What is the spatial resolution of mass spectrometry imaging? What is the difference between MSI DPI and MSI LDPI?

Spatial resolution refers to the smallest spatial scale that an image can resolve, and is determined jointly by the ‘ionisation spot size’ and the ‘scanning step size’. The two imaging sources from Neo Source INSTRUMENT cover a range from the tissue scale to the single-cell scale.

MSI DPI utilises desorption/electrospray ionisation coupled with photochemical secondary ionisation, offering a spatial resolution of 20–200 μm. It is suitable for larger-scale samples such as tissue sections, imprints, traditional Chinese medicinal materials and blood. It is characterised by high throughput, simple operation and no need for matrix spraying, whilst its positive and negative ion modes complementarily cover hundreds of metabolites and lipids.

MSI LDPI is based on laser desorption/ionisation (DESI) coupled with post-ionisation photochemical ionisation, with a spatial resolution of 2–3 μm; when optimised, it can achieve a resolution of approximately 4 μm in mouse hippocampal tissue, reaching the single-cell scale. It is matrix-free and free from matrix background interference, with small molecule coverage ranging from approximately m/z 70–1000, making it suitable for applications in life sciences, environmental toxicology and other fields requiring high spatial detail.

Common features of both: they utilise photoionisation ‘post-ionisation’ to achieve non-polarity discrimination, and both produce signals 1–3 orders of magnitude stronger than their respective control techniques (DESI alone / laser ablation alone). In terms of sensitivity, both sources demonstrate a 1–3-order-of-magnitude increase in signal strength compared to their respective control techniques (DESI alone / laser ablation alone); specifically, DPI delivers an approximately 205-fold increase in cholesterol detection in rat brain tissue, a 14.5-fold increase in theanine in tea leaves, and a 61-fold increase in caffeine, demonstrating a clear advantage in quantification. Consequently, the choice between the two ultimately comes down to a trade-off between scale and sample type: DPI is preferred for macroscopic tissue distribution, whilst LDPI is preferred for subcellular heterogeneity.