Optical Detection of Listeria in the Chilled Food Environment using Bionanosensors

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This programme of research involves the development of an innovative bionanosensor with superior performance for the detection of bacterial pathogens in a sensitive, quantitative and multiplexed manner for use in chilled food production. This will involve developing nanoparticle based analytical technology for the detection of multiple bacterial pathogens (L. monocytogenesis and enterobacteriaceae) associated with food contamination in the chilled food industry. Current methods for detecting bacteria are time consuming (1-2 days in the case of bacteria culturing on selective media, but in reality 7 day turnaround for food production facilities where laboratories are located offsite), expensive and require specialised personnel and equipment. Therefore, there is a strong need for faster, simpler and reliable isolation and detection of bacterial pathogens that can be carried out in the production environment. To address this need we will develop a simple, portable detection platform capable of point of use (POU) detection for bacteria.Successful bacteria detection in food production is crucial for the health of the general public. Within the chilled food sector, Listeria is of particular concern since it is an unusually resilient bacterium which can survive in temperatures from 4 to 42 degrees C. Listeria monocytogenes causes one of the most severe forms of foodborne infection with an overall mortality rate of 30 %, rising to 40 % in vulnerable individuals. Those most at risk of acquiring the disease are pregnant women, the elderly and the immuno-compromised and in some cases listeriosis can develop into meningitis and septicaemia if infection of the blood occurs. However, outbreaks of Listeria are rare due to strict controls on food safety however our industrial partner, Bradgate Bakery, who manufacture sandwiches and salads, require the ability to locate, detect and contain any contamination within food production lines.The research involves the use of an optical detection technique called Raman scattering which will be developed for the POU detection of bacterial pathogens. If light of a particular wavelength is directed onto a molecule then some of the scattered light will change wavelength. This change in wavelength is related to the structure of the molecules and provides a molecular fingerprint that can be used for definitive identification. However Raman scattering is an intrinsically weak process and the signal can be greatly enhanced if the molecule is coloured and is adsorbed onto a roughened metal surface (surface enhanced resonance Raman). The metal can be thought of as essentially amplifying the Raman scattering from a molecule on the surface and in this case will take the form of metal nanoparticles. Since a fingerprint unique to the molecule is produced, the composition of mixtures can easily be identified without separation. A novel bionanosensor for the detection of multiple bacterial pathogens, namely L. monocytogenesis and enterobacteriaceae in one assay combined with enhanced Raman detection will be developed. This will use magnetic nanoparticles which have a biomolecule on the surface known as a lectin which will bind to the surface of bacteria. This will allow isolation and separation of bacteria from the surrounding medium upon application of a magnetic. Additionally, silver nanoparticles which are functionalised with a coloured molecule or label, resulting in intense surface enhanced Raman signals, and a biomolecule which will bind specifically to a particular strain of bacteria (antibody or aptamer) will be added. When the correct bacteria are present binding will occur resulting in magnetic isolation and concentration of the bacteria from the matrix. By using a different label for each bacteria, a unique spectrum will be achieved for each bacteria allowing multiple to be detected simultaneously. A portable Raman spectrometer will then be used to detect the bacteria present.