Miniaturization of oxygen and enzyme sensors for blood gas analyzers using highly crystalline graphene electrodes

The growing demand for point-of-care testing technologies has accelerated the development of rapid diagnostics that can be used outside clinical settings. Blood gas analyzers, commonly used in emergency care, assess respiratory and metabolic status using arterial blood. They provide real-time information on oxygenation (pO2), ventilation (pCO2), and acid-base balance. Modern systems also measure concentrations of electrolytes (e.g., Na+, K+, Ca2+, and Cl−), glucose, and lactate. As the range of analytes increases and healthcare increasingly shifts toward home and decentralized settings, there is a growing need for miniaturized, low-cost, and reliable electrochemical sensors. However, miniaturization is hindered by key technical issues, including the lack of stable reference electrodes and interference issues in enzymatic glucose sensors that require complex structures and expensive Pt electrodes. We introduce graphene-coated porous silica spheres loaded with Prussian-blue (PB/G/PSS) as a versatile material platform to solve these problems. Because of the extremely low solubility of PB, PB/G/PSS serves as a stable and reliable reference electrode for miniaturized oxygen sensors. In addition, the unique electrochemical activity of Prussian blue, with a hydrogen peroxide reduction potential positioned between the oxidation potential of ascorbic acid and the reduction potential of oxygen, enables PB/G/PSS to function effectively as a working electrode even in the presence of interfering species.