This work was supported by the Shenzhen fundamental research funding (Grant No. JCYJ 20150630170146829, JCYJ20160531195439665 and JCYJ20160317152359560). The authors would like to thank Prof. Y. Chen at the Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences for supports.

1. Mold Fabrication
<ol>
	<li>Design two photomasks using a drawing software. Describe the outline of microchannel structure and use two separate layers for mask 1 and 2 in the same drawing file, so ensure all connections between different channels. Print different layers independently to chrome plate on the glass by a vendor with 1 &#181;m resolution. Ensure that the photomasks are dark with transparent designed structures, as a negative polarity. 
	Note: The mask 1 contains the dispersed phase inlet channel and an orifice. The mask 2 contains the continuous phase inlet channel, the filter, and the outlet.</li>
	<li>In designated photolithography lab, clean a 3-inch diameter silicon wafer. Place the wafer on a spin coater, turn on the vacuum to affix the wafer to the spin chuck. Spin-coat 2-3 mL of SU-8 2025 negative photoresist onto the wafer for 10 s at 1,000 rpm, then 30 s at 3,000 rpm, providing the first layer thickness of 20 &#181;m.</li>
	<li>Soft bake on a 95 &#176;C hotplate for 6 min. After the coated wafer cools to room temperature (RT), expose it via the mask 1 under a collimated 15 mW/cm2, 365 nm of UV for 18 s. Post-exposure, bake on a 95 &#176;C&#160;hotplate for 6 min, then allow the wafer to cool to RT.</li>
	<li>Repeat the spin-coating process. Apply 2-3 mL of SU-8 2100 negative photoresist onto the wafer for 10 s at 1,000 rpm, then 30 s at 2,000 rpm, providing the second layer thickness of 130 &#181;m. After soft bake on a 95 &#176;C&#160;hotplate for 35 min, place the mask 2 on the second layer photoresist to expose for 30 s, which was aligned with the dispersed phase channel layer by a UV aligner. Post-exposure, bake on a 95 &#176;C&#160;hotplate for 7 min.</li>
	<li>Develop the wafer by immersing in a stirred bath of 50 mL of propylene glycol methyl ether acetate until features become clear on the wafer, then wash it with ethyl alcohol. Finally, place the wafer on the thermostatic platform for hard-baking for 2 h.</li>
</ol>
2. Semi-3D Flow-focusing Microfluidic Chip Fabrication
<ol>
	<li>Mix PDMS monomer and its curing agent in a slightly different weight ratio for the top and the bottom layers, typically 10:1 for the top layer, and 8:1 for the bottom layer, using automatic ointment agitator for 4 min. 
	Note: The top and bottom PDMS slabs are prepared in a slightly different ratio (10:1 and 8:1 respectively) of PDMS base to curing agent, enhancing the bonding strength. When 5:1 ratio is chosen for the bottom layer, the stiffer bottom PDMS slab makes alignment difficult and reduces bonding strength due to lack of flexibility. In addition, the thickness of the bottom PDMS slab is about 1 mm for adapting the working distance of microscope. The chip easily deforms under high pressure when 15:1 ratio is chosen.</li>
	<li>Pour the mixture into the completed silicon mold in a 90-mm petri dish and provide a thickness of 2~3 mm. Place it in a vacuum chamber and degas until all air bubbles disappear. Cure at 80 &#176;C&#160;for 1 h in an oven.</li>
	<li>Allow the PDMS to cool to RT. Use a scalpel to cut the device at least 3 mm away from the features and slowly peel off the PDMS layer from the silicon wafer. Punch the dispersed phase inlet, the continuous phase inlet and the outlet in the top PDMS layer using a 0.75 mm diameter punch.</li>
	<li>Clean the PDMS with adhesive tape to remove dust particles. Plasma treat both the top and bottom PDMS layers simultaneously for 2 min in a 300 W plasma cleaner. Place the top layer on the bottom layer surface and slide the surfaces relatively until features are aligned viewing through a stereo microscope.</li>
	<li>Cure the device in an oven at 120 &#176;C&#160;for one day to enhance the strength and complete bonding.</li>
</ol>
3. Reagents Preparation
<ol>
	<li>Prepare the solution ofthe continuous phase: Hexadecane by dissolving 18 vol% silicone-based nonionic surfactant.</li>
	<li>Prepare the solution of the dispersed phase: hydrophilic poly (ethylene glycol) diacrylate (PEGDA, MW 255,) containing 2-hydroxy-4&#39;-(2-hydroxyethoxy)-2-methylpropiophenone (98%, MW 224) at a concentration of 5 mg/mL as the photo-initiator, and rhodamine B (95%, MW 479.01) at a concentration of 1 mmol/L as the fluorescent dyes.</li>
	<li>Fill the 1 mL reservoirs of pneumatic pressure controller with the continuous phase. Fill the 200 &#181;L gel loading tip with the dispersed phase.</li>
</ol>
4. System Preparation
<ol>
	<li>Place the semi-3D microfluidic device on the stage of an inverted optical microscope, viewing with a high-speed camera.</li>
	<li>Connect the fluorinated ethylene propylene (FEP) tube to the punched hole of the continuous phase by attaching a short stainless-steel tube, then insert the end of a gel loading tip into the punched hole of the dispersed phase. Insert a 20-cm length of FEP tube into the outlet in the device and place the end in a 15-mL centrifuge tube. 
	Note: The configuration of the system is illustrated in Figure 1.</li>
</ol>
5. Droplets Formation
<ol>
	<li>Place the device on the workbench of an inverted microscope, and ensure that the junction of different channels is roughly located in the position of the light source of the microscope. Focus the inverted microscope on a region that contains two-phases intersection, the orifice region, and the downstream channel.</li>
	<li>Set pressures of two phases using pneumatic pressure controller to deliver fluid slowly to the intersecting region, with 15 mbar for the dispersed phase and 30 mbar for the continuous phase. Wait 3 min for stabilization and equilibration until stable fluid flow carrying no bubbles and PDMS residue.</li>
	<li>Input the parameters on the user interface of the control software. Set the pressure of the dispersed phase as the base-level pressure of the system to a constant, for example, maintain it at 45 mbar. Increase the pressure of continuous phase until the emulsion breakup mode is changed from the jetting to the tip-streaming mode, then wait 5 min for stabilization.</li>
	<li>Place the FEP tube end connecting the outlet hole to the centrifuge tube to collect the droplets.</li>
</ol>
6. PEGDA Particles Collection and Characterization
<ol>
	<li>Fix the centrifuge tube aslant in the fixture. Obtain the PEGDA particles through the rapid solidification by UV exposure when liquid phase flow to the tube.</li>
	<li>When finishing the collecting process, sample and observe the PEGDA particles through the fluorescent microscope with 20X or 60X objects respectively. 
	Note.The digital fluorescent images captured by the camera are analyzed by a custom-made software routine. The image is first deconvolution based on the R-L algorithm17&#160;to eliminate the blurring effect of out-of-focusing light, and the sphere objects in the image are extracted based on the Canny edge detection method; finally, the diameter of each sphere object can be calculated using Hough transformation18. As a result, mean and standard deviation of the diameters of sphere objects in each image can be estimated.</li>
</ol>

<ol>
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The authors have nothing to disclose.

The generation of droplets in the flow-focusing mode using 2D and semi-3D microfluidic device has previously been developed in a variety of reports8,9,15,19,20,21. In these systems, the aqueous liquid that could not be solidified was chosen as the dispersed phase, such as deionized water8,<s...

Droplet-based microfluidic systems have the ability to produce highly monodisperse droplets from nanometer to micrometer diameter range1 and hold great potential in the high-throughput drug discovery2, synthesis of biomolecules3,4, and the diagnostic testing5. Due to the unique advantages of smaller droplets, such as the greater surface area to volume ratio and the large-scale applications with consuming a few microliters of sample, the technology has attracted extensive interest in a broad range of fields. The emulsification of two immiscible liquids is one of the most typical methods to generate droplet. In previous reports in the field, researchers have developed a variety of different droplet formation geometries, including T-junction, flow-focusing and co-flowing geometries. In the T-junction geometry, the dispersed phase is delivered through a perpendicular channel into the main channel, in which the continuous phase flows6,7. In the typical two-dimensional (2D) flow-focusing8,9&#160;geometry, the dispersed phase flow is sheared from the lateral; and for the co-flowing geometry10,11, on the other hand, a capillary introducing the dispersed phase flow is placed co-axially inside a bigger capillary for co-flowing geometry, so that the dispersed phase flow is sheared from all directions.
The droplet size is controlled by adjusting channel size and flow rate ratio, and the minimum size produced by co-flowing or T-junction is limited to dozens of micrometers. For flow-focusing droplet formation system, three modes of droplet breakup form by adjusting the pressure ratio of two-phase and surfactant concentration, including the dripping regime, the jetting regime, and tip-streaming15. Tip-streaming mode is also called thread formation, and the appearance of a thin the thread drawing out from the tip of dispersed phase flow cone will be observed.Previous studies have demonstrated droplets less than a few micrometers could be generated though tip-streaming process in 2D or semi-3D flow-focusing device8,12. However, as an aqueous solution containing a very low concentration of PEGDA was used as the dispersed phase, the shrinkage ratio of PEGDA particles was about 60% of the original droplets in diameter after photo-polymerization, while PEGDA without dilution as the dispersed phase led to unstable tip-streaming mode12. Interfacial tension is an important parameter of emulsion process and it will decrease due to the addition of the surfactant into the continuous phase liquid,leading to decrease in droplet size, higher generation frequency13, highly curved tip, and preventing instability14. Furthermore, when the bulk surfactant concentration is much higher than the critical micelle concentration, the interfacial tension is approximately invariable in the saturated state13 and the tip-streaming mode can occur15.
Based on the above observations, in this paper, we developed a facile approach for PEGDA droplets generation using a semi-3D flow-focusing microfluidic device, fabricated by multi-layer soft lithography method. Different from the typical 2D flow-focusing device, the semi-3D flow-focusing device has a shallow dispersed phase channel and a deep continuous phase channel, so that the dispersed phase can be sheared from up and down beside lateral. This provides larger adjusting range for flow-focusing mode by reducing the energy and pressure required for droplet breakup. Different from the previous report12, the dispersed phase is pure PEGDAcontaining photo-initiator, making sure that the shrinkage ratio of PEGDA particles is lower than 10%16; and the continuous phase is the mixture of hexadecane dissolving with a high bulk concentration of the silicone-based nonionic surfactant. Size-controllable and uniform droplets were produced by adjusting the pressure ratio of two phases. The diameter of the droplets changes from 80 &#181;m to 1 &#181;m as the droplet breakup processes changes from the jetting mode to tip-streaming mode. In addition, the PEGDA particle was synthesized through photo-polymerization process under UV exposure. The droplet generation microfluidic system with ease of fabrication will provide more possibilities for biological applications.

<table border="0" cellpadding="0" cellspacing="0" style="width:572px;" width="573">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="37">
			<td height="37" style="height:37px;width:216px;">Silicon wafer</td>
			<td style="width:71px;">Huashi Co., Ltd</td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="37">
			<td height="37" style="height:37px;width:216px;">SU-8 2025, 2100</td>
			<td style="width:71px;">Microchem Co.</td>
			<td style="width:119px;">Y111069</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="37">
			<td height="37" style="height:37px;width:216px;">SU-8 developer</td>
			<td style="width:71px;">Microchem Co.</td>
			<td style="width:119px;">Y020100</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="91">
			<td height="91" style="height:91px;width:216px;">Chromium mask</td>
			<td style="width:71px;">Qingyi Precision Mask Making Co., Ltd</td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="37">
			<td height="37" style="height:37px;width:216px;">polydimethylsiloxane(PDMS)</td>
			<td style="width:71px;">Dow Corning</td>
			<td style="width:119px;">Sylgard 184</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="37">
			<td height="37" style="height:37px;width:216px;">poly(ethylene glycol) diacrylate (PEGDA)</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">26570-48-9</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="37">
			<td height="37" style="height:37px;width:216px;">2-hydroxy-40-(2-hydroxyethoxy)-2-methylpropiophenone</td>
			<td style="width:71px;">TCI</td>
			<td style="width:119px;">H1361-5G</td>
			<td style="width:167px;">photoinitiator</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Hexadecane</td>
			<td style="width:71px;">Sigma</td>
			<td style="width:119px;">544-76- 3</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">ABIL EM 90</td>
			<td style="width:71px;">CHT</td>
			<td style="width:119px;">144243-53-8</td>
			<td style="width:167px;">surfactants</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Rhodamine B</td>
			<td style="width:71px;">Aladdin</td>
			<td style="width:119px;">81-88-9</td>
			<td style="width:167px;">fluorescent dye</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Spin Coater</td>
			<td style="width:71px;"></td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Lithography machine</td>
			<td style="width:71px;"></td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Automatic ointment agitator</td>
			<td style="width:71px;">Thinky</td>
			<td style="width:119px;">ARV-310</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Oven</td>
			<td style="width:71px;">BluePard</td>
			<td style="width:119px;"></td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:216px;">Optical microscope</td>
			<td style="width:71px;">OLYMPUS</td>
			<td style="width:119px;">IX71</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="37">
			<td height="37" style="height:37px;width:216px;">High-speed camera</td>
			<td style="width:71px;">Hamamatsu, Japan</td>
			<td style="width:119px;">ORCA-flash</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="37">
			<td height="37" style="height:37px;width:216px;">MAESFLO Microfluidic Fluid Control System</td>
			<td style="width:71px;">FLUIGENT</td>
			<td style="width:119px;">MFCS-EZ</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="41">
			<td height="41" style="height:41px;width:216px;">UV lamp</td>
			<td style="width:71px;">FUTANSI</td>
			<td style="width:119px;"></td>
			<td style="width:167px;">365 nm UV light, 8000 MW/CM2</td>
		</tr>
	</tbody>
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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. This paper proposes a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation. The polydimethylsiloxane (PDMS) chip was fabricated using the multi-layer soft lithography method. Hexadecane containing surfactant was used as the continuous phase, and PEGDA with the ultraviolet (UV) photo-initiator was the dispersed phase. Surfactants allowed the local surface tension to drop and formed a more cusped tip which promoted breaking into tiny micro-droplets. As the pressure of dispersed phase was constant, the size of droplets became smaller with increasing continuous phase pressure before dispersed phase flow was broken off. As a result, droplets with size variation from 1 &#181;m to 80 &#181;m in diameter could be selectively achieved by changing the pressure ratio in two inlet channels, and the average coefficient of variation was estimated to be below 7%. Furthermore, droplets could turn into micro-beads by UV exposure for photo-polymerization. Conjugating biomolecules on such micro-beads surface have many potential applications in the fields of biology and chemistry.

The semi-3D flow-focusing microfluidic chip was fabricated using multi-layer soft lithography techniques as described above. The fabrication process and results for master mold in the protocolare shown in Figure 2. The first layer, which provides a 65 &#181;m wide channel for introducing the dispersed phase and a 50 &#181;m wide orifice (Figure 2a), is 20 &#181;m in thickness. An addition 130 &#181;m thickness la...

Watch this Scientific Journal Video about Generation of Size-controlled Poly ethylene Glycol Diacrylate Droplets via Semi-3-Dimensional Flow Focusing Microfluidic Devices at JoVE.com

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

Here, we present a protocol to illustrate the fabrication processes and verifying experiments of a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation.

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. ...

generation-size-controlled-poly-ethylene-glycol-diacrylate-droplets

Research

JoVE Journal

Engineering

7.7K Views.  Tsinghua University. Here, we present a protocol to illustrate the fabrication processes and verifying experiments of a semi-three-dimensional (semi-3D) flow-focusing microfluidic chip for droplet formation.

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

Determining 3D Flow Fields via Multi-camera Light Field Imaging

In the field of fluid mechanics, the resolution of computational schemes has outpaced experimental methods and widened the gap between predicted and observed phenomena in fluid flows. Thus, a need exists for an accessible method capable of resolving three-dimensional (3D) data sets for a range of problems. We present a novel technique for performing quantitative 3D imaging of many types of flow fields. The 3D technique enables investigation of complicated velocity fields and bubbly flows. Measurements of these types present a variety of challenges to the instrument. For instance, optically dense bubbly multiphase flows cannot be readily imaged by traditional, non-invasive flow measurement techniques due to the bubbles occluding optical access to the interior regions of the volume of interest. By using Light Field Imaging we are able to reparameterize images captured by an array of cameras to reconstruct a 3D volumetric map for every time instance, despite partial occlusions in the volume. The technique makes use of an algorithm known as synthetic aperture (SA) refocusing, whereby a 3D focal stack is generated by combining images from several cameras post-capture 1. Light Field Imaging allows for the capture of angular as well as spatial information about the light rays, and hence enables 3D scene reconstruction. Quantitative information can then be extracted from the 3D reconstructions using a variety of processing algorithms. In particular, we have developed measurement methods based on Light Field Imaging for performing 3D particle image velocimetry (PIV), extracting bubbles in a 3D field and tracking the boundary of a flickering flame. We present the fundamentals of the Light Field Imaging methodology in the context of our setup for performing 3DPIV of the airflow passing over a set of synthetic vocal folds, and show representative results from application of the technique to a bubble-entraining plunging jet.

A technique for performing quantitative three-dimensional (3D) imaging for a range of fluid flows is presented. Using concepts from the area of Light Field Imaging, we reconstruct 3D volumes from arrays of images. Our 3D results span a broad range including velocity fields and multi-phase bubble size distributions.

In the field of fluid mechanics, the resolution of computational schemes has outpaced experimental methods and widened the gap between predicted and ...

Thermal Measurement Techniques in Analytical Microfluidic Devices

Thermal measurement techniques have been used for many applications such as thermal characterization of materials and chemical reaction detection. Micromachining techniques allow reduction of the thermal mass of fabricated structures and introduce the possibility to perform high sensitivity thermal measurements in the micro-scale and nano-scale devices. Combining thermal measurement techniques with microfluidic devices allows performing different analytical measurements with low sample consumption and reduced measurement time by integrating the miniaturized system on a single chip. The procedures of thermal measurement techniques for particle detection, material characterization, and chemical detection are introduced in this paper.

Here, we present three protocols for thermal measurements in microfluidic devices.

Thermal measurement techniques have been used for many applications such as thermal characterization of materials and chemical reaction detection. ...

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 ...

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.

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 ...

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 ...

Microfluidic Imaging Flow Cytometry by Asymmetric-detection Time-stretch Optical Microscopy (ATOM)

Scaling the number of measurable parameters, which allows for multidimensional data analysis and thus higher-confidence statistical results, has been the main trend in the advanced development of flow cytometry. Notably, adding high-resolution imaging capabilities allows for the complex morphological analysis of cellular/sub-cellular structures. This is not possible with standard flow cytometers. However, it is valuable for advancing our knowledge of cellular functions and can benefit life science research, clinical diagnostics, and environmental monitoring. Incorporating imaging capabilities into flow cytometry compromises the assay throughput, primarily due to the limitations on speed and sensitivity in the camera technologies. To overcome this speed or throughput challenge facing imaging flow cytometry while preserving the image quality, asymmetric-detection time-stretch optical microscopy (ATOM) has been demonstrated to enable high-contrast, single-cell imaging with sub-cellular resolution, at an imaging throughput as high as 100,000 cells/s. Based on the imaging concept of conventional time-stretch imaging, which relies on all-optical image encoding and retrieval through the use of ultrafast broadband laser pulses, ATOM further advances imaging performance by enhancing the image contrast of unlabeled/unstained cells. This is achieved by accessing the phase-gradient information of the cells, which is spectrally encoded into single-shot broadband pulses. Hence, ATOM is particularly advantageous in high-throughput measurements of single-cell morphology and texture &#8211; information indicative of cell types, states, and even functions. Ultimately, this could become a powerful imaging flow cytometry platform for the biophysical phenotyping of cells, complementing the current state-of-the-art biochemical-marker-based cellular assay. This work describes a protocol to establish the key modules of an ATOM system (from optical frontend to data processing and visualization backend), as well as the workflow of imaging flow cytometry based on ATOM, using human cells and micro-algae as the examples.

Microfluidic Imaging Flow Cytometry by Asymmetric-detection Time-stretch Optical Microscopy ATOM

This protocol describes the implementation of an asymmetric-detection time-stretch optical microscopy system for single-cell imaging in ultrafast microfluidic flow and its applications in imaging flow cytometry.

Scaling the number of measurable parameters, which allows for multidimensional data analysis and thus higher-confidence statistical results, has been the ...

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 ...

Experimental Investigation of the Flow Structure over a Delta Wing Via Flow Visualization Methods

It is well known that the flow field over a delta wing is dominated by a pair of counter rotating leading edge vortices (LEV). However, their mechanism is not well understood. The flow visualization technique is a promising non-intrusive method to illustrate the complex flow field spatially and temporally. A basic flow visualization setup consists of a high-powered laser and optic lenses to generate the laser sheet, a camera, a tracer particle generator, and a data processor. The wind tunnel setup, the specifications of devices involved, and the corresponding parameter settings are dependent on the flow features to be obtained.
Normal smoke wire flow visualization uses a smoke wire to demonstrate the flow streaklines. However, the performance of this method is limited by poor spatial resolution when it is conducted in a complex flow field. Therefore, an improved smoke flow visualization technique has been developed. This technique illustrates the large-scale global LEV flow field and the small-scale shear layer flow structure at the same time, providing a valuable reference for later detailed particle image velocimetry (PIV) measurement.
In this paper, the application of the improved smoke flow visualization and PIV measurement to study the unsteady flow phenomena over a delta wing is demonstrated. The procedure and cautions for conducting the experiment are listed, including wind tunnel setup, data acquisition, and data processing. The representative results show that these two flow visualization methods are effective techniques for investigating the three-dimensional flow field qualitatively and quantitatively.

Here, we present a protocol to observe unsteady vortical flows over a delta wing using a modified smoke flow visualization technique and investigate the mechanism responsible for the oscillations of the leading-edge vortex breakdown locations.

It is well known that the flow field over a delta wing is dominated by a pair of counter rotating leading edge vortices (LEV). However, their mechanism is ...

Safe Experimentation in Optical Levitation of Charged Droplets Using Remote Labs

The work presents an experiment that allows the study of many fundamental physical processes, such as photon pressure, diffraction of light or the motion of charged particles in electrical fields. In this experiment, a focused laser beam pointing upwards levitate liquid droplets. The droplets are levitated by the photon pressure of the focused laser beam which balances the gravitational force. The diffraction pattern created when illuminated with laser light can help measure the size of a trapped droplet. The charge of the trapped droplet can be determined by studying its motion when a vertically directed electrical field is applied. There are several reasons motivating this experiment to be remotely controlled. The investments required for the setup exceeds the amount normally available in undergraduate teaching laboratories. The experiment requires a laser of Class 4, which is harmful to both skin and eyes and the experiment uses voltages that are harmful.

Optical levitation is a method for levitating micrometer-sized dielectric objects using laser light. Utilizing computers and automation systems, an experiment on optical levitation can be controlled remotely. Here, we present a remotely controlled optical levitation system that is used both for educational and research purposes.

The work presents an experiment that allows the study of many fundamental physical processes, such as photon pressure, diffraction of light or the motion ...