Method for the Detection of Microorganisms by Fiber Optics

Abstract

The objective of the present invention is the detection/monitoring of microorganisms present in the air, water or foodstuffs through the use of a fiber optic biosensor with an evanescent-field. A first concretization of the present invention concerns a method for detection of contamination by specific microorganisms through the use of the evanescent-field of a sensitive fiber optic characterized by stages of: a) exposing the evanescent-field of the sensitive fiber optic using an appropriate technique based on physical and chemical properties; (b) permitting immediate contact of the exposed evanescent-field obtained in the stage (a) with the sample to be examined, with the aforementioned sample having a form adequate so as to obtain the generation of an optical signal in response to the presence of microorganisms in the sample; and, (c) demodulating the optical signal generated in stage (b) and using this value to quantify the microorganisms through an appropriate method. In a second concretization, the invention is directed to a composition for use in the detection of microorganisms characterized by comprising a selective culture medium for microorganisms needing to be detected and reactants capable of altering the properties of the medium to favor the interaction of the system fiber-microorganism interaction. In a third concretization the invention refers to a device for surveying microorganisms through the insertion of a sensitive fiber optic ( 11 ), with an adequately exposed evanescent-field, into a surface or volume of a biological culture medium ( 12 ) specific for the microorganism to be detected, comprising a demodulation system based on a fiber optic circuit and related components.

1 . Method for detection of contamination by specific microorganisms through the application of the evanescent field of a sensitive fiber optic characterized by the stages of: 
 (a) exposing the evanescent-field of the sensitive fiber optic using an appropriate technique based on physical and chemical properties;    (b) permitting the immediate contact of the exposed evanescent-field obtained in the stage (a) with the sample to be examined, with the aforementioned sample having a form adequate so as to obtain the generation of an optical signal in response to the presence of microorganisms in the sample:    (c) demodulating the optical signal generated in stage (b) and using this value to quantify the microorganisms through an appropriate method.    
     
     
         2 . Method in accordance with  claim 1  wherein the appropriate technique for stage (a) is chemical etching performed with a strong acid.  
     
     
         3 . Method in accordance with  claim 2  wherein the strong acid is hydrofluoric acid.  
     
     
         4 . Method in accordance with  claim 3  wherein the time of treatment and the concentration of the hydrofluoric acid solution is adjusted in a manner to permit the etching of the sheath of the fiber optic until it approaches a thickness of 0.5 a 1 μm from the core.  
     
     
         5 . Method in accordance with  claim 4  wherein the time of treatment is 11 minutes and the concentration of the acid is 38%.  
     
     
         6 . Method in accordance with  claim 1  wherein the sample to be examined is in a support containing the culture medium appropriate to permit the growth of microorganisms.  
     
     
         7 . Method in accordance with  claim 6  wherein the support is a Petri dish containing Agar medium and specific nutrients.  
     
     
         8 . Method in accordance with  claim 6  wherein reactants are incorporated to the culture medium capable of altering the properties of the culture medium in a manner as to permit a better detection of the index of refraction of the microorganisms.  
     
     
         9 . Method in accordance with  claim 1  wherein the sensitive fiber has integrated to itself one or more concentric layers of a material selected from the group consisting of dielectricals, metallics, superconductors or semiconductors in a manner so as to alter the transversal spatial distribution of the evanescent-field and thus optimizing the contact with the medium containing the specific microorganism.  
     
     
         10 . Method in accordance with  claim 9  wherein the material is a polymer selected from a group consisting of polyvinyl chloride, polyurethanes, polyureas and polyesters.  
     
     
         11 . Method in accordance with  claim 1  wherein the monitoring of the environment is to occur in real time.  
     
     
         12 . Composition for the use in the detection of microorganisms characterized by comprising a selective culture medium for the microorganism to be detected and reactants capable of altering the properties of the medium in a manner as to favor the interaction of the system fiber-microorganism.  
     
     
         13 . Composition in accordance with  claim 12  wherein the alteraction is in the index of refraction of the system.  
     
     
         14 . Device for the survey of microorganisms through the insertion of a sensitive fiber optic ( 11 ), with an adequately exposed evanescent-field, into a surface or volume of a biological culture medium ( 12 ) specific for the microorganism to be detected, characterized by comprising the following system for demodulation based on a fiber optic circuit and related components: 
 optical source ( 1 ), coupling to an optical fiber of the 2×1 type ( 2 ), coupling to an optical fiber of the 2×2 type ( 5 ), an optical fiber extension ( 8 ) termed sensitive element containing a polarization controller ( 10 ), a segment of sensitive optical fiber ( 11 ) with the exposed evanescent-field being in direct physical contact with the biological culture medium ( 12 ), an extremity ( 15 ) from which exits the light that enters the photodetector ( 16 ), another extension of optical fiber ( 9 ) termed reference element containing a polarization controller ( 17 ), an extremity ( 18 ) from which exits the light that enters the photodetector ( 19 ) in a manner as to compose a device that functions based on the modulation of the intensity (or amplitude) of light.    
     
     
         15 . Device for the survey of microorganisms through the insertion of a sensitive fiber optic ( 11 ), with an adequately exposed evanescent-field, into a surface or volume of a biological culture medium ( 12 ) specific for the microorganism to be detected, characterized by comprising the following system for demodulation based on a fiber optic circuit and related components: 
 i) optical source ( 1 ), coupling to an optical fiber of the 2×1 type ( 2 ), coupling to an optical fiber of the 2×2 type ( 5 ), an optical fiber extension ( 8 ) termed sensitive element containing a polarization controller ( 10 ), two connection links ( 13 ) and ( 14 ), a segment of sensitive optical fiber ( 11 ) with the exposed evanescent-field being in direct physical contact with the biological culture medium ( 12 ) and having both semi-reflective extremities localized at points ( 13 ) and ( 14 ), an extremity ( 15 ) from which exits the light that enters the photodetector ( 16 ), another extension of optical fiber ( 9 ) termed reference element containing a polarization controller ( 17 ), an extremity ( 18 ) from which exits the light that enters the photodetector ( 19 ) in a manner as to compose a device that functions based on the modulation of the complete phase of light of the Fabry-Perot type interferometer.    
     
     
         16 . Device for the survey of microorganisms through the insertion of a sensitive fiber optic ( 11 ), with an adequately exposed evanescent-field, into a surface or volume of a biological culture medium ( 12 ) specific for the microorganism to be detected, characterized by comprising the following system for demodulation based on a fiber optic circuit and related components: 
 optical source ( 1 ), coupling to an optical fiber of the 2×1 type ( 2 ), coupling to an optical fiber of the 2×2 type ( 5 ), an optical fiber extension ( 8 ) termed sensitive element containing a polarization controller ( 10 ), a segment of sensitive optical fiber ( 11 ) with the exposed evanescent-field being in direct physical contact with the biological culture medium ( 12 ), an extremity of reflective optical fiber ( 15 ), another extension of optical fiber ( 9 ) termed reference element containing a polarization controller ( 17 ) and a extremity of reflective optical fiber ( 18 ), an extremity of optical fiber ( 3 ) from which exits the light that enters the photodetector ( 4 ) and an extremity of optical fiber ( 6 ) from which exits the light that enters the photodetector ( 7 ) in a manner as to compose a device that functions based on the modulation of the complete light phase of the Michelson type interferometer.    
     
     
         17 . Device for the survey of microorganisms through the insertion of a sensitive fiber optic ( 11 ), with an adequately exposed evanescent-field, into a surface or volume of a biological culture medium ( 12 ) specific for the microorganism to be detected, characterized by comprising the following system for demodulation based on a fiber optic circuit and related components: 
 optical source ( 1 ), coupling to an optical fiber of the 2×1 type ( 2 ), coupling to an optical fiber of the 2×2 type ( 5 ), an optical fiber extension ( 8 ) termed sensitive element containing a polarization controller ( 10 ), a segment of sensitive optical fiber ( 11 ) with the exposed evanescent-field being in direct physical contact with the biological culture medium ( 12 ), an extremity of optical fiber ( 15 ) directly linked to the extremity of optical fiber ( 21 ) belonging to the coupling of the optical fiber of the 2×2 type ( 20 ), an extremity of optical fiber ( 25 ) from which exits the light that enters the photodetector ( 23 ), another extension of optical fiber ( 9 ) termed reference element containing a polarization controller ( 17 ), an extremity of optical fiber ( 18 ) directly linked to the extremity of optical fiber ( 22 ) and an extremity of optical fiber ( 26 ) from which exits the light that enters the detector ( 24 ) in a manner as to compose a device that functions based on the modulation of the complete light phase of the Mach-Zehnder type interferometer.    
     
     
         18 . Device in accordance with  claim 14  wherein the sensitive optical fiber ( 11 ) contains a Bragg grating engraved within its core in a manner as to compose a device that functions based on the modulation of the length of the light wave.  
     
     
         19 . Device in accordance with  claim 14  wherein the sensitive optical fiber ( 11 ) consists of a high birefringency fiber of the type that maintains polarization in such a manner as to compose a device that functions based on the modulation of the polarization of light.  
     
     
         20 . Device in accordance with  claim 14  wherein the sensitive optical fiber ( 11 ) consists of a high birefringency fiber of the type that maintains polarization containing a Bragg grating engraved within its core in a manner as to compose a device that functions based on the modulation of the length of the light wave and/or light polarization.