| Abstract: | In emergency medicine, blood lactate levels are commonly measured to assess the severity and response to treatment of hypoperfusion‐related diseases (e.g., sepsis, trauma, cardiac arrest). Clinical blood lactate testing is conducted with laboratory analyzers, leading to a delay of 3 h between triage and lactate result. Here, a fluorescence‐based blood lactate assay, which can be utilized for bedside testing, based on measuring the hydrogen peroxide generated by the enzymatic oxidation of lactate is described. To establish a hydrogen peroxide assay, near‐infrared cyanine derivatives are screened and sulfo‐cyanine 7 is identified as a new horseradish peroxidase (HRP) substrate, which loses its fluorescence in presence of HRP and hydrogen peroxide. As hydrogen peroxide is rapidly cleared by erythrocytic catalase and glutathione peroxidase, sulfo‐cyanine 7, HRP, and lactate oxidase are encapsulated in a liposomal reaction compartment. In lactate‐spiked bovine whole blood, the newly developed lactate assay exhibits a linear response in a clinically relevant range after 10 min. Substituting lactate oxidase with glucose and alcohol oxidase allows for blood glucose, ethanol, and methanol biosensing, respectively. This easy‐to‐use, rapid, and versatile assay may be useful for the quantification of a variety of enzymatically oxidizable metabolites, drugs, and toxic substances in blood and potentially other biological fluids. |
