Negligible sample heating from synchrotron infrared beam

The use of synchrotron sources for infrared (IR) spectromicroscopy provides greatly increased brightness that enables high-quality IR measurements at diffraction-limited spatial resolutions. This capability permits synchrotron-based IR spectromicroscopy to be applied to biological applications at spatial resolutions on the order of the size of a single mammalian cell. The question then arises, "Does the intense synchrotron beam harm biological samples?" Mid-IR photons are too low in energy to break bonds directly; however, they could cause damage to biological molecules due to heating. In this work, we present measurements that show negligible sample heating effects from a diffraction-limited synchrotron IR source. The sample used is fully hydrated lipid bilayers composed of dipalmitoylphosphatidylcholine (DPPC), which undergoes a phase transition from a gel into a liquid-crystalline state at about 315 K during heating. Several IR-active vibrational modes clearly shift in frequency when the sample passes through the phase transition. We calibrate and then use these shifting vibrational modes as an in situ temperature sensor.

@Article\{MTCM01,
  author       = "Martin, Michael C. and Tsvetkova, Nelly M. and Crowe, John H. and McKinney, Wayne R.",
  title        = "Negligible sample heating from synchrotron infrared beam",
  journal      = "Applied Spectroscopy",
  number       = "2",
  volume       = "55",
  pages        = "111-113",
  month        = "February",
  year         = "2001",
  note         = "LBNL-46804, 1.4.3",
  keywords     = "Synchrotron; Infrared; FT-IR; Spectromicroscopy; Dipalmitoylphosphatidylcholine; DPPC; Beam; Heating.",
  url          = "http://infrared.als.lbl.gov/Publications/2001/MTCM01"
}