No abstract

A simple, sensitive and label-free optical sensor method was developed for allergens analysis using α-casein as the biomarker for cow's milk detection, to be used directly in final rinse samples of cleaning in place systems (CIP) of food manufacturers. A Surface Plasmon Resonance (SPR) sensor chip consisting of four sensing arrays enabling the measurement of samples and control binding events simultaneously on the sensor surface was employed in this work. SPR offers several advantages in terms of label free detection, real time measurements and superior sensitivity when compared to ELISA based techniques. The gold sensor chip was used to immobilise α-casein-polyclonal antibody using EDC/NHS coupling procedure. The performance of the assay and the sensor was first optimised and characterised in pure buffer conditions giving a detection limit of 58ngmL as a direct binding assay. The assay sensitivity can be further improved by using sandwich assay format and amplified with nanoparticles. However, at this stage this is not required as the detection limit achieved exceeded the required allergens detection levels of 2µgmL for α-S1-casein. The sensor demonstrated good selectivity towards the α-casein as the target analyte and adequate recoveries from CIP final rinse wash samples. The sensor would be useful tool for monitoring allergen levels after cleaning procedures, providing additional data that may better inform upon wider food allergen risk management decision(s) that are made by food manufacturer. In particular, this sensor could potentially help validate or optimise cleaning practices for a given food manufacturing process.

An empirically derived formula, which can be used to predict the average residual reflection that can be expected from an antireflection (AR) coating design as a function of bandwidth, overall thickness, available indices of the coating materials, number of layers, etc., is presented. This formula can be a useful tool not only for the thin-film designer but also for the nondesigner or system engineer to estimate the performance limits of an AR coating for a given application before the design is accomplished. The general predictions are also found to be consistent with the results of two recent AR design competitions involving many independent investigators. Some insight with respect to the basic underlying principles of AR coatings can also be gleaned from the results and the process by which they are found.

This study compares and quantifies the simulated effects of noise, index errors, and photometric level errors on different optical monitoring layer termination strategies. A computer program to simulate optical thin film monitoring has been written for this work. The study looked at these termination methods: quartz crystal monitoring, photometric level cut, two types of turning point termination, and percent of optical extrema monitoring. A narrow bandpass filter and a four-layer antireflection coating design were simulated as examples.

Narrow bandpass filters have historically been designs of quarter waves at the passband wavelength, and have been monitored at the turning points using the passband wavelength. By direct monitoring at the passband wavelength, errors have been shown to be primarily self compensated, and have allowed much better performance than could otherwise be expected. The turning points are difficult to detect precisely and accurately because the change in transmittance with thickness becomes zero at the desired termination point. By proper design with non-quarter-wave layers, essentially the same spectral performance can be achieved by layer terminations that are far enough from turning points to be significantly more sensitive termination points. The design approach is to maintain the optical thickness of the reflector layer pairs at one half-wave of the passband wavelength, but change the ratio of the optical thicknesses of the high and low index layers. These can be adjusted enough so that the thicker layers contain two turning points and the last turning point in the layer can be more accurately and precisely determined. The error compensation benefit from the historic method should be maintained. This leads to potentially improved control during deposition and monitoring of narrow bandpass filters.