Name: in vivo imaging of biological tissues with combined two-photon fluorescence and stimulated raman scattering microscopy
Uploaded: 2021-12-20T14:00:00
Description: Watch this Scientific Journal Video about In vivo Imaging of Biological Tissues with Combined Two-Photon Fluorescence and Stimulated Raman Scattering Microscopy at JoVE.com

This work was supported by the Hong Kong Research Grants Council through grants 16103215, 16148816, 16102518, 16102920, T13-607/12R, T13-706/11-1, T13-605/18W, C6002-17GF, C6001-19E, N_HKUST603/19, the Innovation and Technology Commission (ITCPD/17-9), the Area of Excellence Scheme of the University Grants Committee (AoE/M-604/16, AOE/M-09/12), and the Hong Kong University of Science &#38; Technology (HKUST) through grant RPC10EG33.

All animal procedures performed in this work are conducted according to the guidelines of the Laboratory Animal Facility of the Hong Kong University of Science and Technology (HKUST) and have been approved by the Animal Ethics Committee of HKUST. Safety training for laser handling is required to set up and operate the TPEF-SRS microscope. Always wear laser safety goggles with appropriate wavelength range when dealing with laser.
1. Setup of the TPEF-SRS microscope (for setup schematic se...

In this protocol, the basic setup of the TPEF-SRS microscope is described in detail. For SRS imaging, the pump and Stokes beams are temporally and spatially overlapped inside the OPO.&#160;However, this overlapping can be disrupted after passing through the microscope system. Therefore, both spatial and temporal optimization of the colocalization of the pump and Stokes beams is necessary and critical to achieving optimal SRS imaging. The temporal delay between the pump and Stokes beam is related to the optical path diffe...

Raman microscopy1,2 is emerging as a powerful label-free method to image biological tissues based on the characteristic frequencies of various chemical bonds in biomolecules. Owing to its non-invasive and well-adaptive imaging capability, Raman microscopy has been widely used for imaging lipid-enriched components in biological tissues like myelin sheath3,4,5, adipocytes6,7, and lipid droplets8,9,10. Stimulated Raman scattering (SRS) signal acquired as stimulated Raman gain (SRG) or stimulated Raman loss (SRL) is background-free, showing perfect spectral resemblance to spontaneous Raman scattering11,12. In addition, SRL and SRG are linearly dependent on the analyte concentration, allowing for quantitative analysis of biochemical components9,11,13. Two-photon excited fluorescence microscopy (TPEF) has been widely used for in vivo biological imaging owing to its inherent optical sectioning capability, deep penetration depth, and low phototoxicity14,15,16. However, the performance of TPEF imaging depends on the characteristics of fluorescent tags, and the number of resolvable colors is limited due to the broadband fluorescence spectra8,17,18,19. Label-free SRS imaging and fluorescence-based TPEF imaging are two complementary imaging modalities, and their combination can provide abundant biophysical and biochemical information of tissues. These two imaging modalities are both based on the nonlinear optical (NLO) processes, which allows simple integration in one microscope system. The combination of the SRS and TPEF imaging, the so-called dual-modal imaging, enables high-dimensional imaging and profiling of cells and tissues, facilitating a comprehensive understanding of complex biological systems. Specifically, picosecond (ps) SRS microscopy can achieve chemical-bond imaging with high spectral resolution compared with femtosecond (fs) SRS technique11, allowing to differentiate multiple biochemical components in biological tissue, especially in the crowded fingerprint region20,21. In addition, compared with another commonly used dual-modal NLO microscope system with integration of coherent anti-Stokes scattering (CARS) microscope, SRS shows superior performance to CARS in terms of spectral and image interpretation as well as detection sensitivity11. The SRS-TPEF microscope has been used as a powerful tool to study various biological systems, such as Caenorhabditis elegans9,22, Xenopus laevis tadpole brain5, mouse brain23,24, spinal cord25,26, peripheral nerve27, and adipose tissue7, etc.
The spinal cord together with the brain makes up the central nervous system (CNS). Visualizing cellular activities in the CNS in vivo under physiological and pathological conditions is critical for understanding the mechanisms of CNS disorders28,29,30 and for developing corresponding therapies31,32,33. Myelin sheath, which wraps and insulates axons for high-speed action potential conduction, plays a significant role in the development of the CNS. Demyelination is thought of as a hallmark in white matter disorders, such as multiple sclerosis34. In addition, after spinal cord injury35, myelin debris can modulate macrophage activation, contributing to chronic inflammation and secondary injury36. Therefore, in vivo imaging of myelin sheath together with neurons and glial cells in living mouse models is of great help to understand the dynamic processes in CNS disorders.
In this protocol, the fundamental setup procedures of a home-built TPEF-SRS microscope are described and the dual-modal in vivo imaging methods for mouse spinal cord are introduced.

<table border="1" fo:keep-together.within-page="1" fo:keep-with-next.within-page="always">
	<tbody>
		<tr>
			<td>#2 Forceps</td>
			<td>Dumont</td>
			<td>11223-20</td>
			<td>For laminectomy</td>
		</tr>
		<tr>
			<td>10X objective</td>
			<td>Nikon</td>
			<td>CFI Plan Apo Lambda 10X</td>
			<td></td>
		</tr>
		<tr>
			<td>25X objective</td>
			<td>Olympus</td>
			<td>XLPLN25XSVMP2</td>
			<td></td>
		</tr>
		<tr>
			<td>Burn cream</td>
			<td>Betadine</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Camera</td>
			<td>Sony</td>
			<td>&#945;6300</td>
			<td></td>
		</tr>
		<tr>
			<td>Current amplifier</td>
			<td>Stanford research</td>
			<td>SR570</td>
			<td></td>
		</tr>
		<tr>
			<td>Current photomultiplier modules</td>
			<td>Hamamatsu</td>
			<td>H11461-01</td>
			<td></td>
		</tr>
		<tr>
			<td>D2 665 nm long-pass dichroic mirror</td>
			<td>Semrock</td>
			<td>FF665-Di02-25x36</td>
			<td>For directing epi-fluorescence signal to the detection module</td>
		</tr>
		<tr>
			<td>D3 700 nm short-pass dichroic mirror</td>
			<td>Edmund</td>
			<td>69-206</td>
			<td>For separating SRS from TPEF detection path</td>
		</tr>
		<tr>
			<td>Depilating cream</td>
			<td>Veet</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>FS1 975 nm short-pass filter</td>
			<td>Edmund</td>
			<td>86-108</td>
			<td>For blocking stokes beam</td>
		</tr>
		<tr>
			<td>FS1 Bandpass filter</td>
			<td>Semrock</td>
			<td>FF01-850/310</td>
			<td>For blocking stokes beam</td>
		</tr>
		<tr>
			<td>Fs2 Bandpass filter</td>
			<td>Semrock</td>
			<td>FF01-525/50</td>
			<td>For selecting YFP signal</td>
		</tr>
		<tr>
			<td>Fs2 Shortpass filter</td>
			<td>Semrock</td>
			<td>FF01-715/SP-25</td>
			<td>For blocking fs excitation laser beam</td>
		</tr>
		<tr>
			<td>Half-wave plate</td>
			<td>Thorlabs</td>
			<td>SAHWP05M-1700</td>
			<td></td>
		</tr>
		<tr>
			<td>High-speed photodetector</td>
			<td>MenloSystems</td>
			<td>FPD 310-F</td>
			<td>For checking Stokes beam modulation</td>
		</tr>
		<tr>
			<td>Iodine</td>
			<td>Betadine</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>IR Scope</td>
			<td>FJW</td>
			<td>FIND-R-SCOPE Infrared Viewer 2X Kit Model 84499C2X</td>
			<td></td>
		</tr>
		<tr>
			<td>Iris</td>
			<td>Thorlabs</td>
			<td>CPA1</td>
			<td></td>
		</tr>
		<tr>
			<td>L1</td>
			<td>Thorlabs</td>
			<td>AC254-060-B-ML</td>
			<td></td>
		</tr>
		<tr>
			<td>L10</td>
			<td>Thorlabs</td>
			<td>LA4052-A</td>
			<td></td>
		</tr>
		<tr>
			<td>L2</td>
			<td>Thorlabs</td>
			<td>LA1422-B</td>
			<td></td>
		</tr>
		<tr>
			<td>L3</td>
			<td>Thorlabs</td>
			<td>AC254-050-B</td>
			<td></td>
		</tr>
		<tr>
			<td>L4</td>
			<td>Thorlabs</td>
			<td>AC254-060-B-ML</td>
			<td></td>
		</tr>
		<tr>
			<td>L7</td>
			<td></td>
			<td></td>
			<td>f=100 mm, AB coating</td>
		</tr>
		<tr>
			<td>L8</td>
			<td>Thorlabs</td>
			<td>LA4874-A</td>
			<td></td>
		</tr>
		<tr>
			<td>L9</td>
			<td>Thorlabs</td>
			<td>AC254-035-B-ML</td>
			<td></td>
		</tr>
		<tr>
			<td>Lock-in amplifier</td>
			<td>APE</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Mirror</td>
			<td>Thorlabs</td>
			<td>PF10-03-P01</td>
			<td></td>
		</tr>
		<tr>
			<td>Motorized flipper</td>
			<td>Thorlabs</td>
			<td>MFF101/M</td>
			<td></td>
		</tr>
		<tr>
			<td>multifunctional acquisition card</td>
			<td>National Instrument</td>
			<td>PCIe-6363</td>
			<td></td>
		</tr>
		<tr>
			<td>Oscilloscope</td>
			<td>Tektronix</td>
			<td>TDS2012C</td>
			<td></td>
		</tr>
		<tr>
			<td>Photodiode</td>
			<td>APE</td>
			<td></td>
			<td>For detecting SRS signal</td>
		</tr>
		<tr>
			<td>Picosecond laser source</td>
			<td>APE</td>
			<td>picoEmerald</td>
			<td></td>
		</tr>
		<tr>
			<td>Polarizing beam splitter</td>
			<td>Thorlabs</td>
			<td>CCM1-PBS252/M</td>
			<td></td>
		</tr>
		<tr>
			<td>Power meter</td>
			<td>Newport</td>
			<td>843-R</td>
			<td></td>
		</tr>
		<tr>
			<td>Saline</td>
			<td>Braun</td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Scan lens L5</td>
			<td>Thorlabs</td>
			<td>SL50-CLS2</td>
			<td></td>
		</tr>
		<tr>
			<td>Scanning mirror</td>
			<td>Cambridge Technology</td>
			<td>6215H</td>
			<td></td>
		</tr>
		<tr>
			<td>Silicone gel</td>
			<td>World Precision Inc.</td>
			<td>KWIK-SIL</td>
			<td></td>
		</tr>
		<tr>
			<td>Ti:sapphire fs laser</td>
			<td>Coherent</td>
			<td>Chameleon Ultra II</td>
			<td></td>
		</tr>
		<tr>
			<td>Tube lens L6</td>
			<td>Thorlabs</td>
			<td>TTL200-S8</td>
			<td></td>
		</tr>
	</tbody>
</table>

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 dual-modal imaging of spinal axons as well as myelin sheaths is conducted using the Thy1-YFPH transgenic mice, which express EYFP in dorsal root ganglion afferent neurons (Figure 3). These labeled afferent neurons relay the sensory information from the peripheral nerve to the spinal cord, with the central branch located in the spinal cord dorsal column. With the TPEF-SRS microscope, densely distributed myelin sheath can be clearly visualized using label-free SRS imaging, and...

Watch this Scientific Journal Video about In vivo Imaging of Biological Tissues with Combined Two-Photon Fluorescence and Stimulated Raman Scattering Microscopy at JoVE.com

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.

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 ...

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