Multifunctional surface enhanced Raman scattering chip based on double Fano resonance and regulation and control method thereof

Abstract

The invention provides a multifunctional surface enhanced Raman scattering chip realized based on double Fano resonance. The multifunctional surface enhanced Raman scattering chip comprises a three-layer structure film system formed by a periodic gold nanopore array, a gold nanodisk array and photoresist. The multifunctional surface enhanced Raman scattering chip can form independent double Fano resonance and is used for enhancing Raman excitation light and Raman Stokes light at the same time. The invention also provides a regulation and control method of the multifunctional surface enhanced Raman scattering chip. By regulating and controlling the diameter of the gold nanopore, the first Fano resonance of the double Fano resonance is not influenced by tuning parameters and the refractive index change of a culture solution, the excitation light enhancement is stably realized, and the broadband enhancement tuning of the second Fano resonance is realized at the same time. The multifunctional surface-enhanced Raman scattering chip has the functions of low light heat, tunable enhancement of broadband and insensitivity to background refractive index, and is very suitable for in-situ detection of Raman signals of living cells in a culture solution.

Description

Technical Field

[0001] The present invention relates to the field of Raman scattering spectroscopy, and in particular to a multifunctional surface enhanced Raman scattering chip based on double Fano resonance and a control method thereof. Background Art

[0002] Surface enhanced Raman spectroscopy inherits the rich chemical fingerprint information of Raman spectroscopy and has important applications in the detection of extremely low-content substances in scientific research, production and life. The strategy of the prior art is to use metal nanostructures (such as metal nanoparticles or nanostructure arrays) to couple the incident light (excitation light) with the metal structure to produce surface plasmon resonance (SPR). This resonance will generate a strong electromagnetic field locally on the metal surface, thereby greatly increasing the field intensity of the incident light, enhancing the Raman scattering signal of nearby molecules, and establishing reproducible and tunable Raman enhancement. However, the large electric field at the wavelength of the excitation light will produce photothermal damage to biological activity and cause a strong fluorescence background that affects the authenticity and reliability of the measurement. In addition, when changing different culture media, the resonance drift caused by the change in refractive index will seriously affect the results of the same cells under the same experimental conditions.

[0003] Another strategy is to achieve a significant enhancement of the Raman signal by overlapping the two resonances of the excitation light and the Raman Stokes wave. In recent years, a new type of double resonance called Fano resonance has been formed by coherent coupling of the broadband superradiant mode generated by the resonator array and the narrowband subradiant mode generated by the smooth metal film, which can be used to generate a huge near-field electric field enhancement. However, it is difficult to simultaneously adjust the wavelength of its peak and valley to overlap with the excitation light and the Raman Stokes wave, so how to make full use of this resonance remains a challenge. Summary of the invention

[0004] In order to overcome the problems existing in the above-mentioned technologies, the present invention provides a multifunctional SERS chip with low photothermal, tunable broadband enhancement and refractive index insensitivity based on double Fano resonance. The present invention uses a three-layer thin film system composed of a gold nano-hole array, a gold nano-disk array and a photoresist nano-hole array. The periodic nanostructure can effectively excite SPP and generate a narrow-band SPP-Bloch resonance, while the nano-disk array helps to form a surface lattice resonance (SLR), and its resonance spectrum is much narrower than that of a single nano-disk. In addition, the entire chip also supports a broadband continuous super-radiant mode. When the two narrow-band sub-radiant modes are coupled with the broadband continuous super-radiant mode, two independent Fano resonances are formed. When the two Fano resonances are tuned to match the wavelengths of Raman excitation light and Raman Stokes light respectively, a double enhancement of the Raman signal can be achieved. In particular, with the support of the second Fano resonance, the first Fano resonance used to enhance the excitation light can be reduced, thereby reducing the strong fluorescence background and photothermal effect caused by the first Fano resonance.

[0005] A multifunctional surface enhanced Raman scattering chip includes, from bottom to top, a substrate layer, a gold nanodisk array embedded in a photoresist, a photoresist nanohole array and a gold nanohole array. The gold nanodisk array, the photoresist nanohole array and the gold nanohole array have the same period and are all circular in planar shape, wherein the gold nanodisk and the gold nanohole form a complementary geometric structure. The thickness of the gold nanohole array is the same as that of the gold nanodisk array, and both are less than the thickness of the photoresist nanohole. The gold nanohole array and the gold nanodisk array support a narrowband subradiation mode based on SPP-Bloch waves and a narrowband subradiation mode based on surface lattice resonance, respectively. At the same time, the entire chip also supports a broadband continuous superradiation mode. When the two narrowband subradiation modes are coupled with the ultra-wideband continuous superradiation mode, two independent Fano resonances are formed. By matching the two Fano resonances with Raman laser light and Raman Stokes light, dual Raman signal enhancement can be achieved.

[0006] The present invention also provides a method for regulating the multifunctional surface enhanced Raman scattering chip, which can change the wavelength position of the second Fano resonance while keeping the wavelength position of the first Fano resonance unchanged by changing the size of the diameter of the gold nanopore.

[0007] Specifically, the multifunctional surface enhanced Raman scattering chip is manufactured on indium tin oxide (ITO) coated glass using electron beam lithography. The preparation process of the multifunctional SERS chip is as follows: the resist (PMMA950K) is spin-coated onto the underlying substrate, and the electron beam is used to accurately expose the circular area of ​​the resist coating with high resolution. After the exposure is completed, these circular areas will be dissolved by the developer during the development process to form a nanopore array, and finally a gold film is coated on it using an electron beam evaporation method. The thickness of the resist is greater than the thickness of the gold film.

[0008] Compared with the prior art, the present invention has the following advantages:

[0009] (1) Compared with other SERS chips, the present invention integrates dual Fano resonance into a single SERS chip, which can reduce the thermal damage and fluorescence background to biological living cells during Raman signal detection and ensure the authenticity of the measurement.

[0010] (2) Compared with the dual-resonance SERS chip, the present invention can quickly lock the parameters that meet the needs of a specific scenario. Only a single parameter needs to be adjusted to ensure that the first Fano resonance is not affected while tuning the second resonance to achieve broadband Raman enhancement.

[0011] (3) Compared with traditional SERS chips, it has the advantage that the resonance peak does not drift with changes in the background refractive index (culture fluid).

[0012] (4) The present invention is easy to design and prepare, and is insensitive to changes in the refractive index of the culture solution in actual Raman measurements, thereby improving the reliability of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 A schematic diagram of the three-dimensional structure of the multifunctional surface-enhanced Raman scattering chip of the present invention.

[0014] Figure 2 It is a cross-sectional view corresponding to the first embodiment of the present invention.

[0015] Figure 3 This is the reflection spectrum of the double Fano resonance under the parameters set in Example 1.

[0016] Figure 4 This is the electric field enhancement spectrum of the double Fano resonance corresponding to changing the nanopore diameter in Example 2.

[0017] Figure 5 The electric field enhancement spectra corresponding to the different refractive indices of the culture solutions in Example 2.

[0018] Figure 6 This is a diagram showing the enhanced effect of Raman spectra when using SERS chips with different nanopore diameters. DETAILED DESCRIPTION

[0019] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0020] First embodiment

[0021] The multifunctional SERS chip provided by the present invention is as follows Figure 1As shown in FIG. 2 , the surface enhanced Raman chip comprises a silicon dioxide substrate 1, a gold nanodisk array layer 3 embedded in a photoresist disposed on the substrate, a photoresist nanohole array layer 2 disposed on the gold nanodisk array layer 3, and a gold nanohole array layer 4 disposed on the photoresist nanohole array layer 2; the photoresist model is PMMA 950K. The total thickness h of the gold nanodisk array layer and the photoresist nanohole array layer is 120nm, wherein the thickness t of the gold nanodisk array layer is 50nm, the thickness of the photoresist nanohole array layer is 70nm, and the thickness of the gold nanohole array is 50nm; the period of the above three-layer structure array is the same, which is 315nm. The intermediate layer 2 supports the metal layer 4; the metal layer 3 is a periodic gold nanodisk array, the disk diameter d is 270nm, the thickness t is 50nm, and the period p is 315nm; the gold nanodisks, photoresist nanoholes and gold nanoholes are all the same circular shape, and their diameters are 220nm-270nm. The gold nano-holes and gold nano-basins form a complementary structure in geometry, supporting a narrowband sub-radiation mode based on SPP-Bloch waves and a narrowband sub-radiation mode based on surface lattice resonance (SLR), respectively. At the same time, the entire chip system supports an ultra-wideband third continuous super-radiation mode. When the two narrowband sub-radiation modes are coupled with the ultra-wideband continuous super-radiation mode, a double Fano resonance is formed. Figure 3 As shown in the reflection spectrum, when the above parameters are set, a first Fano resonance and a second Fano resonance with a wavelength longer than 632.8 nm appear at a wavelength of 632.8 nm of a commercial He-Ne laser.

[0022] Second embodiment

[0023] The present invention also provides a control method for the multifunctional surface enhanced Raman chip. By adjusting the size of the nanopore diameter d, the wavelength position of the second Fano resonance can be broadband tuned without changing the wavelength position of the first Fano resonance. Figure 4 As shown in the figure, as the nanopore diameter d increases from 220nm to 270nm, the electric field enhancement brought by the first Fano resonance at the excitation light of 632.8nm does not drift, while the electric field enhancement brought by the second Fano resonance moves continuously from 640nm to 781nm, and the tuning Raman wavenumber range can reach 3000cm -1 , in order to achieve broadband enhancement. This independent and broadband tuning capability demonstrates that the multifunctional SERS chip can achieve broadband enhancement in the Raman Stokes light region without causing the resonance peak at the excitation light wavelength to drift during the tuning process, and demonstrates excellent broadband enhancement capability.

[0024] Furthermore, it is also demonstrated that the first Fano resonance can be unaffected by changing the refractive index of the culture medium. When other structural parameters are consistent with those of Example 1, by appropriately adjusting the refractive index (changing the culture medium), such as Figure 5 The resonance spectrum is shown when the refractive index of the culture medium changes from 1.33 to 1.5. As the refractive index changes, the position of the first resonance (dashed line in the figure) remains almost unchanged, reflecting good refractive index insensitivity. In other words, when different culture media are replaced during the experiment, there is no need to readjust the parameters of the SERS chip to match the resonance wavelength with the wavelength of the excitation light. This reflects the flexibility and simplicity of the present invention in selecting the structural dimensions, and also shows that the present invention has room for further optimization and improvement based on actual conditions, and has the potential for further application development.

[0025] Furthermore, we used SERS experiments to demonstrate the enhancement effect of Raman signals. Figure 6 As described above, when d = 220nm, the SLR resonance amplitude is too small, and only one FP mode couples with the SPP-Bloch mode to form a Fano resonance, resulting in a relatively small Raman signal enhancement; as d = 250nm, a double Fano resonance begins to be established, and the Raman signal is further enhanced; when the nanopore diameter d continues to increase to 270nm, the SLR mode is significantly enhanced, even exceeding the SPP-Bloch mode, forming a significant double Fano resonance; the second Fano resonance at 700nm not only increases the resonance near 1584cm -1 The Raman signal at 2250cm was enhanced by 39.7 times, and the mechanism of establishing a large dipole by using the three-mode in-phase vibration was used to increase the Raman signal at 2250cm -1 The Raman signal at the site was amplified 28.9 times.

[0026] The above contents are further detailed descriptions of the present invention in combination with specific preferred implementation modes, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions.

Claims

1. A multifunctional surface-enhanced Raman scattering chip, characterized in that ,Include: The invention comprises, from the bottom layer to the top layer, a substrate layer, a gold nanodisk array embedded in a photoresist, a photoresist nanohole array and a gold nanohole array. The gold nanodisk array, the photoresist nanohole array and the gold nanohole array have the same period, and the plane shape is circular, wherein the gold nanodisk and the gold nanohole form a complementary geometric structure. The thickness of the gold nanohole array is the same as that of the gold nanodisk array, and both are less than the thickness of the photoresist nanohole.

2. The multifunctional surface-enhanced Raman scattering chip according to claim 1, characterized in that: The substrate is a silicon dioxide substrate. The geometric dimensions of the gold nanodisk array are: the diameter d of the gold nanodisk is 220-270nm, and the thickness is 50nm; the thickness of the photoresist nanohole array is 70nm, and the hole diameter and period are the same as those of the gold nanodisk array; the thickness of the gold nanohole is 50nm, and the hole diameter and period are the same as those of the gold nanodisk array.

3. The multifunctional surface-enhanced Raman scattering chip according to claim 2, characterized in that: The gold nanohole array, photoresist nanohole array, and gold nanodisk array have a period of 315 nanometers, forming a first Fano resonance peak at a wavelength of 632.8 nm of a commercial laser, and also forming a second Fano resonance peak.

4. The multifunctional surface-enhanced Raman scattering chip according to claim 3, characterized in that: When the diameter of the nanopore is changed, the position of the second Fano resonance peak can be tuned without changing the position of the first Fano resonance peak.

5. A control method for the multifunctional surface enhanced Raman scattering chip according to claim 3, characterized in that: By changing the diameter of the gold nanopore, the wavelength position of the second Fano resonance can be changed while the wavelength position of the first Fano resonance remains unchanged.

6. The multifunctional surface enhanced Raman scattering chip control method according to claim 5, characterized in that: The diameter of the gold nanopore varies in the range of 220nm-270nm, and the diameter of the gold nanopore can vary continuously.

7. The multifunctional surface enhanced Raman scattering chip control method according to claim 5, characterized in that: When the diameter of the gold nanopore varies in the range of 220nm-270nm, the wavelength of the second Fano resonance can be continuously tuned in the range of 640nm-781nm.

8. The multifunctional surface enhanced Raman scattering chip control method according to claim 5, characterized in that: The multifunctional surface enhanced Raman scattering chip is placed in a culture medium, and when the refractive index of the culture medium is changed, the wavelength of the first Fano resonance can be kept from drifting.

9. The multifunctional surface enhanced Raman scattering chip control method according to claim 8, characterized in that: The refractive index of the culture medium varies from 1.33 to 1.5.

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