gold nanoparticles: strange properties and applications
TRANSCRIPT
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Quality – Consistency – Expertise
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Gold nanoparticles: strange properties and applications in the Life Sciences
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Dr Nick Gee CEO/CSO of Innova Biosciences Inventor of Lightning-Link® and InnovaCoat ® Biochemist with over 20 years experience
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Gold objects
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Gold nanoparticles (10-200nm range)
Gold nanoparticles display shape- and size-dependent properties. Often red, but many other colours are possible.
White light Surface electrons
Gold Gold
- -
- - -
- -
+ + + + + +
Plasmon resonance
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Proximity effects
Aggregation (or a controlled interaction by design) leads to a colour change
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Ratio 650:530 is a useful aggregation parameter
Absorbance scanning of gold nanoparticles
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Gold rods
Rods are blue or brown, depending on the aspect ratio. Extra resonance in the infra-red region.
White light
Longitudinal and transverse plasmon resonance
electrons
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Why does “40nm gold” look different from different suppliers?
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Shape-sensitive region
Size-sensitive region
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Interpretation of absorbance scans – be careful!
40nm gold gives this profile This profile does not always mean you have 40nm gold !
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Profiles of 20nm and 80nm gold
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Profile for a mixture of 20nm and 80nm gold
Gold does not behave like a mixture of coloured organic molecules
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“40nm gold” looks different from different suppliers because the particles have different shapes.
Plasmon resonance (and thus colour) is markedly influenced by shape and by interactions of particles with other particles.
Summary
Covalent attachment of molecules….
Absorbance scans provide useful quantitative information but careful interpretation is required, esp. about size.
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Attachment of molecules to gold
thiol
Alkanethiol
Au-S dative bond
Hydrophobic organic surface
Tail determines the surface properties
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- -
- -
- - -
- -
-
- -
Citrate ions
destabilised
successful coating
dissociation
X + X = COOH or NH2
COOH or NH2
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InnovaCoat surface
Colloidal stabilisation
Different surface chemistries available
Irreversible covalent attachment of analytes and antibodies
InnovaCoat technology
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Effect of InnovaCoat surface on plasmon resonance
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Colloidal stability of naked gold
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Colloidal stability of InnovaCoat GOLD
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A B C D
A - InnovaCoat GOLD 10 OD
B – Washed
C – Naked gold 10 OD
D – Naked gold washed
IgG spotted strips,
BSA blocked
Shielding of metal surface (40nm gold)
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Passive binding of antibody, involves systematic pH and salt titrations to optimise Binding, need blocking steps. Widely used, significant risk of unwanted aggregation.
Covalent binding – add correct amount of antibody to freeze- dried coated gold. Often less antibody required than with passive binding. Gold is already blocked. Very stable product.
Preparation of conjugates – two approaches:
naked coated
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InnovaCoat GOLD conjugations:
Hands-on time 1 minute, conjugate (20 OD) ready in 15 minutes. Can optimise at 1ug antibody scale.
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Maleimide surface for coupling thiolated molecules:
S
maleimide HS +
oligo
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Oriented coupling of whole antibodies:
hydrazide
Hydrazide InnovaCoat derivative
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Oriented coupling – antibody fragments:
maleimide
For coupling Fab’ or engineered antibody fragments expressed with a cys terminus. No protein:metal contact
+ Fab’
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Lateral flow data with InnovaCoat GOLD coupled to Fab’
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Methods of attaching molecules to gold may be passive or covalent.
Summary:
Covalent linking is more stable especially for small thiolated molecules.
Covalent strategies allow oriented coupling to be carried out.
Applications….
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Applications of gold nanoparticles:
• Lateral flow • Optical sensing • Light scattering applications • Drug delivery • Cancer therapy
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Scattering applications: Rayleigh scattering
Mie scattering
reflection
Scattering is particularly pronounced with large gold nanoparticles (>80nm). Smaller particles (e.g. 40nm) absorb rather than scatter.
Dark field microscopy Flow cytometry
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SERS – surface enhanced Raman scattering:
Molecular vibrations (infra-red region) -
- -
- -
- -
+ + + + + +
Enhanced Raman scattering
Irregular surfaces best
laser
Electric field
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Optical sensing principle
Antibody:analyte pair Binding proteins Complementary oligonucleotides
A B
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Biotin-Gold and Streptavidin-Gold interaction
Red>blue colour change
Regular spheres best
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Bio-sensing assay principle:
InnovaCoat streptavidin
+ InnovaCoat biotin
As above, + XS biotin
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Extreme stability of InnovaCoat GOLD:
Survives 2 hours at 70oC in 2.5M NaOH
Potentially useful for DNA sensing applications and applications involving small molecules that cannot be irreversibly attached to naked gold
2h 1 sec
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Delivery of toxic drugs
cisplatin
cisplatin
Acid-sensitive bond
Cisplatin is Released inside cells in the endosomes
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Photothermal therapy
Infrared laser
tumour
Hot
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InnovaCoat GOLD conjugation kits
Conjugate development
Oriented coupling
20 40 80 Custom coating to allow covalent attachment
Lateral flow Scattering
Bulk coated gold
40
Biotin-Gold Streptavidin-Gold
fragments
Abs
Tools
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