Abstract:
An optical isolation element is provided on an optical sensor comprising a light source, at least one photodetector, and indicator material that emits light that is detected by the photodetector when optically excited by the light source. The optical isolation element limits the optical paths by which light may be transmitted by the light source, thereby limiting exposure of the excitation light source to regions of interest. The optical isolation element also limits the optical paths by which light may be transmitted to the photodetector, thereby limiting exposure of the photodetector to light from extraneous sources.

Description:
PRIORITY CLAIM 
     This application claims the benefit under 35 U.S.C. §119(e) of the filing date of provisional patent application Ser. No. 61/973,912 filed Apr. 2, 2014, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates to sensors and, more particularly, sensors having photodetectors for detecting light emissions from a reference material and an optical isolation element for preventing or limiting the amount of extraneous light, not emitted by the reference material, from impinging upon the photodetectors. 
     BACKGROUND 
     Implantable sensors, such as optical, chemical or biochemical sensors, are known which can be implanted within a living animal and which measure the presence or concentration of an analyte or substance of interest in a medium within the living animal. Optical sensors may include one or more light sources, such as one or more LEDs, one or more photodetectors, such as one or more photodiodes, and a layer of indicator molecules that emit a detectable optical signal, e.g., fluoresce, when optically excited by the light source. The light source(s) emits an excitation light signal that impinges upon the indicator molecules, and the indicator molecules emit a signal (which can be a function of the presence and/or concentration of the analyte of interest if present), at least some of which impinges upon the photodetector(s), which convert the detected light into an electrical signal. 
     An exemplary sensor of this type is described in United States Patent Application Publication No. 2013/0211213, the disclosure of which is hereby incorporated by reference. 
     Current sensor configurations allow for light other than that emitted by the indicator molecules, such as ambient light, to impinge on the photodetector(s) from a variety of angles. This “stray” light impinging upon the photodetector(s) adds noise to the measurements. Current sensor configurations also tend to lose much of the desired excitation light to areas of the sensor which are not statistically relevant to light measurement calculation. 
     To subtract out the undesired stray light signals and reduce signal noise due to such stray light, current sensor configurations employ light filters and/or algorithm calculations to subtract out stray light noise and/or employ the location of the indicator molecules relative to the optics components to maximize incident excitation light and detected emission light while minimizing stray light signals. 
     It thus would be desirable to more effectively block the incidence of stray light signals onto the photodetectors of a sensor and to more effectively control the dispersal of the excitation light. 
     SUMMARY 
     Aspects of the disclosure embody an optical isolation element that can be attached to the electronics assembly inside a sensor. The element can be configured and oriented in a manner that at least partially surrounds the optics elements so as to concentrate the excitation light to a specific area of the indicator molecule matrix relative to the location and orientation of the photodetectors that is most relevant to emission signal detection. This can be achieved by, in some embodiments, affixing the optical isolation element to a portion of the senor or by providing a close slip fit between the optical isolation element and the optics elements. The element is preferably opaque so that it will block stray external light from outside sources that normally could be detected by the photodetectors and add noise to the measurements generated by the sensor. Undesired light paths can be blocked or filled in with opaque materials such as overfills, underfills, epoxies, or paints. The optical isolation element can be machined or molded, and it can be made of any suitable material that is sufficiently opaque, is moldable or machinable, and is non-reactive with other components or materials within the sensor. In certain embodiments, suitable materials include plastic, metal, acrylic, glass, porcelains, epoxies, nylon, or Delrin. 
     According to aspects of the disclosure, a sensor for detecting the presence and/or concentration of a substance of interest comprises at least one excitation light source, indicator material positioned and oriented with respect to the excitation light source to receive excitation light emitted therefrom and configured to emit an optical signal when excited by the excitation light source and when contacted by the substance of interest, one or more optical detector elements positioned and oriented with respect to the indicator material to receive at least a portion of the optical signal emitted by the indicator material, and an optical isolation element partially surrounding the light source and the optical detector elements and formed of a material configured to substantially prevent the passage of light therethrough. The optical isolation element is positioned and oriented with respect to the light source, the optical detector elements, and the indicator material and includes an opening formed therein so as to permit at least a portion of the light emitted by the excitation light source to impinge upon the indicator material and to permit at least a portion of the light emitted by the indicator material to impinge upon the optical detector element. 
     According to further aspects, the sensor comprises a housing enclosing the light source, the optical detector elements, and the optical isolation element, and the indicator material is disposed on or embedded in at least a portion of the housing. 
     According to further aspects, the optical isolation element is formed from an opaque material. 
     According to further aspects, the optical isolation material is formed from a material selected from the group consisting of: plastic, metal, acrylic, glass, porcelains, epoxies, Delrin, or nylon. 
     According to further aspects, the optical isolation element comprises first and second opposed end walls and first and second opposed side walls. 
     According to further aspects, the optical isolation element is at least partially shaped to conform to an inner surface of the housing. 
     According to further aspects, the housing has a cylindrical shape, and the optical isolation element comprises first and second end walls that are generally parallel to each other and oriented so as to be perpendicular to a longitudinal axis of the housing and first and second side walls, each extending between the first and second end walls and each being curved so as to conform to a curvature of the housing. 
     According to further aspects, the sensor further comprises a planar substrate on which the light source and the optical detector elements are mounted, and the optical isolation element is cooperatively attached to the substrate so as to substantially prevent light from passing between the optical isolation element and the substrate. 
     According to further aspects, gaps between the optical isolation element and other components of the sensor are filled with opaque materials such as overfills, underfills, epoxies, or paints. 
     Other features and characteristics of the disclosed optical isolation element, as well as the methods of operation, functions of related elements of structure and the combination of parts will become more apparent upon consideration of the following description and the appended claims with reference to the accompanying drawings, all of which form a part of this specification, wherein like reference numerals designate corresponding parts in the various figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The accompanying drawings, which are incorporated herein and form part of the specification, illustrate various, non-limiting embodiments of the optical isolation element. In the drawings, common reference numbers indicate identical or functionally similar elements. 
         FIG. 1  is an exploded perspective view of a sensor of the type in which an optical isolation element embodying aspects of the optical isolation element may be employed. 
         FIG. 2  is a partial side perspective view of an optical sensor of the type in which an optical isolation element may be employed. 
         FIG. 3  is a side view of a sensor with an optical isolation element mounted thereon. 
         FIG. 4  is a side view of the internal components of the sensor and the optical isolation element shown in cross section. 
         FIG. 5  is a transverse cross-sectional view of the sensor and optical isolation element. 
         FIGS. 6A, 6B, 6C, and 6D  are top, end, bottom, and right side views, respectively, of the optical isolation element. 
         FIG. 7  is an end view of the optical isolation element. 
         FIG. 8  is a cross-sectional view of the optical isolation element along the line VIII-VIII in  FIG. 7 . 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     This description may use relative spatial and/or orientation terms in describing the position and/or orientation of a component, apparatus, location, feature, or a portion thereof. Unless specifically stated, or otherwise dictated by the context of the description, such terms, including, without limitation, top, bottom, above, below, under, on top of, upper, lower, left of, right of, in front of, behind, next to, adjacent, between, horizontal, vertical, diagonal, longitudinal, transverse, etc., are used for convenience in referring to such component, apparatus, location, feature, or a portion thereof in the drawings and are not intended to be limiting. 
     Furthermore, unless otherwise stated, any specific dimensions mentioned in this description are merely representative of an exemplary implementation of an optical isolation element and are not intended to be limiting. Unless otherwise indicated or the context suggests otherwise, as used herein, “a” or “an” means “at least one” or “one or more.” 
       FIGS. 1 and 2  are an exploded perspective view and partial side perspective view, respectively, showing an optical sensor  100  of the type in which an optical isolation element embodying aspects disclosed herein may be employed.  FIG. 3  is a side view of a sensor  100  with an exemplary optical isolation element  150  mounted thereon.  FIG. 4  is a side view of the internal components of the sensor and the optical isolation element  150  is shown in cross-section.  FIG. 5  is a transverse cross-sectional view of the sensor  100  and optical isolation element  150 . 
     The sensor  100  may include a sensor housing  102  (i.e., body, shell, sleeve, or capsule). See, for example,  FIGS. 1-3 . The sensor housing  102  may include an end cap  113 . In exemplary embodiments, sensor housing  102  may be formed from a suitable, optically transmissive polymer material, such as, for example, acrylic polymers (e.g., polymethylmethacrylate (PMMA)). 
     The sensor  100  may include an indicator matrix layer  106  (e.g., graft or gel) coated on or embedded in at least a portion of the exterior surface of the sensor housing  102 . The sensor  100  may include indicator molecules  104 , such as fluorescent indicator molecules or absorption indicator molecules distributed throughout all or a portion of the indicator matrix layer  106 . The indicator matrix layer  106  may cover the entire surface of sensor housing  102  or only one or more portions of the surface of housing  102 . Furthermore, as an alternative to coating the indicator matrix layer  106  on the outer surface of sensor housing  102 , the indicator matrix layer  106  may be disposed on the outer surface of the sensor housing  102  in other ways, such as by deposition or adhesion. 
     In some sensors including an indicator matrix layer  106 , the indicator matrix layer  106  may comprise a biocompatible polymer matrix that is prepared according to methods known in the art and coated on the surface of the sensor housing  102 . In certain sensors, the biocompatible matrix materials are permeable to an analyte or substance of interest. Exemplary biocompatible matrix materials that may be used include some methacrylates (e.g., HEMA) and hydrogels that, advantageously, can be made selectively permeable—particularly to the analyte—so as to perform a molecular weight cut-off function. In a sensor that does not include an indicator matrix layer  106 , instead of being distributed throughout an indicator matrix layer  106 , the indicator molecules  104  could simply be coated on the surface of the sensor housing  102 . 
     The sensor  100  includes one or more light sources  108  (a single light source is shown in the figures), which may, for example, comprise a light emitting diode (LED) or other light source that emits radiation, including radiation over a range of wavelengths that interact with the indicator molecules  104 . For example, in the case of a fluorescence-based sensor, light source  108  emits radiation at a wavelength which causes the indicator molecules  104  to fluoresce when the indicator molecules are in the presence of an analyte or substance of interest. However, other LEDs or light sources may be used depending on the specific indicator molecules applied to sensor  100  and the specific analytes or substances of interested to be detected. 
     Sensor  100  also includes one or more photodetectors  110  (e.g., photodiodes, phototransistors, photoresistors or other photosensitive elements) which, in the case of a fluorescence-based sensor, is sensitive to fluorescent light emitted by the indicator molecules  104  such that a signal is generated by the photodetector  110  in response thereto that is indicative of the presence or level of fluorescence of the indicator molecules. The illustrated sensor  100  includes a first photodetector  224  and a second photodetector  226 . 
     The sensor  100  may include one or more optical filters  112 , such as high pass or band pass filters. The one or more optical filters  112  may cover a photosensitive side of the one or more photodetectors  110 . The one or more optical filters  112  may prevent or substantially reduce the amount of radiation generated by the light source  108  from impinging on a photosensitive side of the one or more photodetectors  110 . At the same time, the one or more optical filters  112  may allow light (e.g., fluorescent light) of a specified wavelength, or within a specified range of wavelengths, emitted by indicator molecules  104  to pass through and strike the photosensitive side of the one or more photodetectors  110 . This reduces “noise” attributable to incident radiation from the light source  108  in the light measurement signals output by the one or more photodetectors  110 . An optical isolation element such as described herein may be used in conjunction with or as an alternative to such optical filters  112 . 
     Sensor  100  may be wholly self-contained. In other words, the sensor may be constructed in such a way that no electrical leads extend into or out of the sensor housing  102  to supply power to the sensor (e.g., for driving the light source  108 ) or to transmit signals from the sensor  100 . Instead, in one embodiment, the sensor  100  may be powered by an internal, self-contained power source, such as, for example, microbatteries, micro generators and/or other power sources. However, in one preferred embodiment, sensor  100  may be powered by an external power source (not shown). For example, the external power source may generate a magnetic field to induce a current in an inductive element  114  (e.g., a coil or other inductive element). Additionally, the sensor  100  may use the inductive element  114  to communicate information to an external data reader (not shown). In some embodiments, the external power source and data reader may be the same device. 
     Sensor  100  may include a semiconductor substrate  116 . In an illustrated embodiment, the circuitry is fabricated in the semiconductor substrate  116 . The circuitry may include analog and/or digital circuitry. In a non-limiting embodiment, the circuitry may be formed in the semiconductor substrate  116  using a complementary metal oxide semiconductor (CMOS) process. However, other formation processes (e.g., n-type metal-oxide-semiconductor (NMOS) or n-type metal-oxide-semiconductor (PMOS)) may alternatively be used. 
     The one or more photodetectors  110  may be mounted on the semiconductor substrate  116 , or, alternatively, the one or more photodetectors  110  may be fabricated in the semiconductor substrate  116 . For example, in a non-limiting embodiment, the one or more photodetectors  110  may be monolithically formed in the semiconductor substrate  116 . For instance, in one embodiment, the one or more photodetectors  110  may be monolithically formed in the semiconductor substrate  116  using a complementary metal oxide semiconductor (CMOS) process (e.g., using diffusions from the CMOS process). However, other formation processes (e.g., NMOS or PMOS) alternatively may be used. 
     The light source  108  may be mounted on the semiconductor substrate  116 . For example, in a non-limiting embodiment, the light source  108  may be flip-chip mounted on the semiconductor substrate  116 . Alternatively, the light source  108  may be fabricated in the semiconductor substrate  116 . 
     Sensor  100  may also include one or more capacitors  118 . The one or more capacitors  118  may be, for example, one or more antenna tuning capacitors and/or one or more regulation capacitors. Further, the one or more capacitors  118  may be in addition to one or more capacitors fabricated in the semiconductor substrate  116 . 
     An application for which the sensor  100  was developed—although by no means the only application for which it is suitable—is measuring various biological analytes in the living body of an animal (including a human). For example, sensor  100  may be used to measure glucose, oxygen, toxins, pharmaceuticals or other drugs, hormones, and other metabolic analytes in, for example, the human body. The specific composition of the indicator matrix layer  106  and the indicator molecules  104  may vary depending on the particular analyte the sensor is to be used to detect and/or where the sensor is to be used to detect the analyte (e.g., in the blood or subcutaneous tissues). Preferably, however, indicator matrix layer  106 , if present, should facilitate exposure of the indicator molecules to the analyte. Also, it is preferred that the optical characteristics of the indicator molecules (e.g., the level of fluorescence of fluorescent indicator molecules) be a function of the concentration of the specific analyte to which the indicator molecules are exposed. 
     To facilitate use in-situ in the human body, the sensor housing  102 , in one embodiment, is preferably formed in a smooth, oblong or rounded shape. Other shapes and configurations could be used as well. Advantageously, in certain embodiments, the sensor  100  is on the order of approximately 500 microns to approximately 0.85 inches in length L and on the order of approximately 300 microns to approximately 0.3 inches in diameter D. In certain embodiments, the sensor  100  may have generally smooth, rounded surfaces. This configuration facilitates the sensor  100  to be implanted into the human body, i.e., dermally or into underlying tissues (including into organs or blood vessels) without the sensor interfering with essential bodily functions or causing excessive pain or discomfort. However, given its small size, the sensor  100  may have different shapes and configurations and still be implantable within a human without the sensor interfering with essential bodily functions or causing excessive pain or discomfort. 
     In exemplary configurations, a preferred length of the housing is approximately 0.5 inches to 0.85 inches and a preferred diameter is approx. 0.1 inches to 0.11 inches. However, in other embodiments, the housing may be even smaller. 
       FIGS. 3 and 4  are side views of the sensor  100  with an optical isolation element  150  mounted thereon. The optical isolation element  150  is mounted onto an end portion of the substrate  116  projecting from the inductor  114  and partially surrounds the light source  108 , photodetectors  110 , and optical filters (if present in the sensor)  112 . 
     Details of an exemplary optical isolation element  150  are shown in  FIGS. 6, 7 and 8 . The configuration of the optical isolation element is largely dependent upon the configuration and arrangement of the various components of the sensor, such as the inductor  114 , the substrate  116 , the light source  108 , the photodetectors  110 , and the filters  112 , as well as the internal shape of the housing  102 . The optical isolation element  150  shown in the figures is specifically configured so as to be compatible with the arrangement of the sensor  100 . The configuration of the optical isolation element and the sensor are exemplary and are not intended to be limiting. 
     Referring to  FIGS. 6, 7 and 8 , the optical isolation element  150  includes a first end wall  152 , an opposed second end wall  154 , a first sidewall  156  extending between the first end wall  152  and the second end wall  154  and an opposed second sidewall  164  also extending between the first end wall  152  and the second end wall  154 . An opening  172  is formed in a top portion of the optical isolation element  150 . In one exemplary embodiment, the second end wall  154  has a generally circular shape, and the first end wall  152  has a partial circular shape with a flat bottom edge  176 . The first sidewall  152  has a first sidewall extension  158  extending from a lower edge of the sidewall  152  and a cutout  162  adjacent to the extension  158 . Similarly, the second sidewall  164  has a second sidewall extension  166  extending from a lower edge of the second side wall  164  and a cutout  174  adjacent to the extension  166 . The first and second sidewalls  156 ,  164  have a curved, generally circular shape. As shown in  FIGS. 6( b )  and  7 , the first sidewall extension  158  has a flattened surface  160 , and the second sidewall extension  166  has a flattened surface  168 . 
       FIGS. 4 and 5  show further details of an embodiment of the installation of the optical isolation element  150  on the sensor  100 . In the illustrated embodiment, optical isolation element  150  is mounted on a portion of the semiconductor substrate  116  extending from the inductive element  114 . The first end wall  152  is disposed against an end of the inductive element  114  with the flat edge  176  resting on the top surface of the semiconductor substrate  116 . The second end wall  154  is disposed at an end of the semiconductor substrate  116  and includes a lower portion  174  extending below a top surface of the semiconductor substrate  116 . End walls  152 ,  154  are generally parallel to each other and perpendicular to a longitudinal axis of the cylindrical sensor housing  102 . 
     As shown in  FIG. 5 , the first sidewall  156  and the second sidewall  164  are disposed on opposite sides of the optical elements (photodetectors  224 ,  226  and light source (LED)  108 ) of the sensor  100  and partially enclose the photodetectors  226  and  224  and the light source  108 . The sidewalls  156 ,  164  are generally circular in shape so as to conform to the circular cross-sectional shape of the housing  102 . As shown in  FIG. 5 , the first sidewall extension  158  extends alongside the first photodetector  224  with the flattened portion  160  of the extension  158  providing a light-tight fitting between the sidewall  156  and the photodetector  224 . Similarly, the sidewall extension  166  of the second sidewall  164  is disposed against the second photodetector  226 , and the flattened surface  168  of the second extension  166  provides a light-tight fitting between the sidewall  164  and the photodetector  226 . 
     As shown in  FIG. 3 , in accordance with one non-limiting embodiment, the cutouts  162  and  170  of the first and second sidewalls  156 ,  164 , respectively, rest upon the top surface of the substrate  116 . 
     The optical isolation element can be machined or molded, and it can be made from any suitable material that is sufficiently opaque, is moldable or machinable, and is nonreactive with other components or materials within the sensor  100 . Suitable materials include plastic, metal, acrylic, glass, porcelain, epoxies, nylon or Delrin. Undesired light paths between the optical isolation element  150  and the electronic components of the sensor  100  can be blocked or filled with opaque materials, such as overfills, underfills, epoxies, or paints. As can be appreciated from  FIGS. 5 and 6 , any light emitted by the light source  108  can only escape the optical isolation element  152  through the top opening  172  of the optical isolation element. Thus, light from the light source  108  impinges substantially only on the indicator matrix  106  and does not disperse into other portions of the sensor  100 . Similarly, substantially the only light that will impinge upon the photodetectors  224 ,  226  can reach the photodetectors only through the opening  172  of the optical isolation element  150 . Extraneous light from other sources, such as ambient light, is substantially prevented from reaching the photodetectors  224  and  226  by the optical isolation element  150 . 
     While an optical isolation element has been described and shown in considerable detail with reference to certain illustrative embodiments, including various combinations and sub-combinations of features, those skilled in the art will readily appreciate other embodiments and variations and modifications thereof as encompassed within the scope of the present disclosure. Moreover, the descriptions of such embodiments, combinations, and sub-combinations is not intended to convey that an optical isolation element requires features or combinations of features other than those expressly recited in the claims. Accordingly, the present disclosure is deemed to include all modifications and variations encompassed within the spirit and scope of the following appended claims.