<p></p><p><i>In situ</i>
visualization of proteins of interest at single cell level is attractive in
cell biology, molecular biology and biomedicine, which usually involves photon,
electron or X-ray based imaging methods. Herein, we report an optics-free
strategy that images a specific protein in single cells by time of
flight-secondary ion mass spectrometry (ToF-SIMS) following genetic incorporation
of fluorine-containing unnatural amino acids as a chemical tag into the protein
via genetic code expansion technique. The method was developed and validated by
imaging GFP in E. coli and human HeLa cancer cells, and then utilized to
visualize the distribution of chemotaxis protein CheA in E. coli cells and the
interaction between high mobility group box 1 protein and cisplatin damaged DNA
in HeLa cells. The present work highlights the power of ToF-SIMS imaging
combined with genetically encoded chemical tags for <i>in situ </i>visualization
of proteins of interest as well as the interactions between proteins and drugs
or drug damaged DNA in single cells.</p><p></p>