FEATURE MICROSCOPY
The Invenio Imaging system is capable of imaging ‘naked’ molecules without using fluorophores ➤
way to fluorescence, but without having to add any dyes or stains.’ Coherent Raman scattering (CRS)
microscopy is a dye-free method that images structures by displaying the characteristic intrinsic vibrational contrast of their molecules. The major benefit of this method is that the sample remains almost unaffected. The technique is based on spontaneous Raman scattering, which has been used in analytical R&D applications for years but typically produces very weak signals,
DIAMOND FOR MICROSCOPY
Diamond has long been recognised as an ideal material for use as an optical component, because of its broad range of transmission, high refractive index, robustness and durability compared with traditional materials.
While these properties were first recognised in natural diamonds, continuous development of synthetic single crystal (SC) diamond grown by chemical vapour deposition (CVD) has enabled new optical applications. New
34 ELECTRO OPTICS l OCTOBER 2016
shapes like cones, hemispheres and large prisms have now come within reach for general spectroscopy applications. ‘This has led to the introduction of new spectroscopy tools driving the change from lab-based equipment to in-line spectroscopy for real- time measurements,’ said Daniel Twitchen, director of strategic product development at synthetic diamond maker Element Six. In addition to its use in spectroscopy and conventional
microscopy, diamond is enabling an entirely new microscopy technology – magnetic microscopy. ‘To date, most existing techniques for measuring magnetic fields are limited as they are either very sensitive but only have limited spatial resolution – for example, SQUIDS – or have good spatial sensitivity but not very sensitive, such as Si Hall devices,’ added Twitchen.
Based on recent progress in diamond defect engineering, it is
possible to engineer specific spin defects, called Nitrogen Vacancy (NV) centres, into the diamond lattice, which act as individual magnetic sensing devices. ‘This offers high sensitivity combined with high spatial resolution – literally offering a magnetic microscope for probing objects as diverse as magnetic domains in hard disks drives to quantifying cancer biomarkers expressed by rare tumour cells in a large population of healthy cells,’ Twitchen concluded.
@electrooptics |
www.electrooptics.com
resulting in slow acquisition rates in imaging applications. ‘The big issue with this method is the limited sensitivity – you need to wait a long time before you can get a reliable measurement,’ said Freudiger. CRS provides amplification of the weak spontaneous Raman signal to enable high- speed, label-free chemical imaging. ‘With coherent Raman scattering we take the spontaneous signal and we amplify it by many orders of magnitude – i.e. by a factor of 10,000. So, suddenly, we can do this label-
free measurement at high enough speeds to use it in microscopy.’ In general, coherent Raman scattering refers to two independent, but related, techniques: coherent anti-stokes Raman scattering (CARS) and stimulated Raman scattering (SRS), which both have the speed advantage over spontaneous Raman scattering. As a research assistant and then postdoctoral fellow working with Professor Xiaoling Sunney Xie (developer of CARS) at Harvard University, Freudiger co-invented
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Invenio Imaging
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