Second harmonic generation imaging - a new method for unraveling molecular information of starch.
We present a new method, second harmonic generation (SHG) imaging for the study of starch structure. SHG imaging can provide the structural organization and molecular orientation information of bio-tissues without centrosymmetry. In recent years, SHG has proven its capability in the study of crystallized bio-molecules such as collagen and myosin. Starch, the most important food source and a promising future energy candidate, has, for a decade, been shown to exhibit strong SHG response. By comparing SHG intensity from different starch species, we first identified that the SHG-active molecule is amylopectin, which accounts for the crystallinity in starch granules. With the aid of SHG polarization anisotropy, we extracted the complete χ((2)) tensor of amylopectin, which reflects the underlying molecular details. Through χ((2)) tensor analysis, three-dimensional orientation and packing symmetry of amylopectin are determined. The helical angle of the double-helix in amylopectin is also deduced from the tensor, and the value corresponds well to previous X-ray studies, further verifying amylopectin as SHG source. It is noteworthy that the nm-sized structure of amylopectin inside a starch granule can be determined by this far-field optical method with 1-μm excitation wavelength. Since SHG is a relatively new tool for plant research, a detailed understanding of SHG in starch structure will be useful for future high-resolution imaging and quantitative analyses for food/energy applications.
Zhuo
Zong-Yan
ZY
Department of Physics, National Taiwan University, Taipei 10617, Taiwan ROC.
Liao
Chien-Sheng
CS
Huang
Chen-Han
CH
Yu
Jiun-Yann
JY
Tzeng
Yu-Yi
YY
Lo
Wen
W
Dong
Chen-Yuan
CY
Chui
Hsiang-Chen
HC
Huang
Yu-Chan
YC
Lai
Hsi-Mei
HM
Chu
Shi-Wei
SW
D000687:Amylopectin / Q000737:chemistry*; D000688:Amylose / Q000737:chemistry; D016880:Anisotropy; D021621:Imaging, Three-Dimensional / Q000379:methods*; D018613:Microscopy, Confocal / Q000379:methods; D055095:Optics and Photonics; D012275:Oryza / Q000737:chemistry; D013213:Starch / Q000737:chemistry
D013213:Starch; D000688:Amylose; D000687:Amylopectin