Metallic overcoating as a light attenuating layer for optical sensors

Information

  • Patent Grant
  • 6207110
  • Patent Number
    6,207,110
  • Date Filed
    Friday, August 21, 1998
    26 years ago
  • Date Issued
    Tuesday, March 27, 2001
    23 years ago
Abstract
A liquid permeable metallic coating is utilized in conjunction with a fluorescence based optical sensor. The metallic coating is deposited directly on, and is in physical contact with, the sensing membrane. The metallic coating does not require an intervening substrate layer or other components. When light from a light source is shone through the substantially light transmissive substrate onto the sensing membrane, the metallic overcoating reflects back the excitation light as well as the fluorescence light generated by the sensor such that substantially no light reaches the sample where the light may be scattered and/or absorbed by the sample. Accordingly, the accuracy and repeatability of the sensor is improved while the cost and production times associated with manufacturing the sensor are minimized.
Description




CROSS-REFERENCE TO RELATED APPLICATIONS




Not Applicable




STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT




Not Applicable




BACKGROUND OF THE INVENTION




Fluorescent based optical sensors wherein a sensing membrane is layered onto a light transmissive substrate are known. The sensing membrane of the sensor is brought into contact with a sample while an excitation light reaches the sensing membrane through the substrate. The combination of the excitation light, the sensing membrane and a particular analyte will cause the sensing membrane to emit a fluorescing light. The emission signal from the sensing membrane is then detected through the light transmissive substrate from the back side of the sensor. Due to the fact that the sensing membranes of the sensor are quite thin there is a fairly large amount of the excitation light which passes through the sensing membrane and into the sample or into the sample chamber. The light which passes through the sensing membrane may be scattered, absorbed or reflected by the sample or the chamber walls back into and through the sensing membrane. Additionally, the fluorescing signal emitted from the sensing layer, which is indicative of the detection of the amount of the analyte of interest of the sample under test, may also be absorbed, scattered or reflectedly the sample back to the detector. The scattering, absorbing or reflecting of the excitation light and the fluorescing light emitted by the sensing membrane can combine to provide a four fold change in the signal between a perfectly reflecting and perfectly absorbing signal, thus severely skewing the detection results of the sensor.




Previous attempts to address this issue of unintended light affecting the results of the sensor include coating the sensing membrane with a support layer material which has been impregnated with a second material, or coating the sensing membrane with a plurality of layers such that the amount of light escaping the sensor into the sample and sample chamber is a very small fraction of the total light directed to the sensor. These attempts utilized a complex chemical process to produce an opaque, chemically permeable multilayered structure which is then laminated onto the sensing membrane. For example, U.S. Pat. No. 5,091,800 discloses the construction of an ion permeable cover membrane formed from a cross linked PVOH or cellophane substrate which is stretched onto a form and impregnated with silver, gold or platinum colloidal precipitants through a series of chemical treatments to form the opaque membrane. U.S. Pat. Nos. 5,081,041 and 5,081,042 disclose the use of an ion permeable cover membrane fabricated from a Dextran or cellulose substrate and impregnated with detergent solvated carbon black. U.S. Pat. Nos. 4,919,891 and 5,075,127 utilize cellulose acetate/acetone mixtures of either copper pthalocyanine or carbon black cast as separate coating membranes. U.S. Pat. No. 3,992,158 discloses the incorporation of a separate TiO


2


-containing cellulose acetate for opacity or reflectance to be used in absorbance based chemistries on dry slides. Similarly, U.S. Pat. Nos. 4,042,335, 4,781,890, 4,895,704 and EP 0 142 849 B1 disclose the use of light blocking layers incorporating TiO


2


particles for slide based chemistry tests. Such techniques have proven to be complex, labor intensive and expensive, requiring the utilization of multiple components or multiple layers of materials. It would be desirable to provide an inexpensive and simple to produce sensor including a single light attenuating layer of material deposited directly on the sensing membrane which reflects excitation and emission light back into the sensor without the light being affected by the sample while permitting the analyte of interest to freely diffuse through the light attenuating layer and into the sensing membrane.




BRIEF SUMMARY OF THE INVENTION




A liquid permeable metallic coating is utilized in conjunction with a fluorescence based optical sensor. The metallic coating is deposited directly on, and is in physical contact with, the sensing membrane. The metallic coating does not require an intervening support layer of material, or other components. When light from a light source is shone through the substantially light transmissive substrate onto the sensing membrane, the metallic overcoating reflects back the excitation light as well as the fluorescence light generated by the sensor such that substantially no light reaches the sample where the light may be scattered and/or absorbed by the sample. Reflectance from within the sample cavity is also avoided. Accordingly, the accuracy and repeatability of the sensor is improved while the cost and production times associated with manufacturing the sensor are minimized.











BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING




The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings in which:





FIG. 1

is a block diagram of a prior art sensor;





FIG. 2

is a block diagram of a sensor including the metallic coating of the present invention;





FIG. 3A

is a graph of test results for the prior art sensor of

FIG. 1

; and





FIG. 3B

is a graph of test results for the sensor including the metallic coating of the present invention.











DETAILED DESCRIPTION OF THE INVENTION




A prior art sensing system


10


is shown in FIG.


1


and includes a sensor


15


, a light source


50


, and a detector


60


. Sensor


15


comprises a light transmissive substrate


20


having a sensing membrane


30


layered thereon. In operation, sensing membrane


30


is brought into contact with a sample (not shown) being tested. The light source


50


provides an excitation light to substrate


20


, such as through an optical fiber. Substrate


20


is generally light transmissive, thus the light from light source


50


passes through substrate


20


and falls on sensing membrane


30


. Sensing membrane


30


, in the presence of the excitation light and in the presence of a particular analyte in the sample will emit a fluorescing light to a degree defined by the concentration of the analyte in the sample. This fluorescing light provided by sensing membrane


30


will pass through substrate


20


and be detected by the detector


60


.




Since sensing membrane


30


is relatively thin, excitation light also passes through the membrane


30


and into the sample. Once the excitation light is received by the sample it may be scattered, absorbed and/or reflected back through the sensing membrane


30


, and through substrate


20


to be detected by detector


60


. Additionally, the fluorescing light produced by the sensing membrane may also pass through sensing membrane


30


and into the sample where it may be scattered, absorbed and/or reflected. Again, this light may pass through sensing membrane


30


and through substrate


20


where it will be detected by detector


60


. Accordingly, the measurement results of the sensor can be skewed greatly.




Referring to

FIG. 2

a sensing system


100


is shown. The system


100


includes a sensor


70


, a light source


50


and a detector


60


. The light source


50


and detector


60


are in communication with the sensor


70


through any suitable means, including a fiber optic channel. Sensor


70


includes a substrate


20


, a sensing membrane


30


layered on the substrate


20


and a metallic coating


40


layered on the sensing membrane


30


. Substrate


20


may be made of any substantially light transmissive material such as cellulose acetate, cellulose acetate butyrate, polyethylene terephthalate, bisphenol A polycarbonate, polystyrene, polymethyl methacrylate or preferably glass.




The sensing membrane


30


is deposited onto a surface of the substrate


20


. The sensing membrane


30


may comprise any material or group of materials formed together which provide a detectable indication in response to exposure to a specific analyte of the sample. In a preferred embodiment the sensing membrane


30


is made of copolymer JB3001/23 which comprises a mixture of ethylhexylmethacrylate, methylmethacrylate and an oxygen sensing dye such as octa-ethyl-Pt-porphyrin (OEP).




The sensor


70


further includes a liquid permeable metallic overcoating


40


which is generally nontransmissive to light. The metallic overcoating


40


may comprise Aluminum, TiO


2


or preferably a Gold Palladium mixture. The metallic overcoating


40


may be deposited onto the sensing membrane


30


by sputter coating, evaporating or other means, thus no intervening support layer or substrate is required between the metallic coating


40


and the sensing membrane


30


.




The metallic coating may have an optical density of between approximately 0.2 and approximately 0.893.




In operation, metallic coating


40


is brought into contact with a sample (not shown) being tested. Metallic coating


40


is liquid permeable such that the sample can diffuse through metallic coating


40


and contact sensing membrane


30


. The light source


50


provides an excitation light to substrate


20


. Substrate


20


is generally light transmissive, thus the light from light source


50


passes through substrate


20


and falls on sensing membrane


30


. Sensing membrane


30


in the presence of the excitation light and in the presence of a particular analyte of the sample will emit a fluorescing light. This fluorescing light provided by sensing membrane


30


will pass through substrate


20


and be detected by a detector


60


.




Since sensing membrane


30


is relatively thin, light also passes through the membrane


30


and onto metallic coating


40


. Metallic coating


40


is generally nontransmissive to light and reflects the light back through the sensing membrane


30


without allowing a significant amount of the light to reach the sample where the light can be affected by the sample and be subsequently detected by detector


60


. Additionally, the fluorescing light produced by the sensing membrane may also pass through sensing membrane


30


where it will also encounter metallic coating


40


. Once again, metallic coating


40


will reflect the light back to the sensor without a significant amount of the light passing through to the sample where the light may be affected by the sample and subsequently detected by the detector


60


. Accordingly, the excitation light and fluorescing light are not affected by the sample, thus the sensor provides a much more accurate and repeatable sensing of analytes.




Referring now to

FIG. 3A

a Stern/Volmer plot of a fluorescence intensity in response to varying levels of oxygen is shown as detected by a prior art sensor. A clear, aqueous buffer solution was plotted (denoted by the squares) as was a sample having twenty three grams per deciliter of total hemoglobin (THb) (denoted by triangles) and a sample having nine grams per deciliter of THb (denoted by circles). As seen from the plot, the samples having different THb levels produced a large difference in fluorescence, which can be attributed to the presence and detection of interfering light, such as excitation light which has been scattered, absorbed and reflected by the sample as well as fluorescing light which has been reflected, absorbed or scattered by the sample and has been detected by the detector.




Referring now to

FIG. 3B

it can be seen that the same tests performed using similar solutions with the sensor of the present invention provide a much more uniform response. The sensor here has a liquid permeable metallic coating which has an optical density of approximately 0.893. A Stern/Volmer plot of a fluorescence intensity in response to varying levels of oxygen is shown as detected by the sensor of the present invention. A clear, aqueous buffer solution was plotted (denoted by the squares) as was a sample having twenty one grams per deciliter of THb (denoted by triangles) and a sample having six grams per deciliter of THb (denoted by circles). As seen from the plot, the samples having different THb levels produced a generally uniform fluorescence, which can be attributed to the absence of interfering light, such as excitation light which has been scattered, absorbed and reflected by the sample as well as fluorescing light which has been reflected, absorbed or scattered by the sample. Due to the inclusion of the metallic coating directly on the sensing membrane, very little light passes through the metallic coating and to the sample where in can be reflected, absorbed or scattered and provide interfering light which skews the results.




The incorporation of a metallic coating which is liquid permeable as well as being generally nontransmissive to light provides a substantial improvement in the repeatability of sample testing and for testing a variety of different samples. The metallic coating is applied directly onto the sensing membrane without the use of an intervening support layer or without the use of multiple layers of materials thus providing a cost effective manner of including the metallic overcoating since additional materials and labor are minimized, while performance and reliability are greatly improved.




Having described preferred embodiments of the invention it will now become apparent to those of ordinary skill in the art that other embodiments incorporating these concepts may be used. Accordingly, it is submitted that the invention should not be limited to the described embodiments but rather should be limited only by the spirit and scope of the appended claims.



Claims
  • 1. A sensor comprising:a substrate substantially transmissive to light having a first side and a second side; a sensing membrane layered onto the second side of said substrate; and a liquid permeable, substantially nontransmissive to light metallic coating comprising gold and palladium directly layered on said sensing membrane.
  • 2. The sensor of claim 1 wherein said metallic coating is sputter coated onto said sensing membrane.
  • 3. The sensor of claim 1 wherein said metallic coating is evaporated onto said sensing membrane.
  • 4. The sensor of claim 1 wherein said metallic coating has an optical density of between approximately 0.2 and approximately 0.893.
  • 5. The sensor of claim 1 wherein said sensing membrane comprises a mixture of ethylhexylmethacrylate, methylmethacrylate and an oxygen sensing dye.
  • 6. The sensor of claim 5 wherein said oxygen sensing dye comprises octa-ethyl-Pt-porphyrin (OEP).
  • 7. The sensor of claim 1 wherein said substrate comprises glass.
  • 8. The sensor of claim 1 wherein said substrate is selected from the group consisting of cellulose acetate, cellulose acetate butyrate, polyethylene terephthalate, bisphenol A polycarbonate, polystyrene, and polymethyl methacrylate.
  • 9. The sensor of claim 1 further comprising:a light source in communication with said substrate, said sensing membrane and said metallic coating; and a detector in communication with said substrate, said sensing membrane and said metallic coating.
  • 10. A sensor comprising:a substrate substantially transmissive to light having a first side and a second side; a sensing membrane layered onto the second side of said substrate; and a liquid permeable, substantially nontransmissive to light metallic coating comprising gold and palladium layered directly on said sensing membrane, said metallic coating having an optical density of approximately 0.893; a light source in communication with said substrate, said sensing membrane, and said metallic coating; and a detector in communication with said substrate, said sensing membrane and said metallic coating.
US Referenced Citations (30)
Number Name Date Kind
3992158 Przybylowicz et al. Nov 1976
4003707 Lübbers et al. Jan 1977
4042335 Clément Aug 1977
4248829 Kitajima et al. Feb 1981
4255384 Kitajima et al. Mar 1981
4587101 Marsoner et al. May 1986
4680268 Clark, Jr. Jul 1987
4752115 Murray, Jr. et al. Jun 1988
4781890 Arai et al. Nov 1988
4810655 Khalil et al. Mar 1989
4857472 Wolfbeis Aug 1989
4895156 Schulze Jan 1990
4895704 Arai et al. Jan 1990
4919891 Yafuso et al. Apr 1990
5026139 Klainer et al. Jun 1991
5030420 Bacon et al. Jul 1991
5043286 Khalil et al. Aug 1991
5075127 Yafuso et al. Dec 1991
5081041 Yafuso et al. Jan 1992
5081042 Yafuso et al. Jan 1992
5091800 Offenbacher et al. Feb 1992
5173432 Lefkowitz et al. Dec 1992
5208147 Kagenow et al. May 1993
5326531 Hahn et al. Jul 1994
5341805 Stavridi et al. Aug 1994
5462879 Bentsen Oct 1995
5609823 Harttig et al. Mar 1997
5629213 Kornguth et al. May 1997
5631340 Olstein May 1997
5866433 Schalkhammer et al. Feb 1999
Foreign Referenced Citations (7)
Number Date Country
0409033 Jul 1990 EP
0442276 Jan 1991 EP
0584721 Aug 1993 EP
8700023 Jan 1987 WO
9007107 Jun 1990 WO
9530148 Nov 1995 WO
9737210 Oct 1997 WO
Non-Patent Literature Citations (4)
Entry
MacCraith et al., “Optical Chemical Sensors Based on Sol-Gel Materials: Recent Advances and Critical Issues”, J. Sol-Gel Sci. and Tech., vol. 8, pp. 1053-1061 (1997).
Papkovsky et al., “Phosphorescent Polymer Films for Optical Oxygen Sensors”, Biosensors & Electronics 7, pp 199-206 (1991).
Roffey, “Photopolymerization of Surface Coatings”, Wiley-Interscience, p. 110-117 (1985).
Salame, M. “Transport Properties of Nitrile Polymers”, J. Polymer Sci. Symp. 41, pp 1-15 (1973).