gold nanoparticles: strange properties and applications

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

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:

maleimide HS +

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

Electric field

Optical sensing principle

Antibody:analyte pair Binding proteins Complementary oligonucleotides

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

Acid-sensitive bond

Cisplatin is Released inside cells in the endosomes

Photothermal therapy

Infrared laser

tumour

InnovaCoat GOLD conjugation kits

Conjugate development

Oriented coupling

20 40 80 Custom coating to allow covalent attachment

Lateral flow Scattering

Bulk coated gold

Biotin-Gold Streptavidin-Gold

fragments

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 website and social media channels:

www.innovabiosciences.com/innova/webinars.html

YouTube: www.youtube.com/InnovaBiosciences

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

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