Chemical microscopy of biological samples by dynamic mode secondary ion mass spectrometry.

3D chemical microscopy is one of the emerging applications of secondary ion mass spectrometry (SIMS) in biology. Tissues, cells, extracellular matrices, and polymer films can be imaged at present with a lateral resolution of 50 nm and depth resolution of 1 nm using the latest generation of CAMECA magnetic sector NanoSIMS 50 or with a lower lateral resolution (above 100 nm) using IMS 4f Cameca SIMS equipped with cold stage. Dynamic mode SIMS analysis is performed in ultrahigh vacuum and thus requires specific and careful preparation of biological samples aimed at preserving and minimizing destruction of the original structural and chemical properties of the samples. Here we describe a methodology based on the ultrafast plunge-freezing of biological tissues, preparation of the sample for SIMS analyses and transfer to the SIMS cold stage without interruption of the cold chain during the mounting procedure and subsequent SIMS analyses. Using this strategy, SIMS chemical microscopy can be performed on biological tissue in which unwanted molecular and/or structural reorganization, loss of constituents and chemical modifications are minimized and in which structures are therefore optimally preserved.