Microscopy phase techniques
QPI makes available, at the nanoscale, phase visualization techniques usually associated with optical microscopy, such as Normaski Differential Interference Contrast (DIC), Zernike Phase Contrast and Hoffman Modulation Contrast.
Light microscopy phase contrast images are unavailable at the nanoscale as traditional phase visualization systems are difficult or impractical to fabricate at these small scales.
QPI is capable of mathematically rendering analogs of these conventional phase contrast systems from the quantitative phase data it generates independent of amplitude/intensity data. Uniquely, QPI's digital phase visualization can be achieved with or without intensity (scattering) contrast.
Case study - Radula (liverwort) spore
The following images of a Radula (liverwort) spore were captured by researchers at the University of Melbourne, Australia, 1 and demonstrate the applicability of QPI technology in generating DIC images using transmission electron microscope (TEM) images.
These 75-90mm thick sections were unstained and captured under a TEM at 4,600x magnification. Two defocused images were processed by QPI to generate a phase map.
Brightfield
|
QPI phase map
|
Note that the in-focus brightfield TEM image above shows negligible contrast. The intensity modulation in the image was approximately ±10%. The QPI phase map provides enhanced visualization of phase dependent features.
A DIC image (shown below) was constructed with the phase data generated by QPI by simply differentiating the complex wavefield in a chosen direction. The QPI DIC image displays the characteristic DIC surface relief appearance.
QPI DIC
|
References
-
Quantitative Phase-Amplitude Microscopy II: Differential Interference Contrast Imaging for Biological TEM
P.J.McMahon, E.D.Barone-Nugent, B.E.Allman and K.A. Nugent, Journal of Microscopy, 206, 204-208 (2002).