Lasers & photonics
precision Laser
Linear accelerators, at one time only found in physics laboratories, are today used to focus high energy beams of electrons or X-rays on malignant tumours. Experiments using electromagnetic induction to reconstruct a 3D image of a box by processing the object in slices, laid the groundwork for the creation of the first CT scanner. Perhaps the most recent example of the application of physics to medicine is MALDI-TOF mass spectrometry. Dermot Martin speaks to Rainer Cramer, professor of mass spectrometry and bioanalytical sciences and head of biomedical, molecular and analytical chemistry at Reading University, to discuss the merits of the technology in medicine.
ince its arrival on the stage in the mid-1980s, matrix assisted laser desorption ionisation linked to mass spectrometry (MALDI-MS) has intrigued scientists and researchers. At first, many were uncertain if it could open doors to a better understanding of molecular structure because it seemed the biomolecules sparked from the matrix might be too small. German chemists Franz Hillenkamp and Michael Karas, who coined the term matrix assisted laser desorption ionisation (MALDI), were looking for a way to excite large biomolecules into the gas phase without fragmentation. They found there was a ceiling on how large the analysed molecules could be, with biopolymers such as proteins and carbohydrates being non-volatile due to their large and polar nature. The team had success
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with the amino acid alanine when mixed with tryptophan, with the latter acting as a matrix to enhance the ion yield of the former on a metal plate irradiated with a 266nm pulsed laser. The Hillenkamp-Karas development of a matrix- based technique that could bind an analyte was a significant leap forward, but it was the work of a young electrical engineer working for the Shimadzu Corporation that is credited with thrusting the technique into the spotlight. In 1987, Koichi Tanaka used the “ultra-fine metal plus liquid matrix method” that combined 30nm Cobalt particles in glycerol with a 337nm nitrogen laser for ionisation. With this combination, Koichi was able to ionise biomolecules as large as 34,472 daltons, including the protein carboxypeptidase-A. It was a light-bulb moment, and
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