Name: one-step approach to fabricating polydimethylsiloxane microfluidic channels of different geometric sections by sequential wet etching processes
Uploaded: 2018-09-13T14:00:00
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The authors gratefully acknowledge the support provided by the National Health Research Institutes (NHRI) in Taiwan under the Innovative Research Grant (IRG) (EX106-10523EI), the Taiwan Ministry of Science and Technology (MOST 104-2218-E-032-004, 104-2221-E-001-015-MY3, 105-2221-E-001-002-MY2, 105-2221-E-032-006, 106-2221-E-032-018-MY2), and the Academia Sinica Career Development Award. The authors would like to thank Heng-Hua Hsu for proofreading the manuscript.

1. Fabrication of Microfluidic Devices with Single-Layer Channel Layouts
NOTE: In this paper, the soft lithography method3 is adopted for fabricating microfluidic devices made of PDMS materials, to demonstrate how to manufacture channels with various sections.
<ol>
	<li>Creation of master molds for a PDMS layer with designed topology features
	<ol>
		<li>Design channel layouts on a PDMS layer for a single etching process or etching in sequence.</li>
	...

<ol>
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Over the past decades, microfluidics has offered promising means by which experimental platforms for chemical and biomedical research can be constructed systematically1,2,3,4,5. The platforms have also presented their capabilities of investigating several cellular functions in vivo under physiological microenvironment conditions via in vitro ...

Microfluidic techniques have drawn attention over the past decades because of their intrinsic advantages for a variety of biomedical and chemical research and applications. Several material usage options for constructing microfluidic chips are available nowadays, such as polymers, ceramics, and silicon materials. To the best of our knowledge, among the microfluidic materials, PDMS is the most common one due to its appropriate material properties for various microfluidics research and applications, including its optical and biological compatibilities with particles, fluids, and extremely small living organisms1,2,3,4,5. Furthermore, the surface chemical and structure mechanical properties of PDMS materials can be adjusted to facilitate microelectromechanical and mechanobiological studies by applying such polymer-based microfluidic devices10,11,12. Concerning the manufacturing of microfluidic devices with designed channel patterns, soft lithography replica molding methods are usually applied to create the microfluidic channels by utilizing their corresponding master molds which are composed of photolithography-patterned photoresist layers and silicon wafer substrates12. Owing to the nature of molding approaches using silicon wafers with patterned photoresist layers, the microfluidic channels commonly have regular cross sections of rectangular shapes with identical heights.
Recently, researchers have made significant progress in biomedical studies which deal with, for instance, sorting particles and cells using hydrophoresis, separating blood plasma, and enriching white blood cells by applying microfluidic chips with channels of different heights or geometric sections6,7,8,9. Such sorting and separating functions of microfluidics for biomedical applications are realized by customizing channels with different geometric sections. Several studies have been devoted to the manufacture of microfluidic channels with cross sections of different geometry features by fabricating master molds with specific surface patterns of various heights or non-rectangular cross sections. These studies on mold fabrication include such techniques as multi-step photolithography, photoresist reflow, and grey-scale lithography13,14,15. Inevitably, the existing techniques involve finely crafted photomasks or a precise alignment in multi-step manufacturing processes, which may substantially enhance the complexity levels of the corresponding fabrication of microfluidic channels. So far, several attempts have been made on single-step manufacturing processes for microfluidic channels of various sections, but the respective techniques are highly restricted to specific cross-sectional shapes of channels16.
Over the past two decades, in addition to the molding approaches for fabricating PDMS microfluidic channels with various sections, etching techniques for patterning PDMS channels with geometric features have become the fabrication of choice in a variety of microfluidic applications. For instance, PDMS wet etching is exploited along with multi-layer PDMS bonding for constructing a pneumatic actuated cell culture device of microfluidics with reconstituted organ-level lung functions17. The PDMS wet etching technique is employed together with PDMS casting on cylindrical microwells machined by computer-aided control systems for fabricating 3D PDMS microneedle arrays18. PDMS dry etching is used to make PDMS microstructures as parts of micro-electromechanical actuators19,20. Porous PDMS membranes with designed pore layouts are also fabricated through dry etching processes21. Both the wet and the dry etching techniques can be integrated into patterning PDMS films with designated geometric shapes22.
However, the etching techniques for forming PDMS channel structures with complex section shapes have not been commonly applied because of their intrinsic limitations on microfluidic fabrication. First, while the techniques of PDMS wet etching utilizing laminar flows of chemicals for creating microfluidic channels of various sections have been established, the subsequent channel section formation is still restricted because of the basic characteristics of isotropic chemical etching processes23. Furthermore, even though there seems to be reasonable space for controlling the channel section geometries in a microfluidics fabrication using the PDMS dry etching techniques20, the required etching time is usually too long (in terms of hours) to be practical for manufacturing microfluidic chips. In addition, the etching selectivity between PDMS materials and the corresponding masking photoresist layers might be low in general, and the resulted etched depths for the channels are, thus, not acceptable20.
In this paper, we develop a one-step approach to fabricate microfluidic channels of different geometric cross sections by PDMS sequential wet etching processes (hereafter referred to as SWEP). The SWEP begin with a PDMS microfluidic device with single-layer channels. With assorted layout designs of the channels, fabricating microfluidic channels with different geometric sections of various kinds can be achieved through sequential etching processes. The sequential etching only needs an etchant to be introduced into specific channels of the planned single-layer layouts embedded in PDMS materials. Compared to conventional PDMS fabrication processes, the SWEP just require one further step to fabricate microfluidic channels of non-rectangular sections or various heights. The proposed SWEP provide a straightforward and simple way of fabricating microfluidic channels with various sections along the flow direction, which can significantly simplify the processes in the aforementioned methods.

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			<td style="width:217px;">Sigma-Aldrich Co., St Louis, MO</td>
			<td style="width:135px;">F6300</td>
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			<td style="width:135px;">Ver. 1.51</td>
			<td>Imaging Processing Program&#160;</td>
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			<td style="width:217px;">Leica Microsystems, Wetzlar, Germany</td>
			<td style="width:135px;">DMI 6000 B</td>
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			<td style="width:217px;">Nordson MARCH, Concord CA</td>
			<td style="width:135px;">PX-250</td>
			<td>Oxygen plasma surface treatment</td>
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			<td style="width:217px;">Dow Corning, Midland, MI</td>
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			<td style="width:135px;">427446</td>
			<td>PE 205, 10&#39;</td>
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			<td style="width:217px;">ELS Technology, Hsinchu, Taiwan</td>
			<td style="width:135px;">ELS 306MA</td>
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			<td style="width:135px;">SU-8 2050</td>
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			<td style="width:135px;">Y020100</td>
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		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:211px;">Surgical Blade</td>
			<td style="width:217px;">Feather, Osaka, Japan</td>
			<td style="width:135px;">5005093</td>
			<td>PDMS cutting</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:211px;">Syringe Pump</td>
			<td style="width:217px;">Chemyx, Houston, TX</td>
			<td style="width:135px;">Fusion 400</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:211px;">Tetra-n-butylammonium Fluoride (TBAF)</td>
			<td style="width:217px;">Alfa Aesar, Ward Hill, MA</td>
			<td style="width:135px;">A10588</td>
			<td></td>
		</tr>
	</tbody>
</table>

one-step approach to fabricating polydimethylsiloxane microfluidic channels of different geometric sections by sequential wet etching processes

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. Customized channel layout designs are necessary for specific functions and integrated performance of microfluidic devices in numerous biomedical and chemical applications (e.g., cell culture, biosensing, chemical synthesis, and liquid handling). Owing to the nature of molding approaches using silicon wafers with photoresist layers patterned by photolithography as master molds, the microfluidic channels commonly have regular cross sections of rectangular shapes with identical heights. Typically, channels with multiple heights or different geometric sections are designed to possess particular functions and to perform in various microfluidic applications (e.g., hydrophoresis is used for sorting particles and in continuous flows for separating blood cells6,7,8,9). Therefore, a great deal of effort has been made in constructing channels with various sections through multiple-step approaches like photolithography using several photoresist layers and assembly of different PDMS thin sheets. Nevertheless, such multiple-step approaches usually involve tedious procedures and extensive instrumentation. Furthermore, the fabricated devices may not perform consistently and the resulted experimental data may be unpredictable. Here, a one-step approach is developed for the straightforward fabrication of microfluidic channels with different geometric cross sections through PDMS sequential wet etching processes, that introduces etchant into channels of planned single-layer layouts embedded in PDMS materials. Compared to the existing methods for manufacturing PDMS microfluidic channels with different geometries, the developed one-step approach can significantly simplify the process to fabricate channels with non-rectangular sections or various heights. Consequently, the technique is a way of constructing complex microfluidic channels, which provides a fabrication solution for the advancement of innovative microfluidic systems.

Recently, a large number of studies have been made on the fabrication of microfluidic devices with channels of different sections by lithography replica molding13,14,15 and PDMS etching techniques17,18,19,20,21,<sup class="x...

Watch this Scientific Journal Video about One-Step Approach to Fabricating Polydimethylsiloxane Microfluidic Channels of Different Geometric Sections by Sequential Wet Etching Processes at JoVE.com

One-Step Approach to Fabricating Polydimethylsiloxane Microfluidic Channels of Different Geometric Sections by Sequential Wet Etching Processes

Several methods are available for the fabrication of channels of non-rectangular sections embedded in polydimethylsiloxane microfluidic devices. Most of them involve multistep manufacturing and extensive alignment. In this paper, a one-step approach is reported for fabricating microfluidic channels of different geometric cross sections by polydimethylsiloxane sequential wet etching.

Polydimethylsiloxane (PDMS) materials are substantially exploited to fabricate microfluidic devices by using soft lithography replica molding techniques. ...

This method can help provide key fabrication techniques in the microfluidics field such as for the manufacturing of channels with different geometric cross sections in a polydimethylsiloxane polycarbonate microfluidic device. The main advantage of this technique is that the microfluidic channels can be fabricated through a one-step approach by sequential wet etching processes without tedious procedures and extensive alignments. The implications of this technique extend toward development of complex microfluidic systems because fabrication processes for channels with non-rectangular sections or various highs can be significantly simplified using this method.Though this method can provide insight into microfluidic device fabrication, it can also be applied to other desired microenvironment conditions such as flux distribution or mixture of substance in channels. Begin the procedure with a prepared master mold. In this case, the negative mold created with photoresist is on a four-inch silicon wafer.Here is a computer-aided design image of the inverted topology for the channel layouts. Proceed by combining PDMS and its catalyst in a clean plastic cup and mixing it in a power stirrer. When the mixture is homogenous, put the cup in a desiccator connected to a vacuum pump for 60 minutes.After retrieving the PDMS mixture, take it to the master mold. Pour 20 grams of the mixture on top of the mold. Try not to introduce any bubbles.Next, obtain a Petri dish and pour 30 grams of the PDMS mixture into it. Place the covered mold and the Petri dish in a desiccator to eliminate bubbles. After 60 minutes, transfer the covered mold and the Petri dish to a 60-degree Celsius oven to cure for four hours.Following the curing step, allow the PDMS to cool to room temperature. Then, use a scalpel and tweezers to detach the cured PDMS from the mold. Continue to taylor the PDMS layer with the scalpel so that it covers the channel layout.Use a biopsy punch to open the channel access ports. Now, work with the PDMS in the Petri dish. Use a scalpel and tweezers to remove it from the dish.Then, cut the PDMS layer to the same dimensions as the molded layer. Take the PDMS layers to a surface treatment machine. Orient the layers to expose the designed channels of one PDMS layer and the featureless surface of the other.Expose the layers to oxygen plasma for 40 seconds. When done, the two surfaces have to be bonded. Bond the two layers by placing their treated surfaces in contact.Then, place the bonded PDMS layers in a 60 degrees Celsius oven for at least 30 minutes. Prepare a microfluidic device to characterize PDMS wet etching. Use a simple design with a single layer and a straight rectangular channel.In this device, there is one waste outlet and one inlet. Note that the top and bottom PDMS layers are depicted as separated in this image. Set the device up so that it can be observed and photographed with a microscope.For the etchant solution, use TBAF and NMP in a volume to volume ratio of one to 10. Draw the etchant into a 10 milliliter syringe with a stainless steel blunt needle. Put the syringe on a syringe pump near the microscope.Then, connect it to the inlet of the device. Guide the output from the outlet to a waste container. Run the syringe pump with the etchant at a 150 microliter per minute flow rate.Use bright-field microscope views to make sure the etched channel along the flow direction has uniform width and to help confirm the flow rate and etchant composition. Capture time series images of the channel cross section with four-times magnification during the etching process for analysis. Set up a microscope to view and photograph a microfluidic device.In this case, design the device so that the etchant and buffer inlets flow into different regions. Here is a schematic of the inlets and channels of the device from above and in cross section. Over time, the different action of the etchant versus the buffer will create a new cross section, demonstrated in this schematic of the final cross section and top view photograph.Place the device on the microscope stage. Prepare an etchant solution of TBAF and NMP and an NMP buffer solution. Fill two 10-milliliter syringes with buffer solution and one with etchant.Put the syringes in position on a syringe pump near the device. Make the appropriate connections for the device, including those for waste removal. Run the syringe pump with the etchant at a 50 microliter per minute flow rate.In this video, the initial channel geometry is revealed with red dye. Over time, the etchant causes the channel wall thickness to vary. Time the wet etching process to ensure the process yields the proper channel geometry.Prepare the microscope with the syringe pump nearby. This is the design used to create PDMS channels for a microfluidic mixer with different sections. It has alternating mirrored cross sectional geometry that would be difficult to achieve with standard processes.Set up the device on the microscope and connect it with the syringe pump. Introduce the TBAF NFP etchant solution at the port marked outlet. Observe the microfluidic channel as the chamber evolves over time, as in these top view photos recorded over two hours.Time the wet etching process to ensure the proper channel geometries. When done, characterize the device. Prepare a syringe with distilled water and another with fluorescein sodium salt solution to place in the syringe pump.Place the microfluidic device on the microscope and connect to each syringe to an inlet with a 20-microliter per minute flow rate. Draw waste from the outlet. Take fluorescence microscope images of the channel from above at predetermined positions.For comparison, record images under the same circumstances with an unetched version of the microfluidic device. It is possible to fabricate microfluidic channels with various geometric cross sections with sequential wet etching. This panel summarizes the arrangement of etchant inlets in single-layer PDMS channels to produce the cross-shaped cross section demonstrated in this video.Note the etchant goes into the central channel and the buffer into the side channels. The same arrangement of channels, along with switching the channels that carry etchant and buffer, produces a dumbbell-shaped cross section. A different channel arrangement similar to the microfluidic mixer, produces a bell-shaped cross section using only etchant.While attempting this procedure, it is important to remember to with the inlets of devices to avoid etchant leakage and further induce PDMS leakage at the inlets. After watching this video, you should have a good understanding of how to perform a single-step approach to successfully fabricate PDMS microfluidic devices with different geometric cross section of channels with sequential wet etching processes.

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Research

JoVE Journal

Engineering

Fabricating Metamaterials Using the Fiber Drawing Method

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe their electromagnetic properties to the structure of their constituents, instead of the atoms that compose them. For example, sub-wavelength metal wires can be arranged to possess an effective electric permittivity that is either positive or negative at a given frequency, in contrast to the metals themselves 2. This unprecedented control over the behaviour of light can potentially lead to a number of novel devices, such as invisibility cloaks 3, negative refractive index materials 4, and lenses that resolve objects below the diffraction limit 5. However, metamaterials operating at optical, mid-infrared and terahertz frequencies are conventionally made using nano- and micro-fabrication techniques that are expensive and produce samples that are at most a few centimetres in size 6-7. Here we present a fabrication method to produce hundreds of meters of metal wire metamaterials in fiber form, which exhibit a terahertz plasmonic response 8. We combine the stack-and-draw technique used to produce microstructured polymer optical fiber 9 with the Taylor-wire process 10, using indium wires inside polymethylmethacrylate (PMMA) tubes. PMMA is chosen because it is an easy to handle, drawable dielectric with suitable optical properties in the terahertz region; indium because it has a melting temperature of 156.6 &deg;C which is appropriate for codrawing with PMMA. We include an indium wire of 1 mm diameter and 99.99% purity in a PMMA tube with 1 mm inner diameter (ID) and 12 mm outside diameter (OD) which is sealed at one end. The tube is evacuated and drawn down to an outer diameter of 1.2 mm. The resulting fiber is then cut into smaller pieces, and stacked into a larger PMMA tube. This stack is sealed at one end and fed into a furnace while being rapidly drawn, reducing the diameter of the structure by a factor of 10, and increasing the length by a factor of 100. Such fibers possess features on the micro- and nano- scale, are inherently flexible, mass-producible, and can be woven to exhibit electromagnetic properties that are not found in nature. They represent a promising platform for a number of novel devices from terahertz to optical frequencies, such as invisible fibers, woven negative refractive index cloths, and super-resolving lenses.

Metamaterials at terahertz frequencies offer unique opportunities, but are challenging to fabricate in bulk. We adapt the fabrication procedure for microstructured polymer optical fibers to inexpensively fabricate metamaterials potentially on an industrial scale. We produce polymethylmethacrylate fibers containing ~10 &mu;m diameter indium wires separated by ~100 &mu;m, which exhibit a terahertz plasmonic response.

Metamaterials are man-made composite materials, fabricated by assembling components much smaller than the wavelength at which they operate 1. They owe ...

Simulation of the Planetary Interior Differentiation Processes in the Laboratory

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to that layered structure, (1) percolation of liquid metal in a solid silicate matrix by planet differentiation, and (2) inner core crystallization by subsequent planet cooling. We conduct high-pressure and high-temperature experiments to simulate both processes in the laboratory. Formation of percolative planetary core depends on the efficiency of melt percolation, which is controlled by the dihedral (wetting) angle. The percolation simulation includes heating the sample at high pressure to a target temperature at which iron-sulfur alloy is molten while the silicate remains solid, and then determining the true dihedral angle to evaluate the style of liquid migration in a crystalline matrix by 3D visualization. The 3D volume rendering is achieved by slicing the recovered sample with a focused ion beam (FIB) and taking SEM image of each slice with a FIB/SEM crossbeam instrument. The second set of experiments is designed to understand the inner core crystallization and element distribution between the liquid outer core and solid inner core by determining the melting temperature and element partitioning at high pressure. The melting experiments are conducted in the multi-anvil apparatus up to 27 GPa and extended to higher pressure in the diamond-anvil cell with laser-heating. We have developed techniques to recover small heated samples by precision FIB milling and obtain high-resolution images of the laser-heated spot that show melting texture at high pressure. By analyzing the chemical compositions of the coexisting liquid and solid phases, we precisely determine the liquidus curve, providing necessary data to understand the inner core crystallization process.

The high-pressure and high-temperature experiments described here mimic planet interior differentiation processes. The processes are visualized and better understood by high-resolution 3D imaging and quantitative chemical analysis.

A planetary interior is under high-pressure and high-temperature conditions and it has a layered structure. There are two important processes that led to ...

Knowledge Based Cloud FE Simulation of Sheet Metal Forming Processes

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the efficiency and lowering the development time of such processes, whilst reducing costs involved in trial-and-error prototyping. Recent focus on the substitution of steel components with aluminum alloy alternatives in the automotive and aerospace sectors has increased the need to simulate the forming behavior of such alloys for ever more complex component geometries. However these alloys, and in particular their high strength variants, exhibit limited formability at room temperature, and high temperature manufacturing technologies have been developed to form them. Consequently, advanced constitutive models are required to reflect the associated temperature and strain rate effects. Simulating such behavior is computationally very expensive using conventional FE simulation techniques.
This paper presents a novel Knowledge Based Cloud FE (KBC-FE) simulation technique that combines advanced material and friction models with conventional FE simulations in an efficient manner thus enhancing the capability of commercial simulation software packages. The application of these methods is demonstrated through two example case studies, namely: the prediction of a material's forming limit under hot stamping conditions, and the tool life prediction under multi-cycle loading conditions.

The following paper presents a novel FE simulation technique (KBC-FE), which reduces computational cost by performing simulations on a cloud computing environment, through the application of individual modules. Moreover, it establishes a seamless collaborative network between world leading scientists, enabling the integration of cutting edge knowledge modules into FE simulations.

The use of Finite Element (FE) simulation software to adequately predict the outcome of sheet metal forming processes is crucial to enhancing the ...

Electrochemical Etching and Characterization of Sharp Field Emission Points for Electron Impact Ionization

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. The results of studies in which the etching current and the molarity of the NaOH solution used in the etching process were varied are presented. The investigation of the geometry of the tips, by imaging them with a scanning electron microscope, and by operating them in field emission mode is also described. The field emission tips produced are intended to be used as an electron beam source for ion production via electron impact ionization of background gas or vapor in Penning trap mass spectrometry applications.

A method for electrochemically etching field emission tips is presented. Etching parameters are characterized and the operation of the tips in field emission mode is investigated.

A new variation of the drop-off method for fabricating field emission points by electrochemically etching tungsten rods in a NaOH solution is described. ...

Wicking Tests for Unidirectional Fabrics: Measurements of Capillary Parameters to Evaluate Capillary Pressure in Liquid Composite Molding Processes

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify their influence on void formation in composite parts. Wicking in a fibrous medium described by the Washburn equation was considered equivalent to a flow under the effect of capillary pressure according to the Darcy law. Experimental tests for the characterization of wicking were conducted with both carbon and flax fiber reinforcement. Quasi-unidirectional fabrics were then tested by means of a tensiometer to determine the morphological and wetting parameters along the fiber direction. The procedure was shown to be promising when the morphology of the fabric is unchanged during capillary wicking. In the case of carbon fabrics, the capillary pressure can be calculated. Flax fibers are sensitive to moisture sorption and swell in water. This phenomenon has to be taken into account to assess the wetting parameters. In order to make fibers less sensitive to water sorption, a thermal treatment was carried out on flax reinforcements. This treatment enhances fiber morphological stability and prevents swelling in water. It was shown that treated fabrics have a linear wicking trend similar to those found in carbon fabrics, allowing for the determination of capillary pressure.

An experimental method to measure geometrical parameters and the apparent advancing contact angles describing capillary wicking in unidirectional synthetic and natural fabrics is proposed. These parameters are mandatory for the determination of the capillary pressures that must be taken into account for liquid composite molding (LCM) applications.

During impregnation of a fibrous reinforcement in liquid composite molding (LCM) processes, capillary effects have to be understood in order to identify ...

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 ...

Nerve Stem Cell Differentiation by a One-step Cold Atmospheric Plasma Treatment In Vitro

As the development of physical plasma technology, cold atmospheric plasmas (CAPs) have been widely investigated in decontamination, cancer treatment, wound healing, root canal treatment, etc., forming a new research field named plasma medicine. Being a mixture of electrical, chemical, and biological reactive species, CAPs have shown their abilities to enhance nerve stem cells differentiation both in vitro and in vivo and are becoming a promising way for neurological disease treatment in the future. The much more exciting news is that using CAPs may realize one-step, and safely directed, differentiation of neural stem cells (NSCs) for tissue transportation. We demonstrate here the detailed experimental protocol of using a self-made CAP jet device to enhance NSC differentiation in C17.2-NSCs and primary rat neural stem cells, as well as observing the cell fate by inverted and fluorescence microscopy. With the help of immunofluorescence staining technology, we found both the NSCs showed an accelerated differential rate than the untreated group, and ~75% of the NSCs selectively differentiated into neurons, which are mainly mature, cholinergic, and motor neurons.

Nerve Stem Cell Differentiation by a One-step Cold Atmospheric Plasma Treatment In Vitro

This protocol aims to provide detailed experimental steps of a cold atmospheric plasma treatment on neural stem cells and immunofluorescence detection for differentiation enhancement.

As the development of physical plasma technology, cold atmospheric plasmas (CAPs) have been widely investigated in decontamination, cancer treatment, ...

Drawing and Hydrophobicity-patterning Long Polydimethylsiloxane Silicone Filaments

Polydimethylsiloxane (PDMS) silicone is a versatile polymer that cannot readily be formed into long filaments. Traditional spinning methods fail because PDMS does not exhibit long-range fluidity at melting. We introduce an improved method to produce filaments of PDMS by a stepped temperature profile of the polymer as it cross-links from a fluid to an elastomer. By monitoring its warm-temperature viscosity, we estimate a window of time when its material properties are amendable to drawing into long filaments. The filaments pass through a high-temperature tube oven, curing them sufficiently to be harvested. These filaments are on the order of hundreds of micrometers in diameter and tens of centimeters in length, and even longer and thinner filaments are possible. These filaments retain many of the material properties of bulk PDMS, including switchable hydrophobicity. We demonstrate this capability with an automated corona-discharge patterning method. These patternable PDMS silicone filaments have applications in silicone weavings, gas-permeable sensor components, and model microscale foldamers.

Here, we present a protocol to produce long filaments of polydimethylsiloxane (PDMS) silicone by gravity-drawing through a furnace. Filaments are on the order of hundreds of micrometers in diameter and tens of centimeters in length and are hydrophobically patternable via an Arduino-controlled corona discharge system.

Polydimethylsiloxane (PDMS) silicone is a versatile polymer that cannot readily be formed into long filaments. Traditional spinning methods fail because ...

Fabricating van der Waals Heterostructures with Precise Rotational Alignment

In this work we describe a technique for creating new crystals (van der Waals heterostructures) by stacking distinct ultrathin layered 2D materials. We demonstrate not only lateral control but, importantly, also control over the angular alignment of adjacent layers. The core of the technique is represented by a home-built transfer setup which allows the user to control the position of the individual crystals involved in the transfer. This is achieved with sub-micrometer (translational) and sub-degree (angular) precision. Prior to stacking them together, the isolated crystals are individually manipulated by custom-designed moving stages that are controlled by a programmed software interface. Moreover, since the entire transfer setup is computer controlled, the user can remotely create precise heterostructures without coming into direct contact with the transfer setup, labeling this technique as &#8220;hands-free&#8221;. In addition to presenting the transfer set-up, we also describe two techniques for preparing the crystals that are subsequently stacked.

In this work we describe a technique that is used to create new crystals (van der Waals heterostructures) by stacking ultrathin layered 2D materials with precise control over position and relative orientation.

In this work we describe a technique for creating new crystals (van der Waals heterostructures) by stacking distinct ultrathin layered 2D materials. We ...

Aesthetically Enhanced Silica Aerogel Via Incorporation of Laser Etching and Dyes

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

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

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