Name: a flexible chamber for time-lapse live-cell imaging with stimulated raman scattering microscopy
Uploaded: 2022-08-31T15:00:00
Description: Watch this Scientific Journal Video about A Flexible Chamber for Time-Lapse Live-Cell Imaging with Stimulated Raman Scattering Microscopy at JoVE.com

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 th...

<ol>
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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 ...

The flexible environmental chamber technique enables time-lapse as SRS imaging with transmitted signal detection on an operating microscope frame. SRS microscopy used a high numerical aperture objective and a high ended condenser, leaving only a few millimeters gap where a conventional chamber cannot fit. A flexible chamber solve this problem.Researchers using SRS microscopy can easily adopt this technique. The flexible chamber can also be used on a dissecting or a sterile microscope to maintain the specimen under optimal physiological conditions. To begin, mark the locations of the feet of the SRS microscope frame and the motorized stage using a marker pen on the optical table.After removing microscope frame and stage from the optical table, lay the silicone rubber sheet on the table. Cut the silicone rubber along the marks using a knife. Remove small rubber pieces, and place the square mica ceramic sheets into the same locations.Then 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. After realigning the SRS optical path, assemble the environmental enclosure on top of the thermal insulation foundation to cover the entire microscope frame, using five pieces of large polycarbonate sheets. Seal the edges and interfaces of the box using aluminum foil tape.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. Mount the machined hollow cylindrical aluminum piece 1 to the nose piece of the objective using three set screws. Next, mount the machined hollow cylindrical aluminum piece 2 to the sample holder using four screws.Fit the sample holder with aluminum piece 2 onto the motorized stage and mount it using screws. Place the natural rubber film sleeve between the two machined aluminum pieces and mount it using rubber bands at each end. Connect the compressed CO2 cylinder to the gas mixer module using proper tubing and connectors.Set the CO2 input pressure at 20 to 25 psi. Use the 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.Using proper tubing and connectors, guide the mixed air to the pre-sterilized water bottle placed on the hotplate and then guide the humidified air to the flexible chamber. Set the hotplate at 37 degrees Celsius. Bubble the airflow in the warm water to increase the humidity of the airflow.Disconnect the machine aluminum piece 2 from the sample holder by removing the screws. Wipe all parts of the flexible chamber with 70%ethanol, including the nose piece, the sample holder, and water dipping objective. Decontaminate the entire enclosure system using a UV lamp placed in the enclosure for 20 to 30 minutes.Then load the cell culture dish. Remove the cover of the dish and immobilize it using the clamps. 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. Then insert the sensor. Set the air supply with 5%CO2 and 19%O2 for normal cell culture with an airflow rate of 200 cubic centimeters per minute and temperature to 37 degrees Celsius.Tune the laser wavelength to 805 nanometers to target the 2, 854 centimeter inverse Raman shift, which is attributed to the vibration of CH2 chemical bonds. Use low laser power to reduce photo damage to the cells. 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 by 512 pixels with a pixel dwell time of 4.8 microseconds on the configuration panel. After achieving good focusing, set the imaging resolution to be 2048 by 2048 pixels for a 175 micrometers squared 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 seconds on the main controls channel. Set the acquisition number to 480 for time-lapse imaging over 24 hours. Start automated imaging acquisition using the loop function on the main controls panel.The performance of the flexible chamber system for time-lapse SRS imaging was evaluated. The temperature inside the microscope environmental enclosure reached the expected 37 degrees Celsius and did not significantly affect room temperature. The temperature in the flexible chamber reached 37 degrees Celsius in 1.5 hours and was stably maintained for at least 24 hours.The relative humidity in the flexible chamber reached 85%in one hour and could be maintained for at least 24 hours. The time-lapse SRS imaging of live SKOV3 cells showed the rapid and active movement of intracellular lipid droplets with a temporal resolution of three minutes. By the end of the 24 hour imaging session, the cells still showed normal morphology and density, indicating that the cells were healthy.Next, SKOV3 cells treated with oleic acid were imaged and lipid droplet accumulation was tracked over 10 hours. The lipid droplet amounts were quantified using the lipid droplet to cell body area ratio and total SRS intensity of the lipid droplets. The results indicate that the amount of lipid droplets kept increasing over 10 hours.Simultaneous forward SRS imaging of lipid droplets and backward two photon fluorescence imaging of lysosomes labeled with a fluorescence dye DND-189 was also demonstrated. A very low degree of colocalization of lipid droplets and lysosomes was observed. When attempting this protocol, keep in mind that focal drift is a common issue in live cell imaging.Refocusing may be needed after about two hours of time-lapse imaging. After its development, time-lapse SRS imaging has been used for various studies to track label-free molecules or labeled molecules with Raman text in live cells.

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