The principles of proton probe microanalysis in biology

The proton microprobe, more correctly described as an ion microprobe which operates at MeV energies, complements its parent instrument the electron microprobe. This paper compares the basic principles and performance of the two instruments and relates the evolution of biological analysis on such ion microprobes to that on electron microprobes, covering the development of sample handling techniques and of data handling techniques and comparing beam damage studies. The paper describes the variety of techniques available to the ion microprobe - the initial techniques of Energy Dispersive X-ray analysis, Rutherford Back Scattering and Nuclear Reaction Analysis and the rapid evolution of new techniques, from Scanning Transmission Ion Microscopy to 3-dimensional tomography. All of these new techniques required the advanced computerised data handling which has been a feature of ion microprobe development.