Electrochemical detection method

Abstract

There is disclosed a method of measuring formation of a barrier to restrict or reduce movement of an electroactive species. The method comprises providing an electrochemical cell having a working electrode and a counter electrode spaced from the working electrode, providing a subject component, a testing component and at least one electroactive species within the cell, the subject and testing components being intended to cause the formation of a barrier to restrict or reduce movement of an electroactive species, applying a potential between the working electrode and the counter electrode sufficient to produce a current proportional to the concentration of the electroactive species being measured, and measuring the current at the working electrode to obtain a measure of the formation of the barrier to restrict or reduce movement of the electroactive species.

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         21 . A method of determining whether a target component is present in a subject component, comprising:
 providing an electrochemical cell having a working electrode and a counter electrode spaced from the working electrode;   providing a subject component which may or may not comprise a target component, a testing component and at least one electroactive species within the cell, the subject and testing components being intended to cause the formation of a barrier by an agglutination reaction to restrict or reduce movement of an electroactive species when the target component is present;   applying a potential between the working electrode and the counter electrode sufficient to produce a current related to the rate of mass transport of the electroactive species being measured to the working electrode; and   measuring the current at the working electrode to determine whether a barrier is formed which restricts or reduces movement of the electroactive species, to thereby determine whether said target component is present in said subject component.   
     
     
         22 . A method as claimed in  claim 21 , wherein the formation of a barrier is intended to be caused by an agglutination reaction. 
     
     
         23 . A method as claimed in  claim 21 , comprising applying a potential sufficient to maintain the concentration of the electroactive species at the working electrode. 
     
     
         24 . A method as claimed in  claim 21 , wherein the step of measuring the current comprises measuring the current at a first time before significant barrier formation is expected to occur in the cell and measuring the current again at a second time by which significant barrier formation is expected to occur, and obtaining said measure of barrier formation from the difference in measured current. 
     
     
         25 . A method as claimed in  claim 24 , comprising selecting the first time to correspond to a time when the change in a barrier formation measuring parameter is less than about 20% of the total change in that parameter when the barrier is fully formed and selecting the second time to be a time when the change in the agglutination measuring parameter is more than about 50% of the total change in the sample and more preferably less than about 10% of the total change in that parameter. 
     
     
         26 . A method as claimed in  claim 25 , wherein the first and second times are selected to correspond to less than about 10% and more than about 70% of the total change respectively. 
     
     
         27 . A method as claimed in  claim 21 , comprising obtaining a measure of the diffusion coefficient of the electroactive species from the difference in measured current to thereby obtain a measure of barrier formation. 
     
     
         28 . A method as claimed in  claim 21 , further comprising obtaining a measure of the change in diffusion coefficient from the difference in measured current to thereby obtain a measure of barrier formation. 
     
     
         29 . A method as claimed in  claim 21 , wherein the electroactive species is provided by the barrier formation reaction, the method comprising providing two electrodes which can act as the working electrode and the testing component is provided close to or at one of the two electrodes, the method further comprising varying the applied potential or current measuring circuit connections in order to switch between said working electrodes, and measuring the current at both working electrodes to thereby obtain a measure of barrier formation. 
     
     
         30 . Apparatus for measuring a formation of a barrier to restrict or reduce movement of an electroactive species having:
 an electrochemical cell having a working electrode and a counter electrode spaced from the working electrode, the electrochemical cell being adapted to receive a subject component, a testing component and at least one electroactive species within the cell, the subject and testing components being intended to cause the formation of a barrier by an agglutination reaction to restrict or reduce movement of the at least one electroactive species;   an electric power source for applying a potential between the working electrode and the counter electrode sufficient to produce a current related to the rate of mass transport of the electroactive species being measured to the working electrode;   an ammeter for measuring the current at the working electrode; and   barrier formation measurement means for determining a measure of the formation of a barrier to movement of said at least one electroactive species from the measured current to thereby determine a measure of agglutination.   
     
     
         31 . Apparatus as claimed in  claim 30 , wherein the barrier formation measurement means is an agglutination measurement means for determining a measure of agglutination said agglutination forming said barrier. 
     
     
         32 . Apparatus as claimed in  claim 30 , wherein the electrochemical cell further comprises a separate reference electrode. 
     
     
         33 . Apparatus as claimed in  claim 30 , wherein the counter electrode may be a counter/reference electrode. 
     
     
         34 . Apparatus as claimed in  claim 30 , further comprising detection means for determining the presence of a testing component on the basis of the measure of barrier formation when said apparatus is used to detect the presence of target component in the subject component. 
     
     
         35 . Apparatus as claimed in  claim 30 , wherein said ammeter is configured to measure the current at a first time before at which significant barrier formation is expected to occur in the cell and at a second time by which significant barrier formation is expected to occur and to obtain said measure of barrier formation from the difference in measured current. 
     
     
         36 . Apparatus as claimed in  claim 30 , further comprising sampling means for sampling the current from the ammeter at a first time and a second time, the first time being before significant barrier formation is expected to occur in the cell and the second time being a time by which significant barrier formation is expected to occur, and wherein the barrier formation measurement means determines a measure of the formation of a barrier from the difference in current. 
     
     
         37 . Apparatus as claimed in  claim 30 , wherein said barrier formation measurement means determines a measure of the diffusion co-efficient of the electroactive species from the measure of current to thereby obtain a measure of the barrier formation. 
     
     
         38 . Apparatus as clamed in  claim 30 , wherein the barrier formation measurement means uses the difference in measured current in order to obtain a measure of the change of diffusion co-efficient to thereby obtain a measure of barrier formation. 
     
     
         39 . Apparatus as claimed in  claim 30 , wherein the apparatus comprises two electrodes which can act as the working electrode and means for varying the applied potential or current measuring circuit connections in order to switch working electrodes in order to obtain a measure of the current at both working electrodes.