Dual polarisation interferometry for studying biopolymer interactions relevant to food and the gastrointestinal tract

The interactions of biopolymer surface structures are relevant to many biological events and the industrial usage of biopolymers. More specifically, in a food/pharmaceutical context, these interactions are relevant to the adhesion of pathogenic bacteria to the mucus layer of the gut and the effect of beneficial bacteria in limiting that adhesion; the digestibility of lipid droplets; the role of the mucus layer as a protective barrier for the gut epithelia; interactions of both soluble and particulate allergens with the mucus layer and their sensing by the immune system. In addition, biopolymer surface structures and coatings have potential for the controlled or site-specific release of active ingredients to different regions of the gastrointestinal tract. The characteristics of which will depend on how the coating responds to the different environments encountered in the gastrointestinal tract, and how it interacts with the mucin layer. We propose to study the assembly and properties of surface structures derived from charged natural polymers, which either mimic the structures found in vivo in order to obtain insight into their physicochemical behaviour, or deliver novel properties of potential industrial usefulness. The approach that we will adopt will involve the deposition of the biopolymers on a sensor surface, and the subsequent interrogation of the properties and interactions of that surface layer using different physical techniques. We currently use Fourier transform infrared spectroscopy (FTIR), quartz crystal microbalance with dissipation monitoring (QCMD), atomic force microscopy (AFM) and surface plasmon resonance (SPR), to investigate surface assembly. These techniques allow us to probe different aspects of the structure. AFM gives information on nanostructure; SPR gives information on the mass of polymer assembled at the surface; FTIR information on its chemistry, and the state of ionisation of charged residues within the structure; and QCMD information on the extent of hydration of the surface layers. Although each technique, when used in isolation, will give useful information, it is only through the use of the techniques in an integrated way is it possible to obtain the information required to characterise the surface layer in a physicochemical sense. A particular advantage of the interferometric approach is that both mass and layer thickness are obtained simultaneously, allowing a closer integration of the other approaches. Other advantages derive from its sensitivity and its ability to use a silica sensor. The latter means that it is possible, with the exception of SPR, to monitor assembly of structures on a common surface. This additional factor also aids the integration of the different experimental approaches.

The Institute of Food Research (IFR) is using the tools of bionanotechnology to examine the assembly and interactions of biomaterials and biological surfaces of relevance to their behaviour in the gastrointestinal tract, and use in the food and pharmaceutical industries. Topics that will be investigated include the environmental responsiveness of multilayer structures relevant to their use for targeted delivery of active ingredients; protein/polysaccharide interactions relevant to protein preservation; allergen/mucin interactions in relation to allergenicity; physical chemistry of the selectivity of the mucin layer as a protective barrier; assembly of bacterial surface structures and their interactions with mucin; the modification of the surface layer of the emulsion droplet and its effect on stability and digestibility. The tools that we currently have, or have access to, include surface plasmon resonance (SPR); FTIR-ATR; quartz crystal microbalance with dissipation monitoring (QCMD); and atomic force microscopy (AFM). These techniques give information on the mass of a surface layer; its chemical structure; hydration; and nanostructure. The techniques are complementary and particularly powerful when used in an integrated way. The proposed purchase of the interferometer will surpass the capabilities of SPR, when used to examine the physical chemistry of surface assembly, through providing the simultaneous determination of the mass of the surface layer and its thickness. In addition it will mean that all of the techniques can use sensors with a similar silica surface which is particularly advantageous when using the techniques in an integrated way. The multidisciplinary research environment of IFR can provide support on the underlying physics and physical chemistry of the instrumentation and its use to tackle biological problems.