A new approach is developed for the aqueous phase formation of flake-like and wire-like β-MnO₂ nanomaterials on a DNA scaffold at room temperature (RT) within a shorter time scale. The β-MnO₂ nanomaterials having a band gap energy ∼3.54 eV are synthesized by the reaction of Mn(II) salt with NaOH in the presence of DNA under continuous stirring. The eventual diameter of the MnO₂ particles in the wire-like and flake-like morphology and their nominal length can be tuned by changing the DNA to Mn(II) salt molar ratio and by controlling other reaction parameters. The synthesized β-MnO₂ nanomaterials exhibit pronounced catalytic activity in organic catalysis reaction for the spontaneous polymerization of aniline hydrochloride to emeraldine salt (polyaniline) at RT and act as a suitable electrode material in electrochemical supercapacitor applications. From the electrochemical experiment, it was observed that the β-MnO₂ nanomaterials showed different specific capacitance (C_s) values for the flake-like and wire-like structures. The C_s value of 112 F g⁻¹ at 5 mV s⁻¹ was observed for the flake-like structure, which is higher compared to that of the wire-like structure. The flake-like MnO₂ nanostructure exhibited an excellent long-term stability, retaining 81% of initial capacitance even after 4000 cycles, whereas for the wire-like MnO₂ nanostructure, capacitance decreased and the retention value was only 70% over 4000 cycles. In the future, the present approach can be extended for the formation of other oxide-based materials using DNA as a promising scaffold for different applications such as homogeneous and heterogeneous organic catalysis reactions, Li-ion battery materials or for the fabrication of other high performance energy storage devices.

The in situ formation of shape-selective silver nanoparticles (Ag NPs) in an aqueous solution has been demonstrated within one hour. Ag NPs were synthesized by the reduction of Ag(I) ions in the presence of a new reducing and stabilizing reagent, curcumin, under continuous stirring and heating at 80 °C. Different sizes and shapes of Ag NPs, such as small and large spheres, nanowires and anisotropic nanoflakes, are formed just by tuning the molar ratio of curcumin to Ag(I) ions and controlling the other reaction parameters. The mechanism of formation, the role of curcumin and other reaction parameters for the formation of shape-selective Ag NPs have been examined in detail. The different shaped Ag NPs have been successfully employed for the application in surface enhanced Raman spectroscopy (SERS) studies using methylene blue (MB) as a Raman probe. The shape effect of the NPs has been examined in detail and the corresponding SERS enhancement factor (EF) values have been calculated. The observed EF values are in the range ∼10⁶ to 10⁷. It was found that the anisotropic nanoflake structure has the highest EF compared to other shapes. The synthesis process is straightforward, simple, reproducible, cost-effective and robust. The synthesized Ag NPs are stable for more than two months while kept in a sealed bottle in the refrigerator. In the future, the present process might be helpful for the synthesis of other types of nanomaterials in a small time scale with higher yields. Moreover, the high EF value of the materials should be useful for trace detection of environmentally important biological species, DNA and RNA sequences or even in medical therapeutics.

A new route to the formation of ultra-small Os nanoparticles (NPs) in DNA is reported. The Os NPs that are initially formed are self-assembled together to form Os nanoclusters (NCs) which have wire-like and honeycomb-like morphologies. The synthesis was carried out within a minute using microwave heating by the reaction of Os salt with ethanol. The size of the individual Os NPs varies between 1 and 3 nm and the synthesized particles are stabilized in DNA. The stable Os NCs showed a coupled SPR band near 600 nm in the visible region, which is useful for using the material as a potential SERS substrate. The SERS study was carried out using methylene blue (MB) as a model SERS probe molecule and the observed EF value is ∼10⁷, which is much higher compared to a recent report for Os NPs. Apart from SERS, the Os NCs have also been tested in a catalysis reaction. The catalysis reaction was carried out for the first time for the reduction of organic nitro compounds in the presence of excess NaBH₄. The catalytic reaction rate using Os NCs as a catalyst was found to be superior compared to earlier reports with other metal NPs, like Au or Ag. The improved catalytic and SERS activities of the Os NCs due to their ultra-small size with a high surface area might be useful in future in the field of biosensors, biomedicine, nano devices and other organic catalysis reactions.