MSI DPI Electrospray/Photochemical Ionisation Mass Spectrometry Imaging Source

Currently, the DESI imaging sources widely used internationally are only capable of imaging highly polar components; they exhibit polarity discrimination (which affects the accuracy of many weakly polar and non-polar components) and significant ion suppression (which interferes by suppressing the response signal of the analytes, necessitating sample purification), and are therefore not suitable for all analyte systems.

The MSI DPI-25A electrospray/photochemical ionisation (ESI-PCI) mass spectrometry imaging source, developed based on coupled desorption electrospray and photochemical ionisation technologies, incorporates a photochemical ionisation system and high-efficiency ion transfer tubing downstream of a conventional DESI spray assembly. By switching the photochemical ionisation source on and off, high-sensitivity spatial molecular imaging of both polar and non-polar components can be achieved.

The photoionisation imaging source not only enables the imaging of non-polar compounds in sections of mouse and plant tissues, but also further enhances the signal intensity of polar components, thereby significantly improving the imaging signal-to-noise ratio.

Compared with commercially available mass spectrometry imaging sources, for animal tissues and plant leaves, it can detect hundreds more secondary metabolites—including lipids, terpenoids, flavonoids, amino acids and glycosides—in both positive and negative ion modes; the overall metabolite signal intensity is enhanced by 1–3 orders of magnitude, greatly improving the detection sensitivity of analytes, particularly non-polar components.

Product Features

Operates at atmospheric pressure, with a simple operating environment

Compact and highly adaptable

High-sensitivity spatial imaging of various polar and non-polar components can be achieved by switching the photoionisation source on and off

In both positive and negative ion modes, it can detect hundreds of additional secondary metabolites, such as lipids, terpenes, flavonoids, amino acids and glycosides

Overall metabolite signal intensity is enhanced by 1–3 orders of magnitude

Technical Specifications

Spatial resolution: 20 μm–200 μm

Sample preparation: No matrix spraying required

Desorption method: Desorptive electrospray ionisation

Ionisation method: Secondary photochemical ionisation

Ambient temperature: 15 °C–30 °C;

Relative humidity: 20 per cent–85 per cent;

AC power supply: Voltage 220 V ± 22 V, frequency 50 Hz ± 1 Hz;

Dimensions (W x D x H): 340 x 270 x 250 mm

Weight: 24 kg

Warranty period: 12 months

Product Advantages

1. Dual-ionisation core technology – a breakthrough in principle

DESI (Desorption Electrospray Ionisation) combined with photochemical secondary ionisation overcomes the limitations of traditional single-ionisation technology, significantly improving ion signal transmission efficiency.

2. Fully polar, non-discriminatory detection – covering the full spectrum of organic compounds

Perfectly detects polar, weakly polar and non-polar compounds, filling the gap in non-polar detection left by traditional DESI; the vast majority of organic compounds can be precisely ionised.

3. Leap in sensitivity – precise detection of trace substances

Signal intensity is increased by 1–3 orders of magnitude compared to conventional techniques; for example, the signal for theanine in tea leaves is 14.5 times higher, the signal for caffeine is 61 times higher, and the signal for cholesterol in rat brains is 205 times higher.

4. Strong Resistance to Matrix Interference – No Cumbersome Pretreatment Required

Ion suppression effects are significantly reduced, allowing complex samples to be analysed directly without the need for tissue washing, solvent washing or chemical derivatisation, thereby improving experimental efficiency.

5. Compatible with Agilent, AB SCIEX, Thermo – ready to use and easy to maintain

The MSI DPI-25A is compatible with Agilent mass spectrometers, the MSI DPI-25S with AB SCIEX mass spectrometers, and the MSI DPI-25T with Thermo mass spectrometers. Featuring a proprietary titanium alloy ion transfer tube, the polished front end prevents sample damage, whilst facilitating easy disassembly, cleaning and maintenance.

6. Adjustable high resolution – preserves sample integrity

High-precision spatial resolution of 20–200 μm can be adjusted as required, ensuring accurate, bias-free imaging; tissue sections remain intact after analysis and can be used for subsequent H&E histological examination.

7. Long-term stable operation – more reliable experimental data

Dedicated temperature control design for the ionisation chamber, providing stable heating at 320–350°C over extended periods; precise coordination between the photoionisation module and the scanning platform ensures highly reproducible experimental results.

Application Areas

Metabolomics: Spatial distribution changes of metabolites

Pathological diagnosis: Discovery of disease biomarkers, early diagnosis of diseases, clinical pathology research, bacterial analysis, microbial imaging, determination of tumour grade, hormone receptor status, gene chip testing, cell biology, microbial ecology

Pharmacokinetics: New drug R&D; metabolic processes of drugs and metabolites in different organs at different time points; drug quantification; drug discovery and distribution studies; herbal mixtures

Plant Metabolism: Spatial distribution variations of metabolites; plant metabolism research

Industrial applications: chemical raw materials, packaging materials, dyes, cosmetics, material matrices, food ingredient analysis

Forensic science: forensic analysis, fingerprint scanning, substances of abuse and their metabolites in hair and tissue

Other: toxicology, environmental chemistry, archaeology

Application example: imaging of mouse brain sections

Positive ion mode

DESI mode: limited range of compounds (choline, phosphocholine and PC lipids)

DESI/PI mode: More comprehensive information (neurotransmitters—GABA, creatine, glutamine, glutamate and adenosine, etc., as well as cholesterol and over a dozen neutral GalCer lipids)

Imagery: More comprehensive distribution information

Simultaneous imaging and analysis of neurotransmitters and lipids provides important guidance for research in fields such as neuroscience, pharmacology and neurochemistry

Negative ion mode

DESI mode: minimal matrix effects

Similar compound types: phosphatidylethanolamine (PE), phosphatidylacetal (PE-O), phosphatidylserine (PS), phosphatidylinositol (PI) and sulpholipids (ST)

Imaging results: complementary

Glutamate, etc.: DESI/PI

PE-O/PE: 2–4-fold increase

PI/ST: DESI mode

In negative ion mode, the DESI/PI photoionisation method still offers excellent sensitivity for the analysis of most metabolites and lipids

Imaging of mouse coronal sections

Imaging of mouse transverse sections

Analytical Chemistry, 2019, 91, 110

Rapid Communications in Mass Spectrometry, 2026

Application example: Research into melanocytic naevi/tumours

Positive ion mode

DESI and DESI/PI mass spectra are complementary

Melanocytic nevus region: primarily choline, phosphocholine, S1P, cholesterol, phosphatidylcholine (PC) and sphingomyelin (SM)

In normal tissue: primarily non-polar lipids such as monoacylglycerol (MAG), diacylglycerol (DAG) and triacylglycerol (TG)

The specific distribution of S1P, cholesterol, PC34:1 and PC38:4 in the imaging data shows a high degree of correspondence with the distribution in the nevus area as seen in the H&E staining

Negative ion mode

The DESI and DESI/PI mass spectra are similar

Compound types: fatty acids (FA), phosphatidylethanolamine (PE), phosphatidic acid (PA) and phosphatidyl alcohol (PI)

Imaging results: arachidonic acid, FA-C 22:6, FA-C 24:0, PE O-36:5 and cholesterol sulphate

Fingerprint spectral analysis and imaging of melanocytic naevi

Analysis of imaging data from multiple samples

Multiple samples: commonalities in distribution

Markers: differentiation and diagnosis

Lipids play an important role in the formation of melanocytic naevi

Analysis of immunohistochemical staining

(A) Cholesterol imaging, (B) H&E staining, (D) TSPO enzyme H&E staining and magnified views of the nevus area and normal tissue. In Figures C and D, the solid red line indicates the nevus area, whilst the solid orange line denotes the sample outline; the white and blue areas in the figures represent the nevus area and normal tissue, respectively, corresponding to the magnified image on the right (E) showing the possible mechanism of cholesterol accumulation in the nevus area.

Talanta, 2021, 231, 122380

Application example: Investigating the spatial distribution of plant metabolites

Sage imprint imaging

Positive ion mode

DESI mode: Fewer metabolite types (choline, resin acids, PC lipids)

DESI/PI mode: Abundant plant metabolites (monoterpenes, diterpenes, triterpenes)

Mass spectrometry imaging: 200 μm

Negative ion mode

DESI/PI ion intensity signal increased by one order of magnitude

Ginkgo biloba imprint imaging

Positive ion mode

DESI mode: Fewer metabolite types (choline, disaccharides, glycosides, PA/PC lipids, demagnesium chlorophyll, etc.)

DESI/PI mode: Includes metabolites detected by DESI, plus additional ones (flavonoids, ginkgolic acid, cashew phenol, etc.)

Mass spectrometry imaging: Distribution in secretory compartments

Negative ion mode

DESI/PI ion intensity signals increased by one order of magnitude

Tea leaf imprint imaging

Cation mode

DESI mode: Fewer metabolite types (choline, theanine, caffeine, phosphatidylcholine, etc.)

DESI/PI mode: Additional compounds (amino acids, catechins, flavonoids, etc.); the theanine signal increased 14.5-fold, and the caffeine signal increased 61-fold

Mass spectrometry imaging: The two modes are complementary

The following box-and-whisker plot analysis and t-test analysis: significant differences were observed between the leaf veins and the leaf blade regions

Correlation analysis: high spatial correlation of flavonoid metabolites

Catechin metabolic pathway map: most metabolites in the synthetic pathway from chalcone to catechin were detected

Analytical Chemistry, 2022, 94 (43)

Application example: investigating the spatial distribution of plant metabolites

Imaging of contaminant accumulation in tomatoes

This study investigated the spatially specific toxic effects of carbamazepine (CBZ) in plants. Using DESI/PI-MSI, CBZ and its metabolites were observed primarily at the leaf margins, where concentrations were 2.3 times higher than in the inner regions; this was confirmed by LC-MS.

Transcriptomic and metabolomic analyses revealed significant differences in gene expression and metabolite levels between the inner and outer leaf regions, highlighting the role of spatial location in the CBZ response.

Imaging of perforation marks on tobacco leaves

Imaging of representative compounds in tobacco plants

Spatial distribution of representative compounds in tobacco plants along the longitudinal and transverse axes of the leaf: for substances such as plant alkaloids, amino acids and sugars in tobacco leaves, longitudinal analysis indicates that they are primarily distributed at the leaf tip, whilst transverse analysis indicates that they are primarily distributed along the left and right margins of the leaf.

Imaging of petal imprints

Imprint experiments using a variety of sample types have demonstrated the high detection sensitivity and high ionisation coverage of DESI/PI for plant metabolites.

Environ. Sci. Technol. 2024, 58

Analytical Chemistry, 2024, 52

Application example: Spatial distribution of major components in fresh tobacco leaves

Imaging of tobacco leaf sections

Following sectioning, segmenting and imprinting of fresh tobacco leaves, m/z 104.11 was found to be predominantly distributed at the leaf base, whilst m/z 516.49 was predominantly distributed in the leaf veins. Complete imaging results of small tobacco leaves indicate that the distribution of different metabolites in tobacco leaves exhibits spatial specificity.

Application Case: Revealing the cause of cinnabar-coloured spots in the traditional Chinese medicine Atractylodes macrocephala

Imaging of Atractylodes macrocephala sections

A paper published jointly with the China Academy of Chinese Medical Sciences reveals the cause of the cinnabar-coloured spots in Atractylodes macrocephala; both m/z 183.0807 and m/z 301.2164 show a strong correlation with the coloured SCs in JAR. DESP/PI-MSI results for other polyacetylenes and sesquiterpenes are shown in Figure S7. In summary, the substantial accumulation of Atractylodes macrocephala and (4E,6E,12E)-tetracarbatriene-8,10-diene-1,3-diol diacetate may be the cause of the cinnabar-coloured spots in AR.

Molecular Horticulture, 2025, 5:11

Application Case: Forensic Analysis – Scientific Evidence Collection Support

Chronological Imaging of Vermilion and Ink

Time-lapse analysis of red and black ink: Accurately distinguishes between ‘writing first, then stamping’ and ‘stamping first, then writing’; signal characteristics at the intersection are clear, allowing for unambiguous determination. In the ‘stamp first’ group, there is a distinct signal break in the marker ink at the intersection of the red and black ink; in the ‘write first’ group, the signal from the stamp impression at the intersection is significantly lower than that in the ‘stamp first’ group.

Ink Trace Analysis / Fingerprint Imaging: Successfully distinguished ink traces from different brands of ballpoint pens, clearly identified fingerprint ridges and detected characteristic components such as cholesterol and squalene, suitable for Thermo Fisher forensic examination scenarios.

Fingerprint imaging

Fingerprint ridges are clearly visible; in DESI/PI mode, 369 (cholesterol) and 411 (squalene) were detected, whilst 523, 537 and 549 are likely triglyceride fragments.

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