A multifunctional surface-enhanced Raman scattering chip based on double Fano resonance and its control method

Abstract

The present invention provides a multifunctional surface-enhanced Raman scattering chip based on dual Fano resonance. The multifunctional surface-enhanced Raman scattering chip comprises a three-layer thin film system consisting of a periodic gold nanohole array, a gold nanodisk array, and a photoresist. The multifunctional surface-enhanced Raman scattering chip can form an independent dual Fano resonance for simultaneously enhancing Raman excitation light and Raman Stokes light. The present invention also provides a method for controlling the multifunctional surface-enhanced Raman scattering chip. By regulating the diameter of the gold nanoholes, the first Fano resonance of the dual Fano resonance can be made unaffected by changes in tuning parameters and the refractive index of the culture medium, thereby stably achieving excitation light enhancement and simultaneously achieving broadband enhancement tuning of the second Fano resonance. The multifunctional surface-enhanced Raman scattering chip has the functions of low photothermal, broadband tunable enhancement, and insensitivity to background refractive index, and is very suitable for in-situ detection of Raman signals of living cells in culture medium.

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 field of extremely low-content substance detection in scientific research, production and life. The strategy of the existing technology 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 simultaneously 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 coherently coupling the broadband superradiant mode generated by the resonator array with the narrowband subradiant mode generated by the smooth metal film. This can be used to generate a huge near-field electric field enhancement. However, due to the difficulty in simultaneously adjusting the wavelength of its peak and valley to overlap with the excitation light and the Raman Stokes wave, how to fully utilize 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 dual Fano resonance. The present invention utilizes a three-layer thin film system composed of a gold nanohole array, a gold nanodisk array and a photoresist nanohole array. The periodic nanostructure can effectively excite SPPs and generate narrowband SPP-Bloch resonances, while the nanodisk array helps to form a surface lattice resonance (SLR), whose resonance spectrum is much narrower than that of a single nanodisk. In addition, the entire chip also supports broadband continuous superradiant modes. When the two narrowband subradiant modes are coupled with the broadband continuous superradiant mode respectively, 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 comprises, 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, photoresist nanohole array, and gold nanohole array have the same periodicity and are all circular in planar shape, with the gold nanodisks and gold nanoholes forming a complementary geometric structure. The thickness of the gold nanohole array is the same as that of the gold nanodisk array, both being less than the thickness of the photoresist nanoholes. The gold nanohole array and gold nanodisk array support narrowband subradiant modes based on SPP-Bloch waves and narrowband subradiant modes based on surface lattice resonance, respectively. Simultaneously, the entire chip also supports broadband continuous superradiant modes. When the two narrowband subradiant modes couple with the ultra-broadband continuous superradiant 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 control method for the multifunctional surface-enhanced Raman scattering chip. 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.

[0007] Specifically, the multifunctional surface-enhanced Raman scattering chip is manufactured on indium tin oxide (ITO)-coated glass using electron beam lithography. The multifunctional SERS chip is prepared by spin-coating a resist (PMMA950K) onto an underlying substrate. An electron beam is then applied to the resist coating to precisely expose circular areas at high resolution. After exposure, these circular areas are dissolved by a developer during development, forming a nanopore array. Finally, a gold film is coated on top using electron beam evaporation. The thickness of the resist is greater than that 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 to biological living cells and the fluorescence background during the Raman signal detection process, 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 of not causing resonance peak 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 medium during actual Raman measurement, thereby improving the reliability of the measurement. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0014] Figure 2 This 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 the change of the nanopore diameter in Example 2.

[0017] Figure 5 1 is the electric field enhancement spectrum corresponding to different refractive indices of culture fluid in Example 2.

[0018] Figure 6 This figure shows the enhancement effect of Raman spectrum 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. 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 Figure 2, the surface-enhanced Raman chip comprises a silicon dioxide substrate 1, a gold nanodisk array layer 3 embedded in photoresist disposed above the substrate, a photoresist nanopore array layer 2 disposed on the gold nanodisk array layer 3, and a gold nanopore array layer 4 disposed above the photoresist nanopore array layer 2. The photoresist is PMMA 950K. The total thickness h of the gold nanodisk array layer and the photoresist nanopore array layer is 120 nm, wherein the thickness t of the gold nanodisk array layer is 50 nm, the thickness of the photoresist nanopore array layer is 70 nm, and the thickness of the gold nanopore array layer is 50 nm. The three-layer array structure has the same period of 315 nm. The intermediate layer 2 supports the metal layer 4. The metal layer 3 is a periodic gold nanodisk array with a disk diameter d of 270 nm, a thickness t of 50 nm, and a period p of 315 nm. The gold nanodisks, photoresist nanopores, and gold nanopores are all identically circular, with diameters ranging from 220 nm to 270 nm. The gold nanoholes and gold nanobasins 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 the wavelength of 632.8 nm of the 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 tuned without changing the wavelength position of the first Fano resonance. Figure 4 As shown in Figure 2, as the nanopore diameter d increases from 220 nm to 270 nm, the electric field enhancement brought by the first Fano resonance at 632.8 nm of the excitation light does not drift, while the electric field enhancement brought by the second Fano resonance continuously moves from 640 nm to 781 nm, and the tuned Raman wavenumber range can reach 3000 cm -1 This independent and broadband tunability demonstrates that the multifunctional SERS chip can achieve broadband enhancement in the Raman-Stokes region without causing the resonance peak at the excitation light wavelength to drift during the tuning process, demonstrating excellent broadband enhancement capabilities.

[0024] Furthermore, it is also demonstrated that the first Fano resonance can be controlled without being affected 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 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 mentioned 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 position is amplified 28.9 times.

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

Claims

1. A multifunctional surface-enhanced Raman scattering chip based on double Fano resonance, characterized in that ,Include: From the bottom layer to the top layer, it includes a silicon dioxide substrate layer, a gold nanodisk array with a diameter d of 220-270 nm and a thickness of 50 nm embedded in the photoresist, a photoresist nanohole array with a thickness of 70 nm, and a gold nanohole array with a thickness of 50 nm. The gold nanodisk array, the photoresist nanohole array, and the gold nanohole array all have a period of 315 nm and a planar shape. The gold nanodisk is located in the photoresist nanohole array, forming a complementary geometric structure with the gold nanohole. The thickness of the gold nanohole array is the same as that of the gold nanodisk array, and both are smaller than the thickness of the photoresist nanohole. A first Fano resonance peak is formed at the wavelength of 632.8 nm of a commercial laser, and a second Fano resonance peak is also formed at the same time.

2. The multifunctional surface-enhanced Raman scattering chip based on dual Fano resonance according to claim 1, characterized in that: By changing the diameter of the nanopore, the position of the second Fano resonance peak can be tuned without changing the position of the first Fano resonance peak.

3. A control method for the multifunctional surface-enhanced Raman scattering chip based on double Fano resonance according to claim 1, 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.

4. The control method of the multifunctional surface-enhanced Raman scattering chip based on double Fano resonance according to claim 3, characterized in that: The diameter of the gold nanopore varies in the range of 220 nm to 270 nm, and the diameter of the gold nanopore can vary continuously.

5. The control method of the multifunctional surface-enhanced Raman scattering chip based on double Fano resonance according to claim 3, characterized in that: When the diameter of the gold nanopore varies in the range of 220 nm to 270 nm, the wavelength of the second Fano resonance can be continuously tuned in the range of 640 nm to 781 nm.

6. The control method of the multifunctional surface-enhanced Raman scattering chip based on double Fano resonance according to claim 3, characterized in that: The multifunctional surface-enhanced Raman scattering chip is placed in a culture medium. When the refractive index of the culture medium is changed, the wavelength of the first Fano resonance can be kept from drifting.

7. The control method of the multifunctional surface-enhanced Raman scattering chip according to claim 6, characterized in that: The refractive index of the culture medium varies from 1.33 to 1.5.

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