Preparation method and application of photochromic molecule / alumina nanoporous membrane

Abstract

The application discloses a preparation method of a photochromic molecule / alumina nanoporous membrane and application thereof, and belongs to the field of nanometer material detection. The nanopore of the alumina nanoporous membrane is an array structure with one open end, one sealed end and a nanometer channel in the middle. The sealed end is a barrier layer of the alumina nanoporous membrane and exhibits a hexagonal close-packed hemispherical protrusion array structure in the microstructure. Photochromic molecules are grafted on the open end of the alumina nanoporous membrane and the inner wall of the channel in the middle. When a spiropyran is used as the photochromic molecule, the prepared spiropyran / alumina nanoporous membrane can be controlled to be an inert reactor and an active reactor of SO2 through remote light control to construct a demand detector capable of long-term storage and real-time detection, and quantitative analysis of SO2 can be realized by monitoring the rectified current, which provides a brand-new idea for design and reliable detection of other demand nanofluidic sensing devices.

Description

Technical Field

[0001] This invention relates to the field of nanomaterials technology, and more specifically, to a method for preparing a photochromic molecule / alumina nanoporous membrane and its application. Background Technology

[0002] The diversification of nanofabrication and modification techniques has led to the development of highly efficient and sophisticated artificial nanochannel sensors. However, while various strategies exist for producing nanochannels with structures comparable to their natural counterparts, replicating their precise sensing and transport behaviors, such as controlled switching and on-demand transport, remains challenging. In traditional sensing systems, the reactivity of probes immobilized on nanochannels is always active. Due to the large specific surface area of ​​nanochannels, probes readily interact with other substances, whether exposed to air or immersed in solution. For example, probe molecules may have already partially reacted with analytes present in the natural environment before detecting the intended sample. This "passive reaction" mode inevitably generates background signals, reducing detection accuracy and even damaging the nanochannel sensor. To more closely approximate the precise sensing found in biology, it is necessary to develop tunable nanochannel sensors to meet the requirements of real-time, on-demand detection.

[0003] We envision creatively using light to excite the reactivity of nanochannels before analyte binding, transforming probe molecules from inert to active states, thereby constructing a light-controlled, active target recognition function within the nanochannel. Such a system would enable on-demand detection and unbiased real-time response. Light-controlled nanochannels are attractive due to their non-invasive stimulation and remote spatiotemporal control. In particular, photochromism possesses the unique ability to reversibly interconvert between heterogeneous states through alternating irradiation with ultraviolet and visible light. Besides structural transformations, the reactivity of photochromic molecules can also be reversibly modulated under corresponding light stimulation due to rearrangement of electronic configurations. To date, remote light stimulation controlling the structural transformation of photochromic probes in nanochannel systems has been reported to be highly effective for constructing ion conduction switches (Adv. Mater., Vol. 30, No. 46, 2018; Adv. Mater. 24, 18, 2012). However, its potential role in activating the reactivity of nanochannels to analytes has not been systematically investigated. Specific light radiation can transform a photochromic probe from an isomer that is inert to the analyte into another isomer that is active to the analyte.

[0004] In view of the above problems, it is necessary to provide a method for preparing photochromic molecular / alumina nanoporous membranes and their applications. Summary of the Invention

[0005] The purpose of this invention is to overcome the defects of the prior art and provide a method for preparing photochromic molecular / alumina nanoporous membranes and their applications.

[0006] The technical problem solved by this invention is achieved by the following technical solution.

[0007] This invention provides a photochromic molecule / alumina nanoporous membrane. The nanopores of the alumina nanoporous membrane are open at one end, sealed at the other end, and have a nanochannel array structure in the middle. The sealed end is a barrier layer of the alumina nanoporous membrane and exhibits a hexagonal tightly packed hemispherical protrusion array structure in the microstructure. The photochromic molecule is grafted to the open side at the top of the alumina nanoporous membrane and the inner wall of the middle channel.

[0008] The present invention also provides a method for preparing a photochromic molecule / alumina nanoporous membrane, which includes: grafting a photochromic molecule onto an alumina nanoporous membrane.

[0009] This invention also provides an application of a photochromic molecule / alumina nanoporous membrane as a nanofluidic sensing device with switchable light-controlled inert / active states.

[0010] The present invention has the following beneficial effects:

[0011] This invention provides a method for preparing a photochromic molecular / alumina nanoporous membrane and its application. The alumina porous structure is an open-top, sealed-bottom, and centrally located array of nanochannels, with abundant protonated hydroxyl groups on the inner walls of the channels. The alumina nanochannels can serve as an asymmetric rigid substrate for subsequent covalent functionalization. Through a condensation reaction, carboxyl-functionalized SP probes are patterned on the open side and inner walls of the amino-modified alumina nanochannels. Specific light radiation can convert the photochromic probe from an analyte-inert isomer to an analyte-active isomer. The inertness and activity of the nanochannels can be freely switched remotely via light control, allowing the spiropyran / alumina porous membrane to be activated on demand to actively identify SO2 in its detection applications, achieving sensitive detection of SO2. Attached Figure Description

[0012] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0013] Figure 1Figure 1 shows the changes in ion transport performance and wettability of the SP / AAO nanochannel in Example 1 of the present invention (where 1a is the I-V curve of the spiropyran / alumina nanochannel at different modification times; Figure 1b shows the change in contact angle during the spiropyran modification process).

[0014] Figure 2 This is a device design model for on-demand SO2 detection using an SP / AAO nanochannel membrane with switchable inertness / activity according to Example 1 of the present invention.

[0015] Figure 3 The photoresponse of the SP / AAO nanochannel and the I-V curve and contact angle change of active SO2 detection under photomodulation in Example 1 of the present invention;

[0016] Figure 4 The effect of photoactivated SP / AAO nanochannels on SO2 on-demand response in Example 1 of the present invention (wherein, Figure 4a shows the I-V curves of SP / AAO nanochannels at different UV irradiation times, and the inset shows the corresponding photoresponse current (I0). UV Figures 4b, 4c, 4d, and 4e show the I-V curves of the SP / AAO nanochannels before and after SO2 treatment, respectively, after 1, 5, 10, and 20 minutes of UV activation; Figure 4f shows the corresponding SO2 response current (I0). SO2 ));

[0017] Figure 5 The detection performance of the photoactivated SP / AAO nanochannel in Example 1 of the present invention is shown in Figure 5a, which shows the I-V curves of the photoactivated SP / AAO nanochannel using different analytes; Figure 5b shows the I-V curve of the SP / AAO nanochannel with SO2 response time; Figure 5c shows the I-V curve of the SP / AAO nanochannel with SO2 concentration; and Figure 5d shows the linear relationship between the ion current ratio of the SP / AAO nanochannel and SO2 concentration. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] The purpose of this invention is to address the shortcomings of existing technologies by providing a light-controlled switchable inert / active spiropyran / alumina nanoporous membrane and its application as an on-demand detection device.

[0020] To achieve the above objectives, the technical solution of the present invention is as follows:

[0021] In a first aspect, embodiments of the present invention provide a photochromic molecule / alumina nanoporous membrane, wherein the nanopores of the alumina nanoporous membrane are open at one end, sealed at the other end, and have a nanochannel array structure in the middle. The sealed end is a barrier layer of the alumina nanoporous membrane and exhibits a hexagonal closely packed hemispherical protrusion array structure in the microstructure. The photochromic molecule is grafted onto the open side at the top of the alumina nanoporous membrane and the inner wall of the channel in the middle.

[0022] This invention provides a photochromic molecule / alumina nanoporous membrane. Photochromic molecules are asymmetrically immobilized onto the alumina nanoporous membrane using a diffusion-limited mode (DLP) method. The nanopores of the alumina nanoporous membrane are open at one end, sealed at the other, and form a nanochannel array structure in the middle. This geometrically asymmetric alumina nanochannel can rectify ion currents due to the abundance of protonated hydroxyl groups on its inner surface. Simultaneously, the alumina nanochannel can serve as an asymmetric rigid substrate for subsequent covalent functionalization, grafting photochromic molecules onto the alumina nanoporous membrane. Utilizing the superior photochromic properties of the photochromic molecules, the probe structure and reactivity of the photochromic molecule / alumina nanoporous membrane can reversibly change under alternating visible and ultraviolet light irradiation. This invention constructs a detection device that can be activated on demand via remote light control using the photochromic molecule / alumina nanochannel membrane, providing a novel approach for the design and reliable detection of other on-demand nanofluidic sensing devices.

[0023] In an optional embodiment, the photochromic molecule includes any one of stilbene, azo compounds, and spiropyran, preferably spiropyran.

[0024] In optional embodiments, the nanochannels of the alumina nanoporous membrane include nanotube-like alumina nanochannels, hourglass-shaped alumina nanochannels, funnel-shaped alumina nanochannels, cigar-shaped alumina nanochannels, conical alumina nanochannels, or columnar alumina nanochannels, preferably nanotube-like alumina nanochannels.

[0025] In an optional embodiment, the thickness of the alumina nanoporous membrane is 10-100 μm, and the pore size on the upper surface of the alumina nanoporous membrane is 10-100 nm.

[0026] Secondly, embodiments of the present invention provide a method for preparing a photochromic molecule / alumina nanoporous membrane, which includes: grafting a photochromic molecule onto an alumina nanochannel membrane.

[0027] In an optional embodiment, when the photochromic molecule is spiropyran, the method for preparing the spiropyran / alumina nanoporous membrane includes the following steps:

[0028] The alumina nanoporous membrane was immersed in APTES ethanol solution, then rinsed with ethanol several times, and dried in an oven for later use.

[0029] Then, the APTES-treated alumina nanoporous membrane was placed in the connecting part between two tanks containing carboxyspiropyran ethanol solution and ethanol solution, respectively, to isolate the electrolytes contained in the two tanks.

[0030] At room temperature and in the dark, spiropyran molecules are grafted onto the open side at the top of the alumina nanoporous membrane and the inner wall of the channel in the middle.

[0031] This invention provides a method for preparing a photochromic molecule / alumina nanoporous membrane. First, the alumina porous membrane is immersed in a solution of (3-aminopropyl)triethoxysilane (APTES) for amination. Then, through a condensation reaction, carboxyl-functionalized SP probes are patterned on the APTES-modified nanochannels. Combining a unique DLP method and the tubular structure of the alumina nanochannels with one end closed, spiropyran can be specifically modified onto the open side at the top and the inner wall of the channel in the middle to construct asymmetric spiropyran / alumina nanochannels.

[0032] In an optional implementation, the modification time at room temperature in the dark is 10-600 min;

[0033] Preferably, the volume fraction of the APTES ethanol solution is 1%-50%, and the soaking time is 10-60 min.

[0034] Preferably, the concentration of the carboxyspiropyran ethanol solution is 1-100 mmol / L.

[0035] Thirdly, embodiments of the present invention provide an application of a photochromic molecule / alumina nanoporous membrane as a nanofluidic sensing device with switchable light-controlled inert / active states.

[0036] In an optional implementation, SO2 can be detected in real time on demand using a spiropyran / alumina nanoporous membrane with light-controlled switchable inert / active states.

[0037] In an optional implementation, qualitative and quantitative detection of SO2 is achieved by monitoring the rectified current.

[0038] In the above technical solution, since the spiropyran / alumina nanochannel membrane is inert to SO2 under dark conditions, the ion current of the nanochannel remains unchanged before and after SO2 response. However, under ultraviolet irradiation, SP photoisomerizes to a cyanine morphology, which contains a C=C nucleophilic site that can actively capture SO2, generating a hydrophilic MC-SO3H adduct. Therefore, the wettability of the upper surface of the nanochannel changes from hydrophobic to hydrophilic, forming an asymmetric wettability henness structure with the hydrophobic lower surface. This not only increases the gated ion current but also enhances the rectification performance. Therefore, by monitoring the rectified current, a sensor based on spiropyran / alumina nanochannels with switchable inert / active states can be successfully constructed to achieve on-demand SO2 detection.

[0039] Furthermore, inspired by the principle of the light-controlled inert / active switchable nanochannel detector described above (applying photochromic molecules to nanochannels; the original SP form does not react with SO2, but after UV irradiation, the SP undergoes photoisomerization to form the MC form containing nucleophilic addition sites, which can undergo nucleophilic addition reactions with SO2. Thus, inert / active switchable nanochannels can construct on-demand SO2-responsive devices), we reasonably believe that other nanochannels modified with photoisomerization-type photochromic molecules can also be designed as light-controlled inert / active switchable nanochannel detection devices, such as stilbene, azo groups, etc.

[0040] The present invention presents a photo-controlled SO2 detector based on a spiropyran / alumina nanochannel membrane with switchable inertness / activity. Under ultraviolet irradiation, SP can isomerize to MC, resulting in significant changes in structure and reactivity. The UV-activated MC form possesses an unsaturated carbon-carbon double bond (C=C), which can serve as a nucleophilic site for SO2 attack. Compared to other nanochannel sensors, this invention allows for remote photo-controlled switching of the nanochannel's inertness and activity, enabling the spiropyran / alumina nanochannel to be activated on demand for active SO2 identification in its detection applications. This inertness / activity switch facilitates the elimination of false positive / negative signals and enables real-time on-demand detection, providing a novel approach for the design and reliable detection of other on-demand nanofluidic sensing devices.

[0041] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0042] Example 1

[0043] Spiropyran is abbreviated as SP, cyanine as MC, alumina as AAO, 3-aminopropyltriethoxysilane as APTES, and diffusion-limited mode method as DLP.

[0044] Step 1: This invention provides an inert / active switchable SO2 on-demand detection device, wherein the spiropyran / alumina nanoporous membrane used is prepared by DLP modification technology. The specific steps and preferred processes for preparing the spiropyran / alumina nanoporous membrane are as follows:

[0045] Step 2: Alumina nanochannels with nanotube-like structures are used as a rigid framework. The preferred process involves an alumina nanochannel membrane with pores approximately 25 nm in diameter on its upper surface. The lower surface consists of an alumina barrier layer composed of a tightly packed array of hexagonal hemispherical protrusions. This asymmetric geometry and the nanoconfining effect of the barrier layer result in significant ion rectification behavior in the nanochannel. The preferred process involves an alumina nanochannel membrane thickness of 55 μm.

[0046] Step 3: Amination of the nanochannel surface using APTES. The nanotube-shaped alumina nanochannels are immersed in an APTES ethanol solution. The preferred APTES ethanol solution has a volume fraction of 20%, and the preferred immersion time is 10 min. Amination of the alumina nanochannels facilitates subsequent functionalization modification.

[0047] Step 4: Asymmetric immobilization of spiropyran to nanotube-shaped alumina nanochannels. The aminated alumina film obtained in Step 3 is sandwiched at the connection between two tanks. Optimally, a 10 mM spiropyran ethanol solution and a pure ethanol solution are filled into the tanks respectively. The spiropyran ethanol solution faces the open end, and the pure ethanol solution faces the alumina barrier layer side. As SP diffuses into the nanochannel, the spiropyran probe is covalently grafted onto the upper open surface and inner wall of the nanochannel, without modification of the bottom barrier layer. This allows for the fabrication of spiropyran / alumina nanochannels with asymmetric geometry and surface composition. With increasing diffusion time, more and more SP molecules are modified onto the nanochannel surface.

[0048] The changes in ion transport properties and wettability of the SP / AAO prepared in Example 1 are shown in the following figure. Figure 1 (Figure 1a shows the IV curves of the spiropyran / alumina nanochannels at different modification times; Figure 1b shows the contact angle change during the spiropyran modification process.) Ion transport and surface wettability were measured. Figure 1In sections a and 1b), we further investigated spiropyran / alumina nanochannels with different modification times. With increasing modification time, more and more neutral spiropyran molecules were deposited on the nanochannels, leading to a gradual increase in the top surface contact angle of the nanochannel membrane and a gradual decrease in the transmembrane ion current. After 1 hour of spiropyran modification, the ion current and rectification rate of the nanochannels decreased slightly. This indicates that the available amount of spiropyran is still not high, which may weaken the system's photoresponse and detection sensitivity. However, after 2 hours of modification, both the ion current and rectification rate decreased significantly. This phenomenon suggests that an appropriate number of spiropyran molecules are attached to the APTES surface, resulting in reduced membrane wettability and surface charge. When modification continued for 3 hours, the current decreased to 10⁻⁶. -7 A. This indicates that the immobilization of excessive SP significantly reduces the surface wettability of the nanochannels, resulting in a hydrophobic interface with CA≈105.9° on the top surface. This severely hinders ion transmembrane transport. However, no significant change in contact angle was observed from the bottom surface, suggesting that SP is only finely patterned on the porous side of the tubular nanochannels to establish an asymmetric spiropyran / alumina nanosensor. Comparison of three different modification times shows that the optimal modification state and ion transport properties can be achieved in 2 hours; therefore, the process-optimized diffusion time is 2 hours.

[0049] Step 5: Rinse the membrane obtained in step 4 multiple times with ethanol solution, store it away from light, and air dry it naturally to obtain the spiropyran / alumina nanoporous membrane.

[0050] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0051] The scope of this invention is not limited to the above embodiments; a combination of one or more embodiments can also achieve the purpose of this invention.

[0052] To further verify the superior performance of this invention, the inventors also designed an experimental prototype device with a switchable inert / active nanochannel for on-demand SO2 detection, as detailed below:

[0053] The spiropyran / alumina nanoporous membrane obtained in the examples was used as an inert / active switchable nanochannel membrane to detect SO2 on demand. Figure 2Initially, spiropyran molecules are primarily in a closed spirocyclic spline (SP) state, which is chemically inert to SO2. However, under ultraviolet (UV) irradiation, the CO bond of spiropyran breaks down and isomerizes into an open-ring form, MC, containing C=C linkages. When UV light is turned off and visible light is turned on, the nanochannel reversibly reverts to the original SP state due to the reverse photochemical isomerization from MC to SP. Most notably, the UV-activated MC contains a π-electron-rich C=C, which is reactive to nucleophiles. Therefore, it can actively add SO2 to achieve on-demand detection of SO2.

[0054] First, by measuring typical IV curves and contact angle changes, it was determined that the spiropyran / alumina nanochannels did not react with SO2 before UV irradiation. Figure 3 When the spiropyran-modified nanochannels were exposed to SO2, the ion currents showed no significant difference. IV characterization demonstrated that its reactivity to SO2 was suppressed before UV irradiation. Then, under UV irradiation, SP was photoisomerized to the MC state before the addition of SO2. We observed that once the spiropyran / alumina nanochannels were activated by UV light, the ion current increased, resulting in a photoresponse current, defined as the UV-responsive current (Io). UV Because the CO bonds of the SP probe are opened under ultraviolet light and transformed into the charge-separated MC state in a slightly acidic environment (pH 5.5), the wettability of the nanochannel surface is enhanced. After treating the UV-activated MC-state nanochannel with SO2, the ion current at +2V is significantly enhanced, and a satisfactory SO2 response current (I0.05) is obtained. SO2 The alumina is approximately 215 μA. This is due to the nucleophilic addition reaction between the MC component and SO2, which generates an MC-SO3H adduct. This causes the wettability of the top surface of the nanochannel to reverse from hydrophobic to hydrophilic. Therefore, an asymmetric wettability juxtaposition, i.e., a hydrophilic top surface and a hydrophobic bottom surface, is established on both sides of the spiropyran / alumina nanoporous membrane. This change in wettability arrangement not only controls ion transport within the nanochannel but also achieves ion rectification within the nanochannel. In other words, using the spiropyran / alumina nanoporous membrane as an on-demand SO2 detection device utilizes the photoisomerization of spiropyran to achieve remote light modulation of an inert / active state switchable artificial nanofluidic sensor. This ingenious design facilitates the long-term preservation of the nanochannel sensor and largely avoids interference from false positive signals during detection.

[0055] To further verify the important role of light irradiation in SO2 response, the ultraviolet radiation time was adjusted in the spiropyran / alumina nanochannel sensing system. The effect of the photoactivated SP / AAO nanochannel membrane on the on-demand SO2 response in Example 1 is described in [reference needed]. Figure 4(Figure 4a shows the IV curves of the SP / AAO nanochannels under different UV irradiation times, and the inset shows the corresponding photoresponse current (I0).) UV Figures 4b, 4c, 4d, and 4e show the IV curves of the SP / AAO nanochannels before and after SO2 treatment, respectively, after 1, 5, 10, and 20 minutes of UV activation; Figure 4f shows the corresponding SO2 response current (I0). SO2 )).Depend on Figure 4 It can be seen that controlling the UV irradiation time from 0 to 20 minutes affects the Ig of the spiropyran / alumina nanochannels. UV It increases with increasing radiation time ( Figure 4 a). In the dark, the ion current of the spiropyran / alumina nanochannel system remained at 14.7 μA. With increasing UV irradiation time, the ion current at 2 V gradually increased to approximately 36 μA. This photocurrent response trend demonstrates that remote UV stimulation gradually facilitated the transition of the photochromic nanochannel from the inert SP state to the active MC state, ultimately reaching the highest MC yield and maximum nanochannel activity within 10 minutes. Figure 4 (a. Illustration). Then, the same concentration of SO2 analyte (100 μM) was introduced into detection systems at different activation states to investigate the effect of photomodulation on the SO2 response. Upon contact with SO2, the ion current of the spiropyran / alumina nanochannel increased slightly after 1 minute of UV irradiation, leading to the generation of I... SO2 ≈28.8μA ( Figure 4 b). For the membrane irradiated for 5 minutes, the ion current increased significantly after SO2 stimulation, resulting in an IA of approximately 93.6 μA. SO2 produce( Figure 4 c). Ten minutes after the nanosensor was irradiated, an ion current of -239.2 μA was detected, generating an Ion current as high as 203.1 μA. SO2 ( Figure 4 d). However, further extending the duration of ultraviolet radiation did not result in the observation of I. SO2 Further increase ( Figure 4 e). It is obvious that I SO2 Showing the same as I UV Similar multi-level increasing trends ( Figure 4 f). Detailed comparative results show that irradiation of the nanochannel for ≥10 minutes produces the optimal detection effect, I SO2 The values ​​reached as high as 200 μA. The multi-level increasing characteristics confirm that the increase in UV-driven photoisomerization effectively promoted the generation of MC and the overall performance of SO2 measurement.

[0056] After demonstrating the conceptual active response capability, the performance of the UV-activated spiropyran / alumina nanochannel sensor in detecting SO2 was further evaluated. Figure 5 Figure 5a shows the IV curves of the photoactivated SP / AAO nanochannel using different analytes; Figure 5b shows the IV curve changes of the SP / AAO nanochannel with SO2 response time; Figure 5c shows the IV curve changes of the SP / AAO nanochannel with SO2 concentration; Figure 5d shows the linear relationship between the ion current ratio of the SP / AAO nanochannel and SO2 concentration. The nanochannel sensor's selectivity for SO2 is much higher than that for other analytes (such as thiols, H2O2, and anions). Figure 5 a). Time-dependent current changes indicate that the activated MC state exhibits high reactivity to SO2 within 10 minutes, eventually reaching equilibrium within 15 minutes. Figure 5 b). Concentration-dependent current changes ( Figure 5 c) This demonstrates a strong linear relationship between the current change ratio and the SO2 concentration in the SO2 range of 10 nM to 1 mM (R0). 2 =0.995)( Figure 5 d), which can be used for quantitative SO2 determination.

[0057] Comparative Example 1

[0058] Similar to the steps in Example 1, the only difference is that the volume fraction of the APTES ethanol solution is 80%. The result is that a layer of white solid powder is found on the alumina film, and the pore morphology of the nanochannels is changed, which will affect the smooth transport of ions.

[0059] Comparative Example 2

[0060] Similar to the steps in Example 1, the only difference is that the volume fraction of the APTES ethanol solution is 0.1%. As a result, the alumina film is basically not aminated, which will seriously affect the subsequent chemical modification of the SP probe.

[0061] Comparative Example 3

[0062] Similar to the steps in Example 1, the only difference was that the concentration of the spiropyran ethanol solution was 200 mmol / L. The result was that a distinct green powder was observed at the bottom of the solution, indicating that the high concentration of spiropyran molecules was not completely dissolved. Such a solution not only affects the modification effect during the DLP process but can even cause physical blockage of the nanopores.

[0063] Comparative Example 4

[0064] Similar to the steps in Example 1, the only difference is that the concentration of the spiropyran ethanol solution is 0.1 mmol / L. As a result, only a small number of spiropyran molecules are modified onto the alumina surface, which reduces the photoresponse capability and SO2 detection sensitivity of the nanochannel system.

[0065] In summary, this invention provides a method for preparing a photochromic molecule / alumina nanoporous membrane and its application. Taking spiropyran as the photochromic molecule as an example, the SO2 detection device refers to using a self-made spiropyran / alumina nanochannel membrane as a medium, utilizing the photoisomerization of spiropyran to precisely control the reactivity of the nanochannel to SO2. The spiropyran / alumina nanochannel exhibits reversible switching between ultraviolet and visible light. The original spiropyran / alumina is chemically inert to SO2. However, under ultraviolet irradiation, spiropyran photoisomerizes to a cyanine form containing carbon-carbon double bonds. This cyanine can act as a nucleophilic site to actively bind SO2, forming a hydrophilic complex, causing the wettability of the alumina membrane to shift from symmetric to asymmetric. Therefore, quantitative analysis of SO2 is achieved by monitoring the rectified current. This invention constructs a detection device that can be activated on demand via remote light control using a spiropyran / alumina nanochannel membrane, providing a novel approach for the design and reliable detection of other on-demand nanofluidic sensing devices.

[0066] Compared with existing technologies, the method for preparing a photochromic molecular / alumina nanoporous membrane and its application provided by this invention have the following superior effects:

[0067] 1. This invention provides a simple and universal proof-of-concept prototype of an inert / active switchable sensing device. Utilizing the superior photochromic properties of spiropyran, the probe structure and reactivity of the spiropyran / alumina nanochannel membrane reversibly change under alternating visible and ultraviolet light irradiation. The SP form under visible light is inert to SO2. The MC form activated by ultraviolet light possesses an unsaturated C=C, which can serve as a nucleophilic site for SO2 attack. Therefore, a light-controlled inert / active switchable sensing system is successfully established. Compared to other nanochannel sensors, this invention allows for remote light-controlled switching of the inertness and activity of the nanochannel, enabling the spiropyran / alumina nanochannel to be activated on demand to actively identify SO2 in its detection applications. This provides a novel approach for the design and reliable detection of other on-demand nanofluidic sensing devices.

[0068] 2. The spiropyran / alumina nanochannel membrane prepared in the embodiments of the present invention can be controllably used as an inert reactor and an active reactor for SO2 through remote optical control, so as to construct an on-demand detection device that can be stored for a long time and detected in real time.

[0069] 3. In the embodiments of the present invention, the wettability of the surface of the nanochannel changes from hydrophobic to hydrophilic after SO2 detection, which increases the asymmetry of wettability on both sides of the membrane, resulting in enhanced ion current and rectification properties, and realizing the sensitive detection of SO2 by the nanochannel.

[0070] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. The application of a photochromic molecular / alumina nanoporous membrane in SO2 detection, characterized in that, The alumina nanoporous membrane has nanopores that are open at one end, sealed at the other end, and have a nanochannel array structure in the middle. The nanochannels are nanotube-type alumina nanochannels. The sealed end is a barrier layer of the alumina nanoporous membrane and exhibits a hexagonal array of closely packed hemispherical protrusions in the microstructure. Photochromic molecules are grafted onto the open side at the top of the alumina nanoporous membrane and the inner wall of the channel in the middle. The photochromic molecule is spiropyran, and the photochromic molecule / alumina nanoporous membrane is prepared through the following steps: The alumina nanoporous membrane was immersed in APTES ethanol solution, then rinsed with ethanol several times, and dried for later use. Then, the APTES-treated alumina nanoporous membrane was placed in the connecting part between two tanks containing carboxyspiropyran ethanol solution and ethanol solution, respectively, to isolate the electrolytes contained in the two tanks. Under light-protected conditions at room temperature, the spiropyran molecules are grafted onto the open side at the top and the inner wall of the channel in the middle of the alumina nanoporous membrane, wherein: the modification time at room temperature and in the dark is 10-600 min, the volume fraction of the APTES ethanol solution is 1%-50%, the soaking time is 10-60 min, and the concentration of the carboxyspiropyran ethanol solution is 1-100 mmol / L.

2. The application of the photochromic molecule / alumina nanoporous membrane according to claim 1, characterized in that, The thickness of the alumina nanoporous membrane is 10-100 μm, and the pore size on the upper surface of the alumina nanoporous membrane is 10-100 nm.

3. The application of the photochromic molecular / alumina nanoporous membrane according to any one of claims 1-2, characterized in that, As a nanofluidic sensing device with switchable light-controlled inert / active states.

4. The application of the photochromic molecule / alumina nanoporous membrane according to claim 3, characterized in that, Real-time, on-demand detection of SO2 is achieved using a spiropyran / alumina nanoporous membrane with light-controlled switchable inert / active states.

5. The application of the photochromic molecule / alumina nanoporous membrane according to claim 4, characterized in that, Qualitative and quantitative detection of SO2 can be achieved by monitoring the rectified current.

6. A method for preparing a photochromic molecular / alumina nanoporous membrane according to any one of claims 1-5, characterized in that, It includes: Photochromic molecules were grafted onto alumina nanoporous membranes.

7. The preparation method according to claim 6, characterized in that, When the photochromic molecule is spiropyran, the preparation method of the spiropyran / alumina nanoporous membrane includes the following steps: The alumina nanoporous membrane was immersed in APTES ethanol solution, then rinsed with ethanol several times, and dried for later use. Then, the APTES-treated alumina nanoporous membrane was placed in the connecting part between two tanks containing carboxyspiropyran ethanol solution and ethanol solution, respectively, to isolate the electrolytes contained in the two tanks. Under ambient light conditions at room temperature, the spiropyran molecules are grafted onto the open side at the top of the alumina nanoporous membrane and the inner wall of the channel in the middle.

8. The preparation method according to claim 7, characterized in that, The modification time at room temperature in the dark is 10-600 min.

9. The preparation method according to claim 7, characterized in that, The volume fraction of the APTES ethanol solution is 1%-50%, and the soaking time is 10-60 min.

10. The preparation method according to claim 7, characterized in that, The concentration of the carboxyspiropyran ethanol solution is 1-100 mmol / L.

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