morphology, has been confirmed by X-ray photoelectron spectroscopy and atomic force microscopy measurements. The selective area irradiated samples were then immersed in a biotin-conjugated fluorescein-stained nanospheres solution for 2 hr, resulting in a successful immobilization of the nanospheres in the non-irradiated area. This illustrates the potential of&#160;the method for selective area biofunctionalization and fabrication of advanced Si-based biosensing architectures. We also describe a similar protocol of irradiation of wafers immersed in methanol (CH3OH) using ArF laser operating at pulse fluence of 65 mJ/cm2 and in situ formation of a strongly hydrophobic surface of Si (001) with the CA of 103&#176;. The XPS results indicate ArF laser induced formation of Si&#8211;(OCH3)x compounds responsible for the observed hydrophobicity. However, no such compounds were found by XPS on the Si surface irradiated by KrF laser in methanol, demonstrating the inability of the KrF laser to photodissociate methanol and create -OCH3 radicals.

We report on a process of in situ alteration of HF treated Si (001) surface into a hydrophilic or hydrophobic state by irradiating samples in microfluidic chambers filled with&#160;H2O2/H2O solution (0.01%-0.5%) or methanol solutions using pulsed UV laser of a relative low pulse fluence.

The wettability of silicon (Si) is one of the important parameters in the technology of surface functionalization of this material and fabrication of ...

Silicon Metal-oxide-semiconductor Quantum Dots for Single-electron Pumping

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by quantum mechanical effects such as tunneling through single dopants, scattering via interface defects, and discrete trap charge states. However, progress in silicon technology has shown that these phenomena can be harnessed and exploited for a new class of quantum-based electronics. Among others, multi-layer-gated silicon metal-oxide-semiconductor (MOS) technology can be used to control single charge or spin confined in electrostatically-defined quantum dots (QD). These QD-based devices are an excellent platform for quantum computing applications and, recently, it has been demonstrated that they can also be used as single-electron pumps, which are accurate sources of quantized current for metrological purposes. Here, we discuss in detail the fabrication protocol for silicon MOS QDs which is relevant to both quantum computing and quantum metrology applications. Moreover, we describe characterization methods to test the integrity of the devices after fabrication. Finally, we give a brief description of the measurement set-up used for charge pumping experiments and show representative results of electric current quantization.

The fabrication process and experimental characterization techniques relevant to single-electron pumps based on silicon metal-oxide-semiconductor quantum dots are discussed.

As mass-produced silicon transistors have reached the nano-scale, their behavior and performances are increasingly affected, and often deteriorated, by ...

Synthesis and Functionalization of 3D Nano-graphene Materials: Graphene Aerogels and Graphene Macro Assemblies

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. Additionally, most reported graphene assemblies are held together through physical interactions (e.g., van der Waals forces) rather than chemical bonds, which limit their mechanical strength and conductivity. This video method details recently developed strategies to fabricate mass-producible, graphene-based bulk materials derived from either polymer foams or single layer graphene oxide. These materials consist primarily of individual graphene sheets connected through covalently bound carbon linkers. They maintain the favorable properties of graphene such as high surface area and high electrical and thermal conductivity, combined with tunable pore morphology and exceptional mechanical strength and elasticity. This flexible synthetic method can be extended to the fabrication of polymer/carbon nanotube (CNT) and polymer/graphene oxide (GO) composite materials. Furthermore, additional post-synthetic functionalization with anthraquinone is described, which enables a dramatic increase in charge storage performance in supercapacitor applications.

This video method describes the synthesis of high surface area, monolithic 3D graphene-based materials derived from polymer precursors as well as single layer graphene oxide.

Efforts to assemble graphene into three-dimensional monolithic structures have been hampered by the high cost and poor processability of graphene. ...

Integration of Light Trapping Silver Nanostructures in Hydrogenated Microcrystalline Silicon Solar Cells by Transfer Printing

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly known as plasmonic effects, play an important role. Research in this field has, however, been impeded owing to the difficulty of fabricating devices containing the desired functional metal nanostructures. In order to provide a viable strategy to this issue, we herein show a transfer printing-based approach that allows the quick and low-cost integration of designed metal nanostructures with a variety of device architectures, including solar cells. Nanopillar poly(dimethylsiloxane) (PDMS) stamps were fabricated from a commercially available nanohole plastic film as a master mold. On this nanopatterned PDMS stamps, Ag films were deposited, which were then transfer-printed onto block copolymer (binding layer)-coated hydrogenated microcrystalline Si (&#181;c-Si:H) surface to afford ordered Ag nanodisk structures. It was confirmed that the resulting Ag nanodisk-incorporated &#181;c-Si:H solar cells show higher performances compared to a cell without the transfer-printed Ag nanodisks, thanks to plasmonic light trapping effect derived from the Ag nanodisks. Because of the simplicity and versatility, further device application would also be feasible thorough this approach.

A viable transfer printing-based methodology to introduce plasmonic metal nanostructures in solar cells is described. Using nanopillar poly(dimethylsiloxane) stamps, an Ag-based ordered nanodisk array was integrated with standard hydrogenated microcrystalline Si solar cells, which led to improved device performances due to plasmonic light trapping.

One of the potential applications of metal nanostructures is light trapping in solar cells, where unique optical properties of nanosized metals, commonly ...

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs within the interlayer space of semiconducting layered titania nanosheet (TNS) films was investigated here. Two types of intermediate films (i.e., TNS films containing methyl viologen (TNS/MV2+) and 2-ammoniumethanethiol (TNS/2-AET+)) were prepared. The two intermediate films were soaked in an aqueous tetrachloroauric(III) acid (HAuCl4) solution, whereby considerable amounts of Au(III) species were accommodated within the interlayer spaces of the TNS films. The two types of obtained films were then soaked in an aqueous sodium tetrahydroborate (NaBH4) solution, whereupon the color of the films immediately changed from colorless to purple, suggesting the formation of AuNPs within the TNS interlayer. When only TNS/MV2+ was used as the intermediate film, the color of the film gradually changed from metallic purple to dusty purple within 30 min, suggesting that aggregation of AuNPs had occurred. In contrast, this color change was suppressed by using the TNS/2-AET+ intermediate film, and the AuNPs were stabilized for over 4 months, as evidenced by the characteristic extinction (absorption and scattering) band from the AuNPs.

In Situ Synthesis of Gold Nanoparticles without Aggregation in the Interlayer Space of Layered Titanate Transparent Films

Here, we present a protocol for the in situ synthesis of gold nanoparticles (AuNPs) within the interlayer space of layered titanate films without the aggregation of AuNPs. No spectral change was observed even after 4 months. The synthesized material has expected applications in catalysis, photo-catalysis, and the development of cost-effective plasmonic devices.

Combinations of metal oxide semiconductors and gold nanoparticles (AuNPs) have been investigated as new types of materials. The in situ synthesis of AuNPs ...

Procedure for the Transfer of Polymer Films Onto Porous Substrates with Minimized Defects

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support substrates. Accomplishing this transfer in a highly controlled, mechanized, and reproducible manner can eliminate the creation of macroscale defect structures (e.g., tears, cracks, and wrinkles) within the thin film that compromise device performance and the usable area per sample. Here, we describe a general protocol for the highly controlled and mechanized transfer of a polymeric thin film onto an arbitrary porous support substrate for eventual use as a water filtration membrane device. Specifically, we fabricate a block copolymer (BCP) thin film on top of a sacrificial, water-soluble poly(acrylic acid) (PAA) layer and silicon wafer substrate. We then utilize a custom-designed, 3D-printed transfer tool and drain chamber system to deposit, lift-off, and transfer the BCP thin film onto the center of a porous anodized aluminum oxide (AAO) support disc. The transferred BCP thin film is shown to be consistently placed onto the center of the support surface due to the guidance of the meniscus formed between the water and the 3D-printed plastic drain chamber. We also compare our mechanized transfer-processed thin films to those that have been transferred by hand with the use of tweezers. Optical inspection and image analysis of the transferred thin films from the mechanized process confirm that little-to-no macroscale inhomogeneities or plastic deformations are produced, as compared to the multitude of tears and wrinkles produced from manual transfer by hand. Our results suggest that the proposed strategy for thin film transfer can reduce defects when compared to other methods across many systems and applications.

We present a procedure for highly controlled and wrinkle-free transfer of block copolymer thin films onto porous support substrates using a 3D-printed drain chamber. The drain chamber design is of general relevance to all procedures involving transfer of macromolecular films onto porous substrates, which is normally done by hand in an irreproducible fashion.

The fabrication of devices containing thin film composite membranes necessitates the transfer of these films onto the surfaces of arbitrary support ...

Metal-Assisted Electrochemical Nanoimprinting of Porous and Solid Silicon Wafers

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is capable of direct patterning 3D micro- and nanoscale features in monocrystalline group IV (e.g., Si) and III-V (e.g., GaAs) semiconductors without the need of sacrificial templates and lithographical steps. During this process, a reusable stamp coated with a noble metal catalyst is brought in contact with a Si wafer in the presence of a hydrofluoric acid (HF) and hydrogen peroxide (H2O2) mixture, which leads to the selective etching of Si at the metal-semiconductor contact interface. In this protocol, we discuss the stamp and substrate preparation methods applied in two Mac-Imprint configurations: (1) Porous Si Mac-Imprint with a solid catalyst; and (2) Solid Si Mac-Imprint with a porous catalyst. This process is high throughput and is capable of centimeter-scale parallel patterning with sub-20 nm resolution. It also provides low defect density and large area patterning in a single operation and bypasses the need for dry etching such as deep reactive ion etching (DRIE).

A protocol for metal-assisted chemical imprinting of 3D microscale features with sub-20 nm shape accuracy into solid and porous silicon wafers is presented.

Metal-assisted electrochemical imprinting (Mac-Imprint) is a combination of metal-assisted chemical etching (MACE) and nanoimprint lithography that is ...