The aim of the present work is to explore the combination of atomic force electrochemical microscopy, operated in molecule touching mode (Mt/AFM-SECM), and of dense nanodot arrays, for designing an electrochemically addressable molecular nanoarray platform. A high density nanoarray of single grained gold nanodots (∼15 nm-diameter nanoparticles, 100 nm pitch) is decorated by a model molecular system, consisting of ferrocene (Fc) labeled polyethylene glycol (PEG) disulfide chains. We show that the high resolution of Mt/AFM-SECM enables the electrochemical interrogation of several hundreds of individual nanodots in a single image acquisition. As a result, the statistical dispersion of the nanodot molecular occupancy by Fc-PEG chains can be reliably quantified, evidencing that as little as a few tens of copies of redox-labeled macromolecules immobilized on individual nanodots can be detected. The electrochemical reactivity of individual nanodots can also be reliably sampled over a large population of nanodots. We evidence that the heterogeneous rate constant characterizing the electron transfer between the nanodots and the Fc heads displays some quantifiable variability but that the electron transfer remains in any case in the quasi-reversible regime. Overall, we demonstrate that Mt/AFM-SECM enables high throughput reading of dense nanoarrays, with a sensitivity and a read-out speed considerably higher than previously reported for scanning electrochemical microscopy (SECM) imaging of molecular microarrays.

The fabrication and electrochemical interrogation of very high density single-antibody nanoarrays is reported. Gold nanodots, 15 nm in diameter, arranged in large (cm 2 ) square arrays with a pitch of 200 nm, are used as carriers for primary antibodies (Immunoglobulin G, IgGs), further recognized by secondary redox-labeled detection antibodies. Ensemble scale interrogation of the antibody array by cyclic voltammetry, and nanoscale interrogation of individual nanodots by mediator tethered atomic-force electrochemical microscopy (Mt/AFM-SECM), enable the occupancy of nanodots by single antibody molecules to be demonstrated. Experiments involving the competitive adsorption of antibodies of different species onto the nanodots evidence the possibility of using single-antibody nanoarrays for digital electrochemical immunoassays.