DENSELY PACKED PALSMONIC NANOPARTICLE FILMS OF TUNABLE OPTICAL RESPONSE

Single step synthesis of plasmonic nanoparticle solutions with different capping agents through liquid phase pulsed laser ablation and irradiation

• Synthesis method: Liquid phase pulsed laser ablation (LPPLA)
• Potential applications: Synthesis of nanoparticles of different materials in pure solvents (both organic and inorganic) free from extraneous chemical species or varied concentration of different solutions. LPPLA-grown plasmonic nanoparticle colloids of desired capping of anionic and cationic nature, hold promise for photocatalytic and sensing applications.

Highlights:

• Typical concentration of gold nanoparticles (GNP) ~ 2 x 10¹² /ml, determined from numerical calculations based on Mie theory, for 30 min ablation of Au target in 10 mL water (Fig. 9).

Fig. 9 TEM image of gold nanoparticles prepared by LPPLA.



• The resultant negatively charged nanoparticles readily form aggregates with cationic dyes.
• Dye molecules showed significant life-time quenching in the presence of nanoparticles due to plasmon-mediated non-radiative energy transfer process (Fig. 10).

Fig. 10 (Left) Absorption spectra of GNP-Rh6G composites at different dye concentrations and (right) excited state decay profile of the dye without and with GNPs.

Publications: Shweta Verma, B.T. Rao, et al, Proc. International Symposium on Materials Chemistry, Dec. 2012, Mumbai.

Highlights:

• Silver nanoparticles grown in the presence of various surfactants exhibited continuous increase in absorbance with ablation time (observed for 30 minutes) (Fig. 11).
• Higher pH conditions favored high yield of SNPs in citrate medium.



Fig. 11 (Left) TEM image of SNPs grown in DI water and (right) efect of solution pH on absorption spectra of SNPs.



• A new approach of pulsed laser irradiation of metal salts solutions was exploited for the synthesis of mono and bimetallic nanoparticles with strong LSPR response (Fig. 12).



Fig. 12 Absorption spectra of laser irradiated silver and gold salt solutions mixed at varied concentrations.

Publications:

1. B. Tirumala Rao, Shweta Verma et al, Proc. DAE-BRNS National Laser Symposium-NLS 23, Dec. 3-6, 2014, Tirupati.
2. B.N. Singh, B.T. Rao et al, Proc. DAE BRNS 6th National Symposium on Pulsed Laser Deposition of Thin Films and Nanostructured Materials (PLD), Nov. 14-16, 2013, West Bengal.
3. Sonal Batham, Shweta Verma et al, Proc. DAE-BRNS National Laser Symposium-NLS 24, 2015, RRCAT, Indore.

Highlights:

• Nanosecond pulsed laser irradiation induced shape transformation of gold nanoparticles of different shapes is effective for desired shape of nanoparticles of a particular capping agents.
• Using thermo-plasmonic effect i.e. heating of nanoparticles by plasmon excitation by pulsed laser has been shown to be promising for tuneable plasmonic response of nanoparticles in various capping agents.
• Formation of gold nanoparticles of spherical shape in different capping agents (CTAB and CTAC) produced from gold nanorods (Fig. 13) and gold nanocubes (Fig. 14).



Fig. 13 TEM images of (a) gold nanorods and (b) gold nanospheres after laser irradiation and (c) variation of optical absobance with laser irradiation time.




Fig. 14 TEM images of (a) gold nanocubes and (b) gold nanospheres after laser irradiation and (c) variation of optical absobance with laser irradiation time.



• This study reveals production of multiple shape of nanoparticles in a particular chemical environment by controlling laser fluence, which may not be directly synthesized from chemical route.

Publications:

1. A. Hardel, B. Tirumala Rao et al, Proc. DAE-BRNS National Laser Symposium-NLS 24, 2015, RRCAT, Indore.
2. Ritika Agrawal, Shweta verma et al, Proc. DAE-BRNS National Laser Symposium-NLS 26, 2017, BARC, Mumbai.

Highlights:

• Light based synthesis of Ag nanoparticles of broad wavelength plasmon response.
• Single reagent citrate produced both spherical and triangular shape nanoparticles.
• Nanoparticle concentration control in wide range of citrate concentrations (Fig. 15).



Fig. 15 Effect of citrate concentration on growth of Ag nanoparticles in LPPLA.



• Role of citrate concentration, pH and Ag+ ions on nanoplates formation was studied.
• Laser produced highly stable Ag nanoparticles are efficient seeds for nanoplates (Fig. 16).



Fig. 16 Effect of light irradiation on growth of Ag triangular nanoparticles from LPPLA grown spherical nanoparticles.

Publications:Shweta Verma, B.T. Rao et al. Colloids and Surfaces A, 527, 2017, 23-33.

Highlights:

• Concentration dependent strong interaction in GNPs and Rh6G composites.
• The dye induced aggregation of nanoparticles was strongly affected by the GNPs dilutions.



Fig. 17 (L-R) Absorption spectra of GNP-dye composites, TEM image of the composite with 1 and 10 μM concentration of dye showing varied size aggregates.



• Significant dye fluorescence quenching occurred at low (< 5 μM) dye concentrations with non-linear Stem-Volmer plots (Fig. 18).



Fig. 18 (Left) Fluorescence intensity spectra with Stern-Volmer plot (inset) and (right) time resolved fluorescence spectra of dye-GNP composites. Arrow show increasing GNP concentration.

Publications:Shweta Verma, B.T. Rao et al., Journal of Luminescence, 155, 2014, 156 - 164.

Highlights:

• Gold nanoparticles of spherical, rod and cubic shapes (Fig. 19) with varied sizes exhibiting strong plasmon resonance in 500 - 900 nm wavelength region have been prepared for SERS application.
• Silver nanoparticles of spherical, triangular and disk shapes with varied sizes exhibiting strong plasmon resonance in 400 - 900 nm wavelength region
• These gold and silver nanoparticles have important applications in colorimetric sensors, SERS substrates, enhanced spectroscopy imaging techniques, environmental monitoring and control, thermo-plasmonics, etc.

Fig. 19 Electron microscope images of gold nanoparticles of different shapes

Publications:Shweta Verma, B. Tirumala Rao et al, Proc. DAE-BRNS National Laser Symposium-NLS 25, 2016, KIIT Bhubaneswar, Odisha.