1.Facile tuning of plasmon bands in hollow silver nanoshells using mild reductant and mild stabilizer.
Pattanayak S1, Priyam A, Paik P. Dalton Trans. 2013 Aug 7;42(29):10597-607. doi: 10.1039/c3dt50684c. Epub 2013 Jun 13.
Hollow silver nanoshells with tunable plasmon bands have been synthesized using Ag2O nanoparticles at an optimized temperature of 20 °C. The plasmon peak has been tuned in a wide range from 460 nm to 605 nm employing a combination of mild reductant and a mild stabilizer, hydrazine hydrate and sodium citrate, respectively. In contrast, the combination of strong reductant and strong stabilizer, NaBH4 and hydrophilic thiols, resulted in limited plasmon tunability (455-510 nm). The differential behaviour is attributed to the change in dynamics of the diffusion-reaction process. For thiols, the effect of free end-groups was quite evident as plasmon peak shifted from 449 nm to 470 nm on replacing thioglycolic acid (HS-CH2-COOH) with mercaptoethanol (HS-CH2-CH2-OH). Transmission electron microscopy (TEM) revealed that the aspect ratio [outer diameter (d)/shell thickness (t)] was 2.8 (d: 40.0 ± 1.6 nm, t: 14.0 ± 1.3 nm) and 5 (d: 84 ± 2.3 nm, t: 16.
2.Citrate-hydrazine hydrogen-bonding driven single-step synthesis of tunable near-IR plasmonic, anisotropic silver nanocrystals: implications for SERS spectroscopy of inorganic oxoanions.
Pattanayak S1, Swarnkar A, Priyam A, Bhalerao GM. Dalton Trans. 2014 Aug 21;43(31):11826-33. doi: 10.1039/c4dt01091d.
A simplified, single-step aqueous synthesis route to tunable anisotropic silver nanocrystals (NCs) has been developed by tailoring the hydrogen-bonding interactions between a mild stabilizer, sodium citrate, and a mild reductant, hydrazine hydrate. The structure directing ability of the H-bonding interaction was harnessed by keeping a stoichiometric excess of hydrazine under ambient conditions (pH 7, 25 °C). Decreasing the synthesis temperature to 5 °C imparts rigidity to the citrate-hydrazine H-bonding network, and the plasmon peak moves from 500 to 550 nm (using 40 mM hydrazine). On lowering the pH from 7 to 5, the H-bonding is further strengthened due to partial protonation of citrate and the plasmon peak is tuned to 790 nm. Further, we found that, at 5 °C and pH 5, there also exists a sub-stoichiometric regime in which maximum tunability of the plasmon peak (790→1010 nm) is achieved with 1 mM hydrazine. HR-TEM reveals that the near-IR plasmonic NCs are nanopyramids having a pentagonal base with edge length varying from 15 nm to 30 nm.
3.Synthesis and antibacterial activity of silver nanoparticles against gram-positive and gram-negative bacteria.
Guzman M1, Dille J, Godet S. Nanomedicine. 2012 Jan;8(1):37-45. doi: 10.1016/j.nano.2011.05.007. Epub 2011 Jun 2.
Synthesis of nanosized particles with antibacterial properties is of great interest in the development of new pharmaceutical products. Silver nanoparticles (Ag NPs) are known to have inhibitory and bactericidal effects. In this article we present the synthesis of Ag NPs prepared by chemical reduction from aqueous solutions of silver nitrate, containing a mixture of hydrazine hydrate and sodium citrate as reductants and sodium dodecyl sulfate as a stabilizer. The results of the characterization of the Ag NPs show agglomerates of grains with a narrow size distribution (from 40 to 60 nm), whereas the radii of the individual particles are between 10 and 20 nm. Finally, the antibacterial activity was measured by the Kirby-Bauer method. The results showed reasonable bactericidal activity against Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus. The standard dilution micromethod, determining the minimum inhibitory concentration leading to inhibition of bacterial growth, is still under way.