A soil nitrogen photonic chip sensor and a detection method thereof

Abstract

The present application relates to the technical field of molecular detection, and in particular to a soil nitrogen photonic chip sensor and a detection method thereof.The present application comprises a laser, a photonic chip and two detectors;the photonic chip is provided with two optical interference structures, and the light of the laser enters the photonic chip and is divided into two paths to enter the two optical interference structures;the light is divided into two parallel light rays in the optical interference structure, one light ray passes through an ion selection area;the light ray passing through the ion selection area in the optical interference structure interferes with the other light ray;the ion selection areas in the two optical interference structures are respectively used for screening nitrate nitrogen ions and ammonium nitrogen ions, and the corresponding two detectors respectively analyze the nitrate nitrogen ion concentration and the ammonium nitrogen ion concentration in the to-be-detected solution based on the obtained optical spectrum.The present application greatly improves the detection accuracy, and overcomes the defects of long detection time, complex operation, high cost and difficulty in realizing on-site detection of nitrate nitrogen and ammonium nitrogen in the prior art.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of molecular detection, and particularly relates to a soil nitrogen photonic chip sensor and a detection method thereof. BACKGROUND

[0002] Nitrate and ammonium are the most easily absorbed inorganic nitrogen forms by plants. They are the limiting factors for crop yield, and thus are considered as the main components of nitrogen fertilizer. Nitrate is a stable mobile anion, which is easily transported in soil, while ammonium is a positively charged ion, which is easily adsorbed. Excessive use of nitrogen fertilizer will cause groundwater pollution. Therefore, monitoring nitrogen (nitrate and ammonium) in soil is the key to prevent water resource pollution. Traditional soil nitrogen chemical analysis method is complex, long in period, poor in real-time performance, and high in cost, and is difficult to be applied on a large scale. At present, there is an urgent need for in-situ, rapid and robust sensing technology for soil nitrogen.

[0003] At present, compact sensing methods related to soil nitrogen detection can be divided into two categories: potential method and optical method. For potential measurement methods such as ion-selective electrode and ion-selective field effect transistor, the inherent potential drift of the reference electrode cannot be avoided, and the need for frequent calibration may hinder its practical application, especially in soil sensing. In contrast, optical sensing methods for detecting nitrogen have minimal electrical interference and can eliminate baseline changes. Spectrophotometric methods for nitrate / nitrite determination have been well studied, including ultraviolet-visible spectroscopy, fluorescence and chemiluminescence. However, these techniques require complex sample pretreatment, such as determination schemes involving redox reactions, which is not conducive to on-site, in-situ nitrogen determination. In addition, Fourier transform infrared spectroscopy and Raman spectroscopy are also used to detect nitrogen. Although these methods can provide excellent sensitivity, the need for complex and expensive instruments reduces interest in these techniques outside the laboratory. SUMMARY

[0004] In order to overcome the defects of long detection period, complex operation and high cost of nitrogen detection in the prior art, and to realize on-site detection, the present application provides a soil nitrogen photonic chip sensor, which is ion-selective enhanced, ensures high sensitivity and real-time detection, and greatly improves detection accuracy.

[0005] The soil nitrogen photonic chip sensor provided by the present application comprises a laser, a photonic chip and two detectors; the photonic chip is provided with two optical interference structures, the light of the laser enters the photonic chip and is divided into two paths to enter the two optical interference structures; the two detectors correspond to the two optical interference structures; the light is divided into two parallel light rays in the optical interference structure, one light ray is coupled into the detector after passing through the ion selection area, and the other light ray is directly coupled into the detector;

[0006] The light rays passing through the ion selection region in the optical interference structure interfere with another light ray, and the detector detects the concentration of the selected ion in the ion selection region through spectral analysis; the ion selection regions in the two optical interference structures are used for screening nitrate nitrogen ions and ammonium nitrogen ions respectively, and the two corresponding detectors respectively analyze the nitrate nitrogen ion concentration and the ammonium nitrogen ion concentration in the solution to be measured based on the obtained spectrum.

[0007] Preferably, the optical interference structure comprises an MZI and a front-end coupling grating and a rear-end coupling grating arranged at two ends of the MZI; the light of the laser enters the MZI through the front-end coupling grating and is divided into two paths, and the two paths of light enter the rear-end coupling grating through the sensing arm and the reference arm of the MZI respectively, and then enter the corresponding detector through the rear-end coupling grating; the sensing arm passes through the ion selection region.

[0008] Preferably, it also comprises nitrate nitrogen ion selection material and ammonium nitrogen ion selection material, which are arranged on the sensing arms of the first optical interference structure and the second optical interference structure respectively and form ion selection regions in external flow;

[0009] The nitrate nitrogen ion selection material is composed of dodecyltrimethylammonium nitrate dispersed in a superplastic PVC polymer matrix, and the concentration of the nitrate ion carrier is 6.1%; the ammonium nitrogen ion selection material is prepared from a calixarene material.

[0010] Preferably, the photonic chip further comprises a substrate and a shell; the shell cooperates with the substrate to package the optical interference structure, and the shell is provided with a detection window for adding the solution to be measured; the nitrate nitrogen ions and the ammonium nitrogen ions in the solution to be measured are respectively attached to the corresponding sensing arms through the nitrate nitrogen ion selection material and the ammonium nitrogen ion selection material.

[0011] Preferably, the nitrate nitrogen ion selection material and the ammonium nitrogen ion selection material are respectively coated on the corresponding sensing arms.

[0012] Preferably, the laser adopts a distributed tunable laser.

[0013] Preferably, the detector adopts a silicon detector.

[0014] The application provides a manufacturing method of the soil nitrogen photonic chip sensor, which comprises the following steps:

[0015] After cleaning the substrate, spin-coating photoresist on the substrate, using electron beam exposure to irradiate the waveguide region, etching a strip waveguide after developing and fixing, and forming two MZIs after removing the photoresist;

[0016] The nitrate nitrogen ion selection material and the ammonium nitrogen ion selection material are arranged on the sensing arms of the two MZIs respectively.

[0017] Selecting grating area on both ends of each MZI on the substrate and spin-coating photoresist, irradiating grating area by electron beam exposure, etching out strip waveguide after developing and fixing, and forming front-end coupling grating and rear-end coupling grating at both ends of MZI after removing photoresist;

[0018] The MZI structure is packaged in the shell, and the shell is provided with a detection window.

[0019] The soil nitrogen detection method provided by the application first puts deionized water into the detection window, so that the laser is in a scanning state, and two detectors respectively obtain the resonance wavelength of the nitrate nitrogen sensing arm and the resonance wavelength of the ammonium nitrogen sensing arm The nitrate nitrogen sensing arm is a sensing arm of a material corresponding to nitrate nitrogen ions, and the ammonium nitrogen sensing arm is a sensing arm of a material corresponding to ammonium nitrogen ions.

[0020] The to-be-measured solution is put into the detection window, so that the laser is in a scanning state, and two detectors respectively obtain the resonance wavelength of the nitrate nitrogen sensing arm and the resonance wavelength of the ammonium nitrogen sensing arm .

[0021] The nitrate nitrogen ion concentration is calculated through the resonance shift amount of the nitrate nitrogen ion The ammonium nitrogen ion concentration is calculated through the resonance shift amount of the ammonium nitrogen ion .

[0022] Preferably, the calculation formula of the nitrate nitrogen ion concentration and the ammonium nitrogen ion concentration is:

[0023] .

[0024] .

[0025] Wherein, a and b are nitrate nitrogen parameters, and c and d are ammonium nitrogen parameters; a, b, c and d are obtained by fitting a known data set.

[0026] The application has the following advantages:

[0027] (1) The soil nitrogen photonic chip sensor provided by the application adopts an optical interference structure, combines spectrum analysis technology, detects ion concentration through phase difference changes of two light signals, and has a significantly higher sensitivity than a traditional electrochemical method. Direct coupling design of a laser and a detector can realize rapid and real-time monitoring of soil nitrogen. In the application, two optical interference structures are arranged on the photonic chip, and the two optical interference structures are provided with independent detectors. The concentration of nitrate nitrogen ions and the concentration of ammonium nitrogen ions are simultaneously detected through a single photonic chip, so that the concentration of common nitrogen ions in soil is quickly obtained, the interference of other ions (such as K, Na, Cl - ) in soil is effectively avoided, and the detection accuracy is greatly improved.

[0028] (2) In the application, the MZI is integrated into the photonic chip, combined with grating coupling technology, and the volume of the sensor is greatly reduced, which is convenient for integration and portable application, and a compact photonic chip structure is realized. Different ion selection materials are arranged separately, which can distinguish and quantify the content of different forms of nitrogen in soil, and meet the needs of complex soil environment.

[0029] (3) In the application, the substrate and the shell encapsulate and protect the core components (MZI and grating) of the photonic chip, prevent soil particles or water from invading, prolong the service life of the sensor, and ensure the long-term stability of the sensor. The detection window is directly exposed to the measured solution, and the position of the ion selection material (window or sensing arm) is optimized to ensure efficient penetration and adhesion of ions to the sensing surface, thereby shortening the response time.

[0030] (4) The application adopts electron beam exposure and etching process to prepare waveguides and gratings, which is compatible with semiconductor batch production and is conducive to reducing manufacturing cost. The ion selection material is directly integrated into the sensing arm or the window, which is conducive to avoiding complex packaging steps and improving the yield.

[0031] (5) The distributed tunable laser supports wavelength scanning, adapts to the absorption spectrum requirements of different ion selection materials, and expands the detection range. The silicon detector has fast response and low cost, and has high compatibility with the photonic chip material (such as SOI), and the system integration degree is optimal.

[0032] (6) The soil nitrogen detection method provided by the application directly drops the measured solution into the detection window without complex pretreatment, simplifies the operation steps, and is conducive to realizing a rapid and convenient on-site detection process. Spectrum analysis combined with chemical formula conversion directly outputs the concentration of nitrogen, reduces the dependence on professional instruments, and is suitable for on-site use.

[0033] (7) The soil nitrogen detection method and sensor provided by the application are suitable for various environments such as farmland and greenhouse, meet the demand of precise agricultural nitrogen management, have multi-scene applicability, are friendly to the environment, do not need chemical reagents, avoid secondary pollution, combine photon chips and semiconductor technology, have high performance and low cost, and are beneficial to promote large-scale application.

[0034] (8) The application realizes a significant breakthrough in the sensitivity, selectivity, integration and practicability of the soil nitrogen photon chip sensor, and provides an innovative solution for soil nitrogen monitoring. BRIEF DESCRIPTION OF DRAWINGS

[0035] Figure 1 It is a three-dimensional structure diagram of the soil nitrogen photon chip sensor.

[0036] Figure 2 It is a MZI process flow diagram.

[0037] Figure 3 It is a MZI display.

[0038] Figure 4 It is a MZI and coupling grating connection diagram.

[0039] Figure 5 It is a coupling grating structure.

[0040] Figure 6 It is a coupling grating detail display.

[0041] Figure 7 It is a soil nitrogen detection method flow diagram.

[0042] Illustration: 1-1, first front-end coupling grating; 1-2, second front-end coupling grating; 2-1, first rear-end coupling grating; 2-2, second rear-end coupling grating; 3-1, first sensing arm; 3-2, second sensing arm; 4-1, first reference arm; 4-2, second reference arm; 5, shell; 50, detection window; 6, substrate; 7-1, nitrate ion selective material; 7-2, ammonium ion selective material; 8-1, first detector; 8-2, second detector; 9-1, first optical fiber; 9-2 second optical fiber; 9-3, third optical fiber; 10, laser. DETAILED DESCRIPTION

[0043] With reference to the accompanying drawings: clearly and fully describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application. With reference to the accompanying drawings: clearly and fully describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0044] As shown in Figure 1 , Figure 4 , the present embodiment proposes a soil nitrogen photonic chip sensor, which comprises a laser 10, a photonic chip, a first detector 8-1 and a second detector 8-2. The photonic chip comprises two optical interference structures, which are the same in structure and comprise a front-end coupling grating, a rear-end coupling grating and a Mach-Zehnder interferometer (MZI). The first detector 8-1 and the second detector 8-2 correspond to the two optical interference structures respectively.

[0045] The front-end coupling grating and the rear-end coupling grating of one of the optical interference structures are respectively denoted as a first front-end coupling grating 1-1 and a first rear-end coupling grating 2-1, and the front-end coupling grating and the rear-end coupling grating of the other optical interference structure are respectively denoted as a second front-end coupling grating 1-2 and a second rear-end coupling grating 2-2.

[0046] The laser 10 is connected to the first front-end coupling grating 1-1 and the second front-end coupling grating 1-2 through a first optical fiber 9-1, the first rear-end coupling grating 2-1 is connected to the first detector 8-1 through a second optical fiber 9-2, and the second rear-end coupling grating 2-2 is connected to the second detector 8-2 through a third optical fiber 9-3.

[0047] The laser 10 serves as a light source and can adopt a distributed tunable laser with a center wavelength of 765 nm and a tunable range of 3 nm. The detector can be a silicon detector.

[0048] During operation, the light from laser 10 is split into two paths corresponding to the two optical interference structures via the first optical fiber 9-1. One path passes through the first front-end coupling grating 1-1 and enters the MZI of the first optical interference structure, where it is split into two parallel beams. These beams then pass through the first rear-end coupling grating 2-1 and enter the first detector 8-1. The other path of light output from the first optical fiber 9-1 passes through the second front-end coupling grating 1-2 and enters the MZI of the second optical interference structure, where it is split into two parallel beams. These beams then pass through the second rear-end coupling grating 2-2 and enter the second detector 8-2.

[0049] The first optical fiber 9-1 is a Y-type optical fiber, which facilitates splitting the output light from the laser 10 into two optical interference structures.

[0050] Reference Figure 2 , Figure 3 The first optical interference structure MZI includes a first incident arm, a first sensing arm 3-1, a first reference arm 4-1, and a first exit arm; the first incident arm, the first sensing arm 3-1, the first reference arm 4-1, and the first exit arm are disposed between the first front-end coupling grating 1-1 and the first rear-end coupling grating 2-1. The second optical interference structure MZI includes a second incident arm, a second sensing arm 3-2, a second reference arm 4-2, and a second exit arm; the second incident arm, the second sensing arm 3-2, the second reference arm 4-2, and the second exit arm are disposed between the second front-end coupling grating 1-2 and the second rear-end coupling grating 2-2.

[0051] In the first optical interference structure, the first sensing arm 3-1 and the first reference arm 4-1 are arranged vertically. The first incident arm is located to the left of the first sensing arm 3-1 and the first reference arm 4-1 and connected between them, forming a Y-shaped structure. The first exiting arm is located to the right of the first sensing arm 3-1 and the first reference arm 4-1 and connected between them, forming a Y-shaped structure. The first front-end coupling grating 1-1 is located to the left of the first incident arm, and the first rear-end coupling grating 2-1 is located to the right of the first exiting arm.

[0052] In the second optical interference structure, the second sensing arm 3-2 and the second reference arm 4-2 are arranged vertically. The second incident arm is located to the left of the second sensing arm 3-2 and the second reference arm 4-2 and connected between them, forming a Y-shaped structure. The second exiting arm is located to the right of the second sensing arm 3-2 and the second reference arm 4-2 and connected between them, forming a Y-shaped structure. The second front-end coupling grating 1-2 is located to the left of the second incident arm, and the second rear-end coupling grating 2-2 is located to the right of the second exiting arm.

[0053] That is, in the optical interference structure, the incident arm and the exit arm are both Y-shaped structures, the three ends of the incident arm are respectively connected to the corresponding front-end coupling grating, the sensing arm and the reference arm, and the three ends of the exit arm are respectively connected to the corresponding back-end coupling grating, the sensing arm and the reference arm.

[0054] The light of the laser is split into two by the first optical fiber 9-1, one of which is coupled to the first incident arm through the first front-end coupling grating 1-1, then split into two paths through the first sensing arm 3-1 and the first reference arm 4-1 respectively, and then enters the first back-end coupling grating 2-1 through the first exit arm. The first back-end coupling grating 2-1 guides the coupled light into the corresponding first detector 8-1 for spectral analysis. The first sensing arm 3-1 is provided with nitrate nitrogen ion selective material 7-1.

[0055] The other part of the light split by the first optical fiber 9-1 is coupled to the second incident arm through the second front-end coupling grating 1-2, then split into two paths through the second sensing arm 3-2 and the second reference arm 4-2 respectively, and then enters the second back-end coupling grating 2-2 through the second exit arm. The second back-end coupling grating 2-2 guides the coupled light into the corresponding second detector 8-2 for spectral analysis. The second sensing arm 3-2 is provided with ammonium nitrogen ion selective material 7-2.

[0056] Specifically, the photonic chip further comprises a substrate 6 and a shell 5; the shell 5 cooperates with the substrate 6 to package the optical interference structure, i.e. the first front-end coupling grating 1-1 and the second front-end coupling grating 1-2, the first back-end coupling grating 2-1 and the second back-end coupling grating 2-2, and the two MZIs, and the shell 5 is provided with a detection window 50. When the to-be-measured solution is dropped on the detection window 50, nitrate nitrogen is attached to the first sensing arm 3-1 through the nitrate nitrogen ion selective material 7-1, and ammonium nitrogen is attached to the second sensing arm 3-2 through the ammonium nitrogen ion selective material 7-2.

[0057] It is worth noting that the first sensing arm 3-1 coated with nitrate nitrogen ion selective material 7-1, the second sensing arm 3-2 coated with ammonium nitrogen ion selective material 7-2, the first reference arm 4-1 and the second reference arm 4-2 are all exposed in the detection window 50. After the to-be-measured solution is dropped, the first reference arm 4-1 and the second reference arm 4-2 are directly immersed in the to-be-measured solution; while the first sensing arm 3-1 and the second sensing arm 3-2 are filtered by the corresponding ion selective material.

[0058] In this way, the to-be-measured solution contacts the first sensing arm 3-1, the second sensing arm 3-2, the first reference arm 4-1 and the second reference arm 4-2 through the detection window 50, the first sensing arm 3-1 realizes the ion selection function through the nitrate nitrogen ion selective material 7-1, and the second sensing arm 3-2 realizes the ion selection function through the ammonium nitrogen ion selective material 7-2.

[0059] In this way, the light passing through the first sensing arm 3-1 is affected by the nitrate nitrogen ions, while the light passing through the first reference arm 4-1 is not affected; the light passing through the light interference structure where the nitrate nitrogen ion selective material 7-1 is located is analyzed by the first detector 8-1, and the ion concentration of the nitrate nitrogen can be obtained; the light passing through the second sensing arm 3-2 is affected by the ammonium nitrogen ions, while the light passing through the second reference arm 4-2 is not affected; the light passing through the light interference structure where the ammonium nitrogen ion selective material 7-2 is located is analyzed by the second detector 8-2, and the ion concentration of the ammonium nitrogen can be obtained. In this way, the high correlation indicators of the nitrogen content in the soil, the ion concentration of the nitrate nitrogen and the ion concentration of the ammonium nitrogen, are obtained.

[0060] The preparation process of the photonic chip is divided into two stages: an MZI preparation stage and a coupling grating preparation stage.

[0061] The MZI preparation process is shown in FIG. 2 and is as follows: (1) the substrate 6, i.e., the silicon substrate, is cleaned; (2) SU8 photoresist with a thickness of 220 nm is spin-coated on the substrate 6; (3) the waveguide region is exposed to electron beam exposure, and after development and fixation, a 220 nm strip waveguide is etched by inductively coupled plasma etching technology, and the photoresist is removed, forming two MZIs; (4) the ion selective material is used to functionalize the sensing arm of the MZI. Here, double functionalization is used, i.e., the first sensing arm 3-1 and the second sensing arm 3-2 are respectively modified with nitrate nitrogen and ammonium nitrogen ion selective materials. Figure 2 The coupling grating preparation process includes: (1) SU8 photoresist with a thickness of 220 nm is spin-coated on the grating region (i.e., the two ends of the MZI) of the substrate 6; (2) the grating region is exposed to electron beam exposure, and after development and fixation, a 70 nm square wave waveguide is etched by inductively coupled plasma etching technology, forming four coupling gratings.

[0062] Figure 5 The coupling gratings are shown in FIG. 3, i.e., the first front-end coupling grating 1-1, the second front-end coupling grating 1-2, the first back-end coupling grating 2-1, and the second back-end coupling grating 2-2.

[0063] In a specific embodiment, the waveguide thickness H of the first sensing arm 3-1, the second sensing arm 3-2, the first reference arm 4-1, and the second reference arm 4-2 is set to 0.22 um, the width W is set to 0.5 um, the reference arm length L0 and the sensing arm length L1 are both 1200 um. The radius r of the Y branch of the incident arm and the exit arm is set to 30 um.

[0064] ​The covering length of the nitrate ion selective material 7-1 on the first sensing arm 3-1 and the covering length of the ammonium ion selective material 7-2 on the second sensing arm 3-2 are both L2 = 200 um. The external environment can only interact with the sensing arms through the ion selective materials. The first sensing arm 3-1 is covered with the nitrate ion selective material 7-1, allowing the nitrate nitrogen in the measured environment to pass through and adhere to the first sensing arm 3-1; the second sensing arm 3-2 is covered with the ammonium ion selective material 7-2, allowing the ammonium nitrogen in the measured environment to pass through and adhere to the second sensing arm 3-2.

[0065] The MZI and the integrated coupling grating structure are as shown in Figure 4 The coupling grating structure is as shown in Figure 5 , Figure 6 The grating etching depth is 0.07 um, the width W g is 16 um, the period number n is 32, and the period is 0.615 um.

[0066] In this embodiment, the nitrate ion selective membrane (nitrate nitrogen ion selective material) is composed of tridodecylmethylammonium nitrate (TDDMA) dispersed in a super plasticized PVC polymer matrix. In order to improve the sensitivity of the sensor, the concentration of the nitrate ion carrier is 6.1%, which is 4 times higher than that of the commercial ion selective material carrier (1.5%). The ammonium ion selective membrane (ammonium nitrogen ion selective material) is prepared from a calixarene material. The thickness of the two ion selective materials is 100 um.

[0067] Referring to Figure 7 , the soil nitrogen detection method provided by the embodiment is used for detecting nitrate nitrogen and ammonium nitrogen in a to-be-measured solution. The to-be-measured solution can be a soil solution or soil pore water. The steps are specifically as follows:

[0068] First, deionized water is placed in the detection window 50; the light output by the laser 10 is split by the Y-shaped first optical fiber 9-1, and enters the first front-end coupling grating 1-1 and the second front-end coupling grating 1-2 on the photonic chip respectively; the light output by the first front-end coupling grating 1-1 is divided into two paths through the first incident arm, and enters the first rear-end coupling grating 2-1 along the first sensing arm 3-1 and the first reference arm 4-1 respectively, and then is received by the first detector 8-1 and subjected to spectral analysis; the light output by the second front-end coupling grating 1-2 is divided into two paths through the second incident arm, and enters the second rear-end coupling grating 2-2 along the second sensing arm 3-2 and the second reference arm 4-2 respectively, and then is received by the second detector 8-2 and subjected to spectral analysis; the laser 10 is in a scanning state, and the first detector 8-1 and the second detector 8-2 obtain the resonance wavelength of the nitrate nitrogen sensing arm and the resonance wavelength The nitrate nitrogen sensing arm is a first sensing arm 3-1 corresponding to a nitrate ion selective material, and the ammonium nitrogen sensing arm is a second sensing arm 3-2 corresponding to an ammonium ion selective material;

[0069] The to-be-measured solution is placed in the detection window 50; the first sensing arm 3-1 and the second sensing arm 3-2 respectively select nitrate ions and ammonium ions into the ion selective material under the action of the ion selective material; the laser is in a scanning state, and the first detector 8-1 and the second detector 8-2 respectively obtain the resonance wavelength of the nitrate nitrogen sensing arm and the resonance wavelength of the ammonium nitrogen sensing arm through spectral analysis ;

[0070] Due to the presence of nitrate ions and ammonium ions, the resonance wavelength of the to-be-measured solution has a certain shift from the previously obtained resonance wavelength of the deionized water, and the resonance shift amount is related to the ion concentration, and then the concentrations of nitrate ions and ammonium ions are obtained.

[0071] The resonance shift amounts of nitrate ions and ammonium ions are respectively:

[0072] ;

[0073] ;

[0074] wherein, and are the resonance shift amounts of nitrate ions and ammonium ions respectively.

[0075] The relationship formulas between the resonance shift amounts of nitrate ions and ammonium ions and the concentrations are respectively:

[0076] ;

[0077] ;

[0078] wherein , are the concentrations of nitrate ions and ammonium ions respectively, and a, b are nitrate parameters, and c, d are ammonium parameters. a, b, c, d can be obtained by measuring a series of known soil solutions of nitrate ions and ammonium ions. After a, b, c, d are determined, the resonance shift amount is measured to obtain the concentrations of nitrate ions and ammonium ions.

[0079] ​Of course, the present application is not limited to the details of the above-described exemplary embodiments but comprises the same or similar structures which can be realized in other specific forms without departing from the spirit or essential characteristics of the present application. Therefore, the embodiments should be considered in all respects as illustrative and not restrictive, the scope of the present application being defined by the appended claims rather than the above description, and it is intended that all changes which come within the meaning and range of equivalency of the claims are embraced therein. Any reference signs in the claims should not be construed as limiting the claims to the figures in which the reference signs are used.

[0080] Furthermore, it should be understood that although the description is made on the embodiments, not every embodiment contains only one independent technical solution, and the description of the specification is only for the sake of clarity, and the skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be combined appropriately to form other embodiments which can be understood by the skilled in the art.

[0081] The technologies, shapes, and structural parts not described in detail in the present application are well-known technologies.

Claims

1. A soil nitrogen photonic chip sensor, characterized in that, The application relates to a photonic chip for detecting nitrate nitrogen ions and ammonium nitrogen ions in a solution. The photonic chip comprises a laser, a photonic chip and two detectors; the photonic chip is provided with two optical interference structures, light from the laser enters the photonic chip and is divided into two paths to enter the two optical interference structures; the two detectors correspond to the two optical interference structures; the light is divided into two parallel light rays in the optical interference structure, one light ray is coupled into the detector after passing through an ion selection area, and the other light ray is directly coupled into the detector; the light ray passing through the ion selection area in the optical interference structure interferes with the other light ray, and the detector detects the concentration of the selected ions in the ion selection area through spectral analysis; the ion selection areas in the two optical interference structures are respectively used for screening nitrate nitrogen ions and ammonium nitrogen ions, and the two corresponding detectors respectively analyze the nitrate nitrogen ion concentration and the ammonium nitrogen ion concentration in the solution to be detected based on the obtained spectrum; The optical interference structure comprises an MZI and front-end and rear-end coupling gratings arranged at two ends of the MZI; the light from the laser enters the MZI through the front-end coupling grating and is divided into two paths, the two light rays enter the rear-end coupling grating through the sensing arm and the reference arm of the MZI respectively, and then enter the corresponding detector through the rear-end coupling grating; the sensing arm passes through the ion selection area; The photonic chip further comprises a substrate (6) and a shell (5); the shell (5) encapsulates the optical interference structure in cooperation with the substrate (6), and the shell (5) is provided with a detection window (50) for adding the solution to be detected; the nitrate nitrogen ions and the ammonium nitrogen ions in the solution to be detected respectively adhere to the corresponding sensing arms through nitrate nitrogen ion selection materials and ammonium nitrogen ion selection materials; The MZI of the first optical interference structure comprises a first sensing arm (3-1) and a first reference arm (4-1); the MZI of the second optical interference structure comprises a second sensing arm (3-2) and a second reference arm (4-2); the first sensing arm (3-1) coated with nitrate nitrogen ion selection materials (7-1), the second sensing arm (3-2) coated with ammonium nitrogen ion selection materials (7-2), the first reference arm (4-1) and the second reference arm (4-2) are all exposed in the detection window (50), and after the solution to be detected is dropped, the first reference arm (4-1) and the second reference arm (4-2) are directly soaked in the solution to be detected; The nitrate nitrogen ion selection materials are composed of dodecyltrimethylammonium nitrate dispersed in a superplastic PVC polymer matrix; the ammonium nitrogen ion selection materials are prepared from a calixarene material. The nitrate nitrogen ion selection materials and the ammonium nitrogen ion selection materials are arranged on the sensing arms of the first optical interference structure and the second optical interference structure respectively and form ion selection areas in communication with the outside; 2. The soil nitrogen optical chip sensor of claim 1, wherein, The concentration of the nitrate ion carrier in the nitrate nitrogen ion selection materials is 6.1%. The laser adopts a distributed tunable laser.

3. The soil nitrogen optical chip sensor of claim 1, wherein, The detector adopts a silicon detector.

4. The soil nitrogen optical chip sensor of claim 1, wherein, First, the photonic chip is manufactured, and then the laser and the detector are arranged at two ends of the photonic chip; the manufacturing of the photonic chip comprises the following steps:

5. A method of manufacturing a soil nitrogen photonic chip sensor according to any one of claims 1 to 4, characterized in that, After cleaning the substrate (6), spin-coating photoresist on the substrate (6), using electron beam exposure to irradiate the waveguide area, etching a strip-shaped waveguide after development and fixation, and forming two MZIs after removing the photoresist; ​ Nitrate nitrogen ion selective material and ammonium nitrogen ion selective material are respectively arranged on sensing arms of two MZIs; On the substrate (6), grating regions are selected at both ends of each MZI, photoresist is spin-coated, the grating regions are irradiated by electron beam exposure, after development and fixation, strip waveguides are etched, and after photoresist removal, front end coupling grating and rear end coupling grating located at both ends of the MZI are formed. The shell (5) is arranged to encapsulate the MZI structure, and the shell (5) is provided with a detection window (50).

6. A method for detecting soil nitrogen using the soil nitrogen photonic chip sensor according to any one of claims 1-4, characterized in that, Firstly, the deionized water is put into the detection window (50), the laser (10) is in the scanning state, and two detectors respectively obtain the resonance wavelength of the nitrate nitrogen sensing arm and the resonance wavelength of the ammonium nitrogen sensing arm . The nitrate nitrogen sensing arm is a sensing arm corresponding to a nitrate nitrogen ion selective material, and the ammonium nitrogen sensing arm is a sensing arm corresponding to an ammonium nitrogen ion selective material. Put the solution to be tested into the detection window (50), and make the laser (10) in the scanning state, and two detectors respectively obtain the resonance wavelength of the nitrate nitrogen sensing arm and the resonance wavelength of the ammonium nitrogen sensing arm ; by the amount of resonance shift of nitrate nitrogen ions calculating the concentration of nitrate nitrogen ions by the amount of resonance shift of ammonium nitrogen ions calculating the concentration of ammonium nitrogen ions; nitrate nitrogen ion concentration and ammonium nitrogen ion concentration The calculation formula is: Wherein, a and b are nitrate nitrogen parameters, and c and d are ammonium nitrogen parameters; a, b, c and d are obtained by fitting a known data set.

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