Effects of self-assembled monolayers on amperometric glucose biosensors based on an organic–inorganic hybrid system

Ultrathin-form amperometric glucose biosensors have been fabricated on gold substrates by using self-assembled monolayers (SAMs) of carboxylic acid groups (COOH). The glucose oxidase (GOx) was covalently immobilized on the SAMs and covered with Langmuir–Blodgett films including nanometer-sized clusters of Prussian Blue (PB) playing a role of mediator for glucose detection, which makes the present sensor, Au/SAM/GOx/PB, work at very low potentials of approximately 0.0 V vs. Ag/AgCl. An amperometric biosensor comprising a SAM of 4-mercaptobenzoic acid (MBA) exhibited a fast response current of 3 s, a detection limit of 12.5 μM, a high sensitivity of 50 nA/(cm2 mM), and a long-term stable linearity ranging from12.5 μM to 70 mM. The sensitivity is significantly affected by the conductivity of the SAM layer. The analysis of the electron transfer confirmed a high conductive nature of MBA among carboxylic acid groups. The obtained linearity in a high-concentration region is attributed to both the ultrathin nature and high electron transfer of the MBA SAM.