Name: creating sub-50 nm nanofluidic junctions in pdms microfluidic chip via self-assembly process of colloidal particles
Uploaded: 2016-03-13T15:00:00
Description: Watch this Scientific Journal Video about Creating Sub-50 Nm Nanofluidic Junctions in PDMS Microfluidic Chip via Self-Assembly Process of Colloidal Particles at JoVE.com

This work was supported by NIH R21 EB008177-01A2 and New York University Abu Dhabi (NYUAD) Research Enhancement Fund 2013. We express our thanks to the technical staff of MIT MTL for their support during microfabrication and James Weston and Nikolas Giakoumidis of NYUAD for their support in taking SEM pictures and building a voltage divider, respectively.&#160;The device fabrication in PDMS was conducted in the microfabrication core facility of NYUAD.&#160;Lastly, we would like to thank Rebecca Pittam from the NYUAD Center for Digital Scholarship for video shooting and editing.

1. Preparation of the Silica Colloidal Bead Suspensions
<ol>
	<li>Preparation of 300 nm and 500 nm silica bead suspensions
	<ol>
		<li>Vortex the silica bead stock suspension (10% w/v in water) for 30 sec. to obtain a homogeneous suspension. Pipette a total of 600 &#181;l stock suspension into a 1.5 ml tube and centrifuge it at 2,600 x g for 1 min.</li>
		<li>Substitute the supernatant with 400 &#181;l of 1 mM sodium phosphate buffer (PB, pH 7.0).</li>
		<li>Suspend the silica beads into a final concen...

<ol>
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J., Zharov, I. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ion+transport+in+sulfonated+nanoporous+colloidal+films.">Ion transport in sulfonated nanoporous colloidal films.</a> Langmuir. 24, 2650-2654 (2008).</li><li>Gaspar, A., Hernandez, L., Stevens, S., Gomez, F. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electrochromatography+in+microchips+packed+with+conventional+reversed-phase+silica+particles.">Electrochromatography in microchips packed with conventional reversed-phase silica particles.</a> Electrophoresis. 29, 1638-1642 (2008).</li><li>Lee, S. Y., 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=High-Fidelity+Optofluidic+On-Chip+Sensors+Using+Well-Defined+Gold+Nanowell+Crystals.">High-Fidelity Optofluidic On-Chip Sensors Using Well-Defined Gold Nanowell Crystals.</a> Anal Chem. 83, 9174-9180 (2011).</li><li>Hu, Y. 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=Interconnected+ordered+nanoporous+networks+of+colloidal+crystals+integrated+on+a+microfluidic+chip+for+highly+efficient+protein+concentration.">Interconnected ordered nanoporous networks of colloidal crystals integrated on a microfluidic chip for highly efficient protein concentration.</a> Electrophoresis. 32, 3424-3430 (2011).</li><li>Zhang, D. -. W., 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=Microfabrication-free+fused+silica+nanofluidic+interface+for+on+chip+electrokinetic+stacking+of+DNA.">Microfabrication-free fused silica nanofluidic interface for on chip electrokinetic stacking of DNA.</a> Microfluid Nanofluid. 14, 69-76 (2013).</li><li>Syed, A., Mangano, L., Mao, P., Han, J., Song, Y. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Creating+sub-50+nm+nanofluidic+junctions+in+a+PDMS+microchip+via+self-assembly+process+of+colloidal+silica+beads+for+electrokinetic+concentration+of+biomolecules.">Creating sub-50 nm nanofluidic junctions in a PDMS microchip via self-assembly process of colloidal silica beads for electrokinetic concentration of biomolecules.</a> Lab Chip. 14, 4455-4460 (2014).</li><li>Kim, S. J., Song, Y. 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Following the common device design scheme to study nanofluidics, we fabricated a nanofluidic junction between two microfluidic channels by using the evaporation-driven self-assembly of colloidal nanoparticles instead of lithographically patterning an array of nanochannels. When flowing the colloidal particles into the bead delivery channel, an array of nanotraps with a depth of 700 nm and a width of 2&#160;&#181;m on both sides of the bead delivery channel at a total width of 100&#160;&#956;m prevented the bead suspensio...

Nanofluidics is an emerging research area of &#181;TAS (Micro Total Analysis Systems) to study biological processes or transport phenomena of ions and molecules at the length scale of 101- 102 nm. With the advent of the nanofluidic tools such as nanochannels, transport processes of molecules and ions can be monitored with unprecedented precision and manipulated, if needed, by exploiting features that are available only at this length scale for separation and detection.1,2 One of these characteristic nanoscale features is a high ratio of surface to bulk charge (or Dukhin number) in nanochannels that can cause a charge imbalance and initiate ion concentration polarization (ICP) between the nanochannel and microchannel.3
A common device platform for the study of nanofluidic phenomena consists of a two-microchannel system connected by an array of nanochannels as a junction.4-6 The material of choice for building such a nanofluidic device is the silicon because of its high stiffness that prevents the channel from collapsing during bonding processes.7 However, silicon device fabrication requires expensive masks and substantial amount of processing in the cleanroom facility.8-10 Due to the convenience of device fabrication through molding and plasma bonding, polydimethylsiloxane (PDMS) has widely been accepted as a building material for microfluidics and it would be an ideal material for nanofluidics as well. However, its low Young&#39;s modulus around 360-870 KPa, makes the PDMS channel easily collapsible during plasma bonding. The minimum aspect ratio of the nanochannel (width to depth) has to be less than 10:1 which means that the fabrication of PDMS devices via standard photolithography will become extremely challenging if the nanochannel depth has to be below 100 nm, requiring a channel width less than the current limit of photolithography at around 1 &#181;m. To overcome this limitation, there have been attempts to create nanochannels in PDMS using non-lithographical methods such as stretching to initiate cracks with mean depth of 78 nm11 or to form wrinkles after plasma treatment.12 Collapsing a PDMS channel with mechanical pressure allowed a nanochannel height as low as 60 nm.13
Even though these highly inventive non-lithographic methods allowed building nanochannels below 100 nm in depth, the dimensional controllability of the nanochannel fabrication still poses an obstacle to a wide acceptance of PDMS as a building material for nanofluidic devices. Another critical problem of the nanochannels, whether in silicon or PDMS, is the surface functionalization in case there is a need to alter the surface charge on the channel wall for the manipulation of ions or molecules. After device assembly through bonding, the nanochannels are extremely difficult to reach for surface functionalization due to the diffusion-limited transport. To create a nanoscale channel with high dimensional fidelity and facile surface functionalization, the self-assembly method of colloidal particles induced by evaporation14-16 in microfluidic devices can be one of the promising approaches. Besides the controllability of pore size and surface property, there is even a possibility to tune the size of the pore in-situ when using colloidal particles coated with polyelectrolytes by controlling temperature,17 pH,18,19 and ionic strength.18 Because of these advantages, the self-assembly method of colloidal particles has already found applications for electrochromatography,20 biosensors,21 protein concentration22 and separation of proteins and DNA in microfluidics.14,23 In this study, we deployed this self-assembly method to build an electrokinetic preconcentration device in PDMS that requires a nanofluidic junction between two microchannels.24 The fundamental mechanism behind the electrokinetic concentration is based on ion concentration polarization (ICP).25 A detailed description of fabrication and assembly steps is included in the following protocol.

<table>
	<tbody>
		<tr>
			<td>Poly(Styrenesulfonic Acid) Sodium Salt</td>
			<td>Polysciences&#160;</td>
			<td>08772</td>
			<td></td>
		</tr>
		<tr>
			<td>Poly(allylamine) Solution</td>
			<td>Sigma Aldrich</td>
			<td>479144-5G</td>
			<td></td>
		</tr>
		<tr>
			<td>Silica Microsphere - 300 nm</td>
			<td>Polysciences&#160;</td>
			<td>24321</td>
			<td></td>
		</tr>
		<tr>
			<td>Silica Microsphere - 500 nm</td>
			<td>Polysciences&#160;</td>
			<td>24323</td>
			<td></td>
		</tr>
		<tr>
			<td>Silica Microsphere Carboxyl Functional - 500 nm</td>
			<td>Polysciences&#160;</td>
			<td>24753</td>
			<td></td>
		</tr>
		<tr>
			<td>Silica Microsphere Amine Functional - 500 nm</td>
			<td>Polysciences&#160;</td>
			<td>24756</td>
			<td></td>
		</tr>
		<tr>
			<td>Sylgard 184 Silicone Elastomer kit</td>
			<td>Dow Corning</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Trichlorosilane</td>
			<td>Sigma Aldrich</td>
			<td>175552</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultrasonic Cleaner</td>
			<td>Branson</td>
			<td>3510</td>
			<td></td>
		</tr>
		<tr>
			<td>Tube Rotator&#160;</td>
			<td>VWR</td>
			<td>10136-084</td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex Mixer</td>
			<td>WiseMix</td>
			<td>VM-10</td>
			<td></td>
		</tr>
		<tr>
			<td>Microcentrifuge</td>
			<td>VWR</td>
			<td>Micro 1207</td>
			<td></td>
		</tr>
		<tr>
			<td>Plasma Cleaner</td>
			<td>Harrick Plasma</td>
			<td>PDC-001-HP</td>
			<td></td>
		</tr>
		<tr>
			<td>PDMS Mixer</td>
			<td>Thinky</td>
			<td>ARE-250</td>
			<td></td>
		</tr>
		<tr>
			<td>Oven</td>
			<td>Thermo Scientific</td>
			<td>PR305220M</td>
			<td></td>
		</tr>
		<tr>
			<td>Epi-fluorescence Microscope</td>
			<td>Nikon</td>
			<td>Eclipse Ti</td>
			<td></td>
		</tr>
		<tr>
			<td>CCD Camera</td>
			<td>Andor</td>
			<td>Clara</td>
			<td></td>
		</tr>
		<tr>
			<td>Platinum Electrodes</td>
			<td>Alfa Aesar</td>
			<td>43014</td>
			<td></td>
		</tr>
		<tr>
			<td>Source Meter</td>
			<td>Keithley</td>
			<td>2400</td>
			<td></td>
		</tr>
		<tr>
			<td>Digital Multimeter&#160;</td>
			<td>Extech</td>
			<td>410</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscopy Glass Slides</td>
			<td>Thermo Scientific</td>
			<td>2951-001</td>
			<td></td>
		</tr>
		<tr>
			<td>Tween 20</td>
			<td>Merck Millipore</td>
			<td>822184</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Fisher Scientific</td>
			<td>7646-14-5</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate monobasic</td>
			<td>Sigma Aldrich</td>
			<td>71505</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium phosphate dibasic</td>
			<td>Sigma Aldrich</td>
			<td>S3264</td>
			<td></td>
		</tr>
		<tr>
			<td>DNA</td>
			<td>IDT</td>
			<td></td>
			<td>CAA CCG ATG CCA CAT CAT TAG CTA C</td>
		</tr>
		<tr>
			<td>B-Phycoerythrin</td>
			<td>Life Technologies</td>
			<td>P-800</td>
			<td></td>
		</tr>
		<tr>
			<td>Dynamic light scattering system for Zeta Potential Measurement</td>
			<td>Malvern</td>
			<td>Zetasizer Nano S</td>
			<td></td>
		</tr>
		<tr>
			<td>Photoresist&#160;</td>
			<td>Shipley</td>
			<td>SPR700-1.0</td>
			<td></td>
		</tr>
		<tr>
			<td>Projection lithography</td>
			<td>Nikon</td>
			<td>NSR2005i9</td>
			<td></td>
		</tr>
		<tr>
			<td>Reactive Ion Etcher</td>
			<td>Applied Materials</td>
			<td>AME P5000</td>
			<td></td>
		</tr>
		<tr>
			<td>ICP deep reactive ion etcher</td>
			<td>STS</td>
			<td>STS-6&#34;</td>
			<td></td>
		</tr>
		<tr>
			<td>Contact lithography</td>
			<td>Electronic Visions</td>
			<td>EV620</td>
			<td></td>
		</tr>
		<tr>
			<td>Photoresist Coater Developer</td>
			<td>SSI</td>
			<td>SSI 150</td>
			<td></td>
		</tr>
		<tr>
			<td>Non-contact surface profiler</td>
			<td>Wyko</td>
			<td>NT 9800</td>
			<td></td>
		</tr>
	</tbody>
</table>

creating sub-50 nm nanofluidic junctions in pdms microfluidic chip via self-assembly process of colloidal particles

Polydimethylsiloxane (PDMS) is the prevailing building material to make microfluidic devices due to its ease of molding and bonding as well as its transparency. Due to the softness of the PDMS material, however, it is challenging to use PDMS for building nanochannels. The channels tend to collapse easily during plasma bonding. In this paper, we present an evaporation-driven self-assembly method of silica colloidal nanoparticles to create nanofluidic junctions with sub-50 nm pores between two microchannels. The pore size as well as the surface charge of the nanofluidic junction is tunable simply by changing the colloidal silica bead size and surface functionalization outside of the assembled microfluidic device in a vial before the self-assembly process. Using the self-assembly of nanoparticles with a bead size of 300 nm, 500 nm, and 900 nm, it was possible to fabricate a porous membrane with a pore size of ~45 nm, ~75 nm and ~135 nm, respectively. Under electrical potential, this nanoporous membrane initiated ion concentration polarization (ICP) acting as a cation-selective membrane to concentrate DNA by ~1,700 times within 15 min. This non-lithographic nanofabrication process opens up a new opportunity to build a tunable nanofluidic junction for the study of nanoscale transport processes of ions and molecules inside a PDMS microfluidic chip.

An electrokinetic concentrator chip in PDMS that contains a self-assembled nanofluidic junction between two microchannels is shown in Figure 1A). The channel in the middle of the device is filled with a DNA sample solution and flanked by two buffer solution channels on each side via a 50 &#181;m wide bead delivery channel (Figure 1B). The silica colloidal suspension is flown into the bead delivery channel immediately after plasma bonding to create a nanof...

Watch this Scientific Journal Video about Creating Sub-50 Nm Nanofluidic Junctions in PDMS Microfluidic Chip via Self-Assembly Process of Colloidal Particles at JoVE.com

Creating Sub-50 Nm Nanofluidic Junctions in PDMS Microfluidic Chip via Self-Assembly Process of Colloidal Particles

We propose a simple self-assembly technique of silica colloidal nanoparticles to create a nanofluidic junction between two microchannels in polydimethylsiloxane (PDMS). Using this technique, a nanoporous bead membrane with a pore size down to ~45 nm was built inside a microchannel and applied to electrokinetic preconcentration of DNA samples.

Polydimethylsiloxane (PDMS) is the prevailing building material to make microfluidic devices due to its ease of molding and bonding as well as its ...

Research

JoVE Journal

Engineering

Development of an Experimental Setup for the Measurement of the Coefficient of Restitution under Vacuum Conditions

The Discrete Element Method is used for the simulation of particulate systems to describe and analyze them, to predict and afterwards optimize their ...

Colloidal Synthesis of Nanopatch Antennas for Applications in Plasmonics and Nanophotonics

We present a method for colloidal synthesis of silver nanocubes and the use of these in combination with a smooth gold film, to fabricate plasmonic ...

Adsorption Device Based on a Langatate Crystal Microbalance for High Temperature High Pressure Gas Adsorption in Zeolite H-ZSM-5

We present a high-temperature and high-pressure gas adsorption measurement device based on a high-frequency oscillating microbalance (5 MHz langatate ...

Recombination Dynamics in Thin-film Photovoltaic Materials via Time-resolved Microwave Conductivity

A method for investigating recombination dynamics of photo-induced charge carriers in thin film semiconductors, specifically in photovoltaic materials ...

In Situ Visualization of the Phase Behavior of Oil Samples Under Refinery Process Conditions

In Situ Visualization of the Phase Behavior of Oil Samples Under Refinery Process Conditions

To help address production issues in refineries caused by the fouling of process units and lines, we have developed a setup as well as a method to ...

Challenges in Rheological Characterization of Highly Concentrated Suspensions &#8212; A Case Study for Screen-printing Silver Pastes

Challenges in Rheological Characterization of Highly Concentrated Suspensions ÃƒÆ’Ã‚Â¢ÃƒÂ¢Ã¢â‚¬Å¡Ã‚Â¬ÃƒÂ¢Ã¢â€šÂ¬Ã‚Â A Case Study for Screen-printing Silver Pastes

A comprehensive rheological characterization of highly concentrated suspensions or pastes is mandatory for a targeted product development meeting the ...

Fabrication of Periodic Gold Nanocup Arrays Using Colloidal Lithography

Within recent years, the field of plasmonics has exploded as researchers have demonstrated exciting applications related to chemical and optical sensing ...

Predicting Catalyst Extrudate Breakage Based on the Modulus of Rupture

The mechanical strength of extruded catalysts and their natural or forced breakage by either collision against a surface or by a compressive load in a ...

Generation of Size-controlled Poly (ethylene Glycol) Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Generation of Size-controlled Poly ethylene Glycol Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices

Uniform and size-controllable poly (ethylene glycol) diacrylate (PEGDA) droplets could be produced via the flow focusing process in a microfluidic device. ...

Combining Microfluidics and Microrheology to Determine Rheological Properties of Soft Matter during Repeated Phase Transitions

The microstructure of soft matter directly impacts macroscopic rheological properties and can be changed by factors including colloidal rearrangement ...