A visualizing fluorescent sensor

Abstract

The application discloses a visual fluorescent sensor, wherein a support under PMMA is PDMS with a micron-level inverted pyramid structure, and the whole is defined as PDMS / PMMA-Au / SP. The PDMS / PMMA-Au / SP has a structure similar to an insect compound eye, a large specific surface area and low reflectivity, can provide more attachment sites and higher light absorption efficiency for spiropyrans, and helps to improve the fluorescence intensity of the open ring body MC of the spiropyrans. Meanwhile, the electromagnetic field enhancement effect of Au nanoparticles can further improve the fluorescence intensity of the open ring body MC of the spiropyrans. The brand-new PDMS / PMMA-Au / SP fluorescent sensor is successfully applied to trace detection of metal ions.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of photoelectric materials, and particularly relates to a visual fluorescent sensor. BACKGROUND

[0002] Spiropyrans derivatives have attracted extensive attention due to their ability to bind a variety of metal ions and provide unique spectral responses for each metal ion. As a typical representative of photochromic molecules, it can generate a colored merocyanine (MC) structure due to the rupture of the C-O bond under UV light induction, and also can undergo a ring-closing reaction to return to its initial colorless state (SP) under visible light or heating stimulation. Because the MC form of spiropyrans has a negatively charged phenolic oxygen group that can provide a coordination site for metal ions, resulting in changes in the corresponding absorption and fluorescence spectra, it can be used for colorimetric and fluorescent sensing. However, spiropyrans molecules have the disadvantages of easy photodegradation leading to poor fatigue resistance, MC form aggregation leading to fluorescence weakening and ring-closing reaction failure, etc., which limit their practical application value in the sensing field.

[0003] An effective method to solve this problem is to covalently combine spiropyrans with supports (polymer chains, nanoparticles, etc.). Because the support can greatly affect the switching dynamics of spiropyrans, avoid spiropyrans aggregation, improve their light stability, switchability and processability. According to the dispersed form of spiropyrans, it can be divided into two categories: the first category is to modify spiropyrans inside the support through grafting reaction. For example: Liu et al. grafted spiropyrans molecules into poly(N-vinylcaprolactam) inside by atom transfer radical polymerization (ATRP) method. The phenolic oxygen bond of the ring-opened body MC and the amino group of N-vinylcaprolactam form coordination bonds with metal ions, so colorimetric sensing of Fe 2+ , Cu 2+ , Co 2+ can be achieved. Sousa et al. prepared poly(ε-caprolactone) high polymer grafted with spiropyrans into nanofibers with photochromic properties by electrospinning technology. After UV light treatment, it can realize colorimetric sensing of Mg 2+ , Zn 2+ , Ca 2+ , Cd 2+ , La 3+ , Er 3+However, the dense polymer network not only prolongs the response time of the spiropyran open ring, but also makes it difficult for metal ions to desorb from the interior of the polymer system, which reduces the number of cycles. The second type is to modify the spiropyrane on the surface of the support by interface modification. For example, Maclachlan et al. modified the spiropyrane on the surface of mesoporous silica by amino silane reagent. Due to the mesoporous nature of the substrate, the substrate provides a large number of attachment sites for the spiropyrane, and the substrate exhibits excellent photochromic performance and shows colorimetric response to Zn 2+ , Cu 2+ , Ni 2+ , Sn 2+ show colorimetric response. However, the spiropyrane modified on the surface of the support is usually a monomolecular film, and the colorimetric or fluorescent sensing signal is weak, and so far it still cannot realize trace detection of metal ions. SUMMARY

[0004] This section is intended to summarize some aspects of the embodiments of the present application and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this section and the abstract and title of the specification to avoid obscuring the purpose of this section, the abstract and the title, and such simplifications or omissions cannot be used to limit the scope of the present application.

[0005] In view of the above and / or problems existing in the prior art, the present application is proposed.

[0006] Therefore, the purpose of the present application is to overcome the deficiencies in the prior art and provide a visual fluorescent sensor.

[0007] To solve the above technical problems, the present application provides the following technical solutions: a visual fluorescent sensor, characterized in that the sensor is composed of three layers of structure, the bottom layer is a flexible substrate prepared from polydimethylsiloxane, the middle layer is a metal particle film coated with thermoplastic material and metal nanoparticles, and the upper layer is a sensing layer modified with chlorosilane or alkoxysilane and spiropyrane.

[0008] Another purpose of the present application is to overcome the deficiencies in the prior art and provide a preparation method of a visual fluorescent sensor.

[0009] To solve the above technical problems, the present application provides the following technical solutions:

[0010] Preparation of flexible substrate: etching single crystal silicon with alkaline solution and hydrophobic treatment, pouring polydimethylsiloxane prepolymer and initiator on the silicon template after treatment for curing, cooling to room temperature after curing, and peeling off the polydimethylsiloxane to obtain a polydimethylsiloxane substrate containing inverted pyramid microstructure;

[0011] Coating metal nanoparticle film: gold nanoparticles and thermoplastic material are dissolved in a solvent, ultrasonic dispersion is carried out after continuous stirring, and the stirred mixed solution is spin-coated on a polydimethylsiloxane surface to obtain a polydimethylsiloxane / thermoplastic material-metal nanoparticle substrate after drying;

[0012] First monolayer surface modification: the polydimethylsiloxane / thermoplastic material-metal nanoparticle substrate is subjected to plasma treatment to attach hydroxyl groups to the surface, and then subjected to first monolayer surface modification;

[0013] Second monolayer surface modification: the substrate after the first surface modification is subjected to second monolayer surface modification, and the substrate after the two surface modifications is placed in an organic solvent containing spiropyrans and activators for spiropyrans functionalization modification to obtain a polydimethylsiloxane / thermoplastic material-metal nanoparticle / spiropyrans composite substrate;

[0014] Finally, the polydimethylsiloxane / thermoplastic material-metal nanoparticle / spiropyrans composite substrate is washed and dried to obtain a fluorescence sensor.

[0015] As a preferred embodiment of the preparation method of the application, the thermoplastic material includes polymethyl methacrylate, polystyrene, polyvinylidene chloride, polyurethane, and derivatives of the above materials.

[0016] As a preferred embodiment of the preparation method of the application, the spiropyrans include spiropyrans containing carboxyl groups and spiropyrans derivatives.

[0017] As a preferred embodiment of the preparation method of the application, the metal nanoparticles include gold nanoparticles, silver nanoparticles, and copper nanoparticles; the addition amount is 3.5×10 -5 M~5.6×10 -4 M.

[0018] As a preferred embodiment of the preparation method of the application, the polydimethylsiloxane substrate containing inverted pyramid microstructures has a side angle of about 54.7° with the top surface in a side view, and an inverted pyramid height of 5 μm.

[0019] As a preferred embodiment of the preparation method of the application, in the first monolayer surface modification, the surface modification uses chlorosilane or alkoxysilane containing one or both of alkyl groups and benzene rings, including tert-butyl diphenyl chlorosilane.

[0020] As a preferred embodiment of the preparation method of the application, in the second monolayer surface modification, the surface modification uses chlorosilane or alkoxysilane containing amino groups, including 3-aminopropyl trimethoxysilane.

[0021] As a preferred scheme of the preparation method, the growth time of the spiropyran in the spiropyran functional modification is 3-12 hours.

[0022] Another object of the present application is to overcome the deficiencies in the prior art and provide an application of the visual fluorescent sensor.

[0023] As the application of the visual fluorescent sensor, the fluorescent sensor is applied to the visual trace detection of metal ions.

[0024] The present application has the following advantages:

[0025] (1) The present application provides a method for modifying spiropyran to the surface of PMMA film containing Au nanoparticles inside, and the support under PMMA is PDMS with a micron-level inverted pyramid structure, which is defined as PDMS / PMMA-Au / SP. PDMS / PMMA-Au / SP has a structure similar to the compound eye of insects, and has a large specific surface area and low reflectivity, which can provide more attachment sites and higher light absorption efficiency for spiropyran, and help to improve the fluorescence intensity of the open ring body MC of spiropyran.

[0026] (2) At the same time, the electromagnetic field enhancement effect of Au nanoparticles can further improve the fluorescence intensity of the open ring body MC of spiropyran; this novel PDMS / PMMA-Au / SP successfully prepares a fluorescent sensor, which can be applied to the trace visual detection of metal ions and can be recycled. BRIEF DESCRIPTION OF DRAWINGS

[0027] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor. Among them:

[0028] Figure 1 It is a preparation flowchart of the PDMS / PMMA-Au / SP substrate in the embodiment 1 of the present application;

[0029] Figure 2 It is a SEM morphology characterization diagram of the substrate surface in the embodiment 2 of the present application, wherein (a, d) are pyramid arrays; (b, e) are PDMS surfaces with inverted cone structures; (c, f) are PDMS / PMMA-Au; (g) is an EDS characterization of the substrate surface.

[0030] Figure 3 It is a UV-Vis spectrum diagram of the PDMS / PMMA-Au surface after sequentially grafting different functional substances in the embodiment 2 of the present application;

[0031] Figure 4 This is a diagram showing the change in contact angle after different functionalized substances were sequentially grafted onto the PDMS / PMMA-Au surface in Example 2 of the present invention.

[0032] Figure 5 The images show (a) absorption spectra and (b) fluorescence spectra of PDMS / PMMA-Au / SP composite substrates coated with different concentrations of Au nanoparticles in Example 3 of this invention.

[0033] Figure 6 The images show (a) transmission spectra and (b) fluorescence spectra of PDMS / PMMA-Au / SP composite substrates grafted with different amounts of TBDS in Example 4 of this invention.

[0034] Figure 7 The images show (a) transmission spectra and (b) fluorescence spectra of PDMS / PMMA-Au / SP composite substrates grafted with different amounts of ATMS in Example 5 of this invention.

[0035] Figure 8 The images show (a) transmission spectra and (b) fluorescence spectra of PDMS / PMMA-Au / SP composite substrates with different spiropyran grafting times in Example 6 of this invention.

[0036] Figure 9 The following are examples from Example 7 of this invention: (a) fluorescence spectra of different structures under ultraviolet light irradiation; (b) absorption spectra of PDMS / PMMA-Au (black line); absorption spectra of MC (red line); (c) fluorescence spectra of different structures; and (d) comparison of time-resolved emission spectra of different structures.

[0037] Figure 10 The fluorescence spectra of (a) PDMS / PMMA-Au / SP substrate and 10⁻³ M of different metal ion complexes in Example 8 of this invention are shown, along with the fluorescence spectra of Zn at different concentrations. 2+ (b) Fluorescence spectrum when bound to the substrate; (c) Linear fitting; (d) Detection of Zn on PDMS / PMMA-Au / SP substrate. 2+ (e) and (f) Transmission spectra of different metal ions detected by PDMS / PMMA-Au / SP and corresponding macroscopic photographs.

[0038] Figure 11 This is a side view of the micro pyramid array in Embodiment 2 of the present invention. Detailed Implementation

[0039] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0040] In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present application. However, it will be apparent to one skilled in the art that the present application can be practiced without the specific details set forth in this description. In other instances, well-known methods have not been described in detail in order not to unnecessarily obscure aspects of the present application.

[0041] Second, as used in this description, "one embodiment" or "an embodiment" means a specific implementation of the application that can include a specific feature, structure, or characteristic. This description uses "in one embodiment" and "in another embodiment" or "in some embodiments" to identify specific features, structures, or characteristics that are included in some, but not all embodiments of the application. The specific features, structures, or characteristics can be combined in any suitable manner in one or more embodiments.

[0042] Example 1

[0043] (1) Preparation of PDMS substrate with inverted pyramid microstructure

[0044] First, a silicon template with micro-pyramid structure on the surface was obtained by etching single crystal silicon in KOH solution for 30 min. Then, the silicon template was treated with a fluorosilane reagent to make it hydrophobic, which facilitated the subsequent stripping of PDMS. Subsequently, PDMS prepolymer and initiator were cast on the hydrophobic treated silicon template and cured at 68°C for 3 h. After curing, the PDMS was stripped after cooling to room temperature, and a PDMS substrate with inverted pyramid microstructure was obtained.

[0045] (2) Preparation of PDMS / PMMA-Au substrate

[0046] First, 20 mL of chloroauric acid (0.01 wt%) was added to a round-bottom flask and boiled under stirring and reflux. Then, 0.14 mL of sodium citrate (1 wt%) was quickly added to the boiling solution, and the solution was continued to boil for 30 min. Subsequently, the above solution was cooled to room temperature and centrifuged to obtain Au nanoparticles. Next, 0.0455 g of PMMA was dissolved in 20 g of dichloromethane, and different amounts of Au nanoparticles were added and ultrasonically dispersed uniformly. After sealing, the mixture was stirred at room temperature for 5 h. Finally, 50 μL of the mixed solution of PMMA and Au was spin-coated on the surface of PDMS at a speed of 4500 r / min and for a time of 30 s. The spin-coated sample was dried in an oven at 60°C for 1 h to obtain a PDMS / PMMA-Au substrate.

[0047] (3) TBDS functionalization of PDMS / PMMA-Au substrate

[0048] First, the dried PDMS / PMMA-Au substrate was treated by oxygen plasma for 5 min to attach a large number of hydroxyl groups on the surface. Then, the treated substrate was placed in a DMF solution with different TBDS contents and left at room temperature for 30 min. Finally, the substrate was washed with DMF to modify the surface with a TBDS monolayer.

[0049] (4) Preparation of PDMS / PMMA-Au / SP substrate

[0050] First, the PDMS / PMMA-Au substrate modified with TBDS was placed in a DMF solution containing different ATMS contents and left at room temperature for 30 min. Second, the substrate was washed with ethanol and water to graft amino silane reagents and modify the surface with an ATMS monolayer. Then, the substrate modified with ATMS was placed in a 20 mL ethanol solution containing 35 mg EDC and 5 mg spiropyran and left at room temperature in the dark for different times to complete the functionalization of the substrate surface with spiropyran. Finally, the sample modified with spiropyran was washed with ethanol to obtain a PDMS / PMMA-Au / SP composite substrate and finally a fluorescence sensor.

[0051] Example 2

[0052] Verification of the preparation method of PDMS / PMMA-Au / SP substrate and morphology characterization

[0053] The preparation process of the PDMS / PMMA-Au / SP substrate is shown in Figure 1 First, a silicon substrate containing a micro-pyramid array was obtained on a planar silicon surface by alkaline anisotropic etching. The average height of the micro-pyramid was 5 μm, and the angle between the side surface and the plane was about 54.7°, as shown in Figure 2 (a), (d), and Figure 11 Subsequently, the prepolymer of PDMS was poured onto the surface of the silicon substrate, and after solidification, a PDMS substrate with an inverted pyramid structure on the surface was obtained. As shown in Figure 2 (b) and (e), the inverted pyramid structure on the surface of the PDMS substrate was complementary to the pyramid structure on the surface of the silicon substrate, indicating that the PDMS substrate was successfully replicated.

[0054] This PDMS substrate not only has a larger specific surface area than a planar structure, but also has excellent anti-reflection ability, which is beneficial to improving the light absorption efficiency and enhancing the isomerization efficiency and excitation efficiency of spiropyran. Subsequently, a PMMA film containing Au nanoparticles was spin-coated on the surface of the PDMS substrate. The PMMA dielectric layer can effectively reduce the probability of direct contact between the Au nanoparticles and the spiropyran molecules and reduce the non-radiative energy transfer between Au and the spiropyran molecules.

[0055] In addition, the tertiary butyl diphenyl chlorosilane (TBDS) containing rigid groups was modified to the PMMA surface, which can increase the distance between the spiropyran molecules and provide enough free space for the spiropyran ring-opening isomerization. Finally, the SP-COOH was covalently grafted on the PMMA surface which was not occupied by TBDS through the amino silane reagent as a bridging molecule. Figure 2 (c) and (f) show the morphology of the PDMS / PMMA-Au / SP substrate, which has a similar structure to the compound eye of insects. At the same time, Figure 2 (e) shows the EDS spectrum of the PDMS / PMMA-Au / SP substrate, and each element is uniformly distributed on the substrate surface, which again proves that the composite substrate is successfully prepared.

[0056] In order to further prove the successful modification of the functional molecules on the surface of the composite substrate, the inventors tracked the UV-Vis transmission spectrum of the samples involved in the modification process, as shown in Figure 3 Firstly, the transmission spectrum of the composite substrate surface after modification of TBDS has two characteristic peaks at 250 nm and 365 nm. Then, the characteristic peak of the transmission spectrum of the composite substrate surface after modification of ATMS disappears at 365 nm. Finally, the characteristic peak of the transmission spectrum of the composite substrate surface after grafting of the spiropyran disappears at 250 nm, and two characteristic peaks appear at 265 nm and 340 nm. After the composite substrate modified by the spiropyran is irradiated by ultraviolet light, a strong characteristic peak appears at 550 nm, indicating that the spiropyran isomerizes from the closed ring SP form to the open ring MC form, which proves that the composite substrate is successfully prepared.

[0057] Figure 4 The photos showing the changes of the surface contact angle during the sample preparation process are shown. Both PDMS and PMMA are hydrophobic polymers, so the contact angles of the PDMS substrate and the PDMS / PMMA-Au substrate are about 120°, which do not change significantly. After the PDMS / PMMA-Au is treated by oxygen plasma, a large number of hydroxyl groups are generated on the surface, and the contact angle reaches 30°, showing a certain hydrophilicity. After the PDMS / PMMA-Au surface is modified by TBDS, the contact angle reaches 106.1°. This is because the modified TBDS contains a large number of benzene rings, making the sample surface exhibit a certain hydrophobicity. After grafting ATMS, the contact angle of the substrate surface is reduced to 60.4°, which is due to the presence of a large number of amino groups in ATMS, making the substrate surface hydrophilic. After grafting the spiropyran to the substrate surface through ATMS, the contact angle reaches 103.4°, which is because the spiropyran that has not been ring-opening isomerized is hydrophobic. Finally, under ultraviolet light, the spiropyran on the substrate surface is ring-opening isomerized to the MC form with a zwitterionic form, showing hydrophilic properties, so the contact angle is only 37.0°. The change of the contact angle is completely consistent with the functionalization of the substrate surface at each step, which fully proves that the composite substrate is successfully prepared.

[0058] Example 3

[0059] The present application studies the effect of Au nanoparticle content on the fluorescence enhancement performance of the PDMS / PMMA-Au / SP composite substrate. The following discussion involves composite substrates treated by ultraviolet light for 90s.

[0060] As shown in Figure 5 , when there is no Au nanoparticle, the fluorescence intensity of the composite substrate is very weak under the excitation of incident light.

[0061] With the increase of Au nanoparticle concentration, the fluorescence intensity of the composite substrate also increases, which is caused by the plasmonic effect of Au nanoparticles.

[0062] When the concentration of Au nanoparticles is 1.4×10 -4 M, the fluorescence intensity of the composite substrate reaches the maximum, and the corresponding plasmonic resonance absorption peak is the strongest. However, with the continuous increase of the concentration of Au nanoparticles, the fluorescence intensity decreases, because the accumulation of Au nanoparticles with too high concentration will weaken the electromagnetic field effect.

[0063] Example 4

[0064] The present application studies the effect of TBDS addition amount on the fluorescence enhancement performance of the PDMS / PMMA-Au / SP composite substrate. The following discussion involves composite substrates treated by ultraviolet light for 90s.

[0065] As shown in Figure 6 , when the addition amount of TBDS is 100μL, the transmittance of the composite substrate is the lowest, i.e. the spiropyran discoloration effect on the surface of the substrate is the most obvious, and the fluorescence intensity also reaches the maximum. This is because the addition amount of TBDS will affect the distance between the spiropyran molecules, and then affect the steric hindrance of the ring opening.

[0066] When the addition amount of TBDS is too small, the distance between the spiropyran molecules is too short, which cannot provide sufficient space for the isomerization of the spiropyran, resulting in slow or even impossible ring opening of the spiropyran, and then causing small change in the transmittance of the composite substrate and weak fluorescence intensity. However, when the addition amount of TBDS is too large, the effective modification amount of the subsequent spiropyran on the surface of the composite substrate is reduced, and then the transmittance of the composite substrate changes little and the fluorescence intensity is weak.

[0067] Example 5

[0068] The present application studies the effect of ATMS addition amount on the fluorescence enhancement performance of the PDMS / PMMA-Au / SP composite substrate. The following discussion involves composite substrates treated by ultraviolet light for 90s.

[0069] The amount of ATMS added has a significant impact on the grafting sites of spiropyran. For example... Figure 7 As shown, when the amount of ATMS added is too small, it cannot provide enough active sites for spiropyran grafting on the surface of the composite substrate, resulting in a low amount of spiropyran grafting, which in turn leads to a lower transmittance and weaker fluorescence intensity of the composite substrate.

[0070] With increasing ATMS addition, the transmittance of the composite substrate continuously decreased while the fluorescence intensity gradually increased. The composite substrate exhibited the lowest transmittance and the greatest fluorescence enhancement at an ATMS addition of 10 μL. However, when the ATMS addition exceeded 10 μL, the fluorescence intensity of the composite substrate showed a decreasing trend. This is because the excessive density of grafted active sites caused fluorescence aggregation and quenching of the grafted spiropyran.

[0071] Example 6

[0072] The effect of spiropyran growth time on the fluorescence enhancement properties of PDMS / PMMA-Au / SP composite substrates was investigated. All composite substrates discussed below were treated with UV light for 90 s.

[0073] The growth time of spiropyran is closely related to the number of spiropyran grafts on the composite substrate surface. For example... Figure 8 As shown, when the growth time is short, the number of spiropyran grafts is small, so the transmittance of the composite substrate changes little. With the increase of spiropyran grafting time, the transmittance of the composite substrate continues to decrease, while the fluorescence intensity gradually increases. The change in transmittance of the composite substrate is most significant when the grafting time is 12 hours.

[0074] However, it should be noted that the fluorescence intensity of the composite substrate reached its maximum at 3 hours and then showed a decreasing trend. This may be because after 3 hours, as the growth time of spiropyran continued to increase, its grafting density became too high, resulting in aggregation quenching.

[0075] In this invention, the inventors chose a spiropyran growth time of 3 hours as the optimal condition for subsequent research. This is because although the transmittance of the composite substrate decreased by 3% within 3 to 12 hours, the fluorescence intensity decreased by 1.5 times.

[0076] Meanwhile, this composite substrate needs to be used for subsequent trace detection of metal ions, so excellent fluorescence performance is crucial for the practical application of this substrate.

[0077] Example 7

[0078] In the single-factor optimization process, our invention has proved that the PDMS / PMMA-Au / SP substrate exhibits excellent fluorescence performance when the grafting time of spiropyran is 3h. This fluorescence enhancement is mainly from three aspects, respectively, the anti-reflection ability of inverted pyramid structure, the plasmonic resonance effect of Au nanoparticles, and the low non-radiative energy transfer probability of PMMA spacer layer.

[0079] The inverted pyramid structure has excellent anti-reflection ability, which can improve the excitation efficiency of the spiropyran on the substrate surface, and thus improve its fluorescence intensity.

[0080] In order to prove this point, the fluorescence intensity of the substrate P sample (PDMS / PMMA-Au / SP) with inverted pyramid structure and the substrate F sample Without inverted pyramid structure were compared. As shown in Figure 9 (a), the fluorescence intensity of the former is 19 times that of the latter, and the enhancement factor is as high as 5.06.

[0081] Au nanoparticles can produce enhanced local electromagnetic field under the action of incident light, thereby providing more rapid decay channels for the spiropyran on the substrate surface, reducing its fluorescence lifetime, increasing its spontaneous emission rate, and thus enhancing its fluorescence intensity. In order to prove this point, the fluorescence intensity and fluorescence lifetime of the substrate PDMS / PMMA-Au / SP containing Au nanoparticles and the substrate PDMS / SP without Au nanoparticles were compared. The fluorescence intensity of PDMS / PMMA-Au / SP is significantly greater than that of PDMS / SP, and the fluorescence lifetime of PDMS / PMMA-Au / SP is shorter than that of PDMS / SP, as shown in Figure 9 (c) and (d).

[0082] In addition, the resonance coupling between Au nanoparticles and fluorescent molecules can significantly enhance the fluorescence intensity of the latter. This enhancement effect reaches a maximum when the plasmonic resonance peak of metal nanoparticles overlaps with the absorption peak or excitation peak of fluorescent molecules. As shown in Figure 9 (b), there is a considerable overlap between the plasmonic resonance absorption peak of Au nanoparticles and the absorption peak of spiropyran, which will significantly improve the excitation efficiency and radiation rate of the spiropyran on the substrate surface, and thus improve its fluorescence intensity.

[0083] The design of PMMA spacer layer reduces the probability of non-radiative energy transfer caused by direct contact between Au and MC, thereby improving the fluorescence intensity of the substrate. In order to prove this point, the fluorescence intensity and fluorescence lifetime of the substrate PDMS / PMMA-Au / SP containing PMMA and the substrate PDMS / Au / SP without PMMA were compared, as shown in Figure 9The fluorescence intensity of PDMS / PMMA-Au / SP is greater than that of PDMS / Au / SP, and the fluorescence lifetime of PDMS / PMMA-Au / SP is longer than that of PDMS / Au / SP, indicating that there is more electron transfer between the metal nanoparticles and the spiropyran on the PDMS / Au / SP substrate, which quenches the fluorescence emission of MC.

[0084] Example 8

[0085] After the spiropyran isomerizes into the merocyanine MC form under ultraviolet light irradiation, the fluorescence and colorimetric sensing of metal ions can be achieved by the combination of the phenolic hydroxyl group of merocyanine MC and metal ions.

[0086] As shown in Figure 10 (a), 10 -3 M Zn 2+ , Ni 2+ , Sn 2+ , Cu 2+ ethanol solution is added to the surface of the PDMS / PMMA-Au / SP substrate, and the fluorescence peak of MC is shifted from 620 nm to 615 nm, 610 nm, 625 nm, and 630 nm, respectively, and the fluorescence intensity is significantly quenched. Moreover, the fluorescence intensity of the PDMS / PMMA-Au / SP substrate is linearly related to the concentration of metal ions.

[0087] Taking Zn 2+ as an example, as shown in Figure 10 (b) and (c), the linear analysis equation of the fluorescence intensity of the substrate and the concentration of Zn 2+ is Y=-307433X-319506 (10 -1 M~10 -6 M), and the detection limit (LOD) is 0.281 μM (LOD=3S b / S, S b =0.08613), which indicates that the substrate can achieve trace detection of metal ions.

[0088] In addition, since the complex bond formed between MC and metal ions is unstable, it will release metal ions when exposed to visible light because the spiropyran isomerizes back to the open ring state, and the substrate can be recycled.

[0089] As shown in Figure 10 (d), the PDMS / PMMA-Au / SP substrate does not show any attenuation of sensitivity in 6 cycles. In addition to detecting different metal ions by fluorescence, the PDMS / PMMA-Au / SP substrate can also be achieved by colorimetric method. In order to make the colorimetric response effect obvious, the ultraviolet light pretreatment time of the substrate is extended to 150 s.

[0090] Figure 10 (e) and (f) show the colorimetric macroscopic photos and transmission spectra of the PDMS / PMMA-Au / SP substrate in response to different metal ions. After UV irradiation for 150 s, the spiropyran on the surface of the substrate isomerizes from the colorless closed-ring form SP to the deep purple open-ring form MC, making the entire substrate exhibit a significant color change, which corresponds to the transmission peak of MC at 560 nm.

[0091] Subsequently, when the substrate is complexed with different metal ions, the absorption peak has a significant blue shift, thus exhibiting different color changes. In this way, different metal ions can be distinguished by the color change visible to the naked eye, and the visual recognition method greatly reduces the cost in the ion detection process.

[0092] Example 9

[0093] Example 9 differs from Example 1 in that polystyrene is used instead of PMMA as the substrate material in the preparation of the PDMS / PMMA-Au substrate, and the other conditions are the same as in Example 1.

[0094] Example 10

[0095] Example 10 differs from Example 1 in that polyvinylidene chloride is used instead of PMMA as the substrate material in the preparation of the PDMS / PMMA-Au substrate, and the other conditions are the same as in Example 1.

[0096] Example 11

[0097] Example 11 differs from Example 1 in that polyurethane is used instead of PMMA as the substrate material in the preparation of the PDMS / PMMA-Au substrate, and the other conditions are the same as in Example 1.

[0098] Zn 2+ , Ni 2+ , Sn 2+ ethanol solution was added to the fluorescent sensor in Examples 9-11, which produced a significant fluorescence peak shift, indicating that the fluorescent sensor had been successfully prepared.

[0099] Example 13

[0100] Example 13 differs from Example 1 in that Ag nanoparticles are used instead of Au nanoparticles as the substrate material in the preparation of the PDMS / PMMA-Au substrate, and the preparation method of the Ag nanoparticles is as follows:

[0101] Dissolve 9 mg of AgNO3 in 49 mL of H2O, and heat the solution to boiling under vigorous stirring; add 1 mL of 38.8 mmol / L trisodium citrate dropwise, keep the mixture boiling for half an hour; cool the reaction solution to room temperature; centrifuge the prepared silver colloid at 500 rpm for 10 minutes to remove larger size particles, and then obtain Ag nanoparticles, and the rest of the conditions are the same as in Example 1.

[0102] Example 14

[0103] Example 14 differs from Example 1 in that Cu nanoparticles are used to replace Au nanoparticles as the substrate material in the preparation of the PDMS / PMMA-Au substrate, wherein the preparation method of the Cu nanoparticles is as follows: first, add 20 mL of distilled water to a 100 mL volume round-bottom flask, and add 3 mL of 50 mmol / L Cu(NO3)2 solution under constant stirring, transfer the flask to an ice bath and stir for 1 hour; add 6 mL of freshly prepared 50 mmol / L NaBH4 solution, and stir for 1 hour; the product is collected by high-speed centrifuge (10000 rpm, 20 minutes), and then washed with distilled water and anhydrous ethanol three times respectively. Finally, the obtained Cu nanoparticles are dried in a vacuum drying oven at 50°C for 4 hours; the rest of the conditions are the same as in Example 1. -1

[0104] The replacement of metal ions will partially affect the performance of the fluorescent sensor. When Au is replaced by Ag, the performance of the fluorescent sensor does not change significantly. When Au is replaced by Cu, the fluorescent sensor is more sensitive to Cu2+ and is not affected by other metal ions. 2+

[0105] It should be noted that the above examples are only used to illustrate the technical solutions of the present application and not to limit it. Although the present application has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solutions of the present application can be modified or replaced equivalently without departing from the spirit and scope of the technical solutions of the present application, and they should be covered in the scope of the claims of the present application.​​

Claims

1. A visualizing fluorescent sensor, characterized by: The sensor is composed of three layers, which are bottom layer, middle layer and upper layer from bottom to top; The bottom layer is a flexible substrate made of polydimethylsiloxane, the middle layer is a metal particle film coated with thermoplastic material and metal nanoparticles, and the upper layer is a sensing layer modified by chlorosilane or alkoxysilane and spiropyran; The middle layer is a film structure covering the bottom layer, and the upper layer is connected to the middle layer through chemical reaction, and the bottom layer, the middle layer and the upper layer are tightly attached to each other; The preparation method of the visual fluorescent sensor comprises the following steps: Preparation of flexible substrate: etching single crystal silicon with alkaline solution and hydrophobic treatment, pouring polydimethylsiloxane prepolymer and initiator on the silicon template after treatment, curing, cooling to room temperature and peeling off the polydimethylsiloxane to obtain a polydimethylsiloxane substrate containing inverted pyramid microstructure; Coating metal nanoparticle film: dissolving metal nanoparticles and thermoplastic material in solvent, ultrasonic dispersion and continuous stirring, spin coating the mixed solution after stirring on the surface of polydimethylsiloxane, and drying to obtain polydimethylsiloxane / thermoplastic material-metal nanoparticle substrate; First single molecular layer surface modification: plasma treatment of polydimethylsiloxane / thermoplastic material-metal nanoparticle substrate to make the surface attach hydroxyl, and then first single molecular layer surface modification; The first single molecular layer surface modification is modified by one or both of chlorosilane and alkoxysilane containing alkyl and benzene ring, and the chlorosilane is tert-butyl diphenyl chlorosilane; Second single molecular layer surface modification: second single molecular layer surface modification of the substrate after the first surface modification; The second single molecular layer surface modification is modified by chlorosilane or alkoxysilane containing amino group, and the alkoxysilane is 3-aminopropyl trimethoxysilane; Spiropyran functionalization modification: placing the substrate after twice surface modification into organic solvent containing spiropyran and activator for spiropyran functionalization modification to obtain polydimethylsiloxane / thermoplastic material-metal nanoparticle / spiropyran composite substrate; Finally, the polydimethylsiloxane / thermoplastic material-metal nanoparticle / spiropyran composite substrate is washed and dried to obtain the fluorescent sensor; The metal nanoparticles include one of gold nanoparticles, silver nanoparticles and copper nanoparticles.

2. The visualizing fluorescent sensor of claim 1, wherein: The thermoplastic material includes one or more of polymethyl methacrylate, polystyrene, polyvinylidene chloride, polyurethane and derivatives of the above materials.

3. The visualizing fluorescent sensor of claim 1, wherein: The spiropyran is carboxyl-containing spiropyran or spiropyran derivative.

4. The visualizing fluorescent sensor of claim 1, wherein: The metal nanoparticle is added in an amount of 3.5 x 10 -5 M~5.6 x 10 -4 M.

5. The visualizing fluorescent sensor of claim 1, wherein: The polydimethylsiloxane substrate containing inverted pyramid microstructure, wherein the angle between the side surface and the top surface of the inverted pyramid microstructure is 54.7°, and the height is 5 μm.

6. The visualizing fluorescent sensor of claim 1, wherein: The growth time of spiropyran in the spiropyran functionalization modification is 3-12 hours.

7. Use of a visualizing fluorescent sensor according to claim 1, characterized in that: The application of the fluorescent sensor in visual trace detection of metal ions is included.

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