The most important public health issue in developed and developing countries is the food safety. Due to this reason there is a big interest shown in this field. In the last few years there have been different problems related to food safety. The reason is to protect people from many new food borne diseases which have been identified recently. Foodborne illnesses are diseases derived by pathogens that enter into the body with the consumption of food and can be toxic in nature (ref). The major food borne pathogens involved in these diseases have been identified as Salmonella, Campylobacter, Listeria, Escherichia coli (E.coli), Vibrio cholera and Staphylococcus aureus(ref). In particular, the infections due to E. coli have a relatively low incidence but produce severe and sometimes fatal health consequences in infants, children and the elderly, resulting in most serious food borne infections(ref). Due to these hazards recently, there is a demand to develop rapid and accurate testing methods which are considered essential by the food industry. The purpose led to focus this research work on the development of new detection methods to prevent the diffusion of foodborne pathogens, in order to improve food safety.
Conventional and standard bacterial detection methods such as culture and colony counting methods, immunology-based methods and polymerase chain reaction based methods, may take up to several hours or even a few days to outcome with results(ref). This is time consuming and not user friendly, and recently many researchers are focusing towards the development of fast, accurate and real time methods such as Biosensors. Biosensor is an analytical device which converts a biological response into an electrical signal. Biosensor consists of two main components, a bio receptor or bio recognition element which is used to recognize the target analyte and a transducer for converting the recognition event into a measurable electrical signal.
In this research work a novel nanoparticles based optical method for detection of pathogens in food has been proposed. The development of practical biosensors using nanomaterials, such as magnetite(Fe3O4, Iron oxide) nanoparticles (MNPs), is promising in eliminating the need for expensive or complicated instruments and allowing the fast and accurate pathogen detection and data extraction from the variety of samples. Magnetic nanoparticles possess an additional advantage of being easily modified by permanent magnets, independent of biological processes. The rapid capture of biomolecules for purification or characterization is another application of magnetic nanoparticles (Pankhurst 2003). Magnetic separation is a well-established alternative to centrifugal separation of complex chemical or biological solutions. Firstly the iron oxide particles are chemically synthesized using coprecipitation method. Chemical method is often preferred for synthesis of nanoparticles as it's the best method to enhance homogeneity from the molecular level design of the materials and also to provide a cost effective bulk production. Solution routes also allow control of particle size, size distribution, morphology and agglomerate size through individual manipulation of the parameters that determine nucleation and growth. The MNPs are then functionalized with a chemical agent known to bind to a specific target. Upon placing the C-MNPs in solution, any target cells or molecules can be identified by the functionalized surfaces. A permanent magnet placed at the side of the solution beaker or test tube produces a magnetic moment in each of the freely floating MNPs and sets up a field gradient across the solution. The magnetized nanoparticles will move along the field lines and aggregate together towards the magnet, separating their bound targets from the bulk solution.
For food bacterial detection, MNPs are usually coated with polymers and bounded to the particle through organic linkers. This type of surface functionalization is capable to identify specific molecules and ions for their binding onto the surface of cell wall of bacterium with improved stability. These functionalized MNPs for rapid capture and isolation of pathogens when used in fluorescent biosensors have a very high capacity for charge transfer, which makes them suitable to reach lower detection limits, higher sensitivity and needs few minutes for analysis. Fluorescent dye such as rhodamine, a red light emitting dye in addition to the bio sample and C-MNPs is used for the detection purpose. Magneto fluorescent biosensor is a direct method used to measure parameters of fluorescence, such as intensity and wavelength distribution of emission spectrum after excitation by a certain spectrum of light. These parameters are used to identify the presence and the amount of pathogens in a medium. These are capable of detecting fluorescent molecule concentrations as low as 1 part per trillion.