Metal Nanoparticles of Metal Nanoparticles of Various ShapesVarious Shapes

Jie Gao, Min XuJie Gao, Min XuApr. 1, 2007Apr. 1, 2007

OutlineOutline

• Advantages of metal nanoparticles.Advantages of metal nanoparticles.• Why we need nanorods?Why we need nanorods?• Synthesis of metal nanoparticles.Synthesis of metal nanoparticles.• Synthesis of gold nanorods.Synthesis of gold nanorods.• Growth mechanism of gold nanorods.Growth mechanism of gold nanorods.• Synthesis of gold nanoparticles of different Synthesis of gold nanoparticles of different

shapes.shapes.• Advantage of seed-mediated methodAdvantage of seed-mediated method• Other issues to considerOther issues to consider

Advantages of Metal Advantages of Metal NanoparticleNanoparticle

• Strong plasma absorptionStrong plasma absorption

• Enhance Rayleigh scatteringEnhance Rayleigh scattering

• Surface enhanced Raman scatteringSurface enhanced Raman scattering

Advantage of Metal Advantage of Metal NanoparticlesNanoparticles

• Biological detectorBiological detector

• Biological system imagingBiological system imaging

• Determine chemical information on Determine chemical information on metallic nanoscale substratemetallic nanoscale substrate

Why we need nanorods? Why we need nanorods?

• Limitations of nanospheresLimitations of nanospheres

S. Eustis, M. A. El-Sayed, Chem. Soc. Rev. 2006, 35, 209-217

Synthesis of metal Synthesis of metal nanoparticlesnanoparticles• Bottom up method--assemble atoms to nanBottom up method--assemble atoms to nan

ostructuresostructures 1. Nanosphere lithography.1. Nanosphere lithography. 2. Templating, chemical, electrochemical, so2. Templating, chemical, electrochemical, so

nochemical, thermal and photochemical redunochemical, thermal and photochemical reduction techniques. ction techniques.

• Top down method--cut into pieces in nanosTop down method--cut into pieces in nanoscalecale

1. Photolithography1. Photolithography 2. Electron beam lithography2. Electron beam lithography

Synthesis of metal Synthesis of metal nanoparticlesnanoparticles

• Nanosphere lithography Nanosphere lithography

W. Huang, W. Qian, M. A. El-Sayed, Proc. SPIT Int. Soc. Opt. Eng. 2005, 5927, 592701

Synthesis of metal Synthesis of metal nanoparticlesnanoparticles

• Citrate Reduction Method Citrate Reduction Method

sodium citrate + HAuCl4

Turkevitch in 1951

Synthesis of metal Synthesis of metal nanoparticlesnanoparticles

• Two Phase Reactions Two Phase Reactions

• Inverse Micelles Inverse Micelles

General idea of chemical method: reduction + capping

Synthesis of gold nanorodsSynthesis of gold nanorods

• Seed-mediated methodSeed-mediated method

• Two steps: produce seed particles + Two steps: produce seed particles + seed grow into rodseed grow into rod

C. J. Murphy, T. K. Sau, A. M. Gole, C. J. Orendorff. J. L. Gou, S. E. Hunyadi, T. Li, J. Phys. Chem. B 2005, 109, 13857-13870

Synthesis of gold nanorodsSynthesis of gold nanorods

Synthesis of gold nanorodsSynthesis of gold nanorods

• Factors related to the growth Factors related to the growth 1. Seed size1. Seed size2. Length of “tails” of CTAB (cetyltrimet2. Length of “tails” of CTAB (cetyltrimet

hylammonium bromide )hylammonium bromide )

Synthesis of gold nanorodsSynthesis of gold nanorods

dependence of nanorod aspect ratio on seed size

Synthesis of gold nanorodsSynthesis of gold nanorods

Dependence of aspect ratio on length of tails of CTAB

Growth mechanism of gold nanorodsGrowth mechanism of gold nanorods

““Zipping” fashion formation of gold nanorodsZipping” fashion formation of gold nanorods:C16TAB

Growth mechanism of gold Growth mechanism of gold nanorodsnanorods

crystallography picture of gold nanorods:

pentatetradedral

Planar density of atoms of FCC structure

{111}: 0.907

{100}: 0.785

{110}: 0.555

Growth mechanism of gold nanorodsGrowth mechanism of gold nanorods

• tail contribution to the free energy formtail contribution to the free energy formation of a bilayer on gold ation of a bilayer on gold

ΔG(10)= -29.6 kJ/mol, Δ(12)= -35.8 kJ/mol, Δ(14)= -41.9 kJ/mol,Δ(16)= -48.1 kJ/mol

Growth mechanism of gold nanorodsGrowth mechanism of gold nanorods

Growth mechanism of gold nanorods

Synthesis of gold nanoparticles of diffSynthesis of gold nanoparticles of different shapeserent shapes

• General idea is the same as the growth oGeneral idea is the same as the growth of gold nanorods (seed-mediated methof gold nanorods (seed-mediated method)d)

• Slightly change the conditions when groSlightly change the conditions when growing nanorods (concentration of differewing nanorods (concentration of different reactants)nt reactants)

• Cubes, hexagon, triangle, tetropods, braCubes, hexagon, triangle, tetropods, branchednched

T. K. Sau, C. J. Murphy, J. Am. Chem. Soc. 2004, 126, 8648-8649

Synthesis of gold nanoparticles of Synthesis of gold nanoparticles of different shapesdifferent shapes

[AA] increases from A to C and seed concentration increases from C to D. Scale bar = 100 nm

Synthesis of gold nanoparticles of Synthesis of gold nanoparticles of different shapesdifferent shapes

TEM images showing cubic to rod-shaped gold particles produced with low AA concentration in the presence of small quantity of silver nitrate. [CTAB] is increased (A) to (B, C, D). [Au3+] decreases from B to C, and seed concentration increased form C to D. Scale bar = 100 nm

Synthesis of gold nanoparticles of Synthesis of gold nanoparticles of different shapesdifferent shapes

TEM images of brached Au nanoparticles, varying in the dimension and number of branches

Synthesis of gold nanoparticles of Synthesis of gold nanoparticles of different shapesdifferent shapes

Summary of experimental procedure

1.The concentrations are interdependent

2. Growth mechanism is similar to that of rod

Advantage of water seed-Advantage of water seed-

mediated methodmediated method

• High yieldHigh yield• MonodisperseMonodisperse• Cheap, easyCheap, easy

Other issue to considerOther issue to consider

• The nucleation process in growth of The nucleation process in growth of seed is still mysteriousseed is still mysterious

• Limitation in length and aspect ratioLimitation in length and aspect ratio

maximum length: ~600nmmaximum length: ~600nm

maximum aspect ratio: ~25maximum aspect ratio: ~25

SummarySummary

• Advantages of metal nanoparticles.Advantages of metal nanoparticles.• Why we need nanorods?Why we need nanorods?• Synthesis of metal nanoparticles.Synthesis of metal nanoparticles.• Synthesis of gold nanorods.Synthesis of gold nanorods.• Growth mechanism of gold nanorods.Growth mechanism of gold nanorods.• Synthesis of gold nanoparticles of different Synthesis of gold nanoparticles of different

shapes.shapes.• Advantage of seed-mediated methodAdvantage of seed-mediated method• Other issues to considerOther issues to consider