1. Desorption electrospray ionization (DESI) for mapping the intact omega-3 lipids in Greenshell™ mussels
Matt Miller & Nigel Joyce
10 Sept 2015

2. What is DESI?

3. MS How does DESI work Electrospray Solvent Sample
Free moving sample stage
DESI-MS; Takats, Z., J. M. Wiseman, Cooks, G. et al. Science(2004).

4. PC (16:0/22:6) m/z 762 Polar lipid nomenclature Glycerol Fatty acids
Head group
Fatty acids
Glycerol
PC (16:0/22:6) m/z 762

5. + Intact polar lipid species Glycerol Fatty acids Head group
2 positions
PC, PE, PI, PS, PG
Lyso
Galactolipid? +
= Loads of individual lipid species

6. PE (18:1/18:1) 
LPE (18:1)
DESI spectra averaged over different regions of a human lens section obtained from a 41 y-old individual.
Ellis et a (2010) J. Am. Soc. Mass Spec.

7. DESI - human lens section
Ability to image chemistry directly from tissue.
- our interest is in plant and seafood chemistry.
- but has uses in medical research.
Ellis, S. R., C. Wu, et al. (2010). "Imaging of Human Lens Lipids by Desorption Electrospray Ionization Mass Spectrometry." Journal of the American Society for Mass Spectrometry 21(12):

8. Practical uses of DESI - Cancer
Prof. Graham Cooks – Purdue University
Dog bladder carcinoma (Dill 2010 Anal. Chem.)

9. Lipid mapping & Lipidomics
Shows the distribution of individual lipids
Functionality
Lipidomics
large-scale study of pathways and networks of cellular lipids in biological systems
Eberlin, L. S., et al. (2011) Biochim Biophys.

10. Why do DESI on Mussels Understand where mussels store lipid
Better biochemistry
Lead to new biotech
Lead to how diet effects lipid store
$30 M PA industry in GSM oil

11. MS Imaging – DESI Protocol
30mm
13mm
0.3mm

12. [M+Na]+, 828 (PC) 16:0-22:6 m/z 828 [M+Na]+ 30mm at 200µm/s 13mm
750
760
770
780
790
800
810
820
830
840
850
860
870
880
890
900
m/z
500
1000
1500
2000
2500
3000
[M+Na]+, 828
844
786
806
832
845
855
846
828
817
788
881
858
891
875
843
808
792
758
896
776
849
866
878
755
835
782
895
774
765
885
864
763
(PC) 16:0-22:6
m/z 828 [M+Na]+
30mm at 200µm/s
13mm
0.3mm steps x 43
Total 108 minutes

13. 769 645 478 828 DESI-MS/MS -59 -183 PC(16:0, -22:6(Na)) -350 [M+Na]+
250
300
350
400
450
500
550
600
650
700
750
800
m/z
769.3
645.4
768.5
754.4
770.2
809.2
711.0
644.6
557.2
649.0
478.3
309.2
523.6
605.1
384.5
283.2
345.2
411.0
455.4
246.3
769
-183
645
478
PC(16:0, -22:6(Na)) -350
828
[M+Na]+
Further data is obtained by reanalysing the area of interest and optimising for ms/ms.

14. m/z 828 [M+Na]+
Photo
phosphatidylcholine (PC) 16:0-22:6

15. Final result
Figure 1 DESI image overlaid on an actual image of a GSM segment. The coloured area shows increasing concentrations of the lipid phosphatidylcholine (PC) 16:0-22:6 from m/z 828 [M+Na]+ precursor mass

16. Conclusions Developed a method for DESI for Mussels
Low sensitivity, Low lipid
Future work
Further development of method
Looking at differences (diet, gender, organs)