Ratiometric Bioluminescent Indicator for Simple and Rapid Diagnosis of Bilirubin

Bilirubin in human blood is highly important as a general index of one's physical condition because its concentration changes under the influence of several diseases. In particular, in newborns, jaundice is one of the most common diseases involving unconjugated bilirubin (UCBR), causing serious symptoms such as nuclear jaundice and deafness. Therefore, a frequent measurement of the UCBR levels in the blood is important. Here, we report a ratiometric bioluminescent indicator, BABI (bilirubin assessment with a bioluminescent indicator), that changes the emission color from blue to green depending on the UCBR concentration in a sample. Owing to the use of a bioluminescence signal that has a higher signal-to-noise ratio than the absorption and fluorescence signal, BABI enables highly sensitive and quantitative detection of UCBR for small blood samples using a smartphone camera. The establishment of a UCBR measurement assay using BABI provides the possibility of a simple and rapid method for blood-based diagnosis using bioluminescent indicators and a versatile mobile device.