Optical waveguides – Optical waveguide sensor
Reexamination Certificate
2001-09-28
2003-09-23
Kim, Ellen E. (Department: 2874)
Optical waveguides
Optical waveguide sensor
C385S131000
Reexamination Certificate
active
06625336
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to the field of optical assaying, and more particularly to an optical sensor having a dielectric film stack.
BACKGROUND OF THE INVENTION
Extremely sensitive optical sensors have been constructed by exploiting an effect known as surface plasmon resonance (SPR). These sensors are capable of detecting the presence of a wide variety of materials in concentrations as low as picomoles per liter. SPR sensors have been constructed to detect many biomolecules including keyhole limpet hemocyanin, &agr;-fetoprotein, IgE, IgG, bovine and human serum albumin, glucose, urea, avidin, lectin, DNA, RNA, HIV antibodies, human transferrin, and chymotrypsinogen. Additionally, SPR sensors have been built which detect chemicals such as polyazulene and nitrobenzenes and various gases such as halothane, trichloroethane and carbon tetrachloride.
An SPR sensor is constructed by sensitizing a surface of a substrate to a specific substance. Typically, the surface of the substrate is coated with a thin film of metal such as silver, gold or aluminum. Next, a monomolecular layer of sensitizing material, such as complementary antigens, is covalently bonded to the surface of the thin film. In this manner, the thin film is capable of interacting with a predetermined chemical, biochemical or biological substance. When an SPR sensor is exposed to a sample that includes a targeted substance, the substance attaches to the sensitizing material and changes the effective index of refraction at the surface of the sensor. Detection of the targeted substance is accomplished by observing the optical properties of the surface of the SPR sensor.
There are two common constructions of an SPR sensor.
FIG. 1
illustrates a prism-based SPR sensor
10
that is the most common form of SPR sensors. Sensor
10
includes a disposable slide
20
that is placed on a fixed glass prism
12
. Slide
20
is coated with a metal film
16
and sensitizing material
22
is capable of interacting with target substance
18
in sample
21
. Before placing slide
20
on prism
12
, an operator coats prism
12
with an anti-reflection coating
14
, often a fluid, in order to prevent light beam
24
from reflecting before reaching metal-film layer
16
.
Light source
28
generates light beam
24
that is incident upon sensor
10
. Sensor
10
reflects light beam
24
as light beam
26
received by detector
30
. At a specific angle of incidence of light beam
24
, known as the resonance angle, a very efficient energy transfer and excitation of the surface plasmon occurs in metal film
16
. As a result, reflected light
26
exhibits an anomaly, such as a sharp attenuation, and the resonance angle of sensor
10
can be readily detected. When targeted substance
18
attaches to sensitizing material
22
, a shift in the resonance angle occurs due to the change in the refractive index at the surface of sensor
10
. A quantitative measure of the concentration of targeted substance
18
can be calculated according to the magnitude of shift in the resonance angle.
A second common form of an SPR sensor, known as grating-based SPR sensor, involves the use of a metal diffraction grating instead of glass prism.
FIG. 2
illustrates a grating-based SPR sensor
40
in which substrate
45
is formed to have sinusoidal grooves. In grating-based SPR sensors, the period of the groove profile of substrate
45
typically ranges from 0.4 micrometers to 2.0 micrometers. Thin metal film
42
is formed outwardly from the surface of substrate
45
and comprises any suitable metal such as aluminum, gold or silver. In one embodiment, layer
42
comprises silver having a thickness of approximately 100 nm.
Sensitizing layer
44
is formed outwardly from metal film
42
. Sensitizing layer
44
is selected to interact with a predetermined chemical, biochemical or biological substance
18
contained in sample
21
. In one embodiment, sensitizing layer
44
comprises a layer of antigens capable of trapping a complementary antibody. Recently, several techniques have been developed for attaching antigens as a receptive material to film
42
such as spin coating with a porous silica sol-gel or a hydrogel matrix. Preferably, sensitizing layer
44
is less than 100 nm thick.
In
FIG. 2
, light source
28
produces light beam
24
incident upon sensor
40
such that detector
30
receives reflected light beam
26
. For grating-based SPR sensors, resonance occurs, and reflected light beam
26
exhibits an anomaly, when a polarization component of light beam
24
is perpendicular to the groove direction of the surface of substrate
45
and the angle of incidence of light beam
24
is appropriate for energy transfer and excitation of the surface plasmon in thin metal film
42
.
Grating-based SPR sensors have several distinct advantages over prism-based SPR sensors. For example, the resonance angles of grating-based SPR sensors may be finely tuned by adjusting the groove profile. In addition, grating-based SPR sensors do not require the use of an anti-reflection coating. Grating-based SPR sensors, however, suffer from the fact that the light must propagate through the sample as opposed to prism-based sensors in which the incident light propagates through the prism and strikes the metal film opposite from the sample. Propagation through the sample is disadvantageous because the sample tends to absorb or scatter the incident light. For these reasons, grating-based SPR sensors are ill suited for assaying liquids, such as blood, and are primarily used in gas sensing applications. Furthermore, both of the above-described SPR sensors rely on a highly conducting metallic film to support the surface plasmon resonance. This metal film, however, limits the wavelength of the resonance to the red or infrared region of the light spectrum because at shorter wavelengths the conductivity of even the best metals is not sufficient to generate sharp resonances, thereby resulting in lower sensitivity.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon understanding the present invention, there is a need in the art for an optical sensor having the benefits of grating-based SPR sensor that does not require that the incident light propagate through the sample.
SUMMARY OF THE INVENTION
Described herein is a method and apparatus for optically assaying a targeted substance in a sample using an inventive sensor that overcomes the above-described deficiencies of conventional grating-based and prism-based SPR sensors. The sensor exhibits a sharp resonance that is comparable in magnitude with resonances commonly exhibited by conventional SPR sensors. However, unlike grating-based SPR sensors, a sample may be assayed by reflectance from the substrate side without propagating light through the sample. In addition, the sensor allows a sample to be assayed with transmitted light. One advantage of assaying with transmitted light is the ability to use a diffused light source. Because the sensor does not rely on the use of conductive metals, the sensor enables sharp resonances at shorter wavelengths than conventional SPR sensors.
According to one aspect, the invention is a sensor comprising a dielectric film stack having a plurality of dielectric layers. The dielectric layers operate as a waveguide such that a portion of the incident light propagates within the dielectric film stack for at least one angle of incidence. In one embodiment, the dielectric layers are formed with a dielectric material selected from either a first dielectric material having a first index of refraction or a second dielectric material having a second index of refraction. In one configuration, the dielectric film stack is formed such that the dielectric material of the dielectric layers alternates between the first dielectric material and the second dielectric material. The dielectric film stack may be formed as a dielectric mirror, such that light incident upon the sensor substantially reflects from the sensor, or as an a
Challener William A.
DePuydt James M.
Tolbert William A.
Imation Corp.
Kim Ellen E.
Levinson Eric D.
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