Shape-controlled growth of surface-confined Au nanostructures for electroanalytical applications

We describe the growth of raspberry-like Au nanostructures by surface-confined seed-mediated growth approach at room temperature without using any polymer/surfactant or templates and their electroanalytical applications towards the enzyme-free sensing of glucose and detection of ultratrace amount of toxic Cr(VI). The growth of Au nanostructures involves the initial deposition of Au nanoseeds on a conducting support and the further growth of the seeds by chemical route using a growth solution containing hydroxylamine, potassium iodide and HAuCl4. Raspberry-like nanoparticles with an average size of 370 nm was obtained at low concentration of iodide ions (10 μM) whereas quasispherical nanoparticles with an average size of 220 nm was obtained at high concentration (>100 μM). The preferential adsorption of iodide ions on (1 1 1) plane inhibits the growth of nanoparticles in (1 1 1) direction. The raspberry-like nanoparticles has significantly high electrochemically accessible surface area of 0.29 cm2 with respect to the other nanoparticles. The raspberry-like nanoparticles has excellent catalytic activity towards oxidation of glucose and reduction of Cr(VI). High sensitivity and wide linear response (0.5–12 mM) towards glucose have been achieved in neutral pH without additional mediators or enzymes. The electrochemical detection of Cr(VI) was performed in acidic condition and the nanoparticle-based electrode could detect Cr(VI) at parts-per-billion level. The electrode is highly stable and can be used for repeated measurements without compromising the sensitivity and detection limit. The electrocatalytic performance of raspberry-like nanoparticles is significantly higher than the other nanoparticles. The surface morphology/structure and the particle coverage control the electrocatalytic performance of the particles.