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Scientists have developed a novel optical fibre-based sensor that can detect and degrade 1 bilirubin, a pigment that builds up abnormally in blood and tissues of jaundice-afflicted newborns

and adults. The sensor, which works when placed on the skin, could be a helpful tool in diagnosing and treating jaundice among newborns. Researchers from Kolkata-based S. N. Bose National

Centre for Basic Sciences and Bose Institute, made the device using single silica fibre that when coupled to blue light creates a 'vanishing' field of tiny waves. These waves

detect and degrade bilirubin deposited on the surface of the silica fibre. Samir Kumar Pal, who led a research team, told _Nature India_ that it is possible to use the sensor by placing it

on the skin or just beneath the outer skin. Light has long been in use for medical diagnosis and treatment. In their previous studies, the researchers had explored the potential of zinc

oxide nanoparticles in light-assisted treatment of jaundice. Various other studies are also investigating the prospect of using light to make sensing devices. However, no previous studies

had demonstrated the efficacy of an 'evanescent field' for diagnosis and treatment of jaundice. The researchers set out to do just that. They developed the sensor using etched

silica fibre. Since bilirubin is known to absorb blue light, they attached a blue light-emitting diode to the silica fibre. They also fitted the sensor with an optical power meter that can

continuously detect and monitor the levels of bilirubin as it degrades under the blue light. The waves generated by the evanescent field of blue light strongly interact with the environment

outside the silica fibre and carry spectroscopic information. The waves can penetrate few hundreds of nanometres into the surrounding environment of the fibre. In studies using test

bilirubin solution, the researchers found that spectroscopic signature of the photo-degradation product closely resembled methyl vinyl maleimide, a previously reported photo-oxidation

product of bilirubin. After the degradation of bilirubin on the surface of the fibre, the evanescent field searches for new bilirubin molecules in the solution by increasing the depth of

penetration. To find out whether the sensor could degrade bilirubin in a physiologically relevant environment, the researchers studied the photo-degradation of bilirubin in a mixture of

human serum albumin and haemoglobin, the two major ingredients of human blood. Haemoglobin and bilirubin carry different spectroscopic signatures. Relying on this, they clearly detected

photo-degradation of bilirubin without affecting the haemoglobin count in the mixture. To test the feasibility of using this sensor on the skin of jaundice-affected patients, they simulated

the structure and composition of skin using wet-chromatography paper. The experiments using such paper showed the decrease of bilirubin levels in test solutions. "This work takes us a

step closer to the use of light's evanescent field for diagnosing and treating jaundice," says Pal.