Name: hyperspectral imaging as a tool to study optical anisotropy in lanthanide-based molecular single crystals
Uploaded: 2020-04-14T14:00:00
Description: Watch this Scientific Journal Video about Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals at JoVE.com

The authors thank Mr. Dylan Errulat and Prof. Muralee Murugesu from the Department of Chemistry and Biomolecular Sciences of the University of Ottawa for the provision of [TbEu(bpm)(tfaa)6] single crystals. E.M.R, N.R., and E.H. gratefully acknowledge the financial support provided by the University of Ottawa, the Canadian Foundation for Innovation (CFI), and the Natural Sciences and Engineering Research Council Canada (NSERC).

CAUTION: It is recommended to use safety goggles specific for the excitation wavelength being used at all times when operating the imager.
1. Configuration of the hyperspectral microscope
NOTE: An overview of the hyperspectral imaging system is given in Figure 2a, with the main components of the imager being described. The imaging system can be used for the detection of the visible or the near-infrared (NIR) emission from a sample. Depend...

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The hyperspectral imaging protocol here described provides a straightforward approach that allows to obtain spectroscopic information at precise locations of the sample. Using the described setup, the spatial resolution (x and y mapping) can reach down to 0.5 &#181;m while the spectral resolution can be of 0.2 nm for the mapping at the visible range and 0.6 nm for the NIR range.
In order to conduct hyperspectral mapping on a single crystal, sample preparation follows an easy ...

Hyperspectral Imaging (HSI) is a technique that generates a spatial map where each x-y coordinate contains a spectral information that could be based on any kind of spectroscopy, namely photoluminescence, absorption and scattering spectroscopies1,2,3. As a result, a 3-dimensional set of data (also called &#8220;hyperspectral cube&#8221;) is obtained, where the x-y coordinates are the spatial axes and the z coordinate is the spectral information from the analyzed sample. Therefore, the hyperspectral cube contains both spatial and spectral information, providing a more detailed spectroscopic investigation of the sample than traditional spectroscopy. While HSI has been known for years in the field of remote sensing (e.g., geology, food industries4), it recently emerged as an innovative technique for the characterization of nanomaterials2,5 or probes for biomedical applications3,6,7,8. Generally speaking, it is not limited to the UV/visible/near-infrared (NIR) domain, but can also be extended using other radiation sources, such as X-rays &#8211; for instance in order to characterize elemental distribution in different materials9 &#8211; or Terahertz radiation, where HSI was used to perform thermal sensing in biological tissues8. Further, photoluminescence mapping has been combined with Raman mapping to probe the optical properties of monolayer MoS210. Yet, amongst the reported applications of optical HSI, there are still only a few examples on HSI of lanthanide-based materials11,12,13,14,15,16,17. For instance, we can cite: detection of cancer in tissues6, analysis of the light penetration depth in biological tissues7, multiplexed biological imaging3, analysis of multicomponent energy transfer in hybrid systems11, and investigation of aggregation-induced changes in spectroscopic properties of upconverting nanoparticles12. Clearly, the attractiveness of HSI arises from its suitability for generating knowledge about environment-specific luminescence, providing simultaneous spatial and spectral information about the probe.
Taking advantage of this powerful technique we herein describe a protocol to investigate the optical anisotropy of the heterodinuclear Tb3+-Eu3+ single crystal [TbEu(bpm)(tfaa)6] (Figure 1a)13. The optical anisotropy observed resulted from the different molecular packing of the Ln3+ ions in the different crystallographic directions (Figure 1b), resulting in some crystal faces showing brighter, others showing dimmer photoluminescence. It was suggested that the increased luminescence intensity at specific faces of the crystal was correlated with more efficient energy transfer along those crystallographic directions where the Ln3+&#183;&#183;&#183;Ln3+ ion distances were the shortest13.
Motivated by these results, we propose the establishment of a detailed methodology to analyze optical anisotropy through HSI, opening the path for better understanding of ion-ion energy transfer processes and tunable luminescent properties stemming from specific molecular arrangement18,19. These structure-properties relationships have been recognized as important aspects for innovative optical materials design including, but not limited to waveguide systems and opto-magnetic storage devices at nano and microscale &#8211; addressing the demand for more efficient and miniaturized optic systems20.

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			<td height="21" style="height:21px;width:216px;">Microscope glass slides</td>
			<td style="width:123px;">FisherBrand</td>
			<td style="width:161px;">12-550-15</td>
			<td style="width:167px;">Glass slides used for sample preparation</td>
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		<tr height="42">
			<td height="42" style="height:42px;width:216px;">Visible and Near Infrared Hyperspectral Confocal Imager</td>
			<td style="width:123px;">PhotonETC</td>
			<td style="width:161px;"></td>
			<td>Microscope used for the analysis, builted according to the user needs, therefore it is no catalog number</td>
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</table>

hyperspectral imaging as a tool to study optical anisotropy in lanthanide-based molecular single crystals

In this work, we describe a protocol for a novel application of hyperspectral imaging (HSI) in the analysis of luminescent lanthanide (Ln3+)-based molecular single crystals. As representative example, we chose a single crystal of the heterodinuclear Ln-based complex [TbEu(bpm)(tfaa)6] (bpm=2,2&#8217;-bipyrimidine, tfaa&#8211; =1,1,1-trifluoroacetylacetonate) exhibiting bright visible emission under UV excitation. HSI is an emerging technique that combines 2-dimensional spatial imaging of a luminescent structure with spectral information from each pixel of the obtained image. Specifically, HSI on single crystals of the [Tb-Eu] complex provided local spectral information unveiling variation of the luminescence intensity at different points along the studied crystals. These changes were attributed to the optical anisotropy present in the crystal, which results from the different molecular packing of Ln3+ ions in each one of the directions of the crystal structure. The HSI herein described is an example of the suitability of such technique for spectro-spatial investigations of molecular materials. Yet, importantly, this protocol can be easily extended for other types of luminescent materials (such as micron-sized molecular crystals, inorganic microparticles, nanoparticles in biological tissues, or labelled cells, among others), opening many possibilities for deeper investigation of structure-property relationships. Ultimately, such investigations will provide knowledge to be leveraged into the engineering of advanced materials for a wide range of applications from bioimaging to technological applications, such as waveguides or optoelectronic devices.

To illustrate the configuration of the hyperspectral microscope for the data acquisition on a Ln-based, molecular single crystal (i.e., [TbEu(bpm)(tfaa)6], Figure 1a), Figure 2 shows an overview of the system as well as the right placement of the optical cubes in the setup. Figure 3 shows a screen shot of the PHySpec software containing the menus used during the HSI acquisition. Figure 4 and ...

Watch this Scientific Journal Video about Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals at JoVE.com

Hyperspectral Imaging as a Tool to Study Optical Anisotropy in Lanthanide-Based Molecular Single Crystals

Here, we present a protocol to obtain luminescent hyperspectral imaging data and to analyze optical anisotropy features of lanthanide-based single crystals using a Hyperspectral Imaging System.

In this work, we describe a protocol for a novel application of hyperspectral imaging (HSI) in the analysis of luminescent lanthanide (Ln3+)-based ...

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