Name: quantifying microorganisms at low concentrations using digital holographic microscopy (dhm)
Uploaded: 2017-11-01T15:00:00
Description: Watch this Scientific Journal Video about Quantifying Microorganisms at Low Concentrations Using Digital Holographic Microscopy DHM at JoVE.com

The authors acknowledge the Gordon and Betty Moore Foundation Grants 4037 and 4038 to the California Institute of Technology for funding this work.

1. Growth and Enumeration of Bacteria
NOTE: This is applicable to almost any bacterial strain grown in the appropriate medium36. In our example, we use three strains: Serratia marcescens as a common, easy identifiable lab strain; and a smaller, highly motile environmental strain, Shewanella oneidensis MR-1. To compare detection of motile vs. non-motile cells, a non-motile Shewanella mutant, &#916; FlgM, is also used for comparison<sup class="xre...

<ol>
	<li>Akineden, O., Weirich, S., Abdulmawjood, A., Failing, K., Buelte, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+a+Fluorescence+Microscopy+Technique+for+Detecting+Viable+Mycobacterium+avium+ssp.+paratuberculosis+Cells+in+Milk.">Application of a Fluorescence Microscopy Technique for Detecting Viable Mycobacterium avium ssp. paratuberculosis Cells in Milk.</a> Food Anal. Methods. 8, 499-506 (2015).</li><li>Deibl, J., Paulsen, P., Bauer, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+enumeration+of+total+aerobic+microbial+counts+on+meat+and+in+meat+products+by+means+of+the+direct+epifluorescence+filter+technique.">Rapid enumeration of total aerobic microbial counts on meat and in meat products by means of the direct epifluorescence filter technique.</a> Wien Tierarztl Monat. 85, 327-333 (1998).</li><li>Huang, J., Li, Y., Slavik, M. F., Tao, Y., Huff, G. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+enumeration+of+Salmonella+on+sample+slides+of+poultry+carcass+wash+water+using+image+analysis+with+fluorescent+microscopy.">Identification and enumeration of Salmonella on sample slides of poultry carcass wash water using image analysis with fluorescent microscopy.</a> Transactions of the Asae. 42, 267-273 (1999).</li><li>Durtschi, J. 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=Increased+sensitivity+of+bacterial+detection+in+cerebrospinal+fluid+by+fluorescent+staining+on+low-fluorescence+membrane+filters.">Increased sensitivity of bacterial detection in cerebrospinal fluid by fluorescent staining on low-fluorescence membrane filters.</a> J Med Microbiol. 54, 843-850 (2005).</li><li>Panicker, R. O., Soman, B., Saini, G., Rajan, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Review+of+Automatic+Methods+Based+on+Image+Processing+Techniques+for+Tuberculosis+Detection+from+Microscopic+Sputum+Smear+Images.">A Review of Automatic Methods Based on Image Processing Techniques for Tuberculosis Detection from Microscopic Sputum Smear Images.</a> J Med Syst. 40, (2016).</li><li>Riepl, 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=Applicability+of+solid-phase+cytometry+and+epifluorescence+microscopy+for+rapid+assessment+of+the+microbiological+quality+of+dialysis+water.">Applicability of solid-phase cytometry and epifluorescence microscopy for rapid assessment of the microbiological quality of dialysis water.</a> Nephrol Dial Transplant. 26, 3640-3645 (2011).</li><li>Hwang, C. Y., Cho, B. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Virus-infected+bacteria+in+oligotrophic+open+waters+of+the+East+Sea,+Korea.">Virus-infected bacteria in oligotrophic open waters of the East Sea, Korea.</a> Aquat Microb Ecol. 30, 1-9 (2002).</li><li>Kepner, R. L., Pratt, 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=Use+of+Fluorochromes+for+Direct+Enumeration+of+Total+Bacteria+in+Environmental-Samples+-+Past+and+Present.">Use of Fluorochromes for Direct Enumeration of Total Bacteria in Environmental-Samples - Past and Present.</a> Microbiol Rev. 58, 603-615 (1994).</li><li>Queric, N. V., Soltwedel, T., Arntz, W. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Application+of+a+rapid+direct+viable+count+method+to+deep-sea+sediment+bacteria.">Application of a rapid direct viable count method to deep-sea sediment bacteria.</a> J Microbiol Meth. 57, 351-367 (2004).</li><li>Prieto-Ballesteros, O., Vorobyova, E., Parro, V., Rodriguez Manfredi, J. A., Gomez, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Strategies+for+detection+of+putative+life+on+Europa.">Strategies for detection of putative life on Europa.</a> Adv Space Res. 48, 678-688 (2011).</li><li>Gleeson, D. 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=Biosignature+Detection+at+an+Arctic+Analog+to+Europa.">Biosignature Detection at an Arctic Analog to Europa.</a> Astrobiology. 12, 135-150 (2012).</li><li>Carr, C. E., Zuber, M. T., Ruvkun, G., Ieee, <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> 2013 Ieee Aerospace Conference IEEE Aerospace Conference Proceedings. , (2013).</li><li>Konstantinidis, 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=A+lander+mission+to+probe+subglacial+water+on+Saturn's+moon+Enceladus+for+life.">A lander mission to probe subglacial water on Saturn's moon Enceladus for life.</a> Acta Astronautica. 106, 63-89 (2015).</li><li>McKay, C. P., Anbar, A. D., Porco, C., Tsou, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Follow+the+Plume:+The+Habitability+of+Enceladus.">Follow the Plume: The Habitability of Enceladus.</a> Astrobiology. 14, 352-355 (2014).</li><li>Hoover, R. B., Hoover, R. B., Levin, G. V., Rozanov, A. Y., Wickramasinghe, N. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Instruments, Methods, and Missions for Astrobiology Xvii. , (2015).</li><li>Handelsman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Metagenomics:+application+of+genomics+to+uncultured+microorganisms.">Metagenomics: application of genomics to uncultured microorganisms.</a> Microbiol Mol Biol Rev: MMBR. 68, 669-685 (2004).</li><li>Lebaron, P., Parthuisot, N., Catala, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+of+blue+nucleic+acid+dyes+for+flow+cytometric+enumeration+of+bacteria+in+aquatic+systems.">Comparison of blue nucleic acid dyes for flow cytometric enumeration of bacteria in aquatic systems.</a> Appl Environ Microbiol. 64, 1725-1730 (1998).</li><li>Marie, D., Partensky, F., Jacquet, S., Vaulot, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Enumeration+and+cell+cycle+analysis+of+natural+populations+of+marine+picoplankton+by+flow+cytometry+using+the+nucleic+acid+stain+SYBR+Green+I.">Enumeration and cell cycle analysis of natural populations of marine picoplankton by flow cytometry using the nucleic acid stain SYBR Green I.</a> Appl Environ Microbiol. 63, 186-193 (1997).</li><li>Noble, R. T., Fuhrman, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Use+of+SYBR+Green+I+for+rapid+epifluorescence+counts+of+marine+viruses+and+bacteria.">Use of SYBR Green I for rapid epifluorescence counts of marine viruses and bacteria.</a> Aquat Microb Ecol. 14, 113-118 (1998).</li><li>Forster, S., Snape, J. R., Lappin-Scott, H. M., Porter, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+fluorescent+gram+staining+and+activity+assessment+of+activated+sludge+bacteria.">Simultaneous fluorescent gram staining and activity assessment of activated sludge bacteria.</a> Appl Environ Microbiol. 68, 4772-4779 (2002).</li><li>Lauer, B. A., Reller, L. B., Mirrett, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Comparison+Of+Acridine-Orange+And+Gram+Stains+For+Detection+Of+Microorganisms+In+Cerebrospinal-Fluid+And+Other+Clinical+Specimens.">Comparison Of Acridine-Orange And Gram Stains For Detection Of Microorganisms In Cerebrospinal-Fluid And Other Clinical Specimens.</a> J Clin Microbiol. 14, 201-205 (1981).</li><li>Mason, D. J., Shanmuganathan, S., Mortimer, F. C., Gant, V. 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+fluorescent+gram+stain+for+flow+cytometry+and+epifluorescence+microscopy.">A fluorescent gram stain for flow cytometry and epifluorescence microscopy.</a> Appl Environ Microbiol. 64, 2681-2685 (1998).</li><li>Saida, H., Ytow, N., Seki, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photometric+application+of+the+Gram+stain+method+to+characterize+natural+bacterial+populations+in+aquatic+environments.">Photometric application of the Gram stain method to characterize natural bacterial populations in aquatic environments.</a> Appl Environ Microbiol. 64, 742-747 (1998).</li><li>Sizemore, R. K., Caldwell, J. J., Kendrick, A. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alternate+Gram+Staining+Technique+Using+A+Fluorescent+Lectin.">Alternate Gram Staining Technique Using A Fluorescent Lectin.</a> Appl Environ Microbiol. 56, 2245-2247 (1990).</li><li>Bitton, G., Dutton, R. J., Foran, J. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=New+Rapid+Technique+For+Counting+Microorganisms+Directly+On+Membrane+Filters.">New Rapid Technique For Counting Microorganisms Directly On Membrane Filters.</a> Stain Technology. 58, 343-346 (1983).</li><li>Broadaway, S. C., Barton, S. A., Pyle, B. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Rapid+staining+and+enumeration+of+small+numbers+of+total+bacteria+in+water+by+solid-phase+laser+cytometry.">Rapid staining and enumeration of small numbers of total bacteria in water by solid-phase laser cytometry.</a> Appl Environ Microbiol. 69, 4272-4273 (2003).</li><li>Yagupsky, P., Nolte, F. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+aspects+of+septicemia.">Quantitative aspects of septicemia.</a> Clin Microbiol Rev. 3, 269-279 (1990).</li><li>Kang, D. 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=Rapid+detection+of+single+bacteria+in+unprocessed+blood+using+Integrated+Comprehensive+Droplet+Digital+Detection.">Rapid detection of single bacteria in unprocessed blood using Integrated Comprehensive Droplet Digital Detection.</a> Nat Commun. 5, 5427 (2014).</li><li>Hand, K. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=.">.</a> Report of the Europa Lander Science Definition Team. , (2017).</li><li>Popescu, 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=Optical+imaging+of+cell+mass+and+growth+dynamics.">Optical imaging of cell mass and growth dynamics.</a> Am J Physiol-Cell Physiol. 295, C538-C544 (2008).</li><li>Mir, 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=Optical+measurement+of+cycle-dependent+cell+growth.">Optical measurement of cycle-dependent cell growth.</a> Proc Natl Acad Sci U S A. 108, 13124-13129 (2011).</li><li>Rappaz, B., 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=Noninvasive+characterization+of+the+fission+yeast+cell+cycle+by+monitoring+dry+mass+with+digital+holographic+microscopy.">Noninvasive characterization of the fission yeast cell cycle by monitoring dry mass with digital holographic microscopy.</a> J.Biomed Opt. 14, 034049 (2009).</li><li>Jo, Y., 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=Label-free+identification+of+individual+bacteria+using+Fourier+transform+light+scattering.">Label-free identification of individual bacteria using Fourier transform light scattering.</a> Opt. Express. 23, 15792-15805 (2015).</li><li>Wallace, J. 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=Robust,+compact+implementation+of+an+off-axis+digital+holographic+microscope.">Robust, compact implementation of an off-axis digital holographic microscope.</a> Opt. Express. 23, 17367-17378 (2015).</li><li>Lindensmith, C. A., 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+Submersible,+Off-Axis+Holographic+Microscope+for+Detection+of+Microbial+Motility+and+Morphology+in+Aqueous+and+Icy+Environments.">A Submersible, Off-Axis Holographic Microscope for Detection of Microbial Motility and Morphology in Aqueous and Icy Environments.</a> Plos One. 11, e0147700 (2016).</li><li>Dumas, E. M., Ozenne, V., Mielke, R. E., Nadeau, J. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Toxicity+of+CdTe+Quantum+Dots+in+Bacterial+Strains.">Toxicity of CdTe Quantum Dots in Bacterial Strains.</a> IEEE Trans. NanoBiosci. 8, 58-64 (2009).</li><li>Frisk, A., Jyot, J., Arora, S. K., Ramphal, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+and+functional+characterization+of+flgM,+a+gene+encoding+the+anti-sigma+28+factor+in+Pseudomonas+aeruginosa.">Identification and functional characterization of flgM, a gene encoding the anti-sigma 28 factor in Pseudomonas aeruginosa.</a> J Bacteriol. 184, 1514-1521 (2002).</li><li>Adler, J., Templeton, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+effect+of+environmental+conditions+on+the+motility+of+Escherichia+coli.">The effect of environmental conditions on the motility of Escherichia coli.</a> Journal Gen Microbiol. 46, 175-184 (1967).</li><li>Piedrahita-Quintero, P., Castaneda, R., Garcia-Sucerquia, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Numerical+wave+propagation+in+Image+J.">Numerical wave propagation in Image J.</a> Appl Opt. 54, 6410-6415 (2015).</li><li>Schnars, U., J&#252;ptner, W. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Digital+recording+and+numerical+reconstruction+of+holograms.">Digital recording and numerical reconstruction of holograms.</a> Meas. Sci. Technol. 13, R85 (2002).</li></ol>

Numerical reconstruction of holograms: For the numerical reconstruction of holograms, the angular spectrum method (ASM) is used. This involves the convolution of the hologram with the Green&#39;s Function for the DHM. The complex wavefront of the image at a particular focal plane can be calculated by employing the Fourier Convolution Theorem as follows:
<img alt="Equation 2" src="/files/ftp_upload/56343/56343eq2.jpg" /> (1)
Where&#160;<img alt="Equa...

Determination of accurate bacterial counts in very dilute samples is crucial in many applications: a few examples are water and food quality analysis1,2,3; detection of pathogens in blood, cerebrospinal fluid, or sputum4,5; production of pharmaceutical products, including sterile water6; and environmental community analysis in oligotrophic environments such as the open ocean and sediments7,8,9. There is also increasing interest in detection of possible extant microbial life on the icy moons of Jupiter and Saturn, particularly Europa10,11 and Enceladus12,13,14, which are known to have subsurface liquid oceans. Because no mission since Viking in 1978 has attempted to find extant life on another planet, there has been limited development of technologies and instruments for bacterial identification and counting during space missions15.
Traditional methods of plate count find only culturable cells, which can represent a minority of species in environmental strains, sometimes &#60;1%16. Plates require days or weeks of incubation for maximum success, depending upon the strain. Epifluorescence microscopy has largely replaced plate counts as the gold standard for rapid and accurate microbial enumeration. Nucleic-acid-labeling fluorescent dyes such as 4&#8242;,6-diamidino-2-phenylindole dihydrochloride (DAPI), SYBR Green, or acridine orange that bind to nucleic acids are the typical dyes used17,18,19, though many studies use fluorescent indicators of Gram sign20,21,22,23,24. Using these methods without pre-concentration steps leads to limits of detection (LoDs) of ~105 cells per mL. Improvements in LoD are possible using filtration. A liquid sample is vacuum-filtered onto a membrane, usually polycarbonate and ideally black to reduce background. Low-background dyes such as the DNA stains mentioned above may be applied directly to the filter25. For accurate counting by eye, ~105 cells are required per filter, which means that for samples more dilute than ~105 cells per mL, significant sample volumes must be collected and filtered. Laser-scanning devices have been developed in order to systematically explore all regions of the filter and thus reduce the number of cells required for counting, pushing limits of detection down to ~102 cells per mL26. However, these are not available in most laboratories, and require sophisticated hardware as well as software that permit expert confirmation that observed particles are bacteria and not debris.
For reference, adults with sepsis usually begin showing symptoms at &#60;100 cells/mL of blood, and infants at &#60;10 cells/mL. A blood draw from an adult takes 10 mL, and from an infant, 1 mL. PCR-based methods are inhibited by the presence of human and non-pathogenic flora DNA and by PCR-inhibiting components in the blood27,28. Despite a variety of emerging techniques, cultures remain the gold standard for the diagnosis of bloodstream infections, especially in more rural areas or developing nations. For detection of life on other planets, thermodynamic calculations can estimate the energy budget for life and thus the expected possible biomass. 1 - 100 cells/mL are expected to be thermodynamically reasonable on Europa29. It can be readily seen from these numbers that detection of very small numbers of cells in large amounts of aqueous solution is an important unsolved problem.
In this paper, we demonstrate detection of Serratia marcescens and Shewanella oneidensis (wild-type and non-motile mutant) at concentrations of 105, 104, 103, and 100 cells/mL using an off-axis digital holographic microscope (DHM). The key advantage of DHM over traditional light microscopy is the simultaneous imaging of a thick sample volume at high resolution&#8212;in this implementation, the sample chamber was 0.8 mm thick. These sample chambers were constructed by the soft-lithography of polydimethylsiloxane (PDMS) from a precision-machined aluminum mold with a tolerance of &#177; 50 &#181;m. This represents an approximately 100-fold improvement in depth of field over high-power light microscopy. DHM also provides quantitative phase information, allowing for measurements of optical path length (product of refractive index and thickness). DHM and similar techniques have been used for monitoring bacterial and yeast cell cycle and calculation of bacterial dry mass30,31,32; scattering differences may even be used to differentiate bacterial strains33.
The instrument we use is custom-built specifically for use with microorganisms, as previously published34,35, and its design and construction are demonstrated and discussed. Aqueous solutions are continuously supplied to a 0.25 &#181;L volume sample chamber via syringe pump; the flow rate is determined by camera frame rate in order to ensure imaging of the entire sample volume. A statistical calculation predicts the number of sample volumes that must be imaged in order to detect a significant number of cells at a given concentration.
For cell-detection applications, reconstruction of the holograms into amplitude and phase images was not required; analysis was performed on the raw hologram. This saves significant computational resources and disk space: a 500 Mb hologram video will be 1 - 2 Tb when reconstructed. However, we do discuss reconstruction through depth of the sample to confirm that the holograms represent the desired species. An important feature of DHM is its ability to monitor both intensity and phase of the images. Organisms that are nearly transparent in intensity (such as most biological cells) appear clearly in phase. As it is a label-free technique, no dyes are used. This is an advantage for possible space flight applications, since dyes may not survive the conditions of a mission and&#8212;more importantly&#8212;cannot be assumed to work with extraterrestrial organisms, which may not use DNA or RNA for encoding. It is also an advantage for work in extreme environments such as the Arctic and Antarctic, where dyes may be difficult to bring to the remote location and may degrade upon storage. Reconstruction of images into phase and amplitude is performed using an open-source software package that we have made available on GitHub (SHAMPOO) or using ImageJ.

<table>
	<tbody>
		<tr>
			<td>Bacto Yeast</td>
			<td>BD Biosciences</td>
			<td>212750</td>
			<td></td>
		</tr>
		<tr>
			<td>Bacto Tryptone</td>
			<td>BD Biosciences</td>
			<td>211705</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>7710</td>
			<td>Many options for purchase</td>
		</tr>
		<tr>
			<td>Bacto Agar</td>
			<td>BD Biosciences</td>
			<td>214010</td>
			<td></td>
		</tr>
		<tr>
			<td>10 cm Petri dishes</td>
			<td>VWR</td>
			<td>10053-704</td>
			<td></td>
		</tr>
		<tr>
			<td>15 mL culture tubes</td>
			<td>Falcon (Corning Life Sciences)</td>
			<td>352002</td>
			<td>Loose-capped</td>
		</tr>
		<tr>
			<td>Petroff-Hauser chamber</td>
			<td>Electron Microscopy Sciences</td>
			<td>3920</td>
			<td></td>
		</tr>
		<tr>
			<td>10 mL syringes</td>
			<td>BD Biosciences</td>
			<td>309604</td>
			<td>Luer-Lok tip not necessary</td>
		</tr>
		<tr>
			<td>Male Luer to 1/16&#8221; barbed fitting</td>
			<td>McMaster-Carr</td>
			<td>51525K291</td>
			<td></td>
		</tr>
		<tr>
			<td>Autoclavable 1/16&#8221; ID PVC tubing for flow</td>
			<td>Nalgene</td>
			<td>8000-0004</td>
			<td>Sold by length, purchase accordingly</td>
		</tr>
		<tr>
			<td>Syringe pump</td>
			<td>Harvard Apparatus</td>
			<td>PHD 2000</td>
			<td></td>
		</tr>
		<tr>
			<td>Sample Chamber</td>
			<td>Custom</td>
			<td>n/a</td>
			<td>See Materials Section</td>
		</tr>
		<tr>
			<td>Holographic Microscope</td>
			<td>Custom</td>
			<td>n/a</td>
			<td>See Wallace et al.</td>
		</tr>
		<tr>
			<td>Open-source software</td>
			<td>Custom</td>
			<td>https://github.com/bmorris3/shampoo</td>
			<td></td>
		</tr>
	</tbody>
</table>

quantifying microorganisms at low concentrations using digital holographic microscopy (dhm)

Accurately detecting and counting sparse bacterial samples has many applications in the food, beverage, and pharmaceutical processing industries, in medical diagnostics, and for life detection by robotic missions to other planets and moons of the solar system. Currently, sparse bacterial samples are counted by culture plating or epifluorescence microscopy. Culture plates require long incubation times (days to weeks), and epifluorescence microscopy requires extensive staining and concentration of the sample. Here, we demonstrate how to use off-axis digital holographic microscopy (DHM) to enumerate bacteria in very dilute cultures (100-104 cells/mL). First, the construction of the custom DHM is discussed, along with detailed instructions on building a low-cost instrument. The principles of holography are discussed, and a statistical model is used to estimate how long videos should be to detect cells, based on the optical performance characteristics of the instrument and the concentration of the bacterial solution (Table 2). Video detection of cells at 105, 104, 103, and 100 cells/mL is demonstrated in real time using un-reconstructed holograms. Reconstruction of amplitude and phase images is demonstrated using an open-source software package.

The results should indicate the ability to detect living and dead bacteria at very low levels by DHM. The number of bacteria counted should be consistent with the results obtained using the Petroff-Hauser counting chamber and plate counts. Standard statistical methods provide information about the accuracy of the different detection methods at various bacterial concentrations.
Figure 1 shows the Pet...

Watch this Scientific Journal Video about Quantifying Microorganisms at Low Concentrations Using Digital Holographic Microscopy DHM at JoVE.com

Quantifying Microorganisms at Low Concentrations Using Digital Holographic Microscopy DHM

Digital holographic microscopy (DHM) is a volumetric technique that allows imaging samples 50-100X thicker than brightfield microscopy at comparable resolution, with focusing performed post-processing. Here DHM is used for identifying, counting, and tracking microorganisms at very low densities and compared with optical density measurements, plate count, and direct count.

Quantifying Microorganisms at Low Concentrations Using Digital Holographic Microscopy (DHM)

Accurately detecting and counting sparse bacterial samples has many applications in the food, beverage, and pharmaceutical processing industries, in ...

The overall goal of this experiment is to demonstrate the detection of microorganisms at very low levels using digital holographic microscopy. This technique is more sensitive than traditional light microscopy and provides real-time information about bacterial behaviors. This method can help answer key questions in the biological and cosmological fields such as searching for pathogenic organisms in water or life within our solar system on icy moons.The main advantage of this technique is that DHM is a volumetric technique which means we can capture three-dimensional information on our sample instantaneously without any need to physically refocus. The implications of this technique extend toward the diagnosis of blood stream or cerebrospinal fluid infections because of the ability to detect low bacterial concentrations. To begin this procedure, on the day of the experiment, take a spectrophotometric reading of the bacterial master culture which is expected to be in the range of 0.6 to 0.7.Then take a sample of the master culture and count the cells directly using a Petroff-Hausser counting chamber to enumerate both live and dead cells. Transfer a 10 microliter sample of the undiluted culture with a micropipette to the chamber. Image it under a high dry objective microscope using phase contrast.Subsequently, count the bacteria in at least 20 squares and average them. Calculate the concentration as the average of 20 squares times the dilution factor. To enumerate only live cells, make a serial dilution of each of the selected bacterial samples with sterile 0.9%saline solution by transferring 20 microliters of the bacterial solution to another well and diluting it with 180 microliters of saline.Repeat the procedure until the lowest concentration is approximately 10 to the three cells per milliliter. Next, take 100 microliters of the samples from at least two dilutions and plate them on the appropriate solid media plates. Spread them with a sterile spreader and perform at least three replicates of each dilution.After that, incubate them at an appropriate temperature overnight or until the colonies grow. Then count the colonies. Calculate the colony-forming units and average it over the replicates.In this procedure, make serial dilutions of the master culture for DHM and post-DHM counting of CFU on Lysogeny broth media plates. Dilute the bacteria into 25 milliliters of a minimal medium that will encourage motility but inhibit cell division so that the concentration of cells does not change appreciably during the experiment. To record DHM videos, using a sterile syringe, draw in about 10 milliliters of the dilution of interest.Then connect the syringe to the DHM sample chamber using sterile fittings and tubing. Flow the sample from the syringe through the sample chamber continuously using a syringe pump. As the sample flows through the sample chamber, acquire holograms consecutively at an appropriate frame rate.Allow sufficient time for the entire 10 milliliters of sample to flow through the DHM. To ensure that bacteria are not growing or dying during the experiments, inoculate the enriched media plates with 100 microliters of the spent media post-DHM image capture by spreading it with a sterile spreader. Then incubate them at the appropriate temperature for 24 hours before counting the colonies.Having accurate cell counts is essential to determine the detection limits quantitatively. It is important to make all dilutions with great care using calibrated micropipettes and confirm all counts by optical density, plating, and direct counting in the Petroff-Hausser chamber. To analyze the data for bacterial presence in the acquired hologram videos, conduct medium subtracted filtering by first converting the images to a 32-bit format.Then calculate the median pixel value. Finally, subtract this median value from each respective pixel to eliminate stationary artifacts in the hologram. After that, count the number of visible area rings and in-focus cells manually.Each series of holograms will be accompanied by a timestamp file. Use the timestamp file to calculate the total amount of sample pumped at the time the image was captured. Subsequently, calculate the cell density by dividing the total number of cells detected by the total volume of sample imaged.Average five to 10 frames for accurate statistics. This plot shows the predicted cells per field of view based upon a sample volume of 365 micrometers by 365 micrometers by one millimeter. For concentrations where the number of cells per field of view falls below one, multiple images are required in order to achieve detection.This is a DHM hologram sequence of a Serratia marcescens culture at 2, 100 cells per milliliter measured by plate count. The sequence shows one cell roughly every one to two seconds which is an excellent fit to the prediction. And this is another DHM hologram sequence of a Serratia marcescens culture at 620 cells per milliliter measured by plate count.This sequence shows one cell roughly every six to seven seconds. When using digital holographic microscopy to image cells, remember to use filter sterilization techniques in preparation of all solutions. This will avoid introducing particulate matter into the instrument.While attempting this procedure, it is important to remember to prepare healthy cell cultures and have extra growth medium, plates, and motility medium on hand. Following this procedure, other methods like fluorescent staining can be performed in order to answer additional questions such as the percentage of cells that are alive versus dead. After its development, this technique paved the way for researchers in the field of microbiology to explore three-dimensional motility in cultured cells and environmental samples.After watching this video, you should have a good understanding of how to enumerate bacteria using holographic microscopy and validate the results using other counting techniques. Don't forget that working with bacterial cultures can be extremely hazardous. Appropriate biosafety precautions should always be taken when growing and handling live organisms.

quantifying-microorganisms-at-low-concentrations-using-digital

Research

JoVE Journal

Bioengineering

Separating Beads and Cells in Multi-channel Microfluidic Devices Using Dielectrophoresis and Laminar Flow

Microfluidic devices have advanced cell studies by providing a dynamic fluidic environment on the scale of the cell for studying, manipulating, sorting and counting cells. However, manipulating the cell within the fluidic domain remains a challenge and requires complicated fabrication protocols for forming valves and electrodes, or demands specialty equipment like optical tweezers. Here, we demonstrate that conventional printed circuit boards (PCB) can be used for the non-contact manipulation of cells by employing dielectrophoresis (DEP) for bead and cell manipulation in laminar flow fields for bioactuation, and for cell and bead separation in multichannel microfluidic devices. First, we present the protocol for assembling the DEP electrodes and microfluidic devices, and preparing the cells for DEP. Then, we characterize the DEP operation with polystyrene beads. Lastly, we show representative results of bead and cell separation in a multichannel microfluidic device. In summary, DEP is an effective method for manipulating particles (beads or cells) within microfluidic devices.

Dielectrophoresis (DEP) is an effective method to manipulate cells. Printed circuit boards (PCB) can provide inexpensive, reusable and effective electrodes for contact-free cell manipulation within microfluidic devices. By combining PDMS-based microfluidic channels with coverslips on PCBs, we demonstrate bead and cell manipulation and separation within multichannel microfluidic devices.

Microfluidic devices have advanced cell studies by providing a dynamic fluidic environment on the scale of the cell for studying, manipulating, sorting ...

Low-Cost Cryo-Light Microscopy Stage Fabrication for Correlated Light/Electron Microscopy

The coupling of cryo-light microscopy (cryo-LM) and cryo-electron microscopy (cryo-EM) poses a number of advantages for understanding cellular 
dynamics and ultrastructure. First, cells can be imaged in a near native environment for both techniques. Second, due to the vitrification process, samples are
 preserved by rapid physical immobilization rather than slow chemical fixation. Third, imaging the same sample with both cryo-LM and cryo-EM provides correlation of
 data from a single cell, rather than a comparison of "representative samples". While these benefits are well known from prior studies, the widespread use of correlative 
 cryo-LM and cryo-EM remains limited due to the expense and complexity of buying or building a suitable cryogenic light microscopy stage. Here we demonstrate the 
 assembly, and use of an inexpensive cryogenic stage that can be fabricated in any lab for less than $40 with parts found at local hardware and grocery stores. This 
 cryo-LM stage is designed for use with reflected light microscopes that are fitted with long working distance air objectives. For correlative cryo-LM and cryo-EM 
 studies, we adapt the use of carbon coated standard 3-mm cryo-EM grids as specimen supports. After adsorbing the sample to the grid, previously established protocols 
 for vitrifying the sample and transferring/handling the grid are followed to permit multi-technique imaging. As a result, this setup allows any laboratory with a 
 reflected light microscope to have access to direct correlative imaging of frozen hydrated samples.

We demonstrate the fabrication of a low-cost cryogenic stage designed to fit most reflected light microscopes. This lab-built cryogenic stage enables efficient and reliable correlative imaging between cryo-light and cryo-electron microscopy.

The coupling of cryo-light microscopy (cryo-LM) and cryo-electron microscopy (cryo-EM) poses a number of advantages for understanding cellular 
dynamics ...

Visualization of Cortex Organization and Dynamics in Microorganisms, using Total Internal Reflection Fluorescence Microscopy

TIRF microscopy has emerged as a powerful imaging technology to study spatio-temporal dynamics of fluorescent molecules in vitro and in living cells1. The optical phenomenon of total internal reflection occurs when light passes from a medium with high refractive index into a medium with low refractive index at an angle larger than a characteristic critical angle (i.e. closer to being parallel with the boundary). Although all light is reflected back under such conditions, an evanescent wave is created that propagates across and along the boundary, which decays exponentially with distance, and only penetrates sample areas that are 100-200 nm near the interface2. In addition to providing superior axial resolution, the reduced excitation of out of focus fluorophores creates a very high signal to noise ratios and minimizes damaging effects of photobleaching2,3. Being a widefield technique, TIRF also allows faster image acquisition than most scanning based confocal setups.
At first glance, the low penetration depth of TIRF seems to be incompatible with imaging of bacterial and fungal cells, which are often surrounded by thick cell walls. On the contrary, we have found that the cell walls of yeast and bacterial cells actually improve the usability of TIRF and increase the range of observable structures4-8. Many cellular processes can therefore be directly accessed by TIRF in small, single-cell microorganisms, which often offer powerful genetic manipulation techniques. This allows us to perform in vivo biochemistry experiments, where kinetics of protein interactions and activities can be directly assessed in living cells.
We describe here the individual steps required to obtain high quality TIRF images for Saccharomyces cerevisiae or Bacillus subtilis cells. We point out various problems that can affect TIRF visualization of fluorescent probes in cells and illustrate the procedure with several application examples. Finally, we demonstrate how TIRF images can be further improved using established image restoration techniques.

Total Internal Reflection Fluorescence (TIRF) microscopy is a powerful approach to observe structures close to the cell surface at high contrast and temporal resolution. We demonstrate how TIRF can be employed to study protein dynamics at the cortex of cell wall-enclosed bacterial and fungal cells.

TIRF microscopy has emerged as  a powerful imaging technology to study spatio-temporal dynamics of fluorescent molecules  in vitro and in living cells1. ...

Induction of Adhesion-dependent Signals Using Low-intensity Ultrasound

In multicellular organisms, cell behavior is dictated by interactions with the extracellular matrix. Consequences of matrix-engagement range from regulation of cell migration and proliferation, to secretion and even differentiation. The signals underlying each of these complex processes arise from the molecular interactions of extracellular matrix receptors on the surface of the cell. Integrins are the prototypic receptors and provide a mechanical link between extracellular matrix and the cytoskeleton, as well as initiating some of the adhesion-dependent signaling cascades. However, it is becoming increasingly apparent that additional transmembrane receptors function alongside the integrins to regulate both the integrin itself and signals downstream. The most elegant of these examples is the transmembrane proteoglycan, syndecan-4, which cooperates with &alpha;5&beta;1-integrin during adhesion to fibronectin. In vivo models demonstrate the importance of syndecan-4 signaling, as syndecan-4-knockout mice exhibit healing retardation due to inefficient fibroblast migration1,2. In wild-type animals, migration of fibroblasts toward a wound is triggered by the appearance of fibronectin that leaks from damaged capillaries and is deposited by macrophages in injured tissue. Therefore there is great interest in discovering strategies that enhance fibronectin-dependent signaling and could accelerate repair processes.
The integrin-mediated and syndecan-4-mediated components of fibronectin-dependent signaling can be separated by stimulating cells with recombinant fibronectin fragments. Although integrin engagement is essential for cell adhesion, certain fibronectin-dependent signals are regulated by syndecan-4. Syndecan-4 activates the Rac1 protrusive signal3, causes integrin redistribution1, triggers recruitment of cytoskeletal molecules, such as vinculin, to focal adhesions4, and thereby induces directional migration3. We have looked for alternative strategies for activating such signals and found that low-intensity pulsed ultrasound (LIPUS) can mimic the effects of syndecan-4 engagement5. In this protocol we describe the method by which 30 mW/cm2, 1.5 MHz ultrasound, pulsed at 1 kHz (Fig. 1) can be applied to fibroblasts in culture (Fig. 2) to induce Rac1 activation and focal adhesion formation. Ultrasound stimulation is applied for a maximum of 20 minutes, as this combination of parameters has been found to be most efficacious for acceleration of clinical fracture repair6. The method uses recombinant fibronectin fragments to engage &alpha;5&beta;1-integrin, without engagement of syndecan-4, and requires inhibition of protein synthesis by cycloheximide to block deposition of additional matrix by the fibroblasts., The positive effect of ultrasound on repair mechanisms is well documented7,8, and by understanding the molecular effect of ultrasound in culture we should be able to refine the therapeutic technique to improve clinical outcomes.

This protocol describes the stimulation of cultured fibroblasts with low-intensity pulsed ultrasound, which drives focal adhesion formation and Rac1 activation by mimicking engagement of the transmembrane matrix receptor, syndecan-4. This approach allows investigation of a successful clinical technique at the cellular level, thereby providing opportunities for refinement of the therapy.

In multicellular organisms, cell behavior is dictated by interactions with the extracellular matrix. Consequences of matrix-engagement range from ...

Quantifying the Mechanical Properties of the Endothelial Glycocalyx with Atomic Force Microscopy

Our understanding of the interaction of leukocytes and the vessel wall during leukocyte capture is limited by an incomplete understanding of the mechanical properties of the endothelial surface layer. It is known that adhesion molecules on leukocytes are distributed non-uniformly relative to surface topography 3, that topography limits adhesive bond formation with other surfaces 9, and that physiological contact forces (&asymp; 5.0 &minus; 10.0 pN per microvillus) can compress the microvilli to as little as a third of their resting length, increasing the accessibility of molecules to the opposing surface 3, 7. We consider the endothelium as a two-layered structure, the relatively rigid cell body, plus the glycocalyx, a soft protective sugar coating on the luminal surface 6. It has been shown that the glycocalyx can act as a barrier to reduce adhesion of leukocytes to the endothelial surface 4. In this report we begin to address the deformability of endothelial surfaces to understand how the endothelial mechanical stiffness might affect bond formation. Endothelial cells grown in static culture do not express a robust glycocalyx, but cells grown under physiological flow conditions begin to approximate the glycocalyx observed in vivo 2. The modulus of the endothelial cell body has been measured using atomic force microscopy (AFM) to be approximately 5 to 20 kPa 5. The thickness and structure of the glycocalyx have been studied using electron microscopy 8, and the modulus of the glycocalyx has been approximated using indirect methods, but to our knowledge, there have been no published reports of a direct measurement of the glycocalyx modulus in living cells. In this study, we present indentation experiments made with a novel AFM probe on cells that have been cultured in conditions to maximize their glycocalyx expression to make direct measurements of the modulus and thickness of the endothelial glycocalyx.

The mechanical characteristics of endothelial glycocalyx were measured by indentation using micron sized spheres on AFM cantilevers. Endothelial cells were cultured in a custom chamber under physiological flow conditions to induce glycocalyx expression. Data were analyzed using a thin film model to determine the glycocalyx thickness and modulus.

Our  understanding of the interaction of leukocytes and the vessel wall during  leukocyte capture is limited by an incomplete understanding of the ...

Design and Construction of Artificial Extracellular Matrix (aECM) Proteins from Escherichia coli for Skin Tissue Engineering

Recombinant technology is a versatile platform to create novel artificial proteins with tunable properties. For the last decade, many artificial proteins that have incorporated functional domains derived from nature (or created de novo) have been reported. In particular, artificial extracellular matrix (aECM) proteins have been developed; these aECM proteins consist of biological domains taken from fibronectin, laminins and collagens and are combined with structural domains including elastin-like repeats, silk and collagen repeats. To date, aECM proteins have been widely investigated for applications in tissue engineering and wound repair. Recently, Tjin and coworkers developed integrin-specific aECM proteins designed for promoting human skin keratinocyte attachment and propagation. In their work, the aECM proteins incorporate cell binding domains taken from fibronectin, laminin-5 and collagen IV, as well as flanking elastin-like repeats. They demonstrated that the aECM proteins developed in their work were promising candidates for use as substrates in artificial skin. Here, we outline the design and construction of such aECM proteins as well as their purification process using the thermo-responsive characteristics of elastin.

Design and Construction of Artificial Extracellular Matrix aECM Proteins from Escherichia coli for Skin Tissue Engineering

Recombinant technologies have enabled material designers to create novel artificial proteins with customized functionalities for tissue engineering applications. For example, artificial extracellular matrix proteins can be designed to incorporate structural and biological domains derived from native ECMs. Here, we describe the construction and purification of aECM proteins containing elastin-like repeats.

Recombinant technology is a versatile platform to create novel artificial proteins with tunable properties. For the last decade, many artificial proteins ...

A Guide to Structured Illumination TIRF Microscopy at High Speed with Multiple Colors

Optical super-resolution imaging with structured illumination microscopy (SIM) is a key technology for the visualization of processes at the molecular level in the chemical and biomedical sciences. Although commercial SIM systems are available, systems that are custom designed in the laboratory can outperform commercial systems, the latter typically designed for ease of use and general purpose applications, both in terms of imaging fidelity and speed. This article presents an in-depth guide to building a SIM system that uses total internal reflection (TIR) illumination and is capable of imaging at up to 10 Hz in three colors at a resolution reaching 100 nm. Due to the combination of SIM and TIRF, the system provides better image contrast than rival technologies. To achieve these specifications, several optical elements are used to enable automated control over the polarization state and spatial structure of the illumination light for all available excitation wavelengths. Full details on hardware implementation and control are given to achieve synchronization between excitation light pattern generation, wavelength, polarization state, and camera control with an emphasis on achieving maximum acquisition frame rate. A step-by-step protocol for system alignment and calibration is presented and the achievable resolution improvement is validated on ideal test samples. The capability for video-rate super-resolution imaging is demonstrated with living cells.

This article provides an in depth guide for the assembly and operation of a structured illumination microscope operating with total internal reflection fluorescence illumination (TIRF-SIM) to image dynamic biological processes with optical super-resolution in multiple colors.

Optical super-resolution imaging with structured illumination microscopy (SIM) is a key technology for the visualization of processes at the molecular ...

Circulating MicroRNA Quantification Using DNA-binding Dye Chemistry and Droplet Digital PCR

Circulating (of cell-free) microRNAs (miRNAs) are released from cells into the blood stream. The amount of specific microRNAs in the circulation has been linked to a disease state and has the potential to be used as disease biomarker. A sensitive and accurate method for circulating microRNA quantification using a dye-based chemistry and droplet digital PCR technology has been recently developed. Specifically, using Locked Nucleic Acid (LNA)-based miRNA-specific primers with a green fluorescent DNA-binding dye in a compatible droplet digital PCR system it is possible to obtain the absolute quantification of specific miRNAs. Here, we describe how performing this technique to assess miRNA amount in biological fluids, such as plasma and serum, is both feasible and effective.

A sensitive and accurate method for cell-free microRNAs quantification using a dye-based chemistry and droplet digital PCR technology is described.

Circulating (of cell-free) microRNAs (miRNAs) are released from cells into the blood stream. The amount of specific microRNAs in the circulation has been ...

Rod-based Fabrication of Customizable Soft Robotic Pneumatic Gripper Devices for Delicate Tissue Manipulation

Soft compliant gripping is essential in delicate surgical manipulation for minimizing the risk of tissue grip damage caused by high stress concentrations at the point of contact. It can be achieved by complementing traditional rigid grippers with soft robotic pneumatic gripper devices. This manuscript describes a rod-based approach that combined both 3D-printing and a modified soft lithography technique to fabricate the soft pneumatic gripper. In brief, the pneumatic featureless mold with chamber component is 3D-printed and the rods were used to create the pneumatic channels that connect to the chamber. This protocol eliminates the risk of channels occluding during the sealing process and the need for external air source or related control circuit. The soft gripper consists of a chamber filled with air, and one or more gripper arms with a pneumatic channel in each arm connected to the chamber. The pneumatic channel is positioned close to the outer wall to create different stiffness in the gripper arm. Upon compression of the chamber which generates pressure on the pneumatic channel, the gripper arm will bend inward to form a close grip posture because the outer wall area is more compliant. The soft gripper can be inserted into a 3D-printed handling tool with two different control modes for chamber compression: manual gripper mode with a movable piston, and robotic gripper mode with a linear actuator. The double-arm gripper with two actuatable arms was able to pick up objects of sizes up to 2 mm and yet generate lower compressive forces as compared to elastomer-coated and non-coated rigid grippers. The feasibility of having other designs, such as single-arm or hook gripper, was also demonstrated, which further highlighted the customizability of the soft gripper device, and it's potential to be used in delicate surgical manipulation to reduce the risk of tissue grip damage.

This protocol describes a rod-based approach, combining 3D-printing and soft lithography techniques for fabricating the soft gripper devices. This approach eliminates the need for an external air source by incorporating a chamber component and reduces the chance of occlusion during the sealing process, particularly for miniaturized pneumatic channels.

Soft compliant gripping is essential in delicate surgical manipulation for minimizing the risk of tissue grip damage caused by high stress concentrations ...

Correlative Light- and Electron Microscopy Using Quantum Dot Nanoparticles

A method is described whereby quantum dot (QD) nanoparticles can be used for correlative immunocytochemical studies of human pathology tissue using widefield fluorescence light microscopy and transmission electron microscopy (TEM). To demonstrate the protocol we have immunolabeled ultrathin epoxy sections of human somatostatinoma tumor using a primary antibody to somatostatin, followed by a biotinylated secondary antibody and visualization with streptavidin conjugated 585 nm cadmium-selenium (CdSe) quantum dots (QDs). The sections are mounted on a TEM specimen grid then placed on a glass slide for observation by widefield fluorescence light microscopy. Light microscopy reveals 585 nm QD labeling as bright orange fluorescence forming a granular pattern within the tumor cell cytoplasm. At low to mid-range magnification by light microscopy the labeling pattern can be easily recognized and the level of non-specific or background labeling assessed. This is a critical step for subsequent interpretation of the immunolabeling pattern by TEM and evaluation of the morphological context. The same section is then blotted dry and viewed by TEM. QD probes are seen to be attached to amorphous material contained in individual secretory granules. Images are acquired from the same region of interest (ROI) seen by light microscopy for correlative analysis. Corresponding images from each modality may then be blended to overlay fluorescence data on TEM ultrastructure of the corresponding region.

A method is described whereby quantum dot (QD) nanoparticles can be used for correlative immunocytochemical studies of epoxy embedded human pathology tissue. We employ commercial antibody fragment conjugated QDs that are visualized by widefield fluorescence light microscopy and transmission electron microscopy.

A method is described whereby quantum dot (QD) nanoparticles can be used for correlative immunocytochemical studies of human pathology tissue using ...