Electrical impedance hematocrit and HBA1C biosensor comprising sample plate and sample apparatus
A sampling plate ( 1 ) is provided comprising a sample zone ( 2 ) for receiving a liquid sample, and two drive electrodes ( 3, 4 ) with separate respective electrode terminals spaced by a spacing for receiving a the liquid sample within the sample zone for use in driving an electrical signal through the sample. Two sensing electrodes ( 5, 6 ) are provided with separate respective electrode terminals spaced between the electrode terminals of the two drive electrodes for use in sensing an electrical signal generated by the drive electrodes within a the sample. A sampling apparatus ( 15 ) is provided for use with the plate.
1. A sampling apparatus for use in performing electrical measurements on a liquid sample containing blood, the apparatus comprising:
at least two current output terminals for outputting an alternating current signal applied therebetween;
an alternating electrical current unit in electrical communication with the current output terminals for applying thereto an alternating electrical current of a given amplitude and frequency when said liquid sample is in electrical connection between the current output terminals;
a voltage unit in electrical communication with the current output terminals for applying therebetween a direct (DC) electrical potential difference of a given magnitude;
a first voltage input terminal for receiving a first electrical signal externally input thereto and a separate second voltage input terminal for receiving a second electrical signal externally input thereto when said liquid sample is in electrical connection between the first and second voltage input terminals;
one or more voltage detectors for measuring a first voltage and a second voltage using said first and second electrical signals, respectively;
a control unit arranged to control the electrical current unit to apply said alternating electrical current of said given frequency and concurrently to control the voltage unit and the one or more voltage detectors to measure said first and second voltages both when said direct electrical potential difference is applied and when said direct electrical potential difference is not applied;
a calculating unit comprising a non-transitory computer usable medium comprising a computer readable program code embodied therein, the computer readable program code executable to calculate a first electrical reactance value which is the reactive component of an electrical impedance comprising a resistive component and a reactive component using the first and second voltages measured when said direct electrical potential difference is applied, and to calculate a second electrical reactance value which is the reactive component of an electrical impedance comprising a resistive component and a reactive component measured when said direct electrical potential difference is not applied;
wherein the computer readable program code is executable to generate a value representing the concentration of glycated haemoglobin (HbA1c ) in the liquid sample according to the first electrical reactance value, the second electrical reactance value and a value representing the relative volume of red blood cells in the liquid sample (haematocrit).
2. A sampling apparatus according to claim 1 in which the given frequency has a value in the range 500 KHz to 1.5 MHz.
3. A sampling apparatus according to claim 1 comprising an integrated circuit arranged for measuring said first voltage and said second voltage, and responsive to the control unit to apply said alternating current accordingly.
4. A sampling apparatus according to claim 1 in which said direct (DC) voltage is substantially constant in value.
5. A data carrier comprising non-transitory computer usable medium having a computer readable program code embodied therein to operate the sampling apparatus of claim 1 , the computer readable program code adapted to be executed to implement a sample measurement method for performing electrical measurements on the liquid sample containing blood, the method comprising:
receiving the liquid sample on a sample plate comprising electrode terminals in electrical communication with the current output terminals, the electrode terminals separated by a spacing adapted to be bridged by blood from the liquid sample and which comprise a reagent to react with free glucose in the liquid sample; and
applying to the electrodes the alternating electrical current having the given frequency to generate a first alternating potential difference across the spacing between the electrode terminals;
applying between the electrode terminals the direct (DC) electrical potential difference of the given magnitude;
determining the value of the first electrical reactance of the liquid sample bridging said spacing for said given frequency wherein the reactance is the reactive component of the electrical impedance comprising the resistive component and the reactive component;
removing the direct (DC) electrical potential difference from between the electrode terminals;
applying to the electrodes the alternating electrical current having said given frequency to generate a second alternating potential difference across the spacing between the electrode terminals;
determining the value of the second electrical reactance of the liquid sample bridging said spacing for said given frequency wherein the reactance is the reactive component of the electrical impedance comprising the resistive component and the reactive component;
generating the value representing the concentration of glycated haemoglobin (MAIO in the blood within the sample according to the first electrical reactance value, the second electrical reactance value and the value of the relative volume of red blood cells in the liquid sample (haematocrit).