Magnetoresistive sensor array for molecule detection and related detection schemes
A method of sensing molecules using a detection device, the detection device comprising a plurality of magnetoresistive (MR) sensors and at least one fluidic channel, comprising adding a plurality of molecules to be detected to the at least one fluidic channel, wherein at least some of the plurality of molecules to be detected are coupled to respective magnetic nanoparticles (MNPs), detecting a characteristic of a magnetic noise of a first MR sensor of the plurality of MR sensors, wherein the characteristic of the magnetic noise is influenced by a presence of one or more MNPs in a vicinity of the first MR sensor, and determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor.
1. A method of sensing molecules using a detection device, the detection device comprising a plurality of magnetoresistive (MR) sensors and at least one fluidic channel, the method comprising:
adding a plurality of molecules to be detected to the at least one fluidic channel, wherein at least some of the plurality of molecules to be detected are coupled to respective magnetic nanoparticles (MNPs);
detecting a characteristic of a magnetic noise of a first MR sensor of the plurality of MR sensors, the magnetic noise of the first MR sensor being an intrinsic noise of the first MR sensor due at least in part to thermally-excited fluctuations of a magnetic moment of the first MR sensor about an equilibrium position of the magnetic moment, wherein the characteristic of the magnetic noise is influenced by a presence of one or more MNPs in a vicinity of the first MR sensor; and
determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor.
2. The method of claim 1 , wherein the characteristic comprises one or more of a level, a jitter, or a variance of the magnetic noise.
3. The method of claim 1 , wherein detecting the characteristic of the magnetic noise of the first MR sensor comprises:
causing the first MR sensor to produce a sensor signal.
4. The method of claim 3 , wherein causing the first MR sensor to produce a sensor signal comprises:
generating a bias across the first MR sensor.
5. The method of claim 3 , wherein causing the first MR sensor to produce the sensor signal comprises:
applying a current to at least one line coupled to the first MR sensor.
6. The method of claim 3 , wherein the characteristic of the magnetic noise is an amplitude of the magnetic noise at a particular frequency or within a particular frequency band, a fluctuation of the magnetic noise, or a phase of the magnetic noise.
7. The method of claim 6 , wherein the characteristic of the magnetic noise is the amplitude of the magnetic noise at the particular frequency or within the particular frequency band, and wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor comprises:
measuring the amplitude of the magnetic noise at the particular frequency or within the particular frequency band.
8. The method of claim 7 , wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor comprises:
lowpass filtering and amplifying the sensor signal;
generating a reference signal having a selected frequency chosen to maximize a change in the sensor signal at the selected frequency in response to at least one of the one or more MNPs labeling a particular molecule type being detected by the first MR sensor;
a mixer mixing the sensor signal and the reference signal;
lowpass filtering and amplifying a mixer output signal from the mixer;
providing the filtered and amplified mixer output signal to an envelope detector; and
determining that the first MR sensor detected the presence of the one or more MNPs in the vicinity of the first MR sensor based on a change in an output of the envelope detector.
9. The method of claim 8 , wherein the selected frequency is dependent on a type of the one or more MNPs.
10. The method of claim 7 , wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor comprises:
monitoring a detector output voltage; and
determining, based on a change in the detector output voltage, that the first MR sensor detected the presence of the one or more MNPs in the vicinity of the first MR sensor.
11. The method of claim 6 , wherein the characteristic is the fluctuation of the magnetic noise.
12. The method of claim 11 , wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor comprises:
monitoring a detector output voltage; and
determining, based the detector output voltage being nonzero, that the first MR sensor detected the presence of the one or more MNPs in the vicinity of the first MR sensor.
13. The method of claim 11 , wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor comprises:
detecting changes over time in a detector output voltage.
14. The method of claim 11 , wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor comprises:
filtering the sensor signal;
providing the filtered sensor signal to an envelope detector; and
determining that the first MR sensor detected the presence of the one or more MNPs in the vicinity of the first MR sensor based on an output of the envelope detector being nonzero.
15. The method of claim 14 , further comprising:
amplifying the filtered sensor signal before providing the filtered sensor signal to the envelope detector.
16. The method of claim 6 , wherein the characteristic is the phase of the magnetic noise.
17. The method of claim 16 , wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs in the vicinity of the first MR sensor comprises:
providing an error signal output that corresponds to the phase of the magnetic noise.
18. The method of claim 1 , further comprising:
determining a baseline characteristic of the magnetic noise of the first MR sensor before adding the plurality of molecules to be detected to the at least one fluidic channel,
and wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs within the fluidic channel comprises:
detecting a change in the magnetic noise of the first MR sensor relative to the baseline characteristic.
19. The method of claim 1 , further comprising:
applying a magnetic field across the sensing device, and wherein detecting the characteristic of the magnetic noise of the first MR sensor is performed while the magnetic field is applied across the sensing device.
20. The method of claim 1 , wherein determining, based on the detected characteristic, whether the first MR sensor detected the presence of one or more MNPs within the fluidic channel comprises:
tracking an error signal of a phase locked loop (PLL).