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A Simple and Green Method for Synthesis of Ag and Au Nanoparticles Using Biopolymers

and Sugars as Reducing Agents.

German Ayala, Luci Cristina O. Vercik, Leticcia G. Ferreira, Andres Vercik and Thiago A. Villa Menezes.

Nanotechnology Biosensors Devices Laboratory – NANOBIODEV Basic Sciences Department – FZEA, Pirassununga – SP

University of São Paulo – USP – Brazil

MRS Fall Meeting 2011 – Symposium D11.3 – 12/1 11:15 AM

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Metallic nanoparticles

2

Nanometer range 1 to few hundreds.

Single metal, alloy or metallic oxides (conducting or semiconducting).

Optical, electrical, quantum and magnetic properties.

Au Ag Cu

Pt PdSiO2

D

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(Some) Applications

3

●Imaging of tumors and infections.

●Theranostics of cancer.

●Immobilization of biological

molecules.

●Sensing (optic, electric).

●Our focus is on the last two by

using gold and silver NPs.

We!

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Gold Nanoparticles (AuNP)

4

Au–NH2

(amine)–SH (thiol)

Long known interaction between amine and thiol groups and gold NPs.

Lys

Cys

Proteins contain lysine and cysteine aminoacid residues in their chains.

AuNP can be used to immobilize antibodies, enzymes and structural proteins.

Gole et al., Langmuir 2001, 17, 1674-1679.

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Silver Nanoparticles (AgNP)

5

Cys Protein SH

Ag

SH

Protein S

S

Silver NP is most known by its antibacterial properties.

It is believed that they catalyze disulfide bond formation, what denatures enzymes and proteins.

Yan et al., Chi. J. Cataly. 2009, 30 (9), 856-858

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Nanoparticles Synthesis

6

+ RA + RA–O

Metal ion(solution)

Electron donor

Oxidized agent

Nanoparticle

(colloid)

CA

ChemicalPhysical

Electrochemical,Thermolysis,Radiation etc.

Chemical reduction.Photochemical reduction,Radiolysis etc.

What are the choices for RA and CA?

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Current RAs and CAs

7

NaBH4 N,N-dimethylformamide CitrateMost used

Trace amounts of those and their solvents might hinder applications in biomedicine or as biomaterials.

Less solvents/reagentsMild temperature and pHEnvironmental friendly processes

Can we use green chemistry principles to obtain NPs?

GREEN CHEMISTRY

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Green Reducing Agents

8

Au or Ag

pH ~ Acetic acid

85°C

Few hours

Chitosan as RA and CA

NH3+NH3+

NH3+

Wei uses chitosan as both reducing and capping agents.

Can we extend that method to different reducing sugar and biopolymers?

Wei et al., Coll. Surf. B 2008, 62, 136-142.

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Reducing Sugar

9

Closed – open ring equilibrium in solution

Reducing sugar must have an aldehyde in open form to be oxidized to carboxilic acid

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Objectives

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We further developed the method by Wei, extending it to other cheap and readily available green reducing agents as

carbohydrates, and evaluated what's the relation between pH, temperature,

reducing agent and metal ion parameters.

Wei et al., Coll. Surf. B 2008, 62, 136-142.

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Flowchart Diagram

Metal ion

Sugar

pH adjustment

1

HAuCl4 (8.1 mM)AgNO3 (52 mM)

2

6.92 mg/mL

Heating3

40, 60, 80 and 90

°CReaction time4

3 h for Au12 h for Ag

SPR5

UV-Visspectrum

Next slide.

Wei's methodology.

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Size Name Structure Reducing?

Mono Glucose --- Yes

Galactose --- Yes

Fructose --- Yes

Di Maltose Glu–Glu Yes

Lactose Glu–Gal Yes

Sucrose Glu–Fru No

Poly Starch (Glu)n Yes

Chitosan (DA-Chitin)n Yes

Carbohydrates Used as RAs

Table 1. Summary of sugars used as reducing agents for NP synthesis.

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Ag

12h

Wei's method works for different sugars, but with less efficiency

1

Chitosan is still the best.

2

Wei's Method for Other Sugars

Fig. 1. UV-Vis for different sugars and Wei's method. Chitosan diluted 50%.

90°C

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Obtained

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Ag 12h 90°C

Some results were not as efficient as expected.

1

Fru Lac

Gal

Glu

Sta Chi

Mal

Suc

PolymersMono Di

Expected

Influence of Sugar (for Ag)

We started to investigate parameters.

2

Fig. 2. Digital image for Ag NPs synthesized with different sugars.

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Ag

12h

Higher temperature yields moreNPs for fixed time, metal and RA.

1

Size dispersion seems to be narrow.

2

Influence of Temperature

Starch

Fig. 3. UV-Vis for influence of temperature on AgNPs with starch.

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Au

3h

90°C

Only soluble chitosan worked (pH 3-4 due to acetic acid) 1

Fig X. UV-Vis for AuNP

Is pH influencing chargetransport in redox reaction?

2

Fru Lac

Gal

Glu

Sta Chi

Mal

Suc

PolymersMono Di

ExpectedObtained

Influence of Sugar (for Au)

Fig. 5.

Fig. 4.

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Au

3h

25°C

Glucose

NaOH 0.1M added

pH allows synthesis at room temperature.

There is an optimal pH rangefor which synthesis occurs. 1

2

Fig. 6. UV-Vis for influence of pH on AuNP synthesis using glucose.

Influence of pH (glu)

No further synthesis for increasing temperature.

3

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Au

3h

90°C

Sucrose

NaOH 0.1M added

Maybe sucrose is going alkaline thermal hydrolysis?

For sucrose, pH andtemperature are necessary.

1

2

Fig. 7. UV-Vis for influence of pH on AuNP synthesis using sucrose.

Glu–Fru → Glu + Fru

Influence of pH (suc)

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Au

3h

90°C

Starch

NaOH 0.1M added

Hydrolisis of starch yields several glucoses.

Higher pH enables proper synthesis of AuNP using starch (previously not possible).

1

2

Fig. 8. UV-Vis for influence of pH on AuNP synthesis using starch.

Influence of pH (sta)

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Au

1 min!

25°C

(a) Mentha piperita

Faster synthesis employing common food industry byproducts.

10 min!

(b) Pineapple

(c) Banana

(d) Passion fruit

(e) Mandarin orangeFig. 9. UV-Vis for AuNP reduced by leaves extracts of herbs and fruits.

Sugars from Extracts

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ConclusionsMetal ion Same set of parameters doesn't work for

different metal ions.

Sugars Similar sugars behave differently. Glucosewas the best reducing agent.

pH pH is one key parameter in stabilizing/allowing synthesis.

Extracts

Reaction time

Leaf and fruit peel extracts are viablereducing agents when NaOH stabilized.

Advancement in relation to Wei's: we went from few hours to few minutes using other sugars (glucose).

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We gladly thank:

Nanotechnology Biosensors Devices Laboratory – NANOBIODEVThiago A. Villa Menezesthi.avm@gmail.com

You for listening.