Quantum Dots in Daphnia Magna - Illinois Institute of ...csrri.iit.edu/~segre/phys570/12S/presentations/beck.pdf · 2D/3D Synchrotron Imaging Quantum Dots in Daphnia Magna Matthew

2D/3D Synchrotron ImagingQuantum Dots in Daphnia Magna

Matthew Beck

IIT

April 30, 2012

Matthew Beck (IIT) 2D/3D Synchrotron Imaging April 30, 2012 1 / 14

Table of Contents

1 X-Ray Tomography

2 Quantum DotsPhysics and Application

3 Environmental Exposure and ConsequencesCdSe / ZnS nanoparticles in Daphnia Magna


X-Ray Tomography

1 OverviewI The word tomography is derived from the greek a part and to write.I In XRT, scans of a sample are taken at multiple angles (sinograms).

These scans are then reconstructed together with computer algorithmsto produce a digital image with volumetric information.

I technique is non-destructive and sample prep light.

(a) Tomographic map of ameteor. False color showselemental media makeup(1)

(b) Tomographic map of Herrerasaurus (1)


X-Ray Tomography1 Overview

I The word tomography is derived from the greek a part and to write.

I In XRT, scans of a sample are taken at multiple angles (sinograms).These scans are then reconstructed together with computer algorithmsto produce a digital image with volumetric information.


(c) Tomographic map of ameteor. False color showselemental media makeup(1)

(d) Tomographic map of Herrerasaurus (1)



I The word tomography is derived from the greek a part and to write.I In XRT, scans of a sample are taken at multiple angles (sinograms).



(e) Tomographic map of ameteor. False color showselemental media makeup(1)

(f) Tomographic map of Herrerasaurus (1)






(g) Tomographic map of ameteor. False color showselemental media makeup(1)

(h) Tomographic map of Herrerasaurus (1)






(i) Tomographic map of ameteor. False color showselemental media makeup(1)

(j) Tomographic map of Herrerasaurus (1)


X-Ray Tomography, Cont.

1 Overview2 Details

I The physics at work in the imaging is x-ray attenuation governed byBeers Law

I = I0

Ni

ei x

I Issues arise when trying to calculate from a polychromatic source.I tunable high Q radiation from a synchrotron through monochromators

allow for a direct analysis of the data to calculate either or x.I approximately 50 exposures per angle, 1-3 angular steps, over 180[2]I digital image constructed from multiple scan images through filtered

backprojection algorithm. [2]


X-Ray Tomography, Cont.1 Overview2 Detail

(k) X-Ray linear attenuation coefficient ofwater as a function of energy (3)

3 ConsiderationsI Dominant absorption process is the photoelectric effect at operating

energiesI Lower energies are more sensitive to elemental compositionI Thickness of sample to be scanned is determined by the x-ray energy to

be used.

garnet-biotite-kyanite schist animation[4]


X-Ray Tomography, Cont.1 Overview2 Detail3 Considerations

I Dominant absorption process is the photoelectric effect at operatingenergies

I Lower energies are more sensitive to elemental compositionI Thickness of sample to be scanned is determined by the x-ray energy to

be used.

garnet-biotite-kyanite schist animation[4]

(Loading Animation)


ctrecon.movMedia File (video/quicktime)

Quantum Dots

1 PhysicsI Discovered in the 1980s separately by Ekimov (glass matrices) and

Bruce (colloidal solutions), they are the physical realization of particlein a box with a few refinements (spherical potential, single electronwith multiparticle considerations (holes).

I Band gap is directly related to size of individual crystals [5].

4E = N4 1D (1)

=1

2D (2)

=

(1

32N

)1/3 3D (3)

=~22

mL2(4)


Quantum Dots

1 Physics2 Applications

I Semiconductor industry (photovoltaic devices)I Biology (nanoparticles / plasma resonances)I Computing (Mesoscopic Qubits)


Biological Exposure to Quantum Dots

The Premise [6]With increasing use of quantum dot devices in a wide array ofapplications, it is a natural assumption that a biological exposure rate tothe constituent elements comprising the quantum devices will rise.

Specifically, the paper presented here, Synchrotron X-ray 2D and 3Delemental imaging of CdSe/ZnS quantum dot nanoparticles in Daphniamagna, addresses the toxicity cadmium selenide quantum dots coated withZinc Sulfide and how they are processed by D. Magna.



D. Magna

Macroinvertebrate

Diet consists of algae and nanosized microorganisms

Cd, Zn, Se are all toxic to D. Magna

Sample Exposures Daphenids were exposed to 15 nMol/liter solutions ofred (4.8 nm) and green (2.6 nm) mercaptoundecanoic acid ligands (MUA)CdSe/ZnS quantum dots. After 12, 24 and 36 hour exposures, live sampleswere pulled from the solutions and placed on kapton tape for imaging.



Imaging1 2D Elemental

I X-ray fluorescenceI 13 keV beamI beam spot 10 10 mI 13 element Ge detector arrayI 20 micron steps in x-y at 1-2 s exposure time per pixel

F Note: Only Ca, Se, and Zn k lines could be imagedF 3.7, 12.7, 9.7 keV, respectively

2 TomographyI 13 keV beamI 10 10 m beam spotI 13 element Ge detector array


Biological Exposure to Quantum DotsResults



[7]

(l) (m)



Analysis

Correlation between Zn (cap) and Se (dot) show that the QD does notbreak down from its cap.

After 36 h exposure, all of the QD material can be found in the gut of D.Magna

QD material does not dissociate into component ions, nor does it passthrough cell membranes.

MUA coating ensures water solubility, increases size (25 microns). Mostlikely responsible for non permeation.


Conclusion

X-ray tomography produces 3 dimensional images by convolving multiplex-ray scans at different angles.

Care must be taken in choosing right x-ray energy in order to obtainnecessary intensities through layers.

In conjunction with spectroscopic methods, tomography can provide anelemental position mapping in real space.

Quantum dots do not dissociate within D. Magna from either their capmaterial or into their component ions.

A buildup up of QDs is seen in the gut of of D. Magna after exposure,but does not permeate the cell walls.


References

[1]Science Education Research Center; Carlton College. Sample (i), London Natural History Museum; Sample (j), UniversidadNacional de San Juan, Argentina.

[2] Jones, et al; Study of the Microgeometry of Porous Materials Using Synchrotron Computer Tomography, (Applications ofX-Ray Computed Tomography in the Geosciences, Geological Society of London, 2003)

[3] Coderre, Jeffrey A. 22.01 Introduction to Ionizing Radiation, Fall 2006, (MIT OpenCourseWare, 2006)

[4]http://serc.carleton.edu/files/research education/geochemsheets/techniques/ctrecon.mov (retrieved on April 29, 2012)

[5] Kouwenhoven, Leo, et al; Electron Transport In Quantum Dots, (Mesoscopic Electron Transport, Advanced Study Institute,1997)

[6] Jackson, Brain P. et al; ynchrotron X-ray 2D and 3D elemental imaging of CdSe/ZnS quantum dot nanoparticles in Daphniamagna, (Analytical, Bioanalytical Chemistry, v 394:911-917, 2009)

[7] Kato, Yasuhiko, et al; Environmental Sex Determination in the Branchiopod Crustacean Daphnia magna: Deep Conservation

of a Doublesex Gene in the Sex-Determining Pathway, (PLoS Genet 7(3): e1001345. doi:10.1371/journal.pgen.1001345, 2011)


X-Ray TomographyQuantum DotsPhysics and Application

Environmental Exposure and ConsequencesCdSe / ZnS nanoparticles in Daphnia Magna

Documents

Quantum Dots in Daphnia Magna - Illinois Institute of ...csrri.iit.edu/~segre/phys570/12S/presentations/beck.pdf · 2D/3D Synchrotron Imaging Quantum Dots in Daphnia Magna Matthew