Extended Work Function Shift of Large-Area Biofunctionalized Surfaces Triggered by a Few Single-Molecule Affinity Binding Events

Few binding events are here shown to elicit an extended work function change in a large-area Au-surface biofunctionalized with ≈10⁸ capturing antibodies. This is demonstrated by Kelvin probe force microscopy (KPFM), imaging a ≈10⁵ µm² wide Au-electrodes covered by a dense layer (≈10⁴ µm⁻²) of physisorbed anti-immunoglobulin-M (anti-IgM). A 10 min incubation in 100 µL phosphate buffer saline solution encompassing ≈10 IgM antigens (10⁻¹⁹ mole L⁻¹ ≡ 10² × 10⁻²¹ m) produces a work function shift ΔW ≈ –60 meV. KPFM images prove that this shift involves the whole inspected area. Notably, no work function change occurs upon incubation in highly concentrated (3 × 10⁻¹⁵ m) nonbinding IgG solutions. The ΔW measured by KPFM is in quantitative agreement with the threshold voltage shift of an electrolyte-gated single-molecule large-area transistor (SiMoT). The findings provide direct experimental evidence for the SiMoT ultrahigh sensitivity, by imaging the extensive shift of the gate work function, likely arising from collective surface phenomena, elicited by single-molecule binding events.