Optimum size of silver and gold nanoparticles for the enhancement of Raman intensity in surface enhanced Raman spectroscopy.

1. Seminar
Topic Name;
Optimum size and shape of Nanoparticles for
Surface Enhanced Raman Spectroscopy

2. Surface-enhanced Raman spectroscopy
Surface-enhanced Raman spectroscopy or surface-enhanced Raman
scattering is a surface-sensitive technique that enhances Raman
scattering by molecules adsorbed on rough metal surfaces or by
nanostructures.

3. Why there is need of SERS?
• As only one out of million photons undergo Raman
scattering
• Gives very weak signals in Raman spectra.
• Metal Nanoparticles enhances Raman Signal by Surface
plasmon resonance(SPR)

4. The SERS intensity of adsorbates on surface
of metal nanoparticles is dependent on
• Size of the nanoparticles
• Shape of nanoparticles
• Inter-particle distances

5. How best SERS substrates can be acquired?
Seeded Growth Mechanism
It involves two steps
1. Preparation of seeds of AgNP’s
2. Seeded growth of AgNp’s in larger NP’s

6. 1. Preparation of seeds of AgNP’s
• 0.2 mM AgNO3 + 0.2 mM I-2959 +1 mM trisodium citrate
• Irridiated for 5 min in Luzchem Photoreactor
• I-2959 releases α-hydroxy radical that is a strong reducing
agent.
• Reduces Ag+ Ag° (3.3nm)
• L-Ascorbic acid act as stabilizing agent

7. 2. Seeded growth of AgNP’s
• Again 0.2 mM AgNO3 +1 mM trisodium citrate
• Added seed AgNP’s with varied concentrations
• To these solns. 1mL of 10mM L-ascorbic acid is
added over a period of 10 min with syringe.
• For higher initial concentrations of seed AgNPs, smaller
size AgNP’s obtained.
• For lower initial concentrations of seed AgNPs,
larger size AgNP’s obtained.

8. Seeded growth Scheme
• Notably, it is the best protocol for the synthesis of
desired size of AgNP’s as SERS substrate.
• Any change in the above conditions will not produce
suitable SERS substrate.

9. 2. SEM analysis of AgNP’s
Particles represented in images a−d correspond to sizes of 20, 30, 40,
50, and 60nm respectively.

10. Raman spectra of p-Aminothiophenol
adsorbed on different sized AgNP’s