An Sub-Micron Double-Layer Capacitance of a Microwell Array for Biomolecular Sensing

Abstract

The interface between a solid and a liquid gives rise to the electric double layer (EDL) through the ion redistribution phenomenon. This effectively neutralizes the surface charges of the solid, and the relationship between the EDL and surface potential is crucial. Although surface potential can be a useful indicator of surface properties, measuring it using existing techniques like kelvin probe microscopy and electroosmotic mobility measurement is challenging as they are complex and difficult to implement as in-situ monitoring techniques.To address this demand, we used a vertical metal-oxide-metal microwells array to decrease the distance between electrodes and measure EDL capacitance changes induced by surface modifications. The device was fabricated using a layer-by-layer deposition method followed by photolithography and multiple dry etching steps. The diameter of well is around 3 um as SEM image shows. The distance between two electrodes could be scaled down to 100 nm by this method to achieve outstanding characteristics. Cyclic voltammetry was used to accurately estimate surface potential changes. Based on this method, the slope of charging current vs scan rate will be the EDLC.Next, we demonstrated its potential by detecting Avidin with excellent sensitivity. We applied APTES as the first layer on the sidewall of wells, then NHS-Biotin as the second layer to convert the amine group to an biotin group on the side wall surface. Finally we will immobilize the avidin. The capacitor has significant changed after introducing the avidin onto the sidewall of wells. And the concentration could be low to 100pg/mL for avidin sensing.Our innovative metrological architecture can be used in diverse biochemical applications to characterize surface-interfaces in real-time. Figure 1