Final Report Summary - NANOPACK (Multifunctional Nanomaterials for Intelligent Food Packaging Applications)
Current and future needs for food quality assurance, food safety and food defense strongly require new and improved diagnostics to screen for chemicals, toxins and bacterial pathogens in complex food and liquid food-product sample matrices. The main objectives of this project are to design novel nanomaterials and devices that could perform these diagnostic tasks e.g. detect food-borne pathogens (E. coli is used as model bacteria species) or chemical toxins.
Our biosensors are designed to directly capture the target bacteria cells onto their surface with no prior sample processing (such as cell lysis). Two types of nanostructured optical transducers based on oxidised porous Si (PSiO2) Fabry-Pérot thin films are synthesised and used to construct the biosensors. In the first system, we graft specific monoclonal antibodies onto a neat electrochemically-machined PSiO2 surface, based on well-established silanisation chemistry. The second biosensor class consists of a PSiO2/hydrogel hybrid. The hydrogel, polyacrylamide, is synthesised in situ within the nanostructured PSiO2 host and conjugated with specific monoclonal antibodies to provide the active component of the biosensor. The immobilisation of the capture probes antibodies onto the PSiO2/hydrogel hybrid biosensors surface is achieved via a biotin-streptavidin system. In order to further optimise the performances of the biosensor, we have established an assay for accurate quantification of the immobilised antibodies. By using this assay, we can control and tailor the surface coverage of the capture probe onto the biosensors surface in order to allow a more robust and sensitive sensing. We show that exposure of these modified-surfaces to the target bacteria results in 'direct-cell-capture' onto the biosensor surface. These specific binding events induce predictable changes in the thin-film optical interference spectrum of the biosensor. Our studies demonstrate the applicability of these biosensors for the detection of low bacterial concentrations, in the range of 103-105 cell/ml, within minutes. The sensing performance of the two different platforms, in terms of their stability in aqueous media and sensitivity, are compared. Our studies suggest that biosensors based on PSiO2/hydrogel hybrid outperform the neat PSiO2 system. The concepts presented in this work provide a generic biosensing platform that can be translated to many biosensing applications of a variety of microorganisms. These new biosensing platforms will be implemented next under the framework of a new EU funded project 'RESFOOD', resource efficient and safe food production and processing. Our role in this new consortium is develop and employ innovative Detection and monitoring tools detection of pathogenic contamination to secure food safety.
One limitation of the porous Si/hydrogel hybrids is that they only allow us to monitor changes in the intensity of the reflectivity spectrum, due to direct capture of the targets on top of the hybrid surface. Therefore, we have worked in collaboration with Prof Amir Sa'ar lab from the Hebrew University of Jerusalem, on a new class of two-dimensional photonic crystal array of PSi; where the pore's diameter is designed to fit the size of the target bacteria cell. As typical bacteria cells are 800-2000 nm in size, the pores are in the micron-scale to allow facile penetration of the cells into the microstructure to induce measurable changes in the effective optical thickness (EOT) of the structure. In addition, we functionalise the porous surface with positively charged amine groups. As most bacteria carry a net negative surface charge, adhesion of E. coli is promoted on positively charged surfaces. Our preliminary results demonstrate the applicability of these surfaces for the rapid detection of bacteria. We show that upon proper design, this novel sensing scheme allows simultaneous measurements of EOT and reflectance intensity changes.
Our biosensors are designed to directly capture the target bacteria cells onto their surface with no prior sample processing (such as cell lysis). Two types of nanostructured optical transducers based on oxidised porous Si (PSiO2) Fabry-Pérot thin films are synthesised and used to construct the biosensors. In the first system, we graft specific monoclonal antibodies onto a neat electrochemically-machined PSiO2 surface, based on well-established silanisation chemistry. The second biosensor class consists of a PSiO2/hydrogel hybrid. The hydrogel, polyacrylamide, is synthesised in situ within the nanostructured PSiO2 host and conjugated with specific monoclonal antibodies to provide the active component of the biosensor. The immobilisation of the capture probes antibodies onto the PSiO2/hydrogel hybrid biosensors surface is achieved via a biotin-streptavidin system. In order to further optimise the performances of the biosensor, we have established an assay for accurate quantification of the immobilised antibodies. By using this assay, we can control and tailor the surface coverage of the capture probe onto the biosensors surface in order to allow a more robust and sensitive sensing. We show that exposure of these modified-surfaces to the target bacteria results in 'direct-cell-capture' onto the biosensor surface. These specific binding events induce predictable changes in the thin-film optical interference spectrum of the biosensor. Our studies demonstrate the applicability of these biosensors for the detection of low bacterial concentrations, in the range of 103-105 cell/ml, within minutes. The sensing performance of the two different platforms, in terms of their stability in aqueous media and sensitivity, are compared. Our studies suggest that biosensors based on PSiO2/hydrogel hybrid outperform the neat PSiO2 system. The concepts presented in this work provide a generic biosensing platform that can be translated to many biosensing applications of a variety of microorganisms. These new biosensing platforms will be implemented next under the framework of a new EU funded project 'RESFOOD', resource efficient and safe food production and processing. Our role in this new consortium is develop and employ innovative Detection and monitoring tools detection of pathogenic contamination to secure food safety.
One limitation of the porous Si/hydrogel hybrids is that they only allow us to monitor changes in the intensity of the reflectivity spectrum, due to direct capture of the targets on top of the hybrid surface. Therefore, we have worked in collaboration with Prof Amir Sa'ar lab from the Hebrew University of Jerusalem, on a new class of two-dimensional photonic crystal array of PSi; where the pore's diameter is designed to fit the size of the target bacteria cell. As typical bacteria cells are 800-2000 nm in size, the pores are in the micron-scale to allow facile penetration of the cells into the microstructure to induce measurable changes in the effective optical thickness (EOT) of the structure. In addition, we functionalise the porous surface with positively charged amine groups. As most bacteria carry a net negative surface charge, adhesion of E. coli is promoted on positively charged surfaces. Our preliminary results demonstrate the applicability of these surfaces for the rapid detection of bacteria. We show that upon proper design, this novel sensing scheme allows simultaneous measurements of EOT and reflectance intensity changes.