CN107561057B - Dual-Enhanced Raman Detection System with Localized Surface Plasmon Amplifier - Google Patents

Abstract

The invention discloses a double-enhanced Raman detection system with a localized surface plasma amplifier, comprising an excitation light source, an optical fiber coupler, a detection probe, a localized surface plasma amplifier, a filter and a detector; The volume amplifier is set to avoid the problem that the weak Raman optical signal cannot be amplified due to the noise of spontaneous radiation in the amplifier itself; the energy transfer path of the surface plasmon resonance optical amplifier is "excitation laser" → "localized surface plasmon" → "Signal light", when the intensity of the Raman signal light is much smaller than that of the excitation laser, the signal light can obtain energy from the surface plasmon and be amplified; because the localized plasmon does not have an energy level structure, the amplifier will not be excited by the laser. It produces spontaneous emission light, which can be equivalent to an ideal amplifier with very low noise (very low input signal threshold), so it can amplify very weak Raman signals.

Description

Dual-Enhanced Raman Detection System with Localized Surface Plasmon Amplifier

technical field

The invention relates to the field of Raman detection, in particular to a double-enhanced Raman detection system with a localized surface plasmon amplifier.

Background technique

Those skilled in the art all know that elastic scattering and inelastic scattering occur when light is irradiated onto a substance. The scattered light of elastic scattering has the same wavelength as the excitation light, and the scattered light of inelastic scattering has wavelengths longer and shorter than that of the excitation light. composition, called the Raman effect, and the obtained spectrum is called the Raman spectrum. Raman spectroscopy belongs to molecular vibrational spectroscopy, which is the fingerprint of material molecules. Raman spectrometers based on Raman effect can be used to accurately and qualitatively identify samples. The analysis method of Raman spectroscopy generally does not require pretreatment of the sample, and it is easy to operate and has a short measurement time during the analysis process. The disadvantage is the low sensitivity.

Surface-enhanced Raman scattering (SERS) is a high-sensitivity spectroscopic analysis technique developed with the development of nanotechnology in the 1990s. Like Raman spectroscopy, SERS can be used to accurately and qualitatively identify samples; SERS has ultra-high analytical sensitivity, which is about 6-10 orders of magnitude higher than ordinary Raman analysis, and can analyze studies ranging from single molecules to large cells at the cellular level. object.

However, metal nanostructures (metal nanospheres, nanorods, nanowires, etc.) are generally used to enhance Raman spectroscopy; usually metal nanostructures only have an enhancement effect on light waves in a certain frequency range; The Mann spectrum has a certain width, and usually a part of the Raman frequency domain falls outside the range of the frequency domain that the metal nanostructure can enhance. In this case, the enhancement effect of the high-frequency Raman spectrum of the substance to be measured is weakened, which puts forward extremely high requirements on the sensitivity of the photodetector in the subsequent optical path.

On the other hand, the typical Raman characteristic peaks of the substance to be tested are usually at some specific Raman peak positions (ie, at different wavelengths). The traditional Raman spectrum detection method is to detect the full spectrum, that is, the Raman spectrum carrying the information of the substance to be tested enters the Raman spectrometer to obtain the Raman spectrum signal, and then the information of the substance to be tested is obtained through data processing. Raman spectrometers have complex structures, large volumes and high prices.

In view of the above problems, it is proposed to amplify the Raman signal light through an optical amplifier and then detect it. The current optical amplifiers mainly include EDFA and fiber Raman amplifiers. These amplifiers have spontaneous emission noise, and the lowest threshold of the input signal is about -40dBm (100nw) order of magnitude, and the power of the excitation light source in the actual Raman spectrum detection application is generally small, generally under 1w laser excitation, the signal intensity of Raman scattered light is usually several orders of magnitude of 10pw ~ 1nw, much smaller than these The threshold value of the optical amplifier cannot achieve amplification.

Therefore, in order to solve the above problems, a dual-enhanced Raman detection system is needed, which can effectively detect weak Raman signal light for low-power excitation light sources, and has a simple and compact structure, high detection accuracy, and low cost, which is conducive to popularization. .

SUMMARY OF THE INVENTION

In view of this, the purpose of the present invention is to overcome the defects in the prior art and provide a double-enhanced Raman detection system, which can effectively detect weak Raman signal light for a low-power excitation light source, and has a simple and compact structure and high detection accuracy. High, low cost, conducive to promotion.

The dual-enhanced Raman detection system of the present invention includes an excitation light source, a fiber coupler, a detection probe, a localized surface plasmon amplifier, a filter and a detector;

an excitation light source for generating excitation light and transmitting the excitation light to a fiber coupler through an optical fiber;

The fiber coupler is used to couple the excitation light emitted by the excitation light source and the Raman signal light generated and returned by the detection probe respectively, and transmit the coupled Raman signal light to the local surface plasmon amplifier through the optical fiber. enlarge;

The detection probe, whose input end is connected to the output end of the fiber coupler through an optical fiber, is used to generate and collect the Raman signal light of the substance to be tested under the excitation of the excitation light, and its working surface is provided with a first metal nanostructure to realize the primary Raman surface enhancement;

The localized surface plasmon amplifier is provided with a second metal nanostructure for generating localized plasmon, and the secondary Raman signal amplification is realized by transferring energy to the passing Raman signal light through the localized plasmon;

a filter, the input end of which is connected to the output end of the localized surface plasmon amplifier, and is used for filtering out the light with the same wavelength as the excitation light in the signal and obtaining the Raman light signal with the separated wavelength; the localized surface plasmon The amplifier includes a waveguide structure and a second metal nanostructure arranged in the waveguide structure, and the inside of the waveguide structure is in a vacuum state;

The detector is used to detect the Raman signal light coming out of the filter and convert it into an electrical signal for output processing.

Further, the wavelength corresponding to the absorption spectrum of the second metal nanostructure includes the wavelength of excitation light and the wavelength of Raman signal light.

Further, the filters and detectors are respectively multiple and set in one-to-one correspondence.

Further, the output end of the excitation light source is also connected with the input end of the local surface plasmon amplifier through an optical fiber.

Further, the waveguide is a tubular hollow waveguide, consisting of a hollow cavity and a peripheral tubular dielectric reflection layer, the second metal nanostructure is a metal nanoparticle located on the inner wall of the tubular dielectric reflection layer, and the metal nanoparticle forms a cylindrical shape Shell-core structure, the average particle size of the nanoparticles is d ₁ , the nanoparticle spacing is g ₁ , the length of the cylindrical shell-core structure is h ₁ , the d ₁ is 20-100 nm, and g ₁ is 1-10 nm, h ₁ is 1-100um.

Further, the waveguide is a tubular hollow waveguide, which is composed of a hollow cavity and a peripheral tubular dielectric reflection layer, the second metal nanostructure is a thin film located in the central layer and distributed along the radial direction, and the thin film is provided with periodic A circular hole, the diameter of the circular hole is d ₂ , the distance between the edges of adjacent circular holes is g ₂ , the thickness of the film is h ₂ , the d ₂ is 20-100 nm, g ₂ is 1-10 nm, and h ₂ is 1-100um.

Further, the waveguide is a tubular hollow waveguide, which is composed of a hollow cavity and a peripheral tubular dielectric reflection layer, the second metal nanostructure is a composite film located in the high-refractive index central layer and distributed along the radial direction, and the composite film includes A base film composed of carbon nanotubes and metal nanoparticles attached to the base film, the average particle size of the metal nanoparticles is d ₃ , the distance between adjacent nanoparticles is g ₃ , and the thickness of the base film is h ₃ , so Said _d3 is 20-100nm, g3 is _1-10nm , h3 is _1-100um .

The beneficial effects of the present invention are as follows: the dual-enhanced Raman detection system disclosed by the present invention is set up by a localized surface plasmon amplifier to avoid the fact that the amplifier itself has spontaneous radiation noise and cannot amplify the weak Raman optical signal. question. Traditional optical amplifiers have a minimum input signal threshold (usually 100nw) due to the existence of spontaneous radiation in the working medium. When using 1W laser excitation, the Raman optical signal intensity is about the order of 10pw-1nw, which is smaller than the threshold of traditional optical amplifiers. , so the weak Raman light signal cannot be amplified; and the energy transfer path of the surface plasmon resonance optical amplifier is "excitation laser" → "localized surface plasmon" → "signal light", when the intensity of the Raman signal light is much smaller than the excitation light When the laser is used, it can obtain energy from the surface plasmon and be amplified; because the localized plasmon does not have an energy level structure, it will not generate spontaneous emission light when it is excited by the laser, and it can be equivalent to a very low noise (input It is an ideal amplifier with extremely low signal threshold), so it can amplify very weak Raman signals; the structure is simple and compact, the detection accuracy is high, and the cost is low, which is conducive to popularization.

Description of drawings

Below in conjunction with accompanying drawing and embodiment, the present invention is further described:

Fig. 1 is the structural representation of the present invention;

2 is a schematic structural diagram of a detection probe in the present invention;

3 is a schematic diagram of a structure of a filter in the present invention and a schematic diagram of a corresponding typical Raman characteristic peak;

Fig. 4 is the absorption spectrum corresponding to the second metal nanostructure in the present invention;

Fig. 5 is the first structural schematic diagram of the localized surface plasmon amplifier in the present invention;

Fig. 6 is the second structural schematic diagram of the localized surface plasmon amplifier in the present invention;

FIG. 7 is a schematic diagram of the third structure of the localized surface plasmon amplifier in the present invention.

Detailed ways

1 is a schematic structural diagram of the present invention, FIG. 2 is a structural schematic diagram of a detection probe in the present invention, FIG. 3 is a schematic structural diagram of a filter in the present invention and a schematic diagram of a corresponding typical Raman characteristic peak, and FIG. Absorption spectra corresponding to two metal nanostructures, FIG. 5 is a schematic diagram of the first structure of the local surface plasmon amplifier in the present invention, FIG. 6 is a schematic diagram of the second structure of the local surface plasmon amplifier in the present invention, and FIG. The third structural schematic diagram of the localized surface plasmon amplifier in the invention, as shown in the figure, the double-enhanced Raman detection system in this embodiment includes an excitation light source 1, an optical fiber coupler 2, a detection probe 3, and a localized surface plasmon Amplifier 4, filter 5 and detector 6;

The excitation light source 1 is used to generate excitation light and transmit the excitation light to the fiber coupler 2 through an optical fiber; the excitation light source 1 can be an existing low-power laser light source, which is guaranteed to be suitable for practical application promotion; the intensity ratio of the Raman signal is The threshold of common amplifiers is 2 to 3 orders of magnitude smaller, and the use of high-power excitation light sources has the following disadvantages. On the one hand, continuous lasers with output powers up to 100-1000 watts are expensive and bulky, and are not suitable for use as instrument light sources; On the one hand, high-power lasers are easy to damage the samples to be tested, especially biomolecules; in addition, as the energy of the light source increases, the noise caused by its own power fluctuations will also increase.

The optical fiber coupler 2 is used to couple the excitation light emitted by the excitation light source 1 and the Raman signal light generated and returned by the detection probe 3 respectively, and transmit the coupled Raman signal light to the localized surface plasmon through the optical fiber Amplification is performed in the amplifier 4; the optical signal is split and combined through the optical fiber coupler 2, and the Raman signal light returned from the detection probe 3 is collected;

The detection probe 3, the input end is connected with the output end of the optical fiber coupler 2 through an optical fiber, and is used to generate and collect the Raman signal light of the substance to be tested 11 under the excitation of the excitation light, and its working surface is provided with a first metal nanostructure 7 A Raman surface enhancement is achieved; the first metal nanostructure 7 can be a silver or gold nanoparticle structure, and the first metal nanostructure 7 on which the substance to be tested is attached to the working surface is, under the action of excitation light, a single pull is achieved. Mann surface enhancement to obtain Raman signal light after one signal amplification;

The localized surface plasmon amplifier 4 is provided with a second metal nanostructure 8 for generating localized plasmons, and the secondary Raman signal amplification is realized by transferring energy to the passing Raman signal light through the localized plasmon; The second metal nanostructure 8 can be excited by the localized plasmon through the Rayleigh scattering light generated by the interaction between the excitation light and the first metal nanostructure 7 in the detection probe 3, and the localized surface plasmon amplifier 4 does not need a new laser light source As the excitation light, the Rayleigh scattered light (same wavelength as the original laser) reflected by the fiber Raman probe is used as the excitation light to excite the surface plasmon, and the energy is transferred to the Raman light through the surface plasmon, realizing the secondary The Raman signal is amplified. Since the Raman astigmatism is 2 to 3 orders of magnitude smaller than the above Rayleigh scattering light signal, the energy transfer path is "excitation laser" → "localized surface plasmon" → "Raman signal light", here "Localized surface plasmon" is equivalent to an intermediate transfer link, which transfers the energy of strong light (Rayleigh scattering light) to weak light (Raman light); because localized plasmon has no energy level structure, it is subjected to laser light No spontaneous radiation is generated during excitation, and it is equivalent to an ideal amplifier with extremely low noise, which can amplify very weak Raman signals; the localized surface plasmon amplifier 4 includes a waveguide structure and a second structure arranged in the waveguide structure. Metal nanostructure 8, the interior of the waveguide structure is in a vacuum state; the interior of the waveguide is evacuated to ensure that there is no Raman scattering in the waveguide structure, avoid noise interference, and achieve low-noise amplification of Raman signal light, thereby improving detection accuracy;

The filter 5, the input end of which is connected to the output end of the localized surface plasmon amplifier 4, is used to filter out the Rayleigh scattered light with the same wavelength as the excitation laser in the signal, and the Raman scattered light within a specific wavelength (range) It is extracted to form a series of Raman optical signals with separated wavelengths; as shown in Figure 3, the structure of the filter can be equivalent to a single-input cascaded multi-output bandpass filter, each bandpass filter only Raman light of a specific wavelength is extracted and irradiated on the corresponding detector, and light of other wavelengths can pass through without damage; for a specific substance, it is not necessary to measure the entire Raman spectrum, but only the specific spectral line can be measured. Qualitative and quantitative analysis; therefore, for different substances, different filter combinations are required to filter out specific spectral lines. Different from the traditional Raman spectrometer, its cost will be greatly reduced, and the volume can be made very small, even on a chip; it is characterized by small size and low price, which is convenient for promotion.

The detector 6 is used to detect the Raman signal light coming out of the filter 5 and convert the detected signal into an electrical signal for output processing; qualitative and quantitative analysis of the substance by the signal detected by the detector 6 is the prior art, here No longer.

In this embodiment, the wavelengths corresponding to the absorption spectrum of the second metal nanostructures 8 include the wavelength of the excitation light and the wavelength of the Raman signal light; as shown in the figure, that is, the wavelength of the excitation light λ _pump and the wavelength of the Raman signal light λ _signal All are located in the wavelength band corresponding to the absorption spectrum of the second metal nanostructure 8 ; ensuring that the energy can be successfully transmitted to the signal light.

In this embodiment, the filters 5 and the detectors 6 are respectively multiple and set in one-to-one correspondence; the passing wavelength corresponding to a single filter 5 is the typical characteristic peak corresponding to the substance, and the multiple typical characteristic peaks of the substance are detected. , to improve the detection accuracy; the substance usually has multiple characteristic peaks, and the analysis of the multiple characteristic peaks can realize the qualitative and quantitative of the substance.

In this embodiment, the output end of the excitation light source 1 is also connected with the input end of the localized surface plasmon amplifier 4 through an optical fiber; the surface plasmon intensity of the second metal nanometer is further improved, the energy transfer efficiency is improved, and the Raman signal is facilitated Light intensity is amplified.

In this embodiment, the waveguide structure is a hollow waveguide composed of a hollow cavity 9 with an emissivity n ₁ =1 and a tubular reflective cladding 10 with a refractive index n ₂ greater than 1, and the second metal nanostructure 8 is located in the The metal nanoparticles on the inner wall of the tubular dielectric reflective layer 10, and the metal nanoparticles form a cylindrical shell-core structure, the average particle size of the nanoparticles is d ₁ , the nanoparticle spacing is g ₁ , and the cylindrical shell-core structure has The length is h ₁ , the d ₁ is 20-100 nm, g ₁ is 1-10 nm, and h ₁ is 1-100 um. The inside of the shell-core structure is gold or silver precious metal nanoparticles, and the outer surface is covered with a layer of anti-oxidation film with a thickness of several nanometers, which can protect the metal nanoparticles from being oxidized for a long time and maintain high Raman-enhanced activity; this shell The nuclear structure can be produced by chemical synthesis. By adjusting the chemical reaction time and the formula of the solution, the size of the metal nanoparticles and the thickness of the protective film can be changed; in addition, the atomic layer coating instrument can also be used. The particles are coated with a protective layer to achieve a core-shell structure.

In another embodiment, the waveguide structure is a hollow waveguide composed of a hollow cavity 9 with an emissivity n ₁ =1 and a tubular reflective cladding 10 with a refractive index n ₂ greater than 1, and the second metal nanostructure 8 It is a film located in the hollow cavity 9 and distributed along the radial direction. Periodic circular holes are opened in the film. The diameter of the circular hole is d ₂ , and the distance between the edges of adjacent circular holes is g ₂ . h ₂ , the d ₂ is 20-100 nm, g ₂ is 1-10 nm, and h ₂ is 1-100 um; the metal nanostructure 8 can be processed by existing nano-fabrication methods to ensure its accuracy; specifically, It can be guaranteed by processes such as "nanoimprinting", "nanolithography" or direct writing by focused ion beam (FIB). The reticulated second metal nanostructures 8 can also be directly grown by material chemical methods, and different geometric dimensions can be obtained by adjusting the growth process parameters, so as to ensure the parameter accuracy of the metal nanostructures 8 .

In another embodiment, the waveguide structure is a hollow waveguide composed of a hollow cavity 9 with an emissivity n ₁ =1 and a tubular reflective cladding 10 with a refractive index n ₂ greater than 1, and the second metal nanostructure 8 It is a composite film distributed along the radial direction in the hollow cavity 9, the composite film includes a base film composed of carbon nanotubes 12 and metal nanoparticles attached to the base film, and the average particle size of the metal nanoparticles is d ₃ , the distance between adjacent nanoparticles is g ₃ , the thickness of the base film is h ₃ , the d ₃ is 20-100 nm, g ₃ is 1-10 nm, and h ₃ is 1-100 um. The manufacturing steps of the second metal nanostructure 8 are as follows: the first step, the carbon nanotubes 12 are grown by chemical vapor deposition (CVD) method; the second step, the carbon nanotubes 12 are made into a suspension liquid , and the carbon nanotube base film can be made by vacuum filtration, titration drying or centrifuge spin coating; the third step is to make chemical silver sol or gold sol and coat on the carbon nanotubes On the base film, the second metal nanostructure 8 is formed after drying; or a layer of precious metal film is sputtered on the carbon nanotube base film, and then grown into metal nanoparticles by high temperature annealing. In the three steps, a large number of process tests are required to determine process parameters, so as to ensure the fabrication accuracy of the geometric parameters of the second metal nanostructures 8 .

This embodiment describes three methods for realizing the second metal nanostructure 8, and these three methods can be used alone or in combination to realize the localized surface plasmon amplifier of the present invention.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be Modifications or equivalent substitutions without departing from the spirit and scope of the technical solutions of the present invention should be included in the scope of the claims of the present invention.

Claims (7)

1. a double-enhanced Raman detection system with a localized surface plasmon amplifier, is characterized in that: comprise excitation light source, optical fiber coupler, detection probe, localized surface plasmon amplifier, filter and detector; an excitation light source for generating excitation light and transmitting the excitation light to a fiber coupler through an optical fiber; The fiber coupler is used to couple the excitation light emitted by the excitation light source and the Raman signal light generated and returned by the detection probe respectively, and transmit the coupled Raman signal light to the local surface plasmon amplifier through the optical fiber. enlarge; The detection probe, whose input end is connected to the output end of the fiber coupler through an optical fiber, is used to generate and collect the Raman signal light of the substance to be tested under the excitation of the excitation light, and its working surface is provided with a first metal nanostructure to realize the primary Raman surface enhancement; The localized surface plasmon amplifier is provided with a second metal nanostructure for generating localized plasmon, and the localized plasmon transfers energy to the passing Raman signal light to realize secondary Raman signal amplification; The surface plasmon amplifier includes a waveguide structure and a second metal nanostructure arranged in the waveguide structure, and the inside of the waveguide structure is in a vacuum state; a filter, the input end of which is connected to the output end of the localized surface plasmon amplifier, and is used to filter out the light with the same wavelength as the excitation light in the signal and obtain the Raman light signal with the separated wavelength; The detector is used to detect the Raman signal light coming out of the filter and convert it into an electrical signal for output processing. 2 . The dual-enhanced Raman detection system according to claim 1 , wherein the absorption spectrum of the second metal nanostructure includes excitation light wavelength and Raman signal light wavelength. 3 . 3 . The dual-enhanced Raman detection system according to claim 2 , wherein the filters and the detectors are respectively multiple and set in one-to-one correspondence. 4 . 4 . The dual-enhanced Raman detection system according to claim 1 , wherein the output end of the excitation light source is further connected to the input end of the local surface plasmon amplifier through an optical fiber. 5 . 5 . The dual-enhanced Raman detection system according to claim 1 , wherein the waveguide is a tubular hollow waveguide, which is composed of a hollow cavity and a peripheral tubular dielectric reflection layer, and the second metal nanostructure is located in the tubular shape. 6 . Metal nanoparticles on the inner wall of the dielectric reflection layer, and the metal nanoparticles form a cylindrical shell-core structure, the average particle size of the nanoparticles is d ₁ , the nanoparticle spacing is g ₁ , and the length of the cylindrical shell-core structure is h ₁ , the d ₁ is 20-100 nm, the g ₁ is 1-10 nm, and the h ₁ is 1-100 um. 6 . The dual-enhanced Raman detection system according to claim 1 , wherein the waveguide is a tubular hollow waveguide composed of a hollow cavity and a peripheral tubular dielectric reflection layer, and the second metal nanostructure is located in the center. 7 . The film is radially distributed in the layer. Periodic circular holes are opened in the film. The diameter of the circular hole is d ₂ , the distance between the edges of adjacent circular holes is g ₂ , and the thickness of the film is h ₂ . Said _d2 is 20-100nm, g2 is _1-10nm , h2 is _1-100um . 7 . The dual-enhanced Raman detection system according to claim 1 , wherein the waveguide is a tubular hollow waveguide composed of a hollow cavity and a peripheral tubular dielectric reflection layer, and the second metal nanostructure is located in a high A composite film with a radial distribution in the center layer of refractive index, the composite film includes a base film composed of carbon nanotubes and metal nanoparticles attached to the base film, the average particle size of the metal nanoparticles is d ₃ , and the phase The distance between adjacent nanoparticles is g ₃ , the thickness of the base film is h ₃ , the d ₃ is 20-100 nm, g ₃ is 1-10 nm, and h ₃ is 1-100 um.

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