Method of preventing short sampling of a capillary or wicking fill device

Abstract

The current invention provides a device, and a method for using the device, for ensuring that capillary or wicking fill device is fully filled. In particular this invention is directed to, but not limited to, use with capillary or wicking action filled electrochemical sensors suitable for use in analyzing blood or interstitial fluids.

1 . A device for sampling a fluid, comprising: 
 a pre-chamber having an interior surface and being capable of exerting a first capillary force, a sensing chamber in fluid communication with the pre-chamber, the sensing chamber having an interior surface and being capable of exerting a second capillary force;    wherein a differential exist between the capillary forces, the differential being sufficient to cause flow of fluid from the pre-chamber to the sensing chamber, and wherein the pre-chamber further comprises a volume such that when full the pre-chamber comprises at least as much sample as is needed to substantially fill the sensing chamber.    
     
     
         2 . The device of  claim 2 , wherein the interior surface of the pre-chamber comprises at least first and second pre-chamber walls spaced apart at a first distance to define a pre-chamber height, and wherein the interior surface of the sensing chamber comprises at least first and second sensing chamber walls spaced apart at a second distance to define a sensing chamber height, wherein the height of the sensing is less than the height of the pre-chamber, and wherein the differential capillary force derives at least in part from a difference between the pre-chamber height and the sensing chamber height.  
     
     
         3 . The device of  claim 2 , wherein the height of the sensing chamber is defined by layers within the sensing chamber.  
     
     
         4 . The device of  claim 1 , wherein the height of the sensing chamber is defined by an aperture in a space layer.  
     
     
         5 . The device of  claim 1 , wherein the interior surface of the pre-chamber having a first surface roughness, as first actual surface area, and a first geometric surface area, and the interior surface of the sensing chamber having a second surface roughness, a second actual surface area, and a second geometric surface area, wherein the second surface roughness is greater than the first surface roughness, and wherein the differential capillary force derives from a difference between the second surface roughness and the first surface roughness is defined as the actual surface area divided by the geometric surface area.  
     
     
         6 . The device of  claim 1 , wherein the sensing chamber comprises electrodes capable of use in an electrochemical cell.  
     
     
         7 . The device of  claim 6 , wherein the electrodes are spaced apart by a distance of 600 microns or less.  
     
     
         8 . The device of  claim 6 , wherein the electrodes are spaced apart by a distance of 400 microns or less.  
     
     
         9 . The device of  claim 6 , wherein the electrodes are spaced apart by a distance of 200 microns or less.  
     
     
         10 . The device of  claim 1 , wherein the interior surface of at least the pre-chamber or the sensing chamber comprises a surface treatment, wherein the differential capillary force derives from the surface treatment.  
     
     
         11 . The device of  claim 10 , wherein the surface treatment comprises a hydrophilic substance.  
     
     
         12 . The device of  claim 10 , wherein the surface treatment comprises a hydrophobic substance.  
     
     
         13 . The device of  claim 10 , wherein the surface treatment comprises a substance selected from the group consisting of a surfactant, a block copolymer, a hygroscopic compound, an ionizable substance, and mixtures thereof.  
     
     
         14 . The device of  claim 10 , wherein the interior surface of the pre-chamber comprises a first surface treatment and the interior surface of the sensing chamber comprises a second surface treatment.  
     
     
         15 . A method for ensuring that a sensing device is substantially filled with a sample of fluid comprising: 
 providing a device for sampling a fluid, comprising a pre-chamber having an interior surface and being capable of exerting a first capillary force, a sensing chamber in fluid communication with the pre-chamber, the sensing chamber having an interior surface and being capable of exerting a second capillary force; wherein a differential exist between the capillary forces, the differential being sufficient to cause flow of fluid from the pre-chamber to the sensing chamber, and wherein the pre-chamber further comprises a volume such that when full the pre-chamber comprises at least as much sample as is needed to substantially fill the sensing chamber;    contacting the device with the fluid for a sufficient period of time to allow the fluid to enter the pre-chamber; and    allowing the sample to flow from the pre-chamber to the sensing chamber, such that the sensing chamber is substantially filled.    
     
     
         16 . The method of  claim 15 , wherein the sensing chamber comprises electrodes capable of use in an electrochemical cell.  
     
     
         17 . The method of  claim 16 , wherein the electrodes are spaced apart by a distance of 600 microns or less.  
     
     
         18 . The method of  claim 16 , wherein the electrodes are spaced apart by a distance of 400 microns or less.  
     
     
         19 . The method of  claim 16 , wherein the electrodes are spaced apart by a distance of 200 microns or less.  
     
     
         20 . The method of  claim 15 , the sensing chamber further comprising a chemical for use in the sensing chamber.  
     
     
         21 . The method of  claim 20 , the chemical further comprising a reagent capable of undergoing a redox reaction with an analyte or a reaction product of the analyte.  
     
     
         22 . The method of  claim 15 , further comprising the step of: detecting a condition wherein the pre-chamber contains a volume of fluid sufficient to substantially fill the sensing chamber.  
     
     
         23 . The method of  claim 15 , further comprising the step of: determining a presence or an absence of an analyte in the sample.  
     
     
         24 . The method of  claim 23 , wherein the determining step comprises conducting a quantitative measurement of the analyte.  
     
     
         25 . The method of  claim 23 , wherein the determining step comprises an electrochemical measurement.  
     
     
         26 . The method of  claim 23 , wherein the analyte comprises a substance selected from the group consisting of lactate, cholesterol, enzymes, nucleic acids, lipids, polysaccharides, and metabolites.  
     
     
         27 . The method of  claim 23 , wherein the analyte comprises glucose.  
     
     
         28 . The method of  claim 23 , wherein the sample comprises a biological fluid.  
     
     
         29 . The method of  claim 28 , wherein the biological fluid comprises a body fluid of an animal or a plant.  
     
     
         30 . The method of  claim 29 , wherein the body fluid is selected from the group consisting of interstitial fluid, blood, tears, expectorate, saliva, urine, semen, vomitus, sputum, fruit juice, vegetable juice, plant sap, and nectar.  
     
     
         31 . The method of  claim 28 , wherein the biological fluid comprises a food product.  
     
     
         32 . The method of  claim 23 , wherein the sample comprises a non-biological fluid.  
     
     
         33 . The method of  claim 32 , wherein the non-biological fluid comprises a water-based solution.  
     
     
         34 . The method of  claim 15 , wherein the interior surface of the pre-chamber comprises at least first and second pre-chamber walls spaced apart at a first distance to define a pre-chamber height, and wherein the interior surface of the sensing chamber comprises at least first and second sensing chamber walls spaced apart at a second distance to define a sensing chamber height, wherein the height of the sensing is less than the height of the pre-chamber, and wherein the differential capillary force derives at least in part from a difference between the pre-chamber height and the sensing chamber height.  
     
     
         35 . The method of  claim 15 , wherein the interior surface of the pre-chamber having a first surface roughness, as first actual surface area, and a first geometric surface area, and the interior surface of the sensing chamber having a second surface roughness, a second actual surface area, and a second geometric surface area, wherein the second surface roughness is greater than the first surface roughness, and wherein the differential capillary force derives from a difference between the second surface roughness and the first surface roughness is defined as the actual surface area divided by the geometric surface area.