In-situ Raman detection substrate and preparation method and application thereof

Abstract

The invention belongs to the technical field of optical detection materials, and particularly relates to an in-situ Raman detection substrate and a preparation method and application thereof.The preparation method comprises the following steps that 1, a metal aluminum film is evaporated on a carrier, and after the metal aluminum film is etched, an aluminum oxide nano layer is obtained; and (2) sequentially depositing a silver nano layer and a gold nano layer on the surface of the aluminum oxide nano layer. The substrate of the acrylic glass / aluminum oxide / silver / gold quasi-cavity SERS structure prepared by the method has the advantages of high sensitivity, large size and low cost, and can be used in various in-situ detection environments including a solid-solid interface, a solid-liquid interface and a solid-gas interface.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical detection materials, and in particular relates to an in-situ Raman detection substrate and a preparation method and application thereof. Background Art

[0002] Surface-Enhanced Raman Scattering (SERS) technology is a promising analytical method. With its high sensitivity and wide application potential, it continues to promote scientific research and technological progress in various fields. Whether in chemical analysis, life sciences, or material characterization, SERS has irreplaceable value. However, the SERS substrates prepared by existing processes are mostly targeted at non-in-situ detection application environments, and there are relatively few studies on the preparation process of SERS substrates specifically for in-situ detection application environments. At the same time, the prepared substrates have low sensitivity and are not easy to mass produce. In addition, the medium environment applicable to the substrates is relatively single, which is difficult to meet the in-situ detection environment of multiple interfaces.

[0003] In the prior art, for example, Chen Yulin deposited metals or semiconductors directly on glass substrates by magnetron sputtering in the preparation and characteristic research of surface enhanced SERS substrates based on magnetron sputtering technology. It is difficult to obtain spectral signals with high intensity and signal-to-noise ratio using this method. Theoretically, the integration time should be longer and the sensitivity is lower. In the research on the detection of antibiotic residues and pesticide residues based on porous anodized aluminum film (SERS) substrates, Xiao Dongfang used ion sputtering technology to uniformly load Au NPs on porous anodized aluminum film (AAO) to prepare AAO@Au SERS substrates. However, the preparation process of this AAO is relatively complicated, and it has a conical or cylindrical structure with round holes. It is impossible to achieve the coupling effect of scattered light with the silver layer deposited on its surface and to form volume hot spots and surface hot spots at the same time to obtain a higher electromagnetic enhancement factor. Summary of the invention

[0004] The purpose of the present invention is to provide an in-situ Raman detection substrate and its preparation method and application, and to prepare an acrylic glass / aluminum oxide / silver / gold quasi-cavity SERS structure with high sensitivity, large size and low cost, which can be used in a variety of in-situ detection environments including "solid-solid" interface, "solid-liquid" interface and "solid-gas" interface. The present invention solves the problems of complex mass production process of existing in-situ SERS detection substrates, low sensitivity of related structures, and high material costs.

[0005] In order to achieve the above object, the technical solution of the present invention is:

[0006] In a first aspect, the present invention provides an in-situ Raman detection substrate, comprising a carrier and an aluminum oxide nanolayer, a silver nanolayer and a gold nanolayer sequentially arranged on the surface of the carrier from bottom to top, wherein the aluminum oxide nanolayer has a quasi-nanocavity structure.

[0007] In some other embodiments, the quasi-nano cavity structure is formed by aluminum oxide nanosheets surrounding each other, wherein the thickness of the aluminum oxide nanosheet is 10-40 nm, and the length or width of the aluminum oxide nanosheet is 200-600 nm respectively;

[0008] Preferably, the carrier is glass or silicon wafer, the thickness of the aluminum oxide nanolayer is 300-600 nm; the thickness of the silver nanolayer is 25-45 nm; and the thickness of the gold nanolayer is 3-7 nm.

[0009] During the research process, the inventors found that the aluminum oxide nanolayer is formed by vertical aluminum oxide nanosheets surrounding each other, where the thickness of the nanosheets is 10-40nm, and the length or width is 200-600nm respectively. The size of the cavity structure formed is between 300-600nm. This structure has excellent light trapping properties and can effectively localize the incident light inside the cavity, reducing the reflectivity of the incident light.

[0010] The silver nanolayer is evenly wrapped on the surface of the aluminum oxide nanolayer, with a thickness of about 25-45nm. The main function of the silver nanolayer is to act as a surface plasmon resonance unit, further converting the light captured by the aluminum oxide nanolayer cavity structure into a stronger local electric field, thereby providing surface hot spots for the molecules to be tested in subsequent tests.

[0011] The gold nanolayer is evenly wrapped on the surface of the silver nanolayer, and its thickness is about 3-7nm. Here, the main role of the gold nanolayer is to act as a protective layer to prevent the oxidation reaction of nanosilver due to its high chemical activity during subsequent testing, which will cause its surface plasmon characteristics to decrease. At the same time, plasmon coupling is also easily formed between the gold nanolayer and the silver nanolayer, further enhancing the intensity of the local electric field near the aluminum oxide nanolayer.

[0012] In a second aspect, the present invention provides a method for preparing the in-situ Raman detection substrate according to the first aspect, comprising the following steps:

[0013] (1) vapor-depositing a metal aluminum film on a carrier, and etching the metal aluminum film to obtain an aluminum oxide nanolayer;

[0014] (2) A silver nanolayer and a gold nanolayer are sequentially deposited on the surface of the aluminum oxide nanolayer to obtain a nanolayer.

[0015] In some other embodiments, in step (1), the evaporation conditions of the metal aluminum film are: the vacuum degree is less than 10 - 2 Pa, the thermal evaporation rate is The purity of the aluminum particles used is greater than 99.9%;

[0016] The etching conditions are: treating with an alkaline solution having a pH of 7.5-9.0 at 75-85° C. for 30-45 min;

[0017] The alkali solution is NaOH or KOH solution.

[0018] In some other embodiments, in step (2), the silver nanolayer is deposited by magnetron sputtering using a silver target with a purity greater than 99.99% at a vacuum degree of 2-3 Pa and a sputtering rate of Deposition obtained;

[0019] The gold nanolayer is deposited by magnetron sputtering using a gold target material with a purity greater than 99.9% at a vacuum degree of 1-2 Pa at a sputtering rate of Deposition obtained.

[0020] In some other embodiments, step (1) further includes cleaning the carrier, wherein the cleaning process is: ultrasonic cleaning with isopropanol, ethanol, and deionized water for 10-15 minutes in sequence, then rinsing with deionized water for 1-2 minutes, and then vacuum drying at 50-60°C.

[0021] In a third aspect, the present invention provides a use of the in-situ Raman detection substrate described in the first aspect in Raman detection.

[0022] In some other embodiments, the method is used for Raman detection of toluidine blue, Congo red, malachite green or p-aminothiophenol.

[0023] In a fourth aspect, the present invention provides a method for surface enhanced Raman scattering detection, using the in-situ Raman detection substrate described in the first aspect as an in-situ Raman detection substrate, and the compounds are toluidine blue, Congo red, malachite green, and p-aminothiophenol.

[0024] In some other embodiments, when the compound is toluidine blue, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the toluidine blue concentration is 10 -3 M-10 -9 M;

[0025] When the compound is Congo red, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the Congo red concentration is 10-3 M-10 -8 M;

[0026] When the compound is malachite green, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the malachite green concentration is 10 -4 M-10 -9 M;

[0027] When the compound is p-aminothiophenol, the detection method is: laser, 0.48 mW power, 600 g / mm grating, 8 s integration time, the p-aminothiophenol concentration is 10 -4 M.

[0028] Beneficial effects of the present invention:

[0029] (1) The application scope of the enhanced in situ SERS substrate: It can be applied to various "solid-solid" interface detection environments such as metals, inorganic solids, organic solids, etc.; it can be applied to various "solid-liquid" interface detection environments such as water and ethanol; it can be applied to various "solid-gas" interface detection environments such as nitrogen, oxygen, hydrogen sulfide, carbon dioxide, air, etc.

[0030] (2) Reduce the minimum detection limit of the in situ SERS substrate: For toluidine blue molecules, the minimum detection limit is about 1.0×10 -9 M; for Congo red molecules, the minimum detection limit is about 1.0×10 -8 M; for malachite green molecules, the minimum detection limit is about 1.0×10 -9 M.

[0031] (3) Improving the uniformity of in situ SERS substrate: For p-aminothiophenol molecules, when the detection concentration is 1Δ10 -4 When M, the relative standard deviations of detection between different batches of substrates and different detection sites on the same substrate were 7.88% and 10.12%, respectively.

[0032] (4) Reduce process costs: For a substrate with a size of 1 cm × 1 cm, the cost per piece is reduced from approximately RMB 20 to RMB 3.5, and the unit cost is reduced by approximately 5.7 times. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] The accompanying drawings in the specification, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute improper limitations on the present invention.

[0034] Figure 1 This is a physical picture of the acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity prepared in Example 1 of the present invention;

[0035] Figure 2 This is a low-magnification scanning electron microscope (SEM) image of the acrylic glass / aluminum oxide nanocavity prepared in Example 1 of the present invention;

[0036] Figure 3 This is a high-magnification scanning electron microscope (SEM) image of the acrylic glass / aluminum oxide nanocavity prepared in Example 1 of the present invention;

[0037] Figure 4 This is a low-magnification scanning electron microscope (SEM) image of the acrylic glass / aluminum oxide / silver / gold nanocavity prepared in Example 1 of the present invention;

[0038] Figure 5 This is a high-magnification scanning electron microscope (SEM) image of the acrylic glass / aluminum oxide / silver / gold nanocavity prepared in Example 1 of the present invention;

[0039] Figure 6 The acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity in-situ Raman detection substrate prepared in Example 1 of the present invention has a concentration of 10 -3 M-10 -9 Raman detection spectrum of toluidine blue molecule of M;

[0040] Figure 7 The acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity in-situ Raman detection substrate prepared in Example 1 of the present invention has a concentration of 10 -3 M-10 -8 Raman detection spectrum of Congo red molecule of M;

[0041] Figure 8 The acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity in-situ Raman detection substrate prepared in Example 1 of the present invention has a concentration of 10 -4 M-10 -9 Raman detection spectrum of malachite green molecule of M;

[0042] Fig. 9 The XRD spectrum of the acrylic glass / aluminum oxide / silver / gold nanocavity prepared in Example 1 of the present invention;

[0043] Fig.10 The acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity in-situ Raman detection substrate prepared in Example 1 of the present invention has a concentration of 10 -4 Raman detection mapping of p-aminothiophenol molecule of M, point range: 20μm×20μm, number of points: 400 points. DETAILED DESCRIPTION

[0044] Example 1

[0045] (1) Preparation of acrylic glass / aluminum oxide nanocavity:

[0046] Place a 1mm thick, 5cm×5cm acrylic transparent glass in a glass beaker, and use isopropanol, ethanol, and deionized water to ultrasonically remove surface contaminants for 10-15 minutes. Then take out the acrylic glass, rinse it with deionized water for 1-2 minutes, and place it in a vacuum drying oven at 60°C for vacuum drying. Place the dried acrylic glass in a thermal evaporation coating device and evacuate it to a vacuum degree of 10 -2 Pa or less, and then start to evaporate the metal aluminum film on the surface of the acrylic glass. The metal particles used for evaporation must be aluminum particles with a purity of more than 3N, and the thermal evaporation rate must be controlled at The film thickness is monitored using the quartz crystal oscillator of the thermal evaporation instrument. The thickness of the aluminum film needs to be controlled within 300nm. After the evaporation is completed, wait for the substrate to cool naturally, then take it out and place it in a NaOH aqueous solution. The pH value of the solution needs to be controlled between 7.5. Heat the solution and keep it at 75℃ for 30min. Then, after the solution cools naturally, take out the substrate, rinse it with a large amount of deionized water and place it in a vacuum drying oven at 60℃ for vacuum drying to obtain the acrylic glass / aluminum oxide nano-quasi-cavity structure.

[0047] (2) Preparation of acrylic glass / aluminum oxide / silver / gold nanocavity:

[0048] The substrate was placed in a magnetron sputtering device and vacuumed to 2 Pa. The sputtering rate was adjusted to The sputtering target material is a metal silver target material with a purity of 4N or more. The film thickness is monitored by the quartz crystal oscillator of the magnetron sputtering device. The thickness of the silver film needs to be controlled at 30nm. Subsequently, the target material is replaced with a metal gold target material with a purity of 3N or more. The vacuum degree is adjusted to 1Pa and the sputtering rate is adjusted to The film thickness is monitored by the quartz crystal oscillator of the magnetron sputtering device, and the thickness of the gold film needs to be controlled at 3nm.

[0049] Figure 1 This is a physical picture of the acrylic glass / aluminum oxide / silver / gold nanocavity prepared in Example 1 of the present invention; Figure 1 It can be seen that the size of the prepared acrylic glass / aluminum oxide / silver / gold nanocavity is 1 cm×1 cm.

[0050] Figure 2 This is a low-magnification scanning electron microscope (SEM) image of the acrylic glass / aluminum oxide nanocavity prepared in Example 1 of the present invention; Figure 3 This is a high-magnification scanning electron microscope (SEM) image of the acrylic glass / aluminum oxide nanocavity prepared in Example 1 of the present invention. Figure 2 , Figure 3It can be seen that the aluminum oxide nanolayer is formed by vertical aluminum oxide nanosheets surrounding each other, wherein the thickness of the nanosheet is about 20nm, the length / width are 200-600nm respectively, and the size of the formed cavity structure is 300-600nm.

[0051] Figure 4 This is a low-magnification scanning electron microscope (SEM) image of the acrylic glass / aluminum oxide / silver / gold nanocavity prepared in Example 1 of the present invention; Figure 5 This is a high-magnification scanning electron microscope (SEM) image of the acrylic glass / aluminum oxide / silver / gold nanocavity prepared in Example 1 of the present invention. Figure 4 , Figure 5 It can be seen that the silver / gold nanolayer is uniformly wrapped on the surface of the aluminum oxide nanosheets, and its thickness is about 28-52nm.

[0052] Example 2

[0053] The difference from Example 1 is that in step (1), the metal particles used for plating need to be aluminum particles with a purity of 3N or above, and the thermal evaporation rate is controlled at The film thickness was monitored using the quartz crystal oscillator of the thermal evaporation instrument. The thickness of the aluminum film should be controlled within 500nm. After the evaporation was completed, the substrate was allowed to cool naturally, then taken out and placed in a NaOH aqueous solution. The pH value of the solution should be controlled at 9.0. The temperature was kept at 85℃ for 45min.

[0054] In step (2), the substrate is placed in a magnetron sputtering device, evacuated, the vacuum degree is adjusted to 3 Pa, and the sputtering rate is adjusted to The thickness of the silver film needs to be controlled at 45nm. Then, the target material is replaced with a metal gold target with a purity of more than 3N, the vacuum degree is adjusted to 2Pa, and the sputtering rate is adjusted to The film thickness is monitored using the quartz crystal oscillator provided in the magnetron sputtering device, and the thickness of the gold film needs to be controlled within 5nm.

[0055] The other preparation processes are exactly the same as those in Example 1.

[0056] Example 3

[0057] The difference from Example 1 is that in step (1), the metal particles used for plating need to be aluminum particles with a purity of 3N or above, and the thermal evaporation rate is controlled at The film thickness was monitored using the quartz crystal oscillator of the thermal evaporation instrument. The thickness of the aluminum film was controlled at 400 nm. After the evaporation was completed, the substrate was allowed to cool naturally, then taken out and placed in a KOH aqueous solution. The pH value of the solution was controlled at 8.0. The solution was kept at 80°C for 40 minutes.

[0058] In step (2), the substrate is placed in a magnetron sputtering device, evacuated, the vacuum degree is adjusted to 3 Pa, and the sputtering rate is adjusted to The thickness of the silver film needs to be controlled at 40nm. Then, the target material is replaced with a metal gold target with a purity of more than 3N, the vacuum degree is adjusted to 2Pa, and the sputtering rate is adjusted to The film thickness is monitored using the quartz crystal oscillator provided in the magnetron sputtering device, and the thickness of the gold film needs to be controlled at 4 nm.

[0059] The other preparation processes are exactly the same as those in Example 1.

[0060] Comparative Example 1

[0061] The difference from Example 1 is that step (1) is not performed, and the silver nanolayer and the gold nanolayer are deposited sequentially directly on the acrylic transparent glass. The other preparation processes are exactly the same as those in Example 1.

[0062] Comparative Example 2

[0063] The difference from Example 1 is that in step (1), a metal aluminum film is directly deposited on the surface of the acrylic glass without etching. The other preparation processes are exactly the same as those in Example 1.

[0064] Comparative Example 3

[0065] The difference from Example 1 is that in step (2), only a silver nanolayer is deposited. The other preparation processes are exactly the same as those in Example 1.

[0066] Comparative Example 4

[0067] The difference from Example 1 is that in step (2), only a gold nanolayer is deposited. The other preparation processes are exactly the same as those in Example 1.

[0068] Performance Testing

[0069] The substrates prepared by Examples 1-3 and Comparative Examples 1-4 were used for in-situ Raman detection of the compounds toluidine blue, Congo red, malachite green and p-aminothiophenol.

[0070] When the compound is toluidine blue, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the toluidine blue concentration is 10 -3 M-10 -9 M;

[0071] When the compound is Congo red, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the Congo red concentration is 10 -3 M-10 -8 M;

[0072] When the compound is malachite green, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the malachite green concentration is 10 -4 M-10 -9 M;

[0073] When the compound is p-aminothiophenol, the detection method is: laser, 0.48 mW power, 600 g / mm grating, 8 s integration time, the p-aminothiophenol concentration is 10 -4 M.

[0074] The results show that the test accuracy of Examples 1-3 is significantly better than that of Comparative Examples 1-4. Figure 6 The acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity in-situ Raman detection substrate prepared in Example 1 has a concentration of 10 -3 M-10 -9 Raman detection spectrum of toluidine blue molecule of M. Figure 6 It can be seen that the minimum detection limit is about 1.0×10 -9 M.

[0075] Figure 7 The acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity in-situ Raman detection substrate prepared in Example 1 has a concentration of 10 -3 M-10 -8 Raman detection spectrum of Congo red molecule of M. Figure 7 It can be seen that the minimum detection limit is about 1.0×10 -8 M.

[0076] Figure 8 The acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity in-situ Raman detection substrate prepared in Example 1 has a concentration of 10 -4 M-10 -9 Raman detection spectrum of malachite green molecule of M. Figure 8 It can be seen that the minimum detection limit is about 1.0×10 -9 M.

[0077] Fig. 9 The XRD spectrum of acrylic glass / aluminum oxide / silver / gold nanocavity prepared in Example 1 of the present invention; Fig. 9 It can be seen that the prepared acrylic glass / aluminum oxide / silver / gold nanoquasi-cavity crystals have high crystallinity and no impurity peaks.

[0078] Fig.10 The acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity in-situ Raman detection substrate prepared in Example 1 has a concentration of 10 -4Raman detection mapping of p-aminothiophenol molecule of M, the sampling range is 20μm×20μm, and the number of sampling points is 400. Fig.10 It can be seen that the relative standard deviations of detection between different batches of substrates and different detection sites on the same substrate are 7.88% and 10.12%, respectively.

[0079] It can be seen that the selection of experimental parameters is related to the application of the acrylic glass / aluminum oxide / silver / gold nano-quasi-cavity structure in actual detection. Specifically, the shape of the nano-quasi-cavity usually affects its performance, and the preparation method has an impact on its shape. Obviously, the material prepared by the method described in Example 1 is the most practical.

[0080] The above disclosure is only the preferred embodiment of the present invention, which certainly cannot be used to limit the scope of rights of the present invention. Therefore, equivalent changes made according to the scope of the patent application of the present invention are still within the scope covered by the present invention.

Claims

1. An in-situ Raman detection substrate, characterized in that: The invention comprises a carrier and an aluminum oxide nano layer, a silver nano layer and a gold nano layer which are sequentially arranged on the surface of the carrier from bottom to top, wherein the aluminum oxide nano layer has a quasi-nano cavity structure.

2. The in-situ Raman detection substrate according to claim 1, characterized in that: The quasi-nano cavity structure is formed by aluminum oxide nanosheets surrounding each other, wherein the thickness of the aluminum oxide nanosheet is 10-40 nm, and the length or width of the aluminum oxide nanosheet is 300-600 nm respectively; Preferably, the carrier is glass or silicon wafer; the thickness of the aluminum oxide nanolayer is 300-600 nm; or, the thickness of the silver nanolayer is 25-45 nm; or, the thickness of the gold nanolayer is 3-7 nm.

3. A method for preparing the in-situ Raman detection substrate according to claim 1, characterized in that: The following steps are involved: (1) vapor-depositing a metal aluminum film on a carrier, and etching the metal aluminum film to obtain an aluminum oxide nanolayer; (2) A silver nanolayer and a gold nanolayer are sequentially deposited on the surface of the aluminum oxide nanolayer to obtain a nanolayer.

4. The method for preparing an in-situ Raman detection substrate according to claim 3, characterized in that: In step (1), the evaporation conditions of the metal aluminum film are: the vacuum degree is less than 10 -2 Pa, the thermal evaporation rate is The purity of the aluminum particles used is greater than 99.9%; The etching conditions are: treating with an alkaline solution having a pH of 7.5-9.0 at 75-85° C. for 30-45 min; The alkali solution is NaOH or KOH aqueous solution.

5. The method for preparing an in-situ Raman detection substrate as claimed in claim 3, characterized in that: In step (2), the silver nanolayer is deposited by magnetron sputtering using a silver target material with a purity greater than 99.99% at a vacuum degree of 2-3 Pa and a sputtering rate of Deposition obtained; The gold nanolayer is deposited by magnetron sputtering using a gold target material with a purity greater than 99.9% at a vacuum degree of 1-2 Pa at a sputtering rate of Deposition obtained.

6. The method for preparing an in-situ Raman detection substrate according to claim 3, characterized in that: Step (1) also includes cleaning the carrier, wherein the cleaning process is: ultrasonic cleaning with isopropanol, ethanol, and deionized water for 10-15 minutes in sequence, then rinsing with deionized water for 1-2 minutes, and then vacuum drying at 50-60°C.

7. Use of the in-situ Raman detection substrate according to claim 1 or 2 in Raman detection.

8. The use according to claim 7, characterized in that Application in Raman detection of toluidine blue, Congo red, malachite green and p-aminothiophenol.

9. A method for surface enhanced Raman scattering detection, characterized in that: The in-situ Raman detection substrate according to claim 1 or 2 is used as the in-situ Raman detection substrate, and the compounds are toluidine blue, Congo red, malachite green, and p-aminothiophenol.

10. The method for surface enhanced Raman scattering detection according to claim 9, characterized in that: When the compound is toluidine blue, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the toluidine blue concentration is 10 -3 M-10 -9 M; When the compound is Congo red, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the Congo red concentration is 10 -3 M-10 -8 M; When the compound is malachite green, the detection method is: laser, 0.48-4.8 mW power, 600 g / mm grating, 4-8 s integration time, the malachite green concentration is 10 -4 M-10 -9 M; When the compound is p-aminothiophenol, the detection method is: laser, 0.48 mW power, 600 g / mm grating, 8 s integration time, the p-aminothiophenol concentration is 10 -4 M.

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