11 Mar 2009
Laser-based detection of tuberculosis bacilli could revolutionise screening for TB.
With this year's World TB Day taking place on 24 March, the TB Breathalyser developed by Rapid Biosensor Systems (RBS), based in Cambridge, UK, provides timely hope of non-invasive screening for the disease that should be faster and more effective than traditional methods.
"This is an innovative and unique biophotonics system," said Dennis Camilleri, chief executive officer of RBS. "It is integrated into an easy to use and reliable disposable medical device that can offer screening results for active TB in minutes, and which will be used at the point of care."
The breathalyser and portable reader analyse the patient's sample by performing a displacement assay employing evanescent wave technology. "The TB Breathalyser contains a glass prism biosensor, which is coated by a proprietary biochemical coating designed to interact only with TB bacilli that may be present in a cough sample," Camilleri explained. "When placed into the Reader unit, a diode laser interacts with the biosensor and a fluorescence signal is produced by an evanescent wave method."
In the displacement assay process, the TB antigen reveals itself by displacing fluorescently coated analogues and bonding more strongly to antibodies, causing a reduction in the fluorescent signal after excitation by the laser. The laser detects this signal change and the unit returns a positive result.
Reading and analysis of the sample takes approximately two minutes. This compares with the widely used Mantoux skin test, which looks for swellings on a patient's skin after injection of testing fluid and which can require up to two weeks to deliver results.
No other TB breath test currently available delivers such a rapid response at the point of care, according to Camilleri. "Unlike the Mantoux test, the TB Breathalyser is not compromised by the presence of any other infective agents, so other respiratory tract conditions are discounted and only early stage TB and actively infectious TB will be recognised," he said. "The presence of HIV as a masking agent is ignored – an important consideration in the light of the co-existence of TB and HIV in the populations of many developing countries."
The Breathalyser is being used on World TB day in South Africa and India in final trials, prior to production ramp-up and the launch of the product soon afterwards. A successful trial of the device in Ethiopia has also been completed by the London School of Hygiene and Tropical Medicine.