Nanoparticles with non-centrosymmetric crystal structures exhibit second harmonic generation (SHG) of light when illuminated by a femtosecond pulsed laser. Such nanoparticles can be used as optical biomarkers to circumvent the drawbacks associated with fluorescent proteins and semiconductor quantum dots, such as photobleaching and fluorescent intermittency (blinking). Bulk barium titanate has a tetragonal crystal structure at room temperature however, reduction in particle sizes generally correlates with an increasing phase fraction of cubic material which does not exhibit SHG .
In this study we have produced barium titanate (BaTiO3) and barium-strontium titanate (Ba1-xSrxTiO3) nanoparticles by the hydrothermal method. These nanoparticles appear predominantly cubic by laboratory-XRD but Rietveld refinement on synchrotron X-Ray powder diffraction data suggests a mixture of tetragonal and cubic phases. Transmission electron microscopy (TEM) analysis techniques such as electron energy loss spectroscopy (EELS) and energy-dispersive X-ray (EDX) spectroscopy have been used to determine the inter- and intra-particle phase and composition of BaTiO3 and Ba1-xSrxTiO3 nanoparticles. Prior STEM-EELS work, suggests an intra-particle phase distribution of cubic and tetragonal phases . STEM-EEL linescans by aberration corrected scanning transmission electron microscopy (SuperSTEM) confirm that these hydrothermal samples exhibit intra-particle phase distribution of a tetragonal core and a cubic shell (Figure 1 & 2).
Multi-photon microscopy correlated with SEM demonstrates the SHG signals from the BaTiO3 and Ba1-xSrxTiO3 nanoparticles . The cellular uptake and biocompatibility of the BaTiO3 and Ba1-xSrxTiO3 nanoparticles have been determined by cell viability (MTT) and genotoxicity (Comet) assays. Uptake was confirmed by backscattered Z-contrast imaging by SEM and EDX (Figure 3), along with bright field TEM and HAADF-STEM of resin embedded cell sections. Direct correlation between electron microscopy (SEM & TEM) and multi-photon microscopy will be used to determine SHG characteristics at the individual particle level when taken up by cells.
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To cite this abstract:Omar Matar, Nicole Hondow, Olga Posada, Michael Routledge, David Hernandez-Maldonado, Christoph Wälti, Claire Murray, Rik Brydson, Steve Milne, Andy Brown; Analytical electron microscopy of barium titanate and barium-strontium titanate nanoparticles for second-harmonic biomarkers. The 16th European Microscopy Congress, Lyon, France. https://emc-proceedings.com/abstract/analytical-electron-microscopy-of-barium-titanate-and-barium-strontium-titanate-nanoparticles-for-second-harmonic-biomarkers/. Accessed: December 4, 2023
EMC Abstracts - https://emc-proceedings.com/abstract/analytical-electron-microscopy-of-barium-titanate-and-barium-strontium-titanate-nanoparticles-for-second-harmonic-biomarkers/