Improvements in chemical imaging on B22

Exploiting the brightness of SRIR for faster chemical imaging

The ability to collect spatial and chemical information can give great insights into a range of samples from disease signatures in tissue to aging in varnishes and pigments used in frescoes. On the Multimode InfraRed Imaging And Microspectroscopy (MIRIAM) beamline (B22) the broadband infrared (IR) radiation obtained from the synchrotron is used to collect high quality spectra with better spatial resolution than is possible from a thermal IR source. At the moment these chemical maps are measured point-by-point and can take hours to collect. Advances in IR detection now allows chemical images to be collected all in one go. On B22 we are investigating how to exploit this new detector technology with the synchrotron radiation IR (SRIR) to offer chemical imaging experiments not possible with other IR sources.

     
Limitations of Chemical imaging
The advent of focal plane array (FPA) detectors has revolutionised chemical/molecular imaging microscopy. With these detectors, IR spectra can now be collected over a large field of view simultaneously. While thermal sources are not bright enough to achieve high spatial resolution (<10 µm), SRIR is a broader and brighter source providing a much higher signal to noise. Full field IR microscopy via an FPA detector in combination with SR illumination has been experimentally proven at Diamond Light Source on the MIRIAM beamline (B22) but with some practical limitations. In order to take full advantage of the SRIR brightness the issue to be addressed is spatial structure of the SR beam (Figure 1). This structure causes artefacts in the images collected with the FPA detector, limiting the field of view which can be collected.  Our aim is to implement a pair of deformable mirrors to improve the illumination of the FPA detector and eliminate the SRIR structure.

Figure 1: The adaptive optics employed at B22.

Adaptive Optics

Deformable mirrors have a surface which can be manipulated and shaped; this allows the light reflected from them to be finely controlled. Deformable mirrors have been used in astronomy for many years to correct for atmospheric turbulence which can distort telescopic images. More recently these mirrors have been used in visible microscopy to correct for sample aberrations and also in super resolution techniques. 

Generally deformable mirrors have been used to correct phase errors whereas the application we are implementing on B22 involves shaping the amplitude of our SRIR light source. To achieve this a new optic setup to couple the SRIR with the deformable mirrors and the microscope has been developed and built. The next step is to develop an optimisation scheme to find the mirror shapes, which produce the best illumination of the FPA detector in the IR microscope.

Applications
IR chemical imaging has been increasingly used for the study of cells and tissues as it can determine the identity, concentration, and biochemical properties of a sample. On B22 high resolution chemical images are collected point-by-point, to assemble spectra from an area of interest (even a single cell). These images can take an hour or more. The ability to measure the microscope field of view in one-shot will dramatically increase the speed of data collection which will allow much larger areas to be imaged. Conversely if the area of interest is smaller (within the microscope field of view) this new technique presents the opportunity of real time chemical imaging, allowing biochemistry in living cells to be observed. These exciting experiments will be realised at B22 due to the capacity to culture cell lines on site and the ability to handle biohazard level 2 materials on the beamline.

Figure 2: a) Image of collimated SRIR beam before deformable optic and b) after the deformable optics. (a) shows the 6 part structure of the collected SRIR beam, while (b) shows a simula
 

 

To find out more about the B22 beamline, or to discuss potential applications, please contact Principal Beamline Scientists Dr Gianfelice Cinque: gianfelice.cinque@diamond.ac.uk

References:

1. Quaroni. L, et al. Synchrotron based IR imaging and spectroscopy via FPA on live fibroblasts in D2O medium, Biophys. Chem. 189, 40 (2014)
2. Quaroni. L, Zlateva. T, et al. Infrared imaging of small molecules in living cells: from in vitro metabolic   analysis to cytopathology, Faraday Discussion, 187, 259 (2016)
3. Hirschmulg. C, Gough. K, Fourier Transform Infrared Spectrochemical Imaging: Review of Design and Applications with a Focal Plane Array and Multiple Beam Synchrotron Radiation Source, Applied Spec, 66, 5 (2012)