Optics: measuring and testing – Of light reflection
Reexamination Certificate
2000-05-08
2002-11-12
Rosenberger, Richard A. (Department: 2877)
Optics: measuring and testing
Of light reflection
Reexamination Certificate
active
06480282
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates generally to Surface Plasmon Resonance (SPR) sensor devices, their use in biological and chemical sensing, and their use in multisensor devices and applications.
Field-based biological and chemical sensors are of increasing importance due to their ability to detect natural and man-made hazards such as environmental contamination, biowarfare agents, explosives, and foodborne pathogens. Optical sensors based on surface plasmon resonance (SPR) are attractive for these applications.
Surface plasmon resonance (SPR) is an optoelectronic phenomenon used to construct sensitive thin-film refractometers which may be readily applied to chemical and biological sensing (Liedberg, B. et al. (1995), “Biosensing with surface plasmon resonance—how it all started,” Biosensors & Bloelectron. 10:i-ix; Sambles, J. R. et al. (1991), “Optical excitation of surface plasmons: an introduction,” Contemp. Phys. 32:173-183). One common design of an SPR sensor is shown in
FIG. 1
a
. A prism (
1
) is coated on one side (
2
) with a 50 nm gold (or silver) film (
3
). Monochromatic light (
4
, TM polarized) enters an opposing prism face and strikes the metal-coated face (
2
) at a range of angles above the critical angle. The reflected light (
5
) is measured, and reflectivity (intensity of reflected light) as a function of angle is determined. When plotted, this reflectivity spectrum exhibits an attenuation feature centered at a particular angle (
FIG. 1
b
). This angle is sensitive to the refractive index (RI) within approximately one wavelength of the metal-coated surface: If the RI increases, e.g., due to the presence of an analyte, the angle will increase, as illustrated in
FIG. 1
b
for RI=n
a
=1.33-1.38. Measurement of this angle can be used to measure the effective RI of a thin layer adjacent to the metal surface and to detect changes in RI due to changes in type and concentration of analytes present in that layer.
The planar SPR configuration has practical constraints, including awkward sample handling, requirements for index matching and optical inflexibility, that limit its application. For most SPR sensing experiments, the analyte must smoothly and continuously flow over the planar sensing surface. As illustrated in
FIG. 1
a
, a flat flow cell sealed to the metal surface using gaskets and incorporating input and output fittings for tubing connections is typically employed. Because of the complexity of construction of the cell, sample handling can be awkward and leaks and bubble accumulation, which disrupt sensing, are common problems. Because the prism used in the planar configuration can be an expensive glass component, the SPR metal layer is often deposited on a thin disposable glass slide which is index-matched to the prism. The inexpensive slide may then be changed without disturbing the prism. The use of an index-matching fluid introduces additional complexity in the device, difficulty of use, and other problems including potential sensor drift and analyte contamination. The planar SPR configuration is not readily adaptable to multisensing applications (e.g., simultaneous measurement of several sample properties, particularly optical properties). The planar configuration is designed to measure reflectivity only and only one side of the planar sensing surface is optically accessible. This configuration does not allow other types of optical measurements (e.g., transmissivity or fluorescence) which are of interest in multisensing applications.
SPR sensing technology can be adapted for field sensing applications by improving sensor compactness, ruggedness, and ease of use and by improving the optical flexibility of the SPR sensor by facilitating its use for multiple independent optical measurements.
Several improved sensing SPR configurations, including the ultraminiature fiber-optic SPR probe developed by Jorgenson and Yee, S. S. (1993) “A fiber optic chemical sensor based on surface plasmon resonance,”
Sensors and Actuators
B 12:213-220, the SPR lightpipe developed by Karlson et al. (1996), “First-order surface plasmon resonance sensor system based on a planar light pipe,”
Sensors and Actuators
B 32:137-141, in which the optical substrate may be replaced without the use of index matching fluid, and a miniature planar probe sensor combining the advantages of these devices (Johnston, K. S. et al. (1999), “Prototype of a multi-channel planar substrate SPR probe,”
Sensors and Actuators
B 54:57-65). Another recent development is a compact, rugged integrated SPR sensor in which all sensor components are contained in one small molded package (Melendez, J. (1997), “Development of a surface plasmon resonance sensor for commercial applications,” Sensors and Actuators B 39:375-379).
Several multisensor configurations of SPR devices have been reported. Johnston et al. described how simultaneous measurement of multiple lightpipe sensor “bands” improves the ability of SPR measurements to characterize thin films (Johnston, K. S. (1995), “New analytical technique for characterization of thin films using surface plasmon resonance,”
Mater. Chem. Phys
. 42:242-246.). Nenninger et al. (1998), “Reference-compensated biosensing using a dual-channel surface plasmon resonance sensor system based on a planar lightpipe configuration,”
Sensors and Actuators
B 51:38-45 demonstrated the use of multichannel sensing in the lightpipe geometry to compensate for non-specific binding in SPR biosensing. Chinowsky et al. described the combination of bulk refractive index (RI) measurements with SPR measurements to compensate for interference from temperature or buffer concentration changes (Chinowsky, T. M. and Yee, S. S., U.S. Provisional Application No. 60/132,894, filed May 6, 1999, incorporated by reference herein in its entirety). Chinowsky et al. also demonstrated the use of estimation theory to design optimal linear data analysis techniques for SPR (Chinowsky, T. M. et al. (1999), “Optimal linear data analysis for surface plasmon resonance biosensors,”
Sensors and Actuators
B 54:89-97) and to quantify the ultimate capabilities of such combination measurements (Chinowsky, T. M. and Yee, S. S. (1998), “Quantifying the information content of surface plasmon resonance reflection spectra,”
Sensors and Actuators
B 51:321-330). In related research, Johnston et al. demonstrated a chemometric approach to SPR data analysis and calibration (Johnston, K. S. et al. (1997), “Calibration of surface plasmon resonance refractometers using locally weighted parametric regression,”
Anal. Chem
. 69:1844-1851), and showed that such an approach can enable simplifications in sensor instrumentation (Johnston, K. S. et al. (1999), “Performance comparison between high and low resolution spectrophotometers used in a white light surface plasmon resonance sensor,”
Sensors and Actuators
B 54:80-88).
The present invention overcomes limitations of currently available SPR configurations by providing a novel device configuration that is less complex, simpler to use and adaptable to multisensor applications.
SUMMARY OF THE INVENTION
The present invention provides a capillary SPR sensor. This sensor comprises a capillary substrate, i.e., a tube with an axial cavity, in which at least a portion of the inside surface of the capillary is provided with an SPR-sensing area. The SPR-sensing area comprises an SPR-active conductive layer, which can be a among others, a metal layer (particularly gold or silver), a semiconductor layer or an organic conductor layer. In this SPR sensor configuration, a sample to be analyzed is introduced into the capillary cavity and the capillary substrate is then radially illuminated with light having a TM-polarized component. Light exiting radially from the capillary substrate is detected at selected angles. Radially exiting light that interacts with the SPR-sensing area at angles greater than the critical angle carries SPR features. This light can be detected as a function of incident angle to detect SPR, measure the refractive index of an analyte in t
Chinowsky Timothy M.
Yee Sinclair S.
Greenlee Winner and Sullivan P.C.
Rosenberger Richard A.
University of Washington
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