Gold nanoparticles: strange properties and applications

© Innova Biosciences ltd. 2013. All rights reserved© Innova Biosciences ltd. 2013. All rights reserved
Quality – Consistency – Expertise

Gold nanoparticles: strange
properties and applications in the
Life Sciences

Dr Nick Gee
CEO/CSO of Innova Biosciences
Inventor of Lightning-Link® and InnovaCoat ®
Biochemist with over 20 years experience

Gold objects

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

Proximity effects
Aggregation (or a controlled interaction by design)
leads to a colour change

Ratio 650:530 is a useful aggregation parameter
Absorbance scanning of gold nanoparticles

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

Why does “40nm gold” look different from
different suppliers?

50nm

Shape-sensitive
region
Size-sensitive region

Interpretation of absorbance scans – be careful!
40nm gold gives this profile
This profile does not always
mean you have 40nm gold !

Profiles of 20nm and 80nm gold

Profile for a mixture of 20nm and 80nm gold
Gold does not behave like a mixture of coloured organic molecules

“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.

Attachment of molecules to gold
thiol
Alkanethiol
Au-S dative bond
Hydrophobic organic surface
Tail determines the
surface properties

- -
-
-
-
--
-
-
-
-
-
Citrate ions
destabilised
successful
coating
dissociation
X+
X = COOH or NH2
COOH
or NH2

InnovaCoat
surface
Colloidal stabilisation
Different surface chemistries available
Irreversible covalent attachment of analytes and antibodies
InnovaCoat technology

Effect of InnovaCoat surface on plasmon resonance

Colloidal stability of naked gold

Colloidal stability of InnovaCoat GOLD

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)

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

InnovaCoat GOLD conjugations:
Hands-on time 1 minute, conjugate (20 OD) ready
in 15 minutes. Can optimise at 1ug antibody scale.

Maleimide surface for coupling thiolated molecules:
S
maleimide
HS+
oligo

Oriented coupling of whole antibodies:
hydrazide
Hydrazide
InnovaCoat
derivative

Oriented coupling – antibody fragments:
maleimide
For coupling Fab’ or engineered antibody fragments
expressed with a cys terminus. No protein:metal contact
+
Fab’

Lateral flow data with InnovaCoat GOLD coupled to Fab’

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….

Applications of gold nanoparticles:
• Lateral flow
• Optical sensing
• Light scattering applications
• Drug delivery
• Cancer therapy

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

SERS – surface enhanced Raman scattering:
Molecular
vibrations
(infra-red
region) -
-
-
-
-
-
-
++ ++ +
+
Enhanced Raman scattering
Irregular
surfaces
best
laser
Electric field

Optical sensing principle
Antibody:analyte pair
Binding proteins
Complementary oligonucleotides
A B

Biotin-Gold and Streptavidin-Gold interaction
Red>blue colour change
Regular spheres best

Bio-sensing assay principle:
InnovaCoat streptavidin
+ InnovaCoat biotin
As above,
+ XS biotin

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

Delivery of toxic drugs
cisplatin
cisplatin
Acid-sensitive bond
Cisplatin is
Released inside
cells in the
endosomes

Photothermal therapy
Infrared laser
tumour
Hot

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

© Innova Biosciences ltd. 2013. All rights reserved
Contact
If you would like any more information, please contact us at
info@innovabiosciences.com
Please keep an eye out for our future webinars and other exciting news on our
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© Innova Biosciences ltd. 2013. All rights reserved
Innova Biosciences Ltd.
Babraham Research Campus,
Cambridge, UK,
CB22 3AT
www.innovabiosciences.com
Lightning-Link® and InnovaCoat ® are registered trademarks of Innova Biosciences
DyLight® is a registered trademark of Thermo Fisher Scientific Inc. and its subsidiaries

Gold nanoparticles: strange properties and applications

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