Quantitative imaging of boron, calcium, magnesium, potassium, and sodium distributions in cultured cells with ion microscopy.

A method for the conversion of intensity information in ion micrographs of freeze-fractured, freeze-dried cultured cells to local dry weight elemental concentrations is presented. Homogenates generated from cultured cells are used as calibration standards. Ion microscope (IM) relative sensitivity factors for B, Ca, K, Mg, and Na with respect to the matrix element C are determined by the correlation of IM and inductively coupled plasma atomic emission spectrometry analyses of the cellular homogenates. After calibration of the IM imaging system, the relative sensitivity factors are used to determine local intracellular concentrations of B, Ca, K, Mg, and Na in cultured Swiss 3T3 fibroblasts. Intracellular B was introduced through cellular uptake of Na2B12H11SH, a candidate therapeutic agent for boron neutron capture cancer therapy. The IM intracellular concentration results show good agreement with published electron probe X-ray microanalysis results. Estimated detection limits are in the low- to subparts-per-million dry weight concentration range.