Prussian blue and its analogs (PBA) form an attractive family of materials for sensing and biosensing applications. Due to their open framework structure their electrochemical behavior is closely linked to the intercalation of alkaline ions. Moreover, these compounds show a clear peroxidase activity that makes them excellent transducers in biosensors based on H₂O₂ quantification. In this review, we present in a progressive manner an overview of the structure, composition, and synthesis of PBA. Subsequently we approach the current trends in the use of PBA in the field of electrochemical sensors, providing a critical discussion on their electrochemical behavior and the electrocatalytic activity toward H₂O₂ electrooxidation and electroreduction, along with the determination of toxic, hazardous compounds and drugs.

Enzyme-based electrochemical sensors are important tools for the detection of numerous analytes of biological origin. The immobilization of enzymes onto electrodes is a critical step during the fabrication of these devices. Herein, we report the fabrication of glutamate dehydrogenase (GDH)-based biosensors using two different strategies, and the effect of the immobilization method on the performances of obtained bioelectrodes. The first method consisted in cross-linking GDH on the surface of electrodes with glutaraldehyde. The as obtained biosensors presented numerous drawbacks including (i) the complete loss of enzyme selectivity, and (ii) the impossibility to reutilize the bioelectrode for sensing. As an alternative fabrication protocol, GDH was entrapped within a SOL-GEL matrix formed on the surface of electrodes. With this immobilization method the enzyme's specificity was preserved, and the biosensor displayed fast and reproducible electrochemical signals. With this study we raise the attention on the fact that the well-established glutaraldehyde-based cross-linking method can result an aggressive immobilization approach that may harm enzyme specificity, in contrast to the milder SOL-GEL entrapment.

The disruption of iron homeostasis is an important factor in the loss of mitochondrial function in neural cells, leading to neurodegeneration. Here, we assessed the protective action of gossypitrin (Gos), a naturally occurring flavonoid, on iron-induced neuronal cell damage using mouse hippocampal HT-22 cells and mitochondria isolated from rat brains. Gos was able to rescue HT22 cells from the damage induced by 100 µM Fe(II)-citrate (EC₅₀ 8.6 µM). This protection was linked to the prevention of both iron-induced mitochondrial membrane potential dissipation and ATP depletion. In isolated mitochondria, Gos (50 µM) elicited an almost complete protection against iron-induced mitochondrial swelling, the loss of mitochondrial transmembrane potential and ATP depletion. Gos also prevented Fe(II)-citrate-induced mitochondrial lipid peroxidation with an IC₅₀ value (12.45 µM) that was about nine time lower than that for the tert-butylhydroperoxide-induced oxidation. Furthermore, the flavonoid was effective in inhibiting the degradation of both 15 and 1.5 mM 2-deoxyribose. It also decreased Fe(II) concentration with time, while increasing O₂ consumption rate, and impairing the reduction of Fe(III) by ascorbate. Gos–Fe(II) complexes were detected by UV-VIS and IR spectroscopies, with an apparent Gos-iron stoichiometry of 2:1. Results suggest that Gos does not generally act as a classical antioxidant, but it directly affects iron, by maintaining it in its ferric form after stimulating Fe(II) oxidation. Metal ions would therefore be unable to participate in a Fenton-type reaction and the lipid peroxidation propagation phase. Hence, Gos could be used to treat neuronal diseases associated with iron-induced oxidative stress and mitochondrial damage.