E.coli detected in 20 minutes by fibre sensor

Spectrum after catching bacteria

“Using currently available technologies, which are mostly based on amplification of the sample, it takes several hours to days to detect the presence of bacteria. A fast and accurate detection alternative is, therefore, preferable over the existing technology,” said Saurabh Mani Tripathi, a physicist at the Indian Institute of Technology Kanpur.

The Indian team worked with researchers from the University of Quebec in Outaouais to combine two techniques to make a practical sensor.

Firstly, the optical fibre is sensitised to Escherichia coli by coating it with a specific type of bacteriophage – bacteriophages are viruses that latch onto bacteria.

Surface sensitivity is maximised by operating a long-period fibre grating implanted inthe fibre closest to its turnaround wavelength, according to the paper ‘A compact and cost-effective temperature insensitive bio-sensor based on long period fiber gratings for accurate detection of E.coli bacteria in water‘, Optical Letters.

This arrangement works, but has to be operated at a fixed temperature because refractive index is the parameter being sensed and this is affected both by bacterial load and temperature.

The second technique compensates the bacterial signal against temperature across 20 to 40cegC – making the 3.6cm-long sensor more practical for outdoor applications like on-site monitoring of water reservoirs, Tripathi said, or the food industry or pathology labs.

Temperature insensitivity (to ~1.25 ppm/°C), which could be further reduced with more work, is achieved by selectively exciting a pair of cladding modes with opposite dispersion characteristics using two slightly-different long-period fibre gratings one after the other in the fibre – the paper has full details.

Changing the bacteriophage allows other strains of bacteria to be detected, and Canadian firm Security and Protection International is looking into the commercialising the sensor.