Journal Article

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

Macchia, Eleonora, Ditaranto, Nicoletta, Khaliq, Aniqa, Sarcina, Lucia, Torsi, Luisa, Di Franco, Cinzia, Scamarcio, Gaetano

2023

Overview

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. A few antigen–antibody bindings generate an extended work function shift, assessed by Kelvin probe atomic force microscopy (AFM), in a large‐area biofunctionalized Au‐surface covered by 108 antibodies. This striking result compares with the threshold voltage shift measured by electrolyte‐gated single‐molecule transistor sensors and demonstrates that an amplification mechanism of the electrostatic change triggered by a few affinity binding events works even on a barely physisorbed biolayer.

• Publisher: John Wiley & Sons, Inc,Wiley-VCH
• Subject: Antibodies / Antigens / atomic force microscopy / Binding / biofunctionalized surfaces / Electrodes / electrolyte gated transistors / Interfaces / Kelvin probe force microscopy / Microscopy / Saline solutions / surface potential imaging single‐molecule sensors / Threshold voltage / Transistors / Work functions