Optical Detection of Foodborne Bacterial Pathogens using Nanosensors

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This programme of research involves the development of a new tool based on the use of innovative bionanosensors with superior performance for the detection of bacterial pathogens in a sensitive, quantitative and multiplexed manner. This will involve developing nanoparticle based analytical technology for the simultaneous detection of multiple bacterial pathogens associated with food poisoning. Current methods for detecting bacteria are time consuming (1-2 days in the case of bacteria culturing on selective media), expensive and require specialised personnel and equipment. Therefore, there is a strong need for faster, simpler and more reliable isolation and detection of bacterial pathogens that can be carried out in the field and can simultaneously detect multiple bacteria within a single test. Therefore, development of a simple, portable detection platform is proposed which can carry out multiplexed point of care (POC) detection.Successful pathogen detection is crucial for the health of the general public as the threat of infectious disease is dramatically increasing as a result of bacteria developing resistance to antimicrobial drugs. Major threats to human health from bacterial infections such as E. coli have led to urgent demands to develop highly efficient strategies for isolating and detecting microorganisms in connection with food safety, medical diagnostics, water quality, and counter terrorism. Virulent strains of E. coli can cause gastroenteritis, urinary tract infections, and neonatal meningitis and Salmonella attacks the stomach lining and intestines and in severe cases can result in blood poisoning.The research involves the use of an optical detection technique called Raman scattering which will be developed for the POC 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 the metal 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 diagnostic tool will be developed for the detection of multiple bacterial pathogens, namely Escherichia coli, Salmonella typhimurium and Campylobacter jejunii in a single assay combined with enhanced Raman detection. However, this technology will not be limited to these organisms and can readily be applied to other pathogens. This will involve using magnetic nanoparticles which have a biomolecule on the surface known as a lectin which will bind to the surface of bacterial cells. 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 of the bacteria from the matrix as well as it now having a SERS response. By using a different label for each biomarker, a unique spectrum will be achieved for each biomarker allowing multiple biomarkers to be detected simultaneously. A portable Raman spectrometer will then be used to detect the bacteria present.