Coffee ring cross-enrichment Raman chip and its preparation method and application

Abstract

The present invention provides a coffee ring cross-enrichment Raman chip, a preparation method thereof and an application thereof. The Raman chip comprises a chip with a light trapping structure, a hydrophobic layer is provided on the chip, a nanoparticle coffee ring is provided on the hydrophobic layer, another coffee ring formed by self-assembly of nanoparticle sol and a pollutant to be detected is also provided on the hydrophobic layer, and there is a cross point between the two coffee rings, at which point both the nanoparticles and the pollutants have the highest concentration. The present invention also discloses a preparation method of the coffee ring cross-enrichment Raman chip and its application in the detection of triphenyltin chloride. The chip is based on the enrichment strategy and positioning strategy of the coffee ring cross effect, and quickly locks the detection area through double coffee ring cross imprints, greatly improving the detection efficiency and consistency, while utilizing the assembly of nanoparticles in a micro-nano structure to greatly improve the enhancement performance of the substrate. The light trapping effect and super-hydrophobic effect are utilized to improve the detection limit, so as to solve the problem that the sensitivity, stability and consistency of the traditional surface enhanced Raman scattering substrate are incompatible.

Description

Technical Field

[0001] The invention relates to the technical field of surface enhanced Raman scattering substrates, in particular to a coffee ring cross-enrichment Raman chip for rapid detection of water pollutants, a preparation method thereof and applications thereof. Background Art

[0002] Surface-enhanced Raman spectroscopy is a spectral technique with fingerprint characteristics that can detect molecules quickly and non-destructively. Its detection limit can reach a single-molecule level at least depending on the performance of the substrate. It has been widely used in the field of environmental monitoring and is therefore particularly suitable for on-site detection of environmental pollutants.

[0003] However, although surface-enhanced Raman spectroscopy technology has undergone decades of research and development, there are still certain problems and challenges in its real practical application. Among them, the preparation of surface-enhanced Raman spectroscopy substrates with high sensitivity, strong stability and consistency is the main problem facing surface-enhanced Raman spectroscopy technology. Traditional surface-enhanced Raman scattering substrate preparation includes chip-type and nanoparticle sol-type substrates. Among them, the chip-type substrate has high consistency and stability, but its sensitivity is still limited. The nanoparticle sol substrate has a strong localized surface plasmon resonance effect and dense hotspots, and has high sensitivity, but due to the agglomeration process of the nanoparticle sol and its uncontrollable nature. The traditional superhydrophobic array chip is combined with the nanoparticle sol, and the Raman signals at different positions under the coffee ring effect are extremely different. Summary of the invention

[0004] The present invention provides a coffee ring cross-enrichment Raman chip, a preparation method thereof and an application thereof, based on an enrichment strategy and a positioning strategy of the coffee ring cross effect, which quickly locks the detection area through double coffee ring cross marks, thereby greatly improving the detection efficiency and consistency.

[0005] The technical solution of the present invention is a coffee-ring cross-enrichment Raman chip, comprising a silicon chip with a light-trapping structure, a hydrophobic layer provided on the chip, a single nanoparticle coffee ring or a coffee ring array provided on the hydrophobic layer, and at least one other coffee ring formed by self-assembly of nanoparticle sol and a pollutant to be detected provided on the hydrophobic layer, wherein the coffee ring has an intersection with the aforementioned coffee ring.

[0006] Furthermore, the silicon chip is a column array chip having a reflectivity lower than 10% in the 400-800nm ​​spectral range.

[0007] Furthermore, the hydrophobic layer uses perfluorosilane as a hydrophobic agent.

[0008] Furthermore, the nanoparticles are nanorods, nanocones or nanospheres; and the material of the nanoparticles is gold or silver.

[0009] Furthermore, the dosage ratio of the nanoparticle sol to the pollutant to be detected is 1:1 to 1:10.

[0010] The present invention also relates to a method for preparing the coffee ring cross-enrichment Raman chip, comprising the following steps:

[0011] S1. Using photolithography combined with wet etching to prepare a chip with a light trapping structure;

[0012] S2, performing super-hydrophobic treatment on the chip obtained in S1, and processing the hydrophobic agent onto the chip structure;

[0013] S3, preparing the nanoparticles into nanoparticle sol, dripping a portion of the sol on the upper surface of the chip after superhydrophobic treatment obtained in S2 and drying to obtain a nanoparticle coffee ring, and mixing another portion of the nanoparticle sol with the pollutant and dripping it around the nanoparticle coffee ring to dry to form another coffee ring, with an intersection between the two coffee rings.

[0014] Furthermore, when preparing a chip with a light-trapping structure in S1, chromium is magnetron sputtered on the surface of a silicon wafer as a masking layer, and then a photoresist is spin-coated onto the surface of the silicon wafer. A laser direct writer is used to expose a predetermined pattern on the surface, and a pattern is formed after development. The silicon wafer is then cleaned with a chromium removal solution and a glue remover, respectively, to form a template for the light-trapping structure on the surface of the silicon wafer. Finally, etching and cleaning are performed to remove the surface template.

[0015] Furthermore, during the super-hydrophobic treatment in S2, it was immersed in a 5% perfluorosilane n-hexane solution for 30 minutes, then washed with anhydrous ethanol solvent and dried with a nitrogen gun, and then annealed at 110° C. for 30 minutes to form a hydrophobic layer with a monomolecular thickness;

[0016] Furthermore, before the super-hydrophobic treatment, the chip was cleaned by soaking in a piranha solution, which was a mixture of 70% concentrated sulfuric acid and 30% hydrogen peroxide solution, and the silicon wafer was completely immersed for 12 hours.

[0017] The present invention also relates to the application of the coffee ring cross-enrichment Raman chip in the rapid detection of water pollutants.

[0018] Furthermore, the water pollutant is triphenyltin chloride.

[0019] The present invention provides a chip and a nanoparticle composite substrate based on coffee ring cross enrichment. The substrate has a super-hydrophobic light-trapping structure and a nanoparticle sol with excellent Raman enhancement performance. The two are organically combined. The nanoparticles are pre-assembled in the light-trapping structure by evaporating droplets to form coffee rings in the detection link, and then the object to be tested is fully mixed and adsorbed with the nanoparticle solution, and then dripped on the surface of the chip to form a cross coffee ring mark. Under the action of the coffee ring effect, the nanoparticles are distributed to the edge of the droplets and assembled under the action of capillary force. After the droplets are completely volatilized, the object to be tested is completely adsorbed on the surface of the nanoparticles to form a mixed self-assembly system, so that the object to be tested is fully distributed in the hot spot area. Due to the coffee ring effect, the system is located in the action area of ​​the light-trapping structure, and its electric field strength is further enhanced under the light-trapping effect, thereby improving the stability and consistency of surface enhanced Raman spectroscopy detection. And under the dual effects of the coffee ring effect and super-hydrophobicity, the nanosol and the object to be tested are fully enriched on the coffee ring, further improving the sensitivity of the substrate. The problem of low sensitivity of existing chip-type substrates, as well as the problem of random agglomeration consistency and low stability of nanoparticle sol-type substrates, is solved. In addition, the detection area is locked by cross-positioning of coffee rings, avoiding the influence of heterogeneous distribution characteristics of coffee rings on detection consistency.

[0020] The present invention has the following beneficial effects:

[0021] 1. The super-hydrophobic chip provided by the present invention has both pollutants and nanoparticles enriched and enhanced at the intersection of two coffee rings. The concentration of pollutants and gold nanoparticles is the highest at the intersection, and the pollutants are fully immersed in the gaps between the nanoparticles during the volatilization process, and the enhancement effect is the strongest. After enrichment, it is visible to the naked eye under the micro Raman spectrum, and the pollutants can be quickly located at the intersection of the two coffee rings, while maintaining the consistency of the detection effect. The Raman signal of the target pollutant is obtained by using a Raman spectrometer to detect it.

[0022] 2. The super-hydrophobic treatment of the present invention is modified by perfluoroalkyltrichlorosilane and perfluoroalkyltriethoxysilane, and bonding is performed by removing one molecule of HCl and H2O respectively. Before modifying the chip, it is soaked and cleaned with piranha solution to oxidize the surface of the substrate and introduce hydroxyl reaction sites on the surface for cross-linking with perfluorosilane.

[0023] 3. Detection of target pollutants: Under the superhydrophobic effect, the droplets have a high concentration multiple. Under the guidance of the coffee ring effect, the nanoparticles adsorb the analyte and then deposit on the contact line between the droplet and the substrate. Under the guidance of the light trapping structure, the nanoparticles assemble within the structure to produce sub-nanometer-scale nanogaps, which improves the signal strength and stability. Under the light trapping effect, the signal strength is further enhanced, thereby improving the detection limit of the analyte.

[0024] 4. The present invention also discloses the detection application of triphenyltin chloride. The chip does not require pretreatment, has low cost, can be prepared on a large scale, and can perform highly sensitive quantitative detection of water pollutants.

[0025] 5. The period and spacing of the columnar array structure are adjusted by adjusting the mask, and the height is adjusted by the reactive ion etching time to adapt to the optical properties of the nanoparticles, so that it has a lower reflectivity at its plasmon resonance peak position, and further improves the substrate performance through the light trapping effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 are the microscopic morphologies of the light trapping structure; a, d) the top surface microscopic morphologies of the light trapping structure at different magnifications, b, c) the side surface microscopic morphologies of the light trapping structure at different magnifications.

[0027] Figure 2 The water contact angles of silicon wafer and light trapping structure; a) contact angle of untreated silicon wafer, b) contact angle of untreated light trapping structure, c) contact angle of light trapping structure treated with superhydrophobicity.

[0028] Figure 3 Microscopic morphology and UV-visible spectrum of gold nanorods; a) Microscopic morphology of gold nanorods, b) UV-visible spectrum of gold nanorods.

[0029] Figure 4 It is a double coffee ring cross mark.

[0030] Figure 5 Simulation of electric field distribution of gold nanorods and light trapping structures; a) Simulation of electric field distribution of gold nanorods on silicon wafer surface, b) Simulation of electric field distribution of gold nanorods on light trapping structure surface, c) Simulation of electric field distribution of light trapping structure, d) Simulation of electric field distribution of light trapping structure with gold nanorods distributed on the surface

[0031] Figure 6 Signal intensity and stability of gold nanorods and light-trapping structure-coupled gold nanorods; a) Signal intensity of 20 random points of gold nanorods adsorbed p-ATP, b) Signal intensity of 20 random points of gold nanorods-light-trapping structure adsorbed p-ATP.

[0032] Figure 7 Performance of gold nanorod-light-trapping structure in detecting triphenyltin chloride. a) Detection limit and b) linear regression analysis of gold nanorod-light-trapping structure in detecting TPhT. DETAILED DESCRIPTION

[0033] The embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only used to illustrate the present invention and should not be construed as limiting the scope of the present invention.

[0034] Example 1

[0035] A coffee ring cross-enrichment Raman chip for water pollutant detection. The invention realizes the effect through a gold nanorod composite silicon nanocolumn array structure and uses triphenyltin chloride as a target pollutant for detection as a demonstration of practical application.

[0036] The first step is to prepare a silicon chip with a light-trapping structure. First, magnetron sputter 200nm of chromium as a masking layer on the surface of the silicon wafer, and then spin-coat SU-8 photoresist with a coating speed of 3000rpm on the surface of the silicon wafer to form a 1μm photoresist template. Then, a laser direct writer is used to expose a predetermined pattern on the surface. After development, a pattern is formed, and then the silicon wafer is cleaned with a chrome removal solution and a debonding agent, respectively, to form a template for the structure on the surface of the silicon wafer. The light-trapping structure is prepared by wet etching. The etching solution is a 30%wt KOH solution at 80°C, and the etching rate is about 1μm / min. After the etching is completed, the silicon wafer is washed with deionized water, and then the surface template is removed with a chrome removal solution. Its microscopic morphology is as follows. Figure 1 shown.

[0037] The second step is super hydrophobic treatment. The surface hydrophobic treatment is soaked in 5% 1H, 1H, 2H, 2H-perfluorodecyl trichlorosilane n-hexane solution for 30 minutes, then washed with anhydrous ethanol solvent and blown dry with a nitrogen gun, and then annealed at 110°C for 30 minutes to form a monomolecular thick hydrophobic layer. The perfluorocarbon chain is chemically bonded to the surface of the light trapping structure to reduce the surface energy of the substrate. The water contact angle before and after the hydrophobic treatment is shown in Figure 2. Figure 2 The contact angle increased from 5.64° for the silicon wafer and 104.85° for the light trapping structure without superhydrophobic modification to 150.04° after treatment.

[0038] The third step is the synthesis of nanoparticles. The synthesis of nanoparticles includes but is not limited to nanorods, nanocones, nanospheres, etc. The substrate has no restrictions on the type of nanoparticles. The light field inside the structure is enhanced through the light trapping effect to achieve signal enhancement. In this embodiment, gold nanorods are used for Raman enhancement. The microscopic morphology and ultraviolet-visible spectrum of the gold nanorods are shown in Figure 3 , where the gold nanorods are 43nm in length, 12nm in diameter, and the plasmon resonance peak is 781nm.

[0039] Step 4: Pre-add nanoparticle sol droplets on the chip surface, dry at room temperature, and rinse with deionized water to remove excess surfactant to form the first coffee ring. This embodiment uses 5nM gold nanorod sol, and the surfactant is 5mM hexadecyltrimethylammonium bromide, with an addition amount of 5μL.

[0040] The fifth step is to detect mixed target pollutants. The synthesized nanoparticle sol is mixed with the target pollutant triphenyltin chloride at a ratio of 1:5. After fully mixing and adsorbing for 15 minutes, an appropriate amount of the mixed solution is dripped around the first coffee ring and waited for it to completely dry before forming a second cross coffee ring. The double coffee ring cross mark is as follows: Figure 4 shown.

[0041] The pollutants can be quickly located at the intersection of two coffee rings, and the concentration of pollutants is the highest at the intersection, and the enhancement effect is the strongest. The Raman spectrometer is used to detect it to obtain the Raman signal of the target pollutant.

[0042] In order to prove the superiority of the invention technology, the light trapping performance, Raman enhancement factor and detection effect of triphenyltin chloride of the technical solution were evaluated, and the light source used was a 785nm plane wave. Figure 5 a is the electric field distribution around the gold nanorods on the silicon wafer surface, and its maximum electric field strength is 1.4×10 5 V / m, Figure 5 b is the electric field distribution around the gold nanorods in the light trapping structure, and its maximum electric field intensity is 5.5×10 5 After the gold nanorods were distributed in the light trapping structure, the electric field distribution intensity around them was enhanced by about 4 times.

[0043] The Raman properties of the substrate were characterized, using p-aminothiophenol and rhodamine 6G as signal molecules, respectively. Figure 6 a Comparison of the substrate performance of gold nanorods, light trapping structures, and light trapping structures coupled with gold nanorods. The characteristic peak of p-aminothiophenol in the gold nanorod-light trapping coupled enriched substrate is 1078 cm -1 The average signal intensity was 109805.6, the average signal intensity of the light trapping structure was 373.4, and the average signal intensity of the gold nanorods was 24482.8. Compared with the signal intensity of the substrate and the gold nanorods, it increased by about 4.48 times, and compared with the single light trapping structure, the signal intensity increased by 294.07 times. The sensitivity of the substrate was characterized by using rhodamine 6G, reaching a minimum of 10 -12 The detection limit of M. At the same time, the coefficient of variation of the differences between different p-aminothiophenol peaks was only 0.921%, which had high stability and consistency.

[0044] This technical solution is used to detect triphenyltin chloride, such as Figure 7 The detection limit of the gold nanorod coupled light trapping structure substrate in this embodiment reaches 10-8M, which meets the limit value requirements specified in the water quality standard. And its linear regression coefficient R2 reaches 0.9915, which has the ability of quantitative detection.

[0045] The above-mentioned embodiments are only preferred technical solutions of the present invention and should not be regarded as limitations of the present invention. The embodiments and features in the embodiments of the present application can be arbitrarily combined with each other without conflict. The protection scope of the present invention shall be the technical solutions recorded in the claims, including the equivalent replacement solutions of the technical features in the technical solutions recorded in the claims. That is, equivalent replacement improvements within this scope are also within the protection scope of the present invention.

Claims

1. A coffee ring cross-enrichment Raman chip, characterized in that: It comprises a silicon chip with a light trapping structure, a hydrophobic layer is arranged on the chip, a single nanoparticle coffee ring or a coffee ring array is arranged on the hydrophobic layer, and at least one other coffee ring formed by self-assembly of nanoparticle sol and pollutants to be detected is also arranged on the hydrophobic layer, and there is an intersection between the coffee ring and the aforementioned coffee ring; the silicon chip is a column array chip, and has a reflectivity of less than 10% in the 400-800nm ​​spectral range; the nanoparticles are nanorods, nanocones or nanospheres; the material of the nanoparticles is gold or silver; the dosage ratio of the nanoparticle sol to the pollutants to be detected is 1:1 to 1:

10.

2. The coffee ring cross-enrichment Raman chip according to claim 1, characterized in that: The hydrophobic layer uses perfluorosilane as a hydrophobic agent.

3. The method for preparing the coffee ring cross-enrichment Raman chip according to any one of claims 1 to 2, characterized in that: The following steps are involved: S1. Using photolithography combined with wet etching to prepare a chip with a light trapping structure; S2, performing super-hydrophobic treatment on the chip obtained in S1, and processing the hydrophobic agent onto the chip structure; S3, preparing the nanoparticles into nanoparticle sol, dripping a portion of the sol on the upper surface of the chip after superhydrophobic treatment obtained in S2 and drying to obtain a nanoparticle coffee ring, and mixing another portion of the nanoparticle sol with the pollutant and dripping it around the nanoparticle coffee ring to dry to form another coffee ring, with an intersection between the two coffee rings.

4. The preparation method according to claim 3, characterized in that: When preparing a chip with a light-trapping structure, chromium is magnetron sputtered on the surface of the silicon wafer as a masking layer, and then photoresist is spin-coated onto the surface of the silicon wafer. A laser direct writer is used to expose a predetermined pattern on the surface, and a pattern is formed after development. The silicon wafer is then cleaned with a chromium removal solution and a glue remover, respectively, to form a template for the light-trapping structure on the surface of the silicon wafer. Finally, etching and cleaning are performed to remove the surface template.

5. The preparation method according to claim 3, characterized in that: Before super-hydrophobic treatment, the chip was cleaned by soaking in piranha solution for more than 12 hours.

6. Use of the coffee ring cross-enrichment Raman chip described in any one of claims 1 to 2 in the rapid detection of water pollutants.

7. The use according to claim 6, characterized in that: The water pollutant is triphenyltin chloride.

Images