The paper shows that the use of buckminsterfullerene (C60) primary ions can release the important surface chemical characterization technique time-of-flight secondary ion mass spectrometry (ToF-SIMS) from limitations of low sensitivity and primary ion-induced chemical damage that threatened its future development. Indeed, it has resulted in a completely new analysis paradigm for SIMS. For the first time, molecular depth profiling has become routinely possible with the exciting further possibility of 3D chemical imaging of organic and biological systems.

“For the first time, molecular depth profiling has become routinely possible with the exciting further possibility of 3D chemical imaging of organic and biological systems.”

The paper is therefore of great interest and potential benefit to researchers wishing to use mass spectrometry to probe molecular chemistry in three dimensions in organic materials and biological cells and tissue. It also has considerable significance to the whole field of bombardment-induced atom and molecule emission from materials. The paper may also have excited interest in those interested in potential uses of C60.

The paper describes a new reliable methodology built on observations that date back some 10 years. ToF-SIMS is a powerful technique in surface mass spectrometry. It relies on the phenomenon of "sputtering" whereby a high-energy primary ion (in the past, atomic ions, e.g. argon or gallium) hits the surface and knocks molecules and fragments out of the surface; some are ionized and can be analyzed with a mass spectrometer. Using a focused ion beam, good spatial resolution (<200 nm) is also possible. The technique has great potential as a type of chemical microscopy for biological studies. This potential could be frustrated by limited sensitivity to larger bio-molecules and primary-beam-induced chemical damage.

The team in Manchester, supported by a small instrument manufacturer, showed that an ion beam system could be produced that reliably delivered a C60 primary ion beam. Its use dramatically increases the sensitivity (≥x1000) to large bio-molecules with enormously reduced ion beam damage. Exciting new analytical possibilities are on the horizon, including routine molecular depth profiling of delicate organic and bio-organic materials.

We have given a very important tool for analyzing the surface chemistry of materials an exciting new future by developing a much more effective system for removing the molecules from the surface for analysis. Instead of trying to scoop big molecules off the surface using atomic probes that actually mostly penetrate deep in the material, causing lots of damage, we use big C60 molecules that mainly agitate and gently shake off the surface molecules.

SIMS has been a long-term principal research interest, but some 10 years ago, along with a US Collaborator, Nick Winograd, I became interested in developing the technique as a chemical microscope for biological and medical research. Very quickly, the requirement for increased sensitivity to large molecules and reduced ion beam damage became evident. With support from the UK research councils and a small instrument company, my colleague Nick Lockyer and I initiated a project in 1998 to develop reliable polyatomic primary ion sources to explore their efficiency as a means for increasing sensitivity and reducing ion-beam-induced damage.

The advances in SIMS analysis and 3D chemical imaging resulting from this development should enable the technique to contribute to significant advances in biological research, such as locating the destination of drugs and monitoring their metabolism. There could therefore be significant social benefits as the technology is proved and applied.