New Developments in Quantitative 3D Chemical Imaging

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Time-of-flight secondary ion mass spectrometry (ToF-SIMS) is an outstanding method of chemical analysis, used extensively in academia and industry to characterise complex samples in 2D/3D. Application areas include materials science, biology, healthcare, energy etc. In the analysis the high-energy 'primary' ion projectile impact on a sample surface, causes ejection of 'secondary' molecular ions which are analysed by a mass spectrometer to provide chemically-rich material characterisation. Scanning the primary beam across the sample provides 2D surface imaging (>100 nm lateral resolution) and by sequentially collecting images while the sample is eroded, 3D sub-surface imaging (>3 nm depth resolution). This unique combination of analytical capabilities means ToF-SIMS is unmatched in its potential to determine, in a single analysis, the composition and detailed distribution of multiple, chemicals in complex samples. Importantly, this technology supports 'discovery mode' research, where the analysis is not biased towards pre-selected, labelled compounds, and therefore leads to hypothesis generation. The analysis is highly-multiplexed and comprehensive - hundreds of species can be potentially detected in a single measurement, limited only by the sensitivity of the process, which here we seek to enhance 100-fold.This proposal addresses critical challenges from next-generation samples demanding greater sensitivity, broader chemical coverage and reliable quantification to address issues including sub-cellular drug localisation and nanoscale molecular materials. It builds on our internationally-leading reputation for innovative ToF-SIMS instrumentation. The characteristics of the primary ion are fundamental in determining impact dynamics at the sample surface and the success of the resulting measurement. The challenge of producing intact secondary molecules from the sample has been largely solved using polyatomic cluster projectiles e.g. C60 and Ar2000 which produce ~100 sputtered molecules per impact. However, only ~0.001-0.1% of these molecules are produced as charged ions, which is necessary for their detection. Clearly there is huge room for improvement in the ionisation efficiency. The principle of projectile-initiated chemical reactions promoting ionisation of sputtered species has recently been firmly established by our work and that of others. We must now build on this knowledge and develop complementary approaches to meet the ionisation challenge and deliver quantitative compositional information.We have assembled a multidisciplinary team of international experts from academia and industry, which is uniquely positioned to pursue this important project. Building on >20 years' experience in innovation of SIMS instrumentation, enabled through EPSRC support and close collaboration with UK Industry, we will develop next-generation reactive ion beams and analytical methodology. This will deliver further transformative gains in performance which are critical to meet future application needs. Our novel results will be framed within the context of emerging theory to understand mechanisms of enhanced ionisation and to underpin the optimisation of projectile parameters. They will stimulate further development of theoretical models of the physical processes underlying SIMS and related techniques.The project is highly-adventurous, providing beyond state-of-the-art analytical capability underpinned with new fundamental understanding. We are ideally placed to exploit this through the interdisciplinary research collaborations at the Manchester Institute of Biotechnology and the Sir Henry Royce Institute for Advanced Materials. The vastly increased quality of data will result in new understanding in a wide range of applications spanning many areas of science and technology.