Measurement of Absolute Concentration at the Subcellular Scale.

The concentration of a pharmaceutical drug or bioactive metabolite within the target organelle influences the effects elicited by the drug or metabolite. Although the relative concentrations of many compounds of interest within subcellular compartments have been measured, measurements of absolute concentrations in the organelle remain elusive. In this Perspective, we discuss a significant advance in using nano secondary ion mass spectrometry (nanoSIMS) to measure the absolute concentration of a 13C-labeled metabolite within secretory vesicles, as reported by Thomen et al. in the April issue of ACS Nano.