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In This Article

  • Summary
  • Abstract
  • Introduction
  • Protocol
  • Results
  • Discussion
  • Disclosures
  • Acknowledgements
  • Materials
  • References
  • Reprints and Permissions

Summary

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.

Abstract

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.

Introduction

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 e....

Protocol

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 °C (Figure 1A).

  1. 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.
  2. Remove the microscope frame and the stage from the optical tab....

Results

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 °C within 1 h, which did not significantly affect the room temperature (Figure 3A). The temperature in the flexible chamber reached 37 °C in 1.5 h, and it was stably maintained at 37.......

Discussion

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.......

Disclosures

The authors have no conflicts of interest to disclose.

Acknowledgements

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 for helpful discussions. This research was supported by the National Institutes of Health under Award Number R15GM140444.

....

Materials

NameCompanyCatalog NumberComments
A lab-built SRS microscopehttps://rdcu.be/cP6ve
HF2LI 50 MHz lock-in ampliferZurich InstrumentsHF2LI
Iris diaphragmThorlabs IncSM1D12
Kinematic mirror mountThorlabs IncKM100
Microscope frameNikon IncFN-1
Motorized microscopy stagePrior ScientificZ-Deck
Oil-immersion condenser (C-AA Achromat/Aplanat, NA 1.4)Nikon IncMBL71405
Water-immersion objective (CFI75 Apo 25XC W 1300)Nikon IncMRD77225
Materials and parts for the microscope enclosure (31'' x 29'' x 28'' L x W x H)
Airtherm heater moduleWorld Precision Instruments (WPI)AIRTHERM-SAT-1W
Airtherm heater controller, CO2 and humidity monitorWorld Precision Instruments (WPI)AIRTHERM-SMT-1W
Air/CO2 mixer moduleWorld Precision Instruments (WPI)ECU-HOC-W
Flexible duct hose (2-1/2'' ID, 2-3/4'' OD)McMaster-Carr56675K71
High-temperature glass-mica ceramic, easy-to-machine (6'' x 6'', 1/4'' thickness)McMaster-Carr8489K62
Polycarbonate sheets (thickness 0.25'')McMaster-Carr8574K286
Silicone rubber sheets (36'' x 36'', thickness 1/8'')McMaster-Carr5827T43
Materials and parts for the Flexible chamber
Hot plateMcMaster-Carr31745K11
High-purity inline filter, 1/4 NPTMcMaster-Carr6645T18
Hole saw (cutting diameter 1-7/8 inch)McMaster-Carr4066A34
Hole saw (cutting diameter 50 mm)McMaster-Carr4556A19
High-temperature silicone rubber tubing, soft, 2 mm ID, 5 mm ODMcMaster-Carr5054K313
Inline filter (1/4 NPT, 40 micron)McMaster-Carr98385K843
Multipurpose 6061 Aluminum round tube (1/8'' wall thickness, 4'' OD)McMaster-Carr9056K42
Multipurpose 6061 Aluminum round tube (3/4'' wall thickness, 3-3/4'' OD)McMaster-Carr9056K47
Multipurpose 6061 Aluminum bar (12'' x 12'', thickness 1/4'')McMaster-Carr8975K142
Multipurpose 6061 Aluminum bar (8'' x 8'', thickness 3/8'')McMaster-Carr9246K21
Objective nosepiece (single)Nikon IncFN-MN-H
Sample holder (modified)Prior ScientificHZ202
Ultra-thin natural rubber film (thickness 0.01'')McMaster-Carr8611K13
Vacuum-sealable glass jarMcMaster-Carr3231T44
Software
MATLABMathWorks
ImageJ (Fiji)imagej.net
ScanImageVidrio Technologies, LLCSRS imaging software
Materials for live-cell imaging
Cover glass bottom sterile culture dishes (Dia.x H, 50 x 7 mm)Electron Microscopy Sciences (EMS)70674-02
DMEM cell culture mediumThermoFisher Scientific11965092
Fetal bovine serum (FBS)ThermoFisher Scientific26140079
LysoSensor fluorescent dye DND-189ThermoFisher ScientificL7535 (Invitrogen)
Oleic acidMilliporeSigma364525
SKOV3 cell lineATCCHTB-77

References

  1. Mertz, J. . Introduction to Optical Microscopy. , (2019).
  2. Ettinger, A., Wittmann, T. Fluorescence live cell imaging. Methods in Cell Biology. 123, 77-94 (2014).
  3. Park, Y., Depeursinge, C., Popescu, G.

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