Electro-optical sensing device with reference channel

Abstract

An electro-optical sensing device for detecting the presence and concentration of an analyte in a liquid or gaseous medium includes a pair of indicator elements positioned to receive radiation from a radiation source and transmit radiation to a pair of photosensitive elements. The indicator elements each contain indicator molecules having an optical characteristic responsive to the presence of an analyte; however, one of the indicator elements is covered by an analyte-impermeable chamber that renders the indicator element insensitive to the presence of the analyte in the medium outside the chamber so that it can be used as a reference to cancel environmental and systemic variables that affect both indicator elements. The chamber preferably holds an analyte-containing fluid in contact with the reference indicator element so that the indicator elements operate under nominally identical conditions. The indicator element used to measure the analyte in the external medium is preferably also covered, but in a manner that provides direct contact between the analyte and the indicator element.

1 . An electro-optical sensing device for detecting the presence of an analyte in a medium, said sensing device comprising: 
 a. a radiation source that emits radiation;    b. a first and a second photosensitive elements configured to receive radiation and output an electrical signal in response thereto;    c. a first and a second indicator elements positioned to receive radiation from the radiation source and to transmit radiation to said first and second photosensitive elements, said first and second indicator elements each containing indicator molecules with an optical characteristic responsive to the presence of an analyte; and    wherein said first indicator element is exposed to an exterior of the device and is responsive to a presence of an analyte in a medium external to the device, and wherein said second indicator element is at least partially covered and is insensitive to the presence of the analyte in the medium external to the device.    
     
     
         2 . The sensing device of  claim 1 , comprising an analyte-impermeable chamber covering said second indicator element so as to render said second indicator element insensitive to the presence of the analyte in the medium external to the device.  
     
     
         3 . The sensing device of  claim 2 , wherein said analyte-impermeable chamber is a hermetically sealed chamber.  
     
     
         4 . The sensing device of  claim 2 , wherein said chamber contains a fluid in contact with said second indicator element.  
     
     
         5 . The sensing device of  claim 4 , wherein said fluid is an analyte-containing fluid in contact with said second indicator element.  
     
     
         6 . The sensing device of  claim 5 , wherein said analyte-containing fluid is a liquid.  
     
     
         7 . The sensing device of  claim 5 , wherein said analyte-containing fluid is a gas.  
     
     
         8 . The sensing device of  claim 5 , wherein an analyte in said analyte-containing fluid is the same type of analyte to be detected in the external medium.  
     
     
         9 . The sensing device of  claim 5 , wherein an analyte in said analyte-containing fluid is a different type of analyte than the analyte to be detected in the external medium.  
     
     
         10 . The sensing device of  claim 1 , wherein said indicator molecule has an optical characteristic responsive to the presence of oxygen.  
     
     
         11 . The sensing device of  claim 10 , wherein said indicator molecule is tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) perchlorate.  
     
     
         12 . The sensing device of  claim 2 , further comprising a housing, wherein said first and second indicator elements, said first and second photosensitive elements, and said radiation source are mounted in said housing.  
     
     
         13 . The sensing device of  claim 12 , further comprising an analyte-impermeable cover mounted on the housing which defines at least a portion of the chamber covering the second indicator element.  
     
     
         14 . The sensing device of  claim 13 , wherein said housing has a first opening, and further wherein said analyte-impermeable cover and said second indicator  
     
     
         15 . The sensing device of  claim 14 , wherein said analyte impermeable cover comprises a plug having a flange extending outward from the top of the plug, said flange defining a contact surface for contacting an upper surface of the housing around said second opening and forming a hermetic seal to prevent migration of analyte containing fluids from the external meduim into the chamber.  
     
     
         16 . The sensing device of  claim 13 , wherein said analyte-impermeable cover is formed of a metal.  
     
     
         17 . The sensing device of  claim 13 , further comprising an analyte-permeable cover mounted on the housing over the first indicator element.  
     
     
         18 . The sensing device of  claim 17 , wherein said analyte-permeable cover includes a bore formed therethrough to provide fluid communication between the first indicator element and the external medium.  
     
     
         19 . The sensing device of  claim 17 , wherein said housing has a second opening, and further wherein said analyte-permeable cover and said first indicator element are mounted on opposite sides of said second opening.  
     
     
         20 . The sensing device of  claim 18 , wherein said analyte permeable cover and said analyte-impermeable cover are substantially similar in configuration with the exception of the bore.  
     
     
         21 . The sensing device of  claim 1 , wherein said first indicator element and said first photosensitive comprise a signal channel, and wherein said second indicator element and said second photosensitive element comprise a reference channel.  
     
     
         22 . The sensing device of  claim 21 , wherein said signal channel and said reference channel are incorporated into a chip-like structure with leads extending therefrom.  
     
     
         23 . The sensing device of  claim 12 , wherein said housing comprises a top wall, side walls depending from said top wall, said side walls having bottom edges which are mounted on a top surface of a substrate so as to maintain said top wall in vertically spaced relation to said substrate.  
     
     
         24 . The sensing device of  claim 23 , wherein a region between said housing and said substrate contains a waveguide material.  
     
     
         25 . The sensing device of  claim 1 , wherein said radiation source is a light emitting diode.  
     
     
         26 . The sensing device of  claim 13 , wherein said analyte-impermeable cover is formed of a material having good thermal conductivity so that an interior of the chamber will experience temperature changes similar to temperature changes in the external medium.  
     
     
         27 . The sensing device of  claim 13 , wherein said analyte-impermeable cover is formed of a transparent material.  
     
     
         28 . The sensing device of  claim 7 , wherein said gas is air.  
     
     
         29 . The sensing device of  claim 21 , wherein power to the sensing device is drawn from an external source through said leads.  
     
     
         30 . The sensing device of  claim 1 , wherein power to the sensing device is provided from an internal power source.  
     
     
         31 . The sensing device of  claim 30 , wherein said internal power source is a battery.  
     
     
         32 . The sensing device of  claim 1 , wherein power to the sensing device is provided from an external source through an induction circuit formed in the sensing device.  
     
     
         33 . The sensing device of  claim 1 , wherein said indicator molecule has an optical characteristic responsive to the presence of glucose.