MENU

Membrane-coated optical grating coupler sensors

Development of thin-film coatings for integrated optics
grating couplers in order to enhance their sensitivity,
selectivity and speed of response for sensing applications
in medicine.

An optical waveguide consists of a support on which is deposited a thin, high refractive index waveguiding film, the surface of which can be brought into contact with an analyte solution (covering medium). The key parameter describing the state of the waveguide is its effective refractive index N, which depends on thicknesses and refractive indices of the support, waveguiding film, and covering medium (1). N can be measured rapidly, accurately and conveniently for as many guided modes as the waveguide will support by the recently invented grating coupler (2,3). Upon contact with an analyte solution, three possible interactions may take place: (i) the refractive index of the covering medium changes; (ii) the analyte migrates and binds to the waveguide surface layer, forming an adlayer; (iii) the analyte may penetrate into the waveguiding layer. Each of these changes results in a change in N. However, (ii) is by far the most significant. This opens the way to develop miniature, integrated chemical sensing devices. Typical fluids of interest in medical diagnostics may contain many substances differnt from, and in addition to, the analyte of interest. The key to practical sensing devices is therefore to develop waveguide surface coatings with a high affinity for the analyte, and a low affinity for everything else. Two types of surface coatings are envisaged: (a) Proteins and other biomolecules acting as specific receptors for the analyte of interest whose presence on the surface causes a change in N. This requires the receptor to be immobilised in a stable, active form at the waveguide surface (4); (b) many analytes are small molecules (e.g. drugs and hormones) which do not contain enough atoms to cause a measurable change in N. when bound to a receptor. For detecting these small molecules, which are often lipophilic, it is advantageous to use a bilayer lipid membrane as a surface coating (5). By this means, the signal from the drug can be greatly amplified (6). The main work in this project is: 1. developing suitable immobilization techniques; 2. understanding lipid membrane-analytic interactions, in order to be able to rationally design lipids or other membrane-forming surfactants for maximizing the sensitivity and selectivity of response to a particular analyte or family of analytes; 3. developing waveguide grating coupler materials and manufacturing procedures compatible with thin surface films of biomolecules or lipids. Literature: (1) P. K. Tien, Rev. mod. Phys. 49, 361 (1977). (2) K. Tiefenthaler et al., U.S. Patent No. 4,815,843. (3) K. Tiefenthaler & W. Lukosz, J. opt. Soc. Amer. B 6, 209 (1989). (4) H. Sigrist, H. Gao & B. Wegmueller, Biotechnology 10, 1026 (1992). (5) J. J. Ramsden, Experimentia 49, 688 (1993). (6) J. J. Ramsden, Sensors and Actuators B 15-16, 439 (1993).
Acronym: 
MEMOCS
Project ID: 
947
Start date: 
01-03-1993
Project Duration: 
202months
Project costs: 
2 060 000.00€
Technological Area: 
Sensor Technology related to measurements
Market Area: 

Raising the productivity and competitiveness of European businesses through technology. Boosting national economies on the international market, and strengthening the basis for sustainable prosperity and employment.