NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3...
-
Upload
alexis-burke -
Category
Documents
-
view
220 -
download
0
Transcript of NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3...
![Page 1: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/1.jpg)
NanoSIMS Analysis of Arsenic NanoSIMS Analysis of Arsenic and Selenium in Cereal Grainsand Selenium in Cereal Grains
Supervisor: Chris GrovenorSupervisor: Chris Grovenor
Katie MooreKatie Moore33rdrd year D.Phil year D.Phil
Department of Materials – University of OxfordDepartment of Materials – University of Oxford
![Page 2: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/2.jpg)
Motivation
Why is a materials scientist looking at plants?
Interdisciplinary collaborations allow critical problems in the life sciences, difficult to solve with traditional analysis techniques, to be explored with established physical science techniques.
![Page 3: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/3.jpg)
The Arsenic Problem• Arsenic contamination
of groundwater
• Contaminated groundwater is used to irrigate rice paddy fields
• Resulting in rice grain containing elevated levels of arsenic
• A major problem in Bangladesh, India, China and America.
Ref: X. Y, Xu et al., Environ. Sci. Technol., 42(15), 2008
• Arsenic is a toxic and carcinogenic element
![Page 4: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/4.jpg)
The Selenium Problem• Between 0.5 and 1
billion people worldwide may be deficient in selenium including populations in developed countries.
• In the UK this is caused by a reduction in the amount of wheat imported from America and a fall in the consumption of cereals
• Selenium is an important trace elementDaily selenium intake in the UK is
now about ½ of the reference amount
M. R. Broadley et al., Proc. Nutr. Soc. (65) 2006M. S. Fan et al., Sci. Total Environ. (389), 2008MAFF, Food Surveillance Information Sheet, (126), 1997
Refs:
![Page 5: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/5.jpg)
Agricultural Solutions
• To increase Se:– Add a selenium fertiliser to the soil (practiced in Finland)
• To decrease As:– Polish the grain to remove the high As parts
• Both of these solutions require knowledge of where the trace elements are located in the grain.
• Determining where these very low concentrations are located with sub-cellular resolution is a serious analytical challenge
Ref: M. H. Eurola et al., J. Sci. Food Agric., (56), 1991
![Page 6: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/6.jpg)
Secondary Ion Mass Spectrometry (SIMS)
• Sample is bombarded by positively charged primary ion beam
• This results in sputtering of the top few atomic layers and ejection of atoms, ions and clusters
• Secondary ions are collected and mass analysed
Image adapted from Ref:http://www.eaglabs.com/training/tutorials/sims_theory_tutorial/index.php
![Page 7: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/7.jpg)
The NanoSIMS 50
The Oxford NanoSIMS
Schematic of the NanoSIMS
Ref: CAMECA, http://www.cameca.fr/doc_en_pdf/ns50_instrumentation_booklet.pdf, Instrumentation booklet, June 2007.
![Page 8: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/8.jpg)
Characteristics of SIMS• SIMS
– High sensitivity (down to ppb for some elements)
– Detection of all elements from Hydrogen to Uranium including all isotopes
– High mass resolution
• NanoSIMS – High lateral resolution (50 nm)– Parallel detection of 5 ionic species
Ref: CAMECA, http://www.cameca.fr/doc_en_pdf/ns50_instrumentation_booklet.pdf, Instrumentation booklet, June 2007.
![Page 9: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/9.jpg)
SIMS Sample Preparation
• Sample needs to be flat, conducting, and dry
• Bulk chemical analysis (ICP-MS) showed
trace levels of 2.5 ppm arsenic in the rice and 17 ppm selenium in the wheat
• Rice samples were
grown at Rothamsted Research
• Wheat samples were grown
in a field trial in Nottingham
![Page 10: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/10.jpg)
Structure of Wheat GrainAleurone layer
Starchy endosperm
80µm Embryo
Cross section
![Page 11: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/11.jpg)
Selenium in Wheat Grain
Max selenium counts: 4Max CN- counts: 105,000
31P16O- 80Se-
32S-12C14N-16O-
SE
30µm
Ref: K. L. Moore et al., New Phytol., (185), 2010
![Page 12: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/12.jpg)
Selenium in Wheat GrainAleurone cell Starch grains
31P16O- 80Se- 32S-
12C14N-16O- 12C14N-16O-
80Se-
Ref: K. L. Moore et al., New Phytol., (185), 2010
![Page 13: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/13.jpg)
Selenium in Wheat Grain
High resolution, sub-cellular, localisation of ppm concentrations
Selenium is localised in the protein region around the starch grains
Selenium hotspots are found in the aleurone cells
Starchgrain
31P16O- 80Se- 32S-
16O- 12C14N-16O-
80Se-
32S-
Ref: K. L. Moore et al., New Phytol., (185), 2010
![Page 14: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/14.jpg)
Arsenic in Rice Grain
Arsenic is localised in the sub-aleurone protein
Ref: K. L. Moore et al., New Phytol., (185), 2010
![Page 15: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/15.jpg)
Rice Roots – Experiment setup
Fe plaque No Fe plaque
Variables:•Arsenate or arsenite•With or without Fe plaque•Wild type or lsi2 mutant
Hydroponically grown rice plants
Lsi2 transporter
Ref: Zhao, F.J., et al., New Phytol., 181(4), 2009
![Page 16: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/16.jpg)
Rice Roots – Fe Plaque
25 µm
EPEPExEx
ScSc
SESE
12C14N-
56Fe16O-
31P-28Si-
75As-
![Page 17: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/17.jpg)
Rice Roots – Lsi2 mutant12C14N-
75As-
31P-
SE
28Si-
25 µm
XyXy
EnEn
Colour merge: Red = As, Green = CN, Blue = Si
![Page 18: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/18.jpg)
Conclusions• The NanoSIMS has successfully been used to provide a detailed
analysis of the distribution of trace elements selenium and arsenic in wheat and rice respectively and the distribution of As in roots.
• Selenium is localised in the protein regions around the wheat starch grains with hotspots in the bran layer
• Arsenic is concentrated in the sub-aleurone protein of the rice rather than in the aleurone.
• The Fe plaque has a strong adsorption affinity for As
• The Lsi2 mutant blocks As uptake in the endodermis
• These experiments have demonstrated the unique potential of state-of-the-art SIMS instrumentation to analyse the distribution of ppm levels of important trace elements with sub-cellular resolution
![Page 19: NanoSIMS Analysis of Arsenic and Selenium in Cereal Grains Supervisor: Chris Grovenor Katie Moore 3 rd year D.Phil Department of Materials – University.](https://reader033.fdocuments.net/reader033/viewer/2022061306/5514831f550346b0158b5901/html5/thumbnails/19.jpg)
AcknowledgementsSupervisor: Chris GrovenorNanoSIMS postdoc: Markus Schröder
EPSRC:D.Phil funding
Root Sample Preparation: Barry Martin, Chris Hawes
Collaborators:Fang-jie Zhao, Steve McGrath,Malcolm Hawkesford, Peter Shewry
IOM3:For this opportunity