We propose a novel photonic sensing solution for rapid quantitative analysis of pathogens, such as E. coli bacteria, in bathing water. The proposed system consists of a novel fiber optic sensor probe developed by the team of researchers at TU Dublin, optical interrogation block comprising a broadband optical source (Laser Diode) and Photodiode, and an electronic control and signal processing unit with a user interface.
The operating principle of the proposed sensor probe is based on the whispering gallery modes (WGM) effect in a spherical micro-cavity (µ-cavity) amplified by a thin layer of plasmonic nanoparticles to achieve enhanced sensitivity to the liquid analyte’s refractive index. When the refractive index of the surrounding the probe water sample under test experiences a change, this results in a spectral shift of the transmission spectrum of the fiber coupled to the WGM cavity. The value of this spectral shift can be related to the value of the refractive index change after calibration. To ensure that the change of the water sample’s refractive index is a function of concentration of the pathogen of interest (e.g., E. coli), the WGM cavity must be coated with a functional layer, whose role is to attract and accumulate the pathogens on the surface of the cavity. To detect E. coli concentration in water, the cavity will be functionalized with bacteriophage (T4) as a bio-recognition element. For field trials, a suitable method of packaging and water sampling protocol will also be developed.
The aim of the proposed sensing solution is to provide the capability for rapid and specific label-free detection of E. coli in bathing water. The proposed sensor probe is expected to achieve high refractive index sensitivity (in the order of 10000 nm/RIU), and when functionalised with bacteriophages as recognition elements, real-time and specific label-free detection of E. coli, wih a limit of detection in the order of 100 colony forming units (CFU)/mL. The proposed sensor thus has the potential to reduce the delay between taking samples of the bathing water and obtaining results thus reducing the health risk of waterborne illnesses for public.