# User:Allison K. Alix/Notebook/Thesis Research/2013/05/24

Coating AuNP with Silica Main project page
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## Objectives

• Find procedure for synthesizing silica coated gold nanoparticles as a way to prevent fluorescence quenching

## Notes from Literature

Graf et al. Langmuir. Vol. 19. No. 17, 2003 "A General Method to Coat Colodial Particles with Silica"

-Researchers adsorbed PVP onto collodial surface, yielding particles stable in water an ethanol. particles were directly coated with a silica layer by addition of tetraethoxysilane (TES) to an ammonia-ethanol solution containing the particles in a seeded growth process. Fast method that does not require silane coupling agents or pre-coating with sodium silicate.

Chemicals needed:

• Tetraethoxysilane (TES)
• PVP (avg molar mass 10kg/mol)
• Ethanol
• Acetone
• Ammonia (29.3 wt% in water)
• Hydrofluoric acid (38-40%) (used for cleaning reaction vessels)

Procedure:

1) Prepare small gold colloids of 7-19nm radius using sodium citrate reduction method

2) Functionalize gold surface with 10kg/mol PVP in an amount that provides the gold nanoparticle with 60 PVP molecules per nm2 surface. r for nanoparticles to be used = 7nm, concentration 19.4nM

Calculating # AuNP in solution

19.4nmol/L x (1mol/109nmol) x (6.022x1023AuNP/ 1 mol) x (1 L/1000mL) = 1.168268 x 1013 AuNP/mL

Calculating Surface Area of 1 AuNP (r=7nm)

surface area = 4pi(r)2

= 4pi(7x10-9)2

= 6.1575216 x 10-16m2 x (109nm)2/(1m)2

= 615.75nm2

60 PVP molecules/1nm2 x 615.75nm2 = 36945.13 PVP molecules per AuNP

If 5mL AuNP solution is used:

1.168268 x 1013 AuNP/mL x (5mL) x 36945.13 PVP molecules/AuNP = 2.1581 x 1018 PVP molecules

2.1581 x 1018 PVP molecules x (1 mol PVP/6.022 x 1023 PVP molecules) = 3.5837μmol PVP

3.5837μmol PVP added to 5mL AuNP solution

To change the volume by 10% only, add 500μL of solution

3.5837μmol/0.5mL x 10-6mol/1μmol x 1mL/10-3L = 0.00716M PVP

• Add 500μL of 0.00716M 10kg/mol PVP

To prepare 0.00716M 10kg/mol PVP:

0.00716 mol/L x (10kg/mol) x (1000g/1kg) x 10mL x (1L/1000mL) = 0.716g in 10mL water

3) Dissolve PVP in water by ultrasonication for 15 minutes

4) Mix 500μL PVP with 5mL AuNP with stirring (600rpm) for 24 hours at room temperature

5) Centrifuge, remove supernatant and redisperse in a solution of ammonia in ethanol (4.2 vol% ammonia (29.3 wt% NH3 in water) in ethanol)

6) Immediately after, add TES solution (10 vol% in ethanol) with stirring (600 rpm) for 12 hours

• Reaction vessels used in silica coating step were cleaned with hydrofluoric acid (8 vol%) and rinsed several times with water. All reaction steps carried out under exclusion of light.