Imaging amylopectin's order in starch using 3-dimensional polarization SHG

In minimally destructive SHG biomedical imaging (high resolution optical slicing) is greatly desirable to extract the maximum of information from the light matter interaction. Here we develop a 3-D biophysical model and a methodology, which extracts molecular information below the experimental resolution limit. Firstly, it provides the pitch angle (SHG effective orientation) of the SHG source helix of the sample. This information is used to characterize and categorize the SHG sources among them. And secondly, it provides the degree of organization of the SHG source molecules. This can be used as a quantitative imaging biomarker able to characterize the degree of organization (homeostasis) of the sample. Here we applied the model in dried and hydrated wheat starch granules. Our results show that the SHG source molecule in starch is amylopectin. We also conclude that under hydration, the amylopectin molecules are further organized but they do not change structure. This organization is reflected to the width of the pitch angles pixels’ histograms’ distributions. The shorter the width is, the more organized the amylopectin molecules in starch are.