This article is intended as an overview of bismuth-based electrodes as applied to electrochemical stripping analysis. These electrodes rely on a bismuth or bismuth-modified active surface and, while they have analytical performance comparable to mercury electrodes, are characterized by negligible toxicity in comparison to their mercury counterparts. These properties make them ideally suited as sensors for trace monitoring by electrochemical stripping analysis. Topics covered in this review are the main types of bismuth electrodes and their fabrication, the analytical characteristics and common interferences of bismuth-based electrodes in stripping analysis and typical applications of these sensors in industrial, food, clinical and environmental analysis by stripping techniques. Finally, the future prospects of bismuth electrodes in conjunction with stripping analysis are critically discussed.

Flexible biosensors represent an increasingly important and rapidly developing field of research.

We recently discovered that a Ca²⁺ two-dimensional framework, namely [Ca(H₄L)(DMA)₂]·2DMA (Ca-MOF), was capable of exchanging the Ca²⁺ ions with Cu²⁺ almost quantitatively in a matter of seconds in aqueous solution. Herein, we report that Ca-MOF exhibits the capability of both removal and voltammetric determination of heavy metal ions in aqueous media. Ca-MOF shows one of the highest Pb²⁺ sorption capacities (∼522 mg g⁻¹) reported for MOFs. More importantly, a column filled with Ca-MOF (1% wt) particles dispersed in silica sand (99% wt) can quantitatively remove traces of Pb²⁺ (∼100 ppb) from a relatively large volume of a wastewater simulant solution (containing a large excess of competitive ions). Ca-MOF is also highly efficient for sorption of Cd²⁺, Ni²⁺ and Zn²⁺, even in the presence of several competitive cations. Actually, the Cd²⁺ sorption capacity (∼220 mg g⁻¹) of Ca-MOF is one of the largest reported for MOFs. Furthermore, detailed Ni²⁺ and Zn²⁺ sorption studies of MOFs have not been described prior to this work. The mechanism of the M²⁺ (M²⁺ = Pb²⁺, Cd²⁺, Ni²⁺, Zn²⁺) exchange process was elucidated based on a series of spectroscopic, analytical and X-ray diffraction methods. In addition, a simple ready-to-use electrochemical sensor based on modified graphite paste with Ca-MOF was fabricated and successfully utilized for the determination of Pb²⁺, Cd²⁺, Cu²⁺ and Zn²⁺ at μg L⁻¹ levels in aqueous solutions by anodic stripping voltammetry (ASV). Overall, this work demonstrates, for the first time, a dual function of a MOF as a sorbent and as an electrochemical sensor for heavy metal ions, thus opening a new window for materials with application in both environmental remediation and monitoring.