A preparation method of in-situ controllable inorganic salt micro-nano dendrite based on tris-hcl buffer

Abstract

The application discloses a preparation method of in-situ controllable inorganic salt micro-nano dendritic crystals based on Tris-HCl buffer solution, which comprises the following steps: adjusting the pH value of the Tris-HCl buffer solution by NaOH to generate NaCl in-situ and obtain a precursor solution; and adding the precursor solution on a solid substrate with surface energy modification and evaporating and drying in a constant temperature and humidity environment to spontaneously induce the generation of NaCl micro-nano dendritic crystals with dendritic micro-nano fractal pattern characteristics. The application utilizes the NaCl generated by the in-situ neutralization reaction between NaOH and the original acidic component in the buffer solution as a skeleton material, relies on the high viscoelastic quasi-crystalline network formed by the concentration of the organic medium, breaks the isotropic growth balance of NaCl through space steric adsorption, and realizes the controllable self-assembly of the dendritic crystals. The method has low cost and simple operation, and can control the micro-nano structure of the deposit by only adjusting the contact angle of the substrate surface or the initial concentration of the Tris-HCl, thereby providing a new self-assembly technical approach for the efficient enrichment, directional arrangement and fluorescence enhancement detection of trace biomarkers in biochips.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano materials technology and crystal engineering, and specifically relates to a method for regulating the microstructure of salt deposits by in-situ reaction of organic buffer solution. Background Technology

[0002] With the rapid development of micro-nano fabrication technology in fields such as biochips, flexible electronics, biomimetic surfaces, and microfluidic systems, the demand for micro-nano templates with complex three-dimensional topological structures, high specific surface areas, and controllable wettability is increasing. In particular, biomimetic porous microchannels and superhydrophobic surfaces show broad application prospects in droplet manipulation, cell capture, trace detection, drag reduction, and noise reduction.

[0003] Currently, common methods for constructing such micro / nano topological structures mainly include: photolithography and electron beam lithography (EBL), focused ion beam (FIB) etching, reactive ion etching (RIE), nanoimprint lithography (NIL), and template methods combined with casting processes. Among these, while photolithography and EBL can achieve high-precision patterns, the equipment is expensive, the processes are complex, the yield is low, and it is difficult to achieve large-area, low-cost manufacturing. Although nanoimprint lithography and template methods can replicate micro / nano structures, the preparation of the master template is extremely demanding, and they usually still rely on photolithography or electron beam etching to obtain the original template.

[0004] In recent years, the "sacrificial template" based casting strategy has attracted attention. This involves first preparing a removable micro / nanostructure template, then casting a polymer material (such as PDMS) onto it, and finally selectively removing the template to obtain a porous or columnar array complementary to the original structure. The key to this method lies in whether the template preparation is simple, controllable, low-cost, and easy to remove. Traditional sacrificial templates often employ metal nanoparticles, ZnO nanorods, polystyrene microspheres, etc., but these methods typically require high temperatures, vacuum, electrochemical deposition, or complex surface modifications. Furthermore, the removal process often involves strong acids, strong bases, or organic solvents, which can easily damage the polymer structure or introduce contamination.

[0005] Water-soluble inorganic salts (such as NaCl) are considered ideal "green sacrificial template" materials due to their excellent water solubility and environmental friendliness. However, conventional NaCl crystals tend to grow into thermodynamically stable cubic or funnel-shaped crystals under natural evaporation conditions, making it difficult for them to spontaneously form highly branched, scale-ordered dendritic fractal structures. This limits their application in complex topological templates such as biomimetic porous channels or superhydrophobic surfaces. Although some studies have attempted to control the morphology of NaCl crystals by adding polymers or surfactants, these added reagents often increase system complexity, reduce biocompatibility, and make it difficult to achieve precise morphology control.

[0006] Therefore, developing a method for preparing NaCl micro / nano dendrites that requires no external template agent, is simple in process, low in cost, and allows for precise control of the morphology, and using it as a green sacrificial template for the fabrication of biomimetic porous microchannels or superhydrophobic surfaces, has significant scientific and application value. Summary of the Invention

[0007] The purpose of this invention is to address the problems of high cost and demanding equipment requirements of existing micro-nano patterning methods by providing a low-cost, highly controllable in-situ tunable inorganic salt micro-nano dendrite preparation method based on Tris-HCl buffer.

[0008] To achieve the above objectives, the present invention provides a method for preparing in-situ tunable inorganic salt micro / nano dendrites based on Tris-HCl buffer, comprising the following steps:

[0009] S1. Adjust the pH of the Tris-HCl buffer solution to 6.4–8.4 using NaOH to obtain a precursor solution containing NaCl.

[0010] S2. Surface modification treatment is performed on the solid substrate to obtain the deposition substrate.

[0011] S3. The NaCl-containing precursor solution obtained in S1 is dropped onto the deposition substrate obtained in S2, and evaporated in an environment with constant temperature and humidity to spontaneously induce the formation of NaCl micro-nano dendrites with dendritic micro-nano fractal pattern characteristics.

[0012] Preferably, in step S1, the pH of the Tris-HCl buffer is adjusted to 6.4–8.4 using NaOH, then λ-DNA is added to make the final concentration of λ-DNA in the system 0.001–0.01 μg / μL, and the mixture is homogeneous to obtain a precursor solution containing NaCl.

[0013] Preferably, the initial concentration of the Tris-HCl buffer in S1 is 5–10 mmol / L.

[0014] Preferably, the surface modification treatment in S2 is a hydrophobic modification treatment: a hydrophobic polymer material is coated on the surface of a solid substrate, and a hydrophobic deposition substrate is formed after annealing and curing.

[0015] Preferably, the hydrophobic polymer material is any one of polymethyl methacrylate (PMMA), polystyrene (PS), polycarbonate (PC), polyvinyl chloride (PVC), polypropylene (PP), polyethylene (PE), polyvinylidene fluoride (PVDF), and polydimethylsiloxane (PDMS).

[0016] Preferably, the surface modification treatment in S2 is a hydrophilic modification treatment: the solid substrate is subjected to wet chemical oxidation cleaning to hydroxylate its surface and obtain a hydrophilic deposition substrate.

[0017] Preferably, the wet chemical oxidation cleaning is performed by placing the solid substrate in a 0.1-1 mol / L NaOH aqueous solution and immersing it in a water bath at 50-65°C for 1-2 hours, followed by rinsing and drying.

[0018] Preferably, the constant temperature in S3 is 18–30°C and the relative humidity is 25%–35%.

[0019] The mechanism of this invention is as follows: Utilizing droplet evaporation-induced self-assembly technology, the thermodynamic equilibrium is disrupted through competitive crystallization between the organic medium and the in-situ inorganic salt, affecting the microstructure of the inorganic salt and thus altering its crystal morphology, achieving a morphological transformation from conventional cubic crystals to dendritic crystals. Specifically, as water evaporates, Tris-HCl molecules self-assemble using multiple hydrogen bonds to form a highly viscoelastic quasi-crystalline network, greatly restricting the crystallization of Na+. + and Cl - Long-range mass transport. The bulky Tris-HCl molecule acts as a "soft template," adsorbing onto the high surface energy, flat crystal faces (such as the {100} face) of NaCl crystals through steric hindrance, hindering the layered accumulation of ions. This diffusion hindrance amplifies the Berg effect, forcing NaCl crystals to break their isotropic growth equilibrium and follow a diffusion-restricted aggregation mechanism, preferentially growing at the vertices of least resistance, thus transforming them from a conventional thermodynamically stable cubic structure into a dendritic crystalline structure with micro-nano fractal patterns and cross-scale order. When λ-DNA macromolecules are introduced into the precursor solution, the long chain structure and negative charge of DNA molecules further affect the NaCl crystals. + and Cl - The diffusion behavior and nucleation sites of NaCl crystals are investigated. DNA molecules and the Tris-HCl quasicrystalline network exhibit a synergistic effect, enhancing steric hindrance and providing additional nucleation templates, thus transforming the NaCl crystal growth pattern from a continuous network of dendrites to isolated, dispersed dendritic units. By adjusting the DNA concentration, precise control over the density, size, and branching complexity of the dendritic units can be achieved.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention utilizes the physicochemical phase transition and medium confinement effect induced by Tris-HCl buffer during droplet drying to actively construct complex micro-nano patterns. Based on the self-assembly characteristics of inorganic salts induced by organic media, this method spontaneously induces the generation of NaCl micro-nano dendrites with different microstructures simply by controlling the evaporation conditions and surface properties. Compared to traditional photolithography and electron beam lithography methods, this invention eliminates the need for expensive photolithography equipment and crystallization modifiers, resulting in lower cost, shorter processing time, simpler operation, and faster assembly speed—generally completing the preparation within one hour. This invention cleverly achieves in-situ self-sourced technology, using NaCl generated from the in-situ neutralization reaction between added NaOH and the original acidic components in the Tris-HCl buffer as the framework material, eliminating the need for additional salt sources. By simply changing the surface wettability of the substrate (e.g., adjusting the contact angle through hydrophobic or hydrophilic modification), the evaporation temperature, or the initial concentration of the Tris-HCl buffer, the morphology of the NaCl micro-nano dendrites can be precisely tailored to obtain dendritic structures with different branch densities and fractal dimensions. Furthermore, by introducing biomacromolecules such as λ-DNA into the system, the dendrite morphology can be further controlled from a continuous network to isolated and dispersed dendrite units, meeting the needs of specific application scenarios such as arrayed sensing and single-particle capture, and further expanding the applicability of the method of this invention in morphology control. This invention provides a new approach and direction for the fabrication of micro / nano patterns for biochips. The fabricated micro / nano patterns have controllable morphology and have significant application potential in the fields of efficient enrichment, directional alignment, and fluorescence-enhanced detection of trace biomarkers. Attached Figure Description

[0022] Figure 1 This is a microscopic morphology diagram of the NaCl precipitated after evaporation and drying of the pure NaCl aqueous solution in Comparative Example 1.

[0023] Figure 2 This is the EDS spectrum of NaCl micro / nano dendrites prepared on a hydrophilic glass substrate in Example 1.

[0024] Figure 3 This is the XRD diffraction pattern of NaCl micro-nano dendrites prepared on a hydrophilic glass substrate in Example 1.

[0025] Figure 4 This is a morphology diagram of the NaCl micro / nano dendrites prepared on a hydrophilic glass substrate in Example 1.

[0026] Figure 5 This is a morphology diagram of NaCl micro / nano dendrites prepared on a hydrophobic PMMA substrate in Example 2.

[0027] Figure 6 This is a morphology image of the NaCl micro / nano dendrites prepared on a hydrophobic PMMA substrate in Example 3. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the embodiments described herein are only illustrative of the invention and are not intended to limit the invention; that is, the described embodiments are merely some embodiments of the invention, not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention.

[0029] Comparative Example 1

[0030] Accurately weigh 0.0584 g of solid sodium chloride (NaCl) and place it in a clean 100 mL beaker. Add ultrapure water and stir with a glass rod until completely dissolved. After the solution cools to room temperature, carefully transfer it along the glass rod to a 100 mL volumetric flask. Rinse the beaker and glass rod 2-3 times with ultrapure water, adding all the washings to the volumetric flask. Then, add ultrapure water to the mark, tighten the stopper, and repeatedly invert and shake to obtain 100 mL of a 10 mmol / L NaCl aqueous solution. Use a pipette or dropper to take 2 μL of the prepared NaCl aqueous solution and evenly drop it onto the surface of a clean, dry glass slide. Let it stand to allow the droplets to distribute evenly and dry completely before imaging. Figure 1 As shown, the crystals precipitated from a pure NaCl aqueous solution after complete drying have a cubic structure.

[0031] Example 1

[0032] S1. Weigh Tris-HCl powder and dissolve it in ultrapure water to prepare a Tris-HCl buffer solution with a concentration of 10 mmol / L; at room temperature, use a 5% NaOH aqueous solution to precisely adjust the pH of the buffer solution to 7.4 to obtain a precursor solution containing NaCl.

[0033] S2. The quartz glass slide was ultrasonically cleaned for 10 minutes each with detergent solution, acetone and deionized water. The cleaned quartz glass slide was then immersed in a 0.5 mol / L NaOH aqueous solution in a 65°C water bath for 2 hours. After cooling, it was thoroughly rinsed with deionized water and dried in a 95°C drying oven to obtain a hydrophilic glass substrate with high surface energy.

[0034] S3. Place the hydrophilic glass substrate in a biochemical incubator, set the temperature of the biochemical incubator to 23℃ and the relative humidity to 30%, use a micropipette to take 2μL of precursor solution containing NaCl and drop it vertically onto the surface of the hydrophilic glass substrate, and let it stand to evaporate until the surface of the substrate is dry.

[0035] Depend on Figure 2The EDS spectrum shows that the sedimentary products contain only Na and Cl elements, confirming the chemical composition of the products as NaCl. Figure 3 The XRD pattern shows that the characteristic diffraction peaks of the deposited product are located at 2θ = 27.5°, 31.8°, 45.5°, 56.5°, 66.2°, and 75.3°, corresponding to the (200), (220), (222), (400), (420), and (422) crystal planes of NaCl crystals, respectively. This matches well with the NaCl standard card (PDF#01-0999), further confirming that the obtained crystals are NaCl crystals with high crystallinity. Figure 4 As shown, on a hydrophilic glass substrate, NaCl deposition and crystallization exhibits a dendritic fractal pattern radiating from the center outwards, with clearly visible branches, indicating that hydrophilic modification treatment can induce the formation of NaCl micro- and nano-dendritic crystals. These results demonstrate that this embodiment successfully prepared NaCl micro- and nano-dendritic crystals with dendritic micro- and nano-fractal pattern characteristics.

[0036] Example 2

[0037] S1. Same as S1 in Example 1.

[0038] S2. Weigh PMMA particles and dissolve them in chloroform to prepare a 10% PMMA solution. Spin coat the solution onto a clean quartz glass slide at 300 rpm for 3 seconds and then at 5500 rpm for 30 seconds to homogenize it. Then place it in a vacuum drying oven at 145℃ and bake for 30 minutes to form a film. Cool to room temperature to obtain a low surface energy hydrophobic PMMA substrate.

[0039] S3. Place the hydrophobic PMMA substrate in a biochemical incubator, set the temperature of the biochemical incubator to 23℃ and the relative humidity to 30%, use a micropipette to take 2μL of precursor solution containing NaCl and drop it vertically onto the surface of the hydrophobic PMMA substrate, and let it stand to evaporate until the substrate surface is dry.

[0040] like Figure 5 As shown, on a hydrophobic PMMA substrate, NaCl deposition and crystallization exhibit a highly regular dendritic fractal structure with sharp edges and clear outlines on the main trunk, and branches extending orderly along specific crystallographic directions, demonstrating strict fourfold symmetry and self-similarity. These results indicate that the method of this invention can obtain NaCl micro / nano dendrites with higher order on hydrophobically modified substrates.

[0041] Example 3

[0042] S1. Weigh Tris-HCl powder and dissolve it in ultrapure water to prepare a Tris-HCl buffer solution with a concentration of 10 mmol / L. At room temperature, use a 5% NaOH aqueous solution to precisely adjust the pH of the buffer solution to 7.4. Then, mix the resulting solution with a pre-prepared 0.3 μg / μL λ-DNA aqueous solution at a volume ratio of 100:1 to obtain a precursor solution containing NaCl.

[0043] S2. Same as S2 in Example 2.

[0044] S3. Same as S3 in Example 2.

[0045] like Figure 6 As shown, after adding λ-DNA, NaCl crystals exhibit an isolated dendritic unit morphology. Each unit has a distinct dendritic branch structure, with clearly distinguishable branches, forming an overall flower-like dendritic cluster. Unlike the continuous network dendrites in Example 2, this example yields discrete micro / nano dendritic units, with unit sizes of approximately 30–60 μm, and the units are independent of each other. This isolated dendritic morphology has unique advantages in applications requiring discretized micro / nano structures (such as single-particle capture and array sensing). The above results demonstrate that by adding λ-DNA, morphological control from a continuous dendritic network to isolated dendritic units can be achieved while maintaining the dendritic fractal characteristics, further expanding the controllability of the method of this invention.

Claims

1. A method for preparing in-situ controllable inorganic salt micro-nano dendrites based on Tris-HCl buffer solution, characterized in that, Includes the following steps: S1. Adjust the pH of the Tris-HCl buffer solution to 6.4–8.4 using NaOH to obtain a precursor solution containing NaCl; S2. Surface modification treatment is performed on the solid substrate to obtain the deposition substrate; S3. The NaCl-containing precursor solution obtained in S1 is dropped onto the deposition substrate obtained in S2, and evaporated in an environment with constant temperature and humidity to spontaneously induce the formation of NaCl micro-nano dendrites with dendritic micro-nano fractal pattern characteristics.

2. The method for preparing in-situ controllable inorganic salt micro-nano dendrites based on Tris-HCl buffer solution according to claim 1, characterized in that, In step S1, the pH of the Tris-HCl buffer is adjusted to 6.4–8.4 using NaOH, then λ-DNA is added to bring the final concentration of λ-DNA in the system to 0.001–0.01 μg / μL. The mixture is then thoroughly mixed to obtain a precursor solution containing NaCl.

3. The method for preparing in-situ tunable inorganic salt micro / nano dendrites based on Tris-HCl buffer according to claim 1 or 2, characterized in that, The initial concentration of the Tris-HCl buffer in S1 is 5–10 mmol / L.

4. The method for preparing in-situ tunable inorganic salt micro / nano dendrites based on Tris-HCl buffer according to claim 1, characterized in that, The surface modification treatment in S2 is a hydrophobic modification treatment: a hydrophobic polymer material is coated on the surface of a solid substrate, and after annealing and curing, a hydrophobic deposition substrate is formed.

5. The method for preparing in-situ tunable inorganic salt micro / nano dendrites based on Tris-HCl buffer according to claim 4, characterized in that, The hydrophobic polymer material is any one of polymethyl methacrylate, polystyrene, polycarbonate, polyvinyl chloride, polypropylene, polyethylene, polyvinylidene fluoride, and polydimethylsiloxane.

6. The method for preparing in-situ tunable inorganic salt micro / nano dendrites based on Tris-HCl buffer according to claim 1, characterized in that, The surface modification treatment in S2 is a hydrophilic modification treatment: the solid substrate is subjected to wet chemical oxidation cleaning to make its surface hydroxylated, thereby obtaining a hydrophilic deposition substrate.

7. The method for preparing in-situ tunable inorganic salt micro / nano dendrites based on Tris-HCl buffer according to claim 6, characterized in that, The wet chemical oxidation cleaning process involves placing the solid substrate in a 0.1–1 mol / L NaOH aqueous solution and immersing it in a water bath at 50–65°C for 1–2 hours, followed by rinsing and drying.

8. The method for preparing in-situ tunable inorganic salt micro / nano dendrites based on Tris-HCl buffer according to claim 1, characterized in that, The constant temperature in S3 is 18–30°C, and the relative humidity is 25%–35%.

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