We want to thank the 2019 Undergraduate Senior Design Team (Suk Chul Yoon, Ian Foxton, Louis Mazza, and James Walsh) at Binghamton University for the design, fabrication, and testing of the microscope enclosure box. We thank Scott Hancock, Olga Petrova, and Fabiola Moreno Olivas at Binghamton University&#160;for helpful discussions. This research was supported by the National Institutes of Health under Award Number R15GM140444.

1. Build the microscope environmental enclosure
NOTE: This large microscope environmental enclosure is used to control the temperature of the microscope body and the imaging environment to be stabilized at 37 &#176;C (Figure 1A).
<ol>
	<li>Mark the locations of the feet of the SRS microscope frame and the motorized stage using a marker pen on the optical table. Mount two Iris Diaphragms in front of the Galvanometer scanner of the microscope and adjust to make the pump and Stokes laser beams pass through the center of the Iris Diaphragms.</li>
	<li>Remove the microscope frame and the stage from the optical table.</li>
	<li>Lay the silicone rubber sheet (size: 31 x 29 inches, thickness: 1/8 inch) on the optical table (Figure 1B).</li>
	<li>Cut the silicone rubber along the marks using a knife, remove small rubber pieces, and place the square MICA ceramic sheets (size: 6 x 6 inches, thickness: 1/4 inch) into the same locations. 
	NOTE: MICA ceramic is an easy-to-machine material15. It is as hard as aluminum but is an excellent thermal insulator. MICA ceramic sheets were used to stop heat transfer from the metal microscope frame and stage to the stainless-steel optical table. A few through-holes should be drilled on the MICA sheets to allow the use of &#188;-20 screws for mounting the feet of the frame and the stage.</li>
	<li>Move the microscope frame and the stage back to the optical table and carefully align the feet onto the MICA ceramic sheets along the marker lines. Use &#188;-20 screws to mount the frame and the stage on the table.</li>
	<li>Realign the SRS optical path. Adjust the mirror mounts of Mirror 1 and Mirror 2 to make the laser beam pass through the center of the two premounted Iris Diaphragms (Figure 2). 
	NOTE: Technical details of the lab-built SRS microscope used for the current live-cell imaging work are described previously16. The pulse width of the pump and Stokes beams are ~3-4 ps with glass rod dispersion. The system is controlled using the ScanImage17 software.</li>
	<li>On top of this thermal insulation foundation, assemble the environmental enclosure to cover the entire microscope frame using five pieces of large polycarbonate sheets (size: 31 x 29 x 28 inches, thickness: 0.25 inch). 
	NOTE: The size of the enclosure box is determined based on the dimensions of the microscope frame and the stage. The front panel of the microscope enclosure box will need to be removed temporarily to install the flexible chamber and load the cell culture dish.
	<ol>
		<li>To assemble the enclosure, carry out simple machining work, including cutting, drilling, and tapping screw holes on each edge of the polycarbonate sheets. Cut two large holes with a diameter of 2.6 inches on the right and the left sheets of the enclosure to fit the inlet and outlet tubing, respectively. Cut a small hole with a diameter of 5 mm on the back sheet to allow the laser beams to enter the enclosure.</li>
	</ol>
	</li>
	<li>Seal the edges and interfaces of the box using aluminum foil tape.</li>
	<li>Connect the flexible duct hose to the inlet and the outlet ports of the enclosure box to allow circulated warm airflow pumped and controlled by the heater module. Place the thermal sensor of the heater module in the flexible chamber where the cells are cultured and imaged. Set the targeted temperature at 37 &#176;C. 
	&#8203;NOTE: A diffuser may be used to get a more uniform airflow distribution in the environmental enclosure.</li>
</ol>
2. Assemble the flexible chamber
<ol>
	<li>Mount the machined hollow cylindrical aluminum piece 1 (material: aluminum 6061) to the nosepiece of the objective using three set screws (Figure 2).</li>
	<li>Mount the machined hollow cylindrical aluminum piece 2 to the sample holder using four &#188;-20 screws (Figure 2). 
	NOTE: The sample holder must be modified to hold the 50 mm cover glass-bottom cell culture dish. Drill a through hole in the center of the sample holder using a 1-7/8 inches hole saw. Counterbore the hole using a 50 mm hole saw and keep the depth of the through hole ~1 mm.</li>
	<li>Fit the sample holder with the aluminum piece 2 onto the motorized stage and mount it using screws.</li>
	<li>Place the natural rubber film sleeve (thickness: 0.01 inch; glued with cyanoacrylate adhesive) between the two machined aluminum pieces and mount it using rubber bands at each end.</li>
	<li>Connect the compressed CO2 cylinder to the gas mixer module using proper tubing and connectors. Set the CO2 input pressure at 20-25 psi. Use a built-in CO2 sensor and a controller to ensure the air mixer module can regulate and mix 5% CO2 into the airflow. Use inline filters to clean up the airflow.</li>
	<li>Using proper tubing and connectors, guide the mixed air (with 5% CO2) to the presterilized water bottle placed on the hot plate, and then guide the humidified air to the flexible chamber. Set the hot plate at 37 &#176;C. Bubble the airflow in the warm water to increase the humidity of the airflow.</li>
</ol>
3. Preparation for time-lapse live-cell SRS imaging experiments
<ol>
	<li>Wipe all parts of the flexible chamber with 70% ethanol, including the nosepiece, the water dipping objective, and the sample holder.</li>
	<li>Decontaminate the entire enclosure system using a UV lamp placed in the enclosure for 20 to 30 min. 
	NOTE: Do not stay in the lab room during the UV disinfection process for safety.</li>
	<li>Culture SKOV3 cells in a 50-mm glass-bottom Petri dish for 12 h under normal physiological conditions in a regular incubator. 
	NOTE: Start the SKOV3 cell culture18 in a standard biosafety cabinet.</li>
	<li>Disconnect the machined aluminum piece 2 from the sample holder by removing the screws. 
	NOTE: This is the way to open the flexible chamber to load the cell culture dish.</li>
	<li>Load the cell culture dish. Remember to add immersion oil on the top of the condenser before placing the cell culture dish. Remove the cover of the dish and immobilize the dish using the clamps. 
	NOTE: To avoid contamination, all the operations should be performed with gloves.</li>
	<li>Lower the objective into the cell culture media for coarse focusing. Lower the aluminum piece 2 to enclose the flexible chamber and mount it to the sample holder using screws. 
	NOTE: A 2 mm silicone rubber cushion pad is attached to the bottom of the aluminum piece 2 to seal the gap tightly.</li>
	<li>Set the air supply with 5% CO2 and 19% O2 for normal cell culture with an airflow rate of 200 cc/min. 
	&#8203;NOTE: A lower airflow rate may be used. It depends on how well the flexible chamber is sealed.</li>
</ol>
4. Conduct time-lapse live-cell SRS imaging experiments
<ol>
	<li>Tune the laser wavelength to 805 nm to target the 2854 cm-1 Raman shift, which is attributed to the vibration of CH2 chemical bonds. Use low laser power to reduce photodamage to the cells. To follow this protocol, use ~15 mW average power of the pump laser and ~7.5 mW of the Stokes laser (fixed at 1,045 nm) for long-term live-cell imaging. 
	NOTE: Higher laser power will yield better SRS imaging quality. However, too high laser power will induce photodamage to live cells. There is a tradeoff between image quality and photodamage.</li>
	<li>Adjust and focus the objective to achieve good SRS imaging of the cells using the FOCUS button on the MAIN CONTROLS panel of the software. To perform rapid focusing, set the pixel number to be 512 &#215; 512 pixels with a pixel dwell time of 4.8 &#181;s on the CONFIGURATION panel.</li>
	<li>Set the lock-in amplifier input range (typically 5 mV) to be twice the maximal signal voltage. Set the low-pass filter to be the same as the pixel dwell time (4.8 &#181;s). 
	NOTE: Different lab-built SRS systems may use different data acquisition settings.</li>
	<li>After achieving good focusing, set the imaging resolution to be 2,048 &#215; 2,048 pixels for a 175 &#181;m2 field of view for the acquisition of high-quality images. Check the SAVE function on the MAIN CONTROLS panel and check the SRS channel on the CHANNELS panel. Set the interval time between two frames to be 180 s (3 min) on the MAIN CONTROLS channel. Set the acquisition number to 480 for time-lapse imaging over 24 h. 
	NOTE: A lower imaging&#160;resolution may be used based on the purpose of the experiments.</li>
	<li>Start automated imaging acquisition using the LOOP function on the MAIN CONTROLS panel. 
	NOTE: Check whether there is focal drift due to temperature instability in the first hour of imaging. The first-hour imaging may not be stable. Check focusing every 2-3 h during the time-lapse imaging session.</li>
	<li>Process the collected images using ImageJ19. Use the following two methods for LD quantification: (i) the LD/cell body area ratio, and (ii) the mean SRS intensity of total LDs. Measure the cell body area by thresholding and zeroing the non-cellular pixels in the SRS images at 2,854 cm-1. Measure the LD area and intensity by thresholding and zeroing the non-LD pixels in the SRS images. 
	NOTE: More details about SRS image processing were reported previously16.</li>
</ol>

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The authors have no conflicts of interest to disclose.

Time-lapse live-cell SRS microscopy is an alternative imaging technique for molecule tracking in a label-free manner. Compared to fluorescence labeling, SRS imaging is free from photobleaching, enabling long-term monitoring of molecules. However, to date, the live cell imaging system on an upright SRS microscopy is not commercially available. In this work, a live cell imaging system with a stable thermal-insulated microscope enclosure box and a flexible inner soft chamber was developed to enable transmitted SRS time-laps...

Optical microscopy is used to observe the microstructures of samples. Optical imaging is rapid, less invasive, and less destructive than other technologies1. Live-cell imaging with optical microscopy is developed to capture the dynamics of cultured live cells over a long period2. Different types of optical contrasts provide distinct information about biological samples. For instance, optical phase microscopy shows the subtle difference in the refractive indices across the sample3. Fluorescence microscopy is widely used to image specific biomolecules or cellular organelles. However, the broadband excitation and emission spectra of fluorescence usually result in spectral overlapping when multicolor imaging is performed4. Fluorescent molecules are light-sensitive and can be bleached after long-term, periodic light exposure. In addition, fluorescence labeling may change the biodistribution of the molecules in cells5. SRS microscopy is a label-free chemical imaging technology6. The contrast of SRS relies on the vibrational transition of specific chemical bonds. The vibrational frequency of a chemical bond often exhibits a narrow spectral bandwidth, making it feasible to image multiple Raman bands in the same samples7. SRS microscopy is a unique tool for live-cell imaging, providing multiple chemical contrasts in a label-free manner8.
While SRS imaging of unstained cells has been used for many studies, long-term time-lapse SRS imaging of live cells has not been widely adopted. One reason is that commercial open chambers cannot be directly used for SRS imaging because of their large thickness9,10,11,12. These chambers with a glass lid are mostly designed for brightfield or fluorescence imaging using a single high NA objective with a backward detection scheme. However, SRS imaging prefers transmitted detection using both a high NA objective and a high NA condenser, which leaves only a very short gap (typically a few millimeters) between the objective and the condenser. To overcome this problem, we designed a flexible chamber using a soft material to enable time-lapse SRS imaging of live cells using an upright microscope frame. In this design, the water dipping objective was enclosed in the soft chamber and can freely move in three dimensions for focusing and imaging purposes.
The optimal temperature for culturing most mammalian cells is 37 &#176;C, while the room temperature is always 10&#176; lower than this. Temperature higher or lower than 37 &#176;C has a dramatic effect on cell growth rate13. Therefore, temperature control of the cell culture environment is required in a live-cell imaging system. It is known that temperature instability will lead to defocusing issues during long-term imaging14. To achieve a stable 37 &#176;C environment, we built a large enclosure chamber to cover the entire microscope frame, including a thermal insulation layer underneath the microscope (Figure 1). Within the sizeable temperature-control chamber, the small flexible chamber helps to accurately maintain the physiological humidity and pH via the regulated air flow supplemented with 5% CO2 (Figure 2). The temperature and humidity of the chambers were measured to confirm that the double-chamber design provided the optimal cell culture condition for cell growth under long-term, periodic SRS imaging (Figure 3). We then demonstrated the application of the system for time-lapse imaging and tracking lipid droplets (LDs) in SKOV3 cancer cells (Figure 4, Figure 5, and Figure 6).

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>A lab-built SRS microscope</td>
			<td></td>
			<td></td>
			<td>https://rdcu.be/cP6ve</td>
		</tr>
		<tr>
			<td>HF2LI 50 MHz lock-in amplifer</td>
			<td>Zurich Instruments</td>
			<td>HF2LI</td>
			<td></td>
		</tr>
		<tr>
			<td>Iris diaphragm</td>
			<td>Thorlabs Inc</td>
			<td>SM1D12</td>
			<td></td>
		</tr>
		<tr>
			<td>Kinematic mirror mount</td>
			<td>Thorlabs Inc</td>
			<td>KM100</td>
			<td></td>
		</tr>
		<tr>
			<td>Microscope frame</td>
			<td>Nikon Inc</td>
			<td>FN-1</td>
			<td></td>
		</tr>
		<tr>
			<td>Motorized microscopy stage</td>
			<td>Prior Scientific</td>
			<td>Z-Deck</td>
			<td></td>
		</tr>
		<tr>
			<td>Oil-immersion condenser (C-AA Achromat/Aplanat, NA 1.4)</td>
			<td>Nikon Inc</td>
			<td>MBL71405</td>
			<td></td>
		</tr>
		<tr>
			<td>Water-immersion objective (CFI75 Apo 25XC W 1300)</td>
			<td>Nikon Inc</td>
			<td>MRD77225</td>
			<td></td>
		</tr>
		<tr>
			<td>Materials and parts for the microscope enclosure (31&#39;&#39; x 29&#39;&#39; x 28&#39;&#39; L x W x H)</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Airtherm heater module</td>
			<td>World Precision Instruments (WPI)</td>
			<td>AIRTHERM-SAT-1W</td>
			<td></td>
		</tr>
		<tr>
			<td>Airtherm heater controller, CO2 and humidity monitor</td>
			<td>World Precision Instruments (WPI)</td>
			<td>AIRTHERM-SMT-1W</td>
			<td></td>
		</tr>
		<tr>
			<td>Air/CO2 mixer module</td>
			<td>World Precision Instruments (WPI)</td>
			<td>ECU-HOC-W</td>
			<td></td>
		</tr>
		<tr>
			<td>Flexible duct hose (2-1/2&#39;&#39; ID, 2-3/4&#39;&#39; OD)</td>
			<td>McMaster-Carr</td>
			<td>56675K71</td>
			<td></td>
		</tr>
		<tr>
			<td>High-temperature glass-mica ceramic, easy-to-machine (6&#39;&#39; x 6&#39;&#39;, 1/4&#39;&#39; thickness)</td>
			<td>McMaster-Carr</td>
			<td>8489K62</td>
			<td></td>
		</tr>
		<tr>
			<td>Polycarbonate sheets (thickness 0.25&#39;&#39;)</td>
			<td>McMaster-Carr</td>
			<td>8574K286</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone rubber sheets (36&#39;&#39; x 36&#39;&#39;, thickness 1/8&#39;&#39;)</td>
			<td>McMaster-Carr</td>
			<td>5827T43</td>
			<td></td>
		</tr>
		<tr>
			<td>Materials and parts for the Flexible chamber</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Hot plate</td>
			<td>McMaster-Carr</td>
			<td>31745K11</td>
			<td></td>
		</tr>
		<tr>
			<td>High-purity inline filter, 1/4 NPT</td>
			<td>McMaster-Carr</td>
			<td>6645T18</td>
			<td></td>
		</tr>
		<tr>
			<td>Hole saw (cutting diameter 1-7/8 inch)</td>
			<td>McMaster-Carr</td>
			<td>4066A34</td>
			<td></td>
		</tr>
		<tr>
			<td>Hole saw (cutting diameter 50 mm)</td>
			<td>McMaster-Carr</td>
			<td>4556A19</td>
			<td></td>
		</tr>
		<tr>
			<td>High-temperature silicone rubber tubing, soft, 2 mm ID, 5 mm OD</td>
			<td>McMaster-Carr</td>
			<td>5054K313</td>
			<td></td>
		</tr>
		<tr>
			<td>Inline filter (1/4 NPT, 40 micron)</td>
			<td>McMaster-Carr</td>
			<td>98385K843</td>
			<td></td>
		</tr>
		<tr>
			<td>Multipurpose 6061 Aluminum round tube (1/8&#39;&#39; wall thickness, 4&#39;&#39; OD)</td>
			<td>McMaster-Carr</td>
			<td>9056K42</td>
			<td></td>
		</tr>
		<tr>
			<td>Multipurpose 6061 Aluminum round tube (3/4&#39;&#39; wall thickness, 3-3/4&#39;&#39; OD)</td>
			<td>McMaster-Carr</td>
			<td>9056K47</td>
			<td></td>
		</tr>
		<tr>
			<td>Multipurpose 6061 Aluminum bar (12&#39;&#39; x 12&#39;&#39;, thickness 1/4&#39;&#39;)</td>
			<td>McMaster-Carr</td>
			<td>8975K142</td>
			<td></td>
		</tr>
		<tr>
			<td>Multipurpose 6061 Aluminum bar (8&#39;&#39; x 8&#39;&#39;, thickness 3/8&#39;&#39;)</td>
			<td>McMaster-Carr</td>
			<td>9246K21</td>
			<td></td>
		</tr>
		<tr>
			<td>Objective nosepiece (single)</td>
			<td>Nikon Inc</td>
			<td>FN-MN-H</td>
			<td></td>
		</tr>
		<tr>
			<td>Sample holder (modified)</td>
			<td>Prior Scientific</td>
			<td>HZ202</td>
			<td></td>
		</tr>
		<tr>
			<td>Ultra-thin natural rubber film (thickness 0.01&#39;&#39;)</td>
			<td>McMaster-Carr</td>
			<td>8611K13</td>
			<td></td>
		</tr>
		<tr>
			<td>Vacuum-sealable glass jar</td>
			<td>McMaster-Carr</td>
			<td>3231T44</td>
			<td></td>
		</tr>
		<tr>
			<td>Software</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>MATLAB</td>
			<td>MathWorks</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>ImageJ (Fiji)</td>
			<td></td>
			<td>imagej.net</td>
			<td></td>
		</tr>
		<tr>
			<td>ScanImage</td>
			<td>Vidrio Technologies, LLC</td>
			<td></td>
			<td>SRS imaging software</td>
		</tr>
		<tr>
			<td>Materials for live-cell imaging</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cover glass bottom sterile culture dishes (Dia.x H, 50 x 7 mm)</td>
			<td>Electron Microscopy Sciences (EMS)</td>
			<td>70674-02</td>
			<td></td>
		</tr>
		<tr>
			<td>DMEM cell culture medium</td>
			<td>ThermoFisher Scientific</td>
			<td>11965092</td>
			<td></td>
		</tr>
		<tr>
			<td>Fetal bovine serum (FBS)</td>
			<td>ThermoFisher Scientific</td>
			<td>26140079</td>
			<td></td>
		</tr>
		<tr>
			<td>LysoSensor fluorescent dye DND-189</td>
			<td>ThermoFisher Scientific</td>
			<td>L7535 (Invitrogen)</td>
			<td></td>
		</tr>
		<tr>
			<td>Oleic acid</td>
			<td>MilliporeSigma</td>
			<td>364525</td>
			<td></td>
		</tr>
		<tr>
			<td>SKOV3 cell line</td>
			<td>ATCC</td>
			<td>HTB-77</td>
			<td></td>
		</tr>
	</tbody>
</table>

a flexible chamber for time-lapse live-cell imaging with stimulated raman scattering microscopy

Stimulated Raman scattering (SRS) microscopy is a label-free chemical imaging technology. Live-cell imaging with SRS has been demonstrated for many biological and biomedical applications. However, long-term time-lapse SRS imaging of live cells has not been widely adopted. SRS microscopy often uses a high numerical aperture (NA) water-immersion objective and a high NA oil-immersion condenser to achieve high-resolution imaging. In this case, the gap between the objective and the condenser is only a few millimeters. Therefore, most commercial stage-top environmental chambers cannot be used for SRS imaging because of their large thickness with a rigid glass cover. This paper describes the design and fabrication of a flexible chamber that can be used for time-lapse live-cell imaging with transmitted SRS signal detection on an upright microscope frame. The flexibility of the chamber is achieved by using a soft material - a thin natural rubber film. The new enclosure and chamber design can be easily added to an existing SRS imaging setup. The testing and preliminary results demonstrate that the flexible chamber system enables stable, long-term, time-lapse SRS imaging of live cells, which can be used for various bioimaging applications in the future.

We fabricated and assembled the flexible chamber system for time-lapse SRS imaging (Figure 1 and Figure 2), and then evaluated the performance of the system. The temperature inside the microscope environmental enclosure reached the expected 37 &#176;C within 1 h, which did not significantly affect the room temperature (Figure 3A). The temperature in the flexible chamber reached 37 &#176;C in 1.5 h, and it was stably maintained at 37...

Watch this Scientific Journal Video about A Flexible Chamber for Time-Lapse Live-Cell Imaging with Stimulated Raman Scattering Microscopy at JoVE.com

A Flexible Chamber for Time-Lapse Live-Cell Imaging with Stimulated Raman Scattering Microscopy

We report a stage-top, flexible environmental chamber for time-lapse imaging of live cells using upright stimulated Raman scattering microscopy with transmitted signal detection. Lipid droplets were imaged in SKOV3 cells treated with oleic acid for up to 24 h with a 3 min time interval.

Stimulated Raman scattering (SRS) microscopy is a label-free chemical imaging technology. Live-cell imaging with SRS has been demonstrated for many ...

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Research

JoVE Journal

Bioengineering

1.2K Views.  State University of New York. We report a stage-top, flexible environmental chamber for time-lapse imaging of live cells using upright stimulated Raman scattering microscopy with transmitted signal detection. Lipid droplets were imaged in SKOV3 cells treated with oleic acid for up to 24 h with a 3 min time interval.

Video: A Flexible Chamber for Time-Lapse Live-Cell Imaging with Stimulated Raman Scattering Microscopy

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

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

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

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

Creating Adhesive and Soluble Gradients for Imaging Cell Migration with Fluorescence Microscopy

Cells can sense and migrate towards higher concentrations of adhesive cues such as the glycoproteins of the extracellular matrix and soluble cues such as growth factors. Here, we outline a method to create opposing gradients of adhesive and soluble cues in a microfluidic chamber, which is compatible with live cell imaging. A copolymer of poly-L-lysine and polyethylene glycol (PLL-PEG) is employed to passivate glass coverslips and prevent non-specific adsorption of biomolecules and cells. Next, microcontact printing or dip pen lithography are used to create tracks of streptavidin on the passivated surfaces to serve as anchoring points for the biotinylated peptide arginine-glycine-aspartic acid (RGD) as the adhesive cue. A microfluidic device is placed onto the modified surface and used to create the gradient of adhesive cues (100% RGD to 0% RGD) on the streptavidin tracks. Finally, the same microfluidic device is used to create a gradient of a chemoattractant such as fetal bovine serum (FBS), as the soluble cue in the opposite direction of the gradient of adhesive cues.

A method for the assembly of adhesive and soluble gradients in a microscopy chamber for live cell migration studies is described. The engineered environment combines antifouling surfaces and adhesive tracks with solution gradients and therefore allows one to determine the relative importance of guidance cues.

Cells can sense and migrate towards higher concentrations of adhesive cues such as the glycoproteins of the extracellular matrix and soluble cues such as ...

Sample Drift Correction Following 4D Confocal Time-lapse Imaging

The generation of four-dimensional (4D) confocal datasets; consisting of 3D image sequences over time; provides an excellent methodology to capture cellular behaviors involved in developmental processes.&#160; The ability to track and follow cell movements is limited by sample movements that occur due to drift of the sample or, in some cases, growth during image acquisition. Tracking cells in datasets affected by drift and/or growth will incorporate these movements into any analysis of cell position. This may result in the apparent movement of static structures within the sample. Therefore prior to cell tracking, any sample drift should be corrected. Using the open source Fiji distribution 1 &#160;of ImageJ 2,3 and the incorporated LOCI tools 4, we developed the Correct 3D drift plug-in to remove erroneous sample movement in confocal datasets. This protocol effectively compensates for sample translation or alterations in focal position by utilizing phase correlation to register each time-point of a four-dimensional confocal datasets while maintaining the ability to visualize and measure cell movements over extended time-lapse experiments.

Time-lapse microscopy allows the visualization of developmental processes. Growth or drift of samples during image acquisition reduces the ability to accurately follow and measure cell movements during development. We describe the use of open source image processing software to correct for three dimensional sample drift over time.

The generation of four-dimensional (4D) confocal datasets; consisting of 3D image sequences over time; provides an excellent methodology to capture ...

From Fast Fluorescence Imaging to Molecular Diffusion Law on Live Cell Membranes in a Commercial Microscope

It has become increasingly evident that the spatial distribution and the motion of membrane components like lipids and proteins are key factors in the regulation of many cellular functions. However, due to the fast dynamics and the tiny structures involved, a very high spatio-temporal resolution is required to catch the real behavior of molecules. Here we present the experimental protocol for studying the dynamics of fluorescently-labeled plasma-membrane proteins and lipids in live cells with high spatiotemporal resolution. Notably, this approach doesn&#8217;t need to track each molecule, but it calculates population behavior using all molecules in a given region of the membrane. The starting point is a fast imaging of a given region on the membrane. Afterwards, a complete spatio-temporal autocorrelation function is calculated correlating acquired images at increasing time delays, for example each 2, 3, n repetitions. It is possible to demonstrate that the width of the peak of the spatial autocorrelation function increases at increasing time delay as a function of particle movement due to diffusion. Therefore, fitting of the series of autocorrelation functions enables to extract the actual protein mean square displacement from imaging (iMSD), here presented in the form of apparent diffusivity vs average displacement. This yields a quantitative view of the average dynamics of single molecules with nanometer accuracy. By using a GFP-tagged variant of the Transferrin Receptor (TfR) and an ATTO488 labeled 1-palmitoyl-2-hydroxy-sn-glycero-3-phosphoethanolamine (PPE) it is possible to observe the spatiotemporal regulation of protein and lipid diffusion on &#181;m-sized membrane regions in the micro-to-milli-second time range.

Spatial distribution and temporal dynamics of plasma membrane proteins and lipids is a hot topic in biology. Here this issue is addressed by a spatio-temporal image fluctuation analysis that provides conceptually the same physical quantities of single particle tracking, but it uses small molecular labels and standard microscopy setups.

It has become increasingly evident that the spatial distribution and the motion of membrane components like lipids and proteins are key factors in the ...

Live Cell Imaging during Mechanical Stretch

There is currently a significant interest in understanding how cells and tissues respond to mechanical stimuli, but current approaches are limited in their capability for measuring responses in real time in live cells or viable tissue. A protocol was developed with the use of a cell actuator to distend live cells grown on or tissues attached to an elastic substrate while imaging with confocal and atomic force microscopy (AFM). Preliminary studies show that tonic stretching of human bronchial epithelial cells caused a significant increase in the production of mitochondrial superoxide. Moreover, using this protocol, alveolar epithelial cells were stretched and imaged, which showed direct damage to the epithelial cells by overdistention simulating one form of lung injury in vitro. A protocol to conduct AFM nano-indentation on stretched cells is also provided.

A novel imaging protocol was developed using a custom motor-driven mechanical actuator to allow the measurement of real time responses to mechanical strain in live cells. Relevant to mechanobiology, the system can apply strains up to 20% while allowing near real-time imaging with confocal or atomic force microscopy.

There is currently a significant interest in understanding how cells and tissues respond to mechanical stimuli, but current approaches are limited in ...

Rapid Subtractive Patterning of Live Cell Layers with a Microfluidic Probe

The microfluidic probe (MFP) facilitates performing local chemistry on biological substrates by confining nanoliter volumes of liquids. Using one particular implementation of the MFP, the hierarchical hydrodynamic flow confinement (hHFC), multiple liquids are simultaneously brought in contact with a substrate. Local chemical action and liquid shaping using the hHFC, is exploited to create cell patterns by locally lysing and removing cells. By utilizing the scanning ability of the MFP, user-defined patterns of cell monolayers are created. This protocol enables rapid, real-time and spatially controlled cell patterning, which can allow selective cell-cell and cell-matrix interaction studies.

We present a protocol to perform subtractive patterning of live cell monolayers on a surface. This is achieved by local and selective lysis of adherent cells using a microfluidic probe (MFP). The cell lysate retrieved from local regions can be used for downstream analysis, enabling molecular profiling studies.

The microfluidic probe (MFP) facilitates performing local chemistry on biological substrates by confining nanoliter volumes of liquids. Using one ...

Visualizing Adhesion Formation in Cells by Means of Advanced Spinning Disk-Total Internal Reflection Fluorescence Microscopy

In living cells, processes such as adhesion formation involve extensive structural changes in the plasma membrane and the cell interior. In order to visualize these highly dynamic events, two complementary light microscopy techniques that allow fast imaging of live samples were combined: spinning disk microscopy (SD) for fast and high-resolution volume recording and total internal reflection fluorescence (TIRF) microscopy for precise localization and visualization of the plasma membrane. A comprehensive and complete imaging protocol will be shown for guiding through sample preparation, microscope calibration, image formation and acquisition, resulting in multi-color SD-TIRF live imaging series with high spatio-temporal resolution. All necessary image post-processing steps to generate multi-dimensional live imaging datasets, i.e. registration and combination of the individual channels, are provided in a self-written macro for the open source software ImageJ. The imaging of fluorescent proteins during initiation and maturation of adhesion complexes, as well as the formation of the actin cytoskeletal network, was used as a proof of principle for this novel approach. The combination of high resolution 3D microscopy and TIRF provided a detailed description of these complex processes within the cellular environment and, at the same time, precise localization of the membrane-associated molecules detected with a high signal-to-background ratio.

An advanced microscope that permit fast and high-resolution imaging of both, the isolated plasma membrane and the surrounding intracellular volume, will be presented. The integration of spinning disk and total internal reflection fluorescence microscopy in one setup allows live imaging experiments at high acquisition rates up to 3.5 s per image stack.

In living cells, processes such as adhesion formation involve extensive structural changes in the plasma membrane and the cell interior. In order to ...

Continuous Measurement of Biological Noise in Escherichia Coli Using Time-lapse Microscopy

The protocol developed here offers a tool to enable computer tracking of Escherichia coli division and fluorescent levels over several hours. The process starts by screening for colonies that survive on minimal media, assuming that only Escherichia coli harboring the correct plasmid will be able to thrive in the specific conditions. Since the process of building large genetic circuits, requiring the assembly of many DNA parts, is challenging, circuit components are often distributed between multiple plasmids at different copy numbers requiring the use of several antibiotics. Mutations in the plasmid can destroy transcription of the antibiotic resistance genes and interject with resources management in the cell leading to necrosis. The selected colony is set on a glass-bottom Petri dish and a few focus planes are selected for microscopy tracking in both bright field and fluorescent domains. The protocol maintains the image focus for more than 12 hours under initial conditions that cannot be regulated, creating a few difficulties. For example, dead cells start to accumulate in the lenses' field of focus after a few hours of imaging, which causes toxins to buildup and the signal to blur and decay. Depletion of nutrients introduces new metabolic processes and hinder the desired response of the circuit. The experiment's temperature lowers the effectivity of inducers and antibiotics, which can further damage the reliability of the signal. The minimal media gel shrinks and dries, and as a result the optical focus changes over time. We developed this method to overcome these challenges in Escherichia coli, similar to previous works developing analogous methods for other micro-organisms. In addition, this method offers an algorithm to quantify the total stochastic noise in unaltered and altered cells, finding that the results are consistent with flow analyzer predictions as shown by a similar coefficient of variation (CV).

Continuous Measurement of Biological Noise in Escherichia Coli Using Time-lapse Microscopy

This work presents a microscopy method that allows live imaging of a single cell of Escherichia coli for analysis and quantification of the stochastic behavior of synthetic gene circuits.

The protocol developed here offers a tool to enable computer tracking of Escherichia coli division and fluorescent levels over several hours. The process ...

In vivo Imaging of Biological Tissues with Combined Two-Photon Fluorescence and Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy enables label-free imaging of the biological tissues in its natural microenvironment based on intrinsic molecular vibration, thus providing a perfect tool for in vivo study of biological processes at subcellular resolution. By integrating two-photon excited fluorescence (TPEF) imaging into the SRS microscope, the dual-modal in vivo imaging of tissues can acquire critical biochemical and biophysical information from multiple perspectives which helps understand the dynamic processes involved in cellular metabolism, immune response and tissue remodeling, etc. In this video protocol, the setup of a TPEF-SRS microscope system as well as the in vivo imaging method of the animal spinal cord is introduced. The spinal cord, as part of the central nervous system, plays a critical role in the communication between the brain and peripheral nervous system. Myelin sheath, abundant in phospholipids, surrounds and insulates the axon to permit saltatory conduction of action potentials. In vivo imaging of myelin sheaths in the spinal cord is important to study the progression of neurodegenerative diseases and spinal cord injury. The protocol also describes animal preparation and in vivo TPEF-SRS imaging methods to acquire high-resolution biological images.

In vivo Imaging of Biological Tissues with Combined Two-Photon Fluorescence and Stimulated Raman Scattering Microscopy

Stimulated Raman scattering (SRS) microscopy allows label-free imaging of biomolecules based on their intrinsic vibration of specific chemical bonds. In this protocol, the instrumental setup of an integrated SRS and two-photon fluorescence microscope is described to visualize cellular structures in the spinal cord of live mice.

Stimulated Raman scattering (SRS) microscopy enables label-free imaging of the biological tissues in its natural microenvironment based on intrinsic ...

Real-Time, Two-Color Stimulated Raman Scattering Imaging of Mouse Brain for Tissue Diagnosis

Stimulated Raman scattering (SRS) microscopy has emerged as a powerful optical imaging technique for tissue diagnosis. In recent years, two-color SRS has been shown to be able to provide hematoxylin and eosin (H&amp;E)-equivalent images that allow fast and reliable diagnosis of brain cancer. Such capability has enabled exciting intraoperative cancer diagnosis applications. Two-color SRS imaging of tissue can be done with either a picosecond or femtosecond laser source. Femtosecond lasers have the advantage of enabling flexible imaging modes, including fast hyperspectral imaging and real-time, two-color SRS imaging. A spectral-focusing approach with chirped laser pulses is typically used with femtosecond lasers to achieve high spectral resolution. 
Two-color SRS acquisition can be realized with orthogonal modulation and lock-in detection. The complexity of pulse chirping, modulation, and characterization is a bottleneck for the widespread adoption of this method. This article provides a detailed protocol to demonstrate the implementation and optimization of spectral-focusing SRS and real-time, two-color imaging of mouse brain tissue in the epi-mode. This protocol can be used for a broad range of SRS imaging applications that leverage the high speed and spectroscopic imaging capability of SRS.

Stimulated Raman scattering (SRS) microscopy is a powerful, nondestructive, and label-free imaging technique. One emerging application is stimulated Raman histology, where two-color SRS imaging at the protein and lipid Raman transitions are used to generate pseudo-hematoxylin and eosin images. Here, we demonstrate a protocol for real-time, two-color SRS imaging for tissue diagnosis.

Stimulated Raman scattering (SRS) microscopy has emerged as a powerful optical imaging technique for tissue diagnosis. In recent years, two-color SRS has ...