In situ protein identification and mapping using secondary ion mass spectrometry

Protein characterisation at surfaces currently requires digestion prior to either liquid extraction of the protein for mass spectrometry analysis or in situ matrix-assisted desorption/ionisation. Here, we show that direct assignment of individual proteins and mixtures at surfaces can be achieved by employing secondary ion mass spectrometry (SIMS) with gas cluster ion beam (GCIB) bombardment and an Orbitrap™ analyser. Potential applications of the method are illustrated by demonstrating imaging of a protein film masked by a gold grid and the analysis of a protein monolayer biochip.