Novel bioaffinity sensors for trace analysis based on luminescence excitation by planar waveguides

Abstract

We have developed a novel generation of optical bioaffinity sensors for ultra trace analysis. These sensors are based on luminescence generation in the evanescent field of high-refractive-index single-mode planar waveguides, With the waveguiding layers and the grating parameters chosen, very sharp discrimination of bulk against surface-confined excitation, in combination with high excitation intensities in the evanescent field, can be achieved, leading to unprecedented sensitivity. Experimental data of the optimization of the transducer parameters will be presented. Incoupling of excitation light is performed using diffractive gratings. Different methods for the detection of both transmitted and luminescence light will be presented. The transmitted excitation light can be detected either at the distal waveguide chip end or using a second outcoupling grating. Both isotropically emitted luminescence, collected by a lens located below the transducer substrate (‘volume detection’), and emission coupled back into the waveguiding layer can be monitored, the latter via a second outcoupling grating. First experimental results obtained in model bioaffinity assays will be presented, demonstrating the feasibility of the different detection methods mentioned above, as well as the superior sensitivity of our novel sensor configuration. In still preliminary experiments, 100 attomoles of fluorescently labelled DNA (16-mer oligonucleotide), applied at 100 femtomolar concentration, can be detected.