DNA sensor for leishmaniasis
doi:10.1038/nindia.2011.98 Published online 28 June 2011
Researchers have designed a novel DNA-based sensor that could be useful to sniff out traces of Leishmania parasites in biological samples. The sensor could be a promising diagnostic tool for the detection of Kala-azar and other leishmanial diseases.
Kaia-azar or leishmaniasis is a parasitic disease caused by Leishmania donovani, a parasite transmitted to humans through sandfly. The key to its cure is early detection. Besides conventional microscopic studies of parasite in clinical samples isolated from bone marrow and spleen, researchers resort to complex blood test using specific antigen. So far, however, no sensitive and stable test is available for clinical diagnosis.
To devise a sensitive and stable sensor, the researchers smeared 23-base long single strand of DNA (ss-DNA) specific to Leishmania parasite on nickel oxide (NiO) coated indium tin oxide (ITO) electrode placed on glass plate. The electrochemical response of this ss-DNA/NiO/ITO sensor was studied against different concentrations of target DNA isolated from cultured parasites in the phosphate buffer solution in the presence of methylene blue (MB) as an indicator.
MB has an affinity to bind to guanine bases of DNA. In electrochemical studies, it was observed that magnitude of the current decreases with the increase in target DNA concentrations. This happens because target DNA forms a double helix by binding to ss-DNA of the sensor. The double helix formation at the sensor's surface blocks the guanine sites inhibiting the binding of MB. A significant reduction in current takes place since the guanine bases become inaccessible to MB after hybridization between ss-DNA and target DNA.
The sensor was able to differentiate between DNA of a healthy person and leishmaniasis-affected patients. Besides diagnosis of Kala-azar patients, the sensor holds enormous potential for development of other stable and sensitive sensors, the researchers say.
The authors of this work are from: School of Materials Science and Technology, Institute of Technology, and Infectious Disease Research Laboratory, Department of Medicine, Institute of Medical Sciences, Banaras Hindu University, Varanasi, Uttar Pradesh, India.