Planar waveguides as efficient transducers for bioaffinity sensors

Specific detection of extremely low amounts of antigens or disease markers allowing the diagnosis of deseases and infections at a very early stage has become a major driving force for the development of new generations of biochemical sensors. To match this goal, we propose the substitution of the widely used fiber-shaped evanescent field sensors by planar single-mode metal oxide waveguides. In combination with bioaffinity assays, this transducer geometry offers benefits such as enhanced sensitivity, ease of sensor handling and preparation, sample volume reduction, versatility, and low cost per test. Recently, planar waveguides have been used in sensor schemes exploiting the changes of the so-called effective refractive index (caused by changes in mass of surface-bound biomolecules): grating couplers, surface plasmon resonance, and interferometers. However, compared to luminescence-based sensor schemes, the sensitivities of these label-free methods are inferior. In this paper we report on a new generation of luminescence-based bioaffinity sensors for human diagnostics including optimization of the planar evanescent field transducers, the design of a compact sensor system, and a first study of the binding of fluorophore-labeled IgG to protein A immobilized on the transducer.