A floating multi-parameter water quality monitoring microsystem and a preparation method thereof

Abstract

The application discloses a floating type multi-parameter water quality monitoring microsystem and a preparation method thereof, and belongs to the technical field of water quality monitoring. The water quality monitoring microsystem comprises, from bottom to top, a functionalized floating carrier substrate, a flexible circuit module and an insulating packaging layer. The flexible circuit module comprises a flexible insulating medium layer, a planar spiral inductor coil is arranged on the upper surface of the flexible insulating medium layer, and a plurality of interdigital electrodes are arranged on the lower surface of the flexible insulating medium layer. Each interdigital electrode is connected with the planar spiral inductor coil to form LC resonance loops with different working frequencies. An ion-sensitive film is coated on the surface of each interdigital electrode. A detection window is arranged on the functionalized floating carrier substrate and corresponds to the position of the interdigital electrode, so that the interdigital electrode can directly contact the water body to be detected through the detection window. The insulating packaging layer completely covers the planar spiral inductor coil. The application can monitor water quality and has the advantages of good real-time performance, high detection precision and the like.

Description

Technical Field

[0001] This invention relates to the field of water quality monitoring technology, specifically to a floating multi-parameter water quality monitoring microsystem and a method for preparing the water quality monitoring microsystem. Background Technology

[0002] With the development of modern industry and urbanization, real-time monitoring of water environmental quality has become increasingly important. This is especially true in confined spaces such as household water supply pipes, industrial sewage pipes, and urban underground pipe networks, where ammonium ions (…) are present. ) and chloride ions ( Ammonium ion concentration is an important indicator for assessing the degree of water pollution and the residue of disinfection byproducts. For example, an abnormally high concentration of ammonium ions often indicates that the water body has been polluted by domestic sewage, while the concentration of chloride ions is directly related to the corrosivity of water and its drinking safety.

[0003] Currently, water quality monitoring in these confined spaces primarily relies on two technical methods. The first is the traditional offline sampling and analysis method, which involves manually or using a pump to collect water samples at the pipe outlet and sending them to a laboratory for analysis. While this method offers high accuracy, it lacks real-time capability and cannot accurately trace the specific location of pollution sources. The second method is active online monitoring sensors. These devices typically integrate batteries, signal processing circuits, and wireless communication modules. However, the presence of batteries significantly increases the sensor's size and weight, limiting its passage through narrow pipes. Furthermore, battery life is limited, and replacing batteries in complex pipe networks is extremely costly and sometimes impossible. Discarded batteries, if not recycled, can also cause secondary pollution to the water.

[0004] To address the power supply issue, wireless passive sensing technology based on the inductor-capacitor (LC) resonance principle has emerged. This technology utilizes electromagnetic coupling between an external readout coil and the sensor to transmit signals. However, these sensors are mostly designed for parameters such as temperature and humidity in the air. Applying such conventional planar structures directly to water quality monitoring faces significant technical challenges: First, the high dielectric constant and conductivity of water can cause severe parasitic effects, leading to short circuits or complete signal attenuation if the circuit directly contacts the water. Second, traditional rigid or thin-film substrates cannot guarantee that the sensor maintains a stable floating posture on the water surface, easily causing it to flip or sink, resulting in communication interruption. Third, simple planar structures struggle to effectively isolate the sensing area from circuit components, making it impossible to achieve in-situ contact detection of ions while ensuring wireless communication efficiency. Summary of the Invention

[0005] Based on the above-mentioned technical problems, this invention proposes a floating multi-parameter water quality monitoring microsystem and its preparation method.

[0006] The technical solution adopted in this invention is as follows:

[0007] A floating multi-parameter water quality monitoring microsystem includes, from bottom to top, a functional floating carrier substrate, a flexible circuit module, and an insulating encapsulation layer;

[0008] The flexible circuit module includes a flexible insulating dielectric layer, a planar spiral inductor coil disposed on the upper surface of the flexible insulating dielectric layer, and a first interdigital electrode and a second interdigital electrode disposed on the lower surface of the flexible insulating dielectric layer; the first interdigital electrode and the second interdigital electrode are both electrically connected to the planar spiral inductor coil, thereby reusing the same planar spiral inductor coil to construct two LC resonant circuits with their sensing surfaces facing downwards and their operating frequencies not overlapping.

[0009] The surfaces of the first interdigital electrode and the second interdigital electrode are respectively coated with a first ion-sensitive film and a second ion-sensitive film;

[0010] The functionalized floating carrier substrate has through-hole detection windows at the positions corresponding to the first and second interdigital electrodes, so that the first and second interdigital electrodes can directly contact the water body to be tested below through the detection windows.

[0011] The insulating encapsulation layer completely covers the planar spiral inductor coil; the insulating encapsulation layer is made of polydimethylsiloxane material; the low density of the insulating encapsulation layer provides buoyancy compensation, so that the overall average density of the monitoring microsystem is less than the density of the water being measured, and the planar spiral inductor coil is kept above the water surface and the first interdigital electrode and the second interdigital electrode are submerged below the water surface.

[0012] This invention also provides a method for preparing a floating multi-parameter water quality monitoring microsystem as described above, comprising the following steps:

[0013] Step 1: Fabricate a planar spiral inductor coil and a first interdigital electrode and a second interdigital electrode on the upper and lower surfaces of the flexible insulating dielectric layer, respectively. Make a through hole on the flexible insulating dielectric layer. The first interdigital electrode and the second interdigital electrode are connected to the planar spiral inductor coil through the through hole to form a flexible circuit module.

[0014] Step 2: Modify the surface of the first interdigital electrode with a first ion-sensitive film, and modify the surface of the second interdigital electrode with a second ion-sensitive film.

[0015] Step 3: Prepare a hydrogel precursor liquid doped with magnetic responsive materials and fluorescent microparticles, inject it into a mold with pre-set protrusions, and form a functionalized floating carrier substrate with two detection windows after cross-linking and curing.

[0016] Step 4: Attach the flexible circuit module to the top surface of the functionalized floating carrier substrate, and align the first interdigital electrode and the second interdigital electrode on the lower surface of the flexible circuit module with the two detection windows of the functionalized floating carrier substrate, respectively.

[0017] Step 5: Cast or spin-coat a low-density insulating encapsulation material onto the upper surface of the flexible circuit module, and after curing, form a floating multi-parameter water quality monitoring microsystem.

[0018] The beneficial technical effects of the present invention are as follows:

[0019] This invention's water quality monitoring microsystem employs a floating carrier substrate combined with LC resonance for water quality monitoring. It boasts advantages such as high real-time performance, accurate source tracing, and high detection precision. Furthermore, its compact size ensures maneuverability in narrow pipes. This invention solves the problems of short circuits and dielectric loss in water by using a floating inverted structure. It achieves synchronous wireless monitoring of ammonium and chloride ions by utilizing the dielectric constant change of an ion-selective membrane, and also features magnetic field-driven inspection and passive biofluorescence localization in dark environments. Specifically, it is reflected in the following aspects:

[0020] (1) This invention differs from traditional planar sensor structures by creatively designing a vertical interconnection mode of "upper coil - lower electrode", combined with a functional floating carrier substrate with a bottom window and a top PDMS package. This structure utilizes the low-density characteristics of PDMS to achieve adaptive floating, ensuring that the radio frequency communication coil is always above the water surface, effectively avoiding the shielding and attenuation of radio frequency signals by water with high dielectric constant and high conductivity, and preventing short circuits; at the same time, it ensures that the ion-selective membrane and interdigitated electrodes at the bottom can fully contact the water, achieving a dual guarantee of wireless communication reliability and sensing sensitivity.

[0021] (2) This invention utilizes a single-coil frequency division multiplexing circuit design, specifically by connecting two interdigitated electrodes to a spiral inductor coil on the same plane, to construct two LC resonant circuits with non-overlapping operating frequencies. This achieves simultaneous monitoring of ammonium and chloride ions without increasing the sensor size. Compared to a simple multi-coil stacking scheme, this invention effectively reduces mutual inductance crosstalk and decreases device size, making it highly suitable for multi-parameter water quality monitoring in confined pipe environments.

[0022] (3) By doping magnetic nanoparticles into the soft hydrogel, the present invention endows the water quality monitoring microsystem with the ability to cruise without a cable, and realizes magnetic field driven inspection.

[0023] (4) In view of the characteristics of dark and lightless confined space, the present invention uses inactivated Chlorella as a natural and environmentally friendly "passive fluorescent probe" to be incorporated into the functional floating carrier substrate. Unlike LED auxiliary lighting that relies on battery power, this solution does not require the microsystem to consume its own energy. It only needs external excitation light to emit high-brightness red fluorescence, which greatly improves the visibility of the microsystem in turbid or dark environments, making it easier for operators to locate, track and recover. Attached Figure Description

[0024] Figure 1 This is an exploded schematic diagram of the structural principle of the floating multi-parameter water quality monitoring microsystem of the present invention;

[0025] Figure 2 This is a schematic diagram of the cross-sectional structure of the assembled floating multi-parameter water quality monitoring microsystem of the present invention.

[0026] Figure 3 This is a schematic diagram of the circuit connection structure between the interdigitated electrode and the planar spiral inductor coil in the floating multi-parameter water quality monitoring microsystem of the present invention.

[0027] Figure 4 This is a schematic diagram illustrating the principle of multi-parameter water quality monitoring in the floating multi-parameter water quality monitoring microsystem of the present invention, in which the flexible circuit module cooperates with the external reading coil.

[0028] Figure 5 This is a simulation diagram of the magnetic field distribution of the floating multi-parameter water quality monitoring microsystem of the present invention in a resonant state;

[0029] Figure 6 This is a schematic diagram of the return loss S11 of the floating multi-parameter water quality monitoring microsystem of the present invention, simulated by ANSYS HFSS.

[0030] In the figure: 1-functionalized floating carrier substrate; 2-magnetic driving unit; 3-fluorescent positioning unit; 4-first interdigital electrode; 5-first ion-sensitive membrane; 6-second interdigital electrode; 7-second ion-sensitive membrane; 8-flexible insulating dielectric layer; 9-planar spiral inductor coil; 901-inner ring port; 902-outer ring port; 903-common port; 10-insulating encapsulation layer; 11-detection window; 12-through hole. Detailed Implementation

[0031] This invention provides a floating multi-parameter water quality monitoring microsystem and its fabrication method. This microsystem uses a floating carrier substrate combined with LC resonant sensing for water quality monitoring, offering advantages such as good real-time performance and high detection accuracy, making it suitable for use in confined pipes. Furthermore, the microsystem employs a unique inverted floating structure design, effectively solving problems such as dielectric loss, short circuits, and difficulty in maintaining stable floating sensing posture in aquatic environments. Additionally, by using a functionalized floating carrier substrate, this invention addresses the technical challenges of lacking effective passive visual positioning and motion control methods in confined, dark spaces.

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments.

[0033] Example 1: As Figure 1 , Figure 2 As shown, a floating multi-parameter water quality monitoring microsystem employs a unique inverted layered design, consisting of, from bottom to top: a functional floating carrier substrate 1, a flexible circuit module, and an insulating encapsulation layer 10. Specifically, the functional floating carrier substrate 1 is located at the bottom layer, the flexible circuit module in the middle layer, and the insulating encapsulation layer 10 at the top layer.

[0034] The flexible circuit module includes a flexible insulating dielectric layer 8. A planar spiral inductor coil 9 is disposed on the upper surface of the flexible insulating dielectric layer 8, and a first interdigital electrode 4 and a second interdigital electrode 6 are disposed on the lower surface of the flexible insulating dielectric layer 8. Both the first interdigital electrode 4 and the second interdigital electrode 6 are electrically connected to the planar spiral inductor coil 9, thereby multiplexing the same planar spiral inductor coil 9 to construct two LC resonant circuits with their sensing surfaces facing downwards and their operating frequencies not overlapping.

[0035] like Figure 3 As shown, the planar spiral inductor 9 has a single-coil structure, with an inner coil port 901, an outer coil port 902, and a common port 903 located on the coil. One end of the first interdigital electrode 4 is connected to the outer coil port 902, and the other end of the first interdigital electrode 4 is connected to the common port 903. One end of the second interdigital electrode 6 is connected to the inner coil port 901, and the other end of the second interdigital electrode 6 is connected to the common port 903. A through-hole 12 is provided on the flexible insulating dielectric layer 8. The first interdigital electrode 4 and a portion of the planar spiral inductor 9 form a first resonant circuit, and the second interdigital electrode 6 and another portion of the planar spiral inductor 9 form a second resonant circuit.

[0036] The planar spiral inductor 9 is located at the middle position of the upper surface of the flexible insulating dielectric layer 8. The flexible insulating dielectric layer 8 has a rectangular design. The first interdigital electrode 4 and the second interdigital electrode 6 are located at both ends of the lower surface of the flexible insulating dielectric layer 8. The first interdigital electrode 4 and the second interdigital electrode 6 are located on the left and right sides of the planar spiral inductor 9, respectively.

[0037] The surfaces of the first interdigital electrode 4 and the second interdigital electrode 6 are respectively modified with a first ion-sensitive membrane 5 and a second ion-sensitive membrane 7 targeting different ions. The first ion-sensitive membrane 5 is an ammonium ion-selective membrane, and the second ion-sensitive membrane 7 is a chloride ion-selective membrane. When the concentration of ammonium ions or chloride ions in the water changes, the dielectric constant of the corresponding selective membrane changes, which in turn causes a shift in the resonant frequency of the corresponding LC resonant circuit. The concentration is wirelessly retrieved by detecting this frequency shift using an external reading device.

[0038] Figure 4 This demonstrates the circuit connection principle of a microsystem based on single-coil frequency division multiplexing. By setting a common port on the planar spiral inductor, the single communication coil is electrically divided into two independent inductor segments. These two inductor segments form circuits with the equivalent capacitance of the two sensing units, thereby constructing two resonant circuits with non-overlapping operating frequencies without increasing the number of antennas.

[0039] Figure 5 The magnetic field strength distribution of the flexible circuit module in the resonant state is shown. Simulation results show that, due to the reasonable layout of the common port, the magnetic field distribution in the first interdigital electrode region and the second interdigital electrode region differs, which is reflected in the difference in chromatographic intensity.

[0040] Figure 6 The dual-frequency decoupling characteristics of the microsystem were verified by ANSYS HFSS simulation. The two clear and non-overlapping resonance troughs in the curves (located near 0.58 GHz and 0.72 GHz, respectively) demonstrate that the microsystem successfully constructed independent resonant circuits corresponding to the detection of ammonium and chloride ions, respectively. Sufficient bandwidth spacing (approximately 0.14 GHz) was maintained between the two resonant frequencies. This significant frequency differentiation effectively prevents frequency drift caused by changes in single ion concentration from interfering with the other signal.

[0041] The first interdigitated electrode is connected in parallel with the planar spiral inductor using the number of turns (outer ring portion) from the common port to form a first LC resonant circuit; the second interdigitated electrode is connected in parallel with the planar spiral inductor using the remaining number of turns, i.e., the number of turns (inner ring portion) from the common port to form a second LC resonant circuit; by adjusting the position of the common port 903 (tap position), the resonant frequency differentiation of the two circuits meets the wireless reading requirements.

[0042] The functionalized floating carrier substrate 1 has through-hole detection windows 11 at positions corresponding to the first interdigital electrode 4 and the second interdigital electrode 6, allowing the interdigital electrodes on the lower surface to be exposed to the external environment through the detection windows. That is, the first interdigital electrode 4 and the second interdigital electrode 6 can directly contact the water body below through the corresponding detection windows 11. The insulating encapsulation layer 10 completely covers the upper surface of the flexible insulating dielectric layer 8 and the planar spiral inductor coil 9, forming a hydrophobic protective layer that provides waterproof protection and buoyancy support.

[0043] Example 2: The basic structure is the same as in Example 1, except that the following design is further incorporated: The functionalized floating carrier substrate 1 is made of gel material, in which magnetic drive unit 2 and fluorescent positioning unit 3 are also doped. Magnetic drive unit 2 enables the monitoring microsystem to move under the influence of an external magnetic field, and fluorescent positioning unit 3 is used for passive optical positioning of the monitoring microsystem in dark or turbid waters.

[0044] The aforementioned gel material is a calcium alginate hydrogel, i.e., a hydrophilic polymer gel network, formed by curing sodium alginate solution with a calcium ion crosslinking agent. The magnetic drive unit 2 uses iron oxide nanoparticles (Fe3O4). The particles, or magnetically responsive materials, endow the microsystem with controlled movement and recovery capabilities under the influence of an external magnetic field. The fluorescent positioning unit 3, or fluorescent microparticles, utilizes inactivated Chlorella cells. The chlorophyll components (fluorescent pigments) retained within the cells emit red fluorescence when excited by an external light source of a specific wavelength, enabling passive optical positioning of the microsystem in dark or turbid waters. The functionalized floating carrier substrate 1 is composed of a hydrophilic polymer hydrogel network doped with magnetically responsive particles and microparticles with self-fluorescent properties.

[0045] The ammonium ion selective membrane comprises an ammonium ion carrier, polyvinyl chloride, and a plasticizer, wherein the ammonium ion carrier may be nonactin; the chloride ion selective membrane comprises a chloride ion carrier, polyvinyl chloride, and a plasticizer, wherein the chloride ion carrier may be 5,10,15,20-tetraphenylporphyrin manganese chloride (III) (Chloride ionophore I).

[0046] The insulating encapsulation layer 10 is made of polydimethylsiloxane (PDMS). The low density of the insulating encapsulation layer 10 (density less than that of water) provides buoyancy compensation, so that the overall average density of the monitoring microsystem is slightly less than that of the water being measured, maintaining a stable floating posture in the water with the planar spiral inductor coil 9 above the water surface and the first interdigital electrode 4 and the second interdigital electrode 6 submerged below the water surface.

[0047] This invention solves the problems of short circuits and dielectric loss in LC circuits in water by using a floating inverted structure. The first interdigital electrode 4 and the second interdigital electrode 6 share a planar spiral inductor coil 9, constructing two LC resonant circuits with non-overlapping operating frequencies and downward-facing sensing surfaces. Combined with the floating inverted structure, synchronous wireless monitoring of ammonium and chloride ions is achieved by utilizing changes in the dielectric constant of the sensitive membrane. Furthermore, the floating carrier substrate is functionalized, enabling it to perform both magnetic field-driven inspection and passive biofluorescence localization in dark environments.

[0048] The flexible insulating dielectric layer 8 is made of polyimide film, with copper foil covering both the top and bottom surfaces of the polyimide film. A planar spiral inductor coil 9, a first interdigital electrode 4, and a second interdigital electrode 6 are formed using an etching process. The planar spiral inductor coil 9 has a square or circular spiral structure, a line width of 150-200 μm, a line spacing of 80-100 μm, and 6-10 turns. The first interdigital electrode 4 and the second interdigital electrode 6 have a finger width of 50-60 μm and a finger spacing of 50-60 μm.

[0049] The aforementioned microsystem is a floating wireless passive multi-parameter water quality monitoring microsystem based on a magnetic fluorescent hydrogel carrier. Its overall average density is less than that of the water body to be measured, thereby maintaining a stable floating posture with the insulating encapsulation layer facing upwards and the functionalized floating carrier substrate facing downwards on the water surface.

[0050] This invention relates to a floating multi-parameter water quality monitoring microsystem that overcomes dielectric interference in the aquatic environment, requires no battery power, and possesses visual positioning and flexible movement capabilities in dark or turbid waters. This microsystem integrates a special floating structure, magnetic fluorescent functional materials, and wireless sensing circuitry, making it significant for improving monitoring efficiency in confined water spaces.

[0051] Example 3: Based on Example 2, the following design is further implemented: a conductive polymer layer is further disposed between the first interdigitated electrode 4 and the ammonium ion selective membrane, and between the second interdigitated electrode 6 and the chloride ion selective membrane. The conductive polymer layer is poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid (PEDOT:PSS). This invention uses a conductive polymer layer as an ion-electron transduction layer to reduce interfacial impedance.

[0052] Example 4: A method for preparing a floating multi-parameter water quality monitoring microsystem, comprising the following steps:

[0053] Step 1: Fabricate a planar spiral inductor coil 9 and a first interdigital electrode 4 and a second interdigital electrode 6 on the upper and lower surfaces of the flexible insulating dielectric layer 8, respectively. Then, fabricate through-holes 12 on the flexible insulating dielectric layer 8 using laser drilling and hole metallization processes. The first interdigital electrode 4 and the second interdigital electrode 6 are connected to the planar spiral inductor coil 9 via the through-holes 12, forming a flexible circuit module.

[0054] Step 2: Modify the surface of the first interdigital electrode 4 with a first ion-sensitive membrane 5, and modify the surface of the second interdigital electrode 6 with a second ion-sensitive membrane 7.

[0055] Step 3: Prepare a hydrogel precursor liquid doped with magnetic responsive particles and fluorescent microparticles, inject it into a mold with pre-set bosses, and after cross-linking and curing, form a functionalized floating carrier substrate 1 with two detection windows 11.

[0056] Step 4: Invert the flexible circuit module and attach it to the top surface of the functionalized floating carrier substrate 1, and align the first interdigital electrode 4 and the second interdigital electrode 6 on the lower surface of the flexible circuit module with the two detection windows 11 of the functionalized floating carrier substrate 1, respectively.

[0057] Step 5: Cast or spin-coat a low-density insulating encapsulation material onto the upper surface of the flexible circuit module, and after curing, form a floating multi-parameter water quality monitoring microsystem.

[0058] In step three above, after cross-linking and curing, the functionalized floating carrier substrate 1 is further subjected to freeze-drying or foaming treatment to form a porous structure inside the functionalized floating carrier substrate and reduce the density of the functionalized floating carrier substrate 1.

[0059] The inner wall of the aforementioned through-hole 12 can be made of metal, allowing the interdigitated electrode to be electrically connected to the bottom of the through-hole, and the corresponding positions of the inner and outer coils of the planar spiral inductor to be electrically connected to the top of the through-hole, thereby achieving electrical connection between the interdigitated electrode and the planar spiral inductor. Alternatively, the through-hole can simply be a hole-like structure penetrating the flexible insulating dielectric layer, allowing the ends of the interdigitated electrode to be bent and pass through the through-hole to connect electrically with the planar spiral inductor.

[0060] The preparation method will be explained in more detail below:

[0061] (1) Design and manufacturing of flexible circuit modules;

[0062] The core circuitry is fabricated using double-sided flexible printed circuit board (FPCB) technology.

[0063] Substrate selection: A 25μm thick polyimide (PI) film is selected as the flexible insulating dielectric layer 8, and copper foil with a thickness of 18μm is covered on both the top and bottom sides.

[0064] Circuit patterning:

[0065] A planar spiral inductor coil 9 is formed on the upper surface of a PI film using photolithography and wet etching processes. Preferably, the coil has a square or circular spiral structure, a line width of 200 μm, a line spacing of 100 μm, and 6-10 turns.

[0066] Two sets of staggered interdigitated electrodes (IDEs) are formed on the lower surface of the PI film, namely the first interdigitated electrode 4 and the second interdigitated electrode 6. Preferably, the interdigitated fingers are 50 μm wide and the interdigitated distance is 50 μm.

[0067] Vertical interconnect (via):

[0068] like Figure 1 As shown, laser drilling technology is used to drill holes at specific locations in the PI film, and the holes are then metallized to form through holes 12.

[0069] Circuit connection logic (such as) Figure 3 As shown): The planar spiral inductor coil 9 has an inner coil port 901, an outer coil port 902, and a tap port, or common port 903, located at the middle turn. One end of the first interdigital electrode 4 is connected to the outer coil port of the coil, and the other end is connected to the common port (common ground) of the coil; one end of the second interdigital electrode 6 is connected to the common port (common ground) of the coil, and the other end is connected to the inner coil port of the coil.

[0070] Through the above connection, the first interdigital electrode is connected in parallel to the outer section of the planar spiral inductor (from the outer port 902 to the common port 903), and the inductance of this section and the capacitance of the first interdigital electrode form a first LC resonant circuit; the second interdigital electrode is connected in parallel to the inner section of the coil (from the inner port 901 to the common port 903), and the inductance of the remaining part and the capacitance of the second interdigital electrode form a second LC resonant circuit.

[0071] Because the inner and outer coil sections have different coil lengths and number of turns, the distributed inductance of the two sections differs significantly. With the initial capacitance design values ​​of the two interdigitated electrodes being essentially the same, this asymmetrical inductance segmentation design directly sets the inherent resonant frequencies of the two circuits in non-overlapping frequency bands, thus successfully achieving dual-parameter synchronous decoupled monitoring under a single readout coil.

[0072] Surface treatment: Chemical gold plating is performed on the exposed copper electrode surface to prevent oxidation and improve the adhesion of the subsequent sensitive film.

[0073] (2) Preparation and modification of ion-sensitive membranes;

[0074] The formulation and coating process of the first ion-sensitive membrane 5 (ammonium ion selective membrane) and the second ion-sensitive membrane 7 (chloride ion selective membrane).

[0075] Ion-electron transduction layer modification:

[0076] To reduce interface impedance and improve signal stability, a layer of conductive polymer PEDOT:PSS (poly(3,4-ethylenedioxythiophene)-polystyrene sulfonic acid) was first electrodeposited on the surfaces of the first interdigital electrode 4 and the second interdigital electrode 6. The electrodeposition conditions were: constant current mode, current density 0.2, and time 120 seconds.

[0077] Ammonium ion selective membrane formulation:

[0078] Weigh out 1.0 mg of ammonium ion carrier (nomaramycin), 33.0 mg of polyvinyl chloride (PVC), and 66.0 mg of plasticizer diisooctyl sebacate (DOS), and dissolve them in 660 mL of water. In tetrahydrofuran (THF), ultrasonic oscillation was used until all components were completely dissolved to obtain an ammonium ion selective membrane precursor solution with a total mass of approximately 100 mg.

[0079] Chloride ion selective membrane formulation:

[0080] Weigh out 1.0 mg of chloride ion carrier (5,10,15,20-tetraphenylporphyrin manganese chloride(III)), 33.0 mg of polyvinyl chloride (PVC), and 66.0 mg of plasticizer diisooctyl sebacate (DOS), and dissolve them in 660 mL of water. In tetrahydrofuran (THF), ultrasonic oscillation was used until all components were completely dissolved to obtain a chloride ion selective membrane precursor solution with a total mass of approximately 100 mg.

[0081] Coating to form a film:

[0082] Using a precision microsyringe, the two solutions were respectively drawn up and drop-coated onto the corresponding surfaces of the first interdigital electrode 4 and the second interdigital electrode 6. After air drying at room temperature for 24 hours, a solid ion-selective film was formed after the solvents evaporated.

[0083] (3) Preparation of functionalized floating carrier substrates;

[0084] A functionalized floating carrier substrate 1 was prepared at the bottom layer, and the microsystem was endowed with magnetic and fluorescent properties.

[0085] Step S1: Preparation of precursor solution;

[0086] Weigh 2.0 g of sodium alginate powder (preferably low or medium viscosity) and add it in portions to 100 mL of deionized water. Under water bath conditions of 50-70℃, use a magnetic stirrer to adjust the speed according to the viscosity and continue stirring for 2-4 hours until the sodium alginate is completely dissolved, forming a uniform, transparent, bubble-free 2% (w / v) sodium alginate matrix solution, i.e., the precursor solution.

[0087] Step S2: Doping and dispersion of functional fillers;

[0088] Add 2.0 g of iron oxide nanoparticles (concentration of approximately 2% w / v) and 1.0 g of inactivated Chlorella powder (concentration of approximately 1% w / v) to the above matrix solution to obtain a mixed solution.

[0089] The mixture was then placed in an ultrasonic disperser and treated for 30 minutes at a power of 100 W and a frequency of 40 kHz. Ultrasonic treatment effectively prevented the aggregation of nanoparticles, resulting in a homogeneous suspension that was dark black with a greenish hue.

[0090] Step S3: Molding and cross-linking curing;

[0091] Prepare a 2%-5% (w / v) (preferably 3% in this embodiment) aqueous solution of calcium chloride as a crosslinking agent.

[0092] Slowly pour the mixed suspension obtained in step S2 into a pre-made polytetrafluoroethylene mold (the mold shape corresponds to the base shape of the sensor, such as a rectangle, with a protrusion in the middle to form a detection window). The casting thickness is controlled at 2-3 mm.

[0093] Use a sprayer to evenly spray the calcium chloride solution onto the surface of the mixture, or slowly immerse the mixed suspension along with the mold into the calcium chloride solution. Allow it to stand for 30-60 minutes to crosslink and form a solid hydrogel.

[0094] Step S4: Post-processing;

[0095] The cured hydrogel substrate was removed and rinsed three times with deionized water to remove residual chloride ions and unreacted crosslinking agents from the surface. To further reduce the substrate density and improve floating performance, as a preferred embodiment, the wet gel was pre-frozen at -80 degrees Celsius for 12 hours, and then dried in a freeze dryer for 24 hours to remove internal moisture, resulting in a porous magnetic fluorescent aerogel framework with low density characteristics, i.e., a functionalized floating carrier substrate.

[0096] (4) System assembly and density control;

[0097] Inverted bonding:

[0098] The prepared flexible circuit module is inverted so that the interdigitated electrode region on its lower surface, coated with an ion-sensitive membrane, is precisely aligned with the detection window of the porous magnetic fluorescent hydrogel framework prepared in step S4. A small amount of sodium alginate solution or biocompatible adhesive is applied to the edge of the flexible substrate and tightly bonded to the hydrogel framework. At this point, the sensitive interdigitated electrode is suspended and can contact the water sample without obstruction through the detection window.

[0099] Top encapsulation and buoyancy co-design:

[0100] A polydimethylsiloxane (PDMS) prepolymer and curing agent (mass ratio 10:1) are prepared, and after vacuum degassing, they are cast or spin-coated onto the upper surface of the flexible circuit module (i.e. the spiral inductor coil side) to form an insulating encapsulation layer.

[0101] Density control strategy: The microsystem of this invention adopts a dual density reduction strategy of "porous substrate + low-density packaging".

[0102] On the one hand, the carrier substrate at the bottom forms a porous structure after being freeze-dried in step S4, and its skeleton density is significantly reduced. Although it contains relatively heavy iron oxide particles, it has a large buoyancy redundancy overall.

[0103] On the other hand, the top PDMS encapsulation layer (density approximately 0.965 g / cm³) itself has a density less than that of water.

[0104] By controlling the thickness of the PDMS encapsulation layer (preferably 2-4 mm) to work together with the bottom porous substrate, the average density of the entire microsystem is ensured to be strictly less than 1.0 g / cm³.

[0105] Final curing:

[0106] The assembled microsystem was placed in a 60°C oven and heated for 2 hours to allow PDMS to fully cross-link, ultimately forming a wireless monitoring microsystem with a stable physical structure and buoyancy, namely a floating multi-parameter water quality monitoring microsystem.

[0107] (5) Working principle and effect verification;

[0108] Floating and Motion Test:

[0109] When the prepared microsystem is placed in water, due to the density design and surface tension, the microsystem exhibits a stable floating posture with the circuit on the water and the electrodes underwater.

[0110] Under the pull of an external magnet, the microsystem can move with the magnetic field.

[0111] Dark environment positioning test:

[0112] In a dark environment, the microsystem was illuminated with a blue-violet flashlight with a wavelength of 400-450 nm. Because the inactivated Chlorella doped in the substrate retained its chlorophyll content, the bottom of the microsystem emitted a bright red fluorescence (wavelength of approximately 680 nm), and its outline was clearly visible, achieving passive localization.

[0113] An external readout coil was connected using a vector network analyzer (VNA) and placed close to the microsystem (1 cm away). ANSYS HFSS electromagnetic field simulation results show that this structure can effectively achieve decoupled detection of two parameters and obtain a stable frequency response signal without the need for a reference electrode.

[0114] Of course, the above description is only a preferred embodiment of the present invention. The present invention is not limited to the above-described embodiments. It should be noted that any equivalent substitutions or obvious modifications made by those skilled in the art under the guidance of this specification fall within the scope of this specification and should be protected by the present invention.

Claims

1. A floating multi-parameter water quality monitoring microsystem, characterized in that: It includes, from bottom to top, a functional floating carrier substrate, a flexible circuit module, and an insulating encapsulation layer; The flexible circuit module includes a flexible insulating dielectric layer, a planar spiral inductor coil disposed on the upper surface of the flexible insulating dielectric layer, and a first interdigital electrode and a second interdigital electrode disposed on the lower surface of the flexible insulating dielectric layer; the first interdigital electrode and the second interdigital electrode are both electrically connected to the planar spiral inductor coil, thereby reusing the same planar spiral inductor coil to construct two LC resonant circuits with their sensing surfaces facing downwards and their operating frequencies not overlapping. The surfaces of the first interdigital electrode and the second interdigital electrode are respectively coated with a first ion-sensitive film and a second ion-sensitive film; The functionalized floating carrier substrate has through-hole detection windows at the positions corresponding to the first and second interdigital electrodes, so that the first and second interdigital electrodes can directly contact the water body to be tested below through the detection windows. The insulating encapsulation layer completely covers the planar spiral inductor coil; the insulating encapsulation layer is made of polydimethylsiloxane material; the low density of the insulating encapsulation layer provides buoyancy compensation, so that the overall average density of the monitoring microsystem is less than the density of the water being measured, and the planar spiral inductor coil is kept above the water surface and the first interdigital electrode and the second interdigital electrode are submerged below the water surface.

2. The floating multi-parameter water quality monitoring microsystem according to claim 1, characterized in that: The planar spiral inductor has a single coil structure, with an inner coil port, an outer coil port, and a common port located on the coil; one end of the first interdigital electrode is connected to the outer coil port, and the other end of the first interdigital electrode is connected to the common port; one end of the second interdigital electrode is connected to the inner coil port, and the other end of the second interdigital electrode is connected to the common port; a through-hole is provided on the flexible insulating dielectric layer.

3. The floating multi-parameter water quality monitoring microsystem according to claim 2, characterized in that: The planar spiral inductor is positioned at the middle of the upper surface of the flexible insulating dielectric layer, and the first interdigital electrode and the second interdigital electrode are positioned at both ends of the lower surface of the flexible insulating dielectric layer, with the first interdigital electrode and the second interdigital electrode corresponding to each other on both sides of the planar spiral inductor.

4. The floating multi-parameter water quality monitoring microsystem according to claim 1, characterized in that: A conductive polymer layer is also provided between the first interdigital electrode and the first ion-sensitive membrane, and between the second interdigital electrode and the second ion-sensitive membrane.

5. The floating multi-parameter water quality monitoring microsystem according to claim 1, characterized in that: The functionalized floating carrier substrate is made of gel material, which is also doped with magnetic responsive material and fluorescent microparticles. The magnetic responsive material is used for the controlled movement of the monitoring microsystem under the action of an external magnetic field, and the fluorescent microparticles are used for the passive optical positioning of the monitoring microsystem in dark or turbid waters.

6. A floating multi-parameter water quality monitoring microsystem according to claim 5, characterized in that: The gel material is calcium alginate hydrogel, the magnetic responsive material is iron oxide nanoparticles, and the fluorescent microparticles are inactivated Chlorella.

7. A floating multi-parameter water quality monitoring microsystem according to claim 1, characterized in that: The flexible insulating dielectric layer is made of polyimide film, with copper foil covering both the top and bottom surfaces of the polyimide film, and is processed by etching to form a planar spiral inductor coil, a first interdigital electrode, and a second interdigital electrode.

8. A floating multi-parameter water quality monitoring microsystem according to claim 7, characterized in that: The planar spiral inductor has a square or circular spiral structure, a line width of 150-200μm, a line spacing of 80-100μm, and 6-10 turns; The first interdigital electrode and the second interdigital electrode have a finger width of 50-60 μm and a finger spacing of 50-60 μm.

9. A method for preparing a floating multi-parameter water quality monitoring microsystem as described in any one of claims 1-8, characterized in that... Includes the following steps: Step 1: Fabricate a planar spiral inductor coil and a first interdigital electrode and a second interdigital electrode on the upper and lower surfaces of the flexible insulating dielectric layer, respectively. Make a through hole on the flexible insulating dielectric layer. The first interdigital electrode and the second interdigital electrode are connected to the planar spiral inductor coil through the through hole to form a flexible circuit module. Step 2: Modify the surface of the first interdigital electrode with a first ion-sensitive film, and modify the surface of the second interdigital electrode with a second ion-sensitive film. Step 3: Prepare a hydrogel precursor liquid doped with magnetic responsive materials and fluorescent microparticles, inject it into a mold with pre-set protrusions, and form a functionalized floating carrier substrate with two detection windows after cross-linking and curing. Step 4: Attach the flexible circuit module to the top surface of the functionalized floating carrier substrate, and align the first interdigital electrode and the second interdigital electrode on the lower surface of the flexible circuit module with the two detection windows of the functionalized floating carrier substrate, respectively. Step 5: Cast or spin-coat a low-density insulating encapsulation material onto the upper surface of the flexible circuit module, and after curing, form a floating multi-parameter water quality monitoring microsystem.

10. The method for preparing a floating multi-parameter water quality monitoring microsystem as described in claim 9, characterized in that: In step three, after the cross-linking and curing, the functionalized floating carrier substrate is further subjected to freeze-drying to form a porous structure inside the functionalized floating carrier substrate.

Images