E.F. Schipper

The realization of an integrated Mach-Zehnder waveguide immunosensor in silicon technology

We describe the realization of a symmetric integrated channel waveguide Mach-Zehnder sensor which uses the evanescent field to detect small refractive-index changes (?nmin ? 1 × 10?4) near the guiding-layer surface. This guiding layer consists of ridge structures with a height of 3 nm and a width of 4 ?m made in Si3N4. This layer has a thickness of 100 nm. The sensor device has been tested with glucose solutions of different bulk refractive indices. Results of a slab-model calculation are in good agreement with obtained experimental results. The feasibility of applying this sensor for immunosensing, detecting directly the binding of antigen to an antibody receptor surface, is shown with antibody-antigen binding experiments.

New detection method for atrazine pesticides with the optical waveguide Mach-Zehnder immunosensor

Concentrations of analytes can be determined within a few minutes using on-line analysis of the immunobinding kinetics in a solid phase immunoassay. This approach has been applied to the detection of atrazine. Atrazine is detected, at concentrations around the European Community limit (0.1 ?g/l) by a competitive assay. To this end, the two channels of a Mach-Zehnder waveguide sensor are used simultaneously in a difference measurement. The advantage of this way of measuring is discussed with the atrazine measurements.

Feasibility of optical waveguide immunosensors for pesticide detection: physical aspects

The feasibility of detecting small molecules such as pesticides using optical evanescent-wave sensors is discussed with emphasis on the Mach-Zehnder sensor and a newly developed sensor called a ‘critical’ sensor. For direct detection of an estimated average pesticide layer growth of 2×10−4 nm, the sensitivity of the Mach-Zehnder sensor is almost adequate (1×10−3 nm within one hour), whereas that of the ‘critical’ sensor (2×10−2 nm) is not sufficient. However, the simplicity of this latter sensor is very attractive. Results of α-hSA/hSA immunoreaction experiments obtained with this last type of sensor are presented.

Optical-trapping micromanipulation using 780-nm diode lasers

We have designed and implemented an optical-trapping configuration that uses near-infrared laser diodes. The highly divergent output beam of the diode laser was collimated by using only one aspheric compact disc lens. The resulting output beams are astigmatic and elliptic and have a flat, non-Gaussian intensity profile. Calculations and measurements were performed to investigate the influence of this profile on the trapping forces. The results show that use of a laser diode, collimated with a compact disc lens, provides a near-infrared light source that can be used for optical trapping. The light source is compact and relatively cheap and can be easily incorporated into an existing microscope.