Life science

High resolution tissue imaging with multi-modal O-PTIR

Breast tissue calcification – Demonstration of <1 micron spatial resolution with O-PTIR

A: Optical image (mosaic). Red box indicates IR image measurement area. B: Single frequency image at 1050cm-1 to highlight calcification locations. C: O-PTIR Spectra from colored circle markers in IR image (B). IR image area 200×200 microns at 500nm step size. Image time, ~10mins.

Calcification IR image at 1050cm-1, clearly resolves calcifications averaging only a few microns in size, many even <1 micron. At 1050cm-1, traditional FTIR has a spatial of ~12microns, which is much larger than the actual features, which is why such small an localized calcifications had not been seen before.

Sample courtesy of Prof Nick Stone, Exeter University, UK. Publication in preparation (Dec, 2020)

Mouse Brain tissue section – Multi-modal, label-free chemical imaging

Label-free chemical imaging is essential in life sciences as it visualizes and characterizes biological samples without dyes, preserving their natural state and minimizing artifacts. It enables the direct identification of molecular composition, offering precise insights into biochemical processes with high specificity.
Shown below is a standard histological thin section of mouse brain, chemically imaged for key macromolecules and metabolites.
Label free imaging in 10’s of minutes with high spatial resolution.

Initial brightfield (BF) and Autofluorescence (AutoFL) images are shown on the left hand side. All images, BF, AutoFL and IR chemical images are inherently perfectly spatially registered as there are no optics (objective) or sample movements between these images.

In red, cell nuclei are clearly highlighted in the image by the 1080/1140cm-1 ratio. In green, creatine is highlighted by the 1040/1655cm-1 ratio and lipid is highlighted by the 1738/1665cm-1 ratio.

Representative single point spectra (~400nm spot size) from each of these chemical images is shown in the bottom pane with location marked by white circles.

Asterisks on spectra indicate the image ratio wavenumber positions described above.

Using fluorescence to localize O-PTIR measurements

An Alzheimer’s disease mouse model brain tissue section was stained with Amytracker 630 to highlight amyloid aggregates, AF488 to highlight proteins and DAPI for the nucleus. In the figure to the right is shown a brightfield image, top left, of the stained sample.

In the top right is the RBG composite fluorescence image, which highlights in red/orange the regions of amyloid aggregation. Note how some amyloid aggregates highlighted in the fluorescence image are not readily distinguishable in the brightfield image. At the bottom is an averaged O-PTIR spectra, from the line profile indicated in the fluorescence image, with spectra averaged on (in blue) and off (in red) the aggregate.

The average spectrum of the aggregate shows distinct spectral differences in the amide I band with a significant spectral feature at 1631cm-1, typical of protein beta sheet structures. This clearly demonstrates the utility of combining fluorescence imaging to highlight regions of amyloid aggregation, some of which cannot be readily seen in brightfield microscopy, with submicrometer O-PTIR spectroscopy which can then provide the molecular compositional information, in this case, being particularly sensitive to protein secondary structure, a characteristic strength of IR spectroscopy.

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