Improving Orientation, Packing Density, and Molecular Arrangement in Self-Assembled Monolayers of Bianchoring Ferrocene-Triazole Derivatives by "Click" Chemistry

Origins of non-ideal behaviour in voltammetric analysis of redox-active monolayers

Disorder in redox-active monolayers convolutes electrochemical characterization. This disorder can come from pinhole defects, loose packing, heterogeneous distribution of redox-active headgroups, and lateral interactions between immobilized redox-active molecules. Identifying the source of non-ideal behaviour in cyclic voltammograms can be challenging as different types of disorder often cause similar non-ideal cyclic voltammetry behaviour such as peak broadening, large peak-to-peak separation, peak asymmetry and multiple peaks for single redox processes. This Review provides an overview of ideal voltammetric behaviour for redox-active monolayers, common manifestations of disorder on voltammetric responses, common experimental parameters that can be varied to interrogate sources of disorder, and finally, examples of different types of disorder and how they impact electrochemical responses.

A trivalent aptasensor by using DNA tetrahedron as scaffold for label-free determination of antibiotics

Owing to advantage in high sensitivity and fast response, aptamer based electrochemical biosensors have attracted much more attention. However, inappropriate interfacial engineering strategy leads to poor recognition performance, which ascribe to the following factors of immobilized oligonucleotide strand including steric hindrance, interchain entanglement, and unfavorable conformation. In this work, we proposed a DNA tetrahedron based diblock aptamer immobilized strategy for the construction of label-free electrochemical biosensor. The diblock aptamer sequence is composite of T-rich anchor domain and recognition domain, where T-rich domain enabling anchored on the edge of DNA tetrahedron via Hoogsteen hydrogen bond at neutral condition. The DNA tetrahedron scaffold offers an appropriate lateral space for target recognition of diblock aptamer. More importantly, this trivalent aptamer recognition interface can be regenerated by simply adjusting the pH environment to alkaline, resulting in the dissociation of diblock aptamer. Under the optimum condition, proposed electrochemical aptasensor manifested a satisfied sensitivity for aminoglycosides antibiotic, kanamycin with a limit of detection of 0.69 nM, which is 45-fold lower than traditional Au-S immobilization strategy. Moreover, the proposed aptasensor had also successfully been extended to ampicillin detection by changing the sequence of recognition domain in diblock aptamer. This work paves a new way for the rational design of aptamer-based electrochemical sensor.

Non-Covalent Interactions Mimic the Covalent: An Electrode-Orthogonal Self-Assembled Layer

Charge-transfer events central to energy conversion and storage and molecular sensing occur at electrified interfaces. Synthetic control over the interface is traditionally accessed through electrode-specific covalent tethering of molecules. Covalent linkages inherently limit the scope and the potential stability window of molecularly tunable electrodes. Here, we report a synthetic strategy that is agnostic to the electrode's surface chemistry to molecularly define electrified interfaces. We append ferrocene redox reporters to amphiphiles, utilizing non-covalent electrostatic and van der Waals interactions to prepare a self-assembled layer stable over a 2.9 V range. The layer's voltammetric response and in situ infrared spectra mimic those reported for analogous covalently bound ferrocene. This design is electrode-orthogonal; layer self-assembly is reversible and independent of the underlying electrode material's surface chemistry. We demonstrate that the design can be utilized across a wide range of electrode material classes (transition metal, carbon, carbon composites) and morphologies (nanostructured, planar). Merging atomically precise organic synthesis of amphiphiles with in situ non-covalent self-assembly at polarized electrodes, our work sets the stage for predictive and non-fouling synthetic control over electrified interfaces.