Name: imaging the root hair morphology of arabidopsis seedlings in a two-layer microfluidic platform
Uploaded: 2017-08-15T13:00:00
Description: Watch this Scientific Journal Video about Imaging the Root Hair Morphology of Arabidopsis Seedlings in a Two-layer Microfluidic Platform at JoVE.com

This manuscript has been authored by UT-Battelle, LLC under Contract No. DE-AC05-00OR22725 with the U.S. Department of Energy. The United States Government retains and the publisher, by accepting the article for publication, acknowledges that the United States Government retains a non-exclusive, paid-up, irrevocable, world-wide license to publish or reproduce the published form of this manuscript, or allow others to do so, for United States Government purposes. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan (http://energy.gov/downloads/doe-public-access-plan).
This work was supported in part by the Genomic Science Program, U.S. Department of Energy, Office of Science, Biological and Environmental Research, as part of the Plant Microbe Interfaces Scientific Focus Area (http://pmi.ornl.gov). The fabrication of the microfluidic platforms was carried out in the Nanofabrication Research Laboratory at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility. JAA is supported by an NSF graduate research fellowship DGE -1452154

1. Two-layer Platform Fabrication
<ol>
	<li>Fabrication of multilayer masters
	<ol>
		<li>Spin coat epoxy-based negative photoresist (~63.45% solids, 1,250 cSt) according to the manufacturer&#39;s specifications (2,000 rpm for 45 s) onto a 4 inch diameter silicon wafer to obtain the desired height of 20 &#181;m for the first design layer.</li>
		<li>Soft-bake the resist coated wafers for 4 min at 95 &#176;C. Allow wafer to cool for 5 min. Expose the wafer to UV light for 15 s (~150 mJ/cm2 at...

<ol>
	<li>Pritchard, S. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Soil+organisms+and+global+climate+change.">Soil organisms and global climate change.</a> Plant Pathol. 60 (1), 82-99 (2011).</li><li>Norby, R. J., Ledford, J., Reilly, C. D., Miller, N. E., O'Neill, E. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fine-root+production+dominates+response+of+a+deciduous+forest+to+atmospheric+CO2+enrichment.">Fine-root production dominates response of a deciduous forest to atmospheric CO2 enrichment.</a> Proc. Natll. Acad. Sci. USA. 101 (26), 9689-9693 (2004).</li><li>McCormack, M. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Redefining+fine+roots+improves+understanding+of+below-ground+contributions+to+terrestrial+biosphere+processes.">Redefining fine roots improves understanding of below-ground contributions to terrestrial biosphere processes.</a> New Phytol. 207 (3), 505-518 (2015).</li><li>Mangano, S., Juarez, S. P. D., Estevez, J. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=ROS+regulation+of+polar-growth+in+plant+cells.">ROS regulation of polar-growth in plant cells.</a> Plant Physiol. 171 (3), 1593-1605 (2016).</li><li>Ketelaar, T., Emons, A. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Actin+Cytoskeleton+in+Root+Hairs:+A+Cell+Elongation+Device.">The Actin Cytoskeleton in Root Hairs: A Cell Elongation Device.</a> Root Hairs. , 211-232 (2009).</li><li>Grossmann, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+RootChip:+an+integrated+microfluidic+chip+for+plant+science.">The RootChip: an integrated microfluidic chip for plant science.</a> Plant Cell. 23 (12), 4234-4240 (2011).</li><li>Grossmann, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Time-lapse+fluorescence+imaging+of+Arabidopsis+root+growth+with+rapid+manipulation+of+the+root+environment+using+the+RootChip.">Time-lapse fluorescence imaging of Arabidopsis root growth with rapid manipulation of the root environment using the RootChip.</a> J. Vis. Exp. (65), (2012).</li><li>Jiang, H., Xu, Z., Aluru, M. R., Dong, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant+chip+for+high-throughput+phenotyping+of+Arabidopsis.">Plant chip for high-throughput phenotyping of Arabidopsis.</a> Lab Chip. 14 (7), 1281 (2014).</li><li>Busch, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+microfluidic+device+and+computational+platform+for+high-throughput+live+imaging+of+gene+expression.">A microfluidic device and computational platform for high-throughput live imaging of gene expression.</a> Nat. Methods. 9 (11), (2012).</li><li>Meier, M., Lucchettta, E., Ismagilov, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chemical+Stimulation+of+the+Arabidopsis+thaliana+Root+using+Multi-Laminar+Flow+on+a+Microfluidic+Chip.">Chemical Stimulation of the Arabidopsis thaliana Root using Multi-Laminar Flow on a Microfluidic Chip.</a> Lab Chip. 10 (16), 2147-2153 (2010).</li><li>Ozoe, K., Hida, H., Kanno, I., Higashiyama, T., Notaguchi, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Early+characterization+method+of+plant+root+adaptability+to+soil+environments.">Early characterization method of plant root adaptability to soil environments.</a> Proc. of 28th IEEE Interntl. Conf. Micro. Electro Mech. Syst. , (2015).</li><li>Sanati Nezhad, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+platforms+for+plant+cells+studies.">Microfluidic platforms for plant cells studies.</a> Lab on a chip. , 3262-3274 (2014).</li><li>Parashar, A., Pandey, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Plant-in-chip:+Microfluidic+system+for+studying+root+growth+and+pathogenic+interactions+in+Arabidopsis.">Plant-in-chip: Microfluidic system for studying root growth and pathogenic interactions in Arabidopsis.</a> App. Phys. Lett. 98 (26), 2009-2012 (2011).</li><li>Rigas, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Root+gravitropism+and+root+hair+development+constitute+coupled+developmental+responses+regulated+by+auxin+homeostasis+in+the+Arabidopsis+root+apex.">Root gravitropism and root hair development constitute coupled developmental responses regulated by auxin homeostasis in the Arabidopsis root apex.</a> New Phytolol. 197 (4), 1130-1141 (2013).</li><li>Bengough, A. G., McKenzie, B. M., Hallett, P. D., Valentine, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Root+elongation,+water+stress,+and+mechanical+impedance:+A+review+of+limiting+stresses+and+beneficial+root+tip+traits.">Root elongation, water stress, and mechanical impedance: A review of limiting stresses and beneficial root tip traits.</a> J. Exp. Bot. 62 (1), 59-68 (2011).</li><li>Sia, S. K., Whitesides, G. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+devices+fabricated+in+poly(dimethylsiloxane)+for+biological+studies.">Microfluidic devices fabricated in poly(dimethylsiloxane) for biological studies.</a> Electrophor. 24 (21), 3563-3576 (2003).</li><li>Millet, L. J., Stewart, M. E., Sweedler, J. V., Nuzzo, R. G., Gillette, M. U. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+devices+for+culturing+primary+mammalian+neurons+at+low+densities.">Microfluidic devices for culturing primary mammalian neurons at low densities.</a> Lab chip. 7 (8), 987-994 (2007).</li><li>Nelson, B. K., Cai, X., Nebenf&#252;hr, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+multicolored+set+of+in+vivo+organelle+markers+for+co-localization+studies+in+Arabidopsis+and+other+plants.">A multicolored set of in vivo organelle markers for co-localization studies in Arabidopsis and other plants.</a> Plant J. 51 (6), 1126-1136 (2007).</li><li>Talbot, M. J., White, R. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cell+surface+and+cell+outline+imaging+in+plant+tissues+using+the+backscattered+electron+detector+in+a+variable+pressure+scanning+electron+microscope.">Cell surface and cell outline imaging in plant tissues using the backscattered electron detector in a variable pressure scanning electron microscope.</a> Plant Methods. 9 (1), 40 (2013).</li></ol>

The method described in this article for creating a plant-on-a-chip platform is unique in that the two-layer design confines the root hairs to a single imaging plane and the platform may be deconstructed and used as a substrate for high resolution non-optical imaging. Using high-resolution non-optical imaging can provide valuable information about the plant tissue that could not be obtained from optical imaging alone. For example, AFM imaging can provide force measurements to calculate the elasticity of root tissues duri...

Fine root features increase water and nutrient acquisition for the plant, exploring new soil spaces and increasing the total root surface area. The turnover of these fine root features plays a major role in stimulating the underground food chain1 and the number of fine roots in certain plant species is expected to double under elevated atmospheric carbon dioxide2. Fine roots are generally defined as those smaller than 2 mm in diameter, although new definitions advocate for characterizing fine roots by their function3. Like many fine roots, root hairs provide the function of uptake and absorption but occupy a much smaller space with diameters on the order of microns. Because of their small size, root hairs are difficult to image in situ and are often overlooked as a part of the overall root architecture in field scale experiments and models.
Ex terra root hair studies, such as from seedlings grown on agar plates, have provided the scientific community with valuable information on cellular growth and transport4,5. While agar plates allow root systems to be imaged non-destructively and in real time, they do not offer high environmental control for the addition of experimental treatments such as nutrients, plant hormones, or bacteria. An emerging solution to facilitating high resolution imaging while also affording dynamic environmental control has been the advent of microfluidic platforms for plant studies. These platforms have enabled the non-destructive growth and visualization of several plant species for high throughput phenotyping6,7,8,9, isolated chemical treatments10, force measurements11,12, and the addition of microorganisms13. Microfluidic platform designs have focused on the use of single open space fluidic layers in which the roots may propagate, permitting the root hairs to drift in and out of optical focus during growth or treatment.
Here we present a procedure for developing a two-layer microfluidic platform using photo and soft-lithography methods that builds upon previous plant-on-a-chip designs by confining the seedling root hairs to the same imaging plane as the main root. This allows us to track root hair development in real time, at high resolution, and throughout the experimental treatment process. Our culturing methods allow Arabidopsis thaliana seedlings to be germinated from seed within the platform and cultured for up to a week in a hydrated and sterile environment that does not require the use of syringe pump equipment. Once the time-lapse imaging experiment has concluded, the platform presented here can be opened without disturbing the position of the finer root features. This allows the use of other high resolution imaging methods. Here we provide representative results for the quantification and visualization of root hair morphology in this platform by optical, scanning electron microscopy (SEM), and atomic force microscopy techniques (AFM).

<table width="810">
	<tbody>
		<tr height="72">
			<td height="72" style="width:209px;height:72px;">Silicon Wafer</td>
			<td style="width:191px;">WRS Materials</td>
			<td style="width:283px;">100mm diameter, 500-550um thickness, Prime, 10-20 resistivity, N/Phos&#60;100&#62;</td>
			<td style="width:128px;"></td>
		</tr>
		<tr height="32">
			<td height="32" style="width:209px;height:32px;">Quintel Contact Aligner</td>
			<td style="width:191px;">Neutronix Quintel Corp</td>
			<td style="width:283px;">NXQ 7500 Mask Aligner</td>
			<td style="width:128px;"></td>
		</tr>
		<tr height="32">
			<td height="32" style="width:209px;height:32px;">Fluorescent Microscope</td>
			<td style="width:191px;">Nikon</td>
			<td style="width:283px;">Eclipse Ti-U</td>
			<td style="width:128px;"></td>
		</tr>
		<tr height="30">
			<td height="30" style="width:209px;height:30px;">laboratory tissue</td>
			<td style="width:191px;">Kimberly Clark</td>
			<td>Kimwipe KIMTECH SCIENCE Brand, 34155</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Negative Photoresist Epoxy</td>
			<td style="width:191px;">Microchem</td>
			<td style="width:283px;">SU-8 2000s series</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Photoresist developer</td>
			<td style="width:191px;">Microchem</td>
			<td style="width:283px;">Su-8 developer</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="width:209px;height:42px;">trichloro(1H,1H,2H,2H-perfluoro-octyl)silane</td>
			<td style="width:191px;">Sigma Aldrich</td>
			<td></td>
			<td>use in chemical hood</td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Air Plasma Cleaner</td>
			<td style="width:191px;">Harrick Plasma</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">PDMS</td>
			<td style="width:191px;">Dow Corning</td>
			<td>Sylgard 184 Silicone elastomer base</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">PDMS curing agent</td>
			<td style="width:191px;">Dow Corning</td>
			<td>Sylgard 184 Silicone elastomer curing agent</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Dessicator</td>
			<td style="width:191px;">Bel-Art</td>
			<td>F42010-000</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Scalpel</td>
			<td style="width:191px;">X-acto knife</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Biopsy Punch</td>
			<td style="width:191px;">Ted Pella</td>
			<td>15110-15</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Adhesive tape</td>
			<td style="width:191px;">Staples</td>
			<td>Invisible Tape</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Microfuge tube</td>
			<td style="width:191px;">Eppendorf</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Triton X</td>
			<td style="width:191px;">J.T.Baker XI98-07</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Bleach</td>
			<td style="width:191px;">Chlorox</td>
			<td>concentrated</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="width:209px;height:42px;">Plant-Based Media</td>
			<td style="width:191px;">Phyto Technology Laboratories</td>
			<td>M524</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Agar</td>
			<td style="width:191px;">Teknova</td>
			<td>A7777</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Wax film</td>
			<td style="width:191px;">Parafilm</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">microscope</td>
			<td style="width:191px;">Olympus</td>
			<td>IX51</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Atomic Force Microscope</td>
			<td style="width:191px;">Keysight Technologies</td>
			<td>5500 PicoPlus AFM</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Petri dish</td>
			<td style="width:191px;">VWR</td>
			<td></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="width:209px;height:21px;">Scanning Electron Microscope</td>
			<td>JEOL</td>
			<td>7400</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="width:209px;height:42px;">Dual Gun Electron Beam Evaporator</td>
			<td>Thermionics</td>
			<td>Custom Dual Electron Gun Evaporation System</td>
			<td></td>
		</tr>
	</tbody>
</table>

imaging the root hair morphology of arabidopsis seedlings in a two-layer microfluidic platform

Root hairs increase root surface area for better water uptake and nutrient absorption by the plant. Because they are small in size and often obscured by their natural environment, root hair morphology and function are difficult to study and often excluded from plant research. In recent years, microfluidic platforms have offered a way to visualize root systems at high resolution without disturbing the roots during transfer to an imaging system. The microfluidic platform presented here builds on previous plant-on-a-chip research by incorporating a two-layer device to confine the Arabidopsis thaliana main root to the same optical plane as the root hairs. This design enables the quantification of root hairs on a cellular and organelle level and also prevents z-axis drifting during the addition of experimental treatments. We describe how to store the devices in a contained and hydrated environment, without the need for fluidic pumps, while maintaining a gnotobiotic environment for the seedling. After the optical imaging experiment, the device may be disassembled and used as a substrate for atomic force or scanning electron microscopy while keeping fine root structures intact.

The two-layer PDMS microfluidic devices described here have a 200 &#181;m high channel for the main Arabidopsis root and a 20 &#181;m high chamber to confine laterally growing root hairs (Figure 1A). This design may be used for plant species with similar root diameters as Arabidopsis thaliana and can be readily modified to accommodate species of different sizes. The design incorporates an inlet for the plant as well as 8 side inlets...

Watch this Scientific Journal Video about Imaging the Root Hair Morphology of Arabidopsis Seedlings in a Two-layer Microfluidic Platform at JoVE.com

Imaging the Root Hair Morphology of Arabidopsis Seedlings in a Two-layer Microfluidic Platform

This article demonstrates how to culture Arabidopsis thaliana seedlings in a two-layer microfluidic platform that confines the main root and root hairs to a single optical plane. This platform can be used for real-time optical imaging of fine root morphology as well as for high-resolution imaging by other means.

Imaging the Root Hair Morphology of Arabidopsis Seedlings in a Two-layer Microfluidic Platform

Root hairs increase root surface area for better water uptake and nutrient absorption by the plant. Because they are small in size and often obscured by ...

The overall goal of this microfluidic spaced culturing method, is to grow plants directly from seed in a structured environment that can also be used for controlled treatment and high resolution imaging of the seedlings'roots. This method can help answer key questions in the plant biology field such as, how plant root growth responds to physical and chemical cues at multiple length scales. The main advantage of this platform is that the repairs are confined to a single plain, making it impossible to treat and image them without losing optical focus.Assisting me today will be Dr.Sahar Hasim, she's a research associate professor at the University of Tennessee. To begin, pour a 10:1 ratio of PDMS to curing agent onto a pre-fabricated and selenised master wafer. Degas the PDMS in a vacuum chamber and then, cure the polymer in an oven at 70 degrees celsius for one hour.Next, use a scalpel to cut the PDMS devices and peel them from the master. Then, use a 1.5 milliliter biopsy to punch the seed inlet at a 45 degree angle, to encourage root growth into the main channel. Also, use the same punch to clear the treatment inlets.Use adhesive tape to remove any debris from the device and place it design side down on a glass cover slide. Once assembled, autoclave the devices. Place the Arabidopsis thaliana seeds in a microfuge tube and add a mixture of bleach and detergent to sterilize the seeds.Then, wash the seeds four times with sterile water. Next, stratify the seeds by refrigerating them in the microfuge tube overnight or store them for up to one week at four degrees celsius. Prior to using the sterile devices, place them into a vacuum degassing chamber, to remove air from the gas permeable PDMS and fluidic channels.This will improve the subsequent filling of the devices. Remove the devices from the vacuum chamber and immediately submerge them in a petri dish filled with liquid one quarter strength plant based media, at a pH of 5.7. Using a pipette, pull liquid through the inlets to fill the device.Make sure no air bubbles remain within channels by visually inspecting them before transferring them to individual fresh, dry petri dishes. Next, pour hot agar around the device until the agar level is almost flush with the top of the device. In a sterile environment, use a small pipette and transfer one sterilized seed to the inlet of each device.Then, cover each petri dish with wax film and place them in a light dark cycling growth chamber at room temperature. Orient the petri dish in the growth chamber at room temperature, vertically, so gravity will encourage the roots to grow through the channel. At the desired time and the seedling's development, use a pipette to add a prescribed amount of the experimental treatment to each of the eight side ports on the devices.When finished, reseal the petri dishes with wax film. Then, return them to the growth chamber. Adjust the magnification of an inverted bright field microscope, at between 4x and 20x magnification.Place the entire petri dish containing the device and seedling under the microscope for bright field or differential interference contrast imaging. Optimize the lighting conditions by adjusting exposure times, lamp brightness, aperture and the polarity of the light to elucidate the morphological features that are of interest. Then, drive the stage to the desired area of the root and focus on the root or root hair of interest.Acquire a single time point or a time series of images to visualize the growth of root hairs. For the time series, image the growing root hairs once per minute. To visualize the growth of the main root, acquire one image every 30 minutes.When finished, return the petri dish and the seedlings to growth chamber, in a vertical position. Once the seedling has grown for the desired time, use a pair of forceps to remove the cover slip and the device from the agar. Then, wet a laboratory tissue with ethanol and use it to clean off the bottom of the cover slip.Apply the proper oil to a 63x oil immersion objective and place the cover slip down on the microscope stage. Then, raise the stage to contact the immersion media on the objective. Optimize the lighting conditions, by adjusting exposure times, lamp brightness, aperture and the polarity of the light.Then, drive the stage to the desired area of the root and focus on the root hairs of interest. To quantify root hair growth over time, set up the software to acquire one image per minute, at the location of interest. In order to visualize plant auto fluorescence or fluorescence markers, minimize the fluorescence exposure time, while still retaining an identifiable fluorescent signal.Acquire images of the organelles as quickly as the exposure time will allow. Once the seedling has grown for the desired amount of time, remove the device and cover slip from the petri dish. Turn the device upside down and gently peel away the cover slip so that the root stays within the PDMS channel.Place the PDMS device on a flat reflective substrate, such as, microcoated in gold, and then, mount the device on the AFM specimen holder, root side up. After securing a liquid well attachment on top of the PDMS device, fill it with water to keep the roots hydrated during imaging. Once the specimen has been loaded into the AFM, adjust the z control for the thickness of the PDMS device and drive the cantilever to the region of interest on the root.Using a camera for guidance, align the laser with the tip of the cantilever and use contact mode imaging to exert minimal force on the root during scanning. Slowly lower the scanning mechanism until the cantilever just makes contact with the sample. Then, adjust the scan size for the desired region and choose a scan speed of one line per second with 256 voltage points per line.Finally, acquire the scan. The two layer PDMS microfluidic devices described here, have a 200 micrometer high center channel for the main Arabidopsis root and two 20 micrometer high side chambers, to confine the laterally growing root hairs. This ensures that the root hairs are on the same imaging plane, as the main root.Within the microfluidic platform, root hairs can be quantified on a cellular level, in terms of their length, density and the angularity of their growth from the root. One of the strongest advantages of using a microfluidic platform, is the ability to uniformly add precise concentrations of chemical treatments to the organisms. Here, a seedling is imaged before and after the addition of fluorescent carboxylated polystyrene beads.The addition of this abiotic treatment, did not disrupt the orientation of optical focus of the seedlings'root hairs. Using fluorescent markers, cytoplasmic streaming can be seen in a root hair. The movement of these three organelles are captured in this cumulative distribution plot.In addition to optical imaging, this platform also allows for AFM and SEM imaging, due to its ability to be disassembled, without disturbing the root. Following this procedure, other methods including chemical imaging, can be performed in order to answer additional questions like what do chemical profiles around the root look like.

imaging-root-hair-morphology-arabidopsis-seedlings-two-layer

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JoVE Journal

Bioengineering

High-throughput Protein Expression Generator Using a Microfluidic Platform

Rapidly increasing fields, such as systems biology, require the development and implementation of new technologies, enabling high-throughput and high-fidelity measurements of large systems. Microfluidics promises to fulfill many of these requirements, such as performing high-throughput screening experiments on-chip, encompassing biochemical, biophysical, and cell-based assays1. Since the early days of microfluidics devices, this field has drastically evolved, leading to the development of microfluidic large-scale integration2,3. This technology allows for the integration of thousands of micromechanical valves on a single device with a postage-sized footprint (Figure 1). We have developed a high-throughput microfluidic platform for generating in vitro expression of protein arrays (Figure 2) named PING (Protein Interaction Network Generator). These arrays can serve as a template for many experiments such as protein-protein 4, protein-RNA5 or protein-DNA6 interactions.
The device consist of thousands of reaction chambers, which are individually programmed using a microarrayer. Aligning of these printed microarrays to microfluidics devices programs each chamber with a single spot eliminating potential contamination or cross-reactivity Moreover, generating microarrays using standard microarray spotting techniques is also very modular, allowing for the arraying of proteins7, DNA8, small molecules, and even colloidal suspensions. The potential impact of microfluidics on biological sciences is significant. A number of microfluidics based assays have already provided novel insights into the structure and function of biological systems, and the field of microfluidics will continue to impact biology.

We present a microfluidic approach for the expression of protein arrays. The device consists of thousands of reaction chambers controlled by micro-mechanical valves. The microfluidic device is mated to a microarray-printed gene library. These genes are then transcribed and translated on-chip, resulting in a protein array ready for experimental use.

Rapidly increasing fields, such as systems biology, require the development and implementation of new technologies, enabling high-throughput and ...

Time-lapse Fluorescence Imaging of Arabidopsis Root Growth with Rapid Manipulation of The Root Environment Using The RootChip

The root functions as the physical anchor of the plant and is the organ responsible for uptake of water and mineral nutrients such as nitrogen, phosphorus, sulfate and trace elements that plants acquire from the soil. If we want to develop sustainable approaches to producing high crop yield, we need to better understand how the root develops, takes up a wide spectrum of nutrients, and interacts with symbiotic and pathogenic organisms. To accomplish these goals, we need to be able to explore roots in microscopic detail over time periods ranging from minutes to days.
We developed the RootChip, a polydimethylsiloxane (PDMS)- based microfluidic device, which allows us to grow and image roots from Arabidopsis seedlings while avoiding any physical stress to roots during preparation for imaging1 (Figure 1). The device contains a bifurcated channel structure featuring micromechanical valves to guide the fluid flow from solution inlets to each of the eight observation chambers2. This perfusion system allows the root microenvironment to be controlled and modified with precision and speed. The volume of the chambers is approximately 400 nl, thus requiring only minimal amounts of test solution.
Here we provide a detailed protocol for studying root biology on the RootChip using imaging-based approaches with real time resolution. Roots can be analyzed over several days using time lapse microscopy. Roots can be perfused with nutrient solutions or inhibitors, and up to eight seedlings can be analyzed in parallel. This system has the potential for a wide range of applications, including analysis of root growth in the presence or absence of chemicals, fluorescence-based analysis of gene expression, and the analysis of biosensors, e.g. FRET nanosensors3.

This article provides a protocol for cultivation of Arabidopsis seedlings in the RootChip, a microfluidic imaging platform that combines automated control of growth conditions with microscopic root monitoring and FRET-based measurement of intracellular metabolite levels.

The root functions as the physical anchor of the plant and is the organ responsible for uptake of water and mineral nutrients such as nitrogen, ...

Cell Squeezing as a Robust, Microfluidic Intracellular Delivery Platform

Rapid mechanical deformation of cells has emerged as a promising, vector-free method for intracellular delivery of macromolecules and nanomaterials. This technology has shown potential in addressing previously challenging applications; including, delivery to primary immune cells, cell reprogramming, carbon nanotube, and quantum dot delivery. This vector-free microfluidic platform relies on mechanical disruption of the cell membrane to facilitate cytosolic delivery of the target material. Herein, we describe the detailed method of use for these microfluidic devices including, device assembly, cell preparation, and system operation. This delivery approach requires a brief optimization of device type and operating conditions for previously unreported applications. The provided instructions are generalizable to most cell types and delivery materials as this system does not require specialized buffers or chemical modification/conjugation steps. This work also provides recommendations on how to improve device performance and trouble-shoot potential issues related to clogging, low delivery efficiencies, and cell viability.

Rapid mechanical deformation of cells has emerged as a promising, vector-free method for intracellular delivery of macromolecules and nanomaterials. This protocol provides detailed steps on how to use the system for a broad range of applications.

Rapid mechanical deformation of cells has emerged as a promising, vector-free method for intracellular delivery of macromolecules and nanomaterials. This ...

Microfluidic Platform for Measuring Neutrophil Chemotaxis from Unprocessed Whole Blood

Neutrophils play an essential role in protection against infections and their numbers in the blood are frequently measured in the clinic. Higher neutrophil counts in the blood are usually an indicator of ongoing infections, while low neutrophil counts are a warning sign for higher risks for infections. To accomplish their functions, neutrophils also have to be able to move effectively from the blood where they spend most of their life, into tissues, where infections occur. Consequently, any defects in the ability of neutrophils to migrate can increase the risks for infections, even when neutrophils are present in appropriate numbers in the blood. However, measuring neutrophil migration ability in the clinic is a challenging task, which is time consuming, requires large volume of blood, and expert knowledge. To address these limitations, we designed a robust microfluidic assays for neutrophil migration, which requires a single droplet of unprocessed blood, circumvents the need for neutrophil separation, and is easy to quantify on a simple microscope. In this assay, neutrophils migrate directly from the blood droplet, through small channels, towards the source of chemoattractant. To prevent the granular flow of red blood cells through the same channels, we implemented mechanical filters with right angle turns that selectively block the advance of red blood cells. We validated the assay by comparing neutrophil migration from blood droplets collected from finger prick and venous blood. We also compared these whole blood (WB) sources with neutrophil migration from samples of purified neutrophils and found consistent speed and directionality between the three sources. This microfluidic platform will enable the study of human neutrophil migration in the clinic and the research setting to help advance our understanding of neutrophil functions in health and disease.

This protocol details an assay designed to measure human neutrophil chemotaxis from one droplet of whole blood with robust reproducibility. This approach circumvents the need for neutrophil separation and requires only a few minutes of assay preparation time. The microfluidic chip enables the repeated measure of neutrophil chemotaxis over time in infants or small mammals, where sample volume is limited.

Neutrophils play an essential role in protection against infections and their numbers in the blood are frequently measured in the clinic. Higher ...

The Multi-organ Chip - A Microfluidic Platform for Long-term Multi-tissue Coculture

The ever growing amount of new substances released onto the market and the limited predictability of current in vitro test systems has led to a high need for new solutions for substance testing. Many drugs that have been removed from the market due to drug-induced liver injury released their toxic potential only after several doses of chronic testing in humans. However, a controlled microenvironment is pivotal for long-term multiple dosing experiments,&#160;as even minor alterations in extracellular conditions may greatly influence the cell physiology. We focused within our research program on the generation of a microengineered bioreactor, which can be dynamically perfused by an on-chip pump and combines at least two culture spaces for multi-organ applications. This circulatory system mimics the in vivo conditions of primary cell cultures better and assures a steadier,&#160;more quantifiable extracellular relay of signals to the cells. 
For demonstration purposes, human liver equivalents, generated by aggregating differentiated HepaRG cells with human hepatic stellate cells in hanging drop plates, were cocultured with human skin punch biopsies for up to 28 days inside the microbioreactor. The use of cell culture inserts enables the skin to be cultured at an air-liquid interface, allowing topical substance exposure. The microbioreactor system is capable of supporting these cocultures at near physiologic fluid flow and volume-to-liquid ratios, ensuring stable and organotypic culture conditions. The possibility of long-term cultures enables the repeated exposure to substances. Furthermore, a vascularization of the microfluidic channel circuit using human dermal microvascular endothelial cells yields a physiologically more relevant vascular model.

Here, we present a protocol to coculture primary cells, tissue models and punch biopsies in a microfluidic multi-organ chip for up to 28 days. Human dermal microvascular endothelial cells, liver aggregates and skin biopsies were successfully combined in a common media circulation.

The ever growing amount of new substances released onto the market and the limited predictability of current in vitro test systems has led to a high need ...

Electrotaxis Studies of Lung Cancer Cells using a Multichannel Dual-electric-field Microfluidic Chip

The behavior of directional cell migration under a direct current electric-field (dcEF) is referred to as electrotaxis. The significant role of physiological dcEF in guiding cell movement during embryo development, cell differentiation, and wound healing has been demonstrated in many studies. By applying microfluidic chips to an electrotaxis assay, the investigation process is shortened and experimental errors are minimized. In recent years, microfluidic devices made of polymeric substances (e.g., polymethylmethacrylate, PMMA, or acrylic) or polydimethylsiloxane (PDMS) have been widely used in studying the responses of cells to electrical stimulation. However, unlike the numerous steps required to fabricate a PDMS device, the simple and rapid construction of the acrylic micro&#64258;uidic chip makes it suitable for both device prototyping and production. Yet none of the reported devices facilitate the efficient study of the simultaneous chemical and dcEF effects on cells. In this report, we describe our design and fabrication of an acrylic-based multichannel dual-electric-field (MDF) chip to investigate the concurrent effect of chemical and electrical stimulation on lung cancer cells. The MDF chip provides eight combinations of electrical/chemical stimulations in a single test. The chip not only greatly shortens the required experimental time but also increases accuracy in electrotaxis studies.

Many microfluidic devices have been developed for use in the study of electrotaxis. Yet, none of these chips allows the efficient study of the simultaneous chemical and electric-field (EF) effects on cells. We developed a polymethylmethacrylate-based device that offers better-controlled coexisting EF and chemical stimulation for use in electrotaxis research.

The behavior of directional cell migration under a direct current electric-field (dcEF) is referred to as electrotaxis. The significant role of ...

A Microfluidic Platform for High-throughput Single-cell Isolation and Culture

Studying the heterogeneity of single cells is crucial for many biological questions, but is technically difficult. Thus, there is a need for a simple, yet high-throughput, method to perform single-cell culture experiments. Here, we report a microfluidic chip-based strategy for high-efficiency single-cell isolation (~77%) and demonstrate its capability of performing long-term single-cell culture (up to 7 d) and cellular heterogeneity analysis using clonogenic assay. These applications were demonstrated with KT98 mouse neural stem cells, and A549 and MDA-MB-435 human cancer cells. High single-cell isolation efficiency and long-term culture capability are achieved by using different sizes of microwells on the top and bottom of the microfluidic channel. The small microwell array is designed for precisely isolating single-cells, and the large microwell array is used for single-cell clonal culture in the microfluidic chip. This microfluidic platform constitutes an attractive approach for single-cell culture applications, due to its flexibility of adjustable cell culture spaces for different culture strategies, without decreasing isolation efficiency.

Here, we present a protocol for isolating and culturing single cells with a microfluidic platform, which utilizes a new microwell design concept to allow for high-efficiency single cell isolation and long-term clonal culture.

Studying the heterogeneity of single cells is crucial for many biological questions, but is technically difficult. Thus, there is a need for a simple, yet ...

Microfluidic Platform with Multiplexed Electronic Detection for Spatial Tracking of Particles

Microfluidic processing of biological samples typically involves differential manipulations of suspended particles under various force fields in order to spatially fractionate the sample based on a biological property of interest. For the resultant spatial distribution to be used as the assay readout, microfluidic devices are often subjected to microscopic analysis requiring complex instrumentation with higher cost and reduced portability. To address this limitation, we have developed an integrated electronic sensing technology for multiplexed detection of particles at different locations on a microfluidic chip. Our technology, called Microfluidic CODES, combines Resistive Pulse Sensing with Code Division Multiple Access to compress 2D spatial information into a 1D electrical signal. In this paper, we present a practical demonstration of the Microfluidic CODES technology to detect and size cultured cancer cells distributed over multiple microfluidic channels. As validated by the high-speed microscopy, our technology can accurately analyze dense cell populations all electronically without the need for an external instrument. As such, the Microfluidic CODES can potentially enable low-cost integrated lab-on-a-chip devices that are well suited for the point-of-care testing of biological samples.

We demonstrate a microfluidic platform with an integrated surface electrode network that combines resistive pulse sensing (RPS) with code division multiple access (CDMA), to multiplex detection and sizing of particles in multiple microfluidic channels.

Microfluidic processing of biological samples typically involves differential manipulations of suspended particles under various force fields in order to ...

A Microfluidic Platform for Longitudinal Imaging in Caenorhabditis elegans

In the last decade, microfluidic techniques have been applied to study small animals, including the nematode Caenorhabditis elegans, and have proved useful as a convenient live imaging platform providing capabilities for precise control of experimental conditions in real time. In this article, we demonstrate live imaging of individual worms employing WormSpa, a previously-published custom microfluidic device. In the device, multiple worms are individually confined to separate chambers, allowing multiplexed longitudinal surveillance of various biological processes. To illustrate the capability, we performed proof-of-principle experiments in which worms were infected in the device with pathogenic bacteria, and the dynamics of expression of immune response genes and egg laying were monitored continuously in individual animals. The simple design and operation of this device make it suitable for users with no previous experience with microfluidic-based experiments. We propose that this approach will be useful for many researchers interested in longitudinal observations of biological processes under well-defined conditions.

A Microfluidic Platform for Longitudinal Imaging in Caenorhabditis elegans

In this article, we demonstrate live imaging of individual worms employing a custom microfluidic device. In the device, multiple worms are individually confined to separate chambers, allowing multiplexed longitudinal surveillance of various biological processes.

In the last decade, microfluidic techniques have been applied to study small animals, including the nematode Caenorhabditis elegans, and have proved ...

An Ultrahigh-throughput Microfluidic Platform for Single-cell Genome Sequencing

Sequencing technologies have undergone a paradigm shift from bulk to single-cell resolution in response to an evolving understanding of the role of cellular heterogeneity in biological systems. However, single-cell sequencing of large populations has been hampered by limitations in processing genomes for sequencing. In this paper, we describe a method for single-cell genome sequencing (SiC-seq) which uses droplet microfluidics to isolate, amplify, and barcode the genomes of single cells. Cell encapsulation in microgels allows the compartmentalized purification and tagmentation of DNA, while a microfluidic merger efficiently pairs each genome with a unique single-cell oligonucleotide barcode, allowing &gt;50,000 single cells to be sequenced per run. The sequencing data is demultiplexed by barcode, generating groups of reads originating from single cells. As a high-throughput and low-bias method of single-cell sequencing, SiC-seq will enable a broader range of genomic studies targeted at diverse cell populations.

Single-cell sequencing reveals genotypic heterogeneity in biological systems, but current technologies lack the throughput necessary for the deep profiling of community composition and function. Here, we describe a microfluidic workflow for sequencing &gt;50,000 single-cell genomes from diverse cell populations.

Sequencing technologies have undergone a paradigm shift from bulk to single-cell resolution in response to an evolving understanding of the role of ...