(Invited) Optics-Based Wearable Device for Real-Time Monitoring of Newborn Jaundice
Authors: Ota Hiroki 
Published: February 2020

Novelty
A wearable optical device for real-time monitoring of newborn jaundice was developed (Fig. 1). Jaundice is caused by the accumulation of bilirubin in an infant's blood. Bilirubin levels measured using the newly developed sensor were comparable to those measured using a commercial jaundice meter(R = 0.86). Real-time monitoring of the bilirubin level in infants is required because the level can change rapidly and affect their growth. The real-time monitor evaluates jaundice by calculating the ratio of the reflected light intensity between blue (470 nm) and green (570 nm) wavelengths. The data can be transferred conveniently to a smartphone. The ability of the newly developed sensor to measure bilirubin levels was comparable to that of a commercial jaundice device (R = 0.86), indicating the sensor could successfully evaluate jaundice. This wearable sensor is an important advance in the healthcare of infants, as it provides real-time monitoring of jaundice, one of the most important medical parameters in preliminary medical screening tests for newborns.

Background
The liver of an infant is immature, and its function must be monitored periodically. An important parameter indicating liver function is bilirubin, which is generated during the breakdown of hemoglobin. The immature liver of an infant cannot breakdown the generated bilirubin quickly enough. As a result, bilirubin accumulates in the skin tissue, resulting in jaundice. Without appropriate treatment, bilirubin is deposited into the brain, which can lead to brain damage. Moreover, permissible bilirubin levels are dependent on the baby’s age. Therefore, it is crucial to measure bilirubin levels continuously in newborns in order to discover symptoms of jaundice as early as possible.
Conventionally, bilirubin levels are measured using a blood sampling method[1] or an optical method[2]. The blood sampling method can measure bilirubin levels with high accuracy; however, this method is invasive. In light of this, the non-invasive optical method is more commonly used. However, even with the optical method, it is difficult to measure bilirubin levels continuously because conventional optical devices are large and burdensome to medical staff and infants. Furthermore, it is impossible for these two methods to detect a sudden change in the bilirubin level. The present study proposes the development of a wearable jaundice monitor that can be worn on the forehead of an infant and measure bilirubin levels in real time.
Device Fabrication and Experimental Results
As shown figure 1, the wearable optical jaundice sensor was miniaturized by using two light-emitting diodes (LEDs) of different wavelengths (blue and green) and four photodiodes (PDs)(Fig. 1b). The flexible polyimide substrate of the device fabricated by soft lithography enables conformal coverage of the electronic components on soft, curved surfaces of the skin(Fig. 1c). Transmitted light from the LEDs irradiates the skin surface, and reflected light is detected by the PDs. The sensor detects the difference in the intensity of the reflected blue and green light. In addition, a wireless function, using a Bluetooth wireless network and original smartphone/Tablet applications, permits real-time measurements. The blue light is highly associated with the concentration of bilirubin, compared to the green light. For measurements of the reflected blue and green light, the LEDs are alternately illuminated in 40 ms. Calculation of the bilirubin concentration from the differences in the intensities is based on the Beer-Lambert Law. In a preliminary experiment, the calculated ratio of reflected light intensities was associated with the value measured using a commercial jaundice meter (R = 0.86). The present work represents an important step towards safer, more advanced technologies for infant healthcare made possible by the Internet of Things.
Figure 1: Photograph of an actual wearable jaundice device. a. The package of the device is made of silicone rubber. b, c. Electrical components are mounted on flexible polyimide substrate. Optical sensing part is composed of four PDs, blue and green LEDs.

Figure 1