The red blood cell waveguide has been successfully assembled and worked in zebrafish blood vessels, its light transmission mode is sensitive to the surrounding environment and related to the erythropoietin morphology, and the red blood cell morphology depends on the pH of the blood, so the red blood cell waveguide can be used for the body’s acidity sensing, detection of blood diseases caused by acidity and alkalinity, and measurable pH of 5.0 to 9.0. This evidence concerns the gene EPO and blood disease.