@misc{CisekTokarzKontenisetal.2018,
  author    = {Cisek, Richard and Tokarz, Danielle and Kontenis, Lukas and Barzda, Virginijus and Steup, Martin},
  title     = {Polarimetric second harmonic generation microscopy},
  series = {Starch-Starke},
  volume    = {70},
  journal   = {Starch-Starke},
  number    = {1-2},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {0038-9056},
  doi       = {10.1002/star.201700031},
  pages     = {15},
  year      = {2018},
  abstract  = {Second harmonic generation (SHG) is a nonlinear optical process that inherently generates signal in non-centrosymmetric materials, such as starch granules, and therefore can be used for label-free imaging. Both intensity and polarization of SHG are determined by material properties that are characterized by the nonlinear susceptibility tensor, ((2)). Examination of the tensor is performed for each focal volume of the image by measuring the outgoing polarization state of the SHG signal for a set of incoming laser beam polarizations. Mapping of nonlinear properties expressed as the susceptibility ratio reveals structural features including the organization of crystalline material within a single starch granule, and the distribution of structural properties in a population of granules. Isolated granules, as well as in situ starch, can be analyzed using polarimetric SHG microscopy. Due to the fast sample preparation and short imaging times, polarimetric SHG microscopy allows for a quick assessment of starch structure and permits rapid feedback for bioengineering applications. This article presents the basics of SHG theory and microscopy applications for starch-containing materials. Quantification of ultrastructural features within individual starch granules is described. New results obtained by polarization resolved SHG microscopy of starch granules are presented for various maize genotypes revealing heterogeneity within a single starch particle and between various granules.},
  language  = {en}
}
@article{CisekTokarzKrouglovetal.2014,
  author    = {Cisek, Richard and Tokarz, Danielle and Krouglov, Serguei and Steup, Martin and Emes, Michael J. and Tetlow, Ian J. and Barzda, Virginijus},
  title     = {Second harmonic generation mediated by aligned water in starch granules},
  series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  volume    = {118},
  journal   = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry},
  number    = {51},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1520-6106},
  doi       = {10.1021/jp508751s},
  pages     = {14785 -- 14794},
  year      = {2014},
  abstract  = {The origin of second harmonic generation (SHG) in starch granules was investigated using ab initio quantum mechanical modeling and experimentally examined using polarization-in, polarization-out (PIPO) second harmonic generation microscopy. Ab initio calculations revealed that the largest contribution to the SHG signal from A- and B-type allomorphs of starch originates from the anisotropic organization of hydroxide and hydrogen bonds mediated by aligned water found in the polymers. The hypothesis was experimentally tested by imaging maize starch granules under various hydration and heat treatment conditions that alter the hydrogen bond network. The highest SHG intensity was found in fully hydrated starch granules, and heat treatment diminished the SHG intensity. The PIPO SHG imaging showed that dried starch granules have a much higher nonlinear optical susceptibility component ratio than fully hydrated granules. In contrast, deuterated starch granules showed a smaller susceptibility component ratio demonstrating that SHG is highly sensitive to the organization of the hydroxyl and hydrogen bond network. The polarization SHG imaging results of potato starch granules, representing starch allomorph B, were compared to those of maize starch granules representing allomorph A. The results showed that the amount of aligned water was higher in the maize granules. Nonlinear microscopy of starch granules provides evidence that varying hydration conditions leads to significant changes in the nonlinear susceptibility ratio as well as the SHG intensity, supporting the hypothesis from ab initio calculations that the dominant contribution to SHG is due to the ordered hydroxide and hydrogen bond network.},
  language  = {en}
}
@article{CisekTokarzSteupetal.2015,
  author    = {Cisek, Richard and Tokarz, Danielle and Steup, Martin and Tetlow, Ian J. and Emes, Michael J. and Hebelstrup, Kim H. and Blennow, Andreas and Barzda, Virginijus},
  title     = {Second harmonic generation microscopy investigation of the crystalline ultrastructure of three barley starch lines affected by hydration},
  series = {Biomedical optics express},
  volume    = {6},
  journal   = {Biomedical optics express},
  number    = {10},
  publisher = {Optical Society of America},
  address   = {Washington},
  issn      = {2156-7085},
  doi       = {10.1364/BOE.6.003694},
  pages     = {3694 -- 3700},
  year      = {2015},
  abstract  = {Second harmonic generation (SHG) microscopy is employed to study changes in crystalline organization due to altered gene expression and hydration in barley starch granules. SHG intensity and susceptibility ratio values (R'(SHG)) are obtained using reduced Stokes-Mueller polarimetric microscopy. The maximum R'(SHG) values occur at moderate moisture indicating the narrowest orientation distribution of nonlinear dipoles from the cylindrical axis of glucan helices. The maximum SHG intensity occurs at the highest moisture and amylopectin content. These results support the hypothesis that SHG is caused by ordered hydrogen and hydroxyl bond networks which increase with hydration of starch granules. (C) 2015 Optical Society of America},
  language  = {en}
}