Qualitative co-localization of DNA and RNA through simultaneous imaging of RNA and DNA. Rat embryo fibroblasts were pulsed with 15N-uridine and BrdU as markers of newly synthesized RNA and DNA, respectively. (a,b) Parallel mass images at (a) 12C15N- and (b) 81Br-. (c) Overlay of 12C15N- and 81Br- images. 12C15N- is depicted as red (R) and 81Br- as green (G); the overlap between them shows up as yellow. (d) Overlay of 12C14N- and 12C15N- images. 12C14N- is depicted as red (R) and 12C15N- as green (G); the overlap between them shows up as yellow. Conditions of MIMS analysis: beam current 2pA; beam diameter 100 nm; field 20 × 20 μm.