Researchers have made a novel biosensor1 that can detect minute traces of lysine, an essential amino acid in the human body, frequently used in food and pharmaceutical samples.

They made the sensor using the polymer polyaniline (PANI), lysine oxidase enzyme, gold nanoparticles, modified multi-walled carbon nanotubes (MWCNTs) and a gold electrode.

This biosensor will also be useful in monitoring lysine levels in human serum, as lysine deficiency has been linked to various pathological conditions, such as fatigue, bloodshot eyes, retarded growth, hair loss, anaemia and behavioural problems. Existing methods are complex and time-consuming, so simple and sensitive methods of lysine detection are needed.

To find such a technique, the researchers prepared the lysine biosensor by depositing PANI onto the gold electrode and then attached MWCNTs and gold nanoparticles to the electrode. Next, they smeared lysine oxidase onto the modified gold electrode. They compared the efficacy of the PANI-based biosensor with a similarly produced biosensor that replaced PANI with poly-1,2-diaminobenzene (DAB) in measurements of lysine levels in laboratory, pharmaceutical, food and human serum samples.

Both biosensors were exposed to varying concentrations of lysine in laboratory samples at 0.4 V. The PANI- and DAB-based biosensors showed optimum response showing linear increases in current with increasing lysine concentrations.

The PANI-based biosensor detected lysine even in the presence of interfering biologically relevant amino acids and other organic compounds such as methionine, proline, uric acid, ascorbic acid, arginine and glutamic acid. In addition, the PANI-based biosensor successfully detected lysine in milk samples, amino acid tablets and human serum.

"After being used 100 times and stored at 4°C, the PANI-based biosensor showed a half-life of 120 days, compared to 90 days for the DAB-based biosensor," says lead researcher C. S. Pundir.

The authors of this work are from: Department of Biochemistry, M. D. University, Rohtak, and Department of Biotechnology, UIET, Kurukshetra University, Haryana, India.