Visual high-resolution fluorescent probe for identifying potential fingerprints and preparation method of visual high-resolution fluorescent probe

Abstract

The invention discloses a fluorescent probe for visual high-resolution identification of potential fingerprints and a preparation method of the fluorescent probe, and relates to the technical field of biological imaging, the fluorescent probe is called Zn-TC for short, the structural formula of the fluorescent probe is as follows: # imgabs0, an LFPs image processed by the complex Zn-TC has wide applicability, high definition and high contrast, and the fluorescent probe can be applied to the field of LFPs identification; the complex can obtain LFPs imaging on various substrates in a short time; in addition, under the multi-photon excitation wavelength of 800nm, high-resolution and high-contrast imaging of the complex for identifying the three-level LFPs can be obtained through a confocal development technology.

Description

Technical Field

[0001] The invention relates to the technical field of biological imaging, and in particular to a fluorescent probe for visualizing high-resolution latent fingerprint recognition and a preparation method thereof. Background Art

[0002] Latent fingerprints (LFPs) are traces left when a finger touches the surface of an object. They are mainly composed of water and lipids. LFPs are the most common fingerprint form at crime scenes and are difficult to identify directly with the naked eye. In the field of forensics, LFPs are regarded as key biometric features, and related probes for detecting LFPs are of great value for crime scene investigation and evidence collection.

[0003] Although traditional LFPs materials have been well applied in primary and secondary detail features, these materials inevitably compromise imaging quality, resulting in long response time and low sensitivity and contrast. In recent years, multiphoton aggregation-induced emission (AIE) materials have shown great application potential in the field of LFPs imaging due to their advantages such as deep penetration, high contrast, and high sensitivity. The present invention synthesizes a carbazole tripyridine zinc complex with multiphoton AIE properties, aiming to provide a visualized optical probe material for rapid identification of personal information in criminal investigation activities. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide a fluorescent probe and a preparation method and application thereof. The synthesized carbazole tripyridine zinc complex can specifically identify oleic acid (OA) in LFPs, thereby realizing fast-response high-resolution LFPs imaging; and the multi-photon excitation fluorescence characteristics of the complex are utilized to accurately capture the three-level details of LFPs, thereby realizing high-resolution and high-contrast imaging of the three-level details of fingerprints.

[0005] The technical problem to be solved by the present invention is achieved by adopting the following technical solutions:

[0006] The first object of the present invention is to provide a fluorescent probe, referred to as Zn-TC, whose structural formula is as follows:

[0007]

[0008] The second object of the present invention is to provide a method for preparing the fluorescent probe, comprising the following steps:

[0009] (1) Carbazole and bromhexane undergo a substitution reaction to obtain compound A;

[0010] (2) Compound A and N,N-dimethylformamide (DMF), phosphorus oxychloride (POCl 3 ) undergoes Vilsmeier-Haack reaction to obtain compound B;

[0011] (3) Compound B undergoes an alkylation reaction with 2-acetylpyridine to obtain compound C;

[0012] (4) Compound C undergoes a ring-closing reaction with 1-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide to obtain compound TC;

[0013] (5) Compound TC undergoes coordination reaction with zinc nitrate to obtain the complex Zn-TC.

[0014] The synthetic route is as follows:

[0015]

[0016] Furthermore, the molar ratio of carbazole to hexyl bromide is 1:(1-1.5). By adding an excess of hexyl bromide, the carbazole is reacted as completely as possible.

[0017] Furthermore, the substitution reaction uses sodium hydride (NaH) as a catalyst. NaH acts as a strong base to remove hydrogen from the nitrogen of carbazole, thereby promoting the substitution reaction between carbazole and hexyl bromide.

[0018] Further, the compound A is reacted with DMF, POCl 3 The molar ratio of POCl is 1:(2-4):(3-6). DMF is used as the formylation reagent. 3 Under the catalysis of , a formyl group is introduced on the aromatic ring of compound A.

[0019] Furthermore, the molar ratio of the compound B to 2-acetylpyridine is 1:(1.1-1.2). By adding an excess of 2-acetylpyridine, the compound B is reacted as completely as possible.

[0020] Furthermore, the alkylation reaction is carried out under alkaline conditions, which can be provided by sodium hydroxide. Alkaline conditions can make the hydrogen atom on the α-carbon of the 2-acetylpyridine carbonyl group more easily replaced, thereby promoting the alkylation reaction.

[0021] Furthermore, the molar ratio of the compound C to 1-[2-oxygen-2-(2-pyridyl)ethyl]pyridinium iodide is 1:(1 to 1.1). The 1-[2-oxygen-2-(2-pyridyl)ethyl]pyridinium iodide can be slightly excessive to increase the conversion rate of the compound C.

[0022] Furthermore, the molar ratio of the zinc nitrate to the compound TC is 1:(2-3).

[0023] The third object of the present invention is to provide an application of the fluorescent probe in visually identifying LFP.

[0024] The beneficial effects of the present invention are:

[0025] 1. The 2,2:6',2"-tripyridine in the Zn-TC structure of the complex of the present invention has a strong coordination ability for the transition metal ion Zn(II), and the hexylcarbazole group has a strong electron-donating ability, which is beneficial to the charge transfer within the molecule and regulates the luminescence of the complex; the introduction of the Zn(II) center helps to enhance the charge transfer from the central ion to the ligand and improve the multi-photon excitation fluorescence performance of the complex; and the Zn(II) complex has the advantages of low biological toxicity and good compatibility.

[0026] 2. The complex Zn-TC of the present invention has multiphoton AIE properties, which overcomes the fluorescence quenching caused by self-aggregation of most complexes at high concentrations; AIE phenomenon is observed in Zn-TC in a mixed solution of ethyl acetate, and the fluorescence intensity increases with the increase of the volume fraction of ethyl acetate; when the volume fraction of ethyl acetate is 80%, the three-photon cross section of Zn-TC reaches a maximum value of 19.1×10 -81 cm 6 ·s 2 ·photon -2 .

[0027] 3. The complex Zn-TC of the present invention can specifically identify OA in the range of 0-150 μM, with a detection limit of 6.23 μM. At an excitation wavelength of 1300 nm, the multiphoton fluorescence recognition effect of OA is the best, with a three-photon fluorescence cross section of 5.37×10 - 81 cm 6 ·s 2 ·photon -2 , about 1.9 times that before recognition.

[0028] 4. The LFPs image treated with the complex Zn-TC of the present invention has wide applicability, high definition and high contrast, and can be applied to the field of LFPs identification; the complex can obtain LFPs imaging on a variety of substrates (tin foil, glass, plastic and optical disk, etc.) in a short time; at a multi-photon excitation wavelength of 800nm, high-resolution and high-contrast imaging of the complex identifying tertiary LFPs can be obtained by confocal development technology.

[0029] 5. The complex Zn-TC of the present invention has good stability and resistance to photobleaching. Its fluorescence intensity remains stable within 30 minutes of white light irradiation without obvious photoquenching. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 is the crystal structure formula of the complex Zn-TC;

[0031] Figure 2(a) is the three-photon fluorescence spectrum of Zn-TC at an excitation wavelength of 1150-1550 nm (c = 10 -3 mol / L); Figure 2 (b) is the three-photon absorption cross section of Zn-TC at an excitation wavelength of 1150-1450 nm (c = 10 -3 mol / L); Figure 2 (c) is the three-photon fluorescence spectrum of Zn-TC in mixed solutions with different volume fractions of ethyl acetate at an excitation wavelength of 1300 nm, and the inset is the three-photon fluorescence spectrum of Zn-TC in ethyl acetate at an excitation wavelength of 1300 nm; Figure 2 (d) is the three-photon absorption cross section of Zn-TC in mixed solutions with different ethyl acetate volume fractions at 1300 nm excitation wavelength (c = 10 -3 mol / L);

[0032] Figure 3 (a) is the fluorescence response diagram of Zn-TC to different substances (c = 10 -5 mol / L); Figure 3 (b) is the three-photon fluorescence spectrum of Zn-TC after adding OA at an excitation wavelength of 1150-1550 nm (c = 10 -3 mol / L); Figure 3 (c) is the three-photon fluorescence spectrum of Zn-TC after adding OA (c = 10 -3 mol / L); Figure 3 (d) is the time-dependent fluorescence response of Zn-TC after adding OA at an excitation wavelength of 1300 nm (c = 10 -3 mol / L), error <10%;

[0033] Figure 4 Fluorescence images of LFPs on different substrates (tin foil, glass, plastic, and optical disc) after being soaked in Zn-TC solution (80 μM, λex = 365 nm);

[0034] Figure 5 (a) is the confocal imaging of LFPs on glass after soaking in Zn-TC solution (the leftmost picture is the camera image of LFPs on glass after soaking in Zn-TC solution; the right side (1)(2)(3)(4) are the confocal imaging images of the fingerprint part randomly selected from the left picture, where the first row is the single-photon light source λex=800nm, the second row is the two-photon light source λex=405nm, scale bar=100μM); Figure 5 (b) is the quantitative fluorescence intensity diagram of confocal imaging of LFPs on glass after immersion in Zn-TC solution; Figure 5 (c) Time-dependent fluorescence response diagram of Zn-TC under single photon and two-photon conditions; Figure 5(d) Quantitative fluorescence intensity diagram of the time-dependent fluorescence response of Zn-TC under one-photon and two-photon conditions. DETAILED DESCRIPTION

[0035] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further described below in conjunction with specific embodiments and diagrams.

[0036] Example 1: Preparation of complex Zn-TC

[0037] Preparation of Compound A

[0038] Sodium hydride (2.6 g, 0.11 mol) and 100 mL DMF were added to a 250 mL round-bottom flask, stirred at room temperature for 20 min, then carbazole (9.1 g, 0.054 mol) was added, stirred at room temperature for 20 min, and then bromohexane (8.4 mL, 0.055 mol) was added, and the mixture was heated to 65 ° C for 3 h. After the reaction, the reaction solution was poured into ice water and filtered to obtain a light yellow solid, which was recrystallized from ethanol to obtain white needle-shaped crystals, namely compound A, with a yield of 90%.

[0039] Preparation of compound B

[0040] Take DMF (9.2 g, 0.13 mol) and add it into a 250 mL round-bottom flask. Slowly add POCl in an ice-salt bath. 3 (32g, 0.21mol), then add compound A (10g, 0.042mol) dissolved in 53mL chloroform, heat to 65°C for 8h. After the reaction, pour the reaction solution into ice water, adjust the pH to weak alkalinity with sodium hydroxide, extract with dichloromethane, take the organic layer, distill at atmospheric pressure, purify by column chromatography with petroleum ether and ethyl acetate (10:1, v / v), and freeze to obtain a white solid, namely compound B, with a yield of 90%.

[0041] Preparation of Compound C

[0042] Compound B (8.4 g, 0.030 mol) was dissolved in 200 mL of ethanol and added to a 500 mL flask. The mixture was stirred at room temperature. 2-acetylpyridine (4 mL, 0.033 mol) was then added. A 2% sodium hydroxide solution was then added dropwise until an orange-red solid was generated. The mixture was reacted for 15 h, filtered, and washed with water to obtain a yellow solid, i.e., compound C, with a yield of 45%.

[0043] Preparation of compound TC

[0044] Compound C (1.9 g, 5.0 mmol) and 1-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide (1.6 g, 5.0 mmol) were dissolved in 50 mL of methanol, and ammonium acetate (2.3 g, 30 mmol) was added, and the mixture was refluxed for 24 h. After the reaction, the reaction solution was allowed to stand and cool, and a solid was precipitated, which was washed with water and dried. After atmospheric distillation, the solid was purified by column chromatography with dichloromethane and methanol (10:1, v / v) to obtain a brown solid, namely compound TC, with a yield of 31%.

[0045] Preparation of Complex Zn-TC

[0046] Compound TC (2.3 g, 5 mmol) was dissolved in 40 mL of methanol to obtain solution I; zinc nitrate hexahydrate (0.45 g, 2 mmol) was dissolved in 15 mL of methanol to obtain solution II; solution I and solution II were mixed and reacted at 65°C for 3 h. After the reaction, the reaction solution was cooled to room temperature and filtered to obtain a yellow solid, namely the complex Zn-TC, with a yield of 85%.

[0047] Example 2: Preparation of complex Zn-TC

[0048] Preparation of Compound A

[0049] Sodium hydride (2.6 g, 0.11 mol) and 100 mL DMF were added to a 250 mL round-bottom flask, stirred at room temperature for 20 min, then carbazole (9.1 g, 0.054 mol) was added, stirred at room temperature for 20 min, and then bromohexane (9.7 mL, 0.059 mol) was added, and the mixture was heated to 65 ° C for 3 h. After the reaction, the reaction solution was poured into ice water and filtered to obtain a light yellow solid, which was recrystallized from ethanol to obtain white needle-shaped crystals, namely compound A, with a yield of 92%.

[0050] Preparation of compound B

[0051] Take DMF (11.0 g, 0.15 mol) and add it into a 250 mL round-bottom flask. Slowly add POCl in an ice-salt bath. 3 (32g, 0.21mol), then add compound A (10g, 0.042mol) dissolved in 53mL chloroform, heat to 65°C and react for 8h. After the reaction, pour the reaction solution into ice water, adjust the pH to weak alkalinity with sodium hydroxide, extract with dichloromethane, take the organic layer, distill at atmospheric pressure, purify by column chromatography with petroleum ether and ethyl acetate (10:1, v / v), and freeze to obtain a white solid, namely compound B, with a yield of 91%.

[0052] Preparation of Compound C

[0053] Compound B (8.4 g, 0.030 mol) was dissolved in 200 mL of ethanol and added to a 500 mL flask. The mixture was stirred at room temperature. 2-acetylpyridine (4.4 mL, 0.036 mol) was then added. A 2% sodium hydroxide solution was then added dropwise until an orange-red solid was generated. The mixture was reacted for 15 h, filtered, and washed with water to obtain a yellow solid, i.e., compound C, with a yield of 47%.

[0054] Preparation of compound TC

[0055] Compound C (1.9 g, 5.0 mmol) and 1-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide (1.7 g, 5.3 mmol) were dissolved in 50 mL of methanol, and ammonium acetate (2.3 g, 30 mmol) was added, and the mixture was refluxed for 24 h. After the reaction, the reaction solution was allowed to stand and cool, and a solid was precipitated, which was washed with water and dried. After atmospheric distillation, the solid was purified by column chromatography with dichloromethane and methanol (10:1, v / v) to obtain a brown solid, namely compound TC, with a yield of 35%.

[0056] Preparation of Complex Zn-TC

[0057] Compound TC (2.3 g, 5 mmol) was dissolved in 40 mL of methanol to obtain solution I; zinc nitrate hexahydrate (0.45 g, 2 mmol) was dissolved in 15 mL of methanol to obtain solution II; solution I and solution II were mixed and reacted at 65°C for 5 h. After the reaction, the reaction solution was cooled to room temperature and filtered to obtain a yellow solid, namely the complex Zn-TC, with a yield of 88%.

[0058] Example 3: Preparation of complex Zn-TC

[0059] Preparation of Compound A

[0060] Sodium hydride (2.6 g, 0.11 mol) and 100 mL DMF were added to a 250 mL round-bottom flask, stirred at room temperature for 20 min, then carbazole (9.1 g, 0.054 mol) was added, stirred at room temperature for 20 min, and then bromohexane (8.9 mL, 0.054 mol) was added, and the mixture was heated to 65 ° C for 3 h. After the reaction, the reaction solution was poured into ice water and filtered to obtain a light yellow solid, which was recrystallized from ethanol to obtain white needle-shaped crystals, namely compound A, with a yield of 90%.

[0061] Preparation of compound B

[0062] Take DMF (9.2 g, 0.13 mol) and add it into a 250 mL round-bottom flask. Slowly add POCl in an ice-salt bath. 3(27.6g, 0.18mol), then add compound A (10g, 0.042mol) dissolved in 53mL chloroform, heat to 65°C and react for 8h. After the reaction, pour the reaction solution into ice water, adjust the pH to weak alkalinity with sodium hydroxide, extract with dichloromethane, take the organic layer, distill at atmospheric pressure, purify with column chromatography of petroleum ether and ethyl acetate (10:1, v / v), freeze, and obtain a white solid, namely compound B, with a yield of 89%.

[0063] Preparation of Compound C

[0064] Compound B (8.4 g, 0.030 mol) was dissolved in 200 mL of ethanol and added to a 500 mL flask. The mixture was stirred at room temperature. 2-acetylpyridine (4 mL, 0.033 mol) was then added. A 2% sodium hydroxide solution was then added dropwise until an orange-red solid was generated. The mixture was reacted for 12 h, filtered, and washed with water to obtain a yellow solid, i.e., compound C, with a yield of 43%.

[0065] Preparation of compound TC

[0066] Compound C (1.9 g, 5.0 mmol) and 1-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide (1.7 g, 5.3 mmol) were dissolved in 50 mL of methanol, and ammonium acetate (2.3 g, 30 mmol) was added, and the mixture was refluxed for 24 h. After the reaction, the reaction solution was allowed to stand and cool, and a solid was precipitated, which was washed with water and dried. After atmospheric distillation, the solid was purified by column chromatography with dichloromethane and methanol (10:1, v / v) to obtain a brown solid, namely compound TC, with a yield of 30%.

[0067] Preparation of Complex Zn-TC

[0068] Compound TC (2.3 g, 5 mmol) was dissolved in 50 mL of methanol to obtain solution I; zinc nitrate hexahydrate (0.45 g, 2 mmol) was dissolved in 15 mL of methanol to obtain solution II; solution I and solution II were mixed and reacted at 65°C for 5 h. After the reaction, the reaction solution was cooled to room temperature and filtered to obtain a yellow solid, namely, the complex Zn-TC, with a yield of 89%.

[0069] Example 4: Structural Characterization of Complex Zn-TC

[0070] The complex Zn-TC prepared in Example 1 was characterized by H NMR, C NMR, IR and mass spectrometry. The characterization results are as follows: 1 H NMR (400 MHz, DMSO-d 6)δ9.47(s,2H),9.29(s,2H),9.20(m,4H),9.11(m,2H),8.87(d,J=4.9Hz,1H),8.56(d ,J=8.8Hz,1H),8.44(m,2H),8.36(d,J=7.8Hz,2H),8.29(t,J=7.9Hz,4H),7.93(m,6H ),7.70(dd,J=14.7,8.3Hz,2H),7.50(q,J=6.6,6.0Hz,4H),7.33(dt,J=14.6,7.3Hz, 2H), 4.51 (m, 4H), 1.84 (m, 4H), 1.24 (dd, J=13.5, 6.6Hz, 12H), 0.80 (t, J=7.0Hz, 6H). 13 C NMR (101 MHz, DMSO-d 6 )δ156.10,155.83,151.04,149.87,141.26,141.16,137.97,128.71,126.77,125.23,124.98,123.49,122. 78,121.53,119.74,119.57,118.48,110.63,110.10,42.97,31.51,29.05,26.68,22.55,14.37.IR(KBr,cm -1 ):3431(m),3046(w),2933(m),2856(w),1587(m),1480(s),1411(m),1272(m),883(m),790(m).ESI-MS:[m-2NO 3 - ] / z:calcd for C 66 H 60 N 8 Zn:514.21,found:514.42.

[0071] The above characterization results prove that the complex Zn-TC was successfully prepared in Example 1.

[0072] Example 5: Crystal structure analysis of complex Zn-TC

[0073] The single crystal of the complex Zn-TC was obtained by solvent evaporation method, and the specific process was as follows: an appropriate amount of the complex Zn-TC prepared in Example 1 was dissolved in 10 mL of dichloromethane, then filtered into a 25 mL conical flask, and 5 mL of ethanol was covered on the upper layer, and placed in a dark environment without vibration, and yellow prismatic crystals were obtained after two weeks. The obtained crystals were subjected to X-ray diffraction (XRD) analysis.

[0074] The size of the single crystal is 0.30mm×0.20mm×0.10mm, and it belongs to the monoclinic system and C2 / c space group. Figure 1 The crystal structure of the complex Zn-TC is shown in Figure 1, which proves the exact structure of the molecule. In order to clearly show the crystal structure, the nitrate anion was deleted. In the crystal structure of Zn-TC, carbazole terpyridine is the main ligand coordinated with the central Zn to form a conjugated system, which is conducive to charge exchange and enhances the charge transfer from the central ion to the ligand. NO has a low charge density and is easy to form hydrogen bonds in water solvents. 3 - Increased the solubility of the complex.

[0075] Example 6: AIE property test of complex Zn-TC

[0076] Use acetonitrile (CH 3 CN) and ethyl acetate (EA) were used as good solvent and poor solvent respectively, and mixed in different volume ratios to prepare a mixed solvent with a volume fraction of ethyl acetate between 0 and 98%. -5 mol / L) in mixed solvents.

[0077] from Figure 2 (a) It can be seen that under the continuous excitation wavelength of 1150-1550nm, the fluorescence intensity signal is strongest at 1300nm.

[0078] from Figure 2 (b) It can be seen that at an excitation wavelength of 1400 nm, the maximum three-photon absorption cross section of Zn-TC is 28.1×10 -81 cm 6 ·s 2 ·photon -2 .

[0079] from Figure 2 (c) It can be seen that when the volume fraction of ethyl acetate is 80%, the fluorescence intensity signal of Zn-TC is the strongest.

[0080] from Figure 2 (d) It can be seen that when the volume fraction of ethyl acetate is 80%, the maximum three-photon cross section of Zn-TC reaches 19.1×10 -81 cm 6 ·s 2 ·photon -2 .

[0081] Example 7: Test of the specific recognition ability of the complex Zn-TC to OA

[0082] Take the concentration as 10 -310 mol / L Zn-TC solution in dimethyl sulfoxide (DMSO) was diluted to 10% by PBS buffer (pH = 7.4). -5 mol / L, and then add 200μL of 10 -2 mol / L oleic acid (OA), urea (Urea), sodium chloride (NaCl), lactic acid (HL), glucose (GLu) and cholesterol (CHOL) were used for fluorescence testing. In addition, the solution was irradiated with white light to test the stability of Zn-TC.

[0083] from Figure 3 (a) It can be seen that obvious fluorescence enhancement can be observed only in the solution reacting with OA, while the other components do not cause obvious fluorescence emission.

[0084] from Figure 3 (b) and Figure 3 (c) It can be seen that in DMSO and PBS buffer, Zn-TC has a good fluorescence response to OA, and the recognition effect of OA is strongest at the excitation wavelength of 1300nm. After calculation, the three-photon cross section σ after recognition is 3s 5.37×10 -81 cm 6 ·s 2 ·photon -2 , about 2.43×10 before recognition -81 cm 6 ·s 2 ·photon -2 1.9 times of . The calculation formula is as follows:

[0085]

[0086] Where R represents the standard fluorescent reference rhodamine 6G (1.0×10 -3 mo / L), S represents the sample to be tested, Q, n and c are the quantum yield of fluorescence, the refractive index of the solvent and the concentration of the solution, respectively, f is the overall fluorescence collection efficiency intensity of the fluorescence signal collected by the fiber optic spectrometer, σ 3R is the effective three-photon cross section of rhodamine 6G. The effective three-photon absorption cross section of rhodamine 6G is 6×10 -81 cm 6 ·s 2 ·photon -2 .

[0087] from Figure 3 (d) It can be seen that Zn-TC has good photostability and strong resistance to photobleaching, and no obvious photoattenuation occurs after 30 min of white light irradiation.

[0088] Example 8: LFPs fluorescence imaging of the complex Zn-TC on different substrates

[0089] Touch the forehead with your finger to leave latent fingerprints on the surface of tin foil, glass, plastic and CD, then soak the tin foil, glass, plastic and CD in Zn-TC aqueous solution (c=10 -3 mol / L) and taken out after 2 min for fluorescence imaging.

[0090] from Figure 4 It can be seen that the LFP images with high definition and high contrast are displayed on the tin foil, glass, plastic and CD after Zn-TC treatment. The gray value curve fluctuates greatly and the difference is obvious. Zn-TC shows high contrast under the tin foil, glass, plastic and CD substrates.

[0091] Example 9: Confocal imaging of LFPs on glass of the complex Zn-TC

[0092] Touch the forehead with your finger to leave a latent fingerprint on the glass surface, then soak the glass in a Zn-TC aqueous solution (c = 10 -3 mol / L) and taken out after 2 min. The fine features of the tertiary fingerprint were captured and recorded using the two-photon channel of a confocal microscope.

[0093] from Figure 5 (a) Lipid deposits of different sizes can be seen, which are the tiny units that make up LFPs.

[0094] from Figure 5 (b) It can be seen that the fluorescence intensity of LFPs excited by two-photon light source is higher than that by single-photon light source.

[0095] from Figure 5 (c) It can be seen that the boundaries of LFPs excited by a single-photon light source are blurred, while LFPs excited by a two-photon light source have lower background interference and higher imaging contrast, and the widths of different ridges can be distinguished under a microscope.

[0096] from Figure 5 (d) It can be seen that within 15 min, the fluorescence intensity of LFPs excited by single photons and two-photons did not change significantly, and Zn-TC had a good fluorescence response ability.

[0097] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. It should be understood by those skilled in the art that the present invention is not limited to the above embodiments. The above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention to be protected. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. A fluorescent probe, referred to as Zn-TC, characterized in that: The structural formula of the Zn-TC is shown below:

2. The method for preparing the fluorescent probe according to claim 1, characterized in that: The preparation method comprises the following steps: (1) Carbazole and bromhexane undergo a substitution reaction to obtain compound A; (2) Compound A undergoes Vilsmeier-Haack reaction with DMF and POCl3 to obtain compound B; (3) Compound B undergoes an alkylation reaction with 2-acetylpyridine to obtain compound C; (4) Compound C undergoes a ring-closing reaction with 1-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide to obtain compound TC; (5) Compound TC reacts with zinc nitrate to obtain a complex Zn-TC; The synthetic route is as follows:

3. The preparation method according to claim 2, characterized in that: The molar ratio of carbazole to hexyl bromide is 1:(1-1.5).

4. The preparation method according to claim 2, characterized in that: The substitution reaction uses NaH as a catalyst.

5. The preparation method according to claim 2, characterized in that: The molar ratio of the compound A to DMF and POCl3 is 1:(2-4):(3-6).

6. The preparation method according to claim 2, characterized in that: The molar ratio of the compound B to 2-acetylpyridine is 1:(1.1-1.2).

7. The preparation method according to claim 2, characterized in that: The alkylation reaction is carried out under alkaline conditions.

8. The preparation method according to claim 2, characterized in that: The molar ratio of the compound C to 1-[2-oxo-2-(2-pyridyl)ethyl]pyridinium iodide is 1:(1-1.1).

9. The preparation method according to claim 2, characterized in that: The molar ratio of the zinc nitrate to the compound TC is 1:(2-3).

10. Use of the fluorescent probe according to claim 1 or the fluorescent probe prepared by the preparation method according to any one of claims 2 to 9 in visual identification of LFP.

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