DNA-based biosensor for diagnosing typhoid
doi:10.1038/nindia.2015.101 Published online 11 August 2015
Researchers have developed a sensitive biosensor that can bind to traces of the bacterium Salmonella typhi in urine and blood samples, making it potentially useful for early diagnosis of typhoid fever1.
The bacterium is transmitted to humans through the ingestion of contaminated food and water. Diagnosis techniques such as blood culture are tedious and complex, while methods employing the polymerase chain reaction are faster but expensive.
To devise a simple and effective technique, the researchers fabricated the biosensor by depositing gold nanoaggregates on an indium tin oxide substrate. They then attached a single-stranded DNA probe specific to the bacterium to the surface of nanoaggregates, which had been modified by an organic acid.
When the sensor was exposed to urine and blood samples containing DNA from the bacterium, the peak current decreased when the biosensor bound to complementary DNA sequences from the bacterium. In contrast, no significant current changes were observed when the biosensor was bound to non-complementary DNA sequences, indicating that it selectively binds to DNA sequences from the typhoid-causing bacterium.
The signal of the biosensor decreased by only 8% over two months. Furthermore, the biosensor could be reused even after six electrochemical cycles with a signal-generating efficiency of about 78%.
The researchers say that the biosensor could potentially be used for detecting other pathogens.
1. Singh, A. et al. DNA functionalized direct electro-deposited gold nanoaggregates for efficient detection of Salmonella typhi. Bioelectrochemistry 105, 7–15 (2015)