Donnan potential caused by polyelectrolyte monolayers

Redox Polyelectrolytes with pH-Sensitive Electroactive Functionality in Aqueous Media

A framework of ferrocene-containing polymers bearing adjustable pH- and redox-active properties in aqueous electrolyte environments was developed. The electroactive metallopolymers were designed to possess enhanced hydrophilicity compared to the vinylferrocene (VFc) homopolymer, poly(vinylferrocene) (PVFc), by virtue of the comonomer incorporated into the macromolecule, and could also be prepared as conductive nanoporous carbon nanotube (CNT) composites that offered a variety of different redox potentials spanning a ca. 300 mV range. The presence of charged non-redox-active moieties such as methacrylate (MA) in the polymeric structure endowed it with acid dissociation properties that interacted synergistically with the redox activity of the ferrocene moieties to impart pH-dependent electrochemical behavior to the overall polymer, which was subsequently studied and compared to several Nernstian relationships in both homogeneous and heterogeneous configurations. This zwitterionic characteristic was leveraged for the enhanced electrochemical separation of several transition metal oxyanions using a P(VFc_0.63-co-MA_0.37)-CNT polyelectrolyte electrode, which yielded an almost twofold preference for chromium as hydrogen chromate versus its chromate form, and also exemplified the electrochemically mediated and innately reversible nature of the separation process through the capture and release of vanadium oxyanions. These investigations into pH-sensitive redox-active materials provide insight for future developments in stimuli-responsive molecular recognition, with extendibility to areas such as electrochemical sensing and selective separation for water purification.

Synthesis of a CuNP/chitosan/black phosphorus nanocomposite for non-enzymatic hydrogen peroxide sensing

A copper-chitosan-black phosphorus nanocomposite (CuNPs-Chit-BP) was fabricated by electrochemically depositing copper nanoparticles onto a black phosphorus-modified glassy carbon electrode in chitosan solution. CuNPs demonstrated a uniform distribution on the Chit-BP modified GCE with an average size of 20 nm. Electrochemical methods were used to study the catalytic activity of the CuNPs-Chit-BP nanocomposite toward hydrogen peroxide. The results showed that the synthesized nanocomposite exhibited excellent electrical conductivity, good biocompatibility and highly efficient electrocatalytic activity toward hydrogen peroxide reduction in the range of 10 μM-10.3 mM with a detection limit of 0.390 μM. The present work proposed a new strategy to explore novel BP-based non-enzymatic biosensing platforms.

Binary Thiolate DNA/Ferrocenyl Self-Assembled Monolayers on Gold: A Versatile Platform for Probing Biosensing Interfaces

The properties of DNA self-assembled monolayers (SAMs) have strong influences on the interfacial DNA-analyte binding behavior, which further affect the performance of biosensors built upon. In this work, we prepared binary thiolate DNA/6-ferrocenyl-1-hexanethiol (FcC6SH) SAMs on gold (DNA/FcC6S-Au) for convenient electrochemical characterization and subsequent data analysis. Our cyclic voltammetric (CV) studies confirmed that the redox responses of surface-tethered Fc and electrostatically bound [Ru(NH₃)₆]³⁺ are capable of providing quantitative information regarding the DNA film properties, including the surface density, structural heterogeneity, and molecular orientation under different preparation and measurement conditions. With the binary thiolate DNA/FcC6S-Au SAM prepared in the conventional post-assembly exchange protocol as a trial system, we are demonstrating the capability of introducing redox-active thiols as passivating and labeling reagents for preparing many other DNA-based biosensing interfaces via varied assembly steps and under different measurement conditions.

Self-assembly of catecholic ferrocene and electrochemical behavior of its monolayer

The self-assembly of novel catecholic ferrocene and electrochemical behavior of its monolayer are reported.