Bioimaging of rice tissue with the use of a laser ablation system coupled to the Agilent 7700x ICP-MS (RAFA)

Importance of the Topic

Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) offers direct elemental analysis of solid samples with minimal preparation, enabling high-resolution bioimaging of tissue sections. This approach is pivotal for understanding metal distribution in biological systems, supporting research in plant physiology, nutrition, and environmental monitoring.

Objectives and Study Overview

This study applied LA-ICP-MS to cross-sections of rice grains to map the spatial distribution of essential and trace elements across the seed width. The primary goal was to demonstrate the capability of the technique for generating detailed elemental images in plant tissues.

Methodology

Rice seeds were embedded in paraffin and sectioned longitudinally. The tissue sections were ablated line by line using a UV laser, and the generated aerosol was transported directly to the ICP-MS for real-time elemental detection. Prior to sample analysis, instrument performance was optimized daily using a NIST-612 glass standard to ensure stable sensitivity, low oxide formation, and minimal mass discrimination. Instrument control and optimization were managed via MassHunter software.

Used Instrumentation

• Laser ablation system: NewWave NWR-213 (wavelength: 213 nm)
• Ablation parameters: scan speed 30 µm/s; energy 100%; frequency 20 Hz; spot size 10 µm; helium carrier gas flow 0.8 mL/min
• Mass spectrometer: Agilent 7700x ICP-MS
• ICP-MS settings: plasma power 1400 W; carrier gas 0.49 L/min; sample depth 6 mm
• Software: MassHunter for instrument control; custom bioimaging software by Philip Doble (UTS, Australia) for image reconstruction

Main Results and Discussion

Qualitative elemental maps were obtained for Fe, Mn, Cu, Co, Mg, and Zn across the rice seed width. The images revealed non-uniform distributions, with localized enrichments in specific tissue regions. These patterns reflect differences in elemental uptake, transport, and storage within the grain, offering insights into nutrient allocation and potential bottlenecks in seed development.

Benefits and Practical Applications

• High spatial resolution mapping of nutrients and contaminants in plant tissues
• Minimal sample preparation compared to conventional digestion methods
• Rapid, direct analysis suitable for screening large sample sets
• Applications in agronomic research, plant breeding, food safety, and environmental studies

Future Trends and Potential Applications

Future developments will focus on quantitative bioimaging through the use of matrix-matched standards and isotope dilution approaches. Advances in software automation and three-dimensional sectioning may enable volumetric elemental mapping. Expanded applications could include medical diagnostics, forensic investigations, and the study of elemental dynamics under stress conditions.

Conclusion

The coupling of LA-ICP-MS with high-resolution imaging software successfully generated detailed elemental distribution maps in rice grains. This technique presents a powerful tool for bioimaging studies, with ongoing efforts directed toward quantitative analysis and broader application domains.

References

• [1] D. Hare, J. L. George, R. Grimm, S. Wilkins, P. A. Adlard, R. A. Cherny, A. I. Bush, D. I. Finkelstein, P. Doble. Metallomics, 2010, 2, 745-753.