Analyte sensor and analyte sensing method
A biosensor includes a detection element having an analyte detecting portion which is monotonically increased in mass in response to detection of an analyte; a reference element having a reference measuring portion which exhibits no reactivity to the analyte; a mixer which mixes a detection signal responsive to mass variations in the analyte detecting portion from the detection element and a reference signal from the reference element; a measurement which calculates two candidate phase-change values of a positive value and a negative value, from a signal mixed by the mixer in accordance with a heterodyne system, and determines a phase-change value from the two candidate phase change value by judging whether the phase is positive or negative based on temporal changes in signal strength; and a detection amount calculation portion which calculates a detection amount of the analyte based on the phase change value determined by the measurement portion.
1. An analyte sensor, comprising:
a detection element comprising an analyte detecting portion which is monotonically changed in mass in response to adsorption of a target provided in an analyte or reaction with the target, the detection element configured to output a detection signal of AC responsive to mass variations in the analyte detecting portion;
a reference element comprising a reference measuring portion which undergoes neither adsorption of the target nor reaction with the target, the reference element configured to output a reference signal of AC relative to the detection signal;
a measurement portion which determines two candidate phase-change values of a positive candidate phase-change value and a negative candidate phase-change value, from a measurement signal which is obtained from the detection signal and the reference signal in accordance with a heterodyne system,
the measurement portion configured to output the positive candidate phase-change value as a phase change value when measurement signal strength is decreased with time, and configured to output the negative candidate phase-change value as a phase change value when measurement signal strength is increased with time, in a case where a mass of the analyte detecting portion is monotonically increased and the detection signal is obtained by subtracting the detection signal from the reference signal in accordance with the heterodyne system, or where the mass of the analyte detecting portion is monotonically decreased and the detection signal is obtained by subtracting the reference signal from the detection signal in accordance with the heterodyne system, and
the measurement portion configured to output the negative candidate phase-change value as a phase change value when measurement signal strength is decreased with time, and configured to output the positive candidate phase-change value as a phase change value when measurement signal strength is increased with time, in a case where the mass of the analyte detecting portion is monotonically increased and the detection signal is obtained by subtracting the reference signal from the detection signal in accordance with the heterodyne system, or where the mass of the analyte detecting portion is monotonically decreased and the detection signal is obtained by subtracting the detection signal from the reference signal in accordance with the heterodyne system; and
a detection amount calculation portion which calculates a detection amount of the analyte on a basis of the phase change value.
2. The analyte sensor according to claim 1 , further comprising:
an analyte flow path through which an analyte solution containing the analyte is supplied to the analyte detecting portion and the reference measuring portion in order or simultaneously.
3. The analyte sensor according to claim 1 , wherein
the detection element comprises
a piezoelectric detection element substrate,
the analyte detecting portion, the analyte detecting portion being placed on the piezoelectric detection element substrate,
a detection first IDT electrode placed on the piezoelectric detection element substrate, the detection first IDT electrode configured to produce an elastic wave toward the analyte detecting portion, and
a detection second IDT electrode placed on the piezoelectric detection element substrate, the detection second IDT electrode configured to receive the elastic wave which has passed through the analyte detecting portion,
the reference element comprises
a piezoelectric reference element substrate,
the reference measuring portion, the reference measuring portion being placed on the reference element substrate,
a reference first IDT electrode placed on the reference element substrate, the reference first IDT electrode configured to produce an elastic wave toward the reference measuring portion, and
a reference second IDT electrode placed on the reference element substrate, the reference second IDT electrode configured to receive the elastic wave which has passed through the reference measuring portion,
the detection signal is an AC signal obtained when the elastic wave which has passed through the analyte detecting portion is received by the detection second IDT electrode, and
the reference signal is an AC signal obtained when the elastic wave which has passed through the reference measuring portion is received by the reference second IDT electrode.
4. The analyte sensor according to claim 3 , further comprising:
a π/2 delay line configured to permit passage of the detection signal or the reference signal which are prior to acquisition of the measurement signal by the heterodyne system.
5. The analyte sensor according to claim 3 ,
wherein the detection element substrate and the reference element substrate are formed integrally with each other, and
further comprising a reference potential line located between
a detection element region where the analyte detecting portion, the detection first IDT electrode, and the detection second IDT electrode are disposed, and
a reference element region where the reference measuring portion, the reference first IDT electrode, and the reference second IDT electrode are disposed.
6. The analyte sensor according to claim 5 ,
wherein the detection first IDT electrode, the detection second IDT electrode, the reference first IDT electrode, and the reference second IDT electrode are each composed of a pair of comb-like electrodes, and one of the pair of comb-like electrodes is connected to the reference potential line, respectively.
7. The analyte sensor according to claim 1 , further comprising:
low-noise amplifiers which are disposed between the detection element and the measurement portion, and between the reference element and the measurement portion, respectively, the low-noise amplifiers being configured to amplify the detection signal from the detection element and the reference signal from the reference element, respectively.
8. An analyte sensing method, comprising:
an analyte solution supplying step of supplying an analyte solution containing an analyte in which a target is provided, to an analyte detecting portion of a detection element that is monotonically changed in mass in response to adsorption of the target or reaction with the target, and a reference detecting portion of a reference element that undergoes neither adsorption of the target nor reaction with the target;
a determination step of determining two candidate phase-change values of a positive candidate phase-change value and a negative candidate phase-change value, from a measurement signal which is obtained from a detection signal of AC responsive to mass variations in the analyte detecting portion and a reference signal of AC from the reference detecting portion, relative to the detection signal, in accordance with a heterodyne system,
the positive candidate phase-change value being determined as a phase change value when measurement signal strength is decreased with time, and the negative candidate phase-change value being determined as a phase change value when measurement signal strength is increased with time, in a case where a mass of the analyte detecting portion is monotonically increased and the detection signal is obtained by subtracting the detection signal from the reference signal in accordance with the heterodyne system, or where the mass of the analyte detecting portion is monotonically decreased and the detection signal is obtained by subtracting the reference signal from the detection signal in accordance with the heterodyne system, and
the negative candidate phase-change value being determined as a phase change value when measurement signal strength is decreased with time, and the positive candidate phase-change value being determined as a phase change value when measurement signal strength is increased with time, in a case where the mass of the analyte detecting portion is monotonically increased and the detection signal is obtained by subtracting the reference signal from the detection signal in accordance with the heterodyne system, or where the mass of the analyte detecting portion is monotonically decreased and the detection signal is obtained by subtracting the detection signal from the reference signal in accordance with the heterodyne system; and
a calculation step of calculating an amount of the analyte detected on a basis of the phase change value.
9. The analyte sensing method according to claim 8 ,
wherein, in the determination step, each of the detection signal and the reference signal is amplified, and a measurement signal is obtained on a basis of the detection signal amplified and reference signal amplified by the heterodyne system.