Electrochemical surface structuring with palladium nanoparticles for signal enhancement.

Surface nanostructuring with metal nanoparticles has gained importance because of the unique physicochemical properties of the nanoparticles. We have fabricated nanostructured surfaces on the basis of the sequential electrochemical deposition of palladium nanoparticles (Pd NPs) onto glassy carbon electrodes (GCEs). To increase the number density of the Pd NPs at the GC electrode surface, successive rounds of deposition/protection cycles were realized. Freshly deposited Pd NPs were immediately capped with 6-ferrocenylhexanethiol (Fc-C(6)SH) to prevent secondary nucleation processes from occurring during subsequent deposition rounds. This approach allowed us to maintain a narrow size distribution and, as such, the inherent properties of the deposited Pd NPs. Scanning electron microscopy (SEM) was used to confirm the successful deposition as well as to measure the size and spatial distribution of the deposited Pd NPs. SEM image analysis results showed that the number density of Pd NPs increased in each sequential deposition stage. The anodic peak current signal recorded for the electroactive SAM of Fc-C(6)SH following six consecutive deposition/protection cycles was found to be 75 times higher than that formed on a bulk palladium electrode. Finally, for comparison, gold NPs were deposited on GCEs following the same approach and exhibited considerably reduced signal enhancement properties as compared to the Pd NPs. The work presented here should find wide applicability for enhancing sensor signals by specifically structuring transducer surfaces on the nanoscale.