We thank William Rainey Harper College and the University of Illinois at Chicago for the facility to conduct these experiments. We also thank McGraw Hill Foundation for their generous support.

1. Medium Preparation
<ol>
	<li>Prepare 1 L of Tryptic Soy Broth (TSB): Into 1 L of distilled water, add 15 g of pancreatic digest of casein, 5 g of papaic digest of soybean meal, 3 g of sodium chloride, 2.5 g of dextrose, and 2.5 g of dipotassium phosphate. Sterilize before use.</li>
	<li>For Tryptic Soy Agar (TSA), add 15 g of agar to 1 L of TSB, autoclave. Then let it cool down to room temperature. Next, pour at a ratio of 20 mL per Petri dish (100 mm x 15 mm).</li>
	<li>Biofilm culture medium: Add 10 g of glucose to 1 L of autoclaved TSB. Sterilize by filtration using a 0.2 &#181;m filter.</li>
</ol>
2. S. aureus Biofilm Formation in 96 well Tissue Culture Plate
NOTE: The S. aureus biofilm is cultured as previously described6,21.
<ol>
	<li>Inoculate one individual colony of S. aureus from TSA in 10 mL of TSB and grow overnight at 37 &#176;C.</li>
	<li>Dilute the overnight culture into 10 mL of TSB/glucose (10 g/L) at a 1:100 (v/v) ratio. Vortex gently to mix for a consistent concentration.</li>
	<li>Transfer 200 &#956;L of diluted culture into a total of 18 wells (more for experimental groups, such a non-biofilm control to suggest a relationship to ALP activity6) from one 96 well plate. Use triplets for each time point: 0 min, 15 min, 30 min, 45 min, 60 min, and 75 min. See step 3.2.</li>
	<li>Incubate the 96 well plate at 37 &#176;C for 24 h for biofilm formation6,21.</li>
	<li>Decant the supernatant by aspiration.</li>
	<li>Wash each well with 1x phosphate buffered solution (PBS, pH 7.4), centrifuge for 5 min at 15,000 x g and decant the supernatant by aspiration.</li>
</ol>
3. Measurement of ALP Activity in S. aureus Biofilm
NOTE: ALP activity was measured as described6,18.
<ol>
	<li>Add 75 &#956;L of buffered ALP substrate consisting of commercially available pNPP to each well from step 2.6 and begin recording the time. Record each time point in triplicate.</li>
	<li>After incubation for a varied time: 0 min (control), 15 min, 30 min, 45 min, 60 min, and 75 min respectively, add 75 &#181;L of 5 M NaOH to stop the reaction.</li>
	<li>Centrifuge the plate for 5 min at 15,000 x g.</li>
	<li>Transfer 100 &#181;L of supernatant into a new 96 well plate for colorimetric measurement.</li>
	<li>Measure the absorbance of each well at 405 nm using a 96 well plate reader. Use the 0 min time point wells to control for 405 nm background noise.</li>
	<li>Repeat the entire experiment in three individual 96 well plates.</li>
</ol>

<ol>
	<li>Coleman, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Structure+and+mechanism+of+alkaline+phosphatase.">Structure and mechanism of alkaline phosphatase.</a> Annual Review of Biophysics and Biomolecular Structure. 21, 441-483 (1992).</li><li>Sharma, U., Pal, D., Prasad, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alkaline+Phosphatase:+An+Overview.">Alkaline Phosphatase: An Overview.</a> Indian Journal of Clinical Biochemistry. 29 (3), 269-278 (2014).</li><li>Mitchell, M. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+frequencies+of+elevated+alkaline+phosphatase+activity+and+rickets+exist+in+extremely+low+birth+weight+infants+despite+current+nutritional+support.">High frequencies of elevated alkaline phosphatase activity and rickets exist in extremely low birth weight infants despite current nutritional support.</a> Boston Medical Center Pediatrics. 9, 47 (2009).</li><li>Fawley, J., Gourlay, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intestinal+alkaline+phosphatase:+A+summary+of+its+role+in+clinical+disease.">Intestinal alkaline phosphatase: A summary of its role in clinical disease.</a> Journal of Surgical Research. 202 (1), 225-234 (2016).</li><li>Derman, A. I., Beckwith, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Escherichia+coli+Alkaline+Phosphatase+Localized+to+the+Cytoplasm+Slowly+Acquires+Enzymatic+Activity+in+Cells+Whose+Growth+Has+Been+Suspended:+a+Caution+for+Gene+Fusion+Studies.">Escherichia coli Alkaline Phosphatase Localized to the Cytoplasm Slowly Acquires Enzymatic Activity in Cells Whose Growth Has Been Suspended: a Caution for Gene Fusion Studies.</a> Journal of Bacteriology. 177 (13), 3764-3770 (1995).</li><li>Danikowski, K. M., Cheng, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alkaline+Phosphatase+Activity+of+Staphylococcus+aureus+grown+in+Biofilm+and+Suspension+Cultures.">Alkaline Phosphatase Activity of Staphylococcus aureus grown in Biofilm and Suspension Cultures.</a> Current Microbiology. 75, 1226-1230 (2018).</li><li>Okabayashi, K., Futai, M., Mizuno, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Localization+of+Acid+and+Alkaline+Phosphatases+in+Staphylococcus+aureus.">Localization of Acid and Alkaline Phosphatases in Staphylococcus aureus.</a> Japanese Journal of Microbiology. 18 (4), 287-294 (1974).</li><li>Cheng, K. J., Costerton, J. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Alkaline+Phosphatase+Activity+of+Rumen+Bacteria.">Alkaline Phosphatase Activity of Rumen Bacteria.</a> Applied and Environmental Microbiology. , 586-590 (1997).</li><li>Berezhetskyy, A. 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=Phosphatase+conductometric+biosensor+for+heavy-metal+ions+determination.">Phosphatase conductometric biosensor for heavy-metal ions determination.</a> Innovation and Research in Biomedical Engineering. 29 (2-3), 136-140 (2008).</li><li>Park, E. J., Kang, D. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+use+of+bacterial+alkaline+phosphatase+assay+for+rapid+monitoring+of+bacterial+counts+on+spinach.">The use of bacterial alkaline phosphatase assay for rapid monitoring of bacterial counts on spinach.</a> Journal of Food Science. 73 (5), M236-M238 (2008).</li><li>Barber, M., Kuper, S. W. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Identification+of+Staphylococcus+pyogenes+by+the+phosphatase+reaction.">Identification of Staphylococcus pyogenes by the phosphatase reaction.</a> The Journal of Pathology and Bacteriology. 63, 65-68 (1951).</li><li>Wolf, P. L., Von der Muehll, E., Ludwick, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+test+to+differentiate+Serratia+from+Enterobacter.">A new test to differentiate Serratia from Enterobacter.</a> American Journal of Clinical Pathology. 56, 241-243 (1972).</li><li>Rangam, C. M., Katdare, S. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Phosphatase+activity+of+Staphylococci+as+an+indication+of+their+pathogenicity.">Phosphatase activity of Staphylococci as an indication of their pathogenicity.</a> Indian Journal of Medical Science. 8, 610-613 (1954).</li><li>Flemming, H. -. C., 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=Biofilms:+an+emergent+form+of+bacterial+life.">Biofilms: an emergent form of bacterial life.</a> Nature Reviews Microbiology. 14, 563-575 (2016).</li><li>Hoiby, N., Bjarnsholt, T., Givskov, M., Molin, S., Ciofu, O. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Antibiotic+resistance+of+bacterial+biofilms.">Antibiotic resistance of bacterial biofilms.</a> International Journal of Antimicrobial Agents. 35, 322-332 (2010).</li><li>Ito, A., Taniuchi, A., May, T., Kawata, K., Okabe, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Increased+antibiotic+resistance+of+Escherichia+coli+in+mature+biofilms.">Increased antibiotic resistance of Escherichia coli in mature biofilms.</a> Applied and Environmental Microbiology. 75, 4093-4100 (2009).</li><li>Witherow, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+Ten-Week+Biochemistry+Lab+Project+Studying+Wild-Type+and+Mutant+Bacterial+Alkaline+Phosphatase.">A Ten-Week Biochemistry Lab Project Studying Wild-Type and Mutant Bacterial Alkaline Phosphatase.</a> Biochemistry and Molecular Biology Education. 44 (6), (2016).</li><li>Henthorn, P., Zervos, P., Raducha, M., Harris, H., Kadesch, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Expression+of+a+human+placental+alkaline+phosphatase+gene+in+transfected+cells:+Use+as+a+reporter+for+studies+of+gene+expression.">Expression of a human placental alkaline phosphatase gene in transfected cells: Use as a reporter for studies of gene expression.</a> Proceedings of the National Academy of Science USA. 85, 6324-6346 (1988).</li><li>Horney, B. S., Farmer, A. J., Honor, D. J., MacKenzie, A., Burton, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Agarose+gel+electrophoresis+of+alkaline+phosphatase+isoenzymes+in+the+serum+of+hyperthyroid+cats.">Agarose gel electrophoresis of alkaline phosphatase isoenzymes in the serum of hyperthyroid cats.</a> Veterinary Clinical Pathology. 23 (3), 98-102 (1994).</li><li>Farley, J. R., 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=Quantification+of+Skeletal+Alkaline+Phosphatase+in+Osteoporotic+Serum+by+Wheat+Germ+Agglutinin+Precipitation,+Heat+Inactivation,+and+a+Two-Site+Immunoradiometric+Assay.">Quantification of Skeletal Alkaline Phosphatase in Osteoporotic Serum by Wheat Germ Agglutinin Precipitation, Heat Inactivation, and a Two-Site Immunoradiometric Assay.</a> Clinical Chemistry. 40 (9), 1749-1756 (1994).</li><li>O&#8217;Toole, G. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microtiter+Dish+Biofilm+Formation+Assay.">Microtiter Dish Biofilm Formation Assay.</a> Journal of Visualized Experience. , (2011).</li><li>Nomoto, M., Ohsawa, M., Wang, H. L., Chen, C. C., Yeh, K. W. <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+Extracellular+Alkaline+Phosphatase+from+an+Alkalophilic+Bacterium.">Purification and Characterization of Extracellular Alkaline Phosphatase from an Alkalophilic Bacterium.</a> Agricultural and Biological Chemistry. 52 (7), 1643-1647 (1988).</li></ol>

The authors have nothing to disclose.

In our assay, we used pNPP as the ALP substrate. This is a working solution designed for ELISA and no dilution is needed. After hydrolysis by ALP, a yellow product develops and can be measured at 405 nm. At the end of the enzymatic reaction, we briefly centrifuged the 96 well plate and transferred the supernatant to a fresh 96 well plate to measure absorbance using the plate reader. We found that this extra centrifugation step is critical, since it increases the consistency of absorbance at 405 nm, probably by eliminatin...

Alkaline phosphatase (ALP) is ubiquitously expressed in both prokaryotic and eukaryotic cells1. It can catalyze the hydrolysis of monophosphate from different molecules such as nucleotides, proteins, alkaloids, phosphate esters and anhydrides of phosphoric acid. In humans, eukaryotic ALP is present in many tissues including liver, bone, intestine and placenta2. It plays important roles in protein phosphorylation, cell growth, apoptosis, stem cell processes as well as normal skeletal mineralization. Eukaryotic ALP is also a key serum indicator for the presence of diseases in bone, liver, and other tissues/organs when elevated3,4.
Prokaryotic ALP has been detected in a variety of bacterial cells, including E. coli5, S. aureus6,7 and some common rumen bacteria in the soils8. Bacterial ALP activity has been used as a biosensor in the detection of pesticides, heavy metals9 and bacterial contamination10. The constitutive expression of ALP has been used to identify Staphylococci11 and to differentiate Serratia from Enterobacter12. It is further suggested that constitutive ALP production is correlated with pathogenicity in staphylococci13. Although ALP has been studied in different settings3,4, yet little is reported for its activity and function in biofilms cultures.
A biofilm has been documented to have a differently functioning bacterial life as compared with its free-living bacterial cell counterpart14. In S. aureus, the formation of biofilm has been identified in a variety of clinical conditions and accounts for the antibiotic resistance and chronic inflammation15,16. Many molecules had been reported to be found in a biofilm matrix such as polysaccharides, proteins, nucleic acids, and lipids, but the mechanism of biofilm formation is not fully understood14. To understand the role of ALP in biofilm formation, we cultured S. aureus biofilms in 96 well tissue culture plates and measured the ALP activity using para-nitrophenylphosphate (pNPP).
The molecule pNPP is a ready-to-use substrate for ALP and has been widely used to measure ALP activity6,17,18. This colorimetric assay is based on the conversion of para-nitrophenyl phosphate (pNPP) to para-nitrophenol resulting in a colored product at 405 nm. Compared to other conventional ALP assay, such as agarose gel electrophoresis19, wheat germ agglutinin (WGA) precipitation, and WGA-HPLC20, this assay is highly specific, sensitive, easy to reproduce, and most importantly, allows for high throughput.

<table>
	<tbody>
		<tr>
			<td>Agar</td>
			<td>VWR</td>
			<td>9002-18-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Eppendorf Centrifuge</td>
			<td>Thomas Scientific</td>
			<td>5810</td>
			<td></td>
		</tr>
		<tr>
			<td>Gluose</td>
			<td>VWR</td>
			<td>50-99-7</td>
			<td></td>
		</tr>
		<tr>
			<td>NaOH pellets</td>
			<td>VWR</td>
			<td>SS0550-500GR</td>
			<td></td>
		</tr>
		<tr>
			<td>Para-nitrophenylphosphate (pNPP)&#160;</td>
			<td>Sigma</td>
			<td>P7998-100ML</td>
			<td>Typical concentrations of pNPP liquid substrates, often used in enzyme-linked immunesorbent assays (ELISA), range between 10 to 50 mM. Similar to most ready-to-use pNPP liquid substrates like the one used here, the exact pNPP concentration is not disclosed due to its proprietary nature.</td>
		</tr>
		<tr>
			<td>10X PBS, pH7.4. 
			173 mM NaCl, 
			2.7 mM KCl, 
			8 mM Na2HPO4, 
			2 mM KH2PO4</td>
			<td>Sigma</td>
			<td>P3288-1VL</td>
			<td></td>
		</tr>
		<tr>
			<td>Plate Reader</td>
			<td>Biotek</td>
			<td>ELx808</td>
			<td></td>
		</tr>
		<tr>
			<td>S. aureus</td>
			<td>ATCC</td>
			<td>ATCC25923</td>
			<td></td>
		</tr>
		<tr>
			<td>Tryptic Soy Agar&#160;&#160;&#160;&#160;&#160;&#160; 15g / L TSB</td>
			<td>VWR</td>
			<td>9002-18-0</td>
			<td></td>
		</tr>
		<tr>
			<td>Tryptic Soy Broth:&#160;&#160;&#160;&#160;&#160; g/L 
			Pancreatic Digest of Casein............ 15.0 
			Papaic Digest of Soyben Meal.........5.00 
			Sodium chloride.............................. 3.00 
			Dextrose........................................&#160; 2.50 
			Dipotassium phosphate..................2.50</td>
			<td>VWR</td>
			<td>90006-098</td>
			<td></td>
		</tr>
		<tr>
			<td>96 well tissue culture plates</td>
			<td>BD</td>
			<td>6902D09</td>
			<td>U shaped bottom</td>
		</tr>
	</tbody>
</table>

colorimetric analysis of alkaline phosphatase activity in s. aureus biofilm

Alkaline phosphatase (ALP) is a common enzyme expressed in both prokaryotic and eukaryotic cells. It catalyzes the hydrolysis of phosphate monoesters from many molecules at basic pH and plays an indispensable role in phosphate metabolism. In humans, eukaryotic ALP is one of the most frequently used enzymatic signals in diagnosing various diseases, such as cholestasis and rickets. In S. aureus, ALP is detected exclusively on the cell membrane; it is also expressed as a secretory form as well. Yet, little is known about its function in biofilm formation.
The purpose of this manuscript is to develop a quick and reliable assay to measure ALP activity in S. aureus biofilm that does not require protein isolation. Using p-nitrophenyl phosphate (pNPP) as a substrate, we measured ALP activity in S. aureus biofilm formed in 96-well tissue culture plates. Activity was based on the formation of the soluble reaction product measured by 405 nm absorbance. The high throughput nature of the 96 well tissue culture plate method provides a sensitive and reproducible method for ALP activity assays. The same experimental set up can also be extended to measure other extracellular molecular markers related to biofilm formation.

Figure 1 shows a representative result of ALP activity from biofilm cultures of S. aureus in 96 well tissue culture plates. 75 &#956;L of commercially available pNPP solution was added to each well and incubated at room temperature. After incubation for different times (0 min, 15 min, 30 min, 45 min, 60 min, and 75 min, respectively) 75 &#956;L of 5 M NaOH was added to stop the reaction. The product was then measured in a 96 well plate reader at 405 ...

Watch this Scientific Journal Video about Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm at JoVE.com

Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm

In this manuscript, we established a high throughput method to quantify alkaline phosphatase activity in S. aureus biofilm culture from 96-well tissue culture plate

Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm

Alkaline phosphatase (ALP) is a common enzyme expressed in both prokaryotic and eukaryotic cells. It catalyzes the hydrolysis of phosphate monoesters from ...

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15.4K Views.  Harper College. In this manuscript, we established a high throughput method to quantify alkaline phosphatase activity in S. aureus biofilm culture from 96-well tissue culture plate

Video: Colorimetric Analysis of Alkaline Phosphatase Activity in S. aureus Biofilm

Visualizing Proteins and Macromolecular Complexes by Negative Stain EM: from Grid Preparation to Image Acquisition

Single particle electron microscopy (EM), of both negative stained or frozen hydrated biological samples, has become a versatile tool in structural biology 1. In recent years, this method has achieved great success in studying structures of proteins and macromolecular complexes 2, 3. Compared with electron cryomicroscopy (cryoEM), in which frozen hydrated protein samples are embedded in a thin layer of vitreous ice 4, negative staining is a simpler sample preparation method in which protein samples are embedded in a thin layer of dried heavy metal salt to increase specimen contrast 5. The enhanced contrast of negative stain EM allows examination of relatively small biological samples. In addition to determining three-dimensional (3D) structure of purified proteins or protein complexes 6, this method can be used for much broader purposes. For example, negative stain EM can be easily used to visualize purified protein samples, obtaining information such as homogeneity/heterogeneity of the sample, formation of protein complexes or large assemblies, or simply to evaluate the quality of a protein preparation.
In this video article, we present a complete protocol for using an EM to observe negatively stained protein sample, from preparing carbon coated grids for negative stain EM to acquiring images of negatively stained sample in an electron microscope operated at 120kV accelerating voltage. These protocols have been used in our laboratory routinely and can be easily followed by novice users.

Visualizing protein samples by negative stain electron microscopy (EM) has become a popular structural analysis method. It is useful for quantitative structural analysis, such as calculating a 3D reconstruction of the molecules being studied, and also for qualitative examination of the quality of protein preparations. In this article we present detailed protocols for preparing the EM grids, staining the sample and visualizing the sample in an electron microscope. Novice users can follow these protocols easily and to utilize negative stain EM as a routine assay, in addition to other biochemical assays, for evaluating their protein samples.

Single particle electron microscopy (EM), of both negative stained or frozen hydrated biological samples, has become a versatile tool in structural ...

A Microfluidic Chip for the Versatile Chemical Analysis of Single Cells

We present a microfluidic device that enables the quantitative determination of intracellular biomolecules in multiple single cells in parallel. For this purpose, the cells are passively trapped in the middle of a microchamber. Upon activation of the control layer, the cell is isolated from the surrounding volume in a small chamber. The surrounding volume can then be exchanged without affecting the isolated cell. However, upon short opening and closing of the chamber, the solution in the chamber can be replaced within a few hundred milliseconds. Due to the reversibility of the chambers, the cells can be exposed to different solutions sequentially in a highly controllable fashion, e.g. for incubation, washing, and finally, cell lysis. The tightly sealed microchambers enable the retention of the lysate, minimize and control the dilution after cell lysis. Since lysis and analysis occur at the same location, high sensitivity is retained because no further dilution or loss of the analytes occurs during transport. The microchamber design therefore enables the reliable and reproducible analysis of very small copy numbers of intracellular molecules (attomoles, zeptomoles) released from individual cells. Furthermore, many microchambers can be arranged in an array format, allowing the analysis of many cells at once, given that suitable optical instruments are used for monitoring. We have already used the platform for proof-of-concept studies to analyze intracellular proteins, enzymes, cofactors and second messengers in either relative or absolute quantifiable manner.

In this article we present a microfluidic chip for single cell analysis. It allows the quantification of intracellular proteins, enzymes, cofactors, and second messengers by means of fluorescent assays or immunoassays.&#160;

We present a microfluidic device that enables the quantitative determination of intracellular biomolecules in multiple single cells in parallel. For this ...

Remote Magnetic Actuation of Micrometric Probes for in situ 3D Mapping of Bacterial Biofilm Physical Properties

Bacterial adhesion and growth on interfaces lead to the formation of three-dimensional heterogeneous structures so-called biofilms. The cells dwelling in these structures are held together by physical interactions mediated by a network of extracellular polymeric substances. Bacterial biofilms impact many human activities and the understanding of their properties is crucial for a better control of their development &#8212; maintenance or eradication &#8212; depending on their adverse or beneficial outcome. This paper describes a novel methodology aiming to measure in situ the local physical properties of the biofilm that had been, until now, examined only from a macroscopic and homogeneous material perspective. The experiment described here&#160;involves introducing magnetic particles into a growing biofilm to seed local probes that can be remotely actuated without disturbing the structural properties of the biofilm. Dedicated magnetic tweezers were developed to exert a defined force on each particle embedded in the biofilm. The setup is mounted on the stage of a microscope to enable the&#160;recording of time-lapse images of the particle-pulling period. The particle trajectories are then extracted from the pulling sequence and the local viscoelastic parameters are derived from each particle displacement curve, thereby providing the 3D-spatial distribution of the parameters. Gaining insights into the biofilm mechanical profile is essential from an engineer&#39;s point of view for biofilm control purposes but also from a fundamental perspective to clarify the relationship between the architectural properties and the specific biology of these structures.

Remote Magnetic Actuation of Micrometric Probes for in situ 3D Mapping of Bacterial Biofilm Physical Properties

This paper shows an original methodology based on the remote actuation of magnetic particles seeded in a bacterial biofilm and the development of dedicated magnetic tweezers to measure in situ the local mechanical properties of the complex living material built by micro-organisms at interfaces.

Bacterial adhesion and growth on interfaces lead to the formation of three-dimensional heterogeneous structures so-called biofilms. The cells dwelling in ...

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 ...

Protocol for Biofilm Streamer Formation in a Microfluidic Device with Micro-pillars

Several bacterial species possess the ability to attach to surfaces and colonize them in the form of thin films called biofilms. Biofilms that grow in porous media are relevant to several industrial and environmental processes such as wastewater treatment and CO2 sequestration. We used Pseudomonas fluorescens, a Gram-negative aerobic bacterium, to investigate biofilm formation in a microfluidic device that mimics porous media. The microfluidic device consists of an array of micro-posts, which were fabricated using soft-lithography. Subsequently, biofilm formation in these devices with flow was investigated and we demonstrate the formation of filamentous biofilms known as streamers in our device. The detailed protocols for fabrication and assembly of microfluidic device are provided here along with the bacterial culture protocols. Detailed procedures for experimentation with the microfluidic device are also presented along with representative results.

Protocols for the study of biofilm formation in a microfluidic device that mimics porous media are discussed. The microfluidic device consists of an array of micro-pillars and biofilm formation by Pseudomonas fluorescens in this device is investigated.

Several bacterial species possess the ability to attach to surfaces and colonize them in the form of thin films called biofilms. Biofilms that grow in ...

Methods for Characterizing the Co-development of Biofilm and Habitat Heterogeneity

Biofilms are surface-attached microbial communities that have complex structures and produce significant spatial heterogeneities. Biofilm development is strongly regulated by the surrounding flow and nutritional environment. Biofilm growth also increases the heterogeneity of the local microenvironment by generating complex flow fields and solute transport patterns. To investigate the development of heterogeneity in biofilms and interactions between biofilms and their local micro-habitat, we grew mono-species biofilms of Pseudomonas aeruginosa and dual-species biofilms of P. aeruginosa and Escherichia coli under nutritional gradients in a microfluidic flow cell. We provide detailed protocols for creating nutrient gradients within the flow cell and for growing and visualizing biofilm development under these conditions. We also present protocols for a series of optical methods to quantify spatial patterns in biofilm structure, flow distributions over biofilms, and mass transport around and within biofilm colonies. These methods support comprehensive investigations of the co-development of biofilm and habitat heterogeneity.

Biofilms have complex interactions with their surrounding environment. To comprehensively investigate biofilm-environment interactions, we present here a series of methods to create heterogeneous chemical environment for biofilm development, to quantify local flow velocity, and to analyze mass transport in and around biofilm colonies.

Biofilms are surface-attached microbial communities that have complex structures and produce significant spatial heterogeneities. Biofilm development is ...

Real-time Visualization and Analysis of Chondrocyte Injury Due to Mechanical Loading in Fully Intact Murine Cartilage Explants

Homeostasis of articular cartilage depends on the viability of resident cells (chondrocytes). Unfortunately, mechanical trauma can induce widespread chondrocyte death, potentially leading to irreversible breakdown of the joint and the onset of osteoarthritis. Additionally, maintenance of chondrocyte viability is important in osteochondral graft procedures for optimal surgical outcomes. We present a method to assess the spatial extent of cell injury/death on the articular surface of intact murine synovial joints after application of controlled mechanical loads or impacts. This method can be used in comparative studies to investigate the effects of different mechanical loading regimens, different environmental conditions or genetic manipulations, as well as different stages of cartilage degeneration on short- and/or long-term vulnerability of in situ articular chondrocytes. The goal of the protocol introduced in the manuscript is to assess the spatial extent of cell injury/death on the articular surface of murine synovial joints. Importantly, this method enables testing on fully intact cartilage without compromising native boundary conditions. Moreover, it allows for real-time visualization of vitally stained articular chondrocytes and single image-based analysis of cell injury induced by application of controlled static and impact loading regimens. Our representative results demonstrate that in healthy cartilage explants, the spatial extent of cell injury depends sensitively on load magnitude and impact intensity. Our method can be easily adapted to investigate the effects of different mechanical loading regimens, different environmental conditions or different genetic manipulations on the mechanical vulnerability of in situ articular chondrocytes.

We present a method to assess the spatial extent of cell injury/death on the articular surface of intact murine joints after application of controlled mechanical loads or impacts. This method can be used to investigate how osteoarthritis, genetic factors and/or different loading regimens affect the vulnerability of in situ chondrocytes.

Homeostasis of articular cartilage depends on the viability of resident cells (chondrocytes). Unfortunately, mechanical trauma can induce widespread ...

A Zebrafish Embryo Model for In Vivo Visualization and Intravital Analysis of Biomaterial-associated Staphylococcus aureus Infection

Biomaterial-associated infection (BAI) is a major cause of the failure of biomaterials/medical devices. Staphylococcus aureus is one of the major pathogens in BAI. Current experimental BAI mammalian animal models such as mouse models are costly and time-consuming, and therefore not suitable for high throughput analysis. Thus, novel animal models as complementary systems for investigating BAI in vivo are desired. In the present study, we aimed to develop a zebrafish embryo model for in vivo visualization and intravital analysis of bacterial infection in the presence of biomaterials based on fluorescence microscopy. In addition, the provoked macrophage response was studied. To this end, we used fluorescent protein-expressing S. aureus and transgenic zebrafish embryos expressing fluorescent proteins in their macrophages and developed a procedure to inject bacteria alone or together with microspheres into the muscle tissue of embryos. To monitor bacterial infection progression in live embryos over time, we devised a simple but reliable method of microscopic scoring of fluorescent bacteria. The results from microscopic scoring showed that all embryos with more than 20 colony-forming units (CFU) of bacteria yielded a positive fluorescent signal of bacteria. To study the potential effects of biomaterials on infection, we determined the CFU numbers of S. aureus with and without 10 &#181;m polystyrene microspheres (PS10) as model biomaterials in the embryos. Moreover, we used the ObjectJ project file &#34;Zebrafish-Immunotest&#34; operating in ImageJ to quantify the fluorescence intensity of S. aureus infection with and without PS10 over time. Results from both methods showed higher numbers of S. aureus in infected embryos with microspheres than in embryos without microspheres, indicating an increased infection susceptibility in the presence of the biomaterial. Thus, the present study shows the potential of the zebrafish embryo model to study BAI with the methods developed here.

A Zebrafish Embryo Model for In Vivo Visualization and Intravital Analysis of Biomaterial-associated Staphylococcus aureus Infection

The present study describes a zebrafish embryo model for in vivo visualization and intravital analysis of biomaterial-associated infection over time based on fluorescence microscopy. This model is a promising system complementing mammalian animal models such as mouse models for studying biomaterial-associated infections in vivo.

Biomaterial-associated infection (BAI) is a major cause of the failure of biomaterials/medical devices. Staphylococcus aureus is one of the major ...

High-resolution Patterned Biofilm Deposition Using pDawn-Ag43

Spatial structure and patterning play an important role in bacterial biofilms. Here we demonstrate an accessible method for culturing E. coli biofilms into arbitrary spatial patterns at high spatial resolution. The technique uses a genetically encoded optogenetic construct&#8212;pDawn-Ag43&#8212;that couples biofilm formation in E. coli to optical stimulation by blue light. We detail the process for transforming E. coli with&#160;pDawn-Ag43, preparing the required optical set-up, and the protocol for culturing patterned biofilms using pDawn-Ag43 bacteria. Using this protocol, biofilms with a spatial resolution below 25 &#956;m can be patterned on various surfaces and environments, including enclosed chambers, without requiring microfabrication, clean-room facilities, or surface pretreatment. The technique is convenient and appropriate for use in applications that investigate the effect of biofilm structure, providing tunable control over biofilm patterning. More broadly, it also has potential applications in biomaterials, education, and bio-art.

We demonstrate a method for depositing Escherichia coli bacterial biofilms in arbitrary spatial patterns with a high resolution using optical stimulation of a genetically encoded surface-adhesion construct.

Spatial structure and patterning play an important role in bacterial biofilms. Here we demonstrate an accessible method for culturing E. coli biofilms ...

Measuring Global Cellular Matrix Metalloproteinase and Metabolic Activity in 3D Hydrogels

Three-dimensional (3D) cell culture systems often more closely recapitulate in vivo cellular responses and functions than traditional two-dimensional (2D) culture systems. However, measurement of cell function in 3D culture is often more challenging. Many biological assays require retrieval of cellular material which can be difficult in 3D cultures. One way to address this challenge is to develop new materials that enable measurement of cell function within the material. Here, a method is presented for measurement of cellular matrix metalloproteinase (MMP) activity in 3D hydrogels in a 96-well format. In this system, a poly(ethylene glycol) (PEG) hydrogel is functionalized with a fluorogenic MMP cleavable sensor. Cellular MMP activity is proportional to fluorescence intensity and can be measured with a standard microplate reader. Miniaturization of this assay to a 96-well format reduced the time required for experimental set up by 50% and reagent usage by 80% per condition as compared to the previous 24-well version of the assay. This assay is also compatible with other measurements of cellular function. For example, a metabolic activity assay is demonstrated here, which can be conducted simultaneously with MMP activity measurements within the same hydrogel. The assay is demonstrated with human melanoma cells encapsulated across a range of cell seeding densities to determine the appropriate encapsulation density for the working range of the assay. After 24 h of cell encapsulation, MMP and metabolic activity readouts were proportional to cell seeding density. While the assay is demonstrated here with one fluorogenic degradable substrate, the assay and methodology could be adapted for a wide variety of hydrogel systems and other fluorescent sensors. Such an assay provides a practical, efficient and easily accessible 3D culturing platform for a wide variety of applications.

Here, a protocol is presented for encapsulating and culturing cells in poly(ethylene glycol) (PEG) hydrogels functionalized with a fluorogenic matrix metalloproteinase (MMP)-degradable peptide. Cellular MMP and metabolic activity are measured directly from the hydrogel cultures using a standard microplate reader.

Three-dimensional (3D) cell culture systems often more closely recapitulate in vivo cellular responses and functions than traditional two-dimensional (2D) ...