Researchers have synthesised a sensitive sensor that can detect minute traces of cystatin C, a marker protein in urine1. Since a high concentration of this protein has been linked to abnormal kidney function, the sensor offers a non-invasive way to diagnose the early onset of chronic kidney disease.

Existing diagnostic tools usually detect chronic kidney disease only when it has reached an advanced stage. This delayed treatment increases the risks of death from this disease.

To devise a technique for detecting kidney disease at an early stage, scientists from the CSIR-Institute of Genomics and Integrative Biology, Delhi and Amity University, Rajasthan, both in India, led by Ashok Kumar, prepared the sensor by attaching papain, an enzyme found in papaya, to a screen-printed multi-walled carbon nanotube-based electrode.

When exposed to solutions containing different concentrations of the marker protein, the sensor generated electrical signals. Increasing the concentration of the protein caused the sensor to exhibit a consistent dip in its current response.

According to the researchers, this decrease in current response may be attributed to the stable binding of the marker protein with the papain attached to the sensor. It retained 90 per cent of its original efficiency in detecting the marker protein even after being stored at 4 o C for 12 months.

“A disposable strip made using the sensor can detect the marker protein in a drop of urine. Each test, diagnosing the kidney disease, costs only fifty rupees,” says lead researcher Kumar.