Now, a thumb imprint is all that is required for detecting hyperbilirubinemia, a condition in which the amount of bilirubin in the blood is in excess and turns the sclera of the eye, urine and even the skin yellow. Hyperbilirubinemia is commonly seen in people with jaundice and newborns; a person is said to have jaundice when the bilirubin concentration in the blood typically exceeds 12 ppm in adults and 50 ppm in a newborn.
Researchers at the Indian Institute of Technology (IIT) Guwahati have tested the sensitivity and specificity of a simple, quick, point-of-care test for detecting excess bilirubin in patients with jaundice.
While visual observation of yellow colour of the sclera and/or urine is routine for detecting jaundice, it is confirmed by a blood test. A team led by Prof. Arun Chattopadhyay from the Department of Chemistry and Centre for Nanotechnology, IIT Guwahati used thumb imprints to detect hyperbilirubinemia. The results were published in the journal Scientific Reports.
“When a person has jaundice, the bilirubin gets deposited on the surface of the skin. We wanted to develop a quick test that will confirm whether the bilirubin amount has exceeded the permissible limit in the blood,” says Prof. Chattopadhyay.
The bilirubin forms a complex with copper and restores the yellow luminescence of the gold nanoclusters.
The team has been working on nanotechnology for more than 10 years and in recent years have been working on luminiscent atomic nanoclusters. The nanoclusters are very sensitive to the presence of molecules in the environment.
“Gold nanoclusters that have been functionalised (using chitosan and mercaptopropionic acid) show yellow luminescence under UV light. But when copper salt (copper sulphate) is added to gold nanoclusters the yellow luminescence gets quenched or reduced. When bilirubin is added to the medium, the copper preferentially interacts with bilirubin and forms a complex and the yellow luminescence of the gold nanoclusters gets restored,” he says.
The bilirubin, which forms a complex with copper and restores the yellow luminescence, comes when the thumb is pressed on a gold nanocluster-coated membrane that has copper deposited on it. “Previous independent studies have shown that luminescence of gold nanoclusters is quenched by copper and at the same time copper interacts with bilirubin. So that’s why we chose copper ions,” says Srestha Basu from IIT Guwahati and the first author of the paper.
“You need to press the thumb on the membrane for a few minutes to restore the yellow luminescence in the gold nanoclusters,” he says. Immediately after taking an impression, the same thumb cannot be used on a different membrane to restore the luminescence of copper-deposited gold nanoclusters. “This could be because there is insufficient bilirubin present on the skin of the thumb after the first impression,” says Prof. Chattopadhyay.
The way to test people with different concentration of bilirubin on the skin is by changing the amount of copper that is deposited on the membrane containing gold nanoclusters.
The change in the intensity of luminescence was nearly the same whether copper ions deposited on the membrane had completely dried or not. The shelf life of copper ions deposited on gold nanoclusters is not known. “Most of the experiments were done when the membrane coated with copper was still wet,” Ms. Basu says. “So the detection kit can have membranes already coated with gold nanoclusters and copper ions can be added just before carrying out a test.”
“This was a proof-of-concept study. Large-scale tests have to be carried out for validation,” he says. Amaresh Kumar Sahoo and Prof. Anumita Paul from IIT Guwahati are the other two co-authors of the paper.