Embedded Files
Introduction of Second Harmonic Generation (SHG)
As a member of multi-photon imaging family, second harmonic generation (SHG) microscopy provides the three advantages.
§ Optical section. §
§ Freedom on excitation wavelength selection. §
§ Deep penetration due to long wavelength excitation. §
§ Sensitivity on molecular organization. §
1. SHG-CD Microscopy
In this study, we performed SHG-CD microscopy inside a thick biological tissue for the first time.
The sample is a starch granule whose SHG-active molecule is amylopectin. The radial distribution and intrinsic right-handed chirality of amylopectin make starch an ideal model for SHG-CD demonstration.
Figure shows the SHG-CD optical section of our sample. The SHG-CD signal is indeed significantly larger than conventional CD.
2. Observation of Heat Propagation
In this study, we have demonstrated by using time-lapsed two-photon fluorescence microscopy (2PFM), heat flow in biological tissues can be monitored based on temperature-induced fluorescence change of endogenous molecules.
3. Spectral SHG imaging
Due to the scattering and turbidity in biomaterials, it is hard for light to penetrate into thick tissue. Some method can overcome the problem:
1. Section of bio-tissues.
2. Immersion of bio-tissues in FocusClear, an optical clearing solution.
3. Long wavelength range to avoid scattering.
Since no 1.4-2μm laser except Er:doped fiber laser, the near-infrared (NIR) light source is a home-built optical parametric generation (OPG), which is tunable of wavelength from 1430nm to 1800nm by periodically poled lithium niobate (PPLN). The sample we used is the head of fixed drosophila. The penetration depth of SHG imaging are compared in the very same specimen before and after immersion in FocusClear. As a result, we have demonstrated that FocusClear can indeed improve penetration capability in NIR regime.
CCD imaging of fly brains before and after immersed FocusClear:
SHG xy-plane (a) and 3D (b) imaging of fly brain:
Google Sites
Report abuse