Jeff Blyth

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

Covalent coupling of immunoglobulin G to a poly(vinyl)alcohol-poly(acrylic acid) graft polymer as a method for fabricating the interfacial-recognition layer of a surface plasmon resonance immunosensor

The synthesis of a terminally thiolated poly(vinyl)alcohol (PVA) grafted with Poly (acrylic acid) (PAA) side chains is described. The PVA-PAA graft polymer (PVAg) was end-tethered to silver surfaces via the terminal thiol functionality and the resultant mobile, hydrophilic polymer matrix exploited for the covalent immobilization of large quantities of polyclonal goat (anti-hIgG) antibody (IgG) with low levels of non-specific adsorption. An SPR immunosensor, fabricated with an IgG-PVA-silver interfacial layer proved capable of performing a sensitive label-free assay of human IgG antigen (hIgG) with minimal non-specific binding interference. A detection limit (DL) for hIgG from serum of 0.8 microgram/ml (5 nM) and an assay sensitivity of 0.66 ng hIgG/mm2/nM are reported.

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.

Analyte-responsive holograms for (bio)chemical analysis

Analyte-responsive holograms comprise a holographic grating embedded in a smart hydrogel film. The grating acts as a reporter that enables analyte induced changes in the thickness of the associated polymer film to be accurately determined. Interaction of these materials with a specific analyte or stimuli leads to a change in the colour, image or brightness of the hologram and these changes can be visualised directly or quantified using a simple colour reader. Analyte-responsive holograms are inexpensive, robust and have proven suitable for detection of a wide range of clinically and industrially important analytes.

Holographic sensors in contact lenses for minimally-invasive glucose measurements

A contact lens with an incorporated glucose-sensitive hologram has been designed as a system for non-invasive measurement of glucose levels in diabetic patients. The hologram consists of an acrylamide copolymer hydrogel with phenylboronic acid groups acting as reversible glucose-binding ligands, allowing dynamic changes in glucose to be detected. The colour of white light reflected off the hologram changes as glucose binds to the phenylboronic acid groups, and this change is used to quantify glucose concentrations. Holograms containing the ligand 3-acrylamidophenylboronic acid (3-APB) were incorporated into a contact lens. The lens was chemically extracted to render it non-toxic. After sterilization through autoclaving, the system still maintained its ability to bind glucose reversibly.

Selective holographic glucose sensors [biosensing applications]

A holographic glucose sensor, based on the swelling state of acrylamide co-polymers containing phenylboronic acid groups, has been developed. Boronic acids are known to bind a variety of cis-diols, including glucose and lactate, which are found in physiological fluids. Incorporation of a tertiary amine along with the phenylboronic acid in the copolymer allowed the boronic acid to achieve the reactive tetrahedral state at physiological pH through intermolecular electron donation from the amine. This facilitated the binding of glucose at physiological pH and increased the selectivity for compounds with multiple cis-diol groups. Glucose caused the polymer to contract as it acts as a cross-linker whereas the binding of lactate caused a slight expansion. The sensor is fully reversible and could be used to monitor continuous changes in glucose concentration in physiological fluids.

Optimizing diffraction efficiency for transmission holographic optical elements with Harman holographic materials.

HARMAN technologys new holographic emulsions; red sensitive and green sensitive assisted by smaller grain sizes, novel sensitization and coating technology have been shown to achieve high diffraction efficiencies and narrow band reconstruction capabilities. Authors demonstrate processing optimizations and material behavior characteristics for Transmission image Masters as well as Holographic Optical Elements (HOEs).

Optimizing diffraction efficiency for reflection holograms with HARMAN holographic emulsions while maintaining narrow band reconstruction.

HARMAN technologys new holographic emulsions; red sensitive and green sensitive assisted by smaller grain sizes, novel sensitization and coating technology have been shown to achieve high diffraction efficiencies and narrow band reconstruction capabilities. Authors demonstrate processing optimizations and material behavior characteristics for both narrow band and broadband with controlled playback frequency.

Teaching holography workshops to beginners

This paper is useful for teaching holography workshops in classrooms as well as in makeshift locations such as museums, businesses, and homes. The target audience is very general, young children to adults of any profession, al of whom have no prior experience in making holograms. A typical number of participants is twenty-five, but can vary depending on space and personnel availability. A central original contribution of this paper is the discovery of a new chemical processing regime for the Slavich PFG-03M holographic plates. These silver halide plates have the highest resolution of its kind and some of the worlds best holograms have been recorded on it for several decades. Due to its low sensitivity and long developing time, this material has been excluded form use in workshops. Our new processing regime JARB has the following advantages: It (1) increases the sensitivity of PFG-03M emulsion ten-fold without sacrificing resolution; (2) hardens the emulsion during processing without significant shrinkage; (3) has a ten- to twenty-second development time; (4) is quick drying using squeegee and warm air; and (5) allows the finished hologram to be viewable with laser or incandescent light. Other advantages of JARB are (1) low toxicity, (2) low volatility, (3) non-staining, (4) low cost, and (5) long shelf life.