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?


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

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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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