INTEGRATED OPTICAL MACH-ZEHNDER INTERFEROMETERS AS SIMAZINE IMMUNOPROBES

Immunoassay has become a versatile tool in several fields of analytica l chemistry. We describe the characterization and the application of d ifferent integrated optical channel waveguide Mach-Zehnder interferome ters (MZIs) as label-free immunoprobes. The performance of the classic al MZI is compared with that of a modified structure which incorporate s a 3 X 3 coupler. Characterization of the devices demonstrates a dram atic improvement gained by using the 3 X 3 coupler. Two main advantage s are achieved by the modified device, First, the possibility of refer encing the output signal allows the elimination of signal fluctuations due to coupling and light-source instabilities. An increase of the si gnal-to-noise ratio by a factor of up to 10 is achieved. Secondly, the phase shift between the three outputs allows unambiguous detection wi th optimum sensitivity. For the detection of the herbicide simazine, t he functional properties of the transducer surface are optimized by an appropriate chemical modification. Using this improved device, a sima zine immunoassay has been carried out with a test midpoint of 0.3 ppb and a detection limit of approximately 0.1 ppb. The excellent performa nce, established manufacturing techniques and the potential for simpli fication and parallelization make the device attractive for further de velopment.