Optical standing wave artifacts in reflection-absorption FTIR microspectroscopy of biological materials.

DOI: 10.1088/1742-6596/359/1/012006

Authors: Jacob Filik (Diamond Light Source) , Mark Frogley (Diamond Light Source) , Jacek Pijanka (Keele University) , Katia Wehbe (Diamond Light Source) , Gianfelice Cinque (Diamond Light Source)
Co-authored by industrial partner: No

Type: Conference Paper
Conference: 6th Workshop on Infrared Spectroscopy and Microscopy with Accelerator-Based Sources (WIRMS11)
Peer Reviewed: Yes

State: Published (Approved)
Published: May 2012

Abstract: Reflection-absorption spectra obtained with an infrared microscope should yield the same absorption coefficients as direct micro-transmission measurements as long as the correct effective sample thickness is used, but in practice, severe optical artifacts can complicate the spectra. Using deposited protein gel fdms as a homogenous model for biological cell-like samples, we demonstrate the effect of standing-wave interference of the IR beam at the reflective substrate surface which dramatically and systematically alters the absorbance intensity across the spectrum as a function of sample thickness. To explain the observed spectral artifacts, we simulate the optical standing-wave for the focussed IR beam, and insert the parameters into an existing standing-wave absorption theory. By introducing an additional term to the theory representing a component of the standing-wave resonant with the film thickness, the data are accurately reproduced, and the relative band intensities can be corrected to the direct transmission values. This approach may be generally applicable in reflection-absorption experiments to obtain reliable absorbance spectra of homogenous samples even when the sample thickness is larger than the IR wavelength.

Journal Keywords: Absorption Spectra; Biological Materials; Fourier Transformation; Infrared Radiation; Infrared Spectra; Interference; Light Transmission; Photon Beams; Proteins; Reflection; Standing Waves; Substrates; Surfaces; Thin Films

Subject Areas: Biology and Bio-materials


Instruments: B22-Multimode InfraRed imaging And Microspectroscopy

Added On: 09/03/2012 21:05

Documents:
Filik_2012_J._Phys.%3A_Conf._Ser._359_012006.pdf

Discipline Tags:

Biophysics Life Sciences & Biotech

Technical Tags:

Spectroscopy Infrared Spectroscopy Synchtron-based Fourier Transform Infrared Spectroscopy (SR-FTIR)