阅读说明：本技术 基于MXene的SERS薄膜基底的制备方法及应用 (Preparation method and application of SERS (surface enhanced Raman Scattering) thin film substrate based on MXene ) 是由 王凤平 何志权 李岩 马骏杰 何康 于 2021-07-29 设计创作，主要内容包括：本发明公开了一种基于MXene的SERS薄膜基底制备方法及应用,涉及表面增强拉曼散射光谱技术领域,本发明所述的方法包括使用氟化锂-盐酸为刻蚀分层剂选择性刻蚀掉前驱体MAX材料中的Al原子层,所获得的双过渡金属碳化物二维层状材料用去离子水将其反复清洗、离心；然后将其在去离子水中分散,摇晃,再离心抽滤；得到新型的自支撑SERS薄膜基底。本发明所用的制备方法操作简单,成本低廉,具有灵敏度高,拉曼增强效果好,可重现性高等优点,可应用于环境、食品安全、生物标志物等领域的痕量检测,具有广阔的应用前景。(The invention discloses a preparation method and application of an MXene-based SERS film substrate, and relates to the technical field of surface enhanced Raman scattering spectroscopy, the method comprises the steps of selectively etching an Al atomic layer in a MAX material of a precursor by using lithium fluoride-hydrochloric acid as an etching delaminating agent, and repeatedly cleaning and centrifuging the obtained double-transition metal carbide two-dimensional layered material by using deionized water; then dispersing the mixture in deionized water, shaking, and then carrying out centrifugal suction filtration; obtaining the novel self-supporting SERS film substrate. The preparation method provided by the invention is simple to operate, low in cost, high in sensitivity, good in Raman enhancement effect, high in reproducibility and the like, can be applied to trace detection in the fields of environment, food safety, biomarkers and the like, and has a wide application prospect.)

1. The preparation method of the SERS film substrate based on MXene is characterized in that lithium fluoride-hydrochloric acid is used as an etching layering agent, an Al atomic layer in a MAX material of a precursor is selectively etched, the etched double-transition metal carbide two-dimensional layered material is repeatedly cleaned and centrifuged by deionized water, then is dispersed in the deionized water, is shaken and is subjected to centrifugal filtration, and the SERS film substrate is obtained.

2. The method for preparing the MXene-based SERS film substrate according to claim 1, wherein the method specifically comprises the following steps:

step 1: adding TiVAlC powder serving as a precursor MAX material into a lithium fluoride-dilute hydrochloric acid mixed solution, then placing the mixture at 35-40 ℃ for constant-temperature etching to obtain a suspension, and ensuring the TiVAlC powder to be fully etched in a magnetic stirring manner in the etching process;

step 2: diluting the etched suspension with deionized water, then centrifuging by using a centrifuge at 3500-5000 rpm/min to obtain a precipitate, repeating for several times until the pH value of the centrifuged supernatant is 6-7;

and step 3: dispersing the obtained precipitate in deionized water, repeatedly shaking, centrifuging for 0.5-1 h, and taking supernatant, wherein the supernatant is a colloidal solution of the TiVC nanosheet;

and 4, step 4: and carrying out vacuum filtration on the colloidal solution of the TiVC nano-sheet, and then placing the TiVC nano-sheet in a vacuum drying oven for drying to obtain the SERS film substrate.

3. The method for preparing an MXene-based SERS film substrate according to claim 2, wherein in the step 1, TiVAlC powder is added into the lithium fluoride-diluted hydrochloric acid mixed solution at a speed of (0.5-1 g)/10min at 20-30 ℃ to prevent oxidation of TiVC nanosheets due to overheating.

4. The method for preparing an MXene-based SERS film substrate as claimed in claim 2, wherein in the lithium fluoride-hydrochloric acid mixed solution, the molar ratio of hydrochloric acid to lithium fluoride is (1.5-5): 1.

5. the method for preparing an MXene-based SERS film substrate according to claim 2, wherein the molar ratio of lithium fluoride to TiVAlC is (4-9): 1.

6. the method for preparing an MXene-based SERS film substrate according to claim 2, wherein the centrifugation in step 2 is repeated 7-10 times for 3-5 min.

7. The method for preparing an MXene-based SERS film substrate according to claim 2, wherein in the step 4, the drying temperature is 40-60 ℃ and the drying time is 10-12 h.

8. An application of the SERS film substrate based on MXene is characterized in that 5-10 mu L of organic dye solution is dripped on the surface of the SERS film substrate prepared by the preparation method according to any one of claims 1-7, a sample is prepared after drying at 20-30 ℃, and the sample is used for SERS detection.

9. The application of the MXene-based SERS film substrate as claimed in claim 8, wherein the application of the sample for SERS detection specifically comprises:

placing the sample in a microscopic confocal Raman spectrometer, wherein the laser wavelength is 532nm, the laser attenuation power is 1-10%, and the frequency range is 2000cm^-1-550cm^-1Setting 10-20s exposure time in a continuous mode, collecting Raman spectrum, and completing Raman detection of organic dye molecules with detection limit of 10^-15M。

10. An MXene-based SERS film substrate, wherein the film substrate is prepared based on the preparation method of any one of claims 1 to 7.

Technical Field

The invention relates to the technical field of surface enhanced Raman scattering spectroscopy, in particular to a preparation method and application of an MXene-based SERS film substrate.

Technical Field

The Raman scattering spectrum is a detection and analysis technology for analyzing and researching information in the aspects of molecular vibration and rotation on the scattering spectrum with different incident light frequencies based on the Raman scattering effect discovered by Indian scientist Chandrasekhara Venkata Raman in 1928 to obtain a molecular structure. However, the raman scattering cross-section is small and the resulting raman signal is easily swamped by fluorescence during detection of materials with strong fluorescent background; in addition, the low sensitivity defect in the aspect of trace detection restricts the application of Raman scattering.

Until the middle of the 70's of the 20 th century, 3 research groups respectively led by Fleischmann, VanDuyne and Creighton observed and confirmed the surface enhanced Raman phenomenon respectively, and through calculation, the Raman signal of the pyridine molecule on the surface of the rough silver electrode is 10 of the aqueous solution thereof⁶And (4) doubling. This novel phenomenon is called Surface-enhanced Raman scattering (SERS). Subsequently, gold, silver and copper are developed to be used as SERS substrates, the problem of small scattering cross section is solved, Raman scattering signals can be amplified in a magnitude order, and the method has attracted wide attention in the fields of physics, chemistry, medicine, biology and the like. However, the noble metal materials are complex in preparation process and expensive in price, so that the key for determining whether the SERS technology can be widely applied is to find an SERS substrate material which is low in price, easy to prepare, good in Raman enhancement effect and high in reproducibility.

A two-dimensional layered transition metal carbide Ti is prepared for the first time from the Yury Gogotsi topic group of Derasel university in the United states of 2011₃C₂Since MXenes, two-dimensional transition metal carbides, nitrides or carbonitrides having both high electronic conductivity and hydrophilicity, i.e., MXenes, are rapidly developing at a high level and are widely studied in the fields of energy storage, catalysis, sensing, electromagnetic shielding, and the like. MXene has good surface plasmon resonance effect in the visible light region due to excellent electron transfer capacity and adsorption capacity, so that MXene has good SERS fieldThe application prospect of (1). Typical Ti that the prior art will often produce₃C₂MXene self-supporting layered materials are used as SERS substrates, but the Raman enhancement effect is not ideal.

Disclosure of Invention

In view of the above, the invention provides a preparation method of a double transition metal carbide MXene-based self-supporting layered material and an application of the material as a SERS substrate. The MXene self-supporting film provided by the invention is used as an SERS substrate and has the advantages of high sensitivity, good Raman enhancement effect, high reproducibility and the like.

According to the invention, lithium fluoride-hydrochloric acid is used as an etching delaminating agent to selectively etch off an Al atomic layer in a MAX material of a precursor to obtain a double-transition metal carbide two-dimensional layered material MXene, and the two-dimensional layered material MXene is assembled into a self-supporting film and used as an SERS substrate to detect dye molecules.

According to the first aspect of the invention, the preparation method of the SERS film substrate based on MXene is characterized in that lithium fluoride-hydrochloric acid is used as an etching layering agent, an Al atomic layer in a MAX material of a precursor is selectively etched, the etched double-transition metal carbide two-dimensional layered material is repeatedly cleaned and centrifuged by deionized water, and then is dispersed in the deionized water, shaken and then is subjected to centrifugal filtration to obtain the SERS film substrate.

Further, the preparation method specifically comprises the following steps:

step 1: adding TiVAlC powder serving as a precursor MAX material into a lithium fluoride-dilute hydrochloric acid mixed solution, then placing the mixture at 35-40 ℃ for constant-temperature etching to obtain a suspension, and ensuring the TiVAlC powder to be fully etched in a magnetic stirring manner in the etching process;

step 2: diluting the etched suspension with deionized water, then centrifuging by using a centrifuge at 3500-5000 rpm/min to obtain a precipitate, repeating for several times until the pH value of the centrifuged supernatant is 6-7;

and step 3: dispersing the obtained precipitate in deionized water, repeatedly shaking, centrifuging for 0.5-1 h, and taking supernatant, wherein the supernatant is a colloidal solution of the TiVC nanosheet;

and 4, step 4: and carrying out vacuum filtration on the colloidal solution of the TiVC nano-sheet, and then placing the TiVC nano-sheet in a vacuum drying oven for drying to obtain the SERS film substrate.

Further, in the step 1, TiVAlC powder is added into the lithium fluoride-dilute hydrochloric acid mixed solution at a speed of (0.5-1 g)/10min at 20-30 ℃, so that oxidation of TiVC nano-sheets caused by overheating is prevented.

Furthermore, in the lithium fluoride-hydrochloric acid mixed solution, the molar ratio of hydrochloric acid to lithium fluoride is (1.5-5): 1.

further, the molar ratio of the lithium fluoride to the TiVAlC is (4-9): 1.

further, the centrifugal separation operation in the step 2 is repeated for 7-10 times, and each time lasts for 3-5 min.

Further, in the step 4, the drying temperature is 40-60 ℃, and the drying time is 10-12 hours.

According to the second aspect of the invention, an application of the SERS film substrate based on MXene is provided, wherein 5-10 mu L of organic dye solution is dripped on the surface of the SERS film substrate prepared by the preparation method, a sample is prepared after drying at 20-30 ℃, and the sample is used for SERS detection.

Further, the organic dye solution is an ethanol solution of rhodamine 6G organic dye.

Further, the application of the sample to SERS specifically includes:

placing the sample in a microscopic confocal Raman spectrometer, wherein the laser wavelength is 532nm, the laser attenuation power is 1-10%, and the frequency range is 2000cm^-1-550cm^-1Setting 10-20s exposure time in a continuous mode, collecting Raman spectrum, and completing Raman detection of organic dye molecules with detection limit of 10^-15M。

According to a third aspect of the invention, an MXene-based SERS thin film substrate prepared based on the preparation method is provided.

The design idea of the invention is as follows:

the method uses the TiVAlC powder as a precursor, the TiVAlC powder is soaked in a mixed solution of hydrochloric acid and lithium fluoride, an Al atomic layer in the TiVAlC is selectively etched by a mild mode of generating hydrofluoric acid in situ by the hydrochloric acid and the lithium fluoride, and lithium ions in the mixed solution can simultaneously realize ion intercalation without further ultrasonic dispersion. The obtained TiVC two-dimensional nano-sheet has large single-sheet area, and the thickness of the nano-sheet can be controlled to be a plurality of nano-layers. Through vacuum filtration, the obtained self-supporting film TiVC SERS substrate has the characteristics of good flexibility, high electronic conductivity and the like, and can obtain a Raman enhancement effect with good reproducibility and high stability.

Compared with the prior art, the invention has the advantages and beneficial effects that:

1. the self-supporting two-dimensional layered material TiVC prepared by the invention has the advantages of simple preparation process, low cost and large-scale production, and can obtain excellent SERS enhancement effect and good detection reproducibility aiming at organic dye molecules.

2. According to the self-supporting two-dimensional layered material TiVC prepared by the invention, an Al atomic layer in TiVAlC is selectively etched in a mild mode of generating hydrofluoric acid in situ by hydrochloric acid and lithium fluoride, so that the harm to a human body caused by directly using highly corrosive and volatile hydrofluoric acid is avoided.

3. According to the self-supporting two-dimensional layered material TiVC prepared by the invention, the lithium ions in the mixed solution of hydrochloric acid and lithium fluoride can realize ion intercalation, the interlayer spacing of the two-dimensional layered material TiVC can be enlarged, delamination of the TiVC can be realized only by shaking, further ultrasonic treatment is not needed, and the area of the obtained two-dimensional nano sheet TiVC single sheet is large.

4. The self-supporting two-dimensional layered material TiVC prepared by the method has high purity and no other impurity phase.

5. The self-supporting two-dimensional layered material TiVC serving as the SERS substrate has excellent electronic conductivity (1112S/cm), large specific surface area and good adsorption activity, can be fully adsorbed and combined with rhodamine 6G (R6G) dye molecules, increases the number of hot spots, and further realizes an excellent Raman enhancement effect.

6. The self-supporting two-dimensional layered material TiVC prepared by the invention is used as an SERS substrate, the detection method is simple and convenient, the enhanced Raman spectrum can be obtained only by dripping the dye to be detected on the surface of the substrate, and meanwhile, the self-supporting two-dimensional layered material TiVC has excellent uniformity.

7. The self-supporting two-dimensional layered material TiVC prepared by the invention has flexibility as an SERS substrate, is easy to bend, can be applied to Raman enhancement detection of irregular surfaces, and has a wide application range.

8. The self-supporting two-dimensional layered material TiVC prepared by the invention is used as an SERS substrate to detect R6G, and the detection limit is 10^-15M, is significantly superior to Ti in the prior art₃C₂MXene self-supporting layered material as detection limit of SERS substrate (1.0x 10)^{- 7}M)。

9. The self-supporting two-dimensional layered material TiVC prepared by the invention is used as an SERS substrate to detect R6G, and the Raman enhancement factor of the self-supporting two-dimensional layered material TiVC reaches 3.3 multiplied by 10¹²MXene is the highest value found as SERS substrate.

Drawings

FIG. 1 is a schematic diagram of the synthesis of a self-supporting two-dimensional layered material TiVC.

FIG. 2 is an electron micrograph of a few-layer two-dimensional TiVC nanoplate prepared in example 2; in which fig. 2a is an SEM image and fig. 2b is a TEM image.

Fig. 3 is an SEM image of the TiVC film prepared in example 2; wherein, fig. 3a is a top view of the TiVC film, and fig. 3b is a cross-sectional view of the TiVC film.

Fig. 4 is an XRD spectrum of the self-supporting film TiVC and its precursor TiVAlC prepared in example 2.

Fig. 5 is a raman spectrum of the self-supporting film TiVC and the precursor TiVAlC prepared in example 2.

FIG. 6 shows that the detection concentration of the self-supporting film TiVC prepared in example 2 as the SERS substrate is 1X 10^-3Raman spectrum of R6G for M.

Fig. 7 is a raman spectrum of the self-supporting film TiVC prepared in example 2 as a SERS substrate for detecting R6G at different concentrations.

FIG. 8 shows that the detection concentration of the self-supporting film TiVC prepared in example 2 as the SERS substrate is 1X 10^-6The raman uniformity and reproducibility of R6G for M; wherein, FIG. 8a shows the area of 40 μm × 40 μmFIG. 8b is a Raman spectrum 612cm^-1Intensity maps of different regions.

FIG. 9 shows MXene-R6G (1X 10) in example 2^-6M) raman spectra collected from 20 randomly selected points on the substrate.

Fig. 10 is an SEM image of the self-supporting film TiVC prepared in example 3.

Fig. 11 is a raman spectrum of the self-supporting film TiVC prepared in example 3 as a SERS substrate for detecting R6G at different concentrations.

FIG. 12 is a graph of the band and electron density of TiVC.

Fig. 13 is a typical UPS spectrum of a self-supporting film TiVC.

FIG. 14 is a schematic diagram of energy level distribution and light-induced charge transfer of the R6G-TiVC complex.

Detailed description of the preferred embodiments

Reference will now be made in detail to the exemplary embodiments, examples of which are illustrated in the accompanying drawings. When the following description refers to the accompanying drawings, like numbers in different drawings represent the same or similar elements unless otherwise indicated. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with the present invention. Rather, they are merely examples of apparatus and methods consistent with certain aspects of the invention, as detailed in the appended claims.

The terms first, second and the like in the description and in the claims of the present invention are used for distinguishing between similar elements and not necessarily for describing a particular sequential or chronological order. It is to be understood that the data so used is interchangeable under appropriate circumstances such that the embodiments of the invention described herein are, for example, capable of operation in sequences other than those illustrated or otherwise described herein. Furthermore, the terms "comprises," "comprising," and "having," and any variations thereof, are intended to cover a non-exclusive inclusion, such that a process, method, system, article, or apparatus that comprises a list of steps or elements is not necessarily limited to those steps or elements expressly listed, but may include other steps or elements not expressly listed or inherent to such process, method, article, or apparatus.

A plurality, including two or more; and/or, it should be understood that, as used herein, the term "and/or" is merely one type of association that describes an associated object, meaning that three types of relationships may exist. For example, a and/or B, may represent: a exists alone, A and B exist simultaneously, and B exists alone.

As shown in fig. 1, a method for preparing an SERS film substrate based on MXene (two-dimensional transition metal carbide, nitride or carbonitride, collectively referred to as MXene) and an application thereof specifically include the following steps:

(1) the precursor MAX (MAX has a chemical general formula of M)_n+1AX_n(n ═ 1,2 or 3), wherein M represents a transition metal element, A represents an element of the IIIA group or IVA in the periodic table of elements, and X represents carbon or nitrogen), powder is slowly added into a lithium fluoride-hydrochloric acid mixed solution, an etching system is fully stirred after being sealed, then the mixed solution is placed at 35-40 ℃ for constant-temperature etching, and after the etching reaction is finished, the obtained suspension is centrifugally cleaned and repeated for several times; and then dispersing the obtained two-dimensional layered material MXene in deionized water, shaking for a few minutes, and centrifuging to obtain an upper layer liquid, namely a monolayer or few-layer two-dimensional MXene nanosheet colloidal solution. The obtained two-dimensional MXene nanosheet is large in single-chip area, and the thickness of the nanosheet is 1.5-5 nm;

(2) carrying out vacuum filtration on the MXene nanosheet colloidal solution, and drying in vacuum to obtain a self-supporting flexible MXene film with the thickness of 5-20 microns, namely an SERS substrate;

(3) dripping 5-10 mu L of dye on the surface of the obtained SERS substrate, and drying at 20-30 ℃ to detect the SERS enhancement effect;

(4) placing the detection sample prepared in the step (3) into a microscopic confocal Raman spectrometer (HORIBA HR800), wherein: the laser wavelength is 532nm, the laser attenuation power is 1-10%, and the frequency range is 2000cm^-1—550cm^-1Setting 10-20s exposure time in a continuous mode, collecting Raman spectrum, and completing Raman detection of dye molecules with detection limit of 10^-15M。

Preferably, the precursor MAX is TiVAlC powder, and the obtained double-transition metal carbide two-dimensional layered material MXene is TiVC.

Preferably, the molar ratio of the hydrochloric acid to the lithium fluoride in the mixed solution is (3-5): 1.

preferably, the molar ratio of the lithium fluoride to the TiVAlC is (7.5-9): 1.

preferably, the washing is performed using a centrifuge at 3500rpm/min to remove the acid from the solution.

Preferably, 5-10 mu L of ethanol solution of the dye R6G is dropped on the surface of the SERS substrate at 20-30 ℃.

Example 1

The preparation method of the self-supporting layered material TiVC comprises the following steps:

(1) 30mL of 9M hydrochloric acid is measured and placed in a polytetrafluoroethylene beaker, 2.8g of LiF powder is weighed and dissolved in a hydrochloric acid solution, and the LiF powder is completely dissolved by magnetic stirring for 10min at the temperature of 20-30 ℃. Weighing 2g of TiAlVC powder, slowly adding the TiAlVC powder into a lithium fluoride-dilute hydrochloric acid mixed solution at the speed of 1g/10min, covering a layer of preservative film, and magnetically stirring for 10min at the temperature of 20-30 ℃. The beaker is transferred to a water bath kettle with the constant temperature of 35 ℃, and the reaction is carried out for 72 hours under the magnetic stirring. And after the reaction is finished, transferring the generated sol liquid into a centrifuge tube, adding deionized water, centrifuging by using a centrifuge at 3500rpm/min, fully washing, taking the precipitate, repeating for several times, and 5min each time until the pH value of the centrifuged supernatant is 6-7. Then, in order to obtain a single-layer or few-layer MXene sheet, only deionized water needs to be added, the sheet is hand-shaken for 5min, and then the sheet is placed into a centrifuge to be centrifuged for 1h at 3500rpm/min, and supernatant is taken to obtain TiVC colloid;

(2) and (3) carrying out suction filtration on the obtained colloid to form a disk film, and placing the disk film in a vacuum drying oven at 50 ℃ for drying for 12h to obtain the flexible self-supporting TiVC film serving as an SERS substrate.

And (2) adjusting the reaction temperature and time in the step (1) based on the preparation scheme of the example 1 to realize the preparation of the self-supporting layered material TiVC with different thicknesses.

Example 2

In the present embodiment, the difference from embodiment 1 is:

in the step (1), the reaction system is placed in a water bath kettle with the constant temperature of 40 ℃ for reaction, and finally the self-supporting TiVC film SERS substrate is obtained.

5 μ L of an ethanol solution of R6G with a concentration of 1mM was dropped on the surface of the SERS substrate prepared in example 2, and after it was naturally dried, it was placed under a micro-Raman spectrometer for detection.

As shown in fig. 2a, in an SEM photograph of the two-dimensional TiVC nanosheet prepared in this example 2 on porous alumina, the TiVC nanosheet is highly transparent under electron beam irradiation; fig. 2b is a TEM photograph of the prepared few-layer TiVC nanosheet, and it can be seen that the obtained two-dimensional TiVC nanosheet has 2 layers, which indicates that the prepared two-dimensional material TiVC is a thin-layer nanosheet.

As shown in fig. 3, SEM photograph of the free standing film TiVC obtained by vacuum filtration in example 2. Wherein, FIG. 3a is the SEM picture of the top view of the TiVC film, and FIG. 3b is the SEM picture of the cross section of the TiVC film.

As shown in fig. 4, the XRD spectra of the precursor TiVAlC powder and the self-supporting film TiVC obtained by etching in example 2 are shown. After etching, the (103) phase disappears completely, which indicates that the precursor is fully etched, and compared with TiVAlC, the TiVC film generates a (00l) resonance peak, and the (002) peak of TiVC has obvious left shift, which indicates that the TiVC MXene generates delamination.

Fig. 5 shows a raman spectrum of the self-supporting film TiVC and its precursor TiVAlC prepared in example 2.

As shown in FIG. 6, the detection concentration of the self-supporting film TiVC prepared in the example 2 as the SERS substrate is 10^-3Raman spectrum of M rhodamine (R6G) dye. It can be seen that the TiVC film has an excellent Raman enhancement effect as the SERS substrate.

As shown in fig. 7, a raman spectrum of the self-supporting film TiVC prepared in this example 2 as the SERS substrate for detecting different concentrations of rhodamine (R6G) is shown.

As shown in FIG. 8, the detection concentration of the self-supporting film TiVC prepared in the example 2 as the SERS substrate is 10^-6A raman surface scan of R6G of M; wherein FIG. 8a is an optical photograph of a region of 40 μm × 40 μm; FIG. 8b is a Raman spectrum 612cm^-1In different areasThe Raman intensity distribution graph shows the reproducibility and uniformity of the Raman enhancement effect.

As shown in FIG. 9, the substrate of this example 2, from TiVC-R6G (1X 10)^-6M) collected 20 randomly selected SERS spectra. It can be seen that the TiVC film has excellent enhancement effect and uniformity as the SERS substrate.

Example 3

In the present embodiment, the difference from embodiment 1 is:

in the step (1), the reaction time is set to 84h, and finally the self-supporting film TiVC is obtained.

Fig. 10 shows an SEM photograph of the self-supporting film TiVC of example 3.

As shown in fig. 11, the self-supporting film TiVC prepared in this example 3 as the SERS substrate detects raman spectra of R6G at different concentrations.

As shown in fig. 12, we calculated the band and density of electronic states (DOS) of TiVC, and the results show that: the fact that the TiVC has obvious metal characteristics, the conduction band is mainly composed of Ti 3d orbitals and V3 d orbitals, and the contribution of the V3 d orbitals at the Fermi level is larger than that of the Ti 3d orbitals further explains that the TiVC has excellent electronic conductivity, which is favorable for generating strong surface plasmon resonance, thereby playing a role in enhancing the Raman signal of an object to be detected.

The excellent raman enhancement behavior of the TiVC nanoplates can also be attributed to the enhancement of Chemical Mechanisms (CM) caused by photoinduced charge transfer (PICT). As shown in fig. 13, the ultraviolet electron spectrum (UPS) of TiVC was measured using ultraviolet light with photon energy of 21.2eV, and the electron modulation mechanism of TiVC was studied. The work function of TiVC is 21.2-16.98 ═ 4.22 eV. The energy level distribution and possible PICT processes in the R6G-TiVC complex are shown in FIG. 14. Mu.s_molRepresents a molecular transition. Mu.s_i-CTAnd mu_k-CTRepresenting charge transfer transitions from the molecular ground state to TiVC and from TiVC to the molecular excited state, respectively. According to early research reports (Journal of the American Chemical Society,2011,133(41): 16518) -16523), the Highest Occupied Molecular Orbital (HOMO) and the lowest unoccupied molecular orbital (HOMO) of R6GThe energy levels of the molecular orbital (LUMO) were-5.7 and-3.4 eV, respectively. This energy level distribution makes the PICT possible. In this process, the excited electron can be transferred not only from HOMO of R6G to the fermi level of TiVC, but also from the fermi level of TiVC to LUMO of R6G. Thus, according to The Herzberg-Teller vibrational coupling law (The Journal of chemical physics,1986,84(8):4174-4180), The polarization tensor of The R6G molecule is greatly enhanced by The molecular resonance induced by The interfacial PICT, resulting in a significant enhancement of The Raman signal.

The embodiment result shows that the flexible SERS substrate is simple in manufacturing method and low in price, and has the advantages of high sensitivity, good Raman enhancement effect, high reproducibility and the like when being used as the SERS substrate. The detection limit of the TiVC film as the SERS substrate to R6G dye molecules is as high as 10^-15M, corresponding Raman enhancement factor reaches 3.3 multiplied by 10¹²The Raman detection limit and the Raman enhancement effect of the SERS substrate are the highest values of MXene which is found at present as the SERS substrate. The flexible SERS substrate with low cost and high Raman enhancement activity provided by the invention is expected to have wide application prospect in the aspect of trace detection with ultrahigh sensitivity.