This work was supported by the University of Utah office of the Vice President for Research, as well as by funds in conjunction with grant P30 CA042014 awarded to the Huntsman Cancer Institute and to the CRR Program at the Huntsman Cancer Institute.

1. Fabrication of the Polydimethylsiloxane Negative
<ol>
	<li>Preparation of polydimethylsiloxane
	<ol>
		<li>Measure 18 g of PDMS silicone elastomer and 1.8 g of the curing reagent. Pour the curing reagent into a measuring boat containing the elastomer.</li>
		<li>Mix the elastomer and the curing reagent vigorously for 1 min and put the mixture into a vacuum chamber for 30 min.</li>
		<li>Remove the PDMS from the vacuum, pour 15 g onto the negative using a cookie cutter (radius = 3.8 cm) to keep the PDMS from running off the side, and cover the remaining PDMS mixture.</li>
		<li>Put the mold containing the PDMS into the vacuum chamber for 10 min.</li>
		<li>Remove the mold containing the PDMS from the vacuum chamber, place it on a hot plate set to 150 &#176;C for 60 min to cure, and cover it with aluminum foil.</li>
		<li>Pour the remaining PDMS onto an inverted glass Petri dish (10 cm in diameter), using another cookie cutter as a mold, to create a pad of PDMS. Put this into the vacuum chamber until the PDMS negative is completely cured.</li>
		<li>Transfer the Petri dish with the PDMS from the vacuum to the preheated hot plate to cure at 150 &#176;C for 60 min.</li>
	</ol>
	</li>
	<li>Plasma surface treatment of polydimethylsiloxane
	<ol>
		<li>Insert a sharp razor blade underneath the PDMS and the cookie cutter to carefully remove the PDMS from the negative.</li>
		<li>Use a sharp hobby knife to cut out the negative from the larger piece of PDMS; it should be cut with enough buffer area to attach another piece of PDMS on top of it without obstructing the negative.</li>
		<li>Insert a sharp razor blade underneath the cured PDMS with the negative to carefully remove the PDMS from the Petri dish.</li>
		<li>Use a hobby knife to cut out a piece of PDMS from the pad that is the same size as the piece cut for the negative. Then, cut a rectangle out of the new piece of PDMS with enough room to fit it around the microchannel when it is placed on top of the negative.</li>
		<li>Put both pieces of PDMS (the negative and the rectangle) onto a flat substrate (such as a slide made from glass, quartz, polystyrene, or other material) and insert them into a radio frequency (RF) plasma cleaner. Close the door and seal the chamber by evacuating the air using a vacuum pump. Inject air up to a pressure of 400 mTorr using a digital vacuum pressure controller. 
		NOTE: If the substrate used for the plasma cleaning has not been used in the plasma cleaner, put it into the plasma cleaner by itself for 60 s prior to treating the negative, in order to prevent the acrylic base layer from sticking to the substrate.</li>
		<li>Turn the RF setting to high, and a pink air plasma should appear in the viewing window. Plasma-treat the two pieces of PDMS for 30 s, then turn the RF setting off. Allow air to slowly reenter the chamber in order to prevent a turbulent air flow from disturbing the contents of the chamber.</li>
		<li>Remove the PDMS from the plasma cleaner and place it on a benchtop. Then, carefully invert the PDMS rectangle over the negative and press it down with a pair of forceps. Let it rest for 10 min to allow the two pieces of PDMS to adhere to each other.</li>
	</ol>
	</li>
	<li>Fluorosilane surface treatment of the polydimethylsiloxane negative
	<ol>
		<li>Use a dropper to put 2 drops of trichloro(1H,1H,2H,2H-perfluoro-octyl)silane (PFOTS) into a small weigh boat and insert it into a glass vacuum chamber.</li>
		<li>Invert the PDMS onto a piece of aluminum foil (so that the microchannel negative faces upward) and put it into the glass vacuum chamber. Then, evacuate the chamber continuously for 24 h.</li>
	</ol>
	</li>
</ol>
2. Fabrication of the MY133 Microchannel
<ol>
	<li>Forming the MY133-V2000 microchannel structure
	<ol>
		<li>Fill the PDMS negative with 400 &#181;L of MY133-V2000. 
		NOTE: The negative must be slightly overfilled.</li>
		<li>Place the MY133-V2000-filled PDMS negative into the vacuum chamber for 2 h to remove any bubbles.</li>
		<li>Remove MY133-V2000 from the vacuum and slowly press a glass slide against the top of the slightly overfilled negative to create a flat surface of MY133-V2000 and to prevent oxygen from inhibiting the polymerization. 
		NOTE: PDMS, at the channel surface, will partially inhibit the polymerization, enabling bonding in later stages. The glass slide has a slightly reduced UV transparency (35%) compared to quartz, which helps to prevent any yellowing of the cured device.</li>
		<li>Insert MY133-V2000 into a 400 W UV oven and set the UV radiation to 50% of the maximum intensity for 300 s&#160;to cure the MY133-V2000 microchannel. 
		NOTE: The peak wavelength used to cure the device is approximately 375 nm with a bandwidth of about 25 nm. Approximately 4,500 mJ/cm2 of power was used to cure the microchannel, which is slightly more than double the minimum curing power recommended by the manufacturer.</li>
	</ol>
	</li>
	<li>Building the acrylic holder
	<ol>
		<li>Draw the acrylic base layer using a vector drawing software. Make sure the base layer is a rectangle that is 1.5 mm thick, 75 mm long, and 25 mm wide, with a centered rectangle that measures 25 mm x 11 mm.</li>
		<li>Draw the acrylic mid-layer using a vector drawing software. Make sure the mid-layer is a rectangle (1.5 mm thick, 75 mm long, and 25 mm wide) with a centered square (5 mm x 5 mm) and two circles (both with a diameter of 3 mm) separated by 15 mm.</li>
		<li>Draw the acrylic top layer using a vector drawing software. Make sure the top layer is a rectangle (3 mm thick, 30 mm long, and 25 mm wide) with a centered square (5 mm x 5 mm) and two circles (both with a diameter of 3 mm) separated by 15 mm.</li>
		<li>Cut out the device designs created in the vector drawing software with a laser cutter. Use the sample settings of 100% power and 30% speed. Run the program twice to ensure that the acrylic is cut out.</li>
		<li>Tap the holes in the acrylic top layer using a size M5 0.80-mm tapping tool.</li>
		<li>Wipe the acrylic pieces with acetone to remove any residual marks or burns.</li>
	</ol>
	</li>
	<li>Bonding of MY133-V2000 in the acrylic holder
	<ol>
		<li>Attach the base layer of the acrylic to the glass substrate using an adhesive, such as cyanoacrylate super glue. Place two small drops on the edges of the acrylic and then use a disposable tool to evenly spread the glue. Place the glass substrate onto the acrylic and allow the glue to dry using the weight of the glass to hold it in place.</li>
		<li>Coat the exposed glass with 100 &#181;L of PDMS using a positive displacement pipette; then, insert the base layer into a vacuum spin coater and set it to 1,500 rpm for 2 min to evenly coat the glass with a PDMS film approximately 10-&#181;m thick.</li>
		<li>Remove the base layer from the spin coater and carefully wipe away any excess PDMS that coated the acrylic with acetone and paper towel. Be careful not to disturb the uncured PDMS.</li>
		<li>Bake the base layer with the PDMS in an oven at 65 &#176;C for 2 h to cure the PDMS.</li>
		<li>Pipette 1 mL of PDMS onto a glass slide and, then, use another glass slide to evenly spread the PDMS until it starts to ooze out the sides. Cure this on a hot plate at 150 &#176;C for 10 min.</li>
		<li>Cut the cured PDMS into a rectangle with the same dimensions as the MY133-V2000 device and, then, using the mid-layer of the acrylic as a mold, punch holes for the reservoir and cut a square viewing window in the PDMS to make the PDMS gasket.</li>
		<li>Place the MY133-V2000, channel side up, on the same or a similar flat substrate as used for plasma-treating the PDMS in step 1.2.5. Place the acrylic base layer containing the cured PDMS substrate alongside the MY133-V2000 channel in the O2 plasma cleaner. Set the vacuum pressure to 200 mTorr and the RF level to high and surface-treat the channel and glass substrate for 30 s.</li>
		<li>Using forceps, immediately place the MY133-V2000 channel side-down in the rectangular cutout of the base layer acrylic such that the MY133-V2000 contacts the PDMS.</li>
		<li>Place the PDMS gasket on top of the MY133-V2000 device, lining up the holes in the gasket with the reservoirs in the device.</li>
		<li>Place the unfinished device onto a raised platform above the bench to provide a clamping surface for device assembly.</li>
		<li>Extract 3 mL of acrylic cement using a syringe. Distribute enough acrylic cement on top of the base layer to provide a thin coating. Make the coat as even as possible and do not let the material seep into the channel.</li>
		<li>Place the mid-layer acrylic piece on top of the base layer acrylic. Make sure that the holes line up with the reservoirs of the MY133-V2000 channel.</li>
		<li>Use 3 small clamps to hold the base layer and mid layer together as tightly as possible for 2 min while the acrylic&#160;cement hardens, to bond the pieces of acrylic together. Ensure that the reservoirs are not obstructed during this step to prevent air from being trapped underneath the MY133-V2000 device.</li>
		<li>Remove the pressure from the device and place the acrylic cement on the mid-layer in the places of anticipated contact with the top layer of the acrylic.</li>
		<li>Place the top layer of the acrylic on the mid-layer piece of the acrylic, ensuring that the holes are aligned with the reservoirs, and allow it rest on the bench for 2 min while the acrylic cement dries.</li>
	</ol>
	</li>
</ol>
3. Testing and Use of the MY133-V2000 Device
<ol>
	<li>Leak testing
	<ol>
		<li>Test the MY133-V2000 device by adding 10 &#181;L of food dye or deionized water into one of the reservoir holes to test for the adhesion and flow.</li>
		<li>Insert a tube (with a 1/8-in outer diameter) into the reservoir and connect the other end to a vacuum trap. Turn the vacuum on to pull the dye or water through the channel to ensure that a successful device is created.</li>
		<li>Check under a microscope to verify that there are no leaks in the channel or reservoir, fill the reservoir with ethanol, and allow the ethanol to sit at room temperature for 10 min. Then, pull the ethanol through using the vacuum, to clean the dye or water out of the channel.</li>
		<li>Spray the channel with ethanol and put it into a sterile polystyrene dish. Wrap it tightly with parafilm and store it in a sterile environment until needed. 
		NOTE: At this point, the device must be handled aseptically in order to prevent contamination. When ready to use the device, the outside of the container should be sterilized using ethanol and brought into a biosafety cabinet prior to opening the container.</li>
	</ol>
	</li>
	<li>Plating MCF7 cells in the MY133-V2000 device
	<ol>
		<li>Grow MCF7 cells on 10-cm Petri dishes in a complete media consisting of Dulbecco&#39;s minimum essential medium (DMEM), supplemented with 10% fetal bovine serum, penicillin-streptomycin, glutamine, and non-essential amino acids, in a cell culture incubator that maintains a humid atmosphere containing 5% CO2 and 20% O2 at a temperature of 37 &#176;C. Grow the cells to approximately 80% confluence before seeding them in the microchannel.</li>
		<li>First, spray the polystyrene dish containing the microchannel with 70% ethanol. Then, bring it into the biosafety cabinet before removing the parafilm protecting the channel from the ambient laboratory environment.</li>
		<li>Immobilize human-plasma-derived fibronectin on the microchannel surface by diluting it in Dulbecco&#39;s phosphate-buffered saline (DPBS) to 10 &#181;g/mL. Then, inject 20 &#181;L of this solution into the channel and incubate it at 20 &#176;C for 45 min.</li>
		<li>Wash the fibronectin solution out of the channel by injecting 20 &#181;L of cell culture media into the channel, and allow it to incubate at 20 &#176;C for 10 min.</li>
		<li>Wash the cells with 10 mL of DPBS, and trypsinize the cells by adding 1 mL of 1x trypsin. Incubate the cells at 37 &#176;C for 7 min. Neutralize the trypsin with 9 mL of complete media.</li>
		<li>Inject 20 &#181;L of the cells into the channel and incubate them at 37 &#176;C for 45 - 120 min to allow the attachment to the substrate prior to imaging.</li>
	</ol>
	</li>
</ol>

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The authors have nothing to disclose.

MY133-V2000 can be used as an alternative to traditional soft lithography fabrication materials such as PDMS. Previous work has shown that materials with a high index of refraction, such as PDMS, introduce significant artifacts near the channel walls due to the mismatching indices of refraction between the fabrication material and the aqueous solution inside the channel13. MY133-V2000 enables matching the refractive index of the microfluidic device to the aqueous solutions commonly used in biomedi...

The development of microfluidic technology has enabled a wide range of new biomedical techniques that leverage the unique physics of microscopic-scale flows1,2. This includes the diagnostic techniques built on microfluidic platforms that quantify clinically relevant biomarkers, including cell stiffness3, surface markers4, and growth5. By manipulating single cells, microfluidic devices can also be used to measure biomarker heterogeneity, for example as an indicator of malignancy6. The ability to combine microfluidic applications with microscopy has further increased the utility of these platforms by allowing for devices that measure multiple biomarkers simultaneously7.
QPM is a microscopy technique that measures the phase shift as light passes through and interacts with the matter inside transparent samples. The mass of individual cells can be calculated from QPM measurements, by using the known relationship between the refractive index and the biomass density8,9. Previous work has shown that QPM is capable of measuring clinically relevant parameters such as cell growth10,11 and cell mechanical properties via disorder strength12. When combined with microfluidics, QPM can potentially be used to measure cell behavior in a highly controlled environment in vitro. One of the primary challenges facing combining QPM with microfluidics is the high refractive index of most polymers used to construct microfluidic channels via soft lithography13.
An important challenge facing the combination of microfluidics with various microscopy techniques is the mismatch between the refractive index of the device material relative to the refractive index of water14,15. One method to address this is through the use of a low refractive index polymer such as CYTOP16 or MY133-V200013. The latter is a fluorinated ultraviolet (UV)-curable acrylate polymer that has a refractive index similar to water (n = 1.33) and that is compatible with soft lithography techniques, allowing for a smooth integration into many established microfluidic device fabrication workflows. This makes MY133-V2000 not only suitable for microfluidic device fabrication, but also allows it to be readily combined with QPM and other microscopy approaches, to measure cell behavior both at the colony and on a single-cell scale. MY133-V2000 eliminates artifacts due to phase unwrapping by producing little, if any, phase shift as light passes through the water-MY133 interface.
Although eliminating the mismatch in refractive index, one major challenge associated with the devices fabricated from fluorinated polymers, such as MY133-V2000, is the low adherence to other materials such as glass or PDMS. The present work demonstrates the fabrication of an MY133-V2000 microfluidic device using soft lithography. Using O2 plasma to treat the surface of both the channel and the PDMS substrate combined with a custom-fabricated acrylic holder ensures that the device adheres to the substrate, creating a sealed channel. This device is suitable for cell culture and QPM to measure the mass of cells in the channel, which has important applications for measuring the growth of live cells and the intracellular transport of cell biomass, both of which have clinical relevance in diagnostic medicine and drug discovery.

<table border="0" cellpadding="0" cellspacing="0" style="width:828px;" width="828">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">MY133-V2000</td>
			<td style="width:183px;">MY Polymers</td>
			<td style="width:203px;">MY133-V2000</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">Sylgard 184</td>
			<td style="width:183px;">Ellsworth Adhesives</td>
			<td>184 SIL ELAST KIT 0.5KG</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">Fisher Premium microscope slides</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td>12-544-4</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">.118&#34;(3.0mm) x 12&#34; x 12&#34; Acrylic Sheet</td>
			<td>United States Plastic Corp</td>
			<td>44290</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">.060&#34;(1.5mm) x 12&#34; x 12&#34; Acrylic Sheet</td>
			<td>United States Plastic Corp</td>
			<td>44200</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">SCIGRIP 3 Very Fast Set Acrylic Cement</td>
			<td style="width:183px;">United States Plastic Corp</td>
			<td style="width:203px;">45735</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">Standard Aluminum Foil (.6 mm thick)</td>
			<td style="width:183px;">VWR</td>
			<td>89107-726</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">Kim Wipes</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td style="width:203px;">06-666</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">Insta-Cure+ Super Glue</td>
			<td style="width:183px;">Bob Smith Industries</td>
			<td style="width:203px;">BSI-109</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">1/8&#34; PVC tubing</td>
			<td style="width:183px;">McMaster Carr</td>
			<td style="width:203px;">5231K55</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">McCormick Food Coloring</td>
			<td style="width:183px;">Target</td>
			<td style="width:203px;">13353207</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">X-Acto #1 Precision Knife</td>
			<td style="width:183px;">X-Acto</td>
			<td style="width:203px;">X3201</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">X-Acto #18 Heavyweight wood chiseling blade</td>
			<td style="width:183px;">X-Acto</td>
			<td style="width:203px;">X218</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">VWR Razor Blades</td>
			<td style="width:183px;">VWR</td>
			<td style="width:203px;">55411-055</td>
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			<td height="21" style="height:21px;width:276px;">Surface Treated Cell Culture Dishes</td>
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			<td height="21" style="height:21px;width:276px;">Fibronectin Human Plasma</td>
			<td style="width:183px;">Sigma-Aldritch</td>
			<td style="width:203px;">F0895-1MG</td>
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			<td height="21" style="height:21px;width:276px;">Trypsin-EDTA 10x</td>
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			<td>15-400-054</td>
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			<td height="21" style="height:21px;width:276px;">HyClone Nonessential Amino Acids 100x</td>
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			<td style="width:203px;">SH3023801</td>
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			<td height="42" style="height:42px;width:276px;">Trichloro(1H,1H,2H,2H-perfluorooctyl)silane</td>
			<td style="width:183px;">Sigma-Aldritch</td>
			<td style="width:203px;">448931</td>
			<td>Reacts violently with water</td>
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			<td height="21" style="height:21px;width:276px;">Acetone</td>
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			<td height="21" style="height:21px;width:276px;">Epilog Fusion Laser Cutter, 120 W</td>
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			<td height="21" style="height:21px;width:276px;">Isotemp Stirring Hotplate</td>
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			<td height="21" style="height:21px;width:276px;">Ateco 14111 1.5 inch stainless steel cutter</td>
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			<td style="width:203px;">14111</td>
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			<td height="21" style="height:21px;">Pyrex Glass Cell Culture Dish</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td>08-747B</td>
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			<td height="21" style="height:21px;">Radio Frequency Plasma Cleaner</td>
			<td style="width:183px;">Harrick Plasma</td>
			<td style="width:203px;">PDC-32G</td>
			<td>Used with Oxygen gas</td>
		</tr>
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			<td height="21" style="height:21px;width:276px;">Black Hole Laboratories Digivac</td>
			<td style="width:183px;">Black Hole Laboratories</td>
			<td style="width:203px;">Model 215</td>
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		<tr height="21">
			<td height="21" style="height:21px;width:276px;">Intelli-Ray Ultraviolet Oven</td>
			<td style="width:183px;">Uvitron</td>
			<td style="width:203px;">UVO338</td>
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		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">Compact Spin Coater</td>
			<td style="width:183px;">MTI Corporation</td>
			<td style="width:203px;">VTC-100A</td>
			<td></td>
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		<tr height="21">
			<td height="21" style="height:21px;width:276px;">Fisher Brand Isotemp Oven</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td>15-103-0510</td>
			<td>Forced Air Convection</td>
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		<tr height="42">
			<td height="42" style="height:42px;width:276px;">Gilson Positive Displacement Pipette P1000</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td style="width:203px;">FD10006G</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:276px;">HeraCell VIOS 160i</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td style="width:203px;">13 998 212PM</td>
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		</tr>
	</tbody>
</table>

fabrication of refractive-index-matched devices for biomedical microfluidics

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices can be implemented as part of a robust platform capable of making simultaneous complementary measurements. The primary challenge created by the combination of these two techniques is the mismatch in refractive index between the materials traditionally used to make microfluidic devices and the aqueous solutions typically used in biomedicine. This mismatch can create optical artifacts near the channel or device edges. One solution is to reduce the refractive index of the material used to fabricate the device by using a fluorinated polymer such as MY133-V2000 whose refractive index is similar to that of water (n = 1.33). Here, the construction of a microfluidic device made out of MY133-V2000 using soft lithography techniques is demonstrated, using O2 plasma in conjunction with an acrylic holder to increase the adhesion between the MY133-V2000 fabricated device and the polydimethylsiloxane (PDMS) substrate. The device is then tested by incubating it filled with cell culture media for 24 h to demonstrate the ability of the device to maintain cell culture conditions during the course of a typical imaging experiment. Finally, quantitative phase microscopy (QPM) is used to measure the distribution of mass within the live adherent cells in the microchannel. This way, the increased precision, enabled by fabricating the device from a low index of refraction polymer such as MY133-V2000 in lieu of traditional soft lithography materials such as PDMS, is demonstrated. Overall, this approach for fabricating microfluidic devices can be readily integrated into existing soft lithography workflows in order to reduce optical artifacts and increase measurement precision.

This protocol describes the fabrication of MY133-V2000, a fluorinated polymer with a low refractive index matching that of water. A key feature of this protocol is how to overcome the lack of adhesion that is characteristic of fluorinated polymers by using oxygen plasma and by fabricating the device within an acrylic holder to provide the extra mechanical force required to seal the channel against the PDMS substrate (Figure 1). The low refractive index of the...

Watch this Scientific Journal Video about Fabrication of Refractive-index-matched Devices for Biomedical Microfluidics at JoVE.com

Fabrication of Refractive-index-matched Devices for Biomedical Microfluidics

This protocol describes the fabrication of microfluidic devices from MY133-V2000 to eliminate artifacts that often arise in microchannels due to the mismatching refractive indices between microchannel structures and an aqueous solution. This protocol uses an acrylic holder to compress the encapsulated device, improving adhesion both chemically and mechanically.

The use of microfluidic devices has emerged as a defining tool for biomedical applications. When combined with modern microscopy techniques, these devices ...

fabrication-refractive-index-matched-devices-for-biomedical

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7.4K Views.  University of Utah. This protocol describes the fabrication of microfluidic devices from MY133-V2000 to eliminate artifacts that often arise in microchannels due to the mismatching refractive indices between microchannel structures and an aqueous solution. This protocol uses an acrylic holder to compress the encapsulated device, improving adhesion both chemically and mechanically.

Video: Fabrication of Refractive-index-matched Devices for Biomedical Microfluidics

Fabrication, Operation and Flow Visualization in Surface-acoustic-wave-driven Acoustic-counterflow Microfluidics

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we present the fabrication protocol for a multilayered SAW acoustic counterflow device. The device is fabricated starting from a lithium niobate (LN) substrate onto which two interdigital transducers (IDTs) and appropriate markers are patterned. A polydimethylsiloxane (PDMS) channel cast on an SU8 master mold is finally bonded on the patterned substrate. Following the fabrication procedure, we show the techniques that allow the characterization and operation of the acoustic counterflow device in order to pump fluids through the PDMS channel grid. We finally present the procedure to visualize liquid flow in the channels. The protocol is used to show on-chip fluid pumping under different flow regimes such as laminar flow and more complicated dynamics characterized by vortices and particle accumulation domains.

In this video we first describe fabrication and operation procedures of a surface acoustic wave (SAW) acoustic counterflow device. We then demonstrate an experimental setup that allows for both qualitative flow visualization and quantitative analysis of complex flows within the SAW pumping device.

Surface acoustic waves (SAWs) can be used to drive liquids in portable microfluidic chips via the acoustic counterflow phenomenon. In this video we ...

Analysis of Contact Interfaces for Single GaN Nanowire Devices

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit a strong degradation after annealing due to the occurrence of void formation at the contact/SiO2 interface. This void formation can cause cracking and delamination of the metal film, which can increase the resistance or lead to a complete failure of the NW device. In order to address issues associated with void formation, a technique was developed that removes Ni/Au contact metal films from the substrates to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN NW devices. This procedure determines the degree of adhesion of the contact films to the substrate and NWs and allows for the characterization of the morphology and composition of the contact interface with the substrate and nanowires. This technique is also useful for assessing the amount of residual contamination that remains from the NW suspension and from photolithographic processes on the NW-SiO2 surface prior to metal deposition. The detailed steps of this procedure are presented for the removal of annealed Ni/Au contacts to Mg-doped GaN NWs on a SiO2 substrate.

A technique was developed that removes Ni/Au contact metal films from their substrate to allow for the examination and characterization of the contact/substrate and contact/NW interfaces of single GaN nanowire devices.

Single GaN nanowire (NW) devices fabricated on SiO2 can exhibit  a strong degradation after annealing due to the  occurrence of void formation at the ...

Fabrication and Testing of Microfluidic Optomechanical Oscillators

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including microresonators. However, because of the increased acoustic radiative losses during direct liquid immersion of optomechanical devices, almost all published optomechanical experiments have been performed in solid phase. This paper discusses a recently introduced hollow microfluidic optomechanical resonator. Detailed methodology is provided to fabricate these ultra-high-Q microfluidic resonators, perform optomechanical testing, and measure radiation pressure-driven breathing mode and SBS-driven whispering gallery mode parametric vibrations. By confining liquids inside the capillary resonator, high mechanical- and optical- quality factors are simultaneously maintained.

Parametric optomechanical excitations have recently been experimentally demonstrated in microfluidic optomechanical resonators by means of optical radiation pressure and stimulated Brillouin scattering. This paper describes the fabrication of these microfluidic resonators along with methodologies for generating and verifying optomechanical oscillations.

Cavity optomechanics experiments that parametrically couple the phonon modes and photon modes have been investigated in various optical systems including ...

Fabrication of Gate-tunable Graphene Devices for Scanning Tunneling Microscopy Studies with Coulomb Impurities

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees of freedom to control electronic devices. In particular, the behavior of graphene&#8217;s charge carriers in response to potentials from charged Coulomb impurities is predicted to differ significantly from that of most materials. Scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS) can provide detailed information on both the spatial and energy dependence of graphene&#39;s electronic structure in the presence of a charged impurity.&#160;The design of a hybrid impurity-graphene device, fabricated using controlled deposition of impurities onto a back-gated graphene surface, has enabled several novel methods for controllably tuning graphene&#8217;s electronic properties.1-8 Electrostatic gating enables control of the charge carrier density in graphene and the ability to reversibly tune the charge2 and/or molecular5 states of an impurity. This paper outlines the process of fabricating a gate-tunable graphene device decorated with individual Coulomb impurities for combined STM/STS studies.2-5 These studies provide valuable insights into the underlying physics, as well as signposts for designing hybrid graphene devices.

This paper details the fabrication process of a gate-tunable graphene device, decorated with Coulomb impurities for scanning tunneling microscopy studies. Mapping the spatially dependent electronic structure of graphene in the presence of charged impurities unveils the unique behavior of its relativistic charge carriers in response to a local Coulomb potential.

Owing to its relativistic low-energy charge carriers, the interaction between graphene and various impurities leads to a wealth of new physics and degrees ...

Fabrication and Operation of Acoustofluidic Devices Supporting Bulk Acoustic Standing Waves for Sheathless Focusing of Particles

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must be smaller than the incident wavelength of sound and the width of the fluidic channels are typically tens to hundreds of micrometers across, acoustofluidic devices typically use ultrasonic waves generated from a piezoelectric transducer pulsating at high frequencies (in the megahertz range). At characteristic frequencies that depend on the geometry of the device, it is possible to induce the formation of standing waves that can focus particles along desired fluidic streamlines within a bulk flow. Here, we describe a method for the fabrication of acoustophoretic devices from common materials and clean room equipment. We show representative results for the focusing of particles with positive or negative acoustic contrast factors, which move towards the pressure nodes or antinodes of the standing waves, respectively. These devices offer enormous practical utility for precisely positioning large numbers of microscopic entities (e.g., cells) in stationary or flowing fluids for applications ranging from cytometry to assembly.

Acoustofluidic devices use ultrasonic waves within microfluidic channels to manipulate, concentrate and isolate suspended micro and nanoscopic entities. This protocol describes the fabrication and operation of such a device supporting bulk acoustic standing waves to focus particles in a central streamline without the aid of sheath fluids.

Acoustophoresis refers to the displacement of suspended objects in response to directional forces from sound energy. Given that the suspended objects must ...

Fabrication of Fully Solution Processed Inorganic Nanocrystal Photovoltaic Devices

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal inks. For the photoactive absorber layer, colloidal CdTe and CdSe nanocrystals (3-5 nm) are synthesized using an inert hot injection technique and cleaned with precipitations to remove excess starting reagents. Similarly, gold nanocrystals (3-5 nm) are synthesized under ambient conditions and dissolved in organic solvents. In addition, precursor solutions for transparent conductive indium tin oxide (ITO) films are prepared from solutions of indium and tin salts paired with a reactive oxidizer. Layer-by-layer, these solutions are deposited onto a glass substrate following annealing (200-400 &#176;C) to build the nanocrystal solar cell (glass/ITO/CdSe/CdTe/Au). Pre-annealing ligand exchange is required for CdSe and CdTe nanocrystals where films are dipped in NH4Cl:methanol to replace long-chain native ligands with small inorganic Cl- anions. NH4Cl(s) was found to act as a catalyst for the sintering reaction (as a non-toxic alternative to the conventional CdCl2(s) treatment) leading to grain growth (136&#177;39 nm) during heating. The thickness and roughness of the prepared films are characterized with SEM and optical profilometry. FTIR is used to determine the degree of ligand exchange prior to sintering, and XRD is used to verify the crystallinity and phase of each material. UV/Vis spectra show high visible light transmission through the ITO layer and a red shift in the absorbance of the cadmium chalcogenide nanocrystals after thermal annealing. Current-voltage curves of completed devices are measured under simulated one sun illumination. Small differences in deposition techniques and reagents employed during ligand exchange have been shown to have a profound influence on the device properties. Here, we examine the effects of chemical (sintering and ligand exchange agents) and physical treatments (solution concentration, spray-pressure, annealing time and annealing temperature) on photovoltaic device performance.

This protocol describes the synthesis and solution deposition of inorganic nanocrystals layer by layer to produce thin film electronics on non-conductive surfaces. Solvent-stabilized inks can produce complete photovoltaic devices on glass substrates via spin and spray coating following post-deposition ligand exchange and sintering.

We demonstrate a method for the preparation of fully solution processed inorganic solar cells from a spin and spray coating deposition of nanocrystal ...

Solvent Bonding for Fabrication of PMMA and COP Microfluidic Devices

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each thermoplastic of interest. Solvent bonding is a simple and versatile method that can be used to fabricate devices from a variety of plastics. An appropriate solvent is added between two device layers to be bonded, and heat and pressure are applied to the device to facilitate the bonding. By using an appropriate combination of solvent, plastic, heat, and pressure, the device can be sealed with a high quality bond, characterized as having high bond coverage, bond strength, optical clarity, durability over time, and low deformation or damage to microfeature geometry. We describe the procedure for bonding devices made from two popular thermoplastics, poly(methyl-methacrylate) (PMMA), and cyclo-olefin polymer (COP), as well as a variety of methods to characterize the quality of the resulting bonds, and strategies to troubleshoot low quality bonds. These methods can be used to develop new solvent bonding protocols for other plastic-solvent systems.

Solvent bonding is a simple and versatile method for fabricating thermoplastic microfluidic devices with high quality bonds. We describe a protocol to achieve strong, optically clear bonds in PMMA and COP microfluidic devices that preserve microfeature details, by a judicious combination of pressure, temperature, an appropriate solvent, and device geometry.

Thermoplastic microfluidic devices offer many advantages over those made from silicone elastomers, but bonding procedures must be developed for each ...

Scanning Light Scattering Profiler (SLPS) Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light scattering from intraocular lenses (IOLs) using goniophotometer principles. This protocol describes the SLSP platform and how it employs a 360&#176; rotational photodetector sensor that is scanned around an IOL sample while recording the intensity and location of scattered light as it passes through the IOL medium. The SLSP platform can be used to predict, non-clinically, the propensity for current and novel IOL designs and materials to induce light scatter. Non-clinical evaluation of light scattering properties of IOLs can significantly reduce the number of patient complaints related to unwanted glare, glistening, optical defects, poor image quality, and other phenomena associated with the unintended light scattering. Future studies should be conducted to correlate SLSP data with clinical results to help identify which measured light scatter is most problematic for patients that have undergone cataract surgery subsequent to IOL implantation.

Scanning Light Scattering Profiler SLPS Based Methodology to Quantitatively Evaluate Forward and Backward Light Scattering from Intraocular Lenses

This protocol describes the scanning light scattering profiler (SLSP) that enables the full-angle quantitative evaluation of forward and backward scattering of light from intraocular lenses (IOLs) using goniophotometer principles.

The scanning light scattering profiler (SLSP) methodology has been developed for the full-angle quantitative evaluation of forward and backward light ...

Flow-assisted Dielectrophoresis: A Low Cost Method for the Fabrication of High Performance Solution-processable Nanowire Devices

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of nanowires. DEP is used for nanowire analysis, characterization, and for solution-based fabrication of semiconducting devices. The method works by applying an alternating electric field between metallic electrodes. The nanowire formulation is then dropped onto the electrodes which are on an inclined surface to create a flow of the formulation using gravity. The nanowires then align along the gradient of the electric field and in the direction of the liquid flow. The frequency of the field can be adjusted to select nanowires with superior conductivity and lower trap density. 
In this work, flow-assisted DEP is used to create nanowire field effect transistors. Flow-assisted DEP has several advantages: it allows selection of nanowire electrical properties; control of nanowire length; placement of nanowires in specific areas; control of orientation of nanowires; and control of nanowire density in the device. 
The technique can be expanded to many other applications such as gas sensors and microwave switches. The technique is efficient, quick, reproducible, and it uses a minimal amount of dilute solution making it ideal for the testing of novel nanomaterials. Wafer scale assembly of nanowire devices can also be achieved using this technique, allowing large numbers of samples for testing and large-area electronic applications.

In this paper, flow assisted dielectrophoresis is demonstrated for the self-assembly of nanowire devices. The fabrication of a silicon nanowire field effect transistor is shown as an example.

Flow-assisted dielectrophoresis (DEP) is an efficient self-assembly method for the controllable and reproducible positioning, alignment, and selection of ...

Atmospheric Pressure Fabrication of Large-Sized Single-Layer Rectangular SnSe Flakes

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for applications in two-dimensional nanoelectronics devices. Although many methods to synthesize SnSe nanocrystals have been developed, a simple way to fabricate large-sized single-layer SnSe flakes remains a great challenge. Herein, we show the experimental method to directly grow large-sized single-layer rectangular SnSe flakes on commonly used SiO2/Si insulating substrates using a straightforward two-step fabrication method in an atmospheric pressure quartz tube furnace system. The single-layer rectangular SnSe flakes with an average thickness of ~6.8 &#197; and lateral dimensions of about 30 &#181;m &#215; 50 &#181;m were fabricated by a combination of vapor transport deposition technique and nitrogen etching route. We characterized the morphology, microstructure, and electrical properties of the rectangular SnSe flakes and obtained excellent crystallinity and good electronic properties. This article about the two-step fabrication method can help researchers grow other similar two-dimensional, large-sized, single-layer materials using an atmospheric pressure system.

A protocol is presented demonstrating a two-step fabrication technique to grow large-sized single-layer rectangular shaped SnSe flakes on low-cost SiO2/Si dielectrics wafers in an atmospheric pressure quartz tube furnace system.

Tin selenide (SnSe) belongs to the family of layered metal chalcogenide materials with a buckled structure like phosphorene, and has shown potential for ...