Ion microscopy in biology.

Ion microscopy, a mass spectrometry based isotopic imaging technique, is uniquely suited for ion transport related problems in biological systems. Due to its high sensitivity, it can image the transport and distribution of both major and minor elements (isotopes) at subcellular resolutions. The images of major elements such as K, Na, CI, etc., can be viewed directly and recorded in real-time from the microchannel plate-fluorescent screen detector of the instrument. The low concentration physiologically important elements, such as Ca, need about one minute of integration for good quality imaging. The isotopic imaging capability of ion microscopy provides a unique approach for the use of stable isotopes as tracers. In this way, one can image both the endogenous and the transported isotopes independently. Strict cryogenic sample preparations are essential for ion transport studies. Correlative imaging of the same cell with laser scanning confocal microscopy and ion microscopy can positively identify smaller cytoplasmic compartments such as the Golgi apparatus in calcium images. We have identified the Golgi apparatus as a calcium storing organelle. Another unique application of ion microscopy is the imaging of boron from boronated drugs used in Boron Neutron Capture Therapy (BNCT) of cancer. Ion microscopy is capable of rapid screening of potential drugs for BNCT. This critical information is essential for the fundamental understanding of BNCT. Ion microscopy is now at the stage where it can provide previously unattainable answers to important biomedical questions.