This work is in part supported by grants from the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Canadian Institutes of Health Research (CIHR). We thank the Clinical Institute of Applied Research and Education at the Victoria General Hospital in Winnipeg and Seven Oaks General Hospital in Winnipeg for managing clinical samples from human subjects. We thank Dr. Hagit Peretz-Soroka for helpful discussion about the assay operation strategies.
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We thank Professor Carolyn Ren and Dr. Xiaoming (Cody) Chen from the University of Waterloo for their generous support in the filming process.

All human sample collection protocols were approved by the Joint-Faculty Research Ethics Board at the University of Manitoba, Winnipeg.
1. Microfluidic Device Fabrication (Figure 1A)
<ol>
	<li>Design and print transparency mask.
	<ol>
		<li>Design the device as detailed previously25. See Figure 1A. 
		NOTE: The device includes two layers. The first layer (4 &#181;m high) defines the cell...

<ol>
	<li>Kolaczkowska, E., Kubes, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+recruitment+and+function+in+health+and+inflammation.">Neutrophil recruitment and function in health and inflammation.</a> Nat Rev Immunol. 13 (13), 159-175 (2013).</li><li>Luster, A. D., Alon, R., von Andrian, U. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immune+cell+migration+in+inflammation:+present+and+future+therapeutic+targets.">Immune cell migration in inflammation: present and future therapeutic targets.</a> Nat Immunol. 6 (12), 1182-1190 (2005).</li><li>Griffith, J. W., Luster, A. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Targeting+cells+in+motion:+migrating+toward+improved+therapies.">Targeting cells in motion: migrating toward improved therapies.</a> Eur. J. Immunol. 43 (6), 1430-1435 (2013).</li><li>Laird, D. J., von Andrian, U. H., Wagers, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Stem+cell+trafficking+in+tissue+development,+growth,+and+disease.">Stem cell trafficking in tissue development, growth, and disease.</a> Cell. 132 (4), 612-630 (2008).</li><li>Condeelis, J., Segall, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intravital+imaging+of+cell+movement+in+tumours.">Intravital imaging of cell movement in tumours.</a> Nat Rev Cancer. 3 (12), 921-930 (2003).</li><li>Kruger, P., 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=Neutrophils:+between+host+defence,+immune+modulation,+and+tissue+injury.">Neutrophils: between host defence, immune modulation, and tissue injury.</a> PLoS Pathog. 11 (3), e1004651 (2015).</li><li>M&#243;csai, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Diverse+novel+functions+of+neutrophils+in+immunity,+inflammation,+and+beyond.">Diverse novel functions of neutrophils in immunity, inflammation, and beyond.</a> J Exp Med. 210 (7), 1283-1299 (2013).</li><li>Foxman, E. F., Campbell, J. J., Butcher, E. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Multistep+navigation+and+the+combinatorial+control+of+leukocyte+chemotaxis.">Multistep navigation and the combinatorial control of leukocyte chemotaxis.</a> J Cell Biol. 139 (7), 1349-1360 (1997).</li><li>Tazzyman, S., Niaz, H., Murdoch, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil-mediated+tumour+angiogenesis:+subversion+of+immune+responses+to+promote+tumour+growth.">Neutrophil-mediated tumour angiogenesis: subversion of immune responses to promote tumour growth.</a> Semin Cancer Biol. 23 (3), 149-158 (2013).</li><li>Boyden, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+chemotactic+effect+of+mixtures+of+antibody+and+antigen+on+polymorphonuclear+leucocytes.">The chemotactic effect of mixtures of antibody and antigen on polymorphonuclear leucocytes.</a> J Exp Med. 115 (3), 453-466 (1962).</li><li>Wu, J., Wu, X., Lin, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Recent+developments+in+microfluidics-based+chemotaxis+studies.">Recent developments in microfluidics-based chemotaxis studies.</a> Lab Chip. 13 (13), 2484-2499 (2013).</li><li>Sackmann, E. K., Fulton, A. L., Beebe, D. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+present+and+future+role+of+microfluidics+in+biomedical+research.">The present and future role of microfluidics in biomedical research.</a> Nature. 507 (7491), 181-189 (2014).</li><li>Kim, S., Kim, H. J., Jeon, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biological+applications+of+microfluidic+gradient+devices.">Biological applications of microfluidic gradient devices.</a> Integr Biol. 2 (11-12), 584-603 (2010).</li><li>Irimia, D., 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=Microfluidic+system+for+measuring+neutrophil+migratory+responses+to+fast+switches+of+chemical+gradients.">Microfluidic system for measuring neutrophil migratory responses to fast switches of chemical gradients.</a> Lab Chip. 6 (2), 191-198 (2006).</li><li>Lin, F., 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=Neutrophil+migration+in+opposing+chemoattractant+gradients+using+microfluidic+chemotaxis+devices.">Neutrophil migration in opposing chemoattractant gradients using microfluidic chemotaxis devices.</a> Ann Biomed Eng. 33 (4), 475-482 (2005).</li><li>Ambravaneswaran, V., Wong, I. Y., Aranyosi, A. J., Toner, M., Irimia, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Directional+decisions+during+neutrophil+chemotaxis+inside+bifurcating+channels.">Directional decisions during neutrophil chemotaxis inside bifurcating channels.</a> Integr Biol. 2 (11-12), 639-647 (2010).</li><li>Jones, C. N., 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=Spontaneous+neutrophil+migration+patterns+during+sepsis+after+major+burns.">Spontaneous neutrophil migration patterns during sepsis after major burns.</a> PloS One. 9 (12), e114509 (2014).</li><li>Butler, K. 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=Burn+injury+reduces+neutrophil+directional+migration+speed+in+microfluidic+devices.">Burn injury reduces neutrophil directional migration speed in microfluidic devices.</a> PloS One. 5 (7), e11921 (2010).</li><li>Wu, 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=A+microfluidic+platform+for+evaluating+neutrophil+chemotaxis+induced+by+sputum+from+COPD+patients.">A microfluidic platform for evaluating neutrophil chemotaxis induced by sputum from COPD patients.</a> PloS One. 10 (5), e0126523 (2015).</li><li>Sackmann, E. K., 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=Microfluidic+kit-on-a-lid:+a+versatile+platform+for+neutrophil+chemotaxis+assays.">Microfluidic kit-on-a-lid: a versatile platform for neutrophil chemotaxis assays.</a> Blood. 120 (14), e45-e53 (2012).</li><li>Agrawal, N., Toner, M., Irimia, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil+migration+assay+from+a+drop+of+blood.">Neutrophil migration assay from a drop of blood.</a> Lab Chip. 8 (12), 2054-2061 (2008).</li><li>Jones, C. N., 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=Microfluidic+platform+for+measuring+neutrophil+chemotaxis+from+unprocessed+human+whole+blood.">Microfluidic platform for measuring neutrophil chemotaxis from unprocessed human whole blood.</a> J Vis Exp. (88), (2014).</li><li>Jones, C. N., 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=Microfluidic+assay+for+precise+measurements+of+mouse,+rat,+and+human+neutrophil+chemotaxis+in+whole-blood+droplets.">Microfluidic assay for precise measurements of mouse, rat, and human neutrophil chemotaxis in whole-blood droplets.</a> J Leukocyte Biol. 100 (1), 241-247 (2016).</li><li>Sackmann, E. K. -. H., 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=Characterizing+asthma+from+a+drop+of+blood+using+neutrophil+chemotaxis.">Characterizing asthma from a drop of blood using neutrophil chemotaxis.</a> P Natl Acad Sci. 111 (16), 5813-5818 (2014).</li><li>Wu, 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=An+all-on-chip+method+for+testing+neutrophil+chemotaxis+induced+by+fMLP+and+COPD+patient's+sputum.">An all-on-chip method for testing neutrophil chemotaxis induced by fMLP and COPD patient's sputum.</a> Technology. 04 (02), 104-109 (2016).</li></ol>

In this paper, a detailed protocol to directly isolate neutrophils from whole blood followed by the chemotaxis test, all on a single microfluidic chip, was described. This method offers useful features in its easy operation, negative selection of high purity neutrophils, rapid sample-to-result chemotaxis test, reduced reagents and sample consumption, and accurate cell migration data analysis. As a rough estimate, at least 25% of the neutrophils from the input whole blood sample effectively entered the docking structure i...

Chemotaxis, a process of directed cell migration to soluble chemical concentration gradient, is critically involved in many biological processes including immune response1,2,3, tissue development4 and cancer metastasis5. Neutrophils are the most abundant white blood cell subset and play crucial roles in enabling the body&#39;s innate host defense functions, as well as in mediating adaptive immune responses6,7. Neutrophils are equipped with highly-regulated chemotactic machinery allowing these motile immune cells to respond to both pathogen-derived chemoattractants (e.g. fMLP) and host-derived chemoattractants (e.g. interleukin-8) throughchemotaxis8. Neutrophil migration and chemotaxis mediate various physiological problems and diseases such as inflammation and cancers1,9. Thus, the accurate assessment of neutrophil chemotaxis provides an important functional readout for studying the neutrophil biology and the associated diseases.
Compared to the widely-used conventional chemotaxis assays (e.g. transwell assay10), the microfluidic devices show great promise for quantitative evaluation of cell migration and chemotaxis owing to the precisely controlled chemical gradient generation and miniaturization11,12,13. Over the last two decades or so, various microfluidic devices have been developed to study the chemotaxis of different biological cell types, especially neutrophils11. Significant effort was devoted to characterizing neutrophil migration in spatiotemporally complex chemical gradients that were configured in the microfluidic devices14,15. Interesting strategies were also developed to study directional decision making by neutrophils using the microfluidic devices16.Aside from biologically-oriented research, the applications of microfluidic devices have been extended to test clinical samples for disease evaluation17,18,19. However, the use of many microfluidic devices is limited to specialized research laboratories and requires lengthy neutrophil isolation from large volume of blood samples. Therefore, there has been a growing trend of developing integrated microfluidic devices for rapid neutrophil chemotaxis analysis directly from a drop of whole blood20,21,22,23,24.
Toward this direction, an all-on-chip method was developed that integrates the magnetic negative neutrophil purification and the subsequent chemotaxis assay on a single microfluidic device25. This all-on-chip method has the following novel features: 1) in contrast to previous on-chip strategies that isolate neutrophils from the blood by adhesion-based cell capture or cell size-based filtering20,22, this new method permits high purity, on-chip magnetic separation of the neutrophils from small volumes of whole blood, as well as chemotaxis measurement upon chemoattractant stimulation; 2) the cell docking structure helps align the initial positions of the neutrophils close to the chemical gradient channel and permits simple chemotaxis analysis without single cell tracking; 3) the integration of the neutrophil isolation and chemotaxis assay on a single microfluidic device permits rapid sample-to-result chemotaxis analysis in 25 min when there is no interruption between experimental steps.
This paper provides a detailed protocol for the construction, operation and data analysis method of this all-on-chip chemotaxis assay. The paper demonstrates the effective use of the developed method for performing neutrophil chemotaxis by testing a known recombinant chemoattractant and complex chemotactic samples from patients, followed by a discussion on troubleshooting strategies, limitations and future directions.

<table border="0" cellpadding="0" cellspacing="0" width="581">
	<tbody>
		<tr height="20">
			<td height="20" style="height:20px;width:581px;">Device fabrication</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Mask aligner</td>
			<td>ABM</td>
			<td>N/A</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Spinner</td>
			<td>Solitec</td>
			<td>5000</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Hotplate</td>
			<td>VWR</td>
			<td>11301-022</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Plasma cleaner</td>
			<td>Harrick Plasma</td>
			<td>PDC-001</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Vacuum dessicator</td>
			<td>Fisher Scientific</td>
			<td>08-594-15A</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Digital scale</td>
			<td>Ohaus</td>
			<td>CS200</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SU-8 2000 thinner</td>
			<td>Microchem</td>
			<td>SU-8 2000</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SU-8 2025 photoresist</td>
			<td>Microchem</td>
			<td>SU-8 2025</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">SU-8 developer</td>
			<td>Microchem</td>
			<td>SU-8 developer</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Si wafer</td>
			<td>Silicon, Inc</td>
			<td>LG2065</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">isopropyl alcohol</td>
			<td>Fisher Scientific</td>
			<td>A416-4</td>
			<td></td>
		</tr>
		<tr height="52">
			<td height="52" style="height:52px;width:159px;">(tridecafluoro-1,1,2,2-tetrahydrooctyl) trichlorosilane</td>
			<td>Gelest</td>
			<td>78560-45-9</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:159px;">Polydimethylsiloxane 
			(PDMS)</td>
			<td>Ellsworth Adhesives</td>
			<td>2065622</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Petri Dish</td>
			<td>Fisher Scientific</td>
			<td>FB0875714</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Glass slides</td>
			<td>Fisher Scientific</td>
			<td>12-544-4</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Cutting pad</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Custom-made</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">Punchers</td>
			<td>N/A</td>
			<td>N/A</td>
			<td>Custom-made</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:159px;">Name </td>
			<td>Source</td>
			<td>Catalog Number</td>
			<td>Comments</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">On-chip cell isolation and chemotaxis assay</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:159px;">RPMI 1640</td>
			<td>Fisher Scientific</td>
			<td>SH3025502</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;">DPBS</td>
			<td>Fisher Scientific</td>
			<td>SH3002802</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:159px;">Bovine serum albumin 
			(BSA)</td>
			<td>Sigma-Aldrich</td>
			<td>SH3057402</td>
			<td style="width:164px;"></td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;">Fibronectin</td>
			<td>VWR</td>
			<td>CACB356008</td>
			<td style="width:164px;"></td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;">fMLP</td>
			<td>Sigma-Aldrich</td>
			<td>F3506-10MG</td>
			<td style="width:164px;"></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:159px;">Magnetic disks</td>
			<td style="width:124px;">Indigo Instruments</td>
			<td>44202-1</td>
			<td style="width:164px;">5 mm in diameter, 
			1 mm thick</td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;width:159px;">FITC-Dextran</td>
			<td>Sigma-Aldrich</td>
			<td>FD10S</td>
			<td></td>
		</tr>
		<tr height="20">
			<td height="20" style="height:20px;"> Rhodamine</td>
			<td> 
			Sigma-Aldrich</td>
			<td>R4127-5G</td>
			<td style="width:164px;"></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:159px;">Giemsa stain solution</td>
			<td style="width:124px;">Rowley Biochemical Inc.</td>
			<td style="width:135px;">G-472-1-8OZ</td>
			<td style="width:164px;"></td>
		</tr>
		<tr height="52">
			<td height="52" style="height:52px;width:159px;">EasySep Direct Human 
			Neutrophil Isolation 
			Kit</td>
			<td style="width:124px;">STEMCELL 
			Technologies Inc</td>
			<td>19666</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:159px;">Dithiothreitol</td>
			<td style="width:124px;">Sigma-Aldrich</td>
			<td>D0632</td>
			<td></td>
		</tr>
		<tr height="34">
			<td height="34" style="height:34px;width:159px;"> Nikon Ti-U inverted fluorescent microscope </td>
			<td style="width:124px;">Nikon</td>
			<td>Ti-U</td>
			<td></td>
		</tr>
		<tr height="35">
			<td height="35" style="height:35px;width:159px;">Microscope environmental chamber.</td>
			<td style="width:124px;">InVivo Scientific</td>
			<td>N/A</td>
			<td style="width:164px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:159px;"> CCD camera</td>
			<td style="width:124px;">Nikon</td>
			<td>DS-Fi1</td>
			<td></td>
		</tr>
	</tbody>
</table>

an all-on-chip method for rapid neutrophil chemotaxis analysis directly from a drop of blood

Neutrophil migration and chemotaxis are critical for our body's immune system. Microfluidic devices are increasingly used for investigating neutrophil migration and chemotaxis owing to their advantages in real-time visualization, precise control of chemical concentration gradient generation, and reduced reagent and sample consumption. Recently, a growing effort has been made by the microfluidic researchers toward developing integrated and easily operated microfluidic chemotaxis analysis systems, directly from whole blood. In this direction, the first all-on-chip method was developed for integrating the magnetic negative purification of neutrophils and the chemotaxis assay from small blood volume samples. This new method permits a rapid sample-to-result neutrophil chemotaxis test in 25 min. In this paper, we provide detailed construction, operation and data analysis method for this all-on-chip chemotaxis assay with a discussion on troubleshooting strategies, limitations and future directions. Representative results of the neutrophil chemotaxis assay testing a defined chemoattractant, N-Formyl-Met-Leu-Phe (fMLP), and sputum from a chronic obstructive pulmonary disease (COPD) patient, using this all-on-chip method are shown. This method is applicable to many cell migration-related investigations and clinical applications.

Neutrophils are negatively selected from a drop of whole blood directly in the microfluidic device. The purity of the isolated neutrophils was verified by on-chip Giemsa staining and the results showed the typical ring-shaped and lobe-shaped nuclei of neutrophils (Figure 2A)25. This indicates an effective on-chip neutrophil isolation at high purity from a small volume of whole blood. Furthermore, the docking structure can effectively a...

Watch this Scientific Journal Video about An All-on-chip Method for Rapid Neutrophil Chemotaxis Analysis Directly from a Drop of Blood at JoVE.com

An All-on-chip Method for Rapid Neutrophil Chemotaxis Analysis Directly from a Drop of Blood

This article provides the detailed method of performing a rapid neutrophil chemotaxis assay by integrating the on-chip neutrophil isolation from whole blood and the chemotaxis test on a single microfluidic chip.

Neutrophil migration and chemotaxis are critical for our body's immune system. Microfluidic devices are increasingly used for investigating neutrophil ...

The overall goal of this procedure is to demonstrate a method to separate neutrophils from a drop of whole blood and then perform a subsequent chemotaxis assay using a single microfluidic device. This method provides our code to perform a neutrophil chemotaxis assay using small volume of whole blood. And can be easily applied by researchers to answer biological questions related to immune cell migration.The main advantage of this technique is integration of and our chemotaxis assay on single microfluidic device. This permits assembled and analysis in 25 minutes. To begin, prepare the master maldus described in the accompanying text protocol.Then silanize the surface of the SU8 mold to facilitate the release of PDMS from the mold. Next, mix 40 grams of PDMS base and four grams of the carrying agent in a plastic beaker. Place the prepared SU8 master mold in a petri dish and carefully pour the mixed PDMS solution onto the mold.Place the petri dish in a dessicator and apply a vacuum to de-gas the PDMS solution for 20 minutes. Then, place the petri dish in an oven and cure the PDMS at 80 degrees Celsius for two hours. After baking, carefully cut and peel off the PDMS slab from the SU8 mold.Cut the PDMS slab to separate it into individual devices. Trim the PDMS device to make two walls around the cell loading port for holding the magnets. Next, punch out the cell loading port using a three millimeter diameter puncher.Then, switch to a six millimeter punch and remove the chemical inlet reservoirs in the waste outlet. Using a piece of adhesive tape, remove the dust on the surface of the PDMS slab. Place the clean slab in a clean glass slide into the plasma machine.Apply the vacuum for three minutes. And then turn on the plasma power and set the level to high. Gently adjust the air valve and plasma treat the PDMS and the glass slide for three minutes.When finished, turn off the plasma power and release the vacuum. Carefully take out the PDMS slab in the glass slide using tweezers, immediately place the PDMS slab on top of the glass slide, with channel structures face down gently press the PDMS slab to bond it to the glass and then immediately fill the microfluidic channel with deionized water. The PDMS were generally pressed onto the glass substrate to avoid in the well in barrier channel.Remove the deionized water from the device and add 100 microliters of Fribronectin solution from the outlet. Wait three minutes to insure that all the channels are filled with fibronectin solution. Then, incubate the device in a covered petri dish for an hour at room temperature.Next, remove the fibronectin solution from the device and add 100 microliters of migration medium from the outlet. again, wait three minutes to ensure that all of the channels are filled with the migration medium. Incubate the device for another hour at room temperature before using the device in the chemotaxis experiment.Place ten microliters of whole blood into a 1.5 milliliter tube. Then, add two microliters of the antibody cocktail. And two microliters of magnetic particles from a neutrophil isolation kit and gently mix the tube in order to magnetically label the antibody-tagged cells.Incubate the label mixture for five minutes at room temperature. Next, attach two small magnetic disks to the two sides of the cell loading port of the device. Aspirate the medium from all ports of the device.Then, slowly pipette two microliters of the labeled blood mixture into the microfluidic device from the cell loading port. Place the microfluidic device on the temperature controlled microscope stage at 37 degrees Celsius. Wait a few minutes until enough neutrophils are trapped at the cell docking area.Next, add 100 microliters of the chemoattractant solution and 100 microliters migration medium to their designated inlet reservoirs using two pipettors. This will generate a chemoattracting gradient by continuous laminar flow based chemical mixing. The chemoattractant can be recombinant proteins such as FMLP or a clinical sample such as the supernatant of sputum from patients with COPD.Once flow has stabilized, acquire fluorescence images of the FitZ dextron gradient in the channel. Then, incubate the device on the temperature controlled microscope stage, or in a conventional cell culture incubator for 15 minutes. Following incubation, image the gradient channel using a ten times objective to record the cell's final positions for data analysis.Neutrophils are negatively selected for from a drop of whole blood directly in the microfluidic device using magnetic particle antibody labeling and a pair of magnets. In order to confirm the purity of the on chip isolated neutrophils, Giemsa staining was performed. The results show the typical ring shaped and lobe shaped nuclei of neutrophils.Following cell loading, the docking structure effectively aligns the cells next to the gradient channel before applying a chemical gradient. When exposed to a chemical gradient for 15 minutes chemotaxis occurs. And can be measured using imaging.These results show that after 15 minutes, few cells crawled through the barrier channel in the medium controlled sample. By contrast, many neutrophils rapidly moved through the barrier channel and migrated toward a 100 nanomolar FMLP gradient. Once this can mail chemotaxis directly from our in 25 minutes.This offers a useful tool for researchers to study the mechanics of whole cell migration. And a tool for clinical applications.

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Research

JoVE Journal

Immunology and Infection

16.9K Views.  Chinese Academy of Sciences. The overall goal of this procedure is to demonstrate a method to separate neutrophils from a drop of whole blood and then perform a subsequent chemotaxis assay using a single microfluidic device. This method provides our code to perform a neutrophil chemotaxis assay using small volume of whole blood. And can be easily applied by researchers to answer biological questions related to immune cell migration.The main advantage of this technique is integration of and our chemotaxis assay on ...