A liquid metal assisted laser-induced graphene based paper electrode and a preparation method thereof

Abstract

The application discloses a paper-based electrode based on liquid metal assisted laser-induced graphene and a preparation method thereof, which comprises a substrate layer, a functional layer, a conductive layer and a hydrophobic layer arranged in sequence, the substrate layer is paper, the functional layer is formed by coating liquid metal nanoparticles, the conductive layer is an electrode formed by laser-induced graphene technology, and the hydrophobic layer is a fluid control area formed by wax packaging. The application combines liquid metal with laser-induced graphene technology, performs surface modification through eutectic gallium indium (EGaIn), polyimide (PI) and N-methyl pyrrolidone (NMP) composite slurry, and then forms a conductive electrode pattern on the paper-based surface by using laser-induced graphene (LIG) technology. The method has the advantages of simple preparation, low cost and environmental friendliness, and the prepared paper-based electrochemical biosensor has excellent conductive performance, mechanical flexibility and electrochemical activity.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of flexible electronics and biosensor technology, and particularly relates to a liquid metal assisted laser induced graphene based paper electrode, a biosensor comprising the electrode and a preparation method thereof. BACKGROUND

[0002] A biosensor is a device that combines a biological recognition element and a signal transducer, capable of converting information about specific biological molecules or cellular activities into measurable signals. Its main components include biological sensitive elements (such as enzymes, antibodies, nucleic acids, etc.) and signal transducers (such as electrochemical, spectral, etc. technology). The role of the biological sensitive element is to identify the target substance, mainly including biological substances such as antibodies, enzymes, nucleic acids, cells, etc.; also including some synthetic substances similar to biological substances, such as aptamers (Aptamer), peptides (Peptide), molecularly imprinted polymers (molecularly imprinted polymers). The role of the signal conversion device is to convert the interaction between the biological sensitive element and the target molecule into different signals. For example, enzymes catalyze specific substances to undergo chemical reactions and convert into electrical signals; biological antibodies capture specific antigens and then convert into optical signals through labeled fluorescence.

[0003] Paper-based biosensors have great potential in the field of point-of-care testing due to their low cost, easy handling, and good biocompatibility. However, traditional paper-based biosensors have limitations in sensitivity, conductivity, and mechanical strength, which restrict their application in high-precision biomarker detection. Laser induced graphene (LIG) technology is an emerging method for preparing carbon materials, which can directly form a porous three-dimensional graphene structure on the surface of a carbon-based precursor. It has high specific surface area, excellent electrical conductivity, and good electrochemical activity. LIG electrodes on cellulose paper are expected to realize low-cost, wearable electronic products. However, the surface of traditional LIG cellulose paper-based biosensors lacks aromatic carbon structures, has low graphitization efficiency, limited electrochemical performance, poor mechanical strength, is prone to delamination when bent, and has low chemical reagent resistance, which limits their practical application. SUMMARY

[0004] The present application provides a liquid metal assisted laser induced graphene based paper electrode, which aims to solve the above technical problems.

[0005] The application provides a paper-based electrode based on liquid metal assisted laser-induced graphene, which comprises a substrate layer, a functional layer, a conductive layer and a hydrophobic layer arranged in sequence, the substrate layer is paper, the functional layer is formed by coating liquid metal nanoparticles, the conductive layer is an electrode formed by laser-induced graphene technology, and the hydrophobic layer is a fluid control area formed by wax packaging.

[0006] Further, the paper-based electrode further comprises a functional layer formed by modifying the electrode with a functional material.

[0007] Further, the liquid metal nanoparticles are EGaIn-PI-NMP composite slurry.

[0008] Further, the substrate layer is cellulose paper treated by flame retardant treatment.

[0009] Further, the flame retardant treatment adopts 9-11% ammonium polyphosphate flame retardant.

[0010] Further, the functional material is gold nanoparticles.

[0011] The application further provides a biosensor comprising the paper-based electrode.

[0012] The application further provides a preparation method of the paper-based electrode based on liquid metal assisted laser-induced graphene, which comprises the following steps:

[0013] S1. preparing EGaIn-PI-NMP composite slurry;

[0014] S2. pretreating the substrate layer;

[0015] S3. performing hydrophobic treatment;

[0016] S4. preparing the electrode by laser-induced graphene technology;

[0017] S5. modifying the electrode by functionalization.

[0018] Further, the specific operation of step S1 is as follows:

[0019] a. soaking eutectic gallium indium in 0.45-0.55 M HCl overnight to remove the oxide layer;

[0020] b. dissolving polyimide powder in N-methyl pyrrolidone, and the mass fraction of PI is 12.5-17.5% (W / V) to prepare a PI-NMP solution;

[0021] c. The treated EGaIn is added into the PI-NMP solution, and an ultrasonic cell disruptor is used to perform ice-bath ultrasonic treatment for 80-100 minutes to prepare an EGaIn-PI-NMP composite slurry.

[0022] Further, the working frequency of the ultrasonic treatment is 30%, and the ultrasonic is turned off for 3s and turned on for 2s.

[0023] Further, the specific operation of step S2 is as follows:

[0024] (1) 9-11% wt% ammonium polyphosphate flame retardant is uniformly coated on the surface of the substrate layer, and is dried at 33-40 DEG C;

[0025] (2) The EGaIn-PI-NMP composite slurry is coated on the surface of the flame-retardant treated substrate layer, and is coated repeatedly for more than twice;

[0026] Further, the specific operation of step S3 is as follows: wax sealing treatment is performed by using a wax printer, and the wax is fully penetrated by heating at 72-88 DEG C for 27-33 minutes.

[0027] Further, the specific operation of step S4 is as follows:

[0028] I. An electrode pattern is laser etched on the surface of the pretreated and hydrophobic treated substrate layer by using a CO2 laser;

[0029] II. Silver paste is coated on the surface of the reference electrode, and is dried at 33-40 DEG C.

[0030] Further, the power of the CO2 laser in step I is 3.1%, and the speed is 10 mm / s.

[0031] Further, the specific operation of step S5 is as follows: gold nanoparticle solution is dropped on the surface of the working electrode, and is dried and solidified.

[0032] Further, the gold nanoparticles are prepared by using citric acid reduction method.

[0033] Compared with the prior art, the present application has the following beneficial effects:

[0034] This invention provides a paper-based electrode based on liquid metal-assisted laser-induced graphene and its preparation method. The electrode uses paper as a substrate, combining liquid metal with laser-induced graphene technology. Surface modification is achieved using a composite slurry of eutectic gallium indium (EGaIn), polyimide (PI), and N-methylpyrrolidone (NMP), followed by the formation of conductive electrode patterns on the paper surface using laser-induced graphene (LIG) technology. This method offers advantages such as simple preparation, low cost, and environmental friendliness. The prepared paper-based electrochemical biosensor exhibits excellent conductivity, mechanical flexibility, and electrochemical activity, high mechanical strength, and is not prone to delamination during bending. It also demonstrates high tolerance to chemical reagents. Furthermore, its surface can be modified with different biorecognition molecules to achieve biosensing, enabling the immediate detection of various biomarkers such as proteins (e.g., inflammatory factors (IL-6)), salivary glucose, and pathogens (viruses or bacteria). This provides a new technological pathway for portable diagnostics and new technical means for point-of-care testing, telemedicine, and wearable personal health monitoring, possessing broad application prospects and market value. Specifically:

[0035] (1) Significantly improves mechanical properties: Toughness is increased by more than 100% compared to paper, and tensile strength reaches 11-12 N / mm²;

[0036] (2) Excellent electrical conductivity: The charge transfer resistance of the composite material is significantly reduced, and its electrical conductivity is excellent;

[0037] (3) Good stability: It retains its appearance intact after being soaked in acidic, alkaline and neutral solutions for 72 hours;

[0038] (4) Environmentally friendly and sustainable: Using paper as a base material is in line with the concept of green manufacturing;

[0039] (5) Simple fabrication process: one-step laser etching, no need for complex photolithography process;

[0040] (6) Low cost: Low raw material cost, suitable for large-scale production;

[0041] (7) Good batch reproducibility: the standard deviation of electrochemical parameters is less than 10%. Attached Figure Description

[0042] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0043] Figure 1 Macroscopic morphology of the original cellulose paper prepared in Example 1;

[0044] Figure 2 Macro-morphology of the multi-working electrode paper base;

[0045] Figure 3 Micro-morphology of the cellulose paper prepared for Comparative Example 1, wherein a is a micro-morphology with a scale of 200 μm, and b is a micro-morphology with a scale of 5 μm;

[0046] Figure 4 Micro-morphology of the original cellulose paper prepared for Example 1, wherein a is a micro-morphology with a scale of 200 μm, and b is a micro-morphology with a scale of 5 μm;

[0047] Figure 5 Stability test result graph of the original cellulose paper sample prepared for Example 1 and the modified cellulose paper sample prepared for Example 2;

[0048] Figure 6 Effective area of the paper base electrode;

[0049] Figure 7 Batch difference comparison result of the paper base electrode;

[0050] Figure 8 Stability test of the paper base electrode;

[0051] Figure 9 Comparison result before and after nano-modification of the paper base electrode;

[0052] Figure 10 Detection of biomarkers by using the paper base electrode. DETAILED DESCRIPTION

[0053] In order to make the technical problems to be solved by the present application, technical solutions and beneficial effects more clearly understood, the present application will be further described in detail below in combination with embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application. The present application will be specifically introduced below in combination with specific embodiments.

[0054] The paper base electrode based on liquid metal assisted laser-induced graphene provided by the embodiment of the present application comprises a substrate layer, a functional layer, a conductive layer and a hydrophobic layer arranged in sequence, the substrate layer is paper, the functional layer is formed by coating liquid metal nanoparticles, the conductive layer is an electrode formed by laser-induced graphene technology, and the hydrophobic layer is a fluid control area formed by wax packaging.

[0055] Specifically, the functional layer is formed by modifying the electrode with a functional material.

[0056] Specifically, the liquid metal nanoparticles are EGaIn-PI-NMP composite slurry, liquid metal, especially eutectic gallium-indium alloy, which has unique properties such as liquid at room temperature, high conductivity (3.4*10 6 S / m), good biocompatibility, etc. At present, there is still a lack of paper-based sensor preparation method effectively combining the advantages of liquid metal and laser-induced graphene in the prior art, especially a lack of systematic research in optimizing material ratio, laser parameters and surface modification.

[0057] Specifically, the base layer can be different types of paper, preferably the base layer is cellulose paper treated by flame retardant treatment, which has the advantage of biodegradability.

[0058] Specifically, the flame retardant treatment uses 9-11% ammonium polyphosphate flame retardant (APP flame retardant), preferably 10% ammonium polyphosphate flame retardant.

[0059] Specifically, the functional material is gold nanoparticles, and other functional materials such as single-walled carbon nanotubes, all carbon nanomaterials, all metal nanoparticles or other conductive materials, surface anti-fouling agents, etc. can also be selected.

[0060] The embodiment of the present application also provides a preparation method of the paper-based electrode based on liquid metal assisted laser-induced graphene as described above, comprising the following steps:

[0061] S1. Preparing EGaIn-PI-NMP composite slurry;

[0062] S2. Pre-treating the base layer;

[0063] S3. Hydrophobic treatment;

[0064] S4. Preparing the electrode by laser-induced graphene technology;

[0065] S5. Functional modification of the electrode.

[0066] Specifically, the specific operation of step S1 is:

[0067] a. Soaking the eutectic gallium-indium in 0.45-0.55M HCl overnight to remove the oxide layer;

[0068] b. Dissolving polyimide powder in N-methyl pyrrolidone, the mass fraction of the polyimide is 12.5-17.5% (W / V), to prepare a PI-NMP solution;

[0069] c. Adding the treated eutectic gallium-indium into the PI-NMP solution, using an ultrasonic cell disruptor, ice-bath ultrasonic treatment for 80-100 minutes, to prepare the EGaIn-PI-NMP composite slurry.

[0070] Preferably, the specific operation of step S1 is:

[0071] a. Soak the eutectic gallium indium in 0.5M HCl overnight to remove the oxide layer;

[0072] b. Dissolve the polyimide powder in N-methyl pyrrolidone to obtain a PI-NMP solution, the mass fraction of the polyimide being 15% (W / V);

[0073] c. Add the treated eutectic gallium indium to the PI-NMP solution, and use an ultrasonic cell disruptor to perform ice-bath ultrasonic treatment for 90 minutes to obtain an EGaIn-PI-NMP composite slurry.

[0074] The inventors have optimized the concentration of EGaIn, and determined that the optimal concentration is 6% through dynamic light scattering analysis, at which the particle size distribution is uniform (200-400 nm) and the electrochemical performance is optimal. The concentration of PI has also been optimized, and it is found that the optimal PI concentration is 15%, at which the material has good film-forming property and electrochemical activity, while maintaining appropriate mechanical strength. The ultrasonic time has also been optimized, and it is found that an ultrasonic time of 90 minutes can obtain the best particle dispersion effect and electrochemical performance.

[0075] Specifically, the working frequency of the ultrasonic treatment is 30%, and the ultrasonic off time is 3s and the ultrasonic on time is 2s.

[0076] Specifically, the specific operation of step S2 is:

[0077] (1) Uniformly coat 9-11% wt% ammonium polyphosphate flame retardant on the surface of the substrate layer, and dry at 33-40℃;

[0078] (2) Coat the EGaIn-PI-NMP composite slurry on the surface of the flame-retardant treated substrate layer, and repeat the coating more than twice.

[0079] Preferably, the specific operation of step S2 is:

[0080] (1) Uniformly coat 10% wt% ammonium polyphosphate flame retardant on the surface of the substrate layer, and dry at 37℃;

[0081] (2) Coat the EGaIn-PI-NMP composite slurry on the surface of the flame-retardant treated substrate layer, and repeat the coating twice.

[0082] Specifically, the specific operation of step S3 is: use a wax printer for wax sealing treatment, and heat at 72-88℃ for 27-33 minutes to allow the wax to fully penetrate.

[0083] Preferably, the specific operation of step S3 is that wax printing is used for wax sealing treatment, and the wax is fully penetrated by heating at 80℃ for 30 minutes.

[0084] Specifically, the specific operation of step S4 is that:

[0085] I. using a CO2 laser to laser etch an electrode pattern on the surface of the pretreated and hydrophobic treated substrate layer;

[0086] II. coating silver paste at the reference electrode position, and drying at 33-40℃, preferably 37℃.

[0087] Specifically, the power of the CO2 laser in step I is 3.1%, and the speed is 10 mm / s.

[0088] Among them, the inventors optimize the laser parameters, and determine the optimal parameters as power 3.1% and speed 10 mm / s by systematically studying the influence of laser power (2.2-3.4%) and scanning speed (5-50 mm / s) on resistance.

[0089] Specifically, the specific operation of step S5 is that gold nanoparticle solution is dropped on the surface of the working electrode, and dried and solidified.

[0090] Specifically, 10 μL of gold nanoparticle solution is dropped on the surface of the working electrode.

[0091] Specifically, the gold nanoparticles are prepared by citric acid reduction method, and the specific steps are as follows: 0.5 mM HAuCl4 solution is heated to boiling; 1% sodium citrate solution is quickly added, and boiling is continued for 30-40 minutes; the solution color changes from light yellow to dark red, indicating that gold nanoparticles are formed.

[0092] The embodiment of the application also provides a biosensor comprising the paper-based electrode.

[0093] The embodiment of the application also provides the application of the paper-based electrode or the biosensor as described above in biomarker detection.

[0094] Specifically, the biomarker is an inflammatory factor, salivary glucose or a pathogen.

[0095] Specifically, the inflammatory factor is interleukin-6 (IL-6).

[0096] Specifically, the pathogen is a virus or a bacterium.

[0097] The following will be described in combination with specific embodiments:

[0098] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, etc. used in the following examples can be obtained commercially unless otherwise specified. Techniques not described in detail are performed according to standard methods well known to those skilled in the art.

[0099] Example 1 Preparation of basic electrode

[0100] 1. Material preparation

[0101] Whatman 3MM chromatographic filter paper (a kind of cellulose paper) was selected as the base layer, and a eutectic gallium-indium alloy with a purity of 99.99%, a thermosetting polyimide resin powder, N-methyl pyrrolidone (analytical pure), and an ammonium polyphosphate flame retardant were prepared.

[0102] 2. The basic electrode was prepared according to the following steps:

[0103] (1) Preparation of composite slurry: 10 μL EGaIn was soaked in 500 mL 0.5M HCl overnight; 300 mg of PI powder was dissolved in 2 mL of NMP, and stirred thoroughly until completely dissolved; after removing the HCl, EGaIn was added to the PI-NMP solution, and ultrasonicated at 30 kHz for 90 minutes under ice bath conditions (2 seconds on, 3 seconds off);

[0104] (2) Paper base treatment: 10% APP suspension was uniformly coated on the surface of the cellulose paper, and dried to complete dryness in a 37°C oven; the EGaIn-PI-NMP slurry was uniformly coated, and repeated coating was performed to ensure sufficient infiltration;

[0105] (3) Hydrophobic treatment: patterned wax sealing was performed using a wax printer, and a heating plate at 80°C was used for heating for 30 minutes to allow the wax to fully penetrate;

[0106] (4) Laser etching (LIG treatment): a 55W CO2 laser was used, with a power of 3.1% and a speed of 10 mm / s, and laser etching was performed according to the preset electrode pattern, silver paste was coated at the reference electrode position, and dried at 37°C.

[0107] Example 2 Preparation of functionalized electrode (modified cellulose paper)

[0108] On the basis of Example 1, electrode functionalization modification was also performed, and the specific steps were as follows:

[0109] (5) 40 nm gold nanoparticles were prepared by citric acid reduction method: 0.5 mM HAuCl4 solution was heated to boiling, 1% sodium citrate solution was quickly added, and boiling was continued for 30-40 minutes. The color of the solution changed from light yellow to deep red, indicating the formation of gold nanoparticles;

[0110] (6) Electrode modification: 10 μL of gold nanoparticle solution was dropped onto the surface of the working electrode and dried and cured in an oven at 37°C for 1 hour.

[0111] Comparative Example 1

[0112] The difference from Example 1 is that step (4) laser etching was not performed.

[0113] Example 3 Characterization Analysis

[0114] To ensure the scanning electron microscope (SEM) imaging quality of the original cellulose paper sample prepared in Example 1 and the cellulose paper sample prepared in Comparative Example 1, the following sample preparation and testing methods were implemented:

[0115] The samples were cut into 5 mm × 5 mm squares using a clean blade and fixed to an aluminum stage using double-sided conductive tape. To suppress charge accumulation during high-vacuum SEM observation, a standard sputtering coating process was used to form a 5 nm to 10 nm thick gold-palladium alloy layer on the sample surface (coating parameters: current 15 mA to 20 mA, duration 60 s to 90 s). Raw cellulose paper samples were briefly rinsed with deionized water and then air-dried to remove surface contaminants; modified cellulose paper samples were cleaned only by nitrogen purging to prevent the surface modification layer from dissolving or peeling off.

[0116] SEM testing conditions were optimized to meet the characterization requirements of cellulose fibers: accelerating voltage 5 kV to 15 kV, working distance 8 mm to 12 mm, and beam size 3 to 4. Morphology analysis was performed using secondary electron (SE) mode, and composition analysis using backscattered electron (BSE) mode. Three levels of magnification were implemented as needed: low magnification (50x to 500x) for overall morphology assessment, and medium magnification (1,000x to 5,000x) for fine surface characterization. For raw samples, fiber morphology, surface texture, and pore structure characteristics were recorded; for modified samples, analysis was supplemented to include coating uniformity, fiber-modified layer interface characteristics, and surface microstructure.

[0117] The results are as follows Figures 1-3 As shown, Figure 1 This is a macroscopic morphological image of the original cellulose paper prepared in Example 1. Figure 2 Macroscopic morphology of a multi-working-electrode paper substrate. Figure 3 The images show the microstructure of the cellulose paper prepared in Comparative Example 1, where a is a microstructure image with a scale bar of 200 μm and b is a microstructure image with a scale bar of 5 μm. Figure 4 The images show the microstructure of the original cellulose paper prepared in Example 1, where a is a microstructure image with a scale bar of 200 μm and b is a microstructure image with a scale bar of 5 μm. Figures 1-2 This method demonstrates that it can produce a variety of fine electrode patterns with clear edges, enabling mass printing.Figure 3 and Figure 4 The study revealed a significant change in the surface structure of the modified cellulose paper after LIG treatment: the surface before LIG treatment exhibited a dense EGaIn-PI-NMP particle composite material. Figure 3 (ab), in which EGaIn nanoparticles are partially encapsulated by a thin film ( Figure 3 (b) After LIG treatment, a multi-scale porous graphene network appeared ( Figure 4 (ab), with pore sizes ranging from nanometers to micrometers. At the 200-micrometer scale ( Figure 4 In the middle (a), the EGaIn particle size significantly increases (up to tens of micrometers) and exhibits a round and full morphology, indicating that aggregation occurred during laser-induced graphene processing. At the 5-micrometer scale ( Figure 4 (b) A well-defined porous structure can be observed. The formation of this multi-level porous structure is closely related to the laser-induced carbonization and graphitization process, which is beneficial to improving the specific surface area, conductivity and electrode flexibility of the material.

[0118] Example 4 Performance Testing

[0119] Acid-base stability test:

[0120] The original cellulose paper sample prepared in Example 1 and the modified cellulose paper sample prepared in Example 2 were immersed in different solutions for 72 hours. Appearance was compared to evaluate material stability. All experiments were conducted at room temperature (22±2°C) in 1.5 mL microcentrifuge tubes, with the samples completely submerged. Results are as follows: Figure 5 As shown in the figure, in the figure, ad represents the original cellulose paper sample being immediately immersed in (a) 0.05M PBS buffer, (b) 1M hydrochloric acid, (c) 1M sodium hydroxide and (d) anhydrous ethanol, where a1-d1 are the results after 0 h of immersion, a2-d2 are the results after 24 h of immersion, a3-d3 are the solvent transparency assessment after 24 h of immersion and material removal, and a4-d4 are the integrity evaluation results of the cellulose paper after 72 h of immersion; eh represents the modified cellulose paper sample being immediately immersed in (e) 0.05 M PBS buffer, (f) 1 M hydrochloric acid, (g) 1 M sodium hydroxide and (h) anhydrous ethanol, where e1-f1 are the results after 0 h of immersion, e2-f2 are the results after 24 h of immersion, e3-f3 are the solvent transparency assessment after 24 h of immersion and material removal, and e4-f4 are the integrity evaluation results of the modified cellulose paper after 72 h of immersion.

[0121] The stability test results show that both the modified and unmodified cellulose paper remained relatively stable in 0.05M PBS solution, 1M hydrochloric acid solution, and ethanol solution. Comparing c1-c4 and g1-g4, the unmodified cellulose paper exhibited significant cellulose hydrolysis in 1M NaOH solution, and the paper no longer maintained its integrity. In contrast, the modified cellulose paper sample showed enhanced stability, showing no dissolution or leaching even after 72 hours of immersion. In conclusion, the modified cellulose paper exhibits improved chemical resistance.

[0122] Electrochemical performance testing:

[0123] 1. Effective Area Determination: The effective area of ​​the electrode was calculated using the Randles-Sevcik equation. Cyclic voltammetry tests were performed at different scan rates. The effective area was determined by the linear relationship between the peak current and the square root of the scan rate. The results are as follows: Figure 6 As shown, a represents the CV curves at different scan rates, and b represents the relationship between scan rate and current. With increasing scan rate, the peak current (both positive and negative) increases significantly, indicating that the system is a diffusion-controlled process. Figure 6 In this context, b represents the peak current (Ip) and the square root of the scan rate (v¹). / The linear relationship between Ip and v¹ is fitted by the equation y = 3.93xr = 0.989, indicating that Ip and v¹ / A high linear correlation exists between the two, further confirming that the reaction is diffusion-controlled. Figure 6 Substitute the information from a and b into the formula to calculate the effective electrode area:

[0124]

[0125]

[0126] The results indicate an increase in the specific surface area of ​​the working electrode. The effective electrode area calculated using this electrochemical method is 0.545 cm². 2 Consistent with SEM characterization results.

[0127] 2. Batch reproducibility test: Five batches of electrodes were prepared, with six electrodes per batch. Electrochemical tests were performed in potassium ferricyanide solution. All scans were performed at 25℃ in an iron / ferrous ferricyanide solution at a rate of 50 mV / s (100 mM potassium chloride as electrolyte). Redox peak currents, peak potential differences, and other parameters were statistically analyzed. Results are shown below. Figure 7Figure 6 shows the CV curves of the prepared electrodes, where a is the average peak oxidation (anodic) and reduction (cathodic) current; b is the peak potential difference (ΔEp) between the peak oxidation and reduction potentials; c is the area between the curves (anodic-cathodic scan); d is the resistance of the LIG printed electrode pattern, and the error bars represent the standard deviation of the arithmetic mean (n = 6 per batch). Figure 7 In a, the results show that the anodic and cathodic peak currents are stabilized at around +0.15 mA and -0.15 mA, respectively, with a standard deviation lower than 0.01 mA. Figure 7 In b, the peak potential difference (ΔEp) ranges from 0.25 to 0.27 V, with a coefficient of variation (CV) lower than 10%, indicating uniform electron transfer kinetics. Figure 7 In c, the error is less than 0.005 V / mA, indicating uniform surface area characteristics. Figure 7 In d, the measured resistance is between 340 and 350 Ω, with a difference between batches lower than 3% (standard deviation < 10 Ω). These results show that the prepared electrodes have good reproducibility, with a CV of all key electrochemical parameters lower than 10%, which is significantly better than traditional electrode manufacturing methods, which typically have a difference between batches of 15-25%. This high consistency is attributed to the uniform EGaIn-PI-NMP coating, precise laser-induced graphene parameter control, and enhanced mechanical stability of the modified paper, laying a solid foundation for scalable production of paper-based electrodes with predictable performance, which can be used for commercial electrochemical sensing applications.

[0128] 3. Stability test: The prepared electrodes were subjected to long-term cyclic voltammetry tests, with the electrodes scanned at a scan rate of 50 mv / s for 30 cycles to evaluate the electrochemical stability. Figure 8 The results show that the CV curves after 30 scans have high consistency, demonstrating that the prepared EGPE has excellent stability, showing that the electrode has good electrochemical reversibility and stability.

[0129] 4. The original cellulose paper sample prepared in Example 1 and the modified cellulose paper sample prepared in Example 2 were scanned in a potassium ferricyanide solution to obtain cyclic voltammetry curves, as shown in Figure 9 From Figure 9 It can be seen that the modified cellulose paper sample shows enhanced current and conductivity, indicating that the prepared electrode can be nano-modified to increase the working performance of the electrode.

[0130] Example 5 Application Example

[0131] The prepared paper-based electrochemical electrode can be used to detect various biomarkers, such as inflammatory factor detection. Specifically, by functionalizing with aptamers, inflammatory markers such as interleukin-6 (IL-6) can be detected, with the specific steps as follows:

[0132] To detect IL-6, the electrochemical aptamer sensor with AuNPs-modified working electrode prepared in Example 2 was used. Before use, the IL-6 aptamer was treated by centrifugation (4000 rpm, 1 min, room temperature) to avoid contamination, diluted with ultrapure water, and reduced with tris(2-carboxyethyl)phosphine (TCEP) for 1 h to a final concentration of 4 μΜ, and stored at -20 °C for later use. During electrode preparation, 10 μL of AuNPs solution was dropped on the surface of the cleaned working electrode and dried; then 4 μL of 4 μΜ aptamer solution was added and incubated at 4 °C overnight to achieve the bonding of thiol groups to AuNPs; 10 μL of mercaptohexanol (MCH) was added and incubated for 1 h to inhibit non-specific binding, and then washed thoroughly with 0.05 M PBS and dried at 37 °C. Different concentrations of IL-6 solution were incubated on the electrode surface for 1 h, and then washed with PBS and measured by differential pulse voltammetry (DPV) in 0.05 M PBS solution, and quantified according to the characteristic redox signal. Figure 9 As shown in FIG. 6, before and after modification of gold nanoparticles on the surface of the working electrode, cyclic voltammetry was performed at a speed of 50 mV / s in a ferrous / ferricyanide solution at 25 °C (100 mM potassium chloride as electrolyte), and it can be seen that the electrochemical signal was significantly enhanced after gold nanoparticle modification. The results of IL-6 detection are shown in FIG. 7, where a is the DPV of the EGPE biosensor interface for measuring IL-6 at different concentrations obtained in 0.05 M PBS (pH = 7.4), and b is the calibration curve of IL-6, a plot of peak current versus IL-6 concentration (error bar = standard deviation; n = 3). Figure 10 As shown in FIG. 6, before and after modification of gold nanoparticles on the surface of the working electrode, cyclic voltammetry was performed at a speed of 50 mV / s in a ferrous / ferricyanide solution at 25 °C (100 mM potassium chloride as electrolyte), and it can be seen that the electrochemical signal was significantly enhanced after gold nanoparticle modification. The results of IL-6 detection are shown in FIG. 7, where a is the DPV of the EGPE biosensor interface for measuring IL-6 at different concentrations obtained in 0.05 M PBS (pH = 7.4), and b is the calibration curve of IL-6, a plot of peak current versus IL-6 concentration (error bar = standard deviation; n = 3). Figure 10 As shown in FIG. 6, before and after modification of gold nanoparticles on the surface of the working electrode, cyclic voltammetry was performed at a speed of 50 mV / s in a ferrous / ferricyanide solution at 25 °C (100 mM potassium chloride as electrolyte), and it can be seen that the electrochemical signal was significantly enhanced after gold nanoparticle modification. The results of IL-6 detection are shown in FIG. 7, where a is the DPV of the EGPE biosensor interface for measuring IL-6 at different concentrations obtained in 0.05 M PBS (pH = 7.4), and b is the calibration curve of IL-6, a plot of peak current versus IL-6 concentration (error bar = standard deviation; n = 3).

[0133] Figure 10The corresponding calibration curve shown in FIG. 6B exhibits excellent linearity with a correlation coefficient r of 0.96. The regression equation is defined as y = 0.019x + 2.51, where y represents the peak current in μΑ and x represents the IL-6 concentration in pg / mL. The slope of 0.019 μΑ / pg / mL reflects the high sensitivity of the sensor, while the limit of detection (LOD) is determined to be 20 pg / mL. This LOD is of clinical significance, as IL-6 levels in saliva typically range from a few pg / mL for healthy individuals to several hundred pg / mL for inflamed patients. The performance of EGPEs is more competitive compared to other electrochemical immunosensors reported in the literature, which can typically achieve LODs of 1 to 50 pg / mL, especially given their suitability for complex saliva matrices. Error bars in the calibration plot indicate that the relative standard deviation (RSD) is generally below 10%, which confirms the reproducibility and precision of the analytical method over the entire concentration range. The dynamic range of the EGPEs platform spans three orders of magnitude (1 to 1000 pg / mL), effectively covering physiologically relevant IL-6 concentrations and is well suited for diagnostic screening and monitoring of inflammatory states.

[0134] The above description is merely that of the preferred embodiments of the application, and is not intended to limit the application. Any modification, equivalent replacement and improvement made without departing from the principle of the application shall be included in the protection scope of the application.

Claims

1. A paper-based electrode based on liquid metal-assisted laser-induced graphene, characterized in that, The material comprises a substrate layer, a functional layer, a conductive layer, and a hydrophobic layer arranged sequentially. The substrate layer is paper, the functional layer is formed by coating with liquid metal nanoparticles, the conductive layer is an electrode formed by laser-induced graphene technology, and the hydrophobic layer is a fluid control region formed by wax encapsulation. The liquid metal nanoparticles are EGaIn-PI-NMP composite slurry, where EGaIn represents eutectic gallium indium, PI represents polyimide, and NMP represents N-methylpyrrolidone.

2. The paper-based electrode based on liquid metal-assisted laser-induced graphene as described in claim 1, characterized in that, It also includes a functionalized layer, which is formed by modifying the electrode with a functional material.

3. The paper-based electrode based on liquid metal-assisted laser-induced graphene as described in claim 2, characterized in that, The base layer is flame-retardant cellulose paper; And / or, the flame retardant treatment uses 9-11% ammonium polyphosphate flame retardant; And / or, the functional material is gold nanoparticles.

4. A biosensor, characterized in that, Including the paper-based electrode based on liquid metal-assisted laser-induced graphene as described in any one of claims 1-3.

5. A method for preparing a paper-based electrode based on liquid metal-assisted laser-induced graphene as described in any one of claims 1-3, characterized in that: Includes the following steps: S1. Preparation of EGaIn-PI-NMP composite slurry; S2. Pre-treat the base layer; S3. Perform hydrophobic treatment; S4. Electrode fabrication using laser-induced graphene technology; S5. Functionalize the electrodes.

6. The preparation method according to claim 5, characterized in that, The specific operation of step S1 is as follows: a. Immerse the eutectic gallium indium in 0.45-0.55M HCl overnight to remove the oxide layer; b. Dissolve polyimide powder in N-methylpyrrolidone, wherein the mass fraction of the polyimide is 12.5-17.5% (W / V), to prepare a PI-NMP solution; c. Add the treated eutectic gallium indium to the PI-NMP solution, and use an ultrasonic cell disruptor to sonicate in an ice bath for 80-100 minutes to prepare EGaIn-PI-NMP composite slurry.

7. The preparation method according to claim 6, characterized in that, The ultrasonic processing operates at a frequency of 30%, with the ultrasonic wave off for 3 seconds and on for 2 seconds.

8. The preparation method according to claim 5, characterized in that, The specific operation of step S2 is as follows: (1) Apply 9-11% wt% ammonium polyphosphate flame retardant evenly to the surface of the base layer and dry at 33-40℃; (2) Apply EGaIn-PI-NMP composite slurry to the surface of the flame-retardant treated substrate layer, and repeat the application more than twice; And / or, the specific operation of step S3 is as follows: use a wax printer to perform wax sealing treatment, heat at 72-88℃ for 27-33 minutes to allow the wax to fully penetrate; And / or, the specific operation of step S4 is as follows: I. Electrode patterns are laser-etched on the surface of a pretreated and hydrophobic substrate using a CO2 laser; II. Coat the reference electrode with silver paste and dry at 33-40℃.

9. The preparation method according to claim 8, characterized in that, In step I, the power of the CO2 laser is 3.1% and the speed is 10 mm / s.

10. The preparation method according to claim 5, characterized in that, The specific operation of step S5 is as follows: add gold nanoparticle solution to the surface of the working electrode and dry and solidify it.

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