Prussian Blue-based microsensors in short-circuit mode: a simplified approach for localized hydrogen peroxide...

We report on a Prussian Blue (PB)-based microsensor with an integrated silver quasi-reference electrode (QRE) for selective hydrogen peroxide (H₂O₂) reduction using the excellent electrocatalytic properties of PB in a so-called short-circuit mode. This "single-electrode" configuration eliminates the need for a potentiostat allowing a simplified read-out. The microsensors are either based on PB or on PB-nickel hexacyanoferrate (PB-NiHCF) and demonstrate high sensitivity (1.8 A M^-1 cm^-2 and 0.32 A M^-1 cm^-2 for PB-based and PB-NiHCF-based microsensors, respectively), operational stability (maintaining performance for 4 h under harsh conditions in 1 mM H₂O₂), and selectivity toward H₂O₂ with negligible interference from common reductants such as ascorbic acid and catecholamines. By incorporating a platinum-black (Pt-B) sublayer, the PB film deposition could be significantly improved, yielding a threefold sensitivity increase and a 14-fold enhancement in operational stability. The microsensors were successfully applied as probes for scanning electrochemical microscopy (SECM) measurements to map H₂O₂ evolution. Furthermore, by modification of the PB-modified Pt microelectrode (ME) with glucose oxidase (GOx) and hexokinase (HEX), an adenosine triphosphate (ATP) microbiosensor was developed and applied for extracellular ATP release detection. The ATP determination relies on the competitive GOx- and HEX-catalyzed reactions for glucose. These results highlight the potential of PB-based MEs in short-circuit mode for localized electrochemical studies of not only catalytic systems where monitoring H₂O₂ concentration is of primary interest, but also various biological systems, such as living cells, where H₂O₂ is generated as a byproduct of enzymatic reactions.