Paper-based electrode based on liquid metal-assisted laser-induced graphene and preparation method of paper-based electrode

Abstract

The invention discloses a paper-based electrode based on liquid metal assisted laser-induced graphene and a preparation method thereof.The paper-based electrode comprises a substrate layer, a functional layer, a conductive layer and a hydrophobic layer which are sequentially arranged, the substrate layer is made of paper, the functional layer is formed by coating liquid metal nanoparticles, and the conductive layer is formed by coating liquid metal nanoparticles. The conductive layer is an electrode formed by a laser-induced graphene technology, and the hydrophobic layer is a fluid control area formed by wax packaging. According to the invention, paper is used as a substrate, liquid metal is combined with a laser-induced graphene technology, surface modification is carried out through eutectic gallium indium (EGaIn), polyimide (PI) and N-methyl pyrrolidone (NMP) composite slurry, and then a conductive electrode pattern is formed on the surface of the paper substrate by using a laser-induced graphene (LIG) technology. The method has the advantages of simple preparation, low cost, environmental friendliness and the like, and the prepared paper-based electrochemical biosensor has excellent conductivity, mechanical flexibility and electrochemical activity.

Description

Technical Field

[0001] This invention relates to the fields of flexible electronic devices and biosensors, specifically to a paper-based electrode based on liquid metal-assisted laser-induced graphene, and a biosensor comprising the electrode and its fabrication method. Background Technology

[0002] A biosensor is a device that combines a biosensor element and a signal converter, capable of sensing specific biomolecules or cellular activities and converting this information into measurable signals. Its main components include biosensor elements (such as enzymes, antibodies, and nucleic acids) and signal converters (such as electrochemical and spectroscopic techniques). The role of the biosensor element is to identify target substances, mainly including biological substances such as antibodies, enzymes, nucleic acids, and cells; it also includes some synthetic substances similar to biological substances, such as aptamers, peptides, and molecularly imprinted polymers. The role of the signal converter is to convert the interaction between the biosensor element and the target molecule into different signals. For example, enzymes catalyze specific substances to undergo chemical reactions, converting them into electrical signals; biological antibodies capture specific antigens and then convert them into light signals through labeled fluorescence.

[0003] Paper-based biosensors hold great potential in point-of-care testing due to their low cost, ease of handling, and good biocompatibility. However, traditional paper-based biosensors suffer from limitations in sensitivity, conductivity, and mechanical strength, restricting their application in high-precision biomarker detection. Laser-induced graphene (LIG) technology, as an emerging method for preparing carbon materials, can directly form porous three-dimensional graphene structures on the surface of carbon-based precursors, exhibiting high specific surface area, excellent conductivity, and good electrochemical activity. LIG electrodes on cellulose paper hold promise for enabling low-cost, wearable electronic products. However, traditional LIG cellulose paper-based biosensors suffer from low graphitization efficiency, limited electrochemical performance, poor mechanical strength, easy delamination upon bending, and low tolerance to chemical reagents due to the lack of aromatic carbon structures on their surface. These drawbacks limit their practical applications. Summary of the Invention

[0004] This invention provides a paper-based electrode based on liquid metal-assisted laser-induced graphene, aiming to solve the aforementioned technical problems.

[0005] This invention provides a paper-based electrode based on liquid metal-assisted laser-induced graphene, comprising 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.

[0006] Furthermore, it also includes a functionalized layer, which is formed by modifying the electrode with a functional material.

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

[0008] Furthermore, the base layer is flame-retardant cellulose paper.

[0009] Furthermore, the flame retardant treatment uses 9-11% ammonium polyphosphate flame retardant.

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

[0011] The present invention also provides a biosensor comprising the above-described paper-based electrode.

[0012] This invention also provides a method for preparing a paper-based electrode based on liquid metal-assisted laser-induced graphene as described above, comprising 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.

[0013] Furthermore, the specific operation of step S1 is as follows: a. Immerse the eutectic gallium indium in 0.45-0.55 M HCl overnight to remove the oxide layer; b. Dissolve polyimide powder in N-methylpyrrolidone to obtain a PI-NMP solution with a PI mass fraction of 12.5-17.5% (W / V); c. Add the treated EGaIn to the PI-NMP solution and use an ultrasonic cell disruptor to sonicate in an ice bath for 80-100 minutes to prepare the EGaIn-PI-NMP composite slurry.

[0014] Furthermore, the ultrasonic processing operates at a frequency of 30%, with the ultrasonic wave off for 3 seconds and on for 2 seconds.

[0015] Furthermore, 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; Furthermore, 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.

[0016] Furthermore, 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℃.

[0017] Furthermore, in step I, the power of the CO2 laser is 3.1%, and the speed is 10 mm / s.

[0018] Furthermore, 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.

[0019] Furthermore, the gold nanoparticles are prepared using a citric acid reduction method.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: 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: (1) Significantly improves mechanical properties: Toughness is increased by more than 100% compared to paper, and tensile strength reaches 11-12 N / mm²; (2) Excellent electrical conductivity: The charge transfer resistance of the composite material is significantly reduced, and its electrical conductivity is excellent; (3) Good stability: It retains its appearance intact after being soaked in acidic, alkaline and neutral solutions for 72 hours; (4) Environmentally friendly and sustainable: Using paper as a base material is in line with the concept of green manufacturing; (5) Simple fabrication process: one-step laser etching, no need for complex photolithography process; (6) Low cost: Low raw material cost, suitable for large-scale production; (7) Good batch reproducibility: the standard deviation of electrochemical parameters is less than 10%. Attached Figure Description

[0021] 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.

[0022] Figure 1 Macroscopic morphology 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. Figure 5 The graph shows the stability test results of the original cellulose paper sample prepared in Example 1 and the modified cellulose paper sample prepared in Example 2. Figure 6 This represents the effective area of ​​the paper-based electrode. Figure 7 This is a comparison of batch differences in paper-based electrodes; Figure 8 For paper-based electrode stability testing; Figure 9 The results show the comparison before and after nano-modification of paper-based electrodes; Figure 10 To detect biomarkers using paper-based electrodes. Detailed Implementation

[0023] To make the technical problems to be solved, the technical solutions, and the beneficial effects of the present invention clearer, the present invention will be further described in detail below with reference to embodiments and accompanying drawings. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. The present invention will be specifically described below with reference to specific embodiments.

[0024] This invention provides a paper-based electrode based on liquid metal-assisted laser-induced graphene, comprising 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.

[0025] Specifically, it also includes a functionalized layer, which is formed by modifying the electrode with a functional material.

[0026] Specifically, the liquid metal nanoparticles are EGaIn-PI-NMP composite slurry, and the liquid metal, especially the eutectic gallium indium alloy, has the characteristics of being liquid at room temperature and having high conductivity (3.4 × 10⁻⁶). 6 Unique properties such as S / m and good biocompatibility. Currently, there is a lack of effective methods for fabricating paper-based sensors that combine the advantages of liquid metal and laser-induced graphene, especially in terms of optimizing material ratios, laser parameters, and surface modification.

[0027] Specifically, the base layer can be different types of paper. Preferably, the base layer is flame-retardant cellulose paper, which has the advantage of being biodegradable.

[0028] Specifically, the flame retardant treatment uses 9-11% ammonium polyphosphate flame retardant (APP flame retardant), preferably 10% ammonium polyphosphate flame retardant.

[0029] Specifically, the functional material is gold nanoparticles, but other functional materials may also be selected, such as single-walled carbon nanotubes, all carbon nanomaterials, all metal nanoparticles or other conductive materials, surface antifouling agents, etc.

[0030] This invention also provides a method for preparing a paper-based electrode based on liquid metal-assisted laser-induced graphene as described above, comprising 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.

[0031] Specifically, 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.

[0032] Preferably, the specific operation of step S1 is as follows: a. Immerse the eutectic gallium indium in 0.5M HCl overnight to remove the oxide layer; b. Dissolve polyimide powder in N-methylpyrrolidone, wherein the mass fraction of the polyimide is 15% (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 90 minutes to prepare EGaIn-PI-NMP composite slurry.

[0033] Among these optimizations, the inventors optimized the concentration of EGaIn, determining the optimal concentration to be 6% through dynamic light scattering analysis. At this concentration, the particle size distribution is uniform (200-400nm), and the electrochemical performance is optimal. The concentration of PI was also optimized, revealing that the optimal PI concentration is 15%. At this concentration, the material exhibits good film-forming properties and electrochemical activity while maintaining appropriate mechanical strength. The ultrasonic time was also optimized, finding that an ultrasonic time of 90 minutes yields the best particle dispersion effect and electrochemical performance.

[0034] Specifically, the ultrasonic treatment operates at a frequency of 30%, with the ultrasonic wave off for 3 seconds and on for 2 seconds.

[0035] Specifically, 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 base layer and repeat the application more than twice.

[0036] Preferably, the specific operation of step S2 is as follows: (1) Apply 10% wt% ammonium polyphosphate flame retardant evenly to the surface of the base layer and dry at 37°C; (2) Apply EGaIn-PI-NMP composite slurry to the surface of the flame-retardant base layer, and repeat the application twice.

[0037] Specifically, step S3 involves using a wax printer to perform a wax seal, heating at 72-88℃ for 27-33 minutes to allow the wax to fully penetrate.

[0038] Preferably, step S3 is performed by using a wax printer to perform wax sealing and heating at 80°C for 30 minutes to allow the wax to fully penetrate.

[0039] Specifically, 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°C, preferably at 37°C.

[0040] Specifically, in step I, the power of the CO2 laser is 3.1% and the speed is 10 mm / s.

[0041] The inventors optimized the laser parameters by systematically studying the effects of laser power (2.2-3.4%) and scanning speed (5-50 mm / s) on resistance, and determined the optimal parameters to be 3.1% power and 10 mm / s speed.

[0042] Specifically, step S5 involves adding a gold nanoparticle solution to the surface of the working electrode and then drying and curing it.

[0043] Specifically, 10 μL of gold nanoparticle solution was dropped onto the surface of the working electrode.

[0044] Specifically, the gold nanoparticles are prepared by citric acid reduction, and the specific steps are as follows: heat 0.5mM HAuCl4 solution to boiling; quickly add 1% sodium citrate solution and continue boiling for 30-40 minutes; the solution color changes from light yellow to dark red, indicating that gold nanoparticles have formed.

[0045] This invention also provides a biosensor comprising the above-described paper-based electrode.

[0046] Embodiments of the present invention also provide the application of biosensors such as paper-based motors or paper-based electrodes in biomarker detection.

[0047] Specifically, the biomarkers are inflammatory factors, salivary glucose, or pathogens.

[0048] Specifically, the inflammatory factor is interleukin-6 (IL-6).

[0049] Specifically, the pathogen is a virus or bacteria.

[0050] The following description is based on specific embodiments: Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials and reagents used in the following examples are commercially available, and techniques not described in detail were performed according to standard methods well known to those skilled in the art.

[0051] Example 1: Preparation of basic electrode: 1. Material Preparation Whatman 3MM chromatography filter paper (a type of cellulose paper) was selected as the base layer, and eutectic gallium indium alloy with a purity of 99.99%, thermosetting polyimide resin powder, N-methylpyrrolidone (analytical grade) and ammonium polyphosphate flame retardant were prepared.

[0052] 2. Prepare the basic electrode according to the following steps: (1) Preparation of composite slurry: Soak 10 μL EGaIn in 500 mL 0.5 M HCl overnight; dissolve 300 mg PI powder in 2 mL NMP and stir thoroughly until completely dissolved; after removing HCl, add EGaIn to PI-NMP solution and sonicate at 30 kHz for 90 minutes under ice bath conditions (2 seconds on, 3 seconds off). (2) Paper base treatment: Coat the surface of cellulose paper with 10% APP suspension evenly and dry it in an oven at 37°C until completely dry; coat the EGaIn-PI-NMP slurry evenly and repeat the coating to ensure full impregnation; (3) Hydrophobic treatment: Patterned wax sealing is performed using a wax printer, and the wax is heated at 80°C for 30 minutes to allow the wax to fully penetrate; (4) Laser etching (LIG treatment): Use a 55W CO2 laser, set the power to 3.1% and the speed to 10mm / s, perform laser etching according to the preset electrode pattern, coat the reference electrode position with silver paste, and dry at 37℃.

[0053] Example 2: Preparation of Functionalized Electrode (Modified Cellulose Paper) Based on Example 1, electrode functionalization modification was further performed, and the specific steps were as follows: (5) Preparation of 40nm gold nanoparticles by citric acid reduction method: Heat 0.5mM HAuCl4 solution to boiling, quickly add 1% sodium citrate solution, continue boiling for 30-40 minutes, the solution color changes from light yellow to dark red, indicating the formation of gold nanoparticles; (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.

[0054] Comparative Example 1 The difference from Example 1 is that step (4) laser etching was not performed.

[0055] Example 3 Characterization Analysis 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: 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.

[0056] 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.

[0057] The results are as follows Figure 1-3 As shown, Figure 1 This is a macroscopic morphological image of the original cellulose paper prepared in Example 1. Figure 2 This is a macroscopic morphology diagram of a paper substrate with multiple working electrodes. 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. Figure 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.

[0058] Example 4 Performance Testing Acid-base stability test: 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.

[0059] 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.

[0060] Electrochemical performance testing: 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: 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.

[0061] 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 7 As shown, a represents the average peak oxidation (anodic) and reduction (cathode) currents; b represents the ΔEp (peak potential difference) of the peak oxidation and reduction potentials; c represents the area between the curves (anodic-cathode scan); d represents 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 The results in section a show that the peak currents of the anode and cathode are stable at around +0.15 mA and -0.15 mA, respectively, with a standard deviation of less than 0.01 mA. Figure 7 The potential difference (ΔEp) of the middle b peak ranges from 0.25 to 0.27 V, and the coefficient of variation (CV) is less than 10%, indicating that the electron transfer kinetics are uniform. Figure 7 The error of c is less than 0.005 V / mA, indicating that the surface area characteristics are uniform. Figure 7The measured resistances, as shown in the figure, ranged from 340 Ω to 350 Ω, with batch-to-batch variation of less than 3% (standard deviation < 10 Ω). These results demonstrate the excellent reproducibility of the fabricated electrode, with CVs for all key electrochemical parameters below 10%, significantly outperforming conventional electrode fabrication methods, which typically exhibit batch-to-batch variation of 15–25%. This high consistency is attributed to the uniform EGaIn-PI-NMP coating, precise laser-induced graphene parameter control, and the mechanical stability enhanced by modified paper. This provides a solid foundation for the scalable production of paper-based electrodes with predictable performance, suitable for commercial electrochemical sensing applications.

[0062] 3. Stability test: The prepared electrode was subjected to long-term cyclic voltammetry test. The CV curve was scanned 30 times at a scan rate of 50 mV / s to evaluate the electrochemical stability. Figure 8 The results showed that the CV curves scanned 30 times had a high degree of consistency, proving that the prepared EGPE has excellent stability and demonstrating that the electrode has good electrochemical reversibility and stability.

[0063] 4. Cyclic voltammetry curves were scanned using potassium ferricyanide solution on the original cellulose paper sample prepared in Example 1 and the modified cellulose paper sample prepared in Example 2. The results are as follows: Figure 9 As shown, from Figure 9 As can be seen, the modified cellulose paper sample exhibits enhanced current and conductivity, indicating that the prepared electrode can be nano-modified to increase its working performance.

[0064] Example 5: Application Case The prepared paper-based electrochemical electrode can be used to detect a variety of biomarkers, such as inflammatory factors. Specifically, through aptamer functionalization, it can detect inflammatory markers such as interleukin-6 (IL-6). The specific steps are as follows: To detect IL-6, an electrochemical aptamer sensor with a working electrode modified with gold nanoparticles (AuNP) prepared in Example 2 was used. Before use, the IL-6 aptamer was centrifuged (4000 rpm, 1 min, room temperature) to avoid contamination, diluted with ultrapure water, and reduced with tris(2-carboxyethyl)phosphine (TCEP) for 1 hour, diluted to a final concentration of 4 μM, and stored at -20°C for later use. For electrode preparation, 10 μL of AuNP solution was drop-coated onto the clean working electrode surface and dried; then 4 μL of 4 μM aptamer solution was added, and incubation was performed overnight at 4°C to achieve bonding between the thiol groups and AuNP; 10 μL of mercaptohexanol (MCH) was added and incubated for 1 hour to inhibit non-specific binding; after thorough washing with 0.05 M PBS, the electrode was dried at 37°C. Different concentrations of IL-6 solutions were incubated on the electrode surface for 1 hour, washed with PBS, and electrochemical measurements were performed using differential pulse voltammetry (DPV) in 0.05 M PBS solution, with quantification based on characteristic redox signals. Figure 9 As shown, cyclic voltammetry was performed at 50 mV / s in an iron / ferrocyanide solution at 25 °C before and after gold nanoparticle modification on the working electrode surface (100 mM potassium chloride as electrolyte). The electrochemical signal was significantly enhanced after gold nanoparticle modification. IL-6 detection results are shown below. Figure 10 As shown, a is the DPV of the EGPE biosensor interface of IL-6 measured at different concentrations obtained in 0.05 MPBS (pH=7.4), b is the calibration curve of IL-6, and the relationship between peak current and IL-6 concentration (error bars = standard deviation; n=3). Figure 10 The DPV response curve shown in Figure a exhibits a clear concentration-dependent peak current across the IL-6 concentration range (1 pg / mL to 1000 pg / mL). Specifically, the peak current systematically increases from approximately 2 μA at the lowest concentration to 18 μA at the highest concentration, demonstrating excellent signal-to-noise ratio and minimal baseline drift throughout the measurement range. This pronounced current response underscores the sensitivity of EGPE to changes in IL-6 concentration.

[0065] Figure 10 The corresponding calibration curve shown in Figure b 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 μA) and x represents the IL-6 concentration (in pg / mL). The slope of 0.019 μA / 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 clinically significant because IL-6 levels in saliva typically range from a few pg / mL in healthy individuals to several hundred pg / mL in patients with inflammation. Compared to other electrochemical immunosensors reported in the literature, which typically achieve LODs from 1 to 50 pg / mL, EGPEs demonstrate more competitive performance, especially given their applicability to complex salivary matrices. The error bars in the calibration plot indicate that the relative standard deviation (RSD) is typically below 10%, confirming the reproducibility and precision of this analytical method across the entire concentration range. The EGPEs platform has a dynamic range spanning three orders of magnitude (1 to 1000 pg / mL), effectively covering physiologically relevant IL-6 concentrations, making it ideal for diagnostic screening and monitoring of inflammatory states.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A paper-based electrode based on liquid metal-assisted laser-induced graphene, characterized in that, It includes 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.

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 liquid metal nanoparticles are EGaIn-PI-NMP composite slurry; 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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