Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/28—Electrolytic cell components
  • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
  • G01N27/327—Biochemical electrodes, e.g. electrical or mechanical details for in vitro measurements
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
  • G01N27/00—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means
  • G01N27/26—Investigating or analysing materials by the use of electric, electrochemical, or magnetic means by investigating electrochemical variables; by using electrolysis or electrophoresis
  • G01N27/28—Electrolytic cell components
  • G01N27/30—Electrodes, e.g. test electrodes; Half-cells
  • G01N27/327—Biochemical electrodes, e.g. electrical or mechanical details for in vitro measurements
  • G01N27/3271—Amperometric enzyme electrodes for analytes in body fluids, e.g. glucose in blood
  • G01N27/3274—Corrective measures, e.g. error detection, compensation for temperature or hematocrit, calibration

Definitions

• the present invention relates to a diffusion based analyte concentration measurement that mitigates the effects of diffusion interfering factors.
• Electrochemical-based sensors such as self-monitoring blood glucose (SMBG) strips, are used for measuring/determining analyte concentration in fluid samples, for example whole blood.
• DIF diffusion interfering factors
• Hct blood haematocrit
• DIF mitigation can be categorized into active approaches and passive approaches.
• the former relies on using DIF sensitive signals to have DIF "measurements" which are then used for DIF correction.
• a problem with active approaches is that they require extra mechanisms, such as additional strip elements, more measurement steps, and additional device/meter components/parts.
• passive approaches use DIF insensitive signals or signals with negligible DIF effect for the analyte measurement.
• US8105478B2 describes a method for selecting pulse lengths for measuring the concentration of a redox-active substance as a mediator in a molecular-biological detection system, in which suitable potentials are applied to a working electrode, to cause at least one of an oxidation process and a reduction process, which takes place as a redox reaction.
• the method comprises pulsing the potential of the working electrode and alternately forming measuring phases and relaxation phases; selecting the measuring-phase pulse lengths so that, towards the end of the pulse, the capacitive current is relatively small in comparison with the Faraday current; and selecting the relaxation-phase pulse lengths so that, towards the end of the pulse, the concentration gradient is relaxed so that at the beginning of a following measuring phase, the change in concentration of the mediator, brought about by the consumption of the mediator by the measurement itself, is reversed to the greatest possible extent approaching the original level.
• the concentration gradient may gradually and continuously decrease towards the bulk solution.
• the concentration gradient may fluctuate, whilst generally decreasing towards the bulk solution.
• the at least one electrode may be coated with at least one redox mediator.
• the electrode may be in a solution that includes at least one redox mediator, and so is exposed to the at least one redox mediator.
• the accumulation phase can have a reduction at the working electrode and the measurement phase can have an oxidation at the working electrode.
• the accumulation phase may have an oxidation and the measurement phase can have a reduction at the working electrode depending on nature of redox reaction involving the analyte and mediator(s). As is known in the art, whether the accumulation phase should have reduction or oxidation depends on the mediator state (oxidised or reduced) before it undergoes the heterogeneous reaction at electrode surface. Also, it will be appreciated that more than one mediator may be used for a series of redox reactions.
• further potentials may be applied to the electrode(s). Such further potentials could be applied before the first potential or after the second potential.
• an initiation potential may be applied prior to applying the at least one cycle of pulses, wherein the initiation potential has an open circuit or potential for substantially no redox reaction at the electrodes.
• the initiation potential may be applied prior to applying each cycle of pulses.
• the second potential has to immediately follow the first potential, so that the accumulation phase that forces accumulation of the concentration gradient immediately precedes the measurement phase.
• the second potential is such that after depletion of the established concentration gradient of the mediator another concentration gradient of the mediator builds up (the opposite concentration gradient is established), but with a concentration that increases towards the bulk solution.
• the magnitudes of the first potential and the second potential may be symmetrical relative to a potential which elicits substantially zero current flow (E 0) .
• the magnitudes of the first potential and second potential may be asymmetrical to E 0 .
• Durations of the first potential and the second potential may be the same. Durations of the first potential and the second potential may be different. Durations of the first potential and the second potential may be less than 10 minutes, preferably less than 1 minute, and most preferably less than 5 seconds. Durations of the first potential and the second potential may be between 5 to 100% of the total time of each pulse cycle.
• a test meter for determining analyte concentration using a redox reaction in an electrochemical cell that has at least two electrodes, one of which is a working electrode, at least one electrode exposed to at least a redox mediator, using at least one cycle of pulses, each cycle having a first potential and a second potential, the meter being configured to: apply a first potential to initiate an accumulation phase that forces accumulation of a concentration gradient of the mediator at or close to the working electrode with a concentration that decreases towards the bulk solution; apply a second potential to initiate a measurement phase and deplete the established concentration gradient of the mediator; and measure current associated with the second potential of each cycle.
• the test meter is configured to calculate analyte concentration using the measured current.
• the accumulation phase can be a reduction and the measurement phase can be an oxidation.
• the accumulation phase can be an oxidation and the measurement phase can be a reduction depending on the nature of the redox reaction involving the analyte and mediator(s). Also, it will be appreciated that more than one mediator may be used for a series of redox reactions.
• the second potential may be such that after depletion of the established concentration gradient of the mediator another concentration gradient of the mediator builds up, but with a concentration that increases towards the bulk solution.
• the magnitudes of the first potential and the second potential may be symmetrical relative to a potential that causes substantially zero current flow (E 0 ).
• the magnitudes of the first potential and second potential may be asymmetrical to E 0 .
• Durations of the first potential and the second potential may be the same. Durations of the first potential and the second potential may be different. Durations of the first potential and the second potential may be less than 10 minutes, preferably less than 1 minute, and most preferably less than 5 seconds. Durations of the first potential and the second potential may be between 5 to 100% of the total time for each pulse cycle.
• Figure 1 shows switching redox reactions at two electrodes by controlling potential
• Figure 2 shows an evolution of M red (reduced mediator) concentration gradient at the working electrode E1 with the redox reaction switch in Figure 1 ;
• Figure 3 shows a test waveform and a control waveform for applying to the electrodes of an electrochemical cell
• Figure 4 shows current sensitivity to glucose versus measurement time for various samples taken using the waveforms of Figure 3, where the numbers in the legends are Hct levels as a percentage, and
• Figure 5 shows the percentage biases to the nominal Hct of current sensitivity to glucose at 0.3 seconds of four of the oxidation pulses of the waveforms of Figure 3, where the numbers in legends are the pulse numbers of the waveforms in Figure 3.
• This present invention mitigates the effects of DIF current signals by switching and controlling redox reactions at the working and counter electrodes of electrochemical- based sensors that use mediators. This is done by creating a higher concentration of mediator near the working electrode than in the bulk sample during an accumulation phase, so that a mediator concentration gradient is present at the start of each measurement phase.
• the mediator concentration gradient extends by at least 10nm from the working electrode into the bulk sample.
• the mediator concentration gradient should not reach the counter electrode, and so ideally the maximum extent of the mediator gradient is less than the separation of the working and counter electrodes. In many practical implementations, it is preferred that by the end of the accumulation phase and the start of the measurement phase, the mediator concentration gradient does not extend to beyond half way between the working and counter electrodes.
• Figure 1 shows one pulse cycle and the initiated corresponding redox reactions of an electrochemical test strip with two electrodes, a working electrode E1 and a counter electrode E2.
• the two electrodes are covered with a reagent layer which contains redox mediator (M) and enzyme (Enz).
• M redox mediator
• Enz enzyme
• the working and counter electrodes E1 and E2 respectively are in contact with a whole blood sample and an electrical potential (voltage) is applied between the two electrodes. This results in redox reactions both in the blood (homogeneous redox reactions) and at surfaces of the two electrodes (heterogeneous redox reactions).
• E red reduction potential
• E ox oxidation potential
• E red bias (difference) to E 0 and E ox bias to E 0 can be the same (i.e. symmetrical to E 0 as illustrated in Figure 1 ) or different.
• oxidized mediator (M ox ) undertakes reduction at the working electrode E1 (reaction 3), whilst reduced mediator (M red ) undertakes oxidation at the counter electrode E2 (reaction 2).
• glucose (Glue) reacts with M ox involving the enzyme (Enz) to produce M red in blood (reaction 1 ).
• M red is "accumulated" at the working electrode E1 (both reactions 1 and 3 produce M red ) to a concentration C, higher than the starting M red concentration C 0 and a M red concentration gradient is established with decreasing M red concentration from the working electrode E1 surface towards the bulk solution (see Figure 2A to 2B).
• the heterogeneous redox reactions at the two electrodes are switched over (see Figure 1 ).
• glucose concentration is determined by measuring the rate of reaction 5, e.g. by measuring current.
• Rate of reaction 5 is proportional to M red available at the surface of the working electrode E1 .
• Reaction 5 proceeds at a sufficiently high rate to cause M red depletion to be faster than its supply (through diffusion) at the surface of the working electrode E1 .
• M red concentration drops from , through C 0 , ultimately to C zero (see the dotted concentration gradient line in Figure 2C) with time.
• C g is negative and the rate of reaction 5 decreases with time in a pattern described by the Cottrell equation (see below), and the glucose measurement is Hct dependent.
• the rate of reaction 5 is dependent on M red diffusion and the M red concentration gradient established during the previous reduction pulse.
• Increasing Hct decreases M red diffusion, but increases the M red concentration gradient. Therefore, the Hct effect on the glucose measurement is compensated by manipulating the redox reaction switch.
• the current has to be measured in the concentration gradient depletion phase only, i.e. while the concentration gradient is being depleted. After the depletion phase, when the mediator concentration drops below its start level (i.e. the level prior to the accumulation phase), the current becomes Hct dependent.
• Establishment of the M red concentration gradient during the accumulation phase can be achieved in various ways, including, but not limited to, controlling the potential magnitude and/or polarity of the pulses applied, controlling the effective surface ratio of the two electrodes, controlling the pulse time, controlling reagent layer components and quantity ratios, or any combination of these.
• the potential magnitude of the pulses applied is used to force accumulation of the mediator concentration gradient and subsequently deplete the established mediator concentration gradient at the working electrode.
• other techniques for controlling the accumulation and depletion of mediator concentration are possible.
• Figure 3 shows a control waveform W69 and test waveform W70.
• the difference between the test waveform W70 and the control waveform W69 is that the test waveform W70 has a higher potential magnitude for the reduction pulses (pulses 2, 4, 6, 8) than the control waveform W69 to enhance the establishment of M red concentration gradient at the working electrode E1 during these pulses (see Figure 1 ).
• Both the oxidation and reduction pulses of the test waveform are over-potential. By this it is meant that the potential is of a magnitude that is sufficient for the redox reactions at the electrodes to be dominated by diffusion of the mediator and/or analyte towards the electrode. Magnitudes of the oxidation and reduction pulses are selected and controlled by taking into account the electrochemical properties of the mediator and the electrodes. Both the oxidation and reduction pulses can have positive, negative or zero potentials.
• Pulse 1 is an initiation pulse that is applied once before the start of the repeated cycles of pulses (i.e. it is not part of the repeated cycle of pulses).
• Pulse 1 is an under-potential pulse wherein the rate of redox reactions at the electrodes is dominated by the kinetics of the heterogeneous redox reactions to allow hydration/dissolution of the strip reagent layer (potential of this pulse can be E 0 or close to E 0 to keep redox reaction at both the working electrode E1 and the counter electrode E2 to a minimum). Pulse 1 can also be an open circuit.
• the total test time of the 9 pulses in this experiment was designed for 6.25 seconds, but the test can be completed in 5 seconds (i.e. without pulses 8 and 9) or less.
• the waveforms were applied to the strip using a potentiostat, so that a positive potential lead to oxidation and a negative/zero potential leads to reduction at the working electrode E1 .
• the oxidation current i.e. positive pulse current resulting from reaction 5 in Figure 1
• Techniques for determining glucose concentration using current measured during a redox reaction are well known in the art and so will not be described in detail.
• FIG. 4 shows that in each graph of W69, there are clear separations between the lines of positive pulses (measuring pulses). Higher Hct corresponds to lower current sensitivity. This indicates that W69 measuring currents are sensitive to Hct variation. In contrast, for the graphs of W70, the line separation disappears or is remarkably decreased, i.e. Hct as a DIF is effectively accounted for. W70 leads to significantly higher current sensitivity than W69, i.e. W70 has enhanced current sensitivity to glucose compared to W69.
• W70 lines in Figure 4 have higher magnitude than W69 lines; 2) W70 lines of each pulse have similar/close magnitude (they are on top of each other if overlaid) whilst W69 lines of each pulse decreases with time, i.e. W70 retains current sensitivity throughout the test time whilst W69 does not. This is because the established M red concentration gradient during the reduction pulse leads to enhanced reaction 5 of the subsequent oxidation pulse.
• Figure 5 also show the mitigation of Hct, where percentage bias is the difference in current sensitivity between the Hct of interest and the nominal Hct (defined here as 42%, and so this has zero bias).
• percentage bias is the difference in current sensitivity between the Hct of interest and the nominal Hct (defined here as 42%, and so this has zero bias).
• the current sensitivity at 0.3 seconds of the oxidation pulses 3, 5, 7 and 9 are used.
• the bias to nominal Hct had a range of about 20% to -20% with increased Hct.
• the bias to nominal Hct was reduced with a range less than +/-10%.
• DIF mitigation and in particular Hct mitigation
• Hct mitigation can be achieved by other means. For example, this could be done by increasing the effective surface ratio of the counter electrode E2 to the working electrode E1 , or increasing the duration of the accumulation phase pulses.
• any technique that forces the accumulation of a concentration gradient of the mediator at the working electrode E1 could be used.
• the present invention provides a simple and effective technique for mitigating the effects of DIF providing an Hct insensitive measurement.
• the method could be applied to existing products without making any changes to the strips.

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• 2014
  • 2014-07-08 GB GBGB1412156.0A patent/GB201412156D0/en not_active Ceased
• 2015
  • 2015-07-08 BR BR112017000305A patent/BR112017000305A2/pt not_active Application Discontinuation
  • 2015-07-08 EP EP15747510.4A patent/EP3167282A1/en not_active Withdrawn
  • 2015-07-08 CA CA2953452A patent/CA2953452A1/en not_active Abandoned
  • 2015-07-08 AU AU2015287447A patent/AU2015287447A1/en not_active Abandoned
  • 2015-07-08 KR KR1020177003207A patent/KR20170028408A/ko unknown
  • 2015-07-08 CN CN201580037065.6A patent/CN106687803A/zh active Pending
  • 2015-07-08 JP JP2016573879A patent/JP6619367B2/ja not_active Expired - Fee Related
  • 2015-07-08 RU RU2017103730A patent/RU2680266C2/ru not_active IP Right Cessation
  • 2015-07-08 WO PCT/GB2015/051973 patent/WO2016005743A1/en active Application Filing

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