Mass spectrometry is a powerful tool for elemental, molecular and isotopic analysis which can be used to amass huge amounts of detail about biological, materials and agricultural samples. The technique can be applied to various research fields. This helps us to understand the make-up of cancer tumours, locate and quantify nuclear materials, and investigate advanced materials.

The National Physical Laboratory (NPL) is home to the National Centre of Excellence in Mass Spectrometry Imaging (NiCE-MSI), which aims to advance the development, understanding and application of the principal mass spectrometry imaging techniques.

Mass spectroscopy can be used to take a sample, separate each molecule that makes up that sample, and then provide the data that allow each of those molecules to be identified and quantified. We use mass spectrometry imaging (MSI) to uncover new spatially-resolved information about the molecular and isotopic composition of biological and inorganic materials in unprecedented detail.

NPL is developing world-leading mass spectrometry technologies and the standards for best practice that can be rolled out across the world. We are also developing and applying the latest machine learning techniques to visualise and interpret mass spectrometry data.

MSI (Mass Spectrometry Imaging) is commonly used to investigate the response of drugs in the body, the composition of proteins, the distribution of trace and ultralight elements (e.g.: H, Li) in advanced materials. This is helping us reveal the relationship between genetics and metabolism in cancers through use of stable isotope tracers, the pharmacokinetics of drug formulations and informs the next generation of battery and advanced materials.

Building a ‘Google Earth’ of cancer

NPL is leading a group of international and multidisciplinary chemists, physicists and biologists from the UK as part of a Cancer Research UK Grand Challenge to solve some of the biggest challenges in cancer research. The Rosetta team are developing a reproducible, standardised way to fully map tumours with extraordinary precision.

In the same way cartographers build maps of cities and countries to help people get around, scientists build maps of tumours to better understand their inner workings. But despite significant advances in technology and our understanding of cancer, our tumour maps remain incomplete. What’s missing is our ability to see down to the very core of cancer cells and understand how changes in their metabolism can impact their overall state and function within a tumour. No one has ever mapped tumours in this level of detail before – until now.

“the Rosetta team are developing a reproducible, standardised way to fully map tumours with extraordinary precision”

In mass spectroscopy, the molecules from a thin tissue section are analysed by scanning an ion beam, a laser, or a solvent spray, across the surface of the sample, ionising the molecules and transferring them to a mass spectrometer where the molecular weight and identity of the molecule is determined. The vast data obtained are reconstructed into spatially resolved maps of molecules from the tumour.

Using the mass spectrometer, we’re able to measure thousands of different molecules that are coming from the tissue. Cancer and associated tissues are extremely complex and in order to have new impact on making sure we can find out what treatment is best for a patient and design new drugs that work properly, we need to understand all of the changes that can occur.

The technology used within the Rosetta project allows us to understand how cancer works and by doing this we can spot and diagnose cancer earlier, arrange for more dedicated treatment and ultimately help CRUK in the fight to reduce the number of people who suffer from this disease.

Within the first year of the project the team successfully developed an imaging pipeline that produces an ultra-high resolution picture of the metabolism of tumours – allowing the team to map the distribution of cancer drugs within a tumour, as well as changes in cell metabolism.

More recently the Rosetta consortium has been researching colorectal cancer. The team have studied a particular and common genetic subtype of colon cancer, using well defined genetically engineered models and our metabolic imaging approaches, including mass spectrometry. This research resulted in the discovery of important mechanisms which help us understand how this type of cancer is able to grow. Importantly, these mechanisms identified also provide new ideas about how to treat this type of cancer. This research has been published in Nature Genetics.

Enabling immediate decision making in surgery

The NHS has set a target to provide high quality care and better outcomes to patients using innovations in the field of medical engineering and sciences within the next 10 years and beyond. Automated decision-making tools will be routinely used by surgeons in the operating theatre, as well as medical laboratory staff, allowing for safer surgeries, improved clinical diagnosis and treatment and at a reduced cost.

Ambient ionisation mass spectrometry is an example of such innovations, and has shown its suitability in the prevention, prediction, and diagnosis of disease. Use of innovative ambient ionisation mass spectrometry tools have already successfully been used in real time biomarker phenotyping of colon polyps, as well as in ex-vivo applications such as microbiology, drug screening and cell culture typing. One such potential tool is an innovative mass spectrometry method based on Rapid Evaporative Ionisation Mass Spectrometry (REIMS), pioneered by Zoltan Takats of Imperial College London, that uses a mass spectrometer to analyse the aerosol generated by the vaporisation of cellular material using electrosurgical tools. This smoke has been shown to contain a plethora of molecular information that can been used in near real-time for accurate tissue/cell classification.

“the introduction of lasers can greatly reduce measurement variability whilst also allowing for REIMS based ex-vivo mass spectrometry imaging”

Through collaborations with stakeholders and experts in the field, we have identified sources of measurement variability in electrosurgical based REIMS. Advancements and modifications in the sampling devices have now led to the use of medical and non-medical lasers to replace electrosurgical tools. The introduction of lasers can greatly reduce measurement variability whilst also allowing for REIMS based ex-vivo mass spectrometry imaging. NPL has supported partners at Imperial College London in the design and development of a highly flexible dedicated metrology mass spectrometry imaging stage for laser-based REIMS, allowing the analysis of preserved as well as fresh tissue samples.

Providing new insights

It costs approximately £1.4 billion to produce a new medicine, but this could be reduced if candidates that fail at late stage were identified earlier. Currently, one of the major challenges is to measure the intracellular drug concentration to help answer long-standing questions about whether drug concentrations are sufficiently high in the right places to have a therapeutic effect, or if the medicine is lodging within cellular components and causing toxicity. If anomalies were spotted earlier, it might help to explain toxicities or lack of efficacy of a medicine and reduce costly late-stage failures.

To do this, NPL led a multidisciplinary team including experts in drug discovery at GSK with leading mass spectrometry companies to develop the OrbiSIMS. The instrument combines the high-spatial resolution imaging of secondary ion mass spectrometry (SIMS) with the high-mass resolution of an Orbitrap mass spectrometer, achieving unprecedented chemical and spatial resolution. Such high performance is essential to reveal the biomolecular complexity in a single cell. Using the OrbiSIMS, they have revealed hitherto unknown wide variation in drug uptake between “identical” cells and that, cell-by-cell, the drug accumulation correlates with up-regulation of specific metabolites.

Recently, NPL introduced the Cryo-OrbiSIMS which allows highresolution imaging of biological samples in their native hydrated state. In a collaboration with the Francis Crick Institute (Alex Gould, Physiology and Metabolism Laboratory), they have published a paper in the journal Angewandte Chemie showing that the new cryogenic technique increases the range of different biomolecules that can be imaged, including semi-volatiles. As a proof-of-principle they imaged lipids and other molecules in human fingerprints, plant leaves and also in a popular genetic model organism, the fruit fly, Drosophila.

Now commercialised instruments in Europe and Asia are demonstrating a diverse range of impact including: label-free imaging of proteins in tissue, fundamental lipidomic studies of bone homeostasis, resolving chemistry in compound semiconductors previously confounded by lower resolution mass spectrometers, identification of deposits in fuel injectors and identification of degradation products in organic electronics.

As the UK’s National Metrology Institute, NPL plays a leading role in maintaining the UK’s position as a world leader in translating life sciences research, accelerating access to new diagnosis and treatment techniques, and helping to support rapid adoption of advanced healthcare technologies across the country and with global impact.

NPL’s research into understanding and application of the principal mass spectrometry imaging techniques is vital to the success of the projects previously mentioned. Mass spectrometry imaging methods include a suite of techniques for analysis of small and large molecules, at scales spanning the nano scale to bulk and in vivo surgical measurements. Uptake of the techniques by academia and industry continues to grow, with new applications areas emerging each year.

“recently, NPL introduced the Cryo-OrbiSIMS which allows highresolution imaging of biological samples in their native hydrated state”

Complex phenomena in the desorption ionisation process require ongoing research and metrology to ensure reproducible, quantitative, rapid measurements of molecules from complex samples. NPL are leading metrology programmes in each of the key techniques to address this and to continue to support innovators, developers and users of the techniques.