Cholesterol Biosensor and Its Preparation Method

Abstract

The present invention discloses a cholesterol biosensor, which is characterized in that: a HEMT is used as a transducer, and cholesterol oxidase is fixed on the gate of the transducer, and the gate surface material is gold. The preparation method thereof is also disclosed. The present invention uses a GaN-based high electron mobility transistor (HEMT) structure as a transducer, and fixes cholesterol oxidase on the gold gate of the device to realize the detection of cholesterol. In this way, it not only has the performance of electrochemistry, such as simple testing, simplified structure, real-time reaction, low cost, etc., but also because the intrinsic signal of the HEMT structure is low and it is less affected by other external environments, the sensitivity is greatly improved. It promotes the cholesterol biosensor to improve the accuracy, specificity and stability for cholesterol.

Description

Technical Field

[0001] The present invention relates to a cholesterol biosensor and a preparation method thereof, belonging to the technical field of electrochemical biosensors. Background Art

[0002] Cholesterol is an important lipid substance in the human body, which helps to maintain the permeability and fluidity of cell membranes and is an important component of cell membranes. Either too high or too low cholesterol concentration will cause great harm to humans. When the cholesterol in the human body is too high, it will be one of the important risk factors for atherosclerosis, stroke and cardiovascular diseases. At the same time, if the cholesterol is too low, it is necessary to check whether there is a serious illness or malnutrition, and studies have shown that too low cholesterol will increase psychological diseases such as depression and autism. Therefore, cholesterol must be measured and maintained within a standard range. And high cholesterol is an important factor affecting sudden death and cardiovascular diseases. Therefore, developing a device or method for detecting cholesterol content with high sensitivity has important significance in the medical field.

[0003] So far, many cholesterol detection methods have been reported, such as gas chromatography, liquid chromatography, gas-liquid chromatography-mass spectrometry, temperature measurement method, molecular luminescence method, colorimetry, electrochemical method, etc. These methods can detect cholesterol, but there are still many disadvantages, such as time-consuming, complex equipment, expensive equipment, sample pretreatment required, complex operation, need for experienced operators, inability to respond in time, and more importantly, most of the previous methods have low sensitivity. Although electrochemical analysis methods can overcome these disadvantages, the known electrochemistry methods currently directly use high-performance materials, such as graphene materials. Cholesterol oxidase is directly immobilized on the graphene material, and the high-speed electron mobility of graphene itself is used to detect cholesterol. However, in fact, due to the relatively large intrinsic signal of the graphene material or other high-performance materials themselves in this electrochemical method, and the conduction channels are exposed to the outside, they are greatly affected by the external environment, which further exacerbates the excessive intrinsic signal. And the lower the intrinsic signal, the greater the improvement in sensitivity. The present invention utilizes the unique two-dimensional electron gas property of the GaN-based high electron mobility transistor (HEMT) structure. So far, there has been no report on detecting cholesterol solution based on the GaN-based high electron mobility transistor (HEMT). Summary of the Invention

[0004] The purpose of the present invention is to provide a cholesterol biosensor with high sensitivity.

[0005] The purpose of the present invention is achieved by the following technical solutions:

[0006] A cholesterol biosensor uses a HEMT as a transducer, and cholesterol oxidase is immobilized on the gate of the transducer, and the gate surface material is gold.

[0007] Preferably, the cholesterol oxidase is immobilized on the gate of the HEMT by covalent bonding.

[0008] Preferably, the structure of the HEMT from bottom to top sequentially includes: a substrate layer, a GaN nucleation layer, a carbon-doped GaN buffer layer, a GaN channel layer, an AlN interlayer, an AlGaN / GaN barrier layer or an InAlN / GaN barrier layer, a GaN cap layer, further including a source electrode in contact with the GaN channel layer, and a drain electrode and a gate electrode disposed on the GaN cap layer, and a protective layer covering the source electrode and the drain electrode.

[0009] Preferably, there are two gate electrodes, and the two gate electrodes share the drain electrode, and the source electrode surrounds the induction region formed by the gate electrodes.

[0010] The present invention also discloses a preparation method of the above cholesterol biosensor, which is characterized in that the steps include:

[0011] (1) Washing the gate electrode, drying, and infiltrating the washed gate electrode with 1,6 - hexanedithiol to obtain a gate electrode containing sulfur bonds;

[0012] (2) Dropping a gold nanoparticle solution on the gate electrode to obtain a gate electrode with gold nanoparticles distributed on the surface;

[0013] (3) Treating the gate electrode with a surface containing gold nanoparticles with an 11 - mercaptoundecanoic acid ethanol solution to generate Au - S bonds on the surface of the gold nanoparticles;

[0014] (4) Dropping a cholesterol oxidase solution on the surface of the gate electrode treated with the 11 - mercaptoundecanoic acid ethanol solution to form a cholesterol biosensitive film, thereby obtaining a cholesterol biosensor.

[0015] The present invention uses a GaN - based high - electron - mobility transistor (HEMT) structure as a transducer, immobilizes cholesterol oxidase on the gold gate of the device, and realizes the detection of cholesterol. In this way, it not only has the advantages of electrochemical performance, such as simple testing, simplified structure, real - time reaction, low cost, etc., but also, due to the low intrinsic signal of the HEMT structure and little influence from other external environments, the sensitivity is greatly improved. This promotes the cholesterol biosensor to improve the accuracy, specificity, and stability for cholesterol.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] (1) The total area of the cholesterol biosensor in the present invention is small, but the area of the induction region is greatly increased because a double - gate structure is adopted. The small total area is conducive to better integration and is less affected by other external factors. The larger area of the induction region can improve the detection degree of cholesterol.

[0018] (2) The structure of the cholesterol biosensor in the present invention is a GaN HEMT structure. There is a two-dimensional electron gas with high mobility in the channel layer, which has good electrical conductivity and greatly shortens the reaction time. At the same time, due to the existence of the protective layer, the interference signal of the cholesterol biosensor in the present invention is small, and the sensitivity is also greatly improved.

[0019] (3) The cholesterol oxidase used in the cholesterol biosensor of the present invention specifically binds to cholesterol, has good selectivity and specificity for cholesterol, and can avoid interference from other substances in the blood. Description of the Drawings

[0020] Figure 1 It is a cross-sectional view of the structure of the cholesterol biosensor of the present invention.

[0021] Figure 2 It is a top view of the structure of the cholesterol biosensor of the present invention.

[0022] Figure 3 It is a graph showing the relationship between the sensitivity and the gate length for single-gate and double-gate. Detailed Embodiments

[0023] The following is a clear and complete description of the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0024] Embodiment 1

[0025] As Figure 1 is a schematic cross-sectional view of an embodiment of the high-sensitivity cholesterol sensor of the present invention. As Figure 2 is a schematic top view of an embodiment of the high-sensitivity cholesterol sensor of the present invention. As Figure 1 shown, the device is a double-gate structure. Its structure is generally from bottom to top: substrate layer, nucleation layer, buffer layer, channel layer, interlayer, barrier layer, cap layer, gate (source, drain), protective layer, with corresponding cholesterol biosensitive membrane and related processing.

[0026] The specific steps are as follows

[0027] In this example, the substrate is a sapphire substrate. The nucleation layer is made of GaN material with a growth thickness of 25 nm. The buffer layer is carbon-doped GaN, and the growth thickness can be between 2 - 3 μm. The channel layer is made of GaN material. The interlayer is made of AlN material with a growth thickness of 2 nm. The barrier layer is AlGaN / GaN with a growth thickness of 25 nm, and the content of the Al component is 0.33. The barrier layer serves as the dielectric between the Schottky gate and the two-dimensional electron gas. The cap layer is made of GaN material with a thickness of 3 nm.

[0028] For the source and drain of this embodiment, the materials used are titanium, aluminum, nickel, and gold, with thicknesses of Ti / Al / Ni / Au (30 nm / 150 nm / 50 nm / 100 nm) respectively. And they are thermally annealed in a nitrogen environment at 850 °C to obtain an ohmic contact with a very low resistivity.

[0029] For the gate of this embodiment, the materials used are titanium and gold, with thicknesses of Ti / Au (500 nm / 500 nm) respectively.

[0030] The protective layer of this embodiment is silicon dioxide, which protects the device from other external environments. Its thickness is 250 nm or more to prevent breakdown.

[0031] The gate of this embodiment is a surface gold gate with a thickness of 10 nm, a gate length of 25 μm, and a gate width of 100 μm. The total area of the induction region is 5000 μm 2 .

[0032] The steps of the biological cholesterol-sensitive film in this embodiment are as follows:

[0033] (1) Treat (wash) the gold gate with 70% ethanol and deionized water respectively, and finally dry it in air. Immerse the washed gold gate in 1,6 - hexanedithiol for 24 hours, and then rinse it with deionized water to obtain a gold gate containing sulfur bonds.

[0034] (2) Drop the gold nanoparticle solution on the gold gate for 6 hours to obtain a gold gate with gold nanoparticles distributed on its surface.

[0035] (3) Treat the gold gate with gold nanoparticles on its surface with an 11 - mercaptoundecanoic acid ethanol solution with a concentration of 10 mg / ml for 6 hours to form Au - S bonds on the surface of the gold nanoparticles, which serves as the basis for covalently immobilizing cholesterol oxidase.

[0036] (4) Drop the cholesterol oxidase solution on the gold gate with gold nanoparticles on its surface that has been treated with 11 - mercaptoundecanoic acid ethanol solution for 12 hours to obtain the final cholesterol biosensitive film for cholesterol detection.

[0037] Devices with other structures all being the same as those in Embodiment 1, except that only one gate is provided, are used as comparative examples. The detection characteristics of the devices in Embodiment 1 and the comparative examples are simulated and calculated, as Figure 3 shown. It can be seen from the data graph that, with the same source-drain spacing, the double-gate structure has a great advantage over the single-gate structure in terms of sensitivity. Adopting the double-gate structure can improve the sensitivity of HEMT devices in the field of biosensors.

Claims

1. A cholesterol biosensor, characterized in that: Using HEMT as a transducer, cholesterol oxidase is immobilized on the gate of the transducer, and the gate surface material is gold.

2. The cholesterol biosensor according to claim 1, wherein: The cholesterol oxidase reacts with the Au-S bond on the surface of the HEMT gate and is immobilized on the gate of the HEMT by covalent bonding.

3. The cholesterol biosensor according to claim 2, characterized in that: The structure of the HEMT includes, from bottom to top in sequence: a substrate layer, a GaN nucleation layer, a carbon-doped GaN buffer layer, a GaN channel layer, an AlN interlayer, an AlGaN / GaN barrier layer or an InAlN / GaN barrier layer, a GaN cap layer, and further includes a source electrode in contact with the GaN channel layer, and a drain electrode and a gate electrode provided on the GaN cap layer. A protective layer covers the source electrode and the drain electrode.

4. The cholesterol biosensor according to claim 3, wherein: There are two gate electrodes. The two gate electrodes share a drain electrode, and the source electrode semi-surrounds the induction region formed by the gate electrodes.

5. The preparation method of the cholesterol biosensor according to any one of claims 1-4, characterized in that The steps include: (1) Wash the gate electrodes, dry them, and soak the washed gate electrodes with 1,6-hexanedithiol to obtain gate electrodes containing sulfur bonds. (2) Drop the gold nanoparticle solution on the gate electrodes to obtain gate electrodes with gold nanoparticles distributed on the surface. (3) Treat the gate electrodes with a 11-mercaptoundecanoic acid ethanol solution to generate Au-S bonds on the surface of the gold nanoparticles. (4) Drop the cholesterol oxidase solution on the surface of the gate electrodes treated with the 11-mercaptoundecanoic acid ethanol solution to form a cholesterol biosensitive film, thereby obtaining a cholesterol biosensor.

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