Thin film waveguide, interferometric detection of specific target materials such as bound bio-components and mirco-organisms such as bacteria is based on the fact that such materials are typically surface bound on the waveguide. The desired bio or other material is often at a distance from the waveguide surface and are thus of reduced effect on the waveguide traveling wave and detected interferometrically with less sensitivity than materials, including environmental litter, debris and other contaminants etc. that are bound to the waveguide surface closer and whose influence on the traveling wave is more strongly felt in the interferometric analysis, masking the target material. In other cases the target specimen may be large relative to the litter and though being at the surface it still cannot be separately detected and distinguished from the litter. The effect of bound specimens or other materials is the result of their effect on the apparent index of refraction since it is the change in the index between the guiding layer and the bordering layers. As a result of this effect, the desired specimen may not be detectable, or separately detectable, being masked by the more strongly felt and closely bound litter.
While thin film technology is very effective in creating low cost structures, it is thus often unsuitable and it becomes necessary to use more expensive, slower and more sophisticated testing procedures for these purposes. This often means that testing for important bio-contaminants is unavailable due to cost considerations.
On the other hand, if a low cost and fast testing system were available, even of less precision that the more costly approaches, initial screening could be accomplished on a large number of cases at low cost, saving the higher cost refining testing to only those cases where there is a positive result from the economical test.
The present invention solves this problem by providing at low cost a system for the thin film waveguide, interferometric detection of specific target materials such as bound bio-components and mirco-organisms such as bacteria. Such materials are typically either: bound on the waveguide at a distance from the waveguide surface and are thus of reduced effect on the waveguide traveling wave and detected interferometrically with less sensitivity than materials; or are large and if closely bound are detectable but not distinguishable from litter closely bound. The present invention reduces the influence of litter materials that are closely bound to the waveguide surface and whose influence on the traveling wave is more strongly felt or indistinguishable in the interferometric analysis. This is achieved by applying two radiations of different TE and TM modes and tuning the waveguide dimensions and light wavelength to a point where the difference in the changes of phase of each is a minimum for effects close to the waveguide surface but still of a significant change for those in or partly in the range of distances where materials of interest are bound.
A wave guiding layer of a dielectric material is provided of a predetermined thickness. The layer is bordered by layers of different index of refraction so as to confine a propagating wave, typically the lowest order light wave modes, TE0 and TM0 modes at for example 1300 nm. The two components of the beam are processed to interfere with each other, such as by separating and then recombining them to cause an interference pattern, the position of which can be measured to indicate the degree of phase shift of one relative to the other and in turn of the amount of material in the biolayer.
According to the present invention the waveguide layer thickness and the radiation wavelength λ are selected so that the effects on phase difference between the two radiations applied in the beam are minimal in the response to material in the region directly adjacent the surface of the waveguide, so as to unmask the influence of the more distant material.
These and other features of the invention are more fully set forth below in the description of the invention and in the accompanying drawing of which:
The present invention contemplates a system for the thin film waveguide, interferometric detection of specific target materials such as bound bio-components and mirco-organisms such as bacteria by unmasking it from litter bound close to the waveguide surface. Target materials are in one case surface bound on the waveguide at a distance from the waveguide surface and are thus of reduced effect on the waveguide traveling wave and detected interferometrically with less sensitivity than non target material, including environmental litter, etc. that is bound to the waveguide surface closer and whose influence on the traveling wave is more strongly felt in the interferometric analysis. In another case, the target material is large and even if closely bound to the waveguide surface is indistinguishable from the closely bound litter. The effect on interferometric detection instrumentation of bound specimens or other materials is the result of their effect on the apparent index of refraction since it is the change in the index between the guiding layer and the bordering layers. Thus prior art systems typically are unable to detect objects at a distance in the presence of closely bound litter and are further unable to distinguish litter from large objects even if closely bound.
The dielectric layer 12, commonly of silicon, doped glass or silicon-oxynitrides, has an index of refraction that differs from the layers that border it so as to confine a propagating wave 24 of wavelength λ, typically the lowest order light wave modes, TE0 and TM0 modes, with the electric field vectors respectively horizontal and vertical (nominally) in the view of the figures. The horizontal direction can be large but typically is sufficient to behave as though infinite. The effect of bound materials in the biolayer 22 is to influence the index of refraction which in turn effectively delays one or both modes, creating a phase shift in it or them at the output radiation 26. The two components of the beam 26 are then processed to interfere with each other, such as by separating and then recombining them to cause an interference pattern, the position of which can be measured to indicate the degree of phase shift of one relative to the other and in turn of the amount of material in the biolayer 22.
The closer, non target materials 30, which are typically unavoidable debris and contaminants by being closer will have a stronger influence on that process relative to the specific, distant, target materials 28a. In the case of large, closely bound particles 28b, detection of a phase shift is not conclusive of their presence since the phase shift could be attributable to closely bound litter instead.
According to the present invention the guiding layer thickness 14 and the wavelength λ are selected so that the effects on phase difference between the two radiations applied in the beam 24 are minimal in the region directly adjacent the surface of the waveguide, layer 20, so as to unmask the influence of the more distant materials 28a or large materials 28b with distant components.
The interplay of thickness 14 and the difference in the phase change for the two radiation components is illustrated in a set of curves.
Seen from yet another perspective in
In actual practice of the invention it is convenient to flow the material to be analyzed over the surface of the waveguide in a fluid. For this purpose, the assembly of
The fluid in channel 108 is typically applied as a sequence of fluids as illustrated in
The invention shown above is limited in scope only in accordance with the following claims.
This application claims priority to prior provisional application, Ser. No. 60/220,543, filed Jul. 25, 2000, incorporated herein by reference.
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/US01/12339 | 4/13/2001 | WO | 00 | 1/24/2003 |
Number | Date | Country | |
---|---|---|---|
60220543 | Jul 2000 | US |