A ratiometric electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material, its preparation method and application

Abstract

This invention discloses a ratiometric electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material, achieving highly sensitive detection of luteolin. The sensor utilizes MXene as the substrate material, introducing cuprous oxide (Cu2O) as a stable internal reference signal source through in-situ growth, and combining it with NH2-CNTs to significantly enhance the electrocatalytic response signal to luteolin. By constructing the ratio of the target oxidation peak current to the internal reference signal as the output signal, self-calibration against environmental and background interference is effectively achieved. Experimental results show that the sensor exhibits good linearity in the concentration range of 0.02 μmol / L to 9.56 μmol / L, with a detection limit of 0.0024 μmol / L, and demonstrates excellent anti-interference ability, reproducibility, and stability. In the spiked recovery experiment, the recovery rate reaches 90.73%–106.34%. Furthermore, it shows good application prospects in real-world samples.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical sensor technology, specifically relating to an electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material and its preparation method, as well as the application of the sensor in the detection of luteolin. Background Technology

[0002] Luteolin (3,4,5,7-tetrahydroxyflavone, Lu), with the molecular formula C1... 15 H 10 O6 (Luxelugenin) is an important flavonoid characterized by two benzene rings and a hydroxyl group, contributing to its diverse biological activities. It is primarily extracted from various traditional Chinese medicines, such as Japanese celery, honeysuckle, and schisandra. Due to its numerous health benefits, it has received significant attention in clinical medicine and pharmaceutical research, including antioxidant, anti-inflammatory, and antiviral activities. The pharmacological effects of Luxelugenin in vivo are closely related to its concentration; its dosage, when prescribed, needs strict control. Excessive intake can lead to side effects and damage to vital systems. Therefore, establishing an accurate, sensitive, and rapid method for Luxelugenin detection is crucial for drug quality control, clinical drug testing, and human safety.

[0003] Currently, quantitative analysis for Lu detection mainly relies on high-performance liquid chromatography (HPLC), mass spectrometry (MS), and electrochemiluminescence (ECL). While these methods offer reliable accuracy, their practical application faces significant challenges, such as high cost, complex and time-consuming sample pretreatment processes, and cumbersome procedures, limiting their practical use. Against this backdrop, electrochemical analysis, as a highly promising alternative technology, is gaining increasing popularity in Lu detection. This is primarily due to its significantly lower cost, shorter response time, and simpler detection procedures.

[0004] To construct high-performance electrochemical sensors, it is crucial to find electrode modification materials with good conductivity and large specific surface area. Currently, among several types of materials, including transition metal oxides or sulfides, carbon-based materials, and metal-organic frameworks, two-dimensional materials like MXene are frequently used for electrochemical analysis. MXene possesses excellent mechanical strength, high specific surface area, and good metallic conductivity, providing opportunities for the design of electrochemical sensors. However, due to its inherent structure, MXene suffers from drawbacks such as easy aggregation and rapid oxidation. To address this issue, researchers have combined MXene with other materials for composite modification.

[0005] To date, most electrochemical detection of Lu investigated and reported by researchers relies on single-signal sensing, which suffers from background interference and baseline drift. In contrast, ratiometric electrochemical sensing establishes an internal reference signal, effectively reducing interference from external environmental factors and improving the accuracy and reliability of electrochemical sensing. Commonly used internal reference probes in constructing ratiometric sensors include methylene blue, ferrocene, metal nanoparticles, metal oxides, and thionine. Among these internal reference materials, Cu₂O, as an electroactive nanomaterial, not only boasts advantages such as simple synthesis and good catalytic performance but also possesses a relatively stable internal reference signal, making it ideal for constructing ratiometric electrochemical sensors. This provides a new approach for this study.

[0006] Therefore, Cu2O nanocubes were uniformly loaded onto the surface of MXene using an in-situ growth method, and aminated multi-walled carbon nanotubes (NH2-CNTs) were introduced using ultrasonic composite technology to successfully prepare Cu2O@MXene / NH2-CNTs nanocomposite materials. Utilizing the large specific surface area of ​​MXene as a carrier, the in-situ growth of Cu2O nanocubes effectively suppressed nanoparticle aggregation. Simultaneously, the introduction of NH2-CNTs, leveraging their excellent conductivity and mechanical strength, constructed a three-dimensional conductive network, significantly accelerating interfacial electron transport efficiency. By introducing a ratio sensing strategy, this sensor effectively eliminated environmental interference and matrix effects, achieving high sensitivity and high accuracy in Lu detection, demonstrating significant application potential. Summary of the Invention

[0007] The technical problem this invention aims to solve is to address the issues of insufficient electrode sensitivity, easy aggregation of MXene materials, and interference in single-signal sensing in existing electrochemical detection of luteolin. This invention provides an electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material, its preparation method, and its applications. By in-situ growing Cu2O nanocubes on MXene, the aggregation of nanoparticles is effectively suppressed. Simultaneously, the introduction of NH2-CNTs, utilizing their excellent conductivity and mechanical strength to construct a three-dimensional conductive network, significantly enhances the electron transport capability and electrocatalytic activity of the electrode, achieving highly sensitive and selective detection of luteolin.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A ratiometric electrochemical sensor for detecting luteolin includes a working electrode, a counter electrode, and a reference electrode. The working electrode comprises a glassy carbon electrode substrate and a modification layer loaded on the surface of the glassy carbon electrode substrate. The modification layer is composed of a Cu2O@MXene / NH2-CNTs composite material. The Cu2O is in the form of nanocubic particles and is uniformly distributed between the layers and on the surface of MXene. NH2-CNTs are composited with the Cu2O@MXene. The Cu2O serves as an internal reference electroactive probe to provide an internal reference signal. The ratiometric electrochemical sensor uses the ratio of the oxidation peak current of luteolin to the internal reference signal as the output signal.

[0009] Furthermore, the MXene is Ti3C2T x MXene. The modification layer is formed by drop-coating 8-10 µL of a dispersion of the composite material at a concentration of 0.8-1.2 mg / mL onto the surface of a glassy carbon electrode and then drying it.

[0010] The method for preparing the working electrode in the above-mentioned ratiometric electrochemical sensor includes the following steps: (1) Ti3C2T x Preparation of MXene: Ti3AlC2 powder was added to hydrofluoric acid at a mass-to-volume ratio of 1 g: 10-20 mL. The mixture was stirred at 15-35 °C for 20-28 h, the precipitate was collected, washed and centrifuged until the pH reached 6.5-7.5, and then vacuum dried at 50-70 °C for 10-14 h. The dried precipitate was redispersed in distilled water, sonicated for 1.5-2.5 h, collected by centrifugation, and freeze-dried. (2) Preparation of Cu2O@MXene: Add MXene and CuCl2 solution with a concentration of 0.08~0.12 mol / L to distilled water at a mass-volume ratio of 10 mg: 0.5~1.5 mL, slowly add NaOH solution with a concentration of 0.15~0.25 mol / L, the volume ratio of NaOH solution to CuCl2 solution is 2.5:1~3.5:1, stir for 4~6 min, then add ascorbic acid solution with a concentration of 0.08~0.12 mol / L, the volume ratio of ascorbic acid solution to CuCl2 solution is 1.5:1~2.5:1, age for 0.8~1.2 h, centrifuge to collect the precipitate, and dry at 50~70 ℃ for 10~14 h; (3) Preparation of NH2-CNTs: Carbon nanotubes were ultrasonically dispersed in ethylene glycol, with a mass-to-volume ratio of 2-3 mg:1 mL. Ammonia water was added dropwise, with a volume ratio of 1:30-50 between ammonia water and ethylene glycol. The reaction was carried out at 170-190 °C for 8-12 h using a solvothermal method. The mixture was then washed, centrifuged, and dried at 50-70 °C for 20-28 h. (4) Preparation of Cu2O@MXene / NH2-CNTs composite material: Cu2O@MXene and NH2-CNTs were added to DMF at a mass ratio of 2:1 to 4:1, ultrasonically treated for 1.5 to 2.5 h, centrifuged, washed, and dried at 50 to 70 °C for 10 to 14 h; (5) Preparation of working electrode: The composite material obtained in step (4) is dispersed in DMF to prepare a dispersion with a concentration of 0.8~1.2 mg / mL; after polishing, cleaning and drying the glassy carbon electrode, 8~10 µL of the dispersion is dropped onto the electrode surface and dried to obtain the electrode.

[0011] The ratiometric electrochemical sensor described above or the working electrode prepared by the above method can be used for the detection of luteolin. Differential pulse voltammetry is preferably used for detection in a phosphate buffer solution with a pH of 2.0–4.0, and more preferably in a 0.1 M phosphate buffer solution with a pH of 3.0. The detection is performed within the luteolin concentration range of 0.02–9.56 µmol / L. A standard curve is established for the concentration of luteolin using the ratio of the peak current of luteolin oxidation to the peak current of Cu₂O oxidation, showing a good linear relationship, with a detection limit as low as 0.0024 µmol / L.

[0012] Compared with the prior art, the present invention has the following beneficial effects: 1. Inhibit MXene interlayer stacking and expose more active sites: By embedding Cu2O nanocubes into Ti3C2T x The interlayer and surface of MXene utilize the physical spacing of nanoparticles to effectively prevent irreversible stacking and aggregation of MXene nanosheets, thereby exposing more electrochemical active sites and providing favorable conditions for electrocatalytic reactions.

[0013] 2. Constructing a three-dimensional conductive network to significantly improve electron transport capability: Using highly conductive MXene as the framework, NH2-CNTs are introduced. Utilizing their one-dimensional tubular structure and excellent conductivity and mechanical strength, a highly efficient three-dimensional conductive network is constructed inside the composite material, promoting rapid electron transfer during the electrochemical reaction process and significantly improving the overall conductivity of the composite material.

[0014] 3. Enhancing electrocatalytic performance through the synergistic effect of multiple components: Cu2O nanocubes provide a stable internal reference electrochemical signal, MXene provides a high specific surface area support and conductive pathway, and NH2-CNTs further enhance conductivity and improve interfacial contact. The synergistic effect among the three significantly enhances the electrocatalytic activity for luteolin oxidation. Cyclic voltammetry and electrochemical impedance spectroscopy both show that the Cu2O@MXene / NH2-CNTs modified electrode prepared in this invention exhibits higher redox peak current and lower charge transfer resistance compared to pure MXene, Cu2O@MXene, and bare glassy carbon electrodes.

[0015] 4. Self-calibration of internal reference ratio strategy to improve detection accuracy and reliability: By simultaneously acquiring the dual electrochemical signals of the target analyte luteolin and the Cu2O internal reference probe at the sensing interface, and using the peak current ratio of the two as the output signal, the background interference and baseline drift caused by external factors such as ambient temperature, pH fluctuations, and electrode batch differences in traditional single-signal sensors are effectively overcome, which greatly improves the accuracy and reproducibility of the analysis results.

[0016] 5. High sensitivity and low detection limit: Under optimized conditions, the linear range for detecting luteolin by the sensor of this invention is 0.02~9.56 µmol / L, and the detection limit is 0.0024 µmol / L (S / N=3), which is superior to many reported electrochemical sensors for luteolin, demonstrating excellent high-sensitivity analytical performance.

[0017] 6. Excellent reproducibility, stability, and anti-interference ability: Using the sensor of this invention, the relative standard deviation (RSD) for detecting the same concentration of luteolin with five independently modified electrodes is 7.94%; after the electrodes are stored at 4 °C for 7 days, the peak current ratio of the detection signal remains stable; for quercetin and Cl at 10 times the concentration... - K + Na + Tryptophan, ascorbic acid, uric acid, dopamine, and glucose all showed good anti-interference ability and had no significant impact on the detection signal of luteolin, indicating that it has excellent detection selectivity in complex sample matrices.

[0018] In summary, the ratiometric electrochemical sensor constructed in this invention successfully solves the problems of easy stacking of MXene materials and susceptibility to interference in single-signal detection. It exhibits comprehensive performance such as high sensitivity, low detection limit, good reproducibility, strong stability and excellent anti-interference ability for luteolin. The recovery rate can reach 90.73%~106.34% in the spiked recovery experiment. It has good application prospects in actual sample analysis, especially suitable for drug quality control, clinical drug monitoring and other fields. Attached Figure Description

[0019] Figure 1 The image shows the SEM image of the composite material prepared in the embodiments of the present invention. In the image, A represents MXene, B represents Cu2O, C represents Cu2O@MXene, D represents Cu2O@MXene / NH2-CNTs, and EK represents the EDX elemental mapping (O, C, Ti, N, Cu, F elements) of Cu2O@MXene / NH2-CNTs.

[0020] Figure 2 XRD patterns (A) and Fourier transform infrared absorption spectra (B) of different materials prepared for embodiments of the present invention.

[0021] Figure 3 The high-resolution XPS spectra of Cu2O@MXene / NH2-CNTs prepared in the embodiments of the present invention are shown below; where A is the full spectrum, B is the C 1s high-resolution spectrum, C is the O 1s high-resolution spectrum, D is the N 1s high-resolution spectrum, E is the Ti 2p high-resolution spectrum, and F is the Cu 2p high-resolution spectrum.

[0022] Figure 4 Different modified electrodes prepared for embodiments of the present invention were prepared in the presence of 0.1 M KCl and 1.0 mM [Fe(CN)6]. 3- / 4- Cyclic voltammetry curves in buffer solutions.

[0023] Figure 5 Different modified electrodes prepared for embodiments of the present invention were prepared in the presence of 0.1 M KCl and 5.0 mM [Fe(CN)6]. 3- / 4- Electrochemical impedance spectroscopy in buffer solution.

[0024] Figure 6 The image shows differential pulse voltammetry plots of the electrochemical sensor of this invention in 0.1 M PBS buffer at different pH values ​​(3.0, 4.0, 5.0, 6.0, 7.0).

[0025] Figure 7 The differential pulse voltammograms of the electrochemical sensor of this invention for detecting luteolin in 0.1 M PBS buffer at pH 3.0 under different electrode modifications are shown.

[0026] Figure 8 The figure shows the cyclic voltammetry curves of the electrochemical sensor of the present invention detecting rutin at different scan rates (120, 140, 160, 180, 200, 220, 240 mV / s) in 0.1 M PBS buffer at pH 3.0.

[0027] Figure 9 This is a differential pulse voltammogram showing the detection of different concentrations of luteolin by the electrochemical sensor of the present invention in 0.1 M PBS buffer at pH 3.0.

[0028] Figure 10 for Figure 9 Linear relationship curve between the peak current ratio of oxidative stress and luteolin concentration.

[0029] Figure 11 This is a reproducibility test diagram of the electrochemical sensor of the present invention detecting luteolin in 0.1 M PBS buffer at pH 3.0 using five independently modified electrodes.

[0030] Figure 12 This is a stability test diagram of the electrochemical sensor of the present invention, which was stored in 0.1 M PBS buffer at pH 3.0 for 7 days and detected the same concentration of luteolin daily.

[0031] Figure 13 The electrochemical sensor of this invention was prepared in 0.1 M PBS buffer (pH 4.0, 4 μM rutin) containing 10 times the concentration of quercetin and Cl. - K + Na + Interference resistance test results for tryptophan, ascorbic acid, uric acid, dopamine, and glucose. Detailed Implementation

[0032] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. The following embodiments are for illustrative purposes only and are not intended to limit the scope of protection of the present invention. All technical solutions implemented based on the content of this invention fall within the scope of protection claimed by this invention. Example

[0033] I. Material Preparation 1. Ti3C2T x Preparation of MXene Ti3C2T x The preparation of MXene followed the methods described in existing literature. The specific steps are as follows: 3.0 g of Ti3AlC2 powder was slowly added to a polytetrafluoroethylene beaker containing 40 mL of hydrofluoric acid and stirred at room temperature for 24 h. After the reaction was completed, the black precipitate was collected and repeatedly washed and centrifuged with distilled water and ethanol in a 1:1 volume ratio until the pH of the supernatant was close to neutral. Then, it was vacuum dried at 60 °C for 12 h.

[0034] The precipitate was re-ultrasonicated in 100 mL of distilled water for 2 h. Finally, the product was collected by centrifugation, freeze-dried, and stored at 4 °C for later use. 2. Preparation of Cu2O@MXene 50 mg of MXene and 5 mL of CuCl₂-2H₂O (0.1 mol / L) were added to 200 mL of distilled water. 15 mL of NaOH (0.2 mol / L) was slowly added dropwise while stirring for 5 min. Then, 10 mL of ascorbic acid (0.1 mol / L) was added dropwise for aging for 1 h. The precipitate was obtained by centrifugation, dried at 60 ℃ for 12 h, and stored at 4 ℃ for later use. Cu₂O was prepared by adding MXene.

[0035] 3. Preparation of NH2-CNTs Under ultrasonic conditions, 100 mg of carbon nanotubes were dispersed in 40 mL of ethylene glycol, and then 1 mL of ammonia was added dropwise. The mixture was then transferred to an autoclave and subjected to a solvothermal reaction at 180 °C for 10 h. The product was repeatedly washed with distilled water, centrifuged at 8000 r / min for 5 min, dried at 60 °C for 24 h, and stored at 4 °C for later use.

[0036] 4. Preparation of Cu2O@MXene / NH2-CNTs composite materials 30 mg Cu2O@MXene and 10 mg NH2-CNT powder were added to a beaker containing 30 mL DMF. After sonication for 2 h, the solution was centrifuged, washed with water, and dried at 60 °C overnight to obtain Cu2O@MXene / NH2-CNTs composite material.

[0037] II. Preparation of the working electrode 1. Pretreatment of glassy carbon electrode The glassy carbon electrode (GCE) was polished to a mirror finish on suede using 50 nm alumina polishing powder, washed with ultrapure water, and then dried in a nitrogen stream for 30 min to obtain the pretreated glassy carbon electrode.

[0038] 2. Preparation of Cu2O@MXene / NH2-CNTs / GCE working electrode The Cu2O@MXene / NH2-CNTs composite material prepared above was dispersed in DMF and ultrasonically homogenized to prepare a 1 mg / mL dispersion. 9 µL of this dispersion was drop-coated onto the surface of a pretreated glassy carbon electrode and dried under an infrared lamp to obtain the Cu2O@MXene / NH2-CNTs / GCE working electrode.

[0039] 3. Preparation of the control working electrode (1) MXene / GCE working electrode: MXene was dispersed in distilled water and sonicated to prepare a dispersion of 1 mg / mL. 9 µL of the dispersion was dropped onto the surface of the pretreated glassy carbon electrode and dried under an infrared lamp to obtain the MXene / GCE working electrode.

[0040] (2) Cu2O / GCE working electrode: Cu2O nanocubes were dispersed in distilled water and sonicated to prepare a dispersion of 1 mg / mL. 9 µL of the dispersion was drop-coated onto the surface of the pretreated glassy carbon electrode and dried under an infrared lamp to obtain the Cu2O / GCE working electrode.

[0041] (3) Cu2O@MXene / GCE working electrode: Cu2O@MXene was dispersed in distilled water and sonicated to prepare a 1 mg / mL dispersion. 9 µL of the dispersion was drop-coated onto the surface of the pretreated glassy carbon electrode and dried under an infrared lamp to obtain the Cu2O@MXene / GCE working electrode.

[0042] (4) Bare GCE: The glassy carbon electrode after pretreatment is used directly, which is called bare GCE.

[0043] III. Electrochemical Testing Methods Electrochemical measurements were performed using a three-electrode system: the prepared working electrode was used as the working electrode, the saturated calomel electrode (SCE) as the reference electrode, and the platinum wire electrode as the counter electrode. Cyclic voltammetry (CV) tests were conducted in a solution containing 0.1 M KCl and 1.0 mM [Fe(CN)6]. 3- / 4- The measurements were performed in a buffer solution containing 0.1 mM KCl and 5.0 mM [Fe(CN)6] at a scan rate of 50 mV / s. 3- / 4- The assay was performed in a buffer solution with a frequency range of 0.01 Hz to 100 kHz and an amplitude of 5 mV. Differential pulse voltammetry (DPV) was performed in 0.1 M PBS buffer for the detection of luteolin and the evaluation of its various properties.

[0044] IV. Performance Test Results 1. Morphological characteristics The microstructures of MXene, Cu2O, Cu2O@MXene, and Cu2O@MXene / NH2-CNTs were investigated using scanning electron microscopy (SEM). Figure 1 As shown in Figure A, MXene exhibits a clear accordion-like multilayer structure. Cu₂O, on the other hand, shows an aggregated nanocubic structure. Figure 1 B). In Figure 1 As can be seen in C, Cu₂O nanocubes grow on the surface and between layers of MXene. Simultaneously, through... Figure 1 On the D surface, Cu2O and NH2-CNTs showed good distribution on MXene, initially indicating successful material synthesis. Furthermore, EDX elemental mapping analysis was performed to determine the elemental composition of the Cu2O@MXene / NH2-CNTs composite. Figure 1 As shown in EK, O, C, Ti, N, Cu and F elements exhibit uniform dispersion in Cu2O@MXene / NH2-CNTs composite material, confirming that Cu2O nanocubes are uniformly anchored on MXene and successfully composited with NH2-CNTs.

[0045] 2. XRD and FT-IR spectra of different materials The crystal structures of different materials were characterized using X-ray powder diffraction (PXRD). Figure 2 As shown in Figure A, the peaks at (002), (004), and (110) at 8.85°, 18.19°, and 60.47° are Ti3C2T x Typical peaks of MXene were observed. Meanwhile, characteristic peaks of Cu2O were observed at 36.46°, 42.40°, 46.47°, and 73.57°, respectively. The observation of typical peaks of MXene and Cu2O in the diffraction peaks of Cu2O@MXene indicates that Cu2O is grown on the MXene surface. Furthermore, the peak at 25.93° corresponds to the (002) crystal plane of NH2-CNTs. Notably, the characteristic peaks of all components are retained in the Cu2O@MXene / NH2-CNTs composite material, a result confirming the successful preparation of the composite material.

[0046] Furthermore, Fourier transform infrared spectroscopy indicates that ( Figure 2 B), 564.10 cm -1 The peak at 602.32 cm⁻¹ is attributed to the vibration of the Ti-O bond in MXene. -1 and 433.10 cm -1 A peak attributable to Cu-O stretching vibration was observed at [value missing], and it was also present in Cu2O@MXene and Cu2O@MXene / NH2-CNTs. A peak at 3393.00 cm⁻¹ was observed in the composite sample. -1 The absorption peak observed is due to the stretching vibration of OH, and it is also observed at 1631.22 cm⁻¹. -1 The vibrational absorption peaks belonging to CN are clearly visible, further proving the successful preparation of Cu2O@MXene / NH2-CNTs material.

[0047] 3. XPS testing of composite materials The elemental composition of the Cu2O@MXene / NH2-CNTs composite material was further investigated using XPS. Figure 3As shown in Figure A, the five peaks—C1s, O 1s, N 1s, Ti 2p, and Cu 2p—reveal the presence of C, O, N, Ti, and Cu. The C 1s peaks at 288.06 eV, 285.57 eV, 284.24 eV, 283.11 eV, and 281.65 eV correspond to C=O, CN / CO, CC, CO-Ti, and C-Ti, respectively. Figure 3 B). In the fine spectrum of O 1s ( Figure 3 C), can be deconvolved into five separate component peaks with binding energies of 534.70 eV, 533.52 eV, 531.77 eV, 529.84 eV, and 528.53 eV, respectively, which are attributed to Cu2O and C-Ti-(OH). x Cu-OH, C-Ti-O x TiO2. In the N 1s spectrum ( Figure 3 D) The spectrum at 402.15 eV belongs to R=NR, at 399.80 eV to R-NH-R, and at 398.34 eV to R=NH2. Meanwhile, the Ti 2p spectrum at 464.25 eV and 458.30 eV belongs to Ti-O, and at 462.52 eV and 456.27 eV to Ti 2p. 3 / 2 and Ti 2p 1 / 2 461.07 eV and 455.12 eV are significant peaks for Ti-C. Figure 3 E). For example Figure 3 As shown in Figure F, in the Cu 2p diagram, 932.07 eV and 951.97 eV correspond to Cu, respectively. + 2p 3 / 2 and Cu + 2p 1 / 2 Meanwhile, 933.43 eV and 954.06 eV represent Cu. 2+ 2p 3 / 2 and Cu 2+ 2p 1 / 2 This indicates that Cu2O grows on the MXene surface. 2+ A slight increase. Therefore, XPS analysis confirms the successful formation of Cu2O@MXene / NH2-CNTs nanocomposite materials through the chemical interactions among the three components.

[0048] 4. Cyclic Voltmeter-Ampere Test Bare GCE, Cu2O / GCE, MXene / GCE, Cu2O@MXene / GCE, and Cu2O@MXene / NH2-CNTs / GCE were used as working electrodes in an atmosphere containing 0.1 M KCl and 1.0 mM [Fe(CN)6]. 3- / 4-The CV test was performed in the buffer solution, and the results are as follows: Figure 4 As shown, the bare electrode and Cu2O exhibit lower redox currents due to their weak conductivity. Meanwhile, MXene, with its large specific surface area and good conductivity, shows significantly higher redox currents. After in-situ growth of Cu2O on the MXene surface, the redox current decreases slightly, likely due to the weak conductivity of Cu2O hindering electron transfer. Finally, the highest redox peak current was observed after modification with NH2-CNTs. This is likely attributed to the excellent conductivity of NH2-CNTs and the synergistic effect of the three components, leading to a further enhancement of the redox peak current.

[0049] 5. Electrochemical impedance spectroscopy (EIS) The above four electrodes were placed in a solution containing 0.1 M KCl and 5.0 mM [Fe(CN)6]. 3- / 4- EIS testing was performed in the buffer solution, and the results are as follows: Figure 5 As shown. In the high-frequency region of EIS, a larger semicircle diameter indicates a larger charge transfer resistance (Rct). From Figure 5 As can be seen, Cu2O@MXene / NH2-CNTs exhibit the lowest resistivity. This is consistent with the CV results and demonstrates the efficient fabrication of each material layer.

[0050] 6. pH optimization Experiments were conducted at pH values ​​ranging from 2.0 to 8.0, with all other conditions remaining the same, and the results are as follows: Figure 6 As shown, the oxidation peak current of luteolin shifts to the left with increasing pH, indicating that proton-induced luteolin oxidation plays a crucial role, and the oxidation peak current gradually increases. Notably, at pH 3, the oxidation peak current reaches its maximum, possibly due to the anionic state of luteolin promoting proton release. However, the decrease in oxidation peak current above pH 3 may be due to the lack of protons, resulting in the acquisition of a negative charge. The initial electrostatic attraction weakens, eventually shifting to material repulsion of the negative charge, adversely affecting the redox kinetics of luteolin and leading to a decrease in peak current. This indicates that pH 3 is the optimal condition for this experiment.

[0051] 7. The effect of scan rate The reaction mechanism of luteolin on the composite electrode was investigated at different scan rates. Figure 7 The CV response curves of 160 μmol / L luteolin in the scan range of 80–160 mV / s are shown. The figure shows that the redox peak current gradually increases with increasing scan rate. Meanwhile, Figure 8 It also shows the redox peak current and v 1 / 2The good linearity indicates that the electrochemical behavior of luteolin on Cu2O@MXene / NH2-CNTs / GCE is a diffusion-controlled process.

[0052] 9. Linear range and detection limit Based on the above optimization conditions, this sensor was used to detect different concentrations of luteolin. For example... Figure 9 As shown, with increasing Lu concentration, the oxidation peak current of Cu₂O remains relatively stable, while the oxidation peak current of Lu gradually increases. The results indicate that in the range of 0.02–9.56 μmol / L, the current ratio I... Lu / I Cu2O It shows a good linear relationship with the concentration of Lu.

[0053] Figure 10 As shown, the linear regression equation is: I Lu / I Cu2O = 1.792C Lu + 0.6647,R 2 = 0.9929. Based on LOD = 3σ / K, the detection limit of the sensor can be calculated to be LOD = 0.0024 μmol / L.

[0054] Simultaneously, the linear relationship between a single signal and Lu concentration was investigated, compared to R... 2 The results indicate that the introduction of the Cu2O internal reference signal contributes to the high reliability of the sensor.

[0055] Table 1 compares the detection performance of the sensor of this invention with other luteolin electrochemical sensors reported in the literature. In the table: [1]Wang Z, Peng J, Li H, et al. Dual functionAgNPs@UiO-66 basedratiometric electrochemical sensor for rapid and sensitive determination ofluteolin in plants[J]. Electrochimica acta, 2025, 512: 145505. [2]Liao R, Zhong Y, Deng L, et al. PANI-functionalized MXene / SnO xporous heterostructures as a novel electrochemical sensing platformfordetecting luteolin in food[J]. Microchemical Journal, 2024, 207: 111711. [3]Ye R, Xie C, Guo H, et al. Simple one-step synthesisof nitrogen-doped carbon nanotube-loaded cobalt nano-composites and its electrochemicalsensor of luteolin[J]. Journal of Alloys and Compounds, 2024, 1009: 176836. [4]Gao F, Hong W, Yang T, et al. Expanded interlayerspacing ofSnO2QDs-Decorated MXene for highly selective luteolin detection with Ultra-Low limit of detection[J]. Journal of Colloid and Interface Science, 2024,653: 561-569. [5]Wei Z Q, Shan W L, Li L, et al. Post-modification ofcovalentorganic framework functionalized aminated carbon nanotubes with active site(Fe) for the sensitive detection of luteolin[J]. Food Chemistry, 2025, 462:141063. [6]Wang H, Zhang H, Huang S, et al. NiCoZn oxide nanocageson reduced graphene oxide nanosheets for the electrochemical detection of luteolin[J]. ACS Applied Nano Materials, 2024, 7(18): 21893-21901. Clearly, the developed Cu2O@MXene / NH2-CNTs / GCE sensor has a lower detection limit and a wider linear response range.

[0056] 10. Reproducibility Testing Five glassy carbon electrodes were used, and five Cu2O@MXene / NH2-CNTs / GCE working electrodes were prepared according to the aforementioned method. These five working electrodes were used as the working electrodes of the electrochemical sensor of this invention. DPV tests were performed in 0.1 M PBS buffer containing 4 μM luteolin and pH=3.0, and the oxidation peak current of each electrode was recorded. The results are as follows: Figure 11 As shown in the figure. The results indicate that the peak current variation for detecting the same concentration of luteolin by the five independently modified electrodes is small, with a relative standard deviation (RSD) of 7.94%, indicating that the electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material has good reproducibility.

[0057] 11. Stability Testing The Cu2O@MXene / NH2-CNTs / GCE working electrode was stored at 4℃ for 7 days. Each day, it was removed and subjected to DPV testing in 0.1 M PBS buffer containing 4 μM rutin (pH=3.0). The oxidation peak current was recorded, and the results are as follows: Figure 12 As shown in the figure. The results indicate that the peak current ratio of the sensor remained stable after 7 days of storage, demonstrating that the electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material has good long-term stability.

[0058] 12. Anti-interference capability test In the presence of 10 times the concentration of quercetin and Cl - K + Na + Tryptophan, ascorbic acid, uric acid, dopamine, and glucose were used as interfering agents. The changes in peak current were detected using DPV technology, and the results are as follows: Figure 13As shown in the figure. The results indicate that the presence of the aforementioned interfering substances has almost no effect on the detection peak current of luteolin, demonstrating that the electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material has good anti-interference ability for luteolin.

[0059] In summary, the electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material constructed in this invention exhibits excellent analytical performance for luteolin, with advantages such as high sensitivity, low detection limit, good reproducibility, strong stability, and strong anti-interference ability. The presence of an internal reference signal indicates that the sensor is more stable and reliable, and has good application prospects.

Claims

1. A ratiometric electrochemical sensor based on Cu2O@MXene / NH2-CNTs composite material, characterized in that, The working electrode of the electrochemical sensor includes a glassy carbon electrode and a modification layer loaded on the surface of the glassy carbon electrode. The modification layer is composed of Cu2O@MXene / NH2-CNTs composite material. The Cu2O is in the form of nanocubic particles and is uniformly distributed in the interlayer and surface of MXene. NH2-CNTs are composited with Cu2O@MXene. The Cu2O serves as an internal reference electroactive probe, and the electrochemical sensor uses the ratio of the oxidation peak current of luteolin to the oxidation peak current of Cu2O as the output signal.

2. The ratiometric electrochemical sensor according to claim 1, characterized in that, The MXene is Ti3C2T x MXene.

3. The ratiometric electrochemical sensor according to claim 1, characterized in that, The modification layer is formed by drop-coating 8-10 µL of the Cu2O@MXene / NH2-CNTs composite material dispersion with a concentration of 0.8-1.2 mg / mL onto the surface of a glassy carbon electrode and then drying it.

4. A method for preparing the working electrode in the ratiometric electrochemical sensor according to any one of claims 1 to 3, characterized in that, Includes the following steps: (1) Ti3C2T x Preparation of MXene: Ti3AlC2 powder is added to hydrofluoric acid, the mass-volume ratio of Ti3AlC2 powder to hydrofluoric acid is 1 g:10~20 mL, stirring at 15~35 ℃ for 20~28 h, collecting the precipitate, washing and centrifuging to pH 6.5~7.5, vacuum drying at 50~70 ℃ for 10~14 h; the dried precipitate is redispersed in distilled water, ultrasonic treatment for 1.5~2.5 h, centrifugal collection, freeze-drying; (2) Preparation of Cu2O@MXene: Add MXene and CuCl2 solution with a concentration of 0.08~0.12 mol / L to distilled water at a mass-volume ratio of 10 mg: 0.5~1.5 mL, slowly add NaOH solution with a concentration of 0.15~0.25 mol / L, the volume ratio of NaOH solution to CuCl2 solution is 2.5:1~3.5:1, stir for 4~6 min, then add ascorbic acid solution with a concentration of 0.08~0.12 mol / L, the volume ratio of ascorbic acid solution to CuCl2 solution is 1.5:1~2.5:1, age for 0.8~1.2 h, centrifuge to collect the precipitate, and dry at 50~70 ℃ for 10~14 h; (3) Preparation of NH2-CNTs: Carbon nanotubes were ultrasonically dispersed in ethylene glycol, with a mass-to-volume ratio of 2-3 mg:1 mL. Ammonia was added dropwise, with a volume ratio of 1:30-50 between ammonia and ethylene glycol. The reaction was carried out at 170-190 °C for 8-12 h using a solvothermal method. The mixture was then washed, centrifuged, and dried at 50-70 °C for 20-28 h. (4) Preparation of Cu2O@MXene / NH2-CNTs composite material: Cu2O@MXene and NH2-CNTs were added to DMF at a mass ratio of 2:1 to 4:1, ultrasonically treated for 1.5 to 2.5 h, centrifuged, washed, and dried at 50 to 70 °C for 10 to 14 h; (5) Preparation of working electrode: The composite material obtained in step (4) is dispersed in DMF to prepare a dispersion with a concentration of 0.8~1.2 mg / mL; after polishing, cleaning and drying the glassy carbon electrode, 8~10 µL of the dispersion is dropped onto the electrode surface and dried to obtain the electrode.

5. The application of the ratiometric electrochemical sensor as described in any one of claims 1 to 3 or the working electrode prepared by the method of claim 4 in the detection of luteolin.

6. The application according to claim 5, characterized in that, Differential pulse voltammetry was used to detect the substance in a 0.1 M phosphate buffer solution at pH 3.

0.

7. The application according to claim 5, characterized in that, The linear range of the detection is 0.02~9.56 µmol / L, and the detection limit is 0.0024 µmol / L.

8. The application according to claim 7, characterized in that, A standard curve was established for luteolin concentration based on the ratio of the peak current of luteolin oxidation to the peak current of Cu2O oxidation, and the ratio showed a linear relationship with the concentration.

9. The application according to claim 5, characterized in that, When detecting luteolin, the ratiometric electrochemical sensor has no significant effect on the detection peak current of luteolin when one or more of quercetin, Cl⁻, K⁺, Na⁺, tryptophan, ascorbic acid, uric acid, dopamine, and glucose are present at a concentration of 10 times.

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