Multimodal Ambient Pressure Imaging of Tissue

Melanie Bailey (Department of Chemistry), Josephine Bunch (NPL) and Roger Webb (Surrey Ion Beam Centre)

Summary

Exploring the spatial distribution of trace elements and molecules is critical to investigations spanning a range of fields, including manufacturing, archaeometry, veterinary, forensic and environmental science. In biomedicine, elemental and molecular imaging plays a central role in the study of disease progression, most notably in Alzheimer’s, osteoarthritis, cancer and diabetes. Normally, trace element imaging is carried out independently from molecular imaging. This is because no single technique can spatially map trace elements and molecules under ambient pressure. This limits the probative value of many investigations, particularly in biomedicine, where co-locating elemental and molecular markers under ambient pressure is a key requirement. In this project, we aim to develop and assess the feasibility of a new, internationally unique tool, which will allow ambient pressure multimodal trace element and molecular imaging of tissue. Case for support

Since 2004, an explosion of ambient mass spectrometry techniques have emerged that enable molecular mapping under ambient pressure. The techniques include Desorption Electrospray Ionisation Mass Spectrometry (DESI) and Matrix Assisted Laser Desorption Ionisation (MALDI). NPL has established the National Centre of Excellence for Imaging Mass Spectrometry (NICE-MSI) and have been a key force internationally in demonstrating the utility of these techniques in biomedical investigations. The laboratory has significantly improved the reliability of the techniques and provides a commercial service to a range of users including AstraZeneca and GlaxoSmithKline. A limitation is that these techniques do not provide trace element information.

In contrast, trace element imaging using ion beams has provided key data for biomedical investigations since the 1980s. Ion beam techniques have a leading edge over competing trace element mapping capabilities due to their high sensitivity, spatial resolution (~1 micron) and quantitative power. Recently, the Surrey Ion Beam Centre (a strategic partner of NiCE-MSI) have pioneered the use of ion beams for trace molecular mapping under ambient pressure, so-called MeV-secondary ion mass spectrometry (MeV-SIMS). However, there are two limitations of this approach for tissue imaging. The first is that different ions are required for trace element (H+) and MeV-SIMS (Cl+) mapping, meaning that trace element and molecular imaging cannot be provided in a single run. This makes it impossible to co-locate trace elements and molecules in a cost effective manner. The second is that SIMS and MeV-SIMS are not sensitive to high molecular weight components such as lipids, proteins and peptides. The £4.5M 3D Nano-SIMS project at NPL will tackle some of the latter issues but operates under vacuum only. This means it is necessary to freeze-dry biomedical samples and this precludes analysis of tissue in its native state. Work Programme and Project Objectives

In this project, we will assess the feasibility of carrying out ion beam trace element imaging (using expertise at Surrey) and ambient pressure mass spectrometry molecular imaging (using expertise at NPL) on a single platform. During the initial stages of the project, ion beam analysis will be carried out at Surrey and the student will develop a method to relocate the same area of a sample to survey the same area using a number of ambient mass spectrometry sources at NPL. Later stages of the project will look at the integration of the two methods on a single platform (possibly the subject of an EPSRC grant application, depending on the progress of the student).

The project will provide an excellent training experience for a PhD student, being at the discipline boundary between physics (ion beam analysis), chemistry (ambient mass spectrometry) and biomedical science.

The project objectives are as follows:

To identify a set of key test applications that would benefit from this analysis through literature review and consultation with collaborators of NiCE-MSI

To develop a method for depositing fiduciary markers on a sample for relocation at NPL

To identify the most appropriate ambient mass spectrometry (AMS) methods for integration with ion beam analysis (IBA)

To establish an appropriate workflow / sequence of IBA and AMS techniques

To evaluate the quantitative potential of the combined method

To develop a strategy for data handling (common file formats, data registration and fusion, data reduction and compression, supervised and unsupervised analyses).

The contribution of University and NPL researchers to the programme The student will be co-supervised by Melanie Bailey at Surrey who is lecturer in Analytical and Forensic Science in the Department of Chemistry. Dr Bailey was a previous liaison fellow for the ion beam facility, is a grant holder for the MeV SIMS grant and now leads an industrially funded project on ambient mass spectrometry for drug detection in fingerprints. Prof Roger Webb (Director of the Ion Beam Centre) will provide additional expertise in IBA. At NPL, Josephine Bunch (Co-Director of NiCE MSI and Principal Scientist, leading ambient mass spectrometry) will provide expertise in ambient mass spectrometry, metrology and data fusion. Recent collaboration between Bunch and Bailey’s group has provided fruitful results (for example the detection of cocaine metabolites in fingerprints, which was a front cover article for Analyst and was cited by >500 media outlets worldwide). Outputs There is significant opportunity here to provide high impact publications, as multimodal trace element and molecular imaging does not ever appear to have been achieved under ambient conditions. Internationally, (and largely through efforts at Surrey) the ion beam community now has a keen interest in MeV-SIMS, but appears to be unaware of the potential for fusing IBA with other (potentially more appropriate) molecular imaging techniques. This is where the Surrey-NPL partnership gives a strategic edge.

The project is strategically important to the Surrey Ion Beam Centre, which as part of its business plan aims to augment its analytical capability to continue to increase its user base. This will undoubtedly result in increased ticket income. Once proof of concept has been established, we will apply to EPSRC to carry out the much more challenging task of carrying out imaging on a single platform. Grant applications are also perceived in other application areas – for example to provide a system for automated analysis of aerosol filters, augmenting international capabilities for aerosol detection.

The project is strategically important to NPL because providing this capability will enhance analytical capabilities within NiCE-MSI, but also the use of IBA techniques (which are matrix free) are suitable for analysis of large molecules and may present a more quantitative strategy for surface MS, a strategically important topic to NPL. The project also has synergy with ongoing work at NPL for data fusion using other imaging methods. Outline Project Plan Months 1-6 : Training on IBA, MALDI and DESI. Identification of a set of test applications through literature review and consultation with collaborators of IBC and NPL

Months 6-9: Develop and test a method for depositing fiduciary markers on a sample for relocation at NPL possibly by ink jet printing suitable standards

Months 10-15: Intercomparison study designed to identify the most appropriate ambient mass spectrometry (AMS) methods for integration with ion beam analysis (IBA). Draft publication (by student) and grant submission (by supervisors)

Months 19-24: investigate appropriate workflow / sequence of IBA and AMS techniques

Months 25-29: Develop data handling strategy and evaluate quantitative potential of the method

Months 30-36 : write up Resources and facilities Due to the strategic importance of this project to both groups, access to IBA facilities (Surrey) and AMS (NPL) will be provided with no additional cost to the project. Samples will be provided by users (for example AstraZeneca and the Vet School have already expressed an interest).