The authors acknowledge Dr. Michael J. Friedlander, Director of the Virginia Tech Carilion Research Institute for encouraging our research endeavors. This project was supported by development funds to S.M.M and D.F.K. and in part by the Nano-Bio initiative of the Institute for Critical Technology and Applied Science at Virginia Tech.

1. Prepare Affinity Capture Devices16
<ol>
	<li>Clean the silicon nitride E-chips by incubating them in 15&#160;ml of acetone for 2 min followed by 15&#160;ml of methanol&#160;for 2 min (Figure&#160;1A). Allow chips to dry under laminar air-flow.</li>
	<li>Incubate the dried chips on a heated stir plate (without stirring) for 1.5 hr at 150 &#176;C, then allow them to cool to room temperature before use.</li>
	<li>Use Hamilton syringes to compose lipid mixtures in small glass tubes to contain 25% chloroform, 55% DLPC (1,2-dilauroyl-phosphocholine) in chloroform (1 mg/ml) and 20% Ni-NTA lipid (1,2-dioleoyl-iminodiacetic acid-succinyl-nickel salt) in chloroform (1 mg/ml) for a total volume of 40 &#956;l.</li>
	<li>Apply a 1&#160;&#956;l aliquot of the mixture over each 15&#160;&#956;l drop of Milli-Q water on a piece of Parafilm in a humid Petri dish (Figure&#160;1B). Incubate samples on ice for at least 60 min.</li>
</ol>
2. Capture Macromolecules17
<ol>
	<li>Place an E-chip with a 150&#160;nm integrated spacer on top of a monolayer sample and incubate for 1 min (Figure&#160;1C).</li>
	<li>Gently lift the chip off of the sample and add a 3&#160;&#956;l aliquot of His-tagged Protein A. Incubate for 1 min at room temperature (Figure&#160;1D).</li>
	<li>Blot away the excess drop using Whatman #1 filter paper and immediately add a 3&#160;&#956;l aliquot of antibody solution. Incubate for 1 min at room temperature.</li>
	<li>Remove the excess solution using a Hamilton syringe and immediately add a 1&#160;&#956;l aliquot of&#160;rotavirus DLPs (0.1 mg/ml) in buffer solution containing 50 mM HEPES (pH 7.5), 150 mM NaCl, 10 mM MgCl2 and 10 mM CaCl2. Incubate for at least 2 min at room temperature. The preparation of DLPs has been described previously18.</li>
</ol>
3. Assemble the Microfluidic Chamber and Load the In situ Specimen Holder
<ol>
	<li>Load the wet E-chip containing the viral sample into the tip of the microfluidic specimen holder. Glow-discharge a second flat E-chip for 1 min then loaded on top of the spacer chip (Figure&#160;2, panels 1-5).</li>
	<li>Alternatively, to increase the contrast of biological macromolecules, heavy metal stain (e.g.&#160;0.2% uranyl formate) can be added to wet specimens prior to placing the second E-chip on the wet specimen. However, the E-chip containing the specimen will need to be washed with Milli-Q water prior to adding the contrast reagent.</li>
	<li>Sandwich the entire assembly together to form a sealed enclosure, held in place mechanically within the holder by 3 brass screws (Figure&#160;2, panels 6-8).</li>
	<li>Following assembly, the tip of the holder is pumped to 10-6 Torr using a turbo-pumped dry pumping station before placing the holder inside the TEM.</li>
</ol>
4. Imaging in Liquid Using a Transmission Electron Microscope
<ol>
	<li>Load the&#160;in situ specimen holder into a Transmission Electron Microscope (FEI Company) equipped with a LaB6 filament and operating at 120 kV.</li>
	<li>Turn on the TEM filament and adjust the eucentric height of the microscope stage with respect to the specimen by using the wobbler function to tilt the sample from -15&#176; to +15&#176; back and forth in the column. This procedure adjusts the stage in the z-direction to help account for the proper thickness of the liquid chamber. This step also ensures an accurate magnification is used when recording images.</li>
	<li>Record images along the edges and in the corner regions of the microfluidic chamber first. These areas typically contain the thinnest solution. Record images of specimens under low-dose conditions (1-3 electrons/&#197;2) using a CCD camera. Use nominal magnifications of 6,000X - 30,000X.</li>
	<li>Determine the proper defocus value by focusing at the edge of fluidic chamber. Use a value of -1.5 &#956;m to record images at 30,000X magnification. If thick solution is encountered or if contrast agent is not used in the specimen preparation, use higher defocus values in the range of -2 to -4 &#956;m.</li>
	<li>To ensure solution is contained in the microfluidic chamber throughout the experiments, focus the electron beam until the bubbles are formed in the liquid within the device.</li>
</ol>

<ol>
	<li>Zhou, Z. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Towards+atomic+resolution+structural+determination+by+single-particle+cryo-electron+microscopy.">Towards atomic resolution structural determination by single-particle cryo-electron microscopy.</a> Curr. Opin. Struct. Biol. 18, 218-228 (2008).</li><li>Wolf, M., Garcea, R. L., Grigorieff, N., Harrison, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subunit+interactions+in+bovine+papillomavirus.">Subunit interactions in bovine papillomavirus.</a> Proc. Natl. Acad. Sci. U.S.A. 107, 6298-6303 (2010).</li><li>Dubochet, J., 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=Cryo-electron+microscopy+of+vitrified+specimens.">Cryo-electron microscopy of vitrified specimens.</a> Q. Rev. Biophys. 21, 129-228 (1988).</li><li>Unwin, P. N., Henderson, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+structure+determination+by+electron+microscopy+of+unstained+crystalline+specimens.">Molecular structure determination by electron microscopy of unstained crystalline specimens.</a> J. Mol. Biol. 94, 425-440 (1975).</li><li>Ohi, M., Li, Y., Cheng, Y., Walz, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Negative Staining and Image Classification - Powerful Tools in Modern Electron Microscopy. Biol. Proced. Online. 6, 23-34 (2004).</li><li>Adrian, M., Dubochet, J., Fuller, S. D., Harris, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cryo-negative+staining.">Cryo-negative staining.</a> Micron. 29, 145-160 (1998).</li><li>Parsons, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+of+wet+specimens+in+electron+microscopy.+Improved+environmental+chambers+make+it+possible+to+examine+wet+specimens+easily.">Structure of wet specimens in electron microscopy. Improved environmental chambers make it possible to examine wet specimens easily.</a> Science. 186, 407-414 (1974).</li><li>Parsons, D. F., Matricardi, V. R., Moretz, R. C., Turner, J. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+microscopy+and+diffraction+of+wet+unstained+and+unfixed+biological+objects.">Electron microscopy and diffraction of wet unstained and unfixed biological objects.</a> Adv. Biol. Med. Phys. 15, 161-270 (1974).</li><li>Hui, S. W., Parsons, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+diffraction+of+wet+biological+membranes.">Electron diffraction of wet biological membranes.</a> Science. 184, 77-78 (1974).</li><li>Hui, S. W., Parsons, D. F., Cowden, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Electron+diffraction+of+wet+phospholipid+bilayers.">Electron diffraction of wet phospholipid bilayers.</a> Proc. Natl. Acad. Sci. U.S.A. 71, 5068-5072 (1974).</li><li>Ring, E. A., de Jonge, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microfluidic+system+for+transmission+electron+microscopy.">Microfluidic system for transmission electron microscopy.</a> Microsc. Microanal. 16, 622-629 (2010).</li><li>Dukes, M. J., Ramachandra, R., Baudoin, J. P., Gray Jerome, W., de Jonge, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Three-dimensional+locations+of+gold-labeled+proteins+in+a+whole+mount+eukaryotic+cell+obtained+with+3nm+precision+using+aberration-corrected+scanning+transmission+electron+microscopy.">Three-dimensional locations of gold-labeled proteins in a whole mount eukaryotic cell obtained with 3nm precision using aberration-corrected scanning transmission electron microscopy.</a> J. Struct. Biol. 174, 552-562 (2011).</li><li>Yuk, J. M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-resolution+EM+of+colloidal+nanocrystal+growth+using+graphene+liquid+cells.">High-resolution EM of colloidal nanocrystal growth using graphene liquid cells.</a> Science. 336, 61-64 (2012).</li><li>Peckys, D. B., de Jonge, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualizing+gold+nanoparticle+uptake+in+live+cells+with+liquid+scanning+transmission+electron+microscopy.">Visualizing gold nanoparticle uptake in live cells with liquid scanning transmission electron microscopy.</a> Nano Lett. 11, 1733-1738 (2011).</li><li>Klein, K. L., Anderson, I. M., de Jonge, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Transmission+electron+microscopy+with+a+liquid+flow+cell.">Transmission electron microscopy with a liquid flow cell.</a> J. Microsc. 242, 117-123 (2011).</li><li>Degen, K., Dukes, M., Tanner, J. R., Kelly, D. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+development+of+affinity+capture+devices-a+nanoscale+purification+platform+for+biological+in+situ+transmission+electron+microscopy.">The development of affinity capture devices-a nanoscale purification platform for biological in situ transmission electron microscopy.</a> Rsc. Adv. 2, 2408-2412 (2012).</li><li>Gilmore, B. 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=Visualizing+viral+assemblies+in+a+nanoscale+biosphere.">Visualizing viral assemblies in a nanoscale biosphere.</a> Lab Chip. 13, 216-219 (2013).</li><li>Bican, P., Cohen, J., Charpilienne, A., Scherrer, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Purification+and+characterization+of+bovine+rotavirus+cores.">Purification and characterization of bovine rotavirus cores.</a> J. Virol. 43, 1113-1117 (1982).</li><li>Frank, J., 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=SPIDER+and+WEB:+processing+and+visualization+of+images+in+3D+electron+microscopy+and+related+fields.">SPIDER and WEB: processing and visualization of images in 3D electron microscopy and related fields.</a> J. Struct. Biol. 116, 190-199 (1996).</li><li>Zhang, X., 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=Near-atomic+resolution+using+electron+cryomicroscopy+and+single-particle+reconstruction.">Near-atomic resolution using electron cryomicroscopy and single-particle reconstruction.</a> Proc. Natl. Acad. Sci. U.S.A. 105, 1867-1872 (2008).</li><li>Scheres, S. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Bayesian+view+on+cryo-EM+structure+determination.">A Bayesian view on cryo-EM structure determination.</a> J. Mol. Biol. 415, 406-418 (2012).</li><li>Kelly, D. F., Abeyrathne, P. D., Dukovski, D., Walz, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+Affinity+Grid:+a+pre-fabricated+EM+grid+for+monolayer+purification.">The Affinity Grid: a pre-fabricated EM grid for monolayer purification.</a> J. Mol. Biol. 382, 423-433 (2008).</li></ol>

The author, Madeline J. Dukes, is an employee of Protochips, Inc.

In our presented work, we employed the affinity capture approach to tether rotavirus DLPs to a microfluidic platform. This allowed for in situ imaging of macromolecular complexes in a liquid microenvironment. The capture approach is significant with respect to other microfluidic imaging techniques because it localizes biological specimens to the imaging window to negate large diffusive issues that arise while recording images in liquid. However, one of the most critical steps in our protoc...

<a href="https://app.jove.com/t/6605">This corrects</a> the article <a href="https://dx.doi.org/10.3791/50936">10.3791/50936</a>

An erratum was issued for:&#160;<a href="https://www.jove.com/t/50936">In situ TEM of Biological Assemblies in Liquid</a>. The Representative Results and References sections were&#160;updated.

Erratum: In situ TEM of Biological Assemblies in Liquid

A common goal of biologists and engineers is to understand the inner-workings of molecular machines. Transmission Electron Microscopes (TEMs) are ideal instruments to visualize these intricate details at near-atomic resolution1-2. In order to sustain the high vacuum system of a TEM, biological samples are typically embedded in thin films of vitreous ice3, sugars4, heavy metal salts5, or some combination thereof6. As a result, images of embedded specimens may reveal only limited snapshots of dynamic processes.
Early attempts to maintain biological specimens hydrated in environmental liquid chambers were undertaken by Parsons and colleagues using differential pumping stages. Electron diffraction patterns of unstained catalase crystals were successfully recorded to a resolution of 3&#160;&#197; in a hydrated state7-8. In addition, phase-separated lipid domains could be examined in hydrated membranes of human erythrocytes9-10. However, motion caused by diffusing liquid and its interference with the electron beam, resulted in severe resolution loss and further experiments using biological specimens were not attempted until recently.
Newly developed microfluidic specimen holders have been introduced that utilize semiconductor microchips to form a micro-scaled environmental chamber. These devices can maintain samples in liquid while they are positioned in a TEM column11-12. This technical breakthrough in TEM imaging has allowed researchers to view, for the first time, progressive events at the molecular level13. We refer to this new modality as &#8220;in situ molecular microscopy&#8221; as experiments can now be performed &#8220;inside&#8221; the EM column14-15. The overall goal of this method is to image biological assemblies in liquid in order to observe their dynamic behaviors at nanometer resolution. The rationale behind the developed technique is to record real-time observations and examine new properties of biological machinery in solution. This methodology expands the use of TEMs for broader purposes in cellular and molecular biology12-16.
In the current video article, we present a comprehensive protocol to assemble and use a commercially available microfluidic specimen holder. These specialized holders utilize silicon nitride microchips produced with integrated spacers to form a liquid chamber that encloses minute volumes of solution. Thin, transparent windows are etched into the microchips for imaging purposes12. We demonstrate the proper use of a microfluidic holder to examine simian rotavirus double-layered particles (DLPs) in liquid using a TEM. To ensure that biological assemblies, such as DLPs, do not rapidly diffuse over great distances while imaging, we employ the Affinity Capture approach to tether them to the surface of the microfluidic chamber16. This molecular capture step has a major advantage over alternative techniques for imaging biological specimens in liquid because it allows for the acquisition of images that will be used for downstream processing routines. This capture step used in conjunction with microfluidic imaging is unique to our procedures17. Readers employing structural biology applications using TEM or microfluidic imaging chambers may consider the use of affinity capture techniques when dynamic observations at the molecular level are the end goal.

<table border="0" cellpadding="0" cellspacing="0" width="832">
	<colgroup>
		<col />
		<col />
		<col />
		<col />
	</colgroup>
	<tbody>
		<tr height="43">
			<td height="43" style="height:43px;width:237px;">E-chips, spacer chip</td>
			<td style="width:183px;">Protochips, Inc.</td>
			<td style="width:245px;">EPB-52TBD</td>
			<td style="width:167px;">400 &#956;m x 50 &#956;m window</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:237px;">E-chip, top chip</td>
			<td style="width:183px;">Protochips, Inc.</td>
			<td style="width:245px;">EPT-45W</td>
			<td style="width:167px;">400 &#956;m x 50 &#956;m window</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Ni-NTA lipid</td>
			<td style="width:183px;">Avanti Polar Lipids</td>
			<td style="width:245px;">790404P</td>
			<td style="width:167px;">Powder form</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">DLPC (12:0) lipid</td>
			<td style="width:183px;">Avanti Polar Lipids</td>
			<td style="width:245px;">850335P</td>
			<td style="width:167px;">Powder form</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Volumetric flasks&#160;</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td style="width:245px;">20-812A; 20-812C</td>
			<td style="width:167px;">1 ml; 5 ml&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Hamilton Syringes</td>
			<td style="width:183px;">Hamilton Co.</td>
			<td style="width:245px;">80300, 80400</td>
			<td style="width:167px;">1-10 &#956;l; 1-25 &#956;l</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Whatman #1 filter paper</td>
			<td style="width:183px;">Whatman</td>
			<td style="width:245px;">1001 090</td>
			<td style="width:167px;">100 pieces, 90 mm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Glass Petri dishes</td>
			<td style="width:183px;">Corning&#160;</td>
			<td style="width:245px;">70165-101</td>
			<td style="width:167px;">100 mm x 15 mm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Glass Pasteur pipettes</td>
			<td style="width:183px;">VWR</td>
			<td style="width:245px;">14673-010</td>
			<td style="width:167px;">14673-010</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Glass culture tubes</td>
			<td style="width:183px;">VWR</td>
			<td style="width:245px;">47729-566</td>
			<td style="width:167px;">6 mm x 50 mm</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Acetone</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td style="width:245px;">&#160;A11-1</td>
			<td style="width:167px;">1 L</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Methanol</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td style="width:245px;">&#160;A412-1</td>
			<td style="width:167px;">1 L</td>
		</tr>
		<tr height="30">
			<td height="30" style="height:31px;width:237px;">Chloroform&#160;</td>
			<td style="width:183px;">Electron Microcopy Sciences</td>
			<td style="width:245px;">12550</td>
			<td style="width:167px;">100 ml&#160;</td>
		</tr>
		<tr height="30">
			<td height="30" style="height:31px;width:237px;">His-tagged Protein A</td>
			<td style="width:183px;">Abcam, Inc.</td>
			<td style="width:245px;">ab52953</td>
			<td style="width:167px;">10 mg</td>
		</tr>
		<tr height="30">
			<td height="30" style="height:31px;width:237px;">Milli-Q water system</td>
			<td style="width:183px;">EMD Millipore Corp.</td>
			<td style="width:245px;">Z00QSV001</td>
			<td style="width:167px;">Ultrapure Water</td>
		</tr>
		<tr height="30">
			<td height="30" style="height:31px;width:237px;">HEPES</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td style="width:245px;">BP310-500</td>
			<td style="width:167px;">500 g</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:237px;">Equipment&#160;</td>
			<td style="width:183px;"></td>
			<td style="width:245px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:237px;">Poseidon In situ specimen holder</td>
			<td style="width:183px;">Protochips, Inc.</td>
			<td style="width:245px;"></td>
			<td>&#160;FEI compatible</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:237px;">FEI Spirit BioTwin TEM</td>
			<td style="width:183px;">FEI Co.</td>
			<td style="width:245px;"></td>
			<td>120 kV</td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:237px;">Eagle 2k HS CCD camera</td>
			<td style="width:183px;">FEI Co.</td>
			<td style="width:245px;"></td>
			<td>10&#160;&#197;/pixel sampling at 30,000X</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:237px;">Gatan 655 Dry pump station</td>
			<td style="width:183px;">Gatan, Inc.</td>
			<td style="width:245px;"></td>
			<td>Pump holder tip to 10-6&#160;range</td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:237px;">PELCO easiGlow, glow discharge unit</td>
			<td style="width:183px;">Ted Pella, Inc.</td>
			<td style="width:245px;"></td>
			<td>&#160;Negative polarity mode</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:237px;">Isotemp heated stir plate</td>
			<td style="width:183px;">Fisher Scientific</td>
			<td style="width:245px;"></td>
			<td>Heat to 150 &#186;C for 1.5 hr</td>
		</tr>
	</tbody>
</table>

in situ tem of biological assemblies in liquid

Researchers regularly use Transmission Electron Microscopes (TEMs) to examine biological entities and to assess new materials. Here, we describe an additional application for these instruments- viewing viral assemblies in a liquid environment. This exciting and novel method of visualizing biological structures utilizes a recently developed microfluidic-based specimen holder. Our video article demonstrates how to assemble and use a microfluidic holder to image liquid specimens within a TEM. In particular, we use simian rotavirus double-layered particles (DLPs) as our model system. We also describe steps to coat the surface of the liquid chamber with affinity biofilms that tether DLPs to the viewing window. This permits us to image assemblies in a manner that is suitable for 3D structure determination. Thus, we present a first glimpse of subviral particles in a native liquid environment.

Representative images of DLPs in liquid using E-chips that were glow-discharged (Figure&#160;3A) show fewer DLPs in a given viewing area, presumably due to diffusion, in comparison to DLPs that are enriched on Affinity Capture devices (Figure&#160;3B). The addition of uranyl formate in the imaging chamber enhances the contrast of the specimen and hence the visibility of individual DLPs in solution (Figure&#160;3C, top panel). Better contrast allows for downstream image p...

Watch this Scientific Journal Video about In situ TEM of Biological Assemblies in Liquid at JoVE.com

In situ TEM of Biological Assemblies in Liquid

Here we describe a procedure to image viral complexes in liquid at nanometer resolution using a transmission electron microscope.

In situ TEM of Biological Assemblies in Liquid

Researchers regularly use Transmission Electron Microscopes (TEMs) to examine biological entities and to assess new materials. Here, we describe an ...

in-situ-tem-of-biological-assemblies-in-liquid

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Bioengineering

9.9K Views.  Protochips, Inc.. Here we describe a procedure to image viral complexes in liquid at nanometer resolution using a transmission electron microscope.

Video: In situ TEM of Biological Assemblies in Liquid

Fluorescent Nanoparticles for the Measurement of Ion Concentration in Biological Systems

Tightly regulated ion homeostasis throughout the body is necessary for the prevention of such debilitating states as dehydration.1 In contrast, rapid ion fluxes at the cellular level are required for initiating action potentials in excitable cells.2 Sodium regulation plays an important role in both of these cases; however, no method currently exists for continuously monitoring sodium levels in vivo 3 and intracellular sodium probes 4 do not provide similar detailed results as calcium probes. In an effort to fill both of these voids, fluorescent nanosensors have been developed that can monitor sodium concentrations in vitro and in vivo.5,6 These sensors are based on ion-selective optode technology and consist of plasticized polymeric particles in which sodium specific recognition elements, pH-sensitive fluorophores, and additives are embedded.7-9 Mechanistically, the sodium recognition element extracts sodium into the sensor. 10 This extraction causes the pH-sensitive fluorophore to release a hydrogen ion to maintain charge neutrality within the sensor which causes a change in fluorescence. The sodium sensors are reversible and selective for sodium over potassium even at high intracellular concentrations.6 They are approximately 120 nm in diameter and are coated with polyethylene glycol to impart biocompatibility. Using microinjection techniques, the sensors can be delivered into the cytoplasm of cells where they have been shown to monitor the temporal and spatial sodium dynamics of beating cardiac myocytes.11 Additionally, they have also tracked real-time changes in sodium concentrations in vivo when injected subcutaneously into mice.3 Herein, we explain in detail and demonstrate the methodology for fabricating fluorescent sodium nanosensors and briefly demonstrate the biological applications our lab uses the nanosensors for: the microinjection of the sensors into cells; and the subcutaneous injection of the sensors into mice.

Fluorescent nanoparticles produced in our lab are used for imaging ion concentrations and ion fluxes in biological systems such as cells during signaling and interstitial fluid during physiological homeostasis.

Tightly regulated ion homeostasis throughout the body is necessary for the prevention of such debilitating states as dehydration.1 In contrast, rapid ion ...

Multiparametric Optical Mapping of the Langendorff-perfused Rabbit Heart

Optical imaging and fluorescent probes have significantly advanced research methodology in the field of cardiac electrophysiology in ways that could not have been accomplished by other approaches1. With the use of the calcium- and voltage-sensitive dyes, optical mapping allows measurement of transmembrane action potentials and calcium transients with high spatial resolution without the physical contact with the tissue. This makes measurements of the cardiac electrical activity possible under many conditions where the use of electrodes is inconvenient or impossible1. For example, optical recordings provide accurate morphological changes of membrane potential during and immediately after stimulation and defibrillation, while conventional electrode techniques suffer from stimulus-induced artifacts during and after stimuli due to electrode polarization1. 
The Langendorff-perfused rabbit heart is one of the most studied models of human heart physiology and pathophysiology. Many types of arrhythmias observed clinically could be recapitulated in the rabbit heart model. It was shown that wave patterns in the rabbit heart during ventricular arrhythmias, determined by effective size of the heart and the wavelength of reentry, are very similar to that in the human heart2. It was also shown that critical aspects of excitation-contraction (EC) coupling in rabbit myocardium, such as the relative contribution of sarcoplasmic reticulum (SR), is very similar to human EC coupling3. Here we present the basic procedures of optical mapping experiments in Langendorff-perfused rabbit hearts, including the Langendorff perfusion system setup, the optical mapping systems setup, the isolation and cannulation of the heart, perfusion and dye-staining of the heart, excitation-contraction uncoupling, and collection of optical signals. These methods could be also applied to the heart from species other than rabbit with adjustments to flow rates, optics, solutions, etc.
Two optical mapping systems are described. The panoramic mapping system is used to map the entire epicardium of the rabbit heart4-7. This system provides a global view of the evolution of reentrant circuits during arrhythmogenesis and defibrillation, and has been used to study the mechanisms of arrhythmias and antiarrhythmia therapy8,9. The dual mapping system is used to map the action potential (AP) and calcium transient (CaT) simultaneously from the same field of view10-13. This approach has enhanced our understanding of the important role of calcium in the electrical alternans and the induction of arrhythmia14-16.

This article describes the basic procedures for conducting optical mapping experiments in the Langendorff-perfused rabbit heart using the panoramic imaging system, and the dual (voltage and calcium) imaging modality.

Optical imaging and fluorescent probes have significantly advanced research methodology in the field of cardiac electrophysiology in ways that could not ...

Cellular Lipid Extraction for Targeted Stable Isotope Dilution Liquid Chromatography-Mass Spectrometry Analysis

The metabolism of fatty acids, such as arachidonic acid (AA) and linoleic acid (LA), results in the formation of oxidized bioactive lipids, including numerous stereoisomers1,2. These metabolites can be formed from free or esterified fatty acids. Many of these oxidized metabolites have biological activity and have been implicated in various diseases including cardiovascular and neurodegenerative diseases, asthma, and cancer3-7. Oxidized bioactive lipids can be formed enzymatically or by reactive oxygen species (ROS). Enzymes that metabolize fatty acids include cyclooxygenase (COX), lipoxygenase (LO), and cytochromes P450 (CYPs)1,8. Enzymatic metabolism results in enantioselective formation whereas ROS oxidation results in the racemic formation of products.
While this protocol focuses primarily on the analysis of AA- and some LA-derived bioactive metabolites; it could be easily applied to metabolites of other fatty acids. Bioactive lipids are extracted from cell lysate or media using liquid-liquid (l-l) extraction. At the beginning of the l-l extraction process, stable isotope internal standards are added to account for errors during sample preparation. Stable isotope dilution (SID) also accounts for any differences, such as ion suppression, that metabolites may experience during the mass spectrometry (MS) analysis9. After the extraction, derivatization with an electron capture (EC) reagent, pentafluorylbenzyl bromide (PFB) is employed to increase detection sensitivity10,11. Multiple reaction monitoring (MRM) is used to increase the selectivity of the MS analysis. Before MS analysis, lipids are separated using chiral normal phase high performance liquid chromatography (HPLC). The HPLC conditions are optimized to separate the enantiomers and various stereoisomers of the monitored lipids12. This specific LC-MS method monitors prostaglandins (PGs), isoprostanes (isoPs), hydroxyeicosatetraenoic acids (HETEs), hydroxyoctadecadienoic acids (HODEs), oxoeicosatetraenoic acids (oxoETEs) and oxooctadecadienoic acids (oxoODEs); however, the HPLC and MS parameters can be optimized to include any fatty acid metabolites13.
Most of the currently available bioanalytical methods do not take into account the separate quantification of enantiomers. This is extremely important when trying to deduce whether or not the metabolites were formed enzymatically or by ROS. Additionally, the ratios of the enantiomers may provide evidence for a specific enzymatic pathway of formation. The use of SID allows for accurate quantification of metabolites and accounts for any sample loss during preparation as well as the differences experienced during ionization. Using the PFB electron capture reagent increases the sensitivity of detection by two orders of magnitude over conventional APCI methods. Overall, this method, SID-LC-EC-atmospheric pressure chemical ionization APCI-MRM/MS, is one of the most sensitive, selective, and accurate methods of quantification for bioactive lipids.

This protocol will demonstrate the extraction and analysis of free and esterified bioactive fatty acids from cells. Fatty acids are accurately quantified using stable isotope dilution, chiral liquid chromatography, electron capture atmospheric chemical ionization multiple reaction monitoring mass spectrometry (SID-LC-ECAPCI-MRM/MS).

The metabolism of fatty acids, such as arachidonic acid (AA) and linoleic acid (LA), results in the formation of oxidized bioactive lipids, including ...

Quantification of Global Diastolic Function by Kinematic Modeling-based Analysis of Transmitral Flow via the Parametrized Diastolic Filling Formalism

Quantitative cardiac function assessment remains a challenge for physiologists and clinicians.&#160;Although historically invasive methods have comprised the only means available, the development of noninvasive imaging modalities (echocardiography, MRI, CT) having high temporal and spatial resolution provide a new window for quantitative diastolic function assessment. Echocardiography is the agreed upon standard for diastolic function assessment, but indexes in current clinical use merely utilize selected features of chamber dimension (M-mode) or blood/tissue motion (Doppler) waveforms without incorporating the physiologic causal determinants of the motion itself.&#160;The recognition that all left ventricles (LV) initiate filling by serving as mechanical suction pumps allows global diastolic function to be assessed based on laws of motion that apply to all chambers. What differentiates one heart from another are the parameters of the equation of motion that governs filling. Accordingly, development of the Parametrized Diastolic Filling (PDF) formalism&#160;has shown that the entire range of clinically observed early transmitral flow (Doppler E-wave) patterns are extremely well fit by the laws of damped oscillatory motion.&#160;This permits analysis of individual E-waves in accordance with a causal mechanism (recoil-initiated suction) that yields three (numerically) unique lumped parameters whose physiologic analogues are chamber stiffness (k), viscoelasticity/relaxation (c), and load (xo).&#160;The recording of transmitral flow (Doppler E-waves) is standard practice in clinical cardiology and, therefore, the echocardiographic recording method is only briefly reviewed. Our focus is on determination of the PDF parameters from routinely recorded E-wave data.&#160;As the highlighted results indicate, once the PDF parameters have been obtained from a suitable number of load varying E-waves, the investigator is free to use the parameters or construct indexes from the parameters (such as stored energy 1/2kxo2, maximum A-V pressure gradient kxo, load independent index of diastolic function, etc.) and select the aspect of physiology or pathophysiology to be quantified.

Accurate, causality-based quantification of global diastolic function has been achieved by kinematic modeling-based analysis of transmitral flow via the Parametrized Diastolic Filling (PDF) formalism. PDF generates unique stiffness, relaxation,&#160;and load parameters and elucidates &#39;new&#39; physiology while providing sensitive and specific indexes of dysfunction.

Quantitative cardiac function assessment remains a challenge for physiologists and clinicians.&#160;Although historically invasive methods have comprised ...

Generation of Scalable, Metallic High-Aspect Ratio Nanocomposites in a Biological Liquid Medium

The goal of this protocol is to describe the synthesis of two novel biocomposites with high-aspect ratio structures. The biocomposites consist of copper and cystine, with either copper nanoparticles (CNPs) or copper sulfate contributing the metallic component. Synthesis is carried out in liquid under biological conditions (37 &#176;C) and the self-assembled composites form after 24 hr. Once formed, these composites are highly stable in both liquid media and in a dried form. The composites scale from the nano- to micro- range in length, and from a few microns to 25 nm in diameter. Field emission scanning electron microscopy with energy dispersive X-ray spectroscopy (EDX) demonstrated that sulfur was present in the NP-derived linear structures, while it was absent from the starting CNP material, thus confirming cystine as the source of sulfur in the final nanocomposites. During synthesis of these linear nano- and micro-composites, a diverse range of lengths of structures is formed in the synthesis vessel. Sonication of the liquid mixture after synthesis was demonstrated to assist in controlling average size of the structures by diminishing the average length with increased time of sonication. Since the formed structures are highly stable, do not agglomerate, and are formed in liquid phase, centrifugation may also be used to assist in concentrating and segregating formed composites.

Here we present a protocol to synthesize novel, high-aspect ratio biocomposites under biological conditions and in liquid media. The biocomposites scale from nanometers to micrometers in diameter and length, respectively. Copper nanoparticles (CNPs) and copper sulfate combined with cystine are the key components for the synthesis.

The goal of this protocol is to describe the synthesis of two novel biocomposites with high-aspect ratio structures. The biocomposites consist of copper ...

In Situ Mapping of the Mechanical Properties of Biofilms by Particle-tracking Microrheology

Bacterial cells are able to form surface-attached biofilm communities known as biofilms by encasing themselves in extracellular polymeric substances (EPS). The EPS serves as a physical and protective scaffold that houses the bacterial cells and consists of a variety of materials that includes proteins, exopolysaccharides and DNA. The composition of the EPS may change, which remodels the mechanic properties of the biofilm to further develop or support alternative biofilm structures, such as streamers, as a response to environmental cues. Despite this, there are little quantitative descriptions on how EPS components contribute to the mechanical properties and function of biofilms. Rheology, the study of the flow of matter, is of particular relevance to biofilms as many biofilms grow in flow conditions and are constantly exposed to shear stress. It also provides measurement and insight on the spreading of the biofilm on a surface. Here, particle-tracking microrheology is used to examine the viscoelasticity and effective crosslinking roles of different matrix components in various parts of the biofilm during development. This approach allows researchers to measure mechanic properties of biofilms at the micro-scale, which might provide useful information for controlling and engineering biofilms.

In Situ Mapping of the Mechanical Properties of Biofilms by Particle-tracking Microrheology

Particle-tracking microrheology investigates the viscoelasticity of materials. Here, the technique is used to determine the viscoelasticity, creep compliance and effective crosslinking roles of different matrix components of a bacterial biofilm. The matrix consists of polymeric substances secreted by the bacteria and its components determine biofilm structure and mechanical properties.

Bacterial cells are able to form surface-attached biofilm communities known as biofilms by encasing themselves in extracellular polymeric substances ...

Alternating Magnetic Field-Responsive Hybrid Gelatin Microgels for Controlled Drug Release

Magnetically-responsive nano/micro-engineered biomaterials that enable a tightly controlled, on-demand drug delivery have been developed as new types of smart soft devices for biomedical applications. Although a number of magnetically-responsive drug delivery systems have demonstrated efficacies through either in vitro proof of concept studies or in vivo preclinical applications, their use in clinical settings is still limited by their insufficient biocompatibility or biodegradability. Additionally, many of the existing platforms rely on sophisticated techniques for their fabrications. We recently demonstrated the fabrication of biodegradable, gelatin-based thermo-responsive microgel by physically entrapping poly(N-isopropylacrylamide-co-acrylamide) chains as a minor component within a three-dimensional gelatin network. In this study, we present a facile method to fabricate a biodegradable drug release platform that enables a magneto-thermally triggered drug release. This was achieved by incorporating superparamagnetic iron oxide nanoparticles and thermo-responsive polymers within gelatin-based colloidal microgels, in conjunction with an alternating magnetic field application system.

We present a facile method to fabricate a biodegradable gelatin-based drug release platform that is magneto-thermally responsive. This was achieved by incorporating superparamagnetic iron oxide nanoparticles and poly(N-isopropylacrylamide-co-acrylamide) within a spherical gelatin micro-network crosslinked by genipin, in conjunction with an alternating magnetic field application system.

Magnetically-responsive nano/micro-engineered biomaterials that enable a tightly controlled, on-demand drug delivery have been developed as new types of ...

A Novel Technique for Generating and Observing Chemiluminescence in a Biological Setting

Intraoperative imaging techniques have the potential to make surgical interventions safer and more effective; for these reasons, such techniques are quickly moving into the operating room. Here, we present a new approach that utilizes a technique not yet explored for intraoperative imaging: chemiluminescent imaging. This method employs a ruthenium-based chemiluminescent reporter along with a custom-built nebulizing system to produce ex vivo or in vivo images with high signal-to-noise ratios. The ruthenium-based reporter produces light following exposure to an aqueous oxidizing solution and re-reduction within the surrounding tissue. This method has allowed us to detect reporter concentrations as low as 6.9 pmol/cm2. In this work, we present a visual guide to our proof-of-concept in vivo studies involving subdermal and intravenous injections in mice. The results suggest that this technology is a promising candidate for further preclinical research and might ultimately become a useful tool in the operating room.

This protocol describes a new intraoperative imaging technique that uses a ruthenium complex as a source of chemiluminescent light emission, thereby producing high signal-to-noise ratios during in vivo imaging. Intraoperative imaging is an expanding field that could revolutionize the way that surgical procedures are performed.

Intraoperative imaging techniques have the potential to make surgical interventions safer and more effective; for these reasons, such techniques are ...

Automated Robotic Liquid Handling Assembly of Modular DNA Devices

Recent advances in modular DNA assembly techniques have enabled synthetic biologists to test significantly more of the available &#34;design space&#34; represented by &#34;devices&#34; created as combinations of individual genetic components. However, manual assembly of such large numbers of devices is time-intensive, error-prone, and costly. The increasing sophistication and scale of synthetic biology research necessitates an efficient, reproducible way to accommodate large-scale, complex, and high throughput device construction.
Here, a DNA assembly protocol using the Type-IIS restriction endonuclease based Modular Cloning (MoClo) technique is automated on two liquid-handling robotic platforms. Automated liquid-handling robots require careful, often times tedious optimization of pipetting parameters for liquids of different viscosities (e.g. enzymes, DNA, water, buffers), as well as explicit programming to ensure correct aspiration and dispensing of DNA parts and reagents. This makes manual script writing for complex assemblies just as problematic as manual DNA assembly, and necessitates a software tool that can automate script generation. To this end, we have developed a web-based software tool, http://mocloassembly.com, for generating combinatorial DNA device libraries from basic DNA parts uploaded as Genbank files. We provide access to the tool, and an export file from our liquid handler software which includes optimized liquid classes, labware parameters, and deck layout. All DNA parts used are available through Addgene, and their digital maps can be accessed via the Boston University BDC ICE Registry. Together, these elements provide a foundation for other organizations to automate modular cloning experiments and similar protocols.
The automated DNA assembly workflow presented here enables the repeatable, automated, high-throughput production of DNA devices, and reduces the risk of human error arising from repetitive manual pipetting. Sequencing data show the automated DNA assembly reactions generated from this workflow are ~95% correct and require as little as 4% as much hands-on time, compared to manual reaction preparation.

Here, an automated workflow to perform modular DNA &#34;device&#34; assembly using a modular cloning DNA assembly method on liquid-handling robots is presented. The protocol uses an intuitive software tool for generating liquid handler picklists for combinatorial DNA device library generation, which we demonstrate using two liquid handling platforms.

Recent advances in modular DNA assembly techniques have enabled synthetic biologists to test significantly more of the available &#34;design space&#34; ...

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and dampen loads in the spine. The IVD consists of a proteoglycan-rich nucleus pulposus (NP) and a collagen-rich annulus fibrosis (AF) sandwiched by cartilaginous end-plates. Together with the adjacent vertebrae, the vertebrae-IVD structure forms a functional spine unit (FSU). These microstructures contain unique cell types as well as unique extracellular matrices. Whole organ culture of the FSU preserves the native extracellular matrix, cell differentiation phenotypes, and cellular-matrix interactions. Thus, organ culture techniques are particularly useful for investigating the complex biological mechanisms of the IVD. Here, we describe a high-throughput approach for culturing whole lumbar mouse FSUs that provides an ideal platform for studying disease mechanisms and therapies for the IVD. Furthermore, we describe several applications that utilize this organ culture method to conduct further studies including contrast-enhanced microCT imaging and three-dimensional high-resolution finite element modeling of the IVD.

An In Vitro Organ Culture Model of the Murine Intervertebral Disc

Whole organ culture of the intervertebral disc (IVD) preserves the native extracellular matrix, cell phenotypes, and cellular-matrix interactions. Here we describe an IVD culture system using mouse lumbar and caudal IVDs in their functional spinal units and several applications utilizing this system.

Intervertebral disc (IVD) degeneration is a significant contributor to low back pain. The IVD is a fibrocartilaginous joint that serves to transmit and ...