Biomedical applications of particle probes and X-ray analysis

Mass and elemental analysis of biological tissues at cellular and subcellul ar levels using X-rays has a history that goes back to the 1940s. In fact, the thesis presented at the Karolinska Institute by Arne Engstrom, "Quantit ative micro- and histochemical elementary analysis" meant a break-through f or a biophysical approach to the study of cells and tissues. The first hand choice was hard mineralised tissues, bone and dental tissue, areas which s till utilise the technique albeit in modern tapping including computer supp ort. The new technique demanded new preparation methods and cryotechniques became mandatory in the special niche of tissue analysis. The arrival in th e beginning of the 1970s of energy dispersive detectors in conjunction with scanning (transmission) electron microscopes allowed a higher resolution a nd subcellular compartments were now possible to analyse. More sophisticate d preparation procedures had to be developed within the realm of cryo-techn iques to match the hard requirements of high resolution analysis. However, trace element sensitivity was not obtained in the STEM and only shortly aft er its development in the 1970s proton induced Xray microanalysis was appli ed to the analysis of important signal substances such as Ca2+, and other i mportant trace elements including Fe and Zn, The development of scanning pr obes. highly collimated beams and sensitive detectors now Feint the way tow ards subcellular resolution even for PIXE. Although not allowing the same s patial resolution newly developed W-ray fluorescent techniques promise high sensitivity analysis also in biological application. The advantages of the se biophysical approaches will be related to other current techniques for t issue and cell analysis. (C) 1999 Elsevier Science B.V. All rights reserved .