Nickel hexacyanoferrate, yarn type electrochemical sensing electrode as well as preparation method and application of yarn type electrochemical sensing electrode

Abstract

The invention belongs to the technical field of electrochemical sensing, and particularly relates to nickel hexacyanoferrate, a yarn type electrochemical sensing electrode and a preparation method and application of the yarn type electrochemical sensing electrode. Nickel hexacyanoferrate NiHCF prepared by a low-temperature coprecipitation method is adopted as an oxidation-reduction probe core, a molecularly imprinted polymer MIP is grown on the oxidation-reduction probe core in situ to serve as a cortisol specific recognition shell, a NiHCF-MIP core-shell nano square block with a cortisol specific sensing function is prepared, a spinning solution is prepared, and the nano square block is used for preparing the cortisol. And spinning sensing active nanofibers by a conjugate electrostatic spinning technology, and wrapping the sensing active nanofibers on a conductive carbon core yarn in one step to obtain the yarn type electrochemical sensing electrode with a cortisol specific sensing function. By adopting a low-temperature co-precipitation preparation method, NiHCF with a nano square structure, the size as low as about 100 nm and the vacancy content up to about 33.3% is obtained, so that the effective specific surface area can be increased, the dispersion uniformity can be improved, the electrochemical charge transfer can be promoted, and the oxidation-reduction activity can be improved.

Description

Technical Field

[0001] This invention belongs to the field of electrochemical sensing technology, specifically relating to a nickel hexacyanoferrite, a yarn-type electrochemical sensing electrode, its preparation method, and its application. Background Technology

[0002] Cortisol is an important biomarker for assessing stress levels and diagnosing conditions such as depression. It can be detected in various bodily fluids, including blood, saliva, urine, and sweat. Compared to traditional blood tests that require venous blood draws and laboratory analysis, wearable cortisol sensors that detect saliva, urine, and sweat offer significant advantages such as non-invasiveness and the ability to perform remote, dynamic monitoring.

[0003] Molecularly imprinted polymers (MIPs) can mimic the key-lock recognition mechanism of natural antibodies, specifically binding to cortisol through pre-designed cavities that are complementary to cortisol molecules in terms of size, shape, and functional groups. This enables highly interference-resistant and highly sensitive sensing of cortisol. Furthermore, MIPs are simple to prepare, highly stable, and can reduce costs and improve sensor durability.

[0004] Coupling MIPs with redox probes allows for the amplification of sensing signals and the detection of cortisol levels through electrochemical techniques, thus enabling the development of electrochemical sensors targeting cortisol. Redox probes primarily contain Fe(CN)6... 4- / Fe(CN)6 3- Nanomaterials with redox active sites are typically represented by Prussian blue (PB) and its analogue PBA. Coprecipitation is one of the main methods for preparing PB and PBA, and the reaction temperature significantly affects their morphology, size, crystal structure, vacancy content, and redox activity. Improving the redox activity of redox probes such as PB and PBA is of great significance for enhancing sensitivity, shortening response time, and lowering the limit of detection.

[0005] Currently, most flexible electrochemical sensing electrodes based on Prussian blue analogues / MIPs are patch-type, which have disadvantages such as poor conformability, easy detachment, lack of breathability, and discomfort. In contrast, fiber-type and yarn-type electrodes can be directly woven into everyday clothing, offering superior softness and comfort.

[0006] Therefore, there is an urgent need in this field to develop a PB and PBA redox probe with high redox activity, which can be processed into fiber-type or yarn-type electrochemical sensing electrodes using continuous production technology, and improve sensitivity, shorten response time, reduce minimum detection limit, and improve specificity, thereby achieving excellent sensing performance. Summary of the Invention

[0007] Based on the aforementioned shortcomings and deficiencies in the prior art, one of the objectives of this invention is to at least solve one or more of the aforementioned problems in the prior art. In other words, one of the objectives of this invention is to provide a nickel hexacyanoferrite yarn-type electrochemical sensing electrode that meets one or more of the aforementioned requirements, as well as its preparation method and application.

[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing nickel hexacyanoferrite includes the following steps: (a) Dissolve ferrous acetate, nickel acetate tetrahydrate, and sodium citrate dihydrate in water to obtain solution A; Potassium ferricyanide was dissolved in water to obtain solution B; (b) Solution A was added dropwise to solution B, and the reaction was stirred at 2–8 °C for 12–36 h. After centrifugation, washing, and vacuum drying, nickel hexacyanoferrate (NiHCF) nanocubes were obtained.

[0009] As a preferred embodiment, the molar ratio of ferrous acetate, nickel acetate tetrahydrate, sodium citrate dihydrate, and potassium ferricyanide is (1-2):(1-2):(2-2.5):1.

[0010] This invention also provides a method for preparing a yarn-type electrochemical sensing electrode, comprising the following steps: (1) Using the NiHCF nanocube prepared by the preparation method described in any of the above schemes as the redox probe core and the molecularly imprinted polymer MIP as the specific recognition shell, NiHCF-MIP core-shell nanocube is prepared. (2) Preparation of spinning solution based on NiHCF-MIP core-shell nanocubes; (3) Using the conjugate electrospinning method, conductive carbon yarn is placed in the middle as the core yarn, and the sensing nanofibers obtained by spinning the spinning solution are wrapped around the conductive carbon yarn to obtain a yarn-type electrochemical sensing electrode with a core-sheath structure.

[0011] As a preferred embodiment, step (1) specifically includes the following steps: (11) Using pyrrole as a monomer, ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent, azobisisobutyronitrile (AIBN) as an initiator, cortisol as a target molecule, water / methanol mixed solution as a solvent, and NiHCF nanosheets as a redox probe, a polymer loaded with the target molecule was obtained through in-situ chemical polymerization. (12) The polymer carrying the target molecule was placed in an acetic acid / methanol mixture and stirred to elute the target molecule and create a cavity, thus obtaining NiHCF-MIP core-shell nanocubes that are specifically recognized by cortisol.

[0012] As a preferred embodiment, in step (11), the volume ratio of NiHCF nanocubes, pyrrole, EGDMA, AIBN, cortisol, and water / methanol mixed solution is 15 mg: 20-30 mmol: 40-60 mmol: 25-37.5 mmol: 8-12 mmol: 10 mL; wherein, the volume ratio of water to methanol in the water / methanol mixed solution is 1:(3-5). In step (12), the volume ratio of acetic acid to methanol in the acetic acid / methanol mixed solution is (1.5~2.5):1.

[0013] As a preferred embodiment, step (2) specifically includes the following steps: (21) Add polyacrylonitrile (PAN), thermoplastic polyurethane (TPU), and poloxamer F127 to DMF and stir in a water bath at 40-50°C until completely dissolved to obtain a light yellow, semi-transparent, viscous solution. (22) Add CNTs to a light yellow, semi-transparent, viscous solution and stir in a water bath at 40-50°C to disperse them evenly; then add NiHCF-MIP core-shell nano cube powder and continue stirring in a water bath at 40-50°C to disperse it evenly. (23) The solution from step (22) is subjected to ultrasonic degassing to obtain spinning solution.

[0014] As a preferred embodiment, the mass ratio of NiHCF-MIP, CNTs, PAN, TPU, and F127 is (3-12):10:300:100:100; The ratio of the sum of the masses of NiHCF-MIP, CNTs, PAN, TPU, and F127 to the solvent DMF is (5.13~5.22) g: 20 mL.

[0015] As a preferred embodiment, step (3) specifically includes the following steps: (31) Place the conductive carbon yarn in the middle as the core yarn, and load the spinning solution into two spinnerets with the needles facing the collecting horn. (32) During the conjugate electrospinning process, the sensing nanofibers formed by the spinning solution are wrapped around the conductive carbon core yarn, and the same conductive carbon core yarn is repeatedly spun 2 to 6 times to obtain a yarn-type electrochemical sensing electrode with a core-sheath structure.

[0016] The present invention also provides a yarn-type electrochemical sensing electrode prepared by the preparation method described in any of the preceding embodiments.

[0017] The present invention also provides the application of the yarn-type electrochemical sensing electrode as described above, as the sensing electrode of a wearable flexible electrochemical sensor for cortisol-specific sensing.

[0018] Compared with the prior art, the beneficial effects of this invention are: (1) The present invention uses a low-temperature co-precipitation method to obtain NiHCF with a nano-cube structure, a size as low as about 100 nm, and a vacancy content as high as about 33.3%, which is beneficial to increase the effective specific surface area, improve the dispersion uniformity, promote electrochemical charge transfer, and improve redox activity. (2) The NiHCF prepared in this invention is combined with MIP with specific recognition function, which is beneficial to improve sensitivity, speed up response, reduce the minimum detection limit, and ultimately improve electrochemical sensing performance. (3) The NiHCF-MIP core-shell nanoblock of the present invention tightly combines the NiHCF core with the redox probe function with the MIP shell structure with the cortisol-specific sensing function. This dual-function core-shell structure design not only facilitates the rapid transmission of the response signal after the cortisol-specific binding, but also avoids the intermittent and inefficient problem of spinning (or spinning yarn) first and then performing multiple functional finishing processes in the prior art, making one-step continuous large-scale processing possible. (4) The conjugate electrospinning preparation method of the present invention can wrap NiHCF-MIP sensing active nanofibers around conductive carbon core yarn, realize the one-step processing and forming of the "conductive core-sensing skin" core-skin structure yarn type electrochemical sensing electrode, and has the industrialization advantages of large-scale manufacturing and one-step continuous production. Attached Figure Description

[0019] Figure 1 This is a schematic diagram of the cortisol-specific sensing principle of the NiHCF-MIP core-shell nanocube of the present invention; Figure 2 This invention relates to a method for preparing NiHCF-MIP core-shell nanocubes. Figure 3 This invention relates to a method for preparing a conjugate electrospinning method for yarn-type electrochemical sensing electrodes; Figure 4 These are high-resolution transmission electron microscope (TEM) images and energy-dispersive X-ray spectroscopy (EDX) scan images of the NiHCF-MIP core-shell nanocubes prepared in Examples 1-5 of this invention. Figure 5 X-ray diffraction (XRD) curves of NiHCF nanocubes prepared in Examples 1-5 of this invention, NiHCF-MIP (BE) before target molecule elution, and NiHCF-MIP core-shell nanocubes after target molecule elution. Figure 6 A photograph of the yarn-type electrochemical sensing electrode prepared in Example 1 of this invention; Figure 7These are scanning electron microscope (SEM) images of the surface and cross-section of the yarn-type electrochemical sensing electrode prepared in Example 2 of this invention. Figure 8 These are images illustrating the fluorescent tracer water absorption properties of the yarn-type electrochemical sensing electrode prepared in Example 2 of this invention. Figure 9 Electrochemical impedance spectroscopy (EIS) of the yarn-type electrochemical sensing electrodes prepared in Examples 1-3 of this invention; Figure 10 The yarn-type electrochemical sensing electrodes prepared in Examples 2, 4, and 5 of this invention are in the absence of cortisol and contain 1 nmol·L⁻¹ -1 ~10 μmol·L -1 Linear sweep voltammetry (LSV) curves of cortisol in phosphate-buffered saline (PBS), resulting in linear fit images and calculated sensitivity and coefficient of determination. R 2 ; Figure 11 The current change of the yarn-type electrochemical sensing electrode prepared in Example 2 of this invention after sequentially adding glucose (Glu), lactate (Lac), uric acid (UA), tryptophan (Try), and cortisol to phosphate-buffered saline (PBS). ΔI Data chart; Figure 12 The images are SEM images of the NiHCF core-shell nanocubes prepared in Examples 1-5 and Comparative Example 1 of this invention. Figure 13 Photographs showing the uniformity of dispersion of the spinning solution prepared in Examples 2 (A, C) and Comparative Examples 1 (B, D) of the present invention; Figure 14 This is a comparison of the LSV curves and linear fitting images of the yarn-type electrochemical sensing electrodes prepared in Comparative Examples 1 and 2 of this invention. Detailed Implementation

[0020] The following provides a detailed description of the nickel hexacyanoferrite, yarn-type electrochemical sensing electrode, their preparation method, and applications of the present invention.

[0021] This invention uses nickel hexacyanoferrate (NiHCF) prepared by low-temperature co-precipitation as a redox probe core, and grows molecularly imprinted polymer (MIP) on it in situ as a cortisol-specific recognition shell to obtain NiHCF-MIP core-shell nanocubes with cortisol-specific sensing function. The nanocubes are then prepared as a spinning solution and spun into sensing active nanofibers by conjugated electrospinning technology. These nanofibers are then wrapped around conductive carbon core yarn in one step to obtain a yarn-type electrochemical sensing electrode with cortisol-specific sensing function.

[0022] The cortisol-specific sensing principle of the present invention is as follows: Figure 1 As shown, the details are as follows: The NiHCF-MIP core-shell nanocube of this invention tightly integrates a NiHCF core with redox probe function and a MIP shell with cortisol-specific sensing function, thus possessing both redox probe and cortisol-specific sensing functions. The MIP shell has a cavity that is complementary to the size, shape, and functional groups of the cortisol molecule. When cortisol in a body fluid sample is recognized by the cavity, it hinders the charge transfer of the redox probe, i.e., the NiHCF core, leading to a weakening of the redox signal peak of the NiHCF core. The concentration of cortisol can be quantified based on the degree of weakening of the redox signal peak. However, when other substances are present in the body fluid sample, such as lactic acid, glucose, uric acid, tryptophan, etc., these substances are incompatible with the cavity and cannot be recognized by it, thus failing to cause a change in the redox signal peak. Therefore, the cortisol-specific sensing function is achieved.

[0023] Among them, NiHCF prepared by low-temperature co-precipitation has the characteristics of nanocube structure, small size (around 100 nm), and high vacancy content (around 33.3%), which is beneficial for increasing the effective specific surface area, improving dispersion uniformity, promoting electrochemical charge transfer, and enhancing redox activity. NiHCF and MIP act as redox probes and cortisol-specific recognition, respectively. This NiHCF-MIP core-shell nanocube structure design can rapidly transmit electrochemical signal changes induced by cortisol. The yarn-type electrochemical sensing electrode prepared by conjugated electrospinning technology has good conductivity, mechanical flexibility, and body fluid sample absorption capacity. It not only has sensing performance with high specificity, high sensitivity, low detection limit, and fast response, but also has the prospect of one-step continuous large-scale production and low-cost commercialization.

[0024] Firstly, the preparation method of NiHCF-MIP core-shell nanocubes is as follows: Figure 2 As shown, the specific steps include the following: (1) Dissolve ferrous acetate, nickel(II) acetate tetrahydrate (i.e., nickel acetate tetrahydrate) and sodium citrate dihydrate in deionized water to obtain solution A; Potassium ferricyanide was dissolved in deionized water to obtain solution B; Solution A is added dropwise to solution B, and the mixture is stirred and reacted at a temperature of 2–8 °C for 12–36 h. After repeated centrifugation, washing, and vacuum drying, NiHCF nanocube powder with a size as low as about 100 nm can be obtained.

[0025] The molar ratio of ferrous acetate, nickel(II) acetate tetrahydrate, sodium citrate dihydrate, and potassium ferricyanide is (1-2):(1-2):(2-2.5):1. The specific molar ratio can be determined according to the actual application requirements.

[0026] (2) NiHCF nano cube powder (redox probe), pyrrole (monomer), EGDMA (crosslinking agent), and cortisol (target molecule) were added to a deionized water / methanol mixed solution (solvent); the vacuum-nitrogen process was repeated three times and the mixture was stirred thoroughly; AIBN (initiator) was added and the vacuum-nitrogen process was repeated three times to remove oxygen and prevent decarboxylation reaction; the reaction was stirred at 40-50℃ for 4-6 h.

[0027] The ratio of NiHCF nanocubes, pyrrole, EGDMA, AIBN, cortisol, and water / methanol mixed solution is 15 mg: 20–30 mmol: 40–60 mmol: 25–37.5 mmol: 8–12 mmol: 10 mL; and the volume ratio of water to methanol in the water / methanol mixed solution is 1:(3–5).

[0028] (3) Collect the powder by centrifugation, immerse it in a mixed acetic acid / methanol solution and stir for 12 h to elute the target molecules and generate the corresponding molecularly imprinted cavities. Wash the powder repeatedly by centrifugation with deionized water and methanol solution, and then vacuum dry it to obtain NiHCF-MIP core-shell nanocube powder. The volume ratio of acetic acid to methanol in the acetic acid / methanol mixed solution is (1.5~2.5):1.

[0029] Secondly, the preparation method of spinning solution based on NiHCF-MIP core-shell nanocubes includes the following steps: (1) Add PAN, TPU and F127 to DMF and stir in a 40 °C water bath for 2 h until completely dissolved to obtain a light yellow semi-transparent viscous solution; add CNTs to the light yellow semi-transparent viscous solution and stir in a 40 °C water bath for 2 h to disperse it evenly; then add NiHCF-MIP core-shell nano cube powder to the light yellow semi-transparent viscous solution and stir in a 40 °C water bath for 1 h to disperse it evenly.

[0030] The mass ratio of NiHCF-MIP, CNTs, PAN, TPU, and F127 is (3-12):10:300:100:100, and the ratio of the sum of the masses of NiHCF-MIP, CNTs, PAN, TPU, and F127 to the solvent DMF is (5.13-5.22) g:20 mL. The specific mass ratio and proportion can be determined according to the actual application requirements.

[0031] (2) The mixed solution was ultrasonically treated at 300 W for 1 h to remove air bubbles, and a stable and uniform spinning solution was obtained.

[0032] Thirdly, the conjugate electrospinning preparation method of yarn-type electrochemical sensing electrodes is as follows: Figure 3 As shown, the specific steps include the following: (1) Conjugate electrospinning apparatus and process as follows Figure 3 As shown, conductive carbon yarn is placed in the middle as the core yarn, and spinning solution is loaded into two spinnerets with the spinneret (i.e., needle) facing the collecting horn. During the conjugate electrospinning process, the sensing nanofibers formed by the spinning solution will wrap around the conductive carbon core yarn to obtain a yarn-type electrochemical sensing electrode.

[0033] The syringe has a capacity of 5 mL and a needle diameter of 20 g. The voltages of the two spinnerets are +12.5 kV and -12.5 kV respectively. The two spinnerets are adjusted to be 15 cm apart and directly facing the center of the collecting horn, 10 cm away from it. The micropump propulsion rate is 1–3 mL·h -1 The core yarn collection speed is 12 cm·min -1 The horn is rotated at a speed of 100–200 r·min. -1 .

[0034] The temperature of the spinning environment was 30±5 ℃ and the relative humidity was 50±10%.

[0035] (2) The conjugate electrospinning process is repeated 2 to 6 times on the same conductive carbon core yarn to obtain a yarn-type electrochemical sensing electrode.

[0036] The preparation temperature of the NiHCF nanocubes of the present invention has a significant impact on the morphology, structure and size, crystal structure and vacancy content, which in turn significantly affects the redox activity and sensing performance. The loading amount of NiHCF-MIP core-shell nanocubes on the yarn also has a significant impact on the sensing performance, which can be adjusted by controlling the number of spinning processes. The spinning process parameters can be processed with reference to the conditions and methods known in the art.

[0037] In the spinning solution formulation of this invention, DMF, CNTs, F127, TPU, and PAN are all common solvents, conductive agents, dispersants, and polymer matrices in the art. The advantage of using a mixture of TPU and PAN as the polymer matrix is ​​that it combines the mechanical elasticity of TPU with the water absorption of PAN, while ensuring the spinnability of nanofibers and the ability to collect bodily fluid samples.

[0038] The characterization method in the following embodiments includes: The core-shell nanocube structure and elemental distribution of NiHCF-MIP were characterized by transmission electron microscopy-energy dispersive X-ray spectroscopy (HRTEM-EDX); the crystal structure was characterized by X-ray diffraction (XRD). The surface and cross-sectional microstructure of the yarn-type electrochemical sensing electrode were characterized by field emission scanning electron microscopy (FESEM); the water absorption of the yarn-type electrochemical sensing electrode was demonstrated by fluorescence tracing.

[0039] The sensing performance testing method in the following embodiments includes: The sensing performance of the yarn-type electrochemical sensing electrode was tested using a three-electrode system and an electrochemical workstation, with Ag / AgCl as the reference electrode, a platinum sheet as the counter electrode, cortisol-sensing yarn as the working electrode, and 0.1 M PBS as the electrolyte solution. The sensitivity was denoted as... s Coefficient of determination R 2 Sensor performance parameters such as the lowest detection limit (LOD) were evaluated using linear sweep voltage-current characteristic (LSV) curves. The test voltage range was -0.6 to 0.2 V, and the scan rate was 10 mV·s. -1 The LSV peak values ​​in PBS containing different concentrations of cortisol were denoted as [missing information]. I i The LSV peak value in blank PBS is denoted as I 0 The change in current is denoted as Δ. I Δ C The difference in cortisol concentration (Δ in this invention) C 10 μmol·L -1 Subtract 1 nmol·L -1 ), sensitivity s The calculation is as follows: s =Δ I / Δ C =( I i - I 0 ) / Δ C ; σ The formula for calculating LOD, which is the average standard deviation, is: LOD=3* σ / s .

[0040] The following specific embodiments further explain and illustrate the present invention, including nickel hexacyanoferrite, yarn-type electrochemical sensing electrode, its preparation method, and its application.

[0041] Example 1: The method for preparing the yarn-type electrochemical sensing electrode in this embodiment includes the following steps: (1) For the preparation method of NiHCF-MIP core-shell nanocube powder, please refer to the appendix. Figure 2 Specifically, it includes the following steps: Preparation of NiHCF nanocube powder: 600 μmol ferrous acetate, 600 μmol nickel(II) acetate tetrahydrate, and 900 μmol trisodium citrate dihydrate were dissolved in 20 mL of deionized water to obtain solution A; 400 μmol potassium ferricyanide was dissolved in 20 mL of deionized water to obtain solution B; solution A was added dropwise to solution B, and the mixture was heated at 5 °C at 1000 r·min. -1 The reaction was stirred at a high speed for 24 h; NiHCF nano cube powder was obtained by repeatedly washing with 60 mL of deionized water 4 times and vacuum drying.

[0042] In-situ chemical polymerization of MIPs with specific cortisol recognition: The chemical polymerization reaction system mainly includes the target molecule (cortisol), monomer (pyrrole), crosslinking agent (EGDMA), and initiator (AIBN). 8 mmol of cortisol, 20 mmol of Py, 40 mmol of EGDMA, and 15 mg of NiHCF nanocube powder were added. 15 mg of NiHCF nanocube powder was added to 10 mL of a deionized water / methanol mixture (volume ratio 1:4) and stirred until homogeneous. The vacuum-nitrogen purging process was repeated three times, followed by induction at 25 °C at 500 r·min. -1 Stirring at a constant speed for 24 h; add 25 mmol of AIBN, and repeat the vacuum-nitrogen purging process three times to remove oxygen and prevent decarboxylation; place the reaction vessel in a 40 °C water bath and set the stirring speed to 500 r·min. -1 The polymerization reaction was carried out for 5 hours, and the powder was collected by centrifugation. Cortisol elution: The powder collected by centrifugation was immersed in 5 mL of a mixed solution of acetic acid / methanol (volume ratio 7:3) and eluted at 500 r·min. -1 Stirring at a high speed for 12 h to remove target molecules and generate corresponding molecularly imprinted cavities; washing three times with deionized water and once with methanol solution, and drying in a vacuum oven at 30 °C for 12 h, yields NiHCF-MIP core-shell nanocube powder with cortisol sensing activity.

[0043] (2) The method for preparing spinning solution includes the following steps: The spinning solution consists of NiHCF-MIP core-shell nanocube powder, CNTs, PAN, TPU, and F127 in a mass ratio of 12:10:300:100:100. The mass fraction of NiHCF-MIP core-shell nanocube powder is approximately 2.4 wt%, and the ratio of solid mass to solvent DMF volume is approximately 5.22 g:20 mL.

[0044] Adding PAN, TPU, and F127 to DMF and stirring in a 40 °C water bath for 2 hours until completely dissolved yields a light yellow, semi-transparent, viscous solution. Adding CNTs to this solution and stirring in a 40 °C water bath for 2 hours ensures uniform dispersion. Adding NiHCF-MIP nanocubes, a cortisol-sensing active material, to this solution and stirring in a 40 °C water bath for 1 hour ensures uniform dispersion. Sonicating the mixture at 300 W for 1 hour removes air bubbles, resulting in a stable and uniform spinning solution.

[0045] (3) The method for preparing the conjugate electrospinning of yarn-type electrochemical sensing electrodes is shown in the appendix. Figure 3 Specifically, it includes the following steps: Conductive carbon yarn was placed in the center as the core yarn. A 5 mL syringe with a 20 G needle diameter (the international standard for needle diameter is G) was used. The voltages of the two spinnerets were set to +12.5 kV and -12.5 kV respectively. The two spinnerets were adjusted to a distance of 15 cm, directly facing the center of the collecting horn and 10 cm away from it. The spinning environment temperature was 30±5 °C, and the relative humidity was 50±10%. The micropump feed rate was 2 mL·h. -1 The core yarn collection speed is 12 cm·min -1 The horn is rotated at a speed of 150 r·min. -1 .

[0046] By performing the above-mentioned conjugate electrospinning process twice (2 cycles) on the same conductive carbon core yarn, the sensing nanofibers formed by the spinning solution can be wrapped around the conductive carbon core yarn to obtain a yarn-type electrochemical sensing electrode.

[0047] like Figure 4 As shown, the obtained NiHCF-MIP powder has a core-shell nanocube structure. EDX elemental surface scan analysis shows that the NiHCF nanocubes rich in Fe and Ni elements form the core, and the MIPs rich in C and N elements form the shell, with the two tightly bonded together.

[0048] like Figure 5 As shown, the XRD characteristic peaks of the obtained NiHCF nanocubes are similar to those of Ni[Fe(CN6)] in PDF card number 86-0501. 0.667H2O 3.333 The results are completely consistent, proving that its crystal structure is cubic phase, space group F̅43m, with a cell parameter of 10.23 Å ​​× 10.23 Å ​​× 10.23 Å ​​and a vacancy content as high as 33.3%. The main diffraction peaks appearing at 17.3°, 24.6°, 35.1°, and 39.4° correspond to the (200), (220), (400), and (420) crystal planes, respectively. Further, in-situ polymerization of MIP and elution of target molecules were carried out on NiHCF nanocubes to obtain NiHCF-MIP(BE) and NiHCF-MIP core-shell nanocubes. The XRD characteristic peaks of the two are almost completely consistent with those of the NiHCF nanocubes, proving that the in-situ polymerization and elution processes have almost no effect on the crystal structure.

[0049] like Figure 6 As shown, the yarn-type electrochemical sensing electrode prepared in Example 1 integrates redox probe and cortisol-specific sensing functions into one NiHCF-MIP core-shell nanocubes. It can be produced in a one-step continuous large-scale process using conjugated electrospinning technology. The yield of Example 1 reached 3.6 m·h. -1 .

[0050] Example 2: The method for preparing the yarn-type electrochemical sensing electrode in this embodiment differs from that in Example 1 in that the number of times the conjugate electrospinning process is performed is adjusted to 4 cycles. Specifically, by performing the above-mentioned conjugate electrospinning process four times (4 cyles) on the same conductive carbon core yarn, the sensing nanofibers formed by the spinning solution can be wrapped around the conductive carbon core yarn to obtain a yarn-type electrochemical sensing electrode. The other steps are the same as in Example 1, and will not be repeated here.

[0051] like Figure 7 As shown, SEM images of the surface and cross-section of the yarn-type electrochemical sensing electrode prepared in this embodiment demonstrate its nanofiber network structure, as well as that of the outer layer. The outer layer is rich in highly hydrophilic substances such as PAN, and the nanofiber network structure further enhances its hydrophilicity, which is beneficial for improving the collection capacity of body fluid samples. This design perfectly combines the high conductivity and flexibility of the conductive carbon core yarn with the strong water absorption, high sensitivity, high specificity, fast response, and low detection limit of the NiHCF-MIP sensing active nanofibers in the outer layer.

[0052] like Figure 8 As shown, when a water-soluble fluorescent dye was added to the yarn-type electrochemical sensing electrode prepared in this embodiment, it was found that the dye droplet could be completely absorbed within 5 seconds, proving its strong water absorption, which is beneficial to improving the collection capacity of body fluid samples.

[0053] Example 3: The difference between the preparation method of the yarn-type electrochemical sensing electrode in this embodiment and that in Example 1 is that the number of times the conjugate electrospinning process is carried out is adjusted to 6 cycles. Specifically, by performing the above-mentioned conjugate electrospinning process 6 times on the same conductive carbon core yarn, the sensing nanofibers formed by the spinning solution can be wrapped around the conductive carbon core yarn to obtain a yarn-type electrochemical sensing electrode. The other steps are the same as in Example 1, and will not be repeated here.

[0054] like Figure 9 As shown, the EIS curves of the yarn-type electrochemical sensing electrodes prepared in Examples 1-3 are illustrated. The semicircle at the front and the sloping line at the back represent the charge transfer resistance and the electrolyte ion diffusion rate, respectively. The smaller the semicircle and the steeper the sloping line, the smaller the charge transfer resistance and the faster the ion diffusion rate. Comparison revealed that the electrochemical performance was optimal when the conjugate electrospinning process was performed four times (4 cycles). Therefore, in the following examples and comparative examples, it was preferred to perform the conjugate electrospinning process four times to further explore the effect of the amount of NiHCF-MIP core-shell nanocube powder.

[0055] Example 4: The difference between the fabrication method of the yarn-type electrochemical sensing electrode in this embodiment and that in Example 2 is as follows: The mass ratio of NiHCF-MIP core-shell nanocube powder, CNTs, PAN, TPU, and F127 in the spinning solution was adjusted to 3:10:300:100:100, with the mass fraction of NiHCF-MIP core-shell nanocube powder being approximately 0.6 wt%. Consequently, the ratio of solid mass to solvent DMF volume became 5.13 g:20 mL. By performing the above-mentioned conjugate electrospinning process four times on the same conductive carbon core yarn, the sensing nanofibers formed by the spinning solution can be wrapped around the conductive carbon core yarn to obtain a yarn-type electrochemical sensing electrode. The other steps are the same as in Example 2, and will not be repeated here.

[0056] Example 5: The difference between the fabrication method of the yarn-type electrochemical sensing electrode in this embodiment and that in Example 2 is as follows: The mass ratio of NiHCF-MIP core-shell nanocube powder, CNTs, PAN, TPU, and F127 in the spinning solution was adjusted to 6:10:300:100:100, with the mass fraction of NiHCF-MIP core-shell nanocube powder being approximately 1.2 wt%. Consequently, the ratio of solid mass to solvent DMF volume became 5.16 g:20 mL. By performing the above-mentioned conjugate electrospinning process four times on the same conductive carbon core yarn, the sensing nanofibers formed by the spinning solution can be wrapped around the conductive carbon core yarn to obtain a yarn-type electrochemical sensing electrode. The other steps are the same as in Example 2, and will not be repeated here; like Figure 10 As shown, the yarn-type electrochemical sensing electrodes prepared in Examples 4, 5, and 2 all respond to changes in cortisol concentration (0 nmol·L⁻¹). -1 1 nmol·L -1 10 nmol·L -1 100 nmol·L -1 1 μmol·L -1 10 μmol·L -1 (This shows the change in current) ΔI Furthermore, Example 2, which used a larger amount of NiHCF-MIP core-shell nanocube powder, exhibited the largest current change. ΔI And sensitivity, the sensitivity reaches 2.08 μA·dec -1 .

[0057] like Figure 11 As shown, the current change of the yarn-type electrochemical sensing electrode prepared in Example 2 after glucose, lactic acid, uric acid, tryptophan, and cortisol were added to PBS sequentially. ΔI The study found that it responded weakly to glucose, lactic acid, uric acid, and tryptophan, but responded strongly to cortisol, demonstrating its cortisol-specific sensing performance.

[0058] Comparative Example 1: The difference between the preparation method of the yarn-type electrochemical sensing electrode in this comparative example and that in Example 2 is that the NiHCF nanocubes are prepared by conventional co-precipitation method at a preparation temperature of 25°C (5°C in Example 2). Specifically, the preparation method of NiHCF / NIP core-shell nanocube powder includes the following steps: Preparation of NiHCF nanocube powder: 600 μmol ferrous acetate, 600 μmol nickel(II) acetate tetrahydrate, and 900 μmol sodium citrate dihydrate were dissolved in 20 mL of deionized water to obtain solution A; 400 μmol potassium ferricyanide was dissolved in 20 mL of deionized water to obtain solution B; solution A was added dropwise to solution B, and the mixture was heated at 25 °C at 1000 r·min. -1 The reaction was stirred at a high speed for 24 h; NiHCF nano cube powder was obtained by repeatedly washing with 60 mL of deionized water 4 times and vacuum drying.

[0059] The other steps are the same as in Example 2, and will not be repeated here.

[0060] like Figure 12 The figures shown are SEM images of NiHCF nanocubes prepared in Examples 1-5 (Figure A, preparation temperature 5 °C) and Comparative Example 1 (Figure B, preparation temperature 25 °C), respectively. It can be seen that the particle size of NiHCF nanocubes obtained by the low-temperature coprecipitation method is about 100 nm, while the particle size of NiHCF obtained by the conventional coprecipitation method increases to about 200 nm.

[0061] like Figure 13 As shown, these are examples 2 ( Figure 13 Examples A and C), Comparative Example 1 ( Figure 13 The images of the dispersion uniformity of the spinning solution prepared by B and D in Example 2 show that the dispersion uniformity of Example 2 is significantly better than that of Comparative Example 1. This is because the NiHCF nano cubes prepared by the low-temperature co-precipitation method in Example 2 have smaller particle sizes, and the resulting NiHCF-MIP nano cubes naturally have smaller particle sizes as well, thus resulting in better dispersion uniformity.

[0062] like Figure 14 The figure shows a comparison of the LSV curves and linear fitting results of the yarn-type electrochemical sensing electrodes prepared in Comparative Example 1 and Example 2. The comparison reveals that the current change in Example 2... ΔI The results are significantly better than those of Comparative Example 1, indicating that it has higher sensitivity. This is because the NiHCF nanocubes prepared by the low-temperature co-precipitation method in Example 2 are cubic Ni[Fe(CN6)] with space group F̅43m. 0.667 H2O 3.333 With a vacancy content as high as 33.3%, it promotes electrochemical charge transfer and improves redox activity. The core role of NiHCF nanocubes in this invention is as a redox probe, and the use of a low-temperature co-precipitation preparation method to improve its redox activity will also enhance the electrochemical sensing performance of the electrode.

[0063] Given that there are numerous embodiments of the present invention, and the raw materials and quantities involved can be selected within a limited range according to actual needs, and that the experimental data for each embodiment are extensive and numerous, it is not suitable to list and describe them one by one here. However, the content to be verified and the final conclusions obtained in each embodiment are similar. Therefore, the verification content of each embodiment will not be described one by one here.

[0064] The above description is merely a detailed explanation of preferred embodiments and principles of the present invention. For those skilled in the art, there may be changes in specific implementation methods based on the ideas provided by the present invention, and these changes should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing nickel hexacyanoferrate, characterized in that, Includes the following steps: (a) Dissolve ferrous acetate, nickel acetate tetrahydrate, and sodium citrate dihydrate in water to obtain solution A; Potassium ferricyanide was dissolved in water to obtain solution B; (b) Solution A was added dropwise to solution B, and the reaction was stirred at 2–8 °C for 12–36 h. After centrifugation, washing, and vacuum drying, nickel hexacyanoferrate (NiHCF) nanocubes were obtained.

2. The preparation method according to claim 1, characterized in that, The molar ratio of ferrous acetate, nickel acetate tetrahydrate, sodium citrate dihydrate, and potassium ferricyanide is (1-2):(1-2):(2-2.5):

1.

3. A method for preparing a yarn-type electrochemical sensing electrode, characterized in that, Includes the following steps: (1) Using the NiHCF nanocube prepared by the preparation method described in claim 1 or 2 as the redox probe core and the molecularly imprinted polymer MIP as the specific recognition shell, NiHCF-MIP core-shell nanocube is prepared. (2) Preparation of spinning solution based on NiHCF-MIP core-shell nanocubes; (3) Using the conjugate electrospinning method, conductive carbon yarn is placed in the middle as the core yarn, and the sensing nanofibers obtained by spinning the spinning solution are wrapped around the conductive carbon yarn to obtain a yarn-type electrochemical sensing electrode with a core-sheath structure.

4. The preparation method according to claim 3, characterized in that, Step (1) specifically includes the following steps: (11) Using pyrrole as a monomer, ethylene glycol dimethacrylate (EGDMA) as a crosslinking agent, azobisisobutyronitrile (AIBN) as an initiator, cortisol as a target molecule, water / methanol mixed solution as a solvent, and NiHCF nanosheets as a redox probe, a polymer loaded with the target molecule was obtained through in-situ chemical polymerization. (12) The polymer carrying the target molecule was placed in an acetic acid / methanol mixture and stirred to elute the target molecule and create a cavity, thus obtaining NiHCF-MIP core-shell nanocubes that are specifically recognized by cortisol.

5. The preparation method according to claim 4, characterized in that, In step (11), the volume ratio of NiHCF nanocubes, pyrrole, EGDMA, AIBN, cortisol, and water / methanol mixed solution is 15 mg: 20-30 mmol: 40-60 mmol: 25-37.5 mmol: 8-12 mmol: 10 mL; wherein, the volume ratio of water to methanol in the water / methanol mixed solution is 1:(3-5). In step (12), the volume ratio of acetic acid to methanol in the acetic acid / methanol mixed solution is (1.5~2.5):

1.

6. The preparation method according to claim 3, characterized in that, Step (2) specifically includes the following steps: (21) Add polyacrylonitrile (PAN), thermoplastic polyurethane (TPU), and poloxamer F127 to DMF and stir in a water bath at 40-50°C until completely dissolved to obtain a light yellow, semi-transparent, viscous solution. (22) Add CNTs to a light yellow, semi-transparent, viscous solution and stir in a water bath at 40-50°C to disperse them evenly; then add NiHCF-MIP core-shell nano cube powder and continue stirring in a water bath at 40-50°C to disperse it evenly. (23) The solution from step (22) is subjected to ultrasonic degassing to obtain spinning solution.

7. The preparation method according to claim 6, characterized in that, The mass ratio of NiHCF-MIP, CNTs, PAN, TPU, and F127 is (3-12):10:300:100:100; The ratio of the sum of the masses of NiHCF-MIP, CNTs, PAN, TPU, and F127 to the solvent DMF is (5.13~5.22) g: 20 mL.

8. The preparation method according to claim 6, characterized in that, Step (3) specifically includes the following steps: (31) Place the conductive carbon yarn in the middle as the core yarn, and load the spinning solution into two spinnerets with the needles facing the collecting horn. (32) During the conjugate electrospinning process, the sensing nanofibers formed by the spinning solution are wrapped around the conductive carbon core yarn, and the same conductive carbon core yarn is repeatedly spun 2 to 6 times to obtain a yarn-type electrochemical sensing electrode with a core-sheath structure.

9. A yarn-type electrochemical sensing electrode prepared by the preparation method according to any one of claims 3-8.

10. The application of the yarn-type electrochemical sensing electrode as described in claim 9, characterized in that, As a sensing electrode for wearable flexible electrochemical sensors, it is used for cortisol-specific sensing.

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