Abstract
Electrochemical biosensors have potential applications for agriculture, food safety, environmental monitoring, sports medicine, biomedicine, and other fields. One of the primary challenges in this field is the immobilization of biomolecular probes atop a solid substrate material with adequate stability, storage lifetime, and reproducibility. This review summarizes the current state of the art for covalent bonding of biomolecules onto solid substrate materials. Early research focused on the use of Au electrodes, with immobilization of biomolecules through ω-functionalized Au-thiol self-assembled monolayers (SAMs), but stability is usually inadequate due to the weak Au–S bond strength. Other noble substrates such as C, Pt, and Si have also been studied. While their nobility has the advantage of ensuring biocompatibility, it also has the disadvantage of making them relatively unreactive towards covalent bond formation. With the exception of Sn-doped In2O3 (indium tin oxide, ITO), most metal oxides are not electrically conductive enough for use within electrochemical biosensors. Recent research has focused on transition metal dichalcogenides (TMDs) such as MoS2 and on electrically conductive polymers such as polyaniline, polypyrrole, and polythiophene. In addition, the deposition of functionalized thin films from aryldiazonium cations has attracted significant attention as a substrate-independent method for biofunctionalization.
Highlights
The first electrochemical biosensors employed Au-thiol self-assembled monolayers (SAMs) created from linker molecules ω-functionalized with reactive groups that can form covalent bonds to biomolecules
Au-thiol chemistry is fundamentally limited by the weak Au–S bond strength, suggesting that this approach is only useful for applications in which the sensor interface is used immediately, or for fundamental studies of biomolecules at interfaces
The use of multidentate thiols increases the number of Au–S bonds, in most cases the formation of a semi-crystalline 2D
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. According to IUPAC, a biosensor is “a device that uses specific biochemical reactions mediated by isolated enzymes, immunosystems, tissues, organelles or whole cells to detect chemical compounds usually by electrical, thermal or optical signals [1]”. This definition is often assumed to include acoustic signal transduction. One important limiting factor for electrochemical biosensors that bridges practical and scientific challenges is the stability, storage lifetime, reproducibility, and reusability of biomolecules attached to an electrically conductive substrate material, which is the topic of this review.
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