An optical waveguide array biosensor suitable for rapid detection of multiple bio-hazardous agents is presented. SpectroSens™ optical microchip sensors contain multiple spatially-separated waveguide channels with integral high-precision Bragg gratings sensitive to changes in refractive-index; selective surface-functionalisation of discrete sensing channels with different antibodies as bio-recognition elements enables selective multi-analyte biological detection. Interactions between target antigens in the test sample and respective surface-immobilised antibodies result in localised changes in refractive-index; the biosensor response manifests as increases in wavelength of light reflected from specific sensing channels. Multiplexed, label-free detection of 8 different biological agents, encompassing bacterial spores, vegetative cells, viruses and proteinaceous toxins has been demonstrated in real-time. Selective detection of Bacillus atrophaeus (BG) spores, Escherichia coli cells, MS2 viruses and ovalbumin (OVA) protein (simulant bio-hazardous agents) was first demonstrated as proof-of-concept; subsequently, detection of Bacillus anthracis (BA) spores (UM23CL2 strain), Franciscella tularensis (FT) cells (live vaccine strain), Vaccinia viruses (heat-killed) and ricin toxin (bio-hazardous agents) was proven. Two optical microchip sensors, each comprising 8 sensing channels were packaged into a single disposable cartridge allowing simultaneous 16-channel data acquisition. The specific antibody deposition sequence used in this study enabled detection of either 4 simulants or 4 bio-hazardous agents using a single consumable. The final device, a culmination of the multidisciplinary convergence of the fields of biology, chemistry, optoelectronics and microfluidics, is man-portable and inherently robust. The performance characteristics of the SpectroSens™ technology platform highlight its potential for exploitation as a 'detect to warn/treat' biodetector in security and defence operations.

A multi-channel optical microchip sensor system suitable for real-time, label-free detection of a wide range of biological agents is presented. SpectroSens (TM) chips containing multiple high-precision planar Bragg gratings are exploited as low-cost, robust refractive index sensors. Sensitivity to biological agents is conferred by functionalising individual sensing regions with different antibodies selected against numerous targets of interest. Antigen binding to the surface-immobilised antibodies results in localised changes in refractive index; upon laser-induced interrogation of the sensing region via optical fibres, these antibody-antigen interactions manifest as increases in wavelength of light reflected from the sensor chip. Real-time detection of multiple biological agents including bacterial cells/spores, viruses and toxins has been demonstrated. Further improvements to sensor performance including physical and chemical methods are also investigated. This multi-analyte capability highlights the potential use of this sensing technology in applications ranging from bio-hazard detection for defence purposes to point-of-care clinical diagnostics.

Orthogonal subspace signal processing algorithms (OSPA) have been developed to extract the optical thickness of a porous silicon layer to within one part in 105 from its reflectivity spectrum. This is equivalent to a limit of detection (LOD) of ∼40 pm change in optical thickness for a 3 µm thick layer, or an LOD of 1/2000 of a monolayer coverage with antibodies, of molecular weight 160 k Daltons, within a layer with pores of 100 nm diameter. A large molecule {horseradish peroxidase (HRP), MWt 40 kDa} has been detected at a concentration of 1 µg/ml by measuring its direct binding to anti‐HRP antibodies immobilised within a porous silicon layer. A competitive assay has been demonstrated for the detection of a small molecule {2, 4, 6 trinitrotoluene (TNT), MWt 227 Da} at 10 µg/ml. The projected LODs for HRP and TNT by these assays are 50 ng/ml and 1 µg/ml respectively. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The sensitivity of the optical reflectivity of porous silicon structures to the refractive index of liquid within the pores is studied for a single layer, a Bragg mirror and a microcavity. Sucrose solutions of concentration in the range 0.05 to 1.0% by weight are introduced into the pores within a flow cell in order to change the refractive index of the liquid in the pores from 1.3330 to 1.3344. Optimum wavelengths for detection via reflectivity changes are determined based on a signal to noise analysis. The optical thickness of the single layer is also monitored by measuring the fringe spacing via a Fourier transform technique. It is just possible to detect the effect of a change in refractive index of liquid in the pores of 0.00007 for both the reflectivity and optical thickness approaches.

To use porous silicon as an optical interferometric biosensor, the pores must be sufficiently large to allow easy ingress of reagents and the layer must also display Fabry-Perot optical cavity modes. Here the detection antibody is rabbit IgG and the analyte is a-rabbit Ige conjugated to horseradish peroxidase (HRP). For. this model system, the pores should be >50 nm in diameter. Such diameters have been obtained in 0.05 Omega cm n-type silicon using anodisation followed by chemical etching in ethanolic KOH and also, by anodising 0.005 Omega cm p-type material. The latter also displays optical cavity modes. Tnt: silicon surface is oxidised in ozone, silanised using aminopropyl-methoxysilanes with one, two or three methoxy groups, and cross linked to Ige using glutaraldehyde. High specific binding is found fur mono-, di- and tri-methoxy silanes, but the lowest nonspecific binding is found fur silanisation with the tri-methoxy silane.

The amplification of a probe beam by stimulated Raman scattering in a disordered medium is experimentally investigated. The measurements are performed in Ba(NO3)2 powders with 532-nm pumping and a 563-nm Raman generated probe. The results fit well with Monte Carlo simulations of the experiment.

Summary form only given. Over the past several years there has been a great deal of renewed interest in multiple scattering systems with both absorption and gain. In the case of gain, laser action has been demonstrated in these systems and has resulted in a number of technological applications. More recently, the effect of amplification on the coherent backscattering signal has been observed. The case of scattering in the presence of absorption typifies most heterogeneous materials such as body tissue. In a recent set of experiments the termination of paths by absorption has been shown to affect the shape of the coherent backscattering cones. Furthermore, in the case of scattering gain media, the optical excitation source or pump experiences a scattering absorption process, which determines the gain value. Owing to the importance of this effect in both types of systems, we undertook a set of experimental measurements to study the effect of absorption on the light distribution within a scattering media. In particular, we performed experiments to quantitatively examine the light distribution in both the transition and diffusion regimes.

The narrow-linewidth laser emission from a scattering gain medium can be forced to oscillate in a narrower emission bandwidth with the introduction of a seed in much the same way as the injection-seeding technique used to produce single-mode oscillation from conventional lasers. The system exhibits complete spectral collapse at all wavelengths other than that of the seed and a large enhancement of the isotropic emission peak intensity. A theory explaining the emission characteristics and the minimum threshold seed energy required for locking is presented.

We report on experimental observations of coherent backscattering signals from high-gain scattering media in the regime where significant amplification takes place over one transport length. Our samples consist of polymer sheets containing optically pumped dyes as the amplifying medium, with TiO(2) nanoparticles providing the scattering. The width of the backscattering cones narrows with increasing amplification, while the enhancement factor remains unchanged.

Nanobit holographic techniques, such as high-energy electron beam lithography, allow apertures of < 50 nm diam. to be fabricated in the metal coating of SPR sensor devices. When the SPR slab waveguide is edge illuminated with a laser, the apertures act as intense scattering centers of the underlying radiation, the scattered light from which is readily detectable by conventional optical microscopy. Given the dimensions of these sub-wavelength optical sources are within an order of magnitude of those of individual biological macromolecules, it should ultimately prove possible to detect interactions between substrate/analyte and individual (labelled) biological macromolecules immobilized in the apertures. The possibility of analyzing the dynamic behavior of single biomacromolecules operating in their natural environment is discussed.

A simple remote sensing single-particle detection system is described which uses light scattering to determine the size and concentration of scatterers. They report the initial results obtained from the system. A dual wavelength conformation consisting of an inner trigger beam and outer analysis beam is used to eliminate edge effects of the Gaussian profile of the laser beam. This is achieved without the use of complicated optics, by employing an optical fibre and a chromatically dispersive gradient index (GRIN) rod lens to give the correct optical configuration in the scattering volume.

Following a recent successful application of p.c.s. to liquid chromatography in the biotechnology industry, its usefulness as a contamination monitor in the fermentation industry was assessed. It was found that: (i) the intensity bias of the technique limits its uses to the detection of contaminants when they are larger than the host; (ii) the inherent heterogeneity of microbial cultures prevents the use of multiangle studies, and (iii) the large size of bacteria make the use of p.c.s. in flowing, on-line systems impractical.

The application of photon correlation spectroscopy (PCS) to detect culture contamination in chemostats was studied. It was found that the presence of a given particle size in a population of particles of a different size could be detected, but this ability was strongly dependent on particles of a different size could be detected, but this ability was strongly dependent on particle size difference and was most sensitive when contaminants are larger than the host. The inherent polydisparity of actively growing and dividing microbial cells negates any advantage in the use of multi-angle PCS to detect contaminants.

Data buses are being employed in avionic applications to simplify the task of systems integration. MIL-STD-1553B is a universally accepted standard developed for military systems and it is this standard that has been identified as a suitable candidate for implementation using fibre optic components. A number of candidate topologies have been evaluated which have led to the design of specific components, eg fibre optic star couplers and the fibre optic transceiver chip set. The other components that are required are fibre optic cables and connectors designed for the avionic environment. Together, these components and the chosen topology provide an effective means to integrate avionic systems and provide for future increases in data rate and wavelength division multiplexing of different types of data. WHL has recently been involved in the design and installation of a MIL-STD-1553B based fibre optic transmission system for a research helicopter programme. This paper describes the techniques and practical problems of using fibre optic technology in aircraft applications.

The Language Unit at Lea Castle Hospital, initially sponsored in part by the British Institute of Mental Handicap, was opened in October, 1975 and was briefly described in Apex (December 1976). The present article describes the running of the Unit and gives some of the results so far. The children

Learning is a process which is not confined to classroom, workshop or training centre but continues throughout the whole day. Hence, all those who have contact with retarded adults are obliged to teach them relevant skills in as efficient a way as possible. To do this they must address themselves to two basic questions, namely, «What skills shold we teach?» and «Hown shall we teach?» This article consideres some of the evidence and ideas relating to these two issues.