US and Italian researchers have developed a new sensor that tracks the progression of autoimmune diseases while dramatically reducing analysis time and requiring no reagents. 

In autoimmune diseases like systematic lupus erythematosus - a disease that affects more than five million people worldwide - the body's immune system turns on itself and produces anti-DNA antibodies that attack various organs. While the quantification of antibodies in the bloodstream plays an important role in monitoring the severity of the illness, current detection methods such as enzyme-linked immunosorbent assay (ELISA) must be performed by skilled clinicians and require hours or even days to generate a result. 

Francesco Ricci and co-workers at University of Rome Tor Vergata have developed a biosensor electrode that can quickly detect anti-DNA antibodies. The sensor uses a short sequence of single stranded DNA which has been modified at one end with a redox-active tag. The other end of this DNA probe is modified with a thiol group that forms a strong bond to a gold electrode surface. 

For efficient electron transfer to occur, the DNA must bend to allow the redox probe to touch the electrode surface. When anti-DNA antibodies in the sample bind to the DNA, the probe is much less flexible and reduces the efficiency with which the redox tag collides with the electrode. This interrupts electron exchange between the probe and the electrode, reducing the electrical current . 

Arben Merkoçi an expert at designing biosensors at the Catalan Institute of Nanotechnology in Spain, says; 'This is a proof of concept of a very interesting alternative for the detection of antibodies against single and double-stranded DNA. It could open the way to develop novel assays for other analytes with interest for clinical applications.' 

Ricci is keen to optimise the sensor design and hopes to commercialise the technology. 'The possibility of having miniaturised sensors, low cost and portable instrumentation and to process large number of samples in a time-effective way is a huge advantage of the electrochemical approach over other techniques which make it among the most suitable for point-of-care testing' he states.

David Sharpe 

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