Optical biosensor techniques for monitoring organic pollutants in the aquatic environment

The principal contribution of Southampton University to the BIOPTICAS project is in the realization of planar optical waveguide probes to determine the optical properties of attached sensing films. Three types of device are being investigated: surface plasmon resonance (SPR), directional coupler and chemiluminescence sensors. Techniques have been established for the deposition of compatible electrodes for electrochemical modulation of sensing reactions as an integral part of devices, and equipment has been set up for the fabrication of waveguides in glass substrates by field-assisted ion-exchange. The modelling and design stages for the devices are now close to completion, and we have begun the fabrication and evaluation of preliminary designs and verification of models. Interaction with partners has resulted in the establishment of standardised sensor chip formals and plans for comparative evaluations of the sensors developed in the project, using standardised sensing reactions are well in hand

Forces on a Rayleigh particle in the cover region of a planar waveguide

We report on the optimization of a waveguide structure for the maximization of the radiation forces exerted on a Rayleigh particle in the cover region. The two main radiation forces involved are the transverse gradient force which attracts a particle into the waveguide and the combined scattering and dissipative forces which drive the particle forward along the channel. The dependence of these forces on parameters including the incident wavelength, the surrounding medium embedding the particles, and the polarizability of the particles is discussed. Both dielectric and metallic gold spheres of radius 10 nm are considered in the model. Special emphasis is devoted to the maximization of the transverse gradient force due to the optical intensity gradient at the waveguide surface, and the wavelength dependence of the polarizability of gold nanoparticles

Waveguide surface plasmon resonance biosensor for the aqueous environment

We report the fabrication and performance of gold coated waveguide surface plasmon resonance biosensors. Biotin-avidin binding reactions at the sensor surface were observed. The output power of the sensor showed a decrease of 32% on binding a dual layer of biotin-avidin

Integrated optical Mach-Zehnder interferometer as simazine immunoprobe

Immunoassay has become a versatile tool in several fields of analytical chemistry. We describe the characterization and the application of different integrated optical channel waveguide Mach-Zehnder interferometers (MZIs) as label-free immunoprobes. The performance of the classical MZI is compared with that of a modified structure which incorporates a 3x3 coupler. Characterization of the devices demonstrates a dramatic improvement gained by using the 3x3 coupler. Two main advantages are achieved by the modified device. First, the possibility of referencing the output signal allows the elimination of signal fluctuations due to coupling and light-source instabilities. An increase of the signal-to-noise ratio by a factor of up to 10 is achieved. Secondly, the phase shift between the three outputs allows unambiguous detection with optimum sensitivity. For the detection of the herbicide simazine, the functional properties of the transducer surface are optimized by an appropriate chemical modification. Using this improved device, a simazine immunoassay has been carried out with a test midpoint of 0.3 ppb and a detection limit of approximately 0.1 ppb. The excellent performance, established manufacturing techniques and the potential for simplification and parallelization make the device attractive for further development

Study of luminol electrochemiluminescence with a planar optical waveguide for peroxide sensor application

The work presented in this paper is aiming at the development of a highly sensitive, specific, cheap and widely applicable new sensor based on the combination of optical and electrochemical techniques. In addition to the analytically valuable information of light intensity generated, the light transient resulting from a double potential step experiment contains kinetic information for both the electrochemical step as well as for the successive diffusion and chemical steps in the reaction layer. The comparison of transients due to short range waveguide-evanescent field coupling as shown in Fig. 2 and those obtained by measuring light over the full depth of the diffusion layer in Fig. 3 can be used to obtain such information

Integrated optical directional coupler sensor for pesticide analysis

Integrated optical transducers for the measurement of interactions between biological molecules and the specific detection of chemical and biochemical species are the subject of growing interest. Targeted applications include environmental monitoring, industrial process control and medical diagnostics. Integrated optical devices are capable of delivering the high detection sensitivity achievable through optical techniques in a compact format, and offer the potential for the detection of several analytes simultaneously through the fabrication of multiple transducers on a single chip. Here we describe the use of a new type of integrated optical sensor applied to the detection of low concentrations of the pesticide atrazine in aqueous solution. The transducer is based on a planar waveguide directional coupler structure fabricated by Ag+-Na+ ion-exchange in a low-index glass substrate. This sensor has the advantage of differential outputs, which gives improved signal-to-noise characteristics and offers the potential for the simultaneous measurement of the real and imaginary parts of the refractive indices of bulk or thin-film analytes

Integrated optical sensor system for beverage analysis

Integrated optical transducers for the detection of chemical and biochemical species and for optical measurements on bulk media are the subject of intense research effort. While many such sensors have been demonstrated in research laboratories worldwide, commercial exploitation of integrated optical sensors has proceeded slowly. Progress towards incorporating multiple-output sensors, based around the use of integrated optical Mach-Zehnder interferometers (MZIs), into a robust and inexpensive instrument is described in this paper. A 1D CCD array is used to acquire the multiple outputs, resulting in ready alignment and a flexible approach to device reconfiguration and offering particular promise for application to multianalyte transducers where several signals must be interrogated simultaneously. The sensitivity and low noise demonstrated by the detection system is expected to allow the use of cheap, stable, LED light sources in practical systems

Determination of complex refractive indices of absorbing media using a directional coupler

A method is presented for the simultaneous measurement of the real and imaginary parts of the refractive indices of absorbing media using an integrated-optical sensor

Integrated optical sensor utilising a 1D CCD array for multiple output addressing

An inexpensive and robust method for acquiring multiple outputs from integrated optical sensor devices using a 1D CCD array is described in this paper. An example is given of the development of an instrument based on the use of an integrated optical Mach-Zehnder interferometer (MZI) refractive index transducer. The technique is especially promising for application to multianalyte sensors where several outputs need to be interrogated simultaneously. The high sensitivity and low noise demonstrated by the system will enable the use of cheap, stable LED light sources in practical instruments. Introduction: Integrated optical transducers for the real-time measurement of interactions between biological molecules and for the specific detection of chemical and biochemical species are the subject of growing interest. Applications of this technology include environmental pollution monitoring, industrial process control and medical diagnostics. Integrated optical sensors provide the high detection sensitivity achievable using optical transduction techniques in a compact and robust format. This approach also offers advantages for the fabrication of multianalyte sensors through the integration of multiple transducers on a single chip by straightforward scaling of the photolithographic production process. Several types of integrated optical sensor have been described (e.g. [1-3]), but no commercially viable multianalyte system currently exists and, in order to fully exploit this technology in practical instrumentation, inexpensive and reliable techniques for addressing the multiple outputs of waveguide devices must be found. Fibre-to-chip pigtailing of integrated optical devices formed in 'passive' materials such as glass, where it is difficult to truly integrate monolithic light sources and detectors, is not the best solution when dealing with multiple outputs due to the necessity of producing and pigtailing fibre arrays. For single input devices, however, fibre input coupling is still a viable option as only a single pigtail needs to be made. In this paper we present measurements on multiple-output integrated optical sensor devices using fibre input coupling and a cheap, readily available, 1D CCD array detector to simultaneously address all outputs. A lens is used to focus the waveguide outputs onto the array, resulting in a compact unit that can be housed in a standard instrument package. A further advantage of this arrangement is that other optical elements such as filters and polarisers can readily be inserted into the beam path