Prompt synthesis of iridium organosol on DNA for catalysis and SERS applications

Abstract

Herein, self-assembled Ir and IrO₂ nanoparticles (NPs) were synthesized on DNA scaffolds for the first time in an organic medium using microwave irradiation just for 30 s. By tuning the DNA to Ir³⁺ molar ratio, stable colloidal Ir and IrO₂ NP solutions were obtained in ethanol via reduction with tetrabutylammonium borohydride (TBABH₄). The same procedure was executed without DNA to obtain discrete Ir NPs and with DNA (of different Ir³⁺:DNA molar ratio) for getting chain-like nano-assemblies of IrO₂ NPs. The average diameter of the Ir-assembled DNA chains was 40 ± 10 nm, and the average particle size was 3.3 ± 0.5 nm. The synthesized Ir NP@DNA was applied in two different applications: catalysis and surface enhanced Raman scattering (SERS). The catalytic study was conducted for the reduction of various nitro compounds. Ir NP@DNA showed better catalytic activity and recyclability (5–14 times) than Ir NPs obtained without DNA scaffolds. Ir NP@DNA and Ir NPs without DNA were applied to the SERS study by taking methylene blue (MB) dye as a Raman probe molecule. An enhancement factor (EF) value of 8 × 10⁵ for Ir NP@DNA was observed, which was much better than that obtained for our synthesized un-stabilized Ir NPs (1.07 × 10⁵) and other reported Ir NPs. The synthesized Ir NP@DNA and IrO₂ NP@DNA were extremely stable for more than 3 months, whereas the Ir NPs synthesized without DNA were not. These stable colloidal solutions were readily re-dispersed in many organic solvents (protic and nonprotic) and could be employed for other potential organic catalysis reactions.