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An improved optical sensor and methods for measuring the presence of various materials or constituents in a fluid sample uses reactive material(s) in a fluid environment. The reactive materials have optical properties that change in the presence of a target material that may be present in the enviro

An improved optical sensor and methods for measuring the presence of various materials or constituents in a fluid sample uses reactive material(s) in a fluid environment. The reactive materials have optical properties that change in the presence of a target material that may be present in the environment. An optical emitter generates light that is directed to the reactive materials, and one or more optical detectors receive reflected light from one or more interfaces in the optical path between the emitter and the detector(s), one or more of the interfaces having a reactive material. The reactive material(s), emitter(s), and detector(s) are selected based on the desired target material to be sensed.

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What is claimed is: 1. An optical sensor, comprising: an optical emitter mounted on a substrate; an optical detector mounted on said substrate adjacent to said optical emitter; and a reactive surface located opposite said substrate, optical emitter and optical detector, wherein an area of said reac

What is claimed is: 1. An optical sensor, comprising: an optical emitter mounted on a substrate; an optical detector mounted on said substrate adjacent to said optical emitter; and a reactive surface located opposite said substrate, optical emitter and optical detector, wherein an area of said reactive surface is exposed to a fluid and an optical property of said reactive surface changes upon exposure to a target material, wherein said optical emitter emits light onto said reactive surface, and said optical detector receives reflected light from said reactive surface and is operable to detect the change in said optical property when said reactive surface is exposed to said target material, the change in optical property being independent of an angle of incidence of said emitted light onto said reactive surface and including at least one of a change in index of refraction, a change in optical absorption, a change in polarization of the reflected light, a change in fluorescence, and a changed optical property resulting from a change in geometry of said reactive surface, and wherein said optical detector comprises a first and a second optical detector, said first optical detector located on said substrate to receive reflected light from a first area of said reactive surface and said second optical detector located on said substrate to receive reflected light from a second area of said reactive surface that is different than said first area. 2. The optical sensor, as claimed in claim 1, further comprising: a transparent window located opposite said substrate, and wherein said reactive surface is located on said transparent window on a side of said transparent window that is opposite said substrate, and wherein said optical emitter emits light that travels through said transparent window, reflects off of said reactive surface, travels back through said transparent window, and the reflected light is received at said optical detector. 3. The optical sensor, as claimed in claim 2, further comprising: an anti-reflective coating located on the side of said transparent window that is towards said substrate. 4. The optical sensor, as claimed in 1 wherein said optical emitter is comprised of at least one of a vertical cavity surface emitting laser, a light emitting diode, and a laser diode. 5. The optical sensor, as claimed in claim 1, wherein said optical emitter comprises a first and a second optical emitter, said first optical emitter emitting light having a first optical characteristic, and said second optical emitter emitting light having a second optical characteristic that is different than said first optical characteristic. 6. The optical sensor, as claimed in claim 5, wherein said first and second optical characteristics are selected from the group consisting of wavelength, polarization, and intensity. 7. The optical sensor, as claimed in claim 1, wherein said optical detector is comprised of at least one of a photo diode, a charge coupled device, and a PIN photo detector. 8. The optical sensor, as claimed in claim 1, wherein said first area of said reactive surface is not exposed to said fluid, and said second area of said reactive surface is exposed to said fluid. 9. An optical sensor, comprising: an optical emitter mounted on a substrate; an optical detector mounted on said substrate adjacent to said optical emitter; and a reactive surface located opposite said substrate, optical emitter and optical detector, wherein an area of said reactive surface is exposed to a fluid and an optical property of said reactive surface changes upon exposure to a target material when said target material is present in said fluid, and wherein said optical emitter emits light onto said reactive surface, and said optical detector receives reflected light from said reactive surface and is operable to detect the change in said optical property when said reactive surface is exposed to said target material; wherein said optical detector comprises a first and a second optical detector, said first optical detector located on said substrate to receive reflected light from a first area of said reactive surface and said second optical detector located on said substrate to receive reflected light from a second area of said reactive surface that is different then said first area; wherein said first area of said reactive surface is not exposed to said fluid, and said second area of said reactive surface is exposed to said fluid; and wherein said first optical detector generates a reference output, and said second optical detector generates a signal output, and a ratio of said reference and signal outputs is used to determine the presence or absence of said target material. 10. The optical sensor, as claimed in claim 1, wherein said reactive surface comprises a plurality of different reactive materials, each of said reactive materials having an optical property that changes in a unique manner relative to other of said reactive materials when exposed to said target material. 11. The optical sensor, as claimed in claim 1, further comprising at least one optical filter located in an optical path between said optical emitter and said optical detector. 12. A method for determining the presence or absence of a target material in an environment, comprising: providing an optical sensor having an optical emitter, optical detector, and a reactive surface located in an optical path between said optical emitter and optical detector; monitoring an optical characteristic of light that is reflected off of a first area of said reactive surface; determining if said optical characteristic has changed, the change in optical characteristic being independent of an angle of incidence of said emitted light onto said reactive surface and including at least one of a change in index of refraction, a change in optical absorption, a change in polarization of the reflected light, a change in fluorescence, and a changed optical property resulting from a change in geometry of said reactive surface, and providing an indication that said target material is present in the environment when it is determined that said optical characteristic has changed, wherein said step of monitoring comprises: receiving light from a first area of said reactive surface at a first optical detector, said first optical detector generating a first output based on the light received at the first optical detector; receiving light from a second area of said reactive surface at a second optical detector, said second optical detector generating a second output based on the light received at the second optical detector; and monitoring a ratio of said first and second outputs. 13. A method for determining the presence or absence of a target material in an environment, comprising: providing an optical sensor having an optical emitter, optical detector, and a reactive surface located in an optical path between said optical emitter and optical detector; monitoring an optical characteristic of light that is reflected off of a first area of said reactive surface; determining if said optical characteristic has changed, and providing an indication that said target material is present in the environment when it is determined that said optical characteristic has changed; wherein said step of determining comprises: receiving light that is reflected from a first area of said reactive surface at a first optical detector, said first optical detector generating a first output based on the light received at the first optical detector; receiving light that is reflected from a second area of said reactive surface at a second optical detector, said second optical detector generating a second output based on the light received at the second optical detector; and multiplying said first output by a scaling factor; subtracting said multiplied first output from said second output to obtain a difference output; amplifying said difference output by a predetermined gain; and monitoring said amplified difference output. 14. The method, as claimed in claim 13, wherein said scaling factor is determined based on nominal first and second outputs so as to provide said multiplied first output that is substantially equal to said nominal second output. 15. An optical sensor, comprising: an optical emitter mounted on a substrate; an optical detector mounted on said substrate adjacent to said optical emitter; a transparent window located opposite said substrate; and a reactive surface located on said transparent window on a side of said transparent window that is away from said substrate, said reactive surface having a reference surface area and a signal surface area, said reference surface area being isolated from an environment being tested and said signal surface area being exposed to the environment being tested, wherein an optical property of said signal surface changes upon exposure to a target material when said target material is present in the environment, and wherein said optical emitter emits light onto said signal and reference surfaces, and said optical detector receives reflected light from said signal and reference surfaces and is operable to detect the change in said optical property when said signal surface is exposed to said target material based on a difference between the reflected light from the signal and reference surfaces. 16. The optical sensor, as claimed in claim 15, wherein said optical detector comprises a first and a second optical detector, said first optical detector located on said substrate to receive reflected light from said signal surface area and said second optical detector located on said substrate to receive reflected light from said reference surface area. 17. The optical sensor, as claimed in claim 15, wherein said reactive surface comprises a plurality of different reactive materials, each of said reactive materials having an optical property that changes in a unique manner relative to other of said reactive materials when exposed to said target material. 18. The optical sensor, as claimed in claim 15, further comprising at least one optical filter located in an optical path between said optical emitter and said optical detector. 19. The optical sensor, as claimed in claim 1, wherein said first optical detector generates a reference output, and said second optical detector generates a signal output, and a ratio of said reference and signal outputs is used to detennine the presence or absence of said target material.