CN207780034U - A kind of biology sample detection device based on magnetic bead - Google Patents

Abstract

The utility model discloses a biological sample detection device based on magnetic beads, which comprises a bracket, two groups of Helmholtz coils, GMR sensors and weak signal detection circuits located at both ends of the bracket, each group of Helmholtz coils includes a first Helmholtz coil The Holtz coil and the second Helmholtz coil, the first Helmholtz coil and the second Helmholtz coil are arranged coaxially and symmetrically, have the same axis midpoint, and the GMR sensor is arranged on the first Helmholtz coil The GMR sensor is fixed with a biological probe for specific detection on the midpoint of the axis of the Helmholtz coil and the second Helmholtz coil, and the weak signal detection circuit is connected with the GMR sensor, the first Helmholtz coil, and the second Helmholtz coil respectively. The coils are connected and supply power to the whole device. The utility model adopts reasonable magnetic field arrangement and circuit design, can realize the qualitative detection of magnetic beads, and has the characteristics of high sensitivity, less biological samples required and high portability.

Description

A biological sample detection device based on magnetic beads

technical field

The utility model relates to the field of biological sensors, in particular to a biological sample detection device based on magnetic beads.

Background technique

With the development of science and technology, it is becoming more and more important to perform rapid qualitative and quantitative detection of a specific biomolecule DNA or RNA. Biosensing technology emerged at the historic moment, and gradually played a huge role in the fields of medical research, clinical diagnosis and ecological agriculture. A biosensor is an analytical device that converts biologically relevant information into measurable information such as electrical signals. The signal detection circuit consists of three parts.

The traditional biological detection steps are: first collect the biological sample to be tested, and then send it to a specialized laboratory. After separation, amplification and chemical modification, the entire detection process can be completed. These processes require large, expensive specialized instruments, and the testing process requires highly trained professionals to operate. Therefore, traditional biological detection methods have gradually failed to meet the requirements of rapid, cheap and easy-to-operate biological detection.

With the discovery of the giant magnetoresistance (Giant Magneto-Resistance, GMR) effect, a new type of sensor based on the giant magnetoresistance effect——GMR sensor, has emerged. The general steps of biodetection with GMR biosensors are: first, the biological probes for specific detection are immobilized on the surface of the sensor; then the test solution containing the target biological sample that has completed the magnetic label flows over the sensor surface, and the target biological sample will be immobilized Bioprobe capture on the surface of the sensor, that is, the immunomagnetic beads are immobilized on the surface of the sensor through the specific binding between the biological samples to be tested; finally, the immunomagnetic beads generate an additional magnetic field under the action of an external excitation magnetic field, and the additional magnetic field will make the GMR The output signal of the sensor changes, so as to realize the qualitative detection of biological samples. The intensity of the signal reflects the amount of magnetic beads in the sample test solution, that is, the intensity of the signal reflects the concentration information of the target biological sample. Since the birth of the concept of GMR biosensor, it has received widespread attention and has become a hotspot of biosensors.

As far as the GMR biosensor is concerned, it uses the GMR sensor to detect the magnetic beads to indirectly realize the detection of biological samples. The detection object of GMR biosensor is immunomagnetic beads, so the performance of GMR sensor for immunomagnetic beads detection directly determines the quality of biological detection. The performance of the output signal detection circuit of GMR biosensor is also crucial to the quality of biological detection. Because the volume of immunomagnetic beads is generally small, the magnetic field generated after magnetization is also very small, and the resulting output signal of the GMR biosensor is also very weak, and the weak effective signal is often buried by strong noise. Therefore, an effective signal detection method is needed to read the signal. The weak sinusoidal signal buried in the strong noise can be effectively extracted by using the phase-locked technology, so the phase-locked amplifier is often used to detect the output signal in the experiment of the GMR biosensor. Commercial lock-in amplifiers should take into account factors such as versatility and multi-functions. They are generally expensive, bulky and heavy, and are not suitable for portable use. Therefore, it is necessary to develop a dedicated phase-lock detection circuit suitable for GMR biosensors.

At present, the research and development of GMR biosensors in China still lags behind developed countries such as the United States. However, whether it is abroad or at home, the biological detection technology based on GMR biosensors has not yet developed to the stage of commercial application.

Contents of the invention

The purpose of this utility model is to provide a biological sample detection device based on magnetic beads to solve at least one of the above technical problems.

According to one aspect of the present invention, there is provided a biological sample detection device based on magnetic beads, a bracket, two sets of Helmholtz coils located at both ends of the bracket, a GMR sensor and a weak signal detection circuit, and each set of Helmholtz coils includes The first Helmholtz coil and the second Helmholtz coil, the first Helmholtz coil and the second Helmholtz coil are arranged coaxially and symmetrically, have the same axis midpoint, and the GMR sensor is arranged at the first On the axis midpoint of the first Helmholtz coil and the second Helmholtz coil, the GMR sensor is fixed with a biological probe for specific detection, and the weak signal detection circuit is connected with the GMR sensor, the first Helmholtz coil, and the second Helmholtz coil respectively. The two Helmholtz coils are connected and supply power to the whole device. Preferably, the coil bobbin radius of the first Helmholtz coil is 8.5 cm, and the coil bobbin radius of the second Helmholtz coil is 10 cm.

Preferably, the first Helmholtz coil applies a DC magnetic field to the GMR sensor.

Preferably, the first Helmholtz coil applies a magnetic field perpendicular to the plane where the GMR sensor is located to the GMR sensor.

Preferably, the GMR sensor is a spin valve GMR sensor.

Preferably, the current direction inside the GMR sensor is parallel to the plane where the GMR sensor is located.

Preferably, the GMR chip used by the GMR sensor is a half-bridge structure, the GMR chip includes a first spin valve GMR and a second spin valve GMR, and the sensitive axes of the first spin valve GMR and the second spin valve GMR are parallel to each other And the pinning direction is opposite, and when there is no external magnetic field, the resistance values of the two are equal; the GMR chip is connected with the first resistor and the second resistor to form a Wheatstone bridge.

Preferably, the weak signal detection circuit includes the following parts: signal pre-processing circuit, quadrature signal generator circuit, correlator circuit, low-pass filter circuit, analog-to-digital conversion circuit, display circuit, Helmholtz coil drive circuit and power supply circuit .

Preferably, the power supply circuit of the weak signal detection circuit provides power supply voltages of +3.3V and +5V.

The utility model explores the influence of the magnetic field direction on the GMR sensor, adopts a reasonable magnetic field layout, and improves the sensitivity of the GMR sensor; explores and simulates circuit design, and obtains a weak signal detection circuit suitable for the biological sample detection device based on magnetic beads of the utility model, so that The portability of the circuit is improved. Each module of the circuit is tested separately. After the test is passed, each module is cascaded for an overall test. The test results show that the designed signal detection circuit has an error of less than 0.5% for an output signal of 100mV; using this The device performs magnetic bead detection experiments. Before and after adding magnetic beads, the signal of GMR sensor has obvious changes, which shows that the whole test system can realize the qualitative detection of magnetic beads.

Description of drawings

Fig. 1 is the detection schematic diagram of the biological sample detection device based on magnetic beads;

2 is a schematic diagram of the positional relationship between the Helmholtz coil and the GMR sensor;

Figure 3 is a front view of the positional relationship between the Helmholtz coil and the GMR sensor;

Fig. 4 is a left view of the positional relationship between the Helmholtz coil and the GMR sensor;

Fig. 5 is a circuit diagram of the Wheatstone bridge of the GMR chip.

Detailed ways

In order to enable those skilled in the art to better understand the present invention, the following will clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only a part of the present invention, rather than Full examples.

Example 1

The giant magnetoresistance detection device of this embodiment mainly includes three parts: a bracket 8 , two sets of Helmholtz coils located at both ends of the branch / 8 , a GMR sensor 1 and a weak signal detection circuit. The detection principle is shown in FIG. 1 . The main function of the Helmholtz coil is to generate a magnetic field. On the one hand, it provides a bias magnetic field for the spin valve GMR sensor; on the other hand, it provides an excitation magnetic field for the magnetization of the magnetic beads on the surface of the spin valve GMR sensor. The role of the spin-valve GMR sensor is to detect changes in the magnetic field. When the magnetic bead is magnetized, the additional magnetic field it generates changes the original magnetic field, and the output signal of the spin valve GMR sensor changes. Usually, the output signal of the GMR sensor is a weak signal, and the corresponding circuit needs to be used to extract and amplify the signal, which is the function of the weak signal detection circuit.

A Helmholtz coil is composed of two coaxial, parallel placed circular coils. The radius of the two coils is the same as the number of turns of the winding wire, the center distance d of the two coils is equal to the radius R of the coil, and when the currents of the same magnitude and the same direction are passed through the two coils, the midpoint on the axis of the two coils A uniform magnetic field exists in a certain region.

This embodiment requires two Helmholtz coils, including a first Helmholtz coil 2 and a second Helmholtz coil 3, and the first Helmholtz coil 2 and the second Helmholtz coil 3 are located at the same Axisymmetrically arranged, with the same axis midpoint, the first Helmholtz coil 2 provides an excitation magnetic field, and the second Helmholtz coil 3 provides a bias magnetic field. In this embodiment, the skeletons of the coils are cut from PVC pipes with different radii, and the coil skeletons are made of 502 glue, so that the radius of the coil skeletons of the first Helmholtz coil 2 is 8.5cm, and the radius of the second Helmholtz coil 2 is 8.5cm. The coil bobbin radius of the Holtz coil 3 is 10 cm. The GMR sensor 1 is arranged on the axis midpoint of the first Helmholtz coil 2 and the second Helmholtz coil 3. In order to facilitate the placement of the GMR sensor 1, the GMR sensor 1 is supported on the bracket 8. It is arranged on a beam located on the central axis of the first Helmholtz coil 2 . FIG. 2 , FIG. 3 and FIG. 4 collectively show the positional relationship between the Helmholtz coil and the GMR sensor 1 .

The first Helmholtz coil 2 applies an external excitation magnetic field to cause the magnetic beads to generate an induced magnetic field, and the GMR sensor 1 is used to detect the induced magnetic field generated by the magnetic beads, and the concentration or quantity information of the magnetic beads can be determined according to the magnitude of the induced magnetic field. According to whether the applied excitation magnetic field is a DC magnetic field or an alternating magnetic field, the working mode of the self-GMR sensor 1 is divided into a DC mode and an AC mode. Compared with the DC mode, the biggest defect of the AC mode is the introduction of electromagnetic noise, which can easily overwhelm the effective signal. Therefore, in this embodiment, the first Helmholtz coil 2 applies a DC magnetic field to the GMR sensor 1, so that the GMR The working mode of sensor 1 is DC mode. The direction of the excitation magnetic field can be parallel to the plane of the GMR sensor or perpendicular to the plane of the GMR sensor. Therefore, the DC mode can be further divided into two types: a parallel DC mode and a vertical DC mode. When detecting magnetic beads with a spin valve sensor, usually in addition to the DC excitation magnetic field, another DC bias magnetic field is required. In the parallel DC mode, the direction of the DC excitation magnetic field is along the transverse direction of the sensor, that is, the sensitive direction of the spin valve sensor, and the direction of the DC bias magnetic field is along the longitudinal direction of the GMR sensor 1; in the vertical DC mode, the bias The magnetic field is along the sensitive direction of the GMR sensor 1 , while the direction of the DC excitation magnetic field is perpendicular to the plane of the GMR sensor 1 . One of the biggest differences between the two DC modes is that when there is no magnetic bead on the surface of the GMR sensor 1, the output signal of the GMR sensor 1 is different. For the parallel DC mode, the GMR sensor 1 has a signal output regardless of whether there are magnetic beads on the surface of the GMR sensor 1 . This is because the excitation DC magnetic field is applied in the sensitive direction of the GMR sensor 1 . In the parallel DC mode, the output signal of the GMR sensor 1 is larger when there is no magnetic bead than when there is a magnetic bead. Therefore, by comparing the output signal of the GMR sensor 1 when there are magnetic beads with the output signal of the sensor when there are no magnetic beads, the magnitude of the effective signal generated by the magnetic field induced by the magnetic beads can be obtained. In the vertical DC mode, since the GMR sensor 1 is not sensitive to the magnetic field in the vertical direction, when there is no magnetic bead on the surface of the GMR sensor 1 , the GMR sensor 1 will not output a signal. In the parallel DC mode, the requirement for the accuracy of the direction of the excitation magnetic field is lower than that in the vertical mode. A slight deviation in the direction of the excitation magnetic field will not have a great impact on the output signal of the GMR sensor 1, because the GMR sensor 1 has a great influence on the vertical GMR sensor. The sensor 1 is insensitive to magnetic fields in the plane direction. In the vertical DC mode, any slight deviation of the excitation field produces a magnetic field component in the plane of the sensor. This magnetic field component results in a corresponding output signal from the GMR sensor 1 . If skewed to a certain extent, the value of this signal is likely to reach a level comparable to the effective signal generated by the magnetic bead, or even exceed the amplitude of the effective signal. Therefore, the direction accuracy of the excitation magnetic field is very high in the vertical DC mode. In summary, the first Helmholtz coil 2 in this embodiment is a magnetic field perpendicular to the GMR sensor 1 and the plane where the GMR sensor 1 is located.

The GMR sensor 1 used in this embodiment is in the form of a spin valve structure. The spin valve GMR sensor 1 has two types according to the transmission direction of the internal current, one is that the current direction is perpendicular to the plane of the GMR film; the other is that the current direction is parallel to the plane of the spin valve film. The spin-valve GMR sensor 1 used in this experiment belongs to the second type. The chip used in this embodiment has a half-bridge structure and includes two spin valve structures, namely the first spin valve GMR 4 and the second spin valve GMR 5 . Sensitive axes of the first spin valve GMR 4 and the second spin valve GMR 5 are parallel to each other, but their pinning directions are opposite. When there is no external magnetic field, the resistance values of the first spin valve GMR 4 and the second spin valve GMR 5 are equal. First, paste the GMR chip on the PCB board made in advance according to its pin characteristics. Then use gold wires with a wire diameter of 50 μm to lead out the electrodes, and then weld them to the electrodes on the PCB board so as to lead out the connecting wires from the larger electrodes on the board. Because the size of the chip is small, the size of its lead end is smaller, and the distance between the lead end and the lead end is very close, so this process should be handled carefully to avoid damage to the chip. Finally, two common resistors—the first resistor 6 and the second resistor 7) are used to form a Wheatstone bridge with the first spin valve GMR 4 and the second spin valve GMR 5 of the GMR chip, in order to make the designed Wheatstone bridge The output of the Stone bridge is zero when there is no external magnetic field, and the resistance of the two additional resistors needs to be adjusted to keep the bridge in a balanced state. The circuit diagram of the Wheatstone bridge of the GMR chip is shown in FIG. 5 , where the dotted arrow indicates the magnetic field direction of the bias magnetic field, and the solid arrow indicates the pinning direction of the first spin valve GMR 4 and the second spin valve GMR 5 .

The GMR sensor 1, the first Helmholtz coil 2, and the second Helmholtz coil 3 are respectively connected to a weak signal detection circuit, and the weak signal detection power circuit is a complete device. Power supply The entire weak signal detection circuit includes signal pre-processing circuit, quadrature signal generator circuit, correlator circuit, low-pass filter circuit, analog-to-digital conversion circuit, display circuit, Helmholtz coil drive circuit and power supply circuit.

The process of signal pre-processing is as follows: ①The signal from GMR sensor 1 is very weak, so it needs to be amplified first to adjust the signal amplitude; ②Use a band-pass filter circuit to filter out the high high-frequency and low-frequency noise; ③ Send the amplified and filtered signal to the correlator for correlation calculation with the reference signal. ①Pre-amplification circuit: use the AD8429 chip produced by AD Company to output the signal of the spin valve sensor; ②Band-pass filter circuit: use the AD820 chip produced by AD Company to design a second-order active band-pass filter, with The center frequency of the pass filter is 1KHz, and the passband bandwidth is 200Hz.

Orthogonal signal generator circuit: use two AD9850 chips produced by AD Company to output a sinusoidal signal required by a related detection circuit, and output two sinusoidal signals with phase quadrature and frequency adjustable signals; use FPGA chip to control it, The control word is input in a parallel manner, and the system reference clock is also provided by the FPGA chip. In order to realize the interconnection with FPGA logic, adopt the voltage source +3.3V to supply power to it.

Correlator circuit: the core part of the correlation detection circuit. Its performance determines the signal detection level of the entire system. The correlation demodulation circuit in this embodiment is realized by the high-precision balanced modulator AD630 chip produced by AD Company. Two One AD630 chip inputs the signal to be tested and the reference sinusoidal signal respectively.

Low-pass filter circuit: In order to filter out the power frequency noise in the output signal and set the cut-off frequency below 50Hz, a second-order active low-pass filter circuit was built using the OP213 operational amplifier chip produced by AD Company.

Analog-to-digital conversion circuit: choose the MAX1179 chip produced by MAXIM to realize analog-to-digital conversion, use two MAX1179 chips to perform analog-to-digital conversion on two analog signals at the same time, and use a +5V voltage source for the analog power supply; considering the logical interconnection with the FPGA chip, The digital circuit is powered by a +3.3V voltage source.

Display circuit: The LED digital tube display circuit is used to display the amplitude of the processed sine signal in real time. The system display requires at least five digits, so it is selected; the eight segment selection pins of a digital tube The segments are respectively connected to the eight segment selection pins of the four digital tubes one by one, and the bit selection pins are independent, and the five bit selection pins are respectively connected to the collectors of the five PNP transistors, and the emitters of the triodes Connect to +3.3V DC power supply, the base of the triode is connected in series with a 470-ohm resistor and then cascaded with the FPGA chip, and the common eight-bit segment selection pin of the five-digit digital tube is also connected to the FPGA chip through a 470-ohm resistor.

Helmholtz coil drive circuit: firstly, the amplifying circuit is used to amplify a sinusoidal reference signal to make it have sufficient driving capability; then the amplified sinusoidal voltage signal is converted into a sinusoidal current signal through a voltage-current conversion circuit, so that the sinusoidal current flows Self-made Helmholtz coil, so that an alternating magnetic field with the same frequency as the reference signal can be generated. The amplifying circuit and the voltage-current conversion circuit respectively require an integrated operational amplifier. This embodiment adopts the dual-channel integrated operational amplifier OP213 produced by AD Company to design, which just meets the requirements.

Power supply circuit: In this circuit system, LM2596 switching voltage regulator is used to design the power supply circuit. The required power supply voltage is +3.3V and +5V, so the fixed output LM2596-3.3 and LM2596-5.0 chips are used to complete the design.

Example 2

Magnetic bead detection experiment

In this embodiment, the magnetic bead-based biological sample detection device in Embodiment 1 is used to detect samples with magnetic beads. The first Helmholtz coil 2 provides a magnetizing magnetic field with a frequency of 1KHz and an amplitude of about 1 Gauss for the magnetic beads, and the second Helmholtz coil 3 uses a DC power supply to provide a bias magnetic field of 16 Gauss for the GMR sensor 1 To ensure that the GMR sensor 1 works in the linear region. In the experiment, a liquid gun is used to inject the magnetic bead solution onto the surface of the GMR sensor 1 .

When no magnetic beads are added, the GMR sensor 1 has a base signal V1 output. When magnetic beads are added, the output signal of GMR sensor 1 is V2. Because the direction of the additional magnetic field generated by the magnetic beads on the surface of the GMR sensor 1 is opposite to the direction of the external excitation magnetic field, that is, the additional magnetic field generated by the magnetic beads weakens the effect of the external magnetic field, so V2<V1, so the effective signal generated by the magnetic beads V is equal to |V2-V1|.

The measurement of V1 and V2 adopts the method of taking the average of multiple measurements, and the test results are as follows:

It can be seen from the above experimental results that the value of V1 is about 110mV. This result can be deduced according to the signal size and circuit parameters. For example, the detected signal is a magnetic field signal with a frequency of 1KHz and an amplitude of 1 Gauss. This magnetic field signal enters the GMR The amplitude detected by sensor 1 is about 11mV, and an output of 110mV is obtained after being processed by an amplifier (enlarged by ten times). When magnetic beads are injected into the surface of GMR sensor 1, the direction of the additional magnetic field generated by the magnetic beads is opposite to that of the original magnetic field, which reduces the total magnetic field. As can be seen from the above table, the value of V2 is smaller than the value of V1, and the difference between the two is about 0.54 mV. It can be seen that when magnetic beads are injected into the surface of the spin valve sensor, the output signal of the sensor has obvious changes. The designed magnetic bead detection system can detect the existence of magnetic beads and realize the qualitative detection of magnetic beads.

The above embodiments are only used to illustrate the technical solutions of the present utility model and not to limit it. Although the utility model has been described in detail with reference to the above embodiments, those of ordinary skill in the art should understand that after reading the description of the application, the technical personnel still The specific implementation of the utility model can be modified or equivalently replaced, but none of these modifications or changes departs from the protection scope of the pending claims of the utility model application.

Claims (9)

1. A biological sample detection device based on magnetic beads, characterized in that: comprise support (8), two groups of Helmholtz coils, GMR sensor (1) and weak signal detection circuit positioned at the two ends of support (8), the Each group of Helmholtz coils includes a first Helmholtz coil (2) and a second Helmholtz coil (3), and the first Helmholtz coil (2) and the second Helmholtz coil The Holtz coils (3) are arranged coaxially and symmetrically, and have the same axis midpoint, and the GMR sensor (1) is arranged between the first Helmholtz coil (2) and the second Helmholtz coil ( 3), the GMR sensor (1) is fixed with a biological probe for specific detection, and the weak signal detection circuit is connected to the GMR sensor (1) and the first Helmholtz coil respectively. (2) The second Helmholtz coil (3) is connected and supplies power to the entire device. 2. The biological sample detection device based on magnetic beads as claimed in claim 1, characterized in that: the coil skeleton radius of the first Helmholtz coil (2) is 8.5cm, and the second Helmholtz coil (3) The coil bobbin radius is 10cm. 3. The biological sample detection device based on magnetic beads according to claim 1, characterized in that: the first Helmholtz coil (2) applies a DC magnetic field to the GMR sensor (1). 4. The biological sample detection device based on magnetic beads as claimed in claim 3, characterized in that: the first Helmholtz coil (2) is applied to the GMR sensor (1) for the GMR sensor (1) The magnetic field perpendicular to the plane. 5. The biological sample detection device based on magnetic beads according to claim 1, characterized in that: the GMR sensor (1) is a spin valve GMR sensor. 6. The biological sample detection device based on magnetic beads according to claim 5, characterized in that: the current direction inside the GMR sensor (1) is parallel to the plane where the GMR sensor (1) is located. 7. The biological sample detection device based on magnetic beads as claimed in claim 6, characterized in that: the GMR chip used by the GMR sensor (1) is a half-bridge structure, and the GMR chip includes a first spin valve GMR ( 4) and the second spin valve GMR (5), the sensitive axes of the first spin valve GMR (4) and the second spin valve GMR (5) are parallel to each other and the pinning directions are opposite, and there is no external magnetic field , the resistance values of the two are equal; the GMR chip is connected with the first resistor (6) and the second resistor (7) to form a Wheatstone bridge. 8. The magnetic bead-based biological sample detection device according to any one of claims 1 to 7, wherein the weak signal detection circuit comprises the following parts: a signal preprocessing circuit, an orthogonal signal generator circuit, a correlator circuit, low-pass filter circuit, analog-to-digital conversion circuit, display circuit, Helmholtz coil drive circuit and power supply circuit. 9. The biological sample detection device based on magnetic beads according to claim 8, wherein the power supply circuit provides power supply voltages of +3.3V and +5V.