Nanoparticle Nanoparticle Optics Part 1Optics Part 1

Gold and Silver Gold and Silver NanoparticlesNanoparticles

Group 1 – Luke, Matt, and Group 1 – Luke, Matt, and JeffJeff

TheoryTheory The color of the sol arises from a combination of absorption and The color of the sol arises from a combination of absorption and

scattering of light and depends on particle size. More scattering of light and depends on particle size. More specifically it is due to a resonance of the free electrons in the specifically it is due to a resonance of the free electrons in the metal particle. The light’s electromagnetic field causes them to metal particle. The light’s electromagnetic field causes them to slosh back and forth (plasmon oscillations).slosh back and forth (plasmon oscillations).

At a characteristic frequency which depends of the size and the At a characteristic frequency which depends of the size and the metal, the sloshing is the most intense. This is the frequency metal, the sloshing is the most intense. This is the frequency where plasmon oscillations are excited. The plasmon resonance where plasmon oscillations are excited. The plasmon resonance is easily seen in the extinction spectrum of the sol.is easily seen in the extinction spectrum of the sol.

The particles experience the constant buffeting of Brownian The particles experience the constant buffeting of Brownian motion which also helps to keep them in suspension.motion which also helps to keep them in suspension.

ObjectiveObjective

Learn about scattering and absorption Learn about scattering and absorption in gold and silver nanoparticles.in gold and silver nanoparticles.

Visually observe how particle size Visually observe how particle size effects scattering.effects scattering.

Learn to use a Tyndall beam.Learn to use a Tyndall beam. Observe sub-diffraction limit Observe sub-diffraction limit

nanoparticles in the optical microscope.nanoparticles in the optical microscope. Become familiar with optical and Become familiar with optical and

electron microscopy.electron microscopy.

Procedure: Gold Procedure: Gold NanoparticlesNanoparticles

Bring to a boil 50 mL of 2.5Bring to a boil 50 mL of 2.5×10×10-4-4 M M chloroauric acid solutionchloroauric acid solution Add 0.16 mL of 34 mM sodium citrate solution to the boiling Add 0.16 mL of 34 mM sodium citrate solution to the boiling

solution while stirringsolution while stirring After a minute will be faint blue and then darkening over 5 min to After a minute will be faint blue and then darkening over 5 min to

a brilliant red a brilliant red Repeat procedure with 0.30 mL and 1.0 mL of sodium citrate to Repeat procedure with 0.30 mL and 1.0 mL of sodium citrate to

produce three samples of different sized gold nanoparticles.produce three samples of different sized gold nanoparticles. Fill cuvette with sample and place in spectrophotometer. Record Fill cuvette with sample and place in spectrophotometer. Record

absorbance of each sample from 200 nm to 800 nm.absorbance of each sample from 200 nm to 800 nm.

Procedure: Optical Procedure: Optical MicroscopyMicroscopy

Use micropipette to place 20 Use micropipette to place 20 L of sample on a L of sample on a microscope slide.microscope slide.

Place cover slip over sample.Place cover slip over sample. Place slide under 20X objective lens for total Place slide under 20X objective lens for total

magnification of about 200X.magnification of about 200X. Use coarse and fine focus knobs to find nanoparticles. Use coarse and fine focus knobs to find nanoparticles.

Use the plane of cover slip and slide as a reference.Use the plane of cover slip and slide as a reference. Observe stationary nanoparticles on cover slip and Observe stationary nanoparticles on cover slip and

slide. Nanoparticles in solution are randomly moving slide. Nanoparticles in solution are randomly moving because of Brownian motion.because of Brownian motion.

Procedure: Electron Procedure: Electron MicroscopyMicroscopy

Using a micropipette, Using a micropipette, put a few drops of put a few drops of sample on light side sample on light side of carbon grid.of carbon grid.

Wick away excess Wick away excess with filter paper.with filter paper.

Let sample dry for Let sample dry for several hours.several hours.

View sample in TEM View sample in TEM and take photos for and take photos for later analysis.later analysis.

Results: Visual InspectionResults: Visual Inspection Solution changed from blue to red within five minutes as Solution changed from blue to red within five minutes as

expected.expected. Sample with 0.16 mL sodium citrate turned a duller red Sample with 0.16 mL sodium citrate turned a duller red

than the other two samples.than the other two samples.

Results: Absorption Results: Absorption SpectraSpectra

Fit of Mie Plot data to Fit of Mie Plot data to Spectrophotometer data resulted Spectrophotometer data resulted in gold nanoparticle radii of 14.8 in gold nanoparticle radii of 14.8 nm, 15.6 nm, and 35 nm (diameter nm, 15.6 nm, and 35 nm (diameter of 29.6 nm, 31.2 nm, and 70 nm).of 29.6 nm, 31.2 nm, and 70 nm).

Shoulder on 0.3 mL sample is Shoulder on 0.3 mL sample is because of larger particles also in because of larger particles also in the solution.the solution.

0.16 mL sodium citrate solution

Wavelength (nm)

400 500 600 700 800

Abs

orb

an

ce

0

1

2

3

4

5

Spectrophotometer dataMie Plot data, 35 nm

0.3 mL sodium citrate solution

Wavelength (nm)

400 500 600 700 800

Abs

orba

nce

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Spectrophotometer dataMie Plot data, 15.6 nm

1 mL sodium citrate solution

Wavelength (nm)

400 500 600 700 800

Ab

sorb

ance

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Spectrophotometer dataMie Plot data, 14.8 nm

Results: TEMResults: TEM

0.16 mL, 100 nm scale 0.16 mL, 100 nm scale

0.3 mL, 20 nm scale

Results: TEMResults: TEM

0.3 mL, 100 nm scale 0.3 mL, 20 nm scale 1 mL, diffraction

Analysis: TEMAnalysis: TEM Particles in each picture were measured with a ruler to get Particles in each picture were measured with a ruler to get

a size distribution.a size distribution. Data agrees well with estimations from absorption spectraData agrees well with estimations from absorption spectra

.16mL Sodium Citrate Gold Nanoparticlesmean = 54.63 nm, stdev = 24.80 nm

0

5

10

15

20

25

30

7.1 20.3 33.5 46.6 60 73 86.2 99.3 More

Nanoparticle Diameter (nm)

Fre

qu

ency

0.3 mL Sodium Citrate Gold Nanoparticlesmean = 30.1 nm, stdev = 4.3 nm

0

5

10

15

20

25

30

35

40

45

50

21.4 23.1 24.7 26.3 27.9 29.5 31.2 32.8 34.4 36.0 37.7 More

Nanoparticle Diameter (nm)

Fre

qu

en

cy

Analysis: TEM DiffractionAnalysis: TEM Diffraction Measured radii of diffraction rings to Measured radii of diffraction rings to

determine lattice constant of gold.determine lattice constant of gold.Measured Measured

Radius (cm)Radius (cm)Miller IndexMiller Index Plane Spacing Plane Spacing

(nm)(nm)Lattice Lattice

Constant (nm)Constant (nm)

QuestionsQuestions Approximate Size: r = 14.8 nm, 15.6 nm, and 35 nmApproximate Size: r = 14.8 nm, 15.6 nm, and 35 nm Atoms per nanoparticleAtoms per nanoparticle

For r = 14.8 nm:For r = 14.8 nm:

lenanopartic

Auatoms

mol

Auatoms

g

mol

cm

g

lenanopartic

cm

cmgandcmrV Au

6233

317

33173

100.810022.697.196

13.191036.1

/3.191036.13

4

For r = 15.6 nm: 9.4 * 10^6 atoms/nanoparticleFor r = 15.6 nm: 9.4 * 10^6 atoms/nanoparticle For r = 35 nm: 106 * 10^6 atoms/nanoparticleFor r = 35 nm: 106 * 10^6 atoms/nanoparticle

QuestionsQuestions Fraction of atoms on surfaceFraction of atoms on surface

For r = 14.8 nm:For r = 14.8 nm:

0035.0100.8

27500

27500101075.2

1075.24

6

215211

2112

lenanoparticinatoms

surfaceonatoms

surfaceonatomsAucm

atomscm

cmrSA

For r = 15.6 nm: 0.0033For r = 15.6 nm: 0.0033 For r = 35 nm: 0.0015For r = 35 nm: 0.0015

QuestionsQuestions

Number of nanoparticles per mLNumber of nanoparticles per mL For r = 14.8 nm:For r = 14.8 nm:

mLlesnanoparticmL

lesnanopartic

lesnanoparticAuatoms

lesnanoparticAuatoms

Auatomsmol

atomsAumol

AumolsolutionmLacidchlorauricM

/1088.150

1041.9

1041.9100.8

11053.7

1053.710022.625.1

25.150105.2

910

106

17

1717

5

For r = 15.6 nm: 1.6 * 10^9 nanoparticles/mLFor r = 15.6 nm: 1.6 * 10^9 nanoparticles/mL For r = 35 nm: 0.14 * 10^9 nanoparticles/mLFor r = 35 nm: 0.14 * 10^9 nanoparticles/mL

QuestionsQuestions

Nanoparticle surface area per mLNanoparticle surface area per mL For r = 14.8 nm:For r = 14.8 nm:

mL

cm

lenanopartic

cm

mL

lesnanopartic 22119 052.01075.21088.1

For r = 15.6 nm: 0.049 cm^2/mLFor r = 15.6 nm: 0.049 cm^2/mL For r = 35 nm: 0.022 cm^2/mLFor r = 35 nm: 0.022 cm^2/mL