Roger Bradley Millington

Single-mode optical fibre surface plasma wave chemical sensor

Abstract We describe a new design of optical fibre surface plasma wave chemical sensor. The basic sensor consists of a tapered single-mode optical fibre with a thin layer of silver evaporated onto the tapered section. The gradually changing diameter of the fibre along the taper and the variation in silver depth around the taper result in a distributed coupling between the guided mode of the fibre and the surface plasma wave. As a result, the coupling to the surface plasma wave occurs over an enlarged spectral range. The device shows good sensitivity to refractive index with refractive index changes of 5 × 10 −4 being detectable. The device is compact, simple to make, and has applications as a biochemical or immunosensor.

A holographic sensor based on a rationally designed synthetic polymer.

A new silver halide‐containing holographic recording material has been designed and developed specifically for holographic chemical sensors. The hologram enables very small volume changes to be measured in a polymer layer throughout which the hologram is located. The holographic film is based on a fine–grain silver bromide emulsion suspended in a poly(vinyl alcohol) matrix crosslinked with Cr(III) ions. Crosslinking gives the material sufficient spatial integrity to allow a holographic image to be recorded, while maintaining adequate porosity and elasticity of the polymer matrix for sensing applications. The new material has been characterized with respect to its response to pH and compared with a traditional gelatin holographic film. The response to some ions and small molecules typically found in analytical samples has also been measured. Functional groups introduced covalently into the poly(vinyl alcohol) matrix transform the base matrix into a pH‐responsive polymer with predictable swelling properties and which can be further derivatized to incorporate specific ligands. A rationally designed holographic sensor for trypsin has been developed from chemically synthesized artificial polymers. A trypsin substrate, the poly(amino acid) poly(L‐lysine), was incorporated into poly(vinyl alcohol) holograms to create a ‘designed’ holographic material which was degraded in a concentration‐dependent manner by trypsin. Extensions of this approach to other hydrolytic enzymes are briefly discussed. Copyright

Imaging surface plasmon resonance system for screening affinity ligands

A surface plasmon resonance (SPR) system for screening ligands for application in affinity chromatography is described. A combinatorial library of 13 ligands was synthesised, characterised and immobilised to agarose beads and gold SPR devices. Binding and elution behaviour and a range of K(AX) values (10(3) to 10(5) M(-1)) were measured against two target proteins, an insulin analogue (MI3) and a recombinant clotting factor (rFVIIa), in order to create a relational database between the traditional chromatographic format and the new SPR screening system. The SPR transducer surface was fabricated with affinity ligands in a two-dimensional, spatially addressable format, which was durable (>100 cycles) and stable over 6 months. The imaging SPR system comprised a direct optical, CCD-based, instrument capable of imaging the change in refractive index created by biochemical interactions and allowed affinity ligands to be evaluated 15-fold faster with 130-fold less target protein than conventional chromatographic methods. The binding and elution data from both the SPR and chromatographic systems for both target proteins were comparable, with the K(AX) value generating a nearly linear correlation (R(2)=0.875) and a slope bias of approximately 2.5+/-0.25-fold higher for the SPR system. The imaging SPR system has proven capable of screening and evaluating affinity ligands for potential use in the recovery of biopharmaceutical proteins.

A diffusion method for making silver bromide based holographic recording material

AbstractA simple diffusion method for the distribution of ultrafine silver bromide grains in pre-coated gelatin and customized polymeric films for holographic recording has been developed. The method involves two steps: immersion of the pre-formed film in a solution of a silver salt, followed by agitation of the film in a solution of a bromide salt containing sensitizing dye. Repetition of the operation on the same film with different sensitizing dyes in the bromide bath enables the production of film with a panchromatic response. Transmission electron microscopy reveals a grain structure very suitable for use in holography. A reflection hologram made by this method has a similar brightness under the same exposure and processing conditions to one made from a proprietary hologram recording material currently available.

A hologram biosensor for proteases

Abstract The concept of using a hologram as the interactive element in a one-shot biosensor is presented. The theoretical basis for a directly observed optical response to biological molecules is introduced. The most immediate application of such a device, restricted to the detection of proteases, is described in this paper. Using spectrographic measurements, a reflection hologram in gelatin in particular has been applied to the detection of 20 μg ml −1 trypsin and 23 μg ml −1 chymotrypsin, showing a greater sensitivity to trypsin. Enhanced specificity to trypsin has been shown following treatment of the hologram with bovine pancreatic trypsin inhibitor (BPTI), although measurements of pancreatin have yielded only a non-calibrated response. Sensitivity to trypsin down to 0.04 μg ml −1 has been shown. The sensitivities described are relevant to normal trypsin levels in duodenal fluid and faeces, suggesting that a holographic biosensor of this type will be useful as a low-cost quantitative screening test for pancreatic disorders manifest by low levels of enzyme. Improvement in specificity and extension of the concept to other types of analytes is likely to require modified gelatin or hologram-bearing materials other than gelatin.

A Holographic Biosensor

The concept of using a hologram as the interactive element in a one-shot biosensor is presented. The theoretical basis for a directly-observed optical response to biological molecules is introduced. The device as described is relevant to low-cost screening for pancreatic disorders by detection of less than 250nM trypsin in duodenal fluid or stool sample [1]. Data is shown for response of a gelatin-based reflection hologram to the serine proteases trypsin and chymotrypsin presented in pure form or in pancreatin. Specificity to detection of trypsin is shown to be feasible by judicious use of a bovine pancreatic trypsin inhibitor (BPTI). Extension of the concept to other enzymes is introduced.

Broadband single-mode optical fiber surface plasma wave chemical sensor

We describe a new design of optical fiber surface plasma wave chemical sensor. The sensor consists of a tapered single mode optical fiber with a thin layer of silver evaporated on to the tapered section. The gradually changing diameter of the fiber along the taper results in a distributed coupling between the guided mode of the fiber and the surface plasma wave. As a result, and in contrast to conventional plasma wave sensors, coupling to the surface plasma wave occurs over a broad spectral range, typically several hundred nm. The device shows good sensitivity to changes in the refractive index of the external environment, with refractive index changes of 10-4 being detectable. The device is compact, simple to make, and has applications as a biochemical or immunosensor.