A substrate fabrication method for surface enhanced raman spectroscopy

Abstract

The invention relates to a fabrication method for the substrate in which the sample to be tested in surface enhanced Raman spectroscopy is placed.

Description

[0001] A SUBSTRATE FABRICATION METHOD FOR SURFACE ENHANCED RAMAN SPECTROSCOPY

[0002] Technical Field

[0003] The invention relates to a substrate fabrication method in which the sample to be tested in Raman spectroscopies is placed.

[0004] State of the Art

[0005] When a beam is directed a molecule / s ample, the photons that make up the beam are absorbed, reflected, passed through the surface, or scattered. In the case of scattering, scattering occurs mostly without any change in the frequency of the beams. This type of scattering is called Rayleigh scattering. Only a small portion of the scattered beams interacts with the electrons of the matter at the vibrational level, either transmitting or receiving some energy. This results in the frequency of the scattered beams being higher or lower than the frequency of the incoming beam, a phenomenon known as Raman scattering. Raman spectroscopyexamines these changesin scattering frequency. Raman spectroscopy provides information about the chemical composition, molecular structure, and binding properties of the sample as the scattering is unique to each molecule,.

[0006] However, Raman scattering is a phenomenon that occurs with a very low probability. Since this causes low sensitivity, it is not possible to determine many molecules by this method. This problem has been largely eliminated with the development of the surface enhanced Raman spectroscopy (SERS) method. In the SERS method, the analysis of the target molecule is performed on a metallic surface such as silver, gold, or copper or in the presence of a nanoparticle with a diameter smaller than the wavelength of the excitation beams in the solution medium. When the aforementioned surface or particle is excited by the beam, the surface plasmon mode is excited and the electromagnetic energy around the target molecule is increased locally. In this way, the intensity of the inelastic scattering beams is significantly increased. In order to take advantage of this situation, various substrates containing SERS active surfaces have been developed. The substrate surface and the material of the surface affect the strength and intensity of the Raman scattering. Raman signal intensity is very low on flat surfaces, and repeatability problems arise on non-homogeneous surfaces.

[0007] Existing SERS substrates in the sector are generally expensive and production methods are difficult. Common methods used for the formation of SERS substrates are methods such as creating a pattern by lithographic methods or chemical abrasion. Although these methods provide effective results, they are slow, cumbersome, and expensive.

[0008] In the method described in WO2015135450A1, gold film-coated perforated structures are formed on the silicone or glass surface using the nano-imprintingtechnique. By using the electrochemical deposition method on these structures, making the metal overflow the hole to form themushroom nano- structure array are obtained.

[0009] The method given in WO2016195389A2 consists of two main parts, the SERS active part and the labeling part on the cellulose chromatography paper. Areas outside the SERS active zone are covered with paraffin and dried by applying temperature. SERS substrates are obtained by printing gold nanoparticles in the template by using an inkjet printer after creating a circular template on the cellulose chromatography paper to form the SERS active part.

[0010] In the method described in CN109467043A, substrate isotropic micro-concave mirror arrays are formed by isotropic wet etching method. Metal film (such as gold, platinum) layers are deposited on the formed array surfaces and these layers are coated with gold nanoparticles.

[0011] In US20210156804A1, chitosan is used for direct reduction of metal nanoparticles on the substrate. The most important step in the process is the incubation of paper-based substrates for one hour under humid and increasing temperature conditions. Metal nanoparticles produced in this way are deposited homogeneously on the paper-based substrate.

[0012] In CN107313046B, firstly, the substrate surface is cleaned and hydrophilized, and then at least one layer of self-assembled array structur r is formed with nanosphere, nanocrystalline or quantum dots. A metal active layer is deposited on the top of formed layer, and the substrate is obtained by coating with carbon-based nanomaterial to slow the oxidation process by cutting the contact of the air with this metal layer .

[0013] As explained above, these methods are high-cost and slow methods.

[0014] All the problems mentioned above have made it necessary to make an innovation in the relevant field as a result.

[0015] Brief Description and Objects of the Invention

[0016] The main object of the invention is to provide a substrate production method for Raman spectroscopy, which does not need faster and higher cost equipment compared to its alternatives.

[0017] An object of the invention is to eliminate the need for further processing of the substrate by methods such as lithographic methods to obtain the desired surface pattern.

[0018] Another object of the invention is to provide a method in which the surface roughness can be controlled.

[0019] In the method of the invention, metal nanopowders are applied to the thermoplastic material surface with a solvent. Then, it is pressed on the application site for a certain vibration period by applying a certain constant compression with a sonotrode vibrating at a frequency in the range of 20-30 kHz. As a result of the effect of heat and solvent released due to ultrasonic vibration, the thermoplastic material softens, and the metal nanopowder is sintered. As the thermoplastic softens due to heating, the sintered metal nanopowder is embedded in these solvent contact areas. At the end of the process, a metal layer of sintered metal nanopowder is formed at the end of a certain cooling process. Constant compression and vibration time affect the amount of sintering and accordingly the surface roughness. In addition, the patterns on the sonotrode surface are directly transferred to the metal layer, thus eliminating the need for further processing of the substrate by methods such as lithographic methods to obtain the desired surface pattern. Alternatively, the metal nanopowder and solvent can be provided in a cavity to contact the plastic part and accordingly, a layer in the same form as the cavity geometry is obtained. Accordingly, preferably, an electrode can be obtained in a microfluidic system.

[0020] Definitions of Figures Describing the Invention

[0021] The figures and related descriptions used to better explain the device developed by this invention are as follows.

[0022] Figure 1. A schematic image of an embodiment for performing the method of the invention.

[0023] Figure la. A schematic image of an embodiment for performing the method of the invention.

[0024] Figure 2.A schematic image of the embodiment using a hollow layer for performing the method of the invention.

[0025] Figure 3.A schematic image of the embodiment using a mold for performing the method of the invention.

[0026] Figure 4. A schematic image of the embodiment using a hollow mold for performing the method of the invention.

[0027] Figure 5. Surface roughness-time-pressure graphs according to an experiment conducted with the method of the invention.

[0028] Figure 6. An image of the substrate surface obtained by the sonotrode with a trace in the form of intertwined circles on the forehead.

[0029] Figure 6a. An image of the substrate surface obtained by the polished sonotrode.

[0030] Figure 7. Four different preferred trace patterns of the substrate surface obtained by the method of the invention.

[0031] Figure 8. SERS spectra obtained from the substrate with traces on its surface and the substrate with a flat surface.

[0032] Definitions of Components / Pieces / Parts of the Invention

[0033] In order to better explain the device developed by this invention, the parts and pieces in the figures are numbered and the corresponding numbers are given below.

[0034] P. Part V. Ultrasonic vibration source

[0035] N. nanopowder

[0036] S. Solvent

[0037] M. Mold

[0038] C. Cavity

[0039] T. Anvil

[0040] A. SERS spectrum of the substrate with traces on its surface

[0041] B. SERS spectrum of the flat substrate

[0042] Detailed Description of the Invention

[0043] The subject matter of the invention relates to a production method for the substrate in which the sample to be tested in Raman spectroscopies is placed.

[0044] Referring to Figure 1, the part (P) is the substrate body made of thermoplastic material.

[0045] The part is made of a thermoplastic that can be dissolved by a solvent (S). The choice of solvent (S) will vary depending on the selected type of thermoplastic. Chloroform can be selected as the solvent (S) if polymethyl methacrylate is preferably used as the thermoplastic material.

[0046] Preferably, said nanopowder (N) is made of a sinterable material. Preferably, the material can be sintered at 100-200°C for 1-10 seconds. The material can be selected as metal, especially gold, silver, and copper. In particular, the use of nanoscale powder is recommended because it is advantageous in terms of sintering time. nanopowder (N) and solvent (S) are applied to a surface of the thermoplastic part (P).

[0047] In said method, after the application of the solvent (S) and the nanopowder (N), ultrasonic vibration is applied to the part (P). The ultrasonic vibration source (V) used to apply the vibration is preferably the sonotrode, a mechanical component that transmits the vibration produced by the actuator connected to a piezoelectric actuator to the part (P). Due to the application of ultrasonic vibration, the nanopowder (N) and the part (P) begin to heat up due to the friction between the surfaces and the atoms. Here, the part (P) begins to soften in the area where the ultrasonic vibration is applied, both due to the effect of the solvent (S) and due to the frictional heating. At this point, said ultrasonic vibration also causes the nanopowder (N) to friction between themselves, causing the nanopowder (D) to be sintered without the need for any extra heat source. The heated and sintered nanopowder (N) is embedded in the parts on the part (P) in contact with the solvent (S).

[0048] Cooling is provided by waiting for a certain period of time after the ultrasonic vibration source is turned off. Preferably, the surface is continued to be pressed by the ultrasonic vibration source (V) during the cooling process, thus preventing the deformation that may occur due to the residual thermal stresses in the part (P) and accordingly in the layer.

[0049] Accordingly, in the present method, at least a part of the surface of the part (P) is brought into contact with the nanopowder (N) and a suitable solvent (S) for the part (P), and ultrasonic vibration is applied to the parts of the part (P) in contact with the solvent (S) and the nanopowder (N) to sinter the nanopowder (N) to form a layer.

[0050] Referring to Figure la, in the preferred embodiment of the invention, the nanopowder (N) is first laid on the part (P) and then the solvent (S) is applied to the relevant area, or the solvent (S) is applied first and then the nanopowder (N) is laid. The solvent (S) can be applied to the surface in the form of liquid or gas. Alternatively, the nanopowder (N) and the solvent (S) are prepared in advance as a solution, especially a colloidal solution, and applied on the part (P). Thus, commercially available suspensions (conductive inks) may also be used. In this preferred embodiment, after the application of the nanopowder (N) and the solvent (S), the ultrasonic vibration is applied on the part (P) by the ultrasonic vibration source (V) through the nanopowder (N) and the solvent (S).

[0051] In the embodiment described above, the cavity (C) or cavities (C) are used to physically limit the nanopowder (N) and the solvent (S) to the surface of the part (P) in order to provide the application of said nanopowder (N) and the solvent (S) in a controlled manner and thus to give a form to the metal layer. The cavities (C) are formed according to the form of the metal layer to be obtained. In this embodiment, said nanopowder (N) and solvent (S) are filled into said cavity (C).

[0052] The cavities (C) are obtained by more than one different method.

[0053] Referring to Figure 2; In an embodiment of the invention, a layer (L) is provided in the part of said part (P) where the layer is desired to be formed. Preferably, the layer (L) is selected as a structure that can be separated from the part (P) later. The cavity (C) or cavities (C) are formed on the layer (L) by providing the discharge or discharges according to the desired metal layer form on said layer (L).

[0054] As mentioned earlier, the nanopowder (N) and the solvent (S) are applied separately or in the form of a solution to the cavities (C) provided on said layer (L).

[0055] Then, the ultrasonic vibration source (V) is pressurized on the surface of the part (P), or layer

[0056] (L) and the ultrasonic vibration source is operated.

[0057] With the ultrasonic vibration provided, the surface of the part (P) corresponding to said cavity (C) is softened due to the temperature or the solvent (S) and the nanopowder (N) is sintered and embedded in the relevant part as described above.

[0058] Preferably, a polymer film (not deformed under pressure) that can withstand higher temperatures compared to the part (P) is used as the layer (L). The cavities (C) are obtained as a result of the cutting process provided on said layer. The cutting process is preferably carried out with the cutting device.

[0059] Referring to Figure 3, in an embodiment of the invention, the metal layer is formed in a mold

[0060] (M). Accordingly, first of all, the nanopowder (N) and the solvent (S) are filled into the mold (M) separately or in the form of a solution.

[0061] Then, the part (P) is placed in the mold (M). Here, the mold (M) has a base and walls arranged to wrap said part (P). nanopowder (N) and solvent (S) are trapped between said mold (M) and part (P) and this part acts as a kind of cavity (C). Alternatively, as shown in Figure 4, the cavity (C) or cavities (C) are formed at the base of the mold (M), which also provides depth. In this embodiment, the nanopowder (N) and the solvent (S) are filled into said cavities (C) in the mold (M).

[0062] In both embodiments, finally, ultrasonic vibration is applied over the mold (M) or part (P). With the ultrasonic vibration provided, the surface of the part (P) corresponding to said cavity (C) is softened due to the temperature or the solvent (S) and the nanopowder (N) is sintered and embedded in the relevant part as described above.

[0063] Said cavities (C) are preferably 1-10 pm deep. After the nanopowder (N) is laid to fill these cavities (C), the solvent (S) in the range of 1-10 pL is used. In the opposite way, it is preferable to apply the solvent (S) first and then to add the nanopowder (N) or to add the nanopowder (N) first and then to apply the solvent (S). If the solvent (S) is applied in the gas phase, it is kept in the solvent vapor of the part for 1-3 minutes.

[0064] Preferably, the volume of nanopowder (N) is at least the amount of the area of the layer to be obtained and the height of the cavity (C).

[0065] In these embodiments described, ultrasonic vibration is preferably applied in the range of 20- 30 kHz.

[0066] Similarly, although the cooling time is predicted to be about 10 seconds, it is obvious that this time may also vary depending on the material and sintering temperature.

[0067] It is clear that a person with expertise in the field can appropriately regulate the selection of cooling time, frequency, time, and material depending on the desired end product.

[0068] Since the current method uses ultrasonic vibration, the cycle time required to produce a single metal layer takes less time than common metal layer fabrication methods. In a study, it was seen that an ultrasonic vibration source (V) with a power of 500 W and producing ultrasonic vibration at a frequency of 28 kHz can provide a temperature of approximately 160°C within 5 seconds, and if gold nanopowders with a diameter of approximately 10 nm are used, it can be calculated that the nanopowders can be sintered at 120°C only within 1 ms according to the following characteristic sintering time equation [1] (The value of the diffusion coefficient in the equation for gold is expressed as s the gas consonant). As a result, the entire process can be completed within a cycle time of 10 seconds.

[0069] In this equation, TSrefers to the characteristic sintering time, to the Boltzmann constant, ? to the temperature, to the nanopowder diameter, C to the process constant, to the diffusion coefficient, y to the surface tension, and a to the atomic dimension.

[0070] As shown in Figure 5, the experiment was carried out on the layered (L) arrangement in Figure 2. As nanopowder (N), gold dust with a diameter of 14 nm was selected and the part (P) was selected to be made of polymethyl methacrylate (PMMA). If the ultrasonic vibration time was 2 seconds, the average surface roughness was measured as 53 nm. When the ultrasonic vibration time was increased to 5 seconds, the average surface roughness value was measured as 39.5 nm. When the ultrasonic vibration time was further increased to 7 seconds, it was observed that the average surface roughness value increased to 130 nm. During the processes, a constant compression of 1.7 MPa was applied on the part (P) by the ultrasonic vibration source (V) to the surface.

[0071] As can be seen from the values obtained, the roughness value primarily decreases as the ultrasonic vibration time increases. However, as the ultrasonic vibration time increases further, the roughness value increases as the part (P) starts to be deformed.

[0072] On the other hand, it was observed that the surface roughness was also affected by the constant compression applied on the thermoplastic part (P) by the ultrasonic vibration source (V). When the ultrasonic vibration time was applied for 5 seconds, it was observed that the constant compression applied on the part (P) by the ultrasonic vibration source (V) was 0.8 MPa, while the surface roughness was 53.3 nm, when it was 1.7 MPa, it was 39.5 nm, when it was 2.7 MPa, it was 108 nm. It is considered that the reason for this behavior is the suppression of the friction between the nanopowder (N) caused by the ultrasonic vibration and the resulting heating effect if the pressure increases above a certain level. As a result, it is seen that the desired surface roughness can be obtained by controlling the ultrasonic vibration time and the constant compression applied on the part (P) by the ultrasonic vibration source (V) using the method in question.

[0073] Referring to Figure 6 and 6a, in the preferred embodiments of the invention shown in Figures la, 2, 3 and 4, the surface of the ultrasonic vibration source (V) contacted to the part (P) by the nanopowder (N) and the solvent (S) can be provided in the form of intertwined circles or in a polished way. Traces in the form of intertwined circles occur naturally if the ultrasonic vibration source is produced by the turning process. In the turning process, the distance between the intertwined circles can vary depending on the tool feed rate. These traces can be removed by sanding, grinding and fine polishing. If the surface of the ultrasonic vibration source (V) contacting the part (P) contains traces in the form of intertwined circles, the same traces will be observed on the metal surface produced by the method of the invention as shown in Figure 6. If the surface of the ultrasonic vibration source (V) contacting the part (P) does not contain a trace, no trace will be observed on the metal surface as seen in Figure 6a. The scale line in Figure 6 and Figure 6a refers to 100 pm. In the preferred embodiment of the invention shown in Figure 1, it is obvious that the traces in the form of circles nested by the turning process should be obtained on the surface of the anvil (T) contacting the part (P) through the nanopowder (N) and the solvent (S) in order to obtain traces in the form of intertwined circles on the metal surface obtained similar to Figure 6a.

[0074] Traces in the form of intertwined circles can be obtained by the turning process. On the other hand, according to the preferred embodiment of the invention, different surface traces can also be obtained if the ultrasonic vibration source (V) or the anvil (T) is produced by different machining methods. Typical surface traces obtained by machining are shown in Figure 7. As can be seen in the figure, it is possible to obtain traces in parallel lines, diagonal lines, intertwined circles and radial forms. These traces can be obtained by machining on the ultrasonic vibration source (V) surface in the preferred embodiment of the method shown in Figure la, Figure 2, Figure 3, and Figure 4, or on the anvil (T) surface in the preferred embodiment of the method shown in Figure 1. It is foreseen that these traces transferred to the substrate surface fabricated by the method of the invention will increase the intensity of the Raman signal.

[0075] As shown in Figure 8, preliminary experiments were carried out to examine the effect of the SERS substrate of the invention on the Raman signal. For this purpose, substrates consisting of the gold layer on the polymethyl methacrylate were formed and tested using the ultrasonic vibration source (V) with nested circle traces on the surface of the part (P) in contact with the part (P) and the surface of the polished ultrasonic vibration source (V) in contact with the part (P). SERS measurements were taken by dropping 5,5'-Dithiobis (2-nitrobenzoic acid) (DTNB) solution on the surface of the substrates. The most significant change in the SERS spectrum is expected to be in the symmetrical NCF band at 1331 cm'1in the structure of the DTNB. Therefore, the SERS signal increases of 1331 cm'1were monitored. In the experiments, it was seen that the permission in the form of intertwined circles caused the Raman intensity to increase significantly as shown in Figure 8.

[0076] REFERENCES

[0077] [1] Coblenz, W. S., Dynys, J. M. and Cannon, R. M. (1980) “Initial stage solid state sintering models. A Critical Analysis and Assessment”, in Kuczynski, G. C. (ed.) “Sintering Processes”, Materials Science Research Vol. 13. New York: Plenum Press, p. 141-157.

Claims

CLAIMS1. A substrate fabrication method for Raman spectroscopy, characterized by:Contacting a solvent (S) and at least part of a surface of a part (P) at least partially soluble in said solvent with nanopowder (N) and said solvent (S),Applying ultrasonic vibration under constant compression for a certain period of time to sinter the nanopowder (N) into a layer on the part (P) in contact with the solvent (S) and the nanopowder (N).

2. A method according to claim 1, characterized in that said nanopowder (N) is gold, silver, or copper.

3. A method according to claim 1, characterized in that said part (P) is made of thermoplastic.

4. A method according to claim 1, characterized in that said part (P) is made of polymethyl methacrylate.

5. A method according to claim 3 or 4, characterized in that said solvent is chloroform.

6. A method according to claim 1, characterized in that said nanopowder (N) and solvent (S) are filled into at least one cavity (C).

7. A method according to claim 6, characterized in that said cavity (C) is formed discharges on a layer (L) provided on the surface of the part (P).

8. A method according to claim 7, characterized in that said layer (L) is a polymer film.

9. A method according to claim 1, characterized in that said nanopowder (N) and solvent (S) and the part (P) are placed in a mold (M).

10. A method according to claim 9, characterized in that said dust (D) and solvent (S) are filled into at least one cavity (C) in the mold (M).

11. A method according to claim 6, characterized in that said cavity (C) is provided on the surface of the thermoplastic part (P).

12. A method according to any one of claims 6-10, characterized in that said nanopowder (N) and solvent (S) are filled into multiple cavities (C).

13. A method according to claims 6-11, characterized in that said volume of nanopowder (N) is at least equal to the area of the layer to be obtained multiplied by the height of the cavity (C).

14. A method according to any one of preceding claims, characterized in that said nanopowder (N) and solvent (S) are provided in suspension form.

15. A method according to any one of preceding claims, characterized in that the surface of said ultrasonic vibration source (V) in contact with said solvent (S) and said nanopowder (N) comprises parallel lines, diagonal lines, intertwined circles or traces in radial form.

16. A method according to any one of claims 6-14, characterized in that the bottom surface of said cavity (C) in contact with said solvent (S) and said nanopowder (N) comprises parallel lines, diagonal lines, intertwined circles or traces in radial form.

17. A substrate obtained by a method according to any one of the preceding claims.

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