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 H 2 O 2 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 H 2 O 2 electrooxidation and electroreduction, along with the determination of toxic, hazardous compounds and drugs.

No abstract

In this work, we report the synthesis and characterization of a bimetallic Prussian blue analogue containing Co and Mn as outer-sphere metals (CoMnHCF). The material was a solid solution and its characterization revealed a chemical composition of Co 2.05 Mn 0.95 [Fe(CN) 6 ] 2 · 12H 2 O. The electrochemistry of this novel material showed the existence of two redox waves displaying quasi-reversible kinetics, as expressed by the larger peak-to-peak separation upon increasing the potential sweep rate. Interestingly, the CoMnHCF solid exhibited high electrocatalytic activity for the oxidation of hydrogen peroxide, thus representing an appealing scaffold for the construction of biosensors. As a proof of concept, cholesterol oxidase was immobilized at the electrode surface by using a sol-gel method, and the cyclic voltammograms were recorded at increasing concentrations of cholesterol. The biosensor showed a detection limit of 30 μM and two linear ranges with excellent sensitivity of 385 mA cm À 2 M À 1 between 50 and 150 μM, and an adequate sensitivity of 80 mA cm À 2 M À 1 between 150 and 1 mM. To the best of our knowledge, this is the first biosensor application of a pre-synthesized bimetallic hexacyanometallate, thus exploiting its potential as an H 2 O 2 electrooxidation catalyst.

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.

No abstract