Quantum dots as tools for cellular imaging

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Quantum dots as tools for cellular imaging

• Presented by
• Debasish Sen
• Department of Physiology and Biophysics
• School of Medicine
• University of California, Irvine

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What are quantum dots ?

• Crystalline fluorophores
• CdSe semiconductor core
• ZnS Shell

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What are quantum dots

• Unique Spectral properties
• Broad absorption
• Narrow emission
• Wavelength depends on size
• Hydrophobic crystals

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Making hydrophobic quantum dots bio-compatible

• Various methods for making them water-soluble
• Derivatizing surface with mercaptoacetic acid
• Encapsulating in phospholipid micelles
• Derivatizing surface with DHLA
• Coating them with amine-modified polyacrylic acid

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Conjugating quantum dots to biomolecules

• Avidin or protein-G with positively charged tail
  conjugated to negatively charged DHLA coat of
  quantum dots

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Quantum dots v/s other fluorescent probes

• Photostability (quantum dots do not photobleach)

Wu et al. 2003
Red qdot 605 Conjugate
Green Alexa488 Conjugate
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Quantum dots v/s other fluorescent probes

• Broader excitation spectrum and narrower gaussian
  emission spectrum
• No spectral overlap between dots of different
  size better for multiplexing

Jaiswal Simon 2004
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Quantum dots v/s other fluorescent probes

• Brighter than other fluorophores

Quantum dots
Fluorescein
Larson et al. 2003
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Quantum dots and imaging
In Xenopus
Dubertret et al. 2002
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Quantum dots and imaging
Quantum dots
FITC-Dextran
In vivo visualization of capillaries
Larson et al. 2002
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Quantum dots and imaging
Wu et al. 2003
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Quantum dots and imaging
Diffusion of single Qdot-GlyRs in synaptic boutons
Glycine Receptors
Dahan et al. 2003
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Quantum dots and imaging
EGF receptor
EGF-QD
Live imaging of receptor mediated endocytosis
Lidke et al. 2004
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Quantum dots and imaging
Individual vesicles
Observing high resolution structure in dendritic
cells
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Quantum dots and imaging
Individual vesicles -Temperature variations
Dendritic cell processes
Observing high resolution structure in dendritic
cells
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Quantum dots and imaging
Single quantum dot crystals can be observed in
electron micrographs
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Quantum dots and imaging

• Quantum dots have been used in FRET
• In conjunction with Texas Red
• In conjunction with fluorescent quenchers

Willard et al. 2003
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Advantages

• Specific labeling of cells and tissues
• Useful for long-term imaging
• No cytotoxicity observed in vitro/in vivo
• Useful for multi-color multiplexing
• Suitable for dynamic imaging of subcellular
  structures
• May be used for FRET-based analysis

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Disadvantages

• Colloidal polymer-coated quantum dots can
  aggregate irreversibly
• Quantum dots are bulkier than many organic
  fluorophores
• Accessibility issues
• Mobility issues
• Cannot diffuse through cell membrane
• Use of invasive techniques may change physiology

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Acknowledgements
Mark Ellisman Tom Deerinck NCMIR, UCSD
Mike Cahalan
Ian Parker
Lu Forrest Mark Miller Sindy Wei Melanie
Matheu Olga Safrina
UCBREP GREAT