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1) Institute for Materials Research, Tohoku University, Sendai, Japan

Theoretical Study of Quantum Dot/Organic Ligand Interface for Application in Early Cancer Detection. R. V. Belosludov 1) , H. Mizuseki 1) , A. Kasuya 2) and Y. Kawazoe 1). 1) Institute for Materials Research, Tohoku University, Sendai, Japan 2) Center for Interdisciplinary Research,

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1) Institute for Materials Research, Tohoku University, Sendai, Japan

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  1. Theoretical Study of Quantum Dot/Organic Ligand Interface for Application in Early Cancer Detection R. V. Belosludov1), H. Mizuseki1),A. Kasuya2) and Y. Kawazoe1) 1)Institute for Materials Research, Tohoku University, Sendai, Japan 2)Center for Interdisciplinary Research, Tohoku University, Sendai, Japan

  2. Semiconductor CdSe/ZnS Nanoparticles (Quantum Dots) for Fluorescence Diagnostics Qdots are highly fluorescent, molecular-sized semiconductor crystals. Tunable size from ~2-10 nm (±3%) Biological Applications Future applications Live cell imaging in vivo imaging,… Bio-labeling: Detection reagents for microscopy, DNA chips, flow cytometry, immunoassays, … QBead encoded beads: Platform for Multiplexed assays

  3. bifunctional crosslinker ZnS shell coating biological macromolecule CdSe core functional group stabilizing groups functional groups Semiconductor CdSe/ZnS Nanoparticles (Quantum Dots) for Fluorescence Diagnostics CdSe/ZnS Nanoparticle–Biomolecule Conjugate CdSe core: fluorescence ZnS shell: increased intensity and stability Coating (organic polymer, DHLA, siloxane) : prevention of cell toxicity Stabilizing groups (phosphonate, PEG, ammonium) : water solubility Functional groups (thiol, amine, carboxyl) : linking to biological macromolecule (DNA, IgG) Bio- conjugation: Electrostatic (surface  ; biomolecule ) or Covalent (via crosslinker) Requirements • Photostability(prevention of the emission quenching in aqueous environment) • Specificity(suppression of nonspecific binding and aggregation) • Biological inertness(no cytotoxicity) I. L. Medintz et al., Nature Materials 4 (2005) 435-446. X. Michalet et al., Science 307 (2005) 538-544.

  4. RESEARCH PURPOSE Limitation:Potential cyclotoxicity correlated with the liberation of free Cd2+ ions due to deterioration of the CdSe lattice A. M. Derfus et al., Nano Lett.4, 11 (2004) Solution:Design and synthesis of new nanocomposites which are more stable than crystalline QDs The compute-aided design and property prediction of nanostructured composites using the first-principles calculations in order to improve upon the materials currently used in diagnosis of cancer

  5. Computational details • Searching for Stable Configuration:Ab initio ultrasoft pseudopotential plane wave method with generalized gradient approximation for the exchange and correlation energy was used. A simple cubic cell with side ranging from 24 Å to 28 Å for different cluster size is used with periodic boundary conditions and an energy cut-off of 210 eV, for the plane wave expansion. • Properties: Absorption spectra, frequencies, QD/ligands interaction have been performed atomic orbitals at GGA level.

  6. Novel Core-Cage Structure Nature Materials, 3, 99 (2004) (CdSe)13 12+1 (CdSe)34 28+6 • More stable than crystal fragment Zincblende Cage-like Wurtzite E=-171.915 eV E=-175.514 eV E=-169.829 eV

  7. Zn-S Cd-Se Design Strategy: Stable Core/Shell Structure • Important for ultra-small nanoparticles CdSe: 2.620 Å Zn-S: 2.342 Å (10.61 %) • Structural defect in shell due to • lattice mismatch • New type nanoparticles

  8. Zn28Cd6S34 Zn28Cd6S28Se6 Zn28Cd6Se34 Cd34Se34 Zn28Pb6S34 EBE= 4.923 eV ESE=+5.57 eV Egap= 1.55 eV (GGA) EBE= 5.162 eV EBE= 5.062 eV EBE= 4.980 eV EBE= 5.052 eV ESE= +0.096 eV ESE=+3.76 eV ESE=+0.716 eV ESE= -3.395 eV Egap= 1.81 eV (GGA) Egap= 1.99 eV (GGA) Egap= 2.01 eV (GGA) Egap= 2.36 eV (GGA) Composition Effect: M28X28M’6X’6 Representative QD core materials scaled as a function of their emission wavelength superimposed over the spectrum I. L. Medintz et al., Nature Materials 4 (2005) 435-446.

  9. Zn28Cd4Se32 Zn28Cd4S32 Zn28Cd4S28Se4 Cd32Se32 Zn28Pb4S32 EBE= 5.142 eV EBE= 4.877 eV ESE= -2.781 eV ESE= +0.805eV Egap= 1.68 eV (GGA) Egap= 1.44 eV (GGA) EBE= 5.146 eV EBE= 5.105 eV EBE= 5.138 eV ESE= -2.92 eV ESE= -1.479eV ESE= -2.672 eV Egap= 2.43 eV (GGA) Egap= 2.48eV (GGA) Egap= 2.74 eV (GGA) Composition Effect: M28X28M’4X’4

  10. Core/Shell Zn31S31Cd3Se3 Clusters Zincblende Cage-like Wurtzite E=-209.488 eV E=-210.198 eV E=-206.627 eV

  11. ‘Cap exchange’ strategy - substitution of the native TOP/TOPO with bifunctional ligands, each presenting a surface-anchoring moiety to bind to the inorganic QD surface and an opposing hydrophilic end group to achieve water-compatibility. Zn28S28Cd4Se4-(MAA) Zn31S31Cd3Se3-MAA

  12. Investigated Configurations Ligand Connection Core/Shell QDs mercaptoacetic acid (MAA) (QD-Zn)-(S-Ligand) Zn28S28Cd4Se4 dithiothreitol (DTT) (QD-S)-(S-Ligand) Zn31S31Cd3Se3 dihydrolipoic acid (DHLA) Zinc-blend Neutral Charged (-1) Cage-like Wurtzite

  13. QDs-mercaptoacetic acid (MAA) Zn31S31Cd3Se3 Zn28S28Cd4Se4 Zinc-blend Cage-like Wurtzite Eint= -27.24 kcal/mol Eint= -29.02 kc al/mol -11.34kcal/mol -10.81 kcal/mol

  14. QDs-mercaptoacetic acid (MAA) Zn31S31Cd3Se3 Zn28S28Cd4Se4 Zinc-blend Cage-like Wurtzite Eint= -97.41 kcal/mol Eint= -123.52 kcal/mol -74.59 kcal/mol -86.49 kcal/mol

  15. QDs-dithiothreitol (DTT) Zn31S31Cd3Se3 Zn28S28Cd4Se4 Zinc-blend Cage-like Wurtzite Eint= -23.23 kcal/mol Eint= -27.02 kcal/mol -24.95 kcal/mol -18.02 kcal/mol

  16. QDs-dithiothreitol (DTT) Zn31S31Cd3Se3 Zn28S28Cd4Se4 Zinc-blend Cage-like Wurtzite Eint= -90.28 kcal/mol Eint= -97.83 kcal/mol -91.78kcal/mol -91.52 kcal/mol

  17. QDs-dihydrolipoic acid (DHLA) Zn31S31Cd3Se3 Zn28S28Cd4Se4 Zinc-blend Cage-like Wurtzite Eint= -39.58 kcal/mol Eint= -19.22 kcal/mol -22.72 kcal/mol -13.87 kcal/mol

  18. QDs-dihydrolipoic acid (DHLA) Zn31S31Cd3Se3 Zn28S28Cd4Se4 Zinc-blend Cage-like Wurtzite Eint= -194.37 kcal/mol Eint= -228.45 kcal/mol -194.09kcal/mol -211.41 kcal/mol

  19. MAA Zn28S28Cd4Se4 Eint=-7.67 kcal/mol

  20. DTT Zn28S28Cd4Se4 Eint=-10.85 kcal/mol

  21. Core/Shell Zn31S31Cd3Se3 with MAA Zincblend

  22. Core/Shell Zn31S31Cd3Se3 with MAA Wurtzite

  23. QDs structure degradation (DHLA case) no DHLA DHLA neutral DHLA charged 2DHLA charged 3DHLA charged

  24. Conclusions • Systematic study of the geometries of ZnmSm/CdnSen clusters is reported. • It has been found that clusters of with 13, 33, 34 CdSe pairs are very stable in agreement with experiment. These nanoparticles with the cage-like structure are remarkably stable. • The new shell-core particles (ZnX)28/(CdSe)4 are found to be energetically stable and the outer cage structure based on ZnS and ZnSe are undistorted. These results indicate the possibility of formation stable shell-core nanoparticles with small concentration of Cd which can significantly reduce the toxic effect of fluorescence II-VI semiconductor QDs. • Using ‘Cap exchange’ strategy, it is important to increase carbon chain of ligand. Using DHLA, it is possible to achieve good water-compatibility. The better coating can be achieved for the cage-like clusters.

  25. Acknowledgments The authors are also grateful for the continuous support of the HITACHI SR1100-K2/51 supercomputing facility by the Computer Science Group at the Institute for Materials Research, Tohoku University. Generous support from the Ministry of Education, Culture, Sports, Science, and Technology of Japan (Grant No. 17686072) is greatly appreciated. Reference: Nature Materials, 3, 99 (2004)

  26. I. L. Medintz et al., Nature Materials 4 (2005) 435-446.

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