An intelligent food packaging material with micro-plastic adsorption and early warning dual functions and a preparation method thereof

Abstract

This invention discloses a smart food packaging material with dual functions of microplastic adsorption and early warning, and its preparation method, belonging to the interdisciplinary field of polymer materials and food safety technology. It consists of an inner chitosan nanofiber modified PE adsorption layer, a middle quantum dot-nanoantibody sensing layer, and an outer PE / EVOH high-barrier layer. The inner layer captures microplastics released from acidic foods through electrostatic adsorption; the middle layer utilizes quantum dot fluorescence signals to achieve real-time monitoring of microplastic concentration, with a color change from green to red indicating a warning when the concentration is ≥28 μg / L; the outer layer blocks external contamination, and a compatible smartphone app enables rapid detection. This packaging material reduces microplastic exposure in acidic foods by ≥80%, solving the technical challenges of traditional packaging's inability to actively intervene and provide real-time feedback.

Description

Technical Field

[0001] This invention relates to the field of interdisciplinary technology of polymer materials and food safety, specifically to a smart food packaging material with dual functions of microplastic adsorption and early warning, and its preparation method. Background Technology

[0002] Microplastic contamination has been listed as an emerging food safety risk by the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO). Existing research confirms that food packaging materials (especially polyethylene, PE) release microplastic particles during processing, storage, and use. The release level in acidic foods (pH < 4.5) can be 3-5 times higher than in neutral foods. These particles migrate from the inner wall of the packaging into the food itself. Current technologies have fundamental limitations: 1. Passive protection limitations: Traditional PE packaging relies solely on its dense structure as a barrier, unable to intervene in microplastic release caused by mechanical wear, thermal oxidation, and acid-catalyzed degradation. Furthermore, its barrier function rapidly declines with aging. 2. Detection lag: Offline detection methods (such as Raman spectroscopy and pyrolysis-GC-MS) take hours to days, failing to reflect the dynamic changes in microplastic concentration during shelf life in real time (Austine et al., 2025). 3. Invisible safety risks: Consumers cannot determine whether the packaging has failed, leading to long-term exposure to unknown risks. Therefore, there is an urgent need to develop a smart packaging material that can actively capture released microplastics and provide real-time feedback on risk levels, thereby achieving a technological leap from "passive protection" to "active risk management". Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, the present invention aims to provide a smart food packaging material with dual functions of microplastic adsorption and early warning, and its preparation method, thereby solving the problem of excessive microplastic release from PE packaging in acidic foods.

[0004] 1. Active capture of packaging-borne microplastics: Through electrostatic adsorption mechanism, microplastics are intercepted in situ at the moment of release (boundary layer <1μm), preventing them from migrating to the food body and reducing the exposure of microplastics in acidic foods by ≥80%.

[0005] 2. Real-time visual risk monitoring: Integrated food-grade fluorescence sensing system allows consumers to obtain microplastic concentration (0.1-1000 μg / L) within 5 seconds via smartphone, with a detection error ≤±15%.

[0006] 3. Intrinsically safe design: It uses heavy metal-free materials from the source and uses encapsulation technology to ensure zero migration of harmful substances under extreme conditions such as strong acid and mechanical friction, which complies with food contact material regulations.

[0007] 4. Intelligent early warning and behavioral intervention: When the microplastic concentration is ≥28 μg / L (EFSA provisional TDI), a reminder will be sent via color change or APP push notification that "it is recommended to consume within 24 hours" to ensure that the risk is controllable.

[0008] The objective of this invention is achieved through the following technical solution:

[0009] A smart food packaging material with dual functions of microplastic adsorption and early warning includes an inner layer, a middle layer, and an outer layer laminated sequentially from the inside out:

[0010] The inner layer is a chitosan nanofiber modified polyethylene food contact layer, wherein the chitosan nanofiber forms a three-dimensional network structure in the polyethylene matrix, which is used to release and migrate microplastic particles from the packaging material into the acidic food through electrostatic adsorption of positively charged amino groups.

[0011] The middle layer is a food-grade fluorescent sensing layer containing carbon quantum dot-labeled anti-polyethylene nanobodies, or carbon quantum dot-labeled anti-polyethylene nanobodies coated with mesoporous silica, used to specifically recognize microplastic particles and generate fluorescent signals.

[0012] The outer layer is a polyethylene / ethylene-vinyl alcohol blend barrier layer with a nano-layered dispersion structure.

[0013] Furthermore, the chitosan nanofibers in the inner layer (1) have a diameter of 50-200 nm, are added at 5-15 wt% of the polyethylene matrix, have a surface amino density ≥2.5 mmol / g, and have a capture efficiency of ≥70% for microplastic particles with a particle size of 200 nm-5 μm in acidic foods with pH <4.5. This efficiency is determined according to the method of GB 31604.1-2015.

[0014] Furthermore, the carbon quantum dots in the middle layer are hydrothermally synthesized from citric acid and urea, with a particle size of 3-5 nm, a fluorescence emission wavelength of 520±10 nm, a quantum yield of ≥60%, and a surface modified with carboxyl functional groups (-COOH) through oxidation treatment, with a carboxyl density of ≥0.8 mmol / g; the anti-polyethylene nanobody is a single-chain variable region fragment (scFv) with a molecular weight of 15-20 kDa, which is connected to the quantum dots through EDC / NHS chemical coupling.

[0015] Furthermore, the mesoporous silica in the middle layer has an MCM-41 structure, a coating layer thickness of 30-60 nm, and a particle size of 100-200 nm after coating. The antibody is coupled to the outer surface of the mesoporous silica. The mesoporous silica conforms to E551 of GB 9685-2016.

[0016] Furthermore, the middle layer implements threshold warning through one of the following two mechanisms:

[0017] Option A: Fluorescence intensity decay mechanism, when the microplastic concentration is ≥28 μg / L, the fluorescence signal intensity decreases by >50%;

[0018] Option B: Fluorescence resonance energy transfer (FRET) color conversion mechanism, comprising green carbon quantum dots and red carbon quantum dots, wherein the fluorescence emission wavelength of the green carbon quantum dots is 520±10nm and the fluorescence emission wavelength of the red carbon quantum dots is 620±10nm, and the fluorescence color significantly changes from green to red when the microplastic concentration is ≥28 μg / L.

[0019] Furthermore, the outer layer contains 20-30 wt% ethylene-vinyl alcohol, and is formed into a nano-layered structure of ≥50 layers through multi-layer co-extrusion, with a single layer thickness of ≤100 nm, and a barrier rate of ≥95% against external microplastic particles.

[0020] Furthermore, it also includes an intelligent monitoring system, which consists of:

[0021] Fluorescence signal of quantum dots in the middle layer;

[0022] Smartphone spectral acquisition module (camera + LED excitation source);

[0023] The components of the APP data analysis module;

[0024] The APP calculates microplastic concentration by converting RGB channel intensity, with a detection range of 0.1-1000μg / L, a detection error of ≤±15%, and a response time of <30 seconds.

[0025] Furthermore, the APP has a built-in EFSA safety threshold database. When the microplastic concentration exceeds the safety threshold of 28 μg / L, it will automatically push a "food unsafe" warning and a recommended consumption period.

[0026] This invention also provides a method for preparing a smart food packaging material with dual functions of microplastic adsorption and early warning, comprising the following steps:

[0027] S1. Inner layer preparation: Chitosan is dissolved in 1% acetic acid solution, and nanofiber membrane is prepared by electrospinning. After being frozen and crushed by liquid nitrogen, it is melt-blended with polyethylene resin at a temperature of 130-150℃ and formed by blow molding or casting.

[0028] S2. Middle Layer Preparation: Option A: Synthesize carbon quantum dots using a hydrothermal method, carboxylate the surface, and then couple anti-polyethylene nanobodies via EDC / NHS. The quantum dot-antibody complex is then uniformly coated onto the inner layer surface using a microgravure plate. Option B: Synthesize mesoporous silica-coated carbon quantum dots (MCM-41@CQDs), then couple them with antibodies, using the same coating process; forming a sensing layer with a thickness of 10-20 μm.

[0029] S3. Outer layer preparation: Polyethylene and ethylene-vinyl alcohol resin are compounded on the outer side of the middle layer through multi-layer co-extrusion technology. The co-extrusion temperature is 180-200℃. The layered structure is achieved by controlling the shear rate.

[0030] S4. Interlayer composite: The hot-press composite process is adopted, with a pressure of 5-10MPa, a temperature of 140-160℃, and a time of 30-60 seconds, to ensure that the interfacial bonding strength between the three layers is ≥5N / 15mm.

[0031] The application of a smart food packaging material with dual functions of microplastic adsorption and early warning in the packaging of acidic liquid foods with a pH value ≤ 4.5, including fruit juice, carbonated beverages, and fermented dairy products; the packaging material reduces the exposure of microplastics in the food by ≥ 80% during the shelf life and provides real-time safety early warning.

[0032] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0033] The present invention provides a smart food packaging material with dual functions of microplastic adsorption and early warning, which significantly reduces the risk of microplastic exposure: in the accelerated test of simulated gastric juice (pH 1.2, 37℃), the packaging material reduced the concentration of microplastics in acidic food from 45±8μg / L to 8±2μg / L, a reduction of 82%, and no adsorption saturation was observed for 120 hours.

[0034] Real-time risk visualization: Consumers can obtain microplastic concentration data within 5 seconds by scanning with their smartphones, which is 4 orders of magnitude faster than traditional offline testing (6-48 hours).

[0035] Providing clear safety boundaries: The FRET color conversion mechanism allows even non-professional users to intuitively judge whether food is safe and avoid accidental ingestion of excessive microplastics.

[0036] Extended packaging safety window: Dynamic adsorption capacity ensures the packaging maintains efficient interception throughout its shelf life, while the APP warning system ensures consumers are reminded to finish consuming the product before the adsorption layer becomes saturated.

[0037] Blocking the risk of co-contamination: The outer barrier design prevents the infiltration of microplastics (which account for 30% of pollution contribution in the literature) from the environment, avoiding superposition with endogenous release.

[0038] Environmental and social value: By reducing microplastic intake, the risk associated with neurodegenerative diseases and immune disorders can be lowered (Balistrerietal., 2025), which aligns with the Healthy China initiative. Detailed Implementation

[0039] The present invention will be further described below with reference to specific embodiments. It should be noted that, without conflict, the embodiments or technical features described below can be arbitrarily combined to form new embodiments.

[0040] A three-layer intelligent food packaging material that is laminated from the inside out:

[0041] Inner layer (food contact layer): Chitosan nanofiber modified PE adsorption layer composition: Chitosan nanofibers are uniformly dispersed in the PE matrix to form a three-dimensional network structure.

[0042] Key technical parameters: Chitosan molecular weight: 50-100kDa, degree of deacetylation ≥85%;

[0043] Nanofibers with diameters of 50-200 nm are prepared by electrospinning followed by high-speed shearing and fragmentation.

[0044] Addition amount: 5-15wt%, dispersed by melt blending;

[0045] Surface amino density: ≥2.5 mmol / g (determined by ninhydrin colorimetric method);

[0046] Layer thickness: 50-100μm.

[0047] Mechanism of action: In acidic foods with pH < 4.5, chitosan undergoes amino protonation (-NH3). + ), and the negatively charged groups (-COO) generated by oxidation on the surface of PE microplastics. - It generates strong electrostatic adsorption (adsorption energy > -50 kJ / mol). The three-dimensional network structure produces a "near-field capture" effect, with a capture efficiency of ≥70% for particles of 200 nm-5 μm, so that microplastics are captured within a range of <10 μm from the surface at the moment of release, and cannot enter the food body (determined according to GB 31604.1-2015 method).

[0048] Middle layer (sensing layer): Composition scheme A (no heavy metals): Carbon quantum dots (CQDs) - nanobody complex

[0049] CQDs: Synthesized via hydrothermal method, particle size 3-5 nm, fluorescence emission 520±10 nm, quantum yield ≥60%.

[0050] Surface carboxylation modification, coupled with anti-PE-scFv antibody via EDC / NHS

[0051] Composition Option B (Double Insurance): Mesoporous Silicon Coated with Carbon Quantum Dots (MCM-41@CQDs)

[0052] MCM-41 mesoporous silicon coating has a thickness of 30-60 nm and a pore size of 2-3 nm.

[0053] After coating, the particle size is 100-200 nm, and the antibody is coupled to the outer surface of the mesoporous silica.

[0054] Regulatory compliance: MCM-41 is E551 approved by GB 9685-2016, and the encapsulation ensures zero migration of CQDs.

[0055] Key technical parameters: Quantum dots: Aqueous phase synthesis, particle size 3-8nm, quantum yield ≥80%, surface carboxylation modification;

[0056] Antibody: Single-chain variable region fragment (scFv), molecular weight 15-20 kDa, affinity for PE microplastics KD < 10 -9 M;

[0057] Coupling density: 2-4 antibody molecules are linked per quantum dot;

[0058] Fluorescence emission: green quantum dots 520±10nm, red quantum dots 620±10nm;

[0059] Layer thickness: 10-20μm;

[0060] Mechanism of action: After penetrating the inner layer, microplastic particles are captured by the antibody, forming a ternary complex of "quantum dot-antibody-microplastic". At a concentration <28 μg / L, green quantum dots dominate the emission; at a concentration ≥28 μg / L, the quantum dot spacing is shortened to the FRET interaction distance (<8 nm), the energy transfer efficiency is >90%, and the fluorescence color changes from green to red, achieving threshold visualization and early warning.

[0061] Outer layer (barrier layer) – PE / EVOH blend high barrier layer composition: PE and ethylene-vinyl alcohol (EVOH) are co-extruded in multiple layers to form a nano-layered structure.

[0062] Key technical parameters: EVOH content: 20-30 wt%, ethylene content: 29-44 mol%

[0063] Layered structure: Layer thickness ≤100nm and number of layers >50 are achieved by controlling the shear rate;

[0064] Oxygen permeability: <0.5 cm³·mm / (m²·day·atm);

[0065] Barrier efficiency: ≥95% barrier efficiency against external microplastic particles (measured by ASTM D6701 method); Layer thickness: 30-50 μm4;

[0066] Hardware: The intelligent monitoring system consists of mid-layer fluorescence signal, smartphone spectral acquisition module (camera + LED excitation light source), and APP data analysis module.

[0067] APP algorithm: The concentration of microplastics is calculated by converting the intensity of RGB channels. The detection range is 0.1-1000μg / L, and the detection error is ≤±15%.

[0068] Threshold warning: Built-in EFSA safety threshold database, automatically pushes "food unsafe" warning and recommended consumption time limit when the concentration is ≥28μg / L.

[0069] Example 1: Preparation of Smart Packaging Materials

[0070] Step 1: Preparation of the inner layer (chitosan nanofiber modified PE layer)

[0071] Preparation of chitosan nanofibers:

[0072] 5g of chitosan (85% deacetylation, 70kDa) was dissolved in 100mL of 1% acetic acid solution to prepare a 5wt% solution. Nanofiber membranes were prepared using an electrospinning apparatus with an average fiber diameter of 120nm. The electrospinning parameters were: voltage 20kV, flow rate 0.5mL / h, receiving distance 15cm, and ambient humidity 45%.

[0073] After freezing the nanofiber membrane in liquid nitrogen, it was broken into short fibers (50-200 μm in length) using a high-speed shearing machine (20,000 rpm).

[0074] Melt blending:

[0075] The broken chitosan nanofibers were mixed with PE resin (melt index MI = 2 g / 10 min, density 0.92 g / cm³). 3 Premix the ingredients at a mass ratio of 10:90 and add them to a twin-screw extruder (screw diameter 35mm, L / D=40). Set the processing parameters as follows: Zone 1 130℃, Zone 2 145℃, Zone 3 150℃, screw speed 150rpm, melt blend for 10 minutes.

[0076] Casting

[0077] After the blend is passed through a melt filter (200 mesh), it is cast through a T-die and cooled at 25°C to obtain an inner film with a thickness of 80 μm.

[0078] Step 2: Preparation of the middle layer (food-grade fluorescent sensing layer)

[0079] Option A: Direct coupling of carbon quantum dots

[0080] Hydrothermal Synthesis of Carbon Quantum Dots

[0081] 2 g citric acid + 1 g urea → 20 mL aqueous solution → hydrothermal at 180℃ for 8 h → dialysis purification.

[0082] TEM characterization: Particle size 4.2 ± 0.5 nm, lattice spacing 0.21 nm (graphite carbon).

[0083] Fluorescence spectrum: λ_em = 525 nm, quantum yield 68% (relative to Rhodamine 6G).

[0084] Antibody conjugate

[0085] Quantum dot solution (10 mg / mL) 5 mL + EDC (20 mM) + NHS (8 mM), activated at room temperature for 30 min.

[0086] Add anti-PE-scFv antibody (KD=5×10) -10 M) 15 mg, react at 4℃ for 2 h.

[0087] Ultrafiltration purification (MWCO 50 kDa), coupling rate >90% (BCA method determination).

[0088] Coating

[0089] The coupling agent was diluted to 0.5 mg / mL and coated using a microgravure coating (200 LPI anilox roller, linear speed 8 m / min).

[0090] Dry at 80℃ for 12 minutes, with a middle layer thickness of 12 μm.

[0091] Option B: Mesoporous silicon coated with carbon quantum dots (MCM-41@CQDs)

[0092] Coating synthesis

[0093] CTAB 1 g + 50 mL water → Dissolve and then add 5 mL of CQDs solution (10 mg / mL) → Stir for 30 min.

[0094] Add 2 mL of TEOS and adjust the pH to 10 with ammonia water → react at 40℃ for 12 h.

[0095] Template removal by reflux of ethanol / hydrochloric acid (10:1) for 24 h → MCM-41@CQDs, particle size 125±15 nm, pore volume 0.85 cm³ 3 / g.

[0096] Antibody conjugate

[0097] MCM-41@CQDs (5 mg / mL) 10 mL + antibody 20 mg + EDC / NHS, shake at 4℃ for 4 h.

[0098] The silanol groups on the surface of mesoporous silica form Si-ON bonds with the amino groups of the antibody, making it more stable.

[0099] The conjugation rate is >85%, and the loading capacity is 0.15 mg antibody / mg vector.

[0100] Coating

[0101] The coupling agent was diluted to 0.5 mg / mL and coated using a microgravure coating (200 LPI anilox roller, linear speed 8 m / min).

[0102] Dry at 80℃ for 12 minutes, with a middle layer thickness of 12 μm.

[0103] Step 3: Preparation of the outer layer (PE / EVOH blend barrier layer)

[0104] PE resin and EVOH resin (ethylene content 32 mol%) were mixed at a mass ratio of 75:25 and added to a multilayer co-extrusion device. By adjusting the melt temperature (180-200℃) and the layer multiplier (multiplication times n=5), a 64-layer alternating layered structure was formed, with a single layer thickness of approximately 80 nm.

[0105] An outer film with a thickness of 40 μm was prepared by blow molding (blow-up ratio 2.5, traction speed 20 m / min).

[0106] Step 4: Three-layer composite

[0107] The inner / middle layer composite film was laminated with the outer thin film in a hot press. Parameters: temperature 150℃, pressure 8MPa, time 45 seconds. The resulting three-layer structure has a total thickness of 135μm and an interlayer peel strength of 6.2N / 15mm (ASTM F904).

[0108] Example 2: Calibration of Intelligent Monitoring System

[0109] Establishing the standard curve:

[0110] Preparation of PE microplastic standard suspension: PE powder (particle size 500nm) was dispersed in pH 3.0 citrate buffer at concentration gradients of 0.1, 1, 10, 50, 100, 500, 1000 μg / L.

[0111] A standard suspension was dropped onto the surface of the middle layer of the material and scanned in a dark box using a smartphone (iPhone 14 Pro). The LED excitation light source had a wavelength of 365nm, and the camera captured the fluorescence image.

[0112] The RGB channel intensities were extracted using ImageJ software, and a standard curve was established between the green / red fluorescence intensity ratio (G / R) and the microplastic concentration: G / R = 2.84 - 0.92logC(R 2 =0.97), detection limit 0.08 μg / L.

[0113] Threshold calibration:

[0114] When C=28 μg / L, G / R=1.0, at which point the red fluorescence intensity first exceeds that of green, and the visual perception of color changes from green to red. This threshold corresponds to the provisional tolerable daily intake (TDI) assessed by EFSA based on neurotoxicity data (Balistreri, CR, Magro, D., & Jadavji, NM (2025). Insights into the toxic effects of micro-nano-plastics on the human brain and their relationship with the onset of neurological diseases: A narrative review. Ageing Res Rev, 111, 102836.doi:10.1016 / j.arr.2025.102836).

[0115] Example 3: Performance Testing

[0116] Microplastic interception efficiency test:

[0117] Simulated gastric juice migration experiment:

[0118] The packaging material from Example 1 was prepared into 50 mL bags and filled with citrate buffer solution at pH 1.2. The bags were stored at 37°C, and samples were taken at 6, 12, 24, 48, and 120 hours. After digestion with nitric acid, the microplastic particles were counted using flow cytometry (FACS).

[0119] Results: After 120 hours, the concentration of microplastics on the food side was 8.2±1.6μg / L, with an interception efficiency of 82% and no adsorption saturation was observed.

[0120] FRET warning response time test:

[0121] The packaging material from Example 1 was brought into contact with a 100 μg / L microplastic suspension, and fluorescence changes were recorded using a high-speed fluorescence spectrometer (sampling frequency 100 Hz).

[0122] Results: It takes 23 seconds from contact to color switching (G / R=1.0), which is faster than the typical opening time for consumers.

[0123] Outer barrier properties test:

[0124] According to ASTM D6701, when 1000 particles / mL of microplastic aerosol (particle size 1μm) is applied to the outside of the packaging, the amount detected on the inside after 48 hours is <5 particles / mL, and the barrier rate is >95%.

[0125] Example 4: Practical Application Verification

[0126] Juice packaging applications:

[0127] The material of this invention is made into 250mL juice packaging bags, filled with pH3.5 orange juice, and stored at room temperature for 30 days.

[0128] APP monitoring: Users scan weekly. In the first week, it showed 12μg / L (green and safe), in the third week it rose to 19μg / L (green), and in the fourth week it reached 31μg / L (red warning).

[0129] Consumer behavior: 80% of users finished drinking the product within 24 hours of receiving a red warning to avoid risky intake.

[0130] Control group: The microplastic concentration in traditional PE packaging bags reached 45 μg / L in the 4th week without any warning, and consumers continued to drink the product.

[0131] The above embodiments are merely preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-substantial changes and substitutions made by those skilled in the art based on the present invention shall fall within the scope of protection claimed by the present invention.

[0132] This degradation reaction can be studied by direct pyrolysis mass spectrometry with negative chemical ionization (NCI), and the results show that cyclic oligomers are the main pyrolysis products of PET and PBT.

Claims

1. A smart food packaging material with dual functions of microplastic adsorption and early warning, characterized in that, It includes an inner layer, a middle layer, and an outer layer, which are layered sequentially from the inside out: The inner layer is a chitosan nanofiber modified polyethylene food contact layer, wherein the chitosan nanofiber forms a three-dimensional network structure in the polyethylene matrix, which is used to release and migrate microplastic particles from the packaging material into the acidic food through electrostatic adsorption of positively charged amino groups. The middle layer is a food-grade fluorescent sensing layer containing carbon quantum dot-labeled anti-polyethylene nanobodies, or carbon quantum dot-labeled anti-polyethylene nanobodies coated with mesoporous silica, used to specifically recognize microplastic particles and generate fluorescent signals. The outer layer (3) is a polyethylene / ethylene-vinyl alcohol blend barrier layer with a nano-layered dispersion structure.

2. The intelligent food packaging material with dual functions of microplastic adsorption and early warning as described in claim 1, characterized in that, The chitosan nanofibers in the inner layer have a diameter of 50-200 nm, are added at 5-15 wt% of the polyethylene matrix, have a surface amino density ≥2.5 mmol / g, and have a capture efficiency of ≥70% for microplastic particles with a particle size of 200 nm-5 μm in acidic foods with pH <4.

5. This efficiency is determined according to the method of GB 31604.1-2015.

3. The intelligent food packaging material with dual functions of microplastic adsorption and early warning as described in claim 1, characterized in that, The carbon quantum dots in the middle layer are hydrothermally synthesized from citric acid and urea, with a particle size of 3-5 nm, a fluorescence emission wavelength of 520±10 nm, a quantum yield of ≥60%, and a surface modified with carboxyl functional groups through oxidation treatment, with a carboxyl density of ≥0.8 mmol / g; the anti-polyethylene nanobody is a single-chain variable region fragment with a molecular weight of 15-20 kDa, which is connected to the quantum dots through EDC / NHS chemical coupling.

4. The intelligent food packaging material with dual functions of microplastic adsorption and early warning as described in claim 3, characterized in that, The mesoporous silica in the middle layer has an MCM-41 structure, a coating layer thickness of 30-60 nm, and a particle size of 100-200 nm after coating. The antibody is coupled to the outer surface of the mesoporous silica. The mesoporous silica conforms to E551 of GB 9685-2016.

5. The intelligent food packaging material with dual functions of microplastic adsorption and early warning as described in claim 1, characterized in that, The middle layer implements threshold warning through one of the following two mechanisms: Option A: Fluorescence intensity decay mechanism, when the microplastic concentration is ≥28 μg / L, the fluorescence signal intensity decreases by >50%; Option B: A fluorescence resonance energy transfer color conversion mechanism, comprising green carbon quantum dots and red carbon quantum dots, wherein the fluorescence emission wavelength of the green carbon quantum dots is 520±10nm and the fluorescence emission wavelength of the red carbon quantum dots is 620±10nm, and the fluorescence color significantly changes from green to red when the microplastic concentration is ≥28 μg / L.

6. The intelligent food packaging material with dual functions of microplastic adsorption and early warning as described in claim 1, characterized in that, The outer layer contains 20-30 wt% ethylene-vinyl alcohol and is formed by multi-layer co-extrusion to create a nano-layered structure of ≥50 layers with a single layer thickness of ≤100 nm, achieving a barrier rate of ≥95% against external microplastic particles.

7. The intelligent food packaging material with dual functions of microplastic adsorption and early warning as described in claim 6, characterized in that, It also includes an intelligent monitoring system, which consists of: Fluorescence signal of quantum dots in the middle layer; Smartphone spectral acquisition module; The components of the APP data analysis module; The APP calculates microplastic concentration by converting RGB channel intensity, with a detection range of 0.1-1000μg / L, a detection error of ≤±15%, and a response time of <30 seconds.

8. The intelligent food packaging material with dual functions of microplastic adsorption and early warning as described in claim 1, characterized in that, The app has a built-in EFSA safety threshold database. When the microplastic concentration exceeds the safety threshold of 28 μg / L, it will automatically push a "food unsafe" warning and a recommended consumption period.

9. A method for preparing a smart food packaging material with dual functions of microplastic adsorption and early warning, as described in any one of claims 1-8, characterized in that, Includes the following steps: S1. Inner layer preparation: Chitosan is dissolved in 1% acetic acid solution, and nanofiber membrane is prepared by electrospinning. After being frozen and crushed by liquid nitrogen, it is melt-blended with polyethylene resin at a temperature of 130-150℃ and formed by blow molding or casting. S2. Preparation of the middle layer: Option A: Synthesize carbon quantum dots by hydrothermal method, carboxylate the surface, and then couple anti-polyethylene nanobodies with EDC / NHS. The quantum dot-antibody complex is uniformly coated on the inner layer surface by microgravure. Option B: Synthesize mesoporous silica to coat carbon quantum dots, and then couple antibodies. The coating process is the same. A sensing layer with a thickness of 10-20 μm is formed. S3. Outer layer preparation: Polyethylene and ethylene-vinyl alcohol resin are compounded on the outer side of the middle layer through multi-layer co-extrusion technology. The co-extrusion temperature is 180-200℃. The layered structure is achieved by controlling the shear rate. S4. Interlayer composite: The hot-press composite process is adopted, with a pressure of 5-10MPa, a temperature of 140-160℃, and a time of 30-60 seconds, to ensure that the interfacial bonding strength between the three layers is ≥5N / 15mm.

10. The application of a smart food packaging material with dual functions of microplastic adsorption and early warning as described in any one of claims 1-8 in the packaging of acidic liquid foods, characterized in that, The acidic liquid food has a pH value ≤ 4.5, including fruit juice, carbonated beverages, and fermented dairy products; the packaging material reduces the exposure of microplastics in the food by ≥ 80% during the shelf life, provides real-time safety warnings, and all material components comply with food contact material regulations.