WO2011066667A1 - 一种基于共振角度测量的spr传感器及其测量方法 - Google Patents

一种基于共振角度测量的spr传感器及其测量方法 Download PDF

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WO2011066667A1
WO2011066667A1 PCT/CN2009/001356 CN2009001356W WO2011066667A1 WO 2011066667 A1 WO2011066667 A1 WO 2011066667A1 CN 2009001356 W CN2009001356 W CN 2009001356W WO 2011066667 A1 WO2011066667 A1 WO 2011066667A1
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spr sensor
refractive index
spr
measurement
resonance angle
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PCT/CN2009/001356
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French (fr)
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汪之又
朱劲松
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国家纳米科学中心
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Priority to PCT/CN2009/001356 priority Critical patent/WO2011066667A1/zh
Publication of WO2011066667A1 publication Critical patent/WO2011066667A1/zh

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N21/00—Investigating or analysing materials by the use of optical means, i.e. using sub-millimetre waves, infrared, visible or ultraviolet light
    • G01N21/17—Systems in which incident light is modified in accordance with the properties of the material investigated
    • G01N21/55—Specular reflectivity
    • G01N21/552—Attenuated total reflection
    • G01N21/553—Attenuated total reflection and using surface plasmons

Definitions

  • the present invention relates to the field of sensors and sensing technology, and more particularly to an SPR sensor based on resonance angle measurement and a measuring method thereof.
  • SPR Surface Plasmon Resonance
  • SPW surface Plasmon Wave
  • ATR attenuated total reflection
  • the ⁇ -polarized beam is parallel to the wave vector component of the interface and the wave vector of the SPW
  • the beam energy is coupled into the SPW through the evanescent wave, causing the reflected light energy reflected by the interface to be weakened.
  • the ratio of energy coupling into SPW is the largest.
  • This phenomenon is called SPR phenomenon, and the reflected light energy is the weakest.
  • the incident angle corresponding to the weakest reflected light energy is called the resonance angle, and the peak of the intensity decay on the response curve of the reflected light intensity is called the resonance absorption peak. Since the change of dielectric thickness or refractive index near the interface will cause the wave vector of SPW to change, and then change the coupling property between the beam and SPW energy, resulting in a change in the resonance angle. Therefore, the change of the resonance angle that is easy to detect can be used to detect the dielectric. A change in thickness or refractive index.
  • the SPR sensor based on resonance angle measurement is a widely used SPR sensor.
  • the detection resolution and response time of the SPR sensor are very important performance indicators, where the resolution is the refractive index of the detector. (Refractive Index Uni t, cartridge called RIU) Minimum measurable change description.
  • SPR sensors based on resonance angle measurements are an important class of SPR sensors.
  • the SPR sensors based on the resonance angle measurement can be mainly classified into two types according to the measurement mode.
  • One of them is to use a collimated beam, and the position of the rotating prism and the unit photodetector is rotated by a mechanical device to realize the scanning of the incident angle.
  • Its disadvantage is that its measurement results are easily affected by mechanical drift, resulting in large errors.
  • the other is the position of fixed prisms and multi-cell photodetectors (such as linear diode arrays, LDA, or charge coupled devices, CCD), which use a focused beam to cover a range of incident angles (K.
  • This type of SPR sensor is capable of eliminating the aforementioned shortcomings of the first type of SPR sensor, but its resolution is affected by the number of detector units covered by the reflected light, and the further the distance between the prism and the multi-unit photodetector, the detection The higher the number of cells, the higher the resolution, but due to the size limitations of the SPR sensor, it is difficult to achieve higher resolution.
  • U.S. Patent No. 6,666,787 proposes a technical solution for adding a dielectric layer which can adjust the refractive index by voltage change between the metal layer and the detecting object.
  • the voltage applied to the dielectric layer is changed to adjust the refractive index, so that the intensity of the reflected light measured by the unit detector is minimized, and the deviation of the resonance angle can be obtained by measuring the voltage change at this time.
  • the amount of shifting further obtains information on the change in the refractive index of the detected object.
  • the unit photodetector is used to measure the intensity of the reflected light at a fixed position and judge whether the measurement result is the minimum value of the intensity, so that the error caused by the mechanical operation is avoided.
  • the detection noise due to the influence of the detection noise, it is difficult to accurately and repeatedly obtain the minimum value of the reflected light intensity, and therefore it is difficult to accurately obtain the offset of the resonance angle.
  • US Pat. No. 6,784,999 proposes a difference in light intensity obtained by a detector array having at least two detector units.
  • the scheme needs to strictly adjust the position of the photodetector array before the detection, so that the position where the intensity of the reflected light is the smallest is in the light.
  • the center of the array of electrical detectors is such that the difference between the difference between the left and right portions of the photodetector array and the sum, that is, the differential signal is close to zero.
  • the deviation of the resonance angle can be obtained by the differential signal, thereby realizing the measurement of the refractive index change of the detected object, and using the scheme when the incident light beam having a wavelength of 635nm resolution up to 3 x 10- 8 RIU (NJ Tao , S. Bous saad, WL Huang, RA Arechaba leta, and J. D'Agnese, H igh resolut ion surf ace plasmon resonance spectroscopy , Review of Sc ient if ic Ins trument s, 70, 12, 4656, 1999 ).
  • the object of the present invention is to provide an SPR sensor based on resonance angle measurement with a short response time, high linearity, and high resolution, and a measurement method thereof.
  • an SPR sensor based on resonance angle measurement comprising:
  • a beam output device for outputting a focused beam of linearly polarized light
  • the SPR sensor chip includes a dielectric layer, a metal layer in contact with the object to be detected, and a sample cell containing the object to be detected;
  • a photodetecting device which is a linear array of differential photodetectors comprising a plurality of photodetector units for receiving a focused beam reflected by an SPR structure reflecting device;
  • An adjustable external field generating device for generating an external field and applying the external field to a dielectric layer of the SPR sensing chip to adjust a refractive index of the dielectric layer;
  • the linear array of the differential photodetectors is a boundary point of the linear array center of the photodetector, and the photodetector unit is divided into two groups of the same number.
  • two sets of photodetector units are respectively Output signal superposition, then two sets of photodetectors
  • the superimposed signals of the detector units are respectively subjected to a difference sum, and the ratio of the difference and the sum is obtained as an output signal of the linear array of the differential photodetectors.
  • a refractive index tunable material such as an acousto-optic material; an external field generated by the tunable external field generating device is applied to the dielectric layer.
  • the electro-optic material is a material having a linear response of a refractive index to an electric field change, that is, a material having an electrooptic effect, and an inorganic electro-optic material such as L iNb03, KDP, ADP, KD*P, L i Ta03 or DAST (4 - mercapto group) may be selected.
  • Organic electro-optic materials such as amino-N-mercapto-nonyl phthalate and their composites.
  • the SPR measurement system further comprises data processing means for receiving an output of the photodetection device and deriving the object (usually a solution) according to an external field applied by the adjustable external field generating device rate.
  • the photodetector of the photodetecting device can select a photoelectric detector sensitive to optical parameters such as a position sensitive detector, a balance detector, a CCD, a multi-unit photon counter, etc., wherein the optical parameters include beam intensity, Phase and amount of light, etc.
  • the external field comprises an electric field, a magnetic field, a sound field or a temperature.
  • the sample cell can be made of glass, plastic or the like.
  • the present invention also provides a method for measuring a refractive index of a detector based on the above SPR sensor, comprising the following steps:
  • the refractive index of the detected object is obtained.
  • the step (1) further includes adjusting the SPR sensor such that the angle of the resonance angle from the center of the detector array of the photodetecting device is less than 0.12 degrees, and then recording the difference of the output of the photodetecting device at this time. Signal as a calibration step differential signal number.
  • the dynamic measurement range of the invention is large, and the measurement automation is high.
  • the measuring system of the invention has a compact structure and strong stability.
  • the measuring method of the present invention has the characteristics of rapid response.
  • the measuring method of the present invention has the characteristics of high detection resolution.
  • the measuring method of the present invention has the characteristics of high linearity.
  • FIG. 1 shows a principle of detection based on a linear array of differential photodetectors, wherein the resonance angle, ⁇ , respectively, covers the range of the incident angle of the detector boundary,
  • part a is a schematic diagram of the structure of the measuring device
  • part b is a WCSPR resonance due to a change in the substance of the detected layer 10 and a voltage applied to the dielectric layer 6.
  • part c is to adjust the dielectric layer 6 applied voltage after the change of the material of the detected layer 10 causes the differential photodetector array output signal to change until the output signal
  • part d is a schematic diagram of the correspondence between the applied voltage of the dielectric layer 6 and the refractive index of the substance of the layer 10 to be detected according to the parts b and c;
  • FIG. 3 is a graph showing a response curve of a resonance angle and intensity of a WCSPR structure according to an embodiment of the present invention as a function of a refractive index of a layer to be detected;
  • FIG. 4 is a graph showing a response curve of a resonance angle and intensity of a WCSPR structure as a function of a refractive index change of a dielectric layer according to an embodiment of the present invention
  • Figure 5 is a diagram showing the resonance angle of the WCSPR structure of one embodiment of the present invention as a function of the refractive index of the layer to be tested;
  • Figure 6 is a graph showing the calculation results of the resonance angle of the WCSPR structure according to an embodiment of the present invention as a function of the refractive index change of the dielectric layer;
  • Figure 7 is a diagram showing the application of the simulated simulation in one embodiment of the present invention. Corresponding relationship between the external field voltage of the layer and the refractive index of different detectors;
  • FIG. 8 is a view showing a correspondence relationship between an external field voltage applied to a dielectric layer and a refractive index of a different detector by a calculation in another embodiment of the present invention
  • Fig. 9 shows a linearity simulation statistical result of the patent US666787
  • Fig. 10 shows a linearity simulation statistical result of the patent US6784999
  • Fig. 11 shows another linearity simulation statistical result of the patent US6784999
  • Figure 13 shows another linearity simulation statistical result of the present invention.
  • the external field compensation is combined with the linear array of differential photodetectors to provide a differential SPR sensor based on external field compensation.
  • the SPR sensor is linear with respect to the existing differential SPR sensor (ie, based on differential photodetector).
  • the array's SPR sensor) improves the linearity of the measurement results.
  • the differential SPR sensor based on the external field compensation of the embodiment can also reduce the operation complexity of the differential SPR sensor and avoid the cumbersome zero adjustment operation.
  • the SPR sensing chip includes an upper metal layer 5, a dielectric layer 6, a lower metal layer 7, and a sample cell 14.
  • the chip may be prepared on the glass substrate 13 or the prism 4, and the sample cell 14 is disposed at the lower surface of the lower metal layer 7, and a gap is left between the lower surface of the lower metal layer 7 and the sample cell 14.
  • the sample cell 14 is used for accommodating the object 10 to be tested, and the liquid level of the object to be detected 10 (the substance to be detected 10 is generally a liquid substance) is in contact with the lower surface of the lower metal layer 7.
  • the present embodiment can also add the biomarker 9 at the interface between the lower metal layer 7 and the object 10 to be tested, depending on the concentration and type of the object to be detected.
  • the refractive index is sensitive to the refractive index of the dielectric layer 6 and the refractive index n 4 of the detected object 10 (which may also be biomarker 9 according to the application) , their expression is as in Equation 1-1.
  • Figure 1 shows the principle of detection based on a linear array of differential photodetectors, wherein the detector signal is defined as Equation 1-2.
  • R is the response of the intensity of the reflected light in the tunable SPR sensor to the angle of incidence.
  • the ⁇ ⁇ value is usually less than 1 degree, which is the deviation of the resonance angle from the center of the detector, and ⁇ is half of the incident angle range covered by the detector array, ⁇ is much larger than
  • Equations 1-9 indicate that the measurement of n 4 can be achieved by measuring the change of n 2 , and the measurement result is independent of whether or not the ⁇ value is zero.
  • a standard having a known refractive index can be selected first to obtain a resonance angle when the SPR sensor chip uses a standard. Then replace the standard of the SPR sensor chip with the object 10 to be detected. It can be seen from Equations 1-9 that by changing the refractive index n 2 of the dielectric layer 6 to an appropriate value, the refractive index change caused by the replacement of the analyte in the SPR sensor chip can be compensated for. Thereby the resonance angle of the entire SPR sensor chip is unchanged.
  • the refractive index n 4 of the object 10 to be tested is reversed.
  • the above principle can be used to change the refractive index n 2 by applying an external field to the dielectric layer 6 to compensate for the change of the refractive index n 4 of the detected object, so that the measurement of n 4 can be converted into a relatively small tube. Single measurement of n 2 .
  • 2J differential detector array A and B are similar in signal size, so J is far less than 1, which also causes ⁇ to be too large (at least 10 degrees), so the solution is discarded.
  • the combination of the external field compensation measurement method and the differential SPR sensor can effectively improve the linearity of the measurement and reduce the system error.
  • the zeroing step of the ordinary differential SPR sensor can be omitted or collapsed. , thus effectively improving the measurement efficiency.
  • the embodiment provides a tunable SPR sensor based on a linear array of differential photodetectors capable of high linearity measurement.
  • the SPR sensor comprises: a wavelength of 980 nm Laser 1, polarizer 2 (if laser 1 output beam is p-polarized, polarizer 2 can be used), lens 3, prism 4 with refractive index of 1.70553 (Q980nm), gold layer 5, dielectric layer 6, lower The gold layer 7, the adjustable voltage output device 8, the object to be detected 10 (which may also be a biomarker 9 depending on the application), the differential photodetector linear array 11, the data processing system 12, and the sample cell 14.
  • the refractive index of gold is
  • the dielectric layer 6 uses a polymer material having an electrooptic effect (Kun Wang, et a l. Hybrid d ifferent ia l interrogation method for sensit ive surf ace plasmon resonance measurement enabled by electro-opt ica l ly tunable SPR sensors, Opt Ics Expres s, 17, 4468, 2009 ), having a refractive index of 1.60388 and a thickness of 2800 nm.
  • the upper metal layer 5, the dielectric layer 6 and the lower metal layer 7 are sequentially prepared on the bottom surface of the prism 4, and the adjustable voltage output device 8 is controlled by the data processing system 12, and the voltage output terminal of the adjustable voltage output device 8 and the upper metal The layer 5 and the lower metal layer 7 are connected.
  • the beam generated by the laser 1 is focused by the lens 3 at the interface of the prism 4 and the upper metal layer 5, and is reflected at this interface into the linear array 11 of the differential photodetectors.
  • a glass substrate 13 may be disposed on the bottom surface of the prism 4, and the glass substrate 13 and the prism 4 have the same refractive index, and the gap between the two is filled with a matching layer having the same refractive index.
  • the upper metal layer 5, the dielectric layer 6, and the lower metal layer 7 are sequentially prepared on the glass substrate 13.
  • the light beam generated by the laser 1 is focused by the lens 3 at the interface of the glass substrate 13 and the metal layer 5, and is reflected at this interface into the differential photodetector linear array 11.
  • the sample cell 14 is used for loading and dropping the object to be tested 10.
  • the material is generally selected from poly(dimethyls iloxane, PDMS).
  • the prism 4, the upper metal layer 5, the dielectric layer 6, the lower metal layer 7, and the object to be detected 10 (which may also be biomarkers 9 according to the application) of the tunable SPR sensor in this embodiment employ waveguide coupling surface plasmon resonance (waveguide) -coupled SPR, WCSPR) structure.
  • the WCSPR reflected optical power expression is 2-1.
  • ⁇ +1 is the reflectivity at the interface of the adjacent layer, which is the thickness of each layer
  • k. x is the wave vector component of the parallel interface in the prism
  • ⁇ is the wavelength of the incident light
  • ⁇ is the incident angle
  • k. z i is the wave vector component of each vertical interface
  • n is the refractive index of each layer.
  • the incident light has a wavelength of 980 nm
  • the prism is a ZF-3 prism
  • the refractive index is 1.7053.
  • the upper metal layer 5 and the lower metal layer 7 are made of Au, and have a refractive index of 0.185145+6.15041.
  • the dielectric layer has a refractive index of 1.60388, a thickness of 2.8 ⁇ , an electro-optic coefficient of 10 pm/V, no biomarker 9, and the detector array covers an incident angle range of 3 degrees.
  • FIG. 3 shows the resonance angle and intensity of the WCSPR structure of the present embodiment with the detected layer
  • the response curve of the refractive index change FIG. 5 shows the response of the resonance angle with the change of the refractive index of the detected layer 9; changing the refractive index of the dielectric layer 6, the reflected light intensity and the resonance angle of the WCSPR structure also change, as shown in FIG.
  • the response curve of the WCSPR structure resonance angle and intensity as a function of the refractive index change of the dielectric layer is shown.
  • the refractive index of the dielectric layer 6 is linearly adjusted by changing the output voltage of the adjustable voltage output device 8 based on the electrooptic effect.
  • Electro-optical effect Electro-Optical
  • An optical material with electro-optic effect can change the refractive index n by ⁇ n by applying an electric field, such as 2-2, where d is the material thickness. V is the voltage applied to the material, and ⁇ 33 is the electro-optic coefficient.
  • the multi-cell photodetector 11 receives the light beam reflected from the WCSPR structure covering a certain angular range, and then divides the unit of the multi-unit detector into two halves along the coverage angle range, which are respectively called A and B parts. By summing the responses of the two parts to the beam, two results are obtained, which are called A and B, respectively, and the calibration signal is obtained by the (AB) I (A+B) operation of part b in Fig. 2. It can be known from (1-9) that the measurement result is independent of the result obtained by the (AB)/(A+B) operation before the measurement is started. Therefore, the embodiment can save the zero adjustment operation of the detector array, and the measurement time is greatly saved. Reduced operational complexity of the measurement.
  • the method of performing refractive index detection using the SPR sensor of the present embodiment includes the following steps:
  • Calibration step A standard of known refractive index (Phosphate Buffer Solution (PBS)) is introduced into the sample cell 14 in the SPR sensor chip.
  • PBS Phosphate Buffer Solution
  • the voltage output end of the adjustable voltage output device 8 is connected to the upper gold layer 5 and the lower gold layer 7, and the output voltage is 0V, and the output beam of the laser 1 passes through the lens 3. (If the output beam of the laser 1 is not P-polarized, it needs to pass through the polarizing plate.
  • (2-2) Initially calculate the voltage value S required to return the differential signal to the calibration point, and then adjust the applied voltage of the dielectric layer 6 in steps of 10 mV in the range of S-5V to S+5V.
  • the differential photodetector linear array 11 receives the reflected beam at the interface of the prism 4 (if the glass substrate 13 is used) and the upper metal layer 5 each time the voltage value is changed, the data processing system 12 is based on the difference
  • the output of the linear array 11 of the photodetector obtains the differential signal (AB) I (A+B) and is compared with the differential signal of the calibration step until the differential signal measured in this step is equal to the differential signal of the calibration step, and the recording is added at this time.
  • the voltage, and the measurement result of the refractive index of the detected object is obtained according to the correspondence relationship between the external field voltage applied to the dielectric layer and the refractive index of the different detected objects, and the measurement result is shown in part d of FIG.
  • the correspondence between the external field voltage applied to the dielectric layer and the refractive index of different detected objects can be
  • FIG. 7 is a view showing a correspondence relationship between an external field voltage applied to a dielectric layer and a refractive index of a different detected object in an embodiment of the present invention; in this embodiment, the detected object 10 has a refractive index of 1.333, and The differential signal of the detector array of the calibration step in this embodiment is 0; FIG. 8 shows the correspondence between the external field voltage applied to the dielectric layer and the refractive index of different detectors calculated by another calculation in the embodiment of the present invention. In this embodiment, the detected object 10 has a refractive index of 1.333, and the differential signal of the detector array of the calibration step is -0.01582.
  • this embodiment does not require a cumbersome zeroing operation in the calibration step. but Yes, in actual measurement, the resonance angle can be matched to the center of the detector array as much as possible according to the actual situation, which helps to further improve the linearity of the measurement. 0 ⁇ The linearity of the measured linearity can be maintained above 0.9999.
  • the fixed detection object is PBS.
  • a part of the incident angle range is selected, and the reflected light intensity calculated by (1-2) is integrated according to the two parts A and B, and the differential signal (AB)/(A+B) is calculated.
  • the value S1 is recorded, and then the refractive index of the detector is changed to perform a refractive index scan of the dielectric layer as in (2-2).
  • the simulation principle of the patent US666787 is to record the angle corresponding to the lowest point of the reflected light before changing the refractive index, and then change the refractive index and the voltage on the dielectric layer so that the angle corresponding to the lowest point of the reflected light at this time coincides with the previous coincidence.
  • the simulation principle of the patent US6784999 is to adjust the resonance angle to the center of the detector before changing the refractive index, and then change the refractive index and record the ratio.
  • Figure 9 is a Monte Carlo calculation of the US666787 linearity under Gaussian noise with a 40dB signal-to-noise ratio.
  • the prism has a refractive index of 1.7053, a gold layer thickness of 40 nm, a refractive index-adjustable dielectric layer thickness of 50 legs, and an incident light wavelength of 980 nm.
  • the linearity expectation is 0. 99903.
  • Figure 10 is a Monte Carlo calculation of the US6784999 linearity under the condition of Gaussian noise with a 40dB signal-to-noise ratio.
  • the refractive index of the prism is 1.7053
  • the thickness of the gold layer is 40 legs
  • the wavelength of the incident light is 980 nm.
  • the resonance angle has no deviation from the center of the detector.
  • the linearity expectation is 0. 99961.
  • Figure 11 shows the Monte Carlo calculation of the US6784999 linearity under the condition of Gaussian noise with a 40dB signal-to-noise ratio.
  • the refractive index of the prism is 1.7053
  • the thickness of the gold layer is 40 nm
  • the wavelength of the incident light is 980 nm
  • the resonance angle is 0.11 degree to the center deviation of the detector.
  • the linearity expectation is 0. 99924.
  • Figure 12 is a Monte Carlo simulation of the linearity of the present invention under Gaussian noise with a 40 dB signal to noise ratio.
  • the laser output beam has a wavelength of 980 legs
  • the prism 4 and the glass substrate 13 have a refractive index of 1.7053 (Q980nm)
  • the refractive index of gold is 0.185145+6.15041
  • the thickness of the gold layer 5 and the lower gold layer 7 are both 30 nm
  • the dielectric layer 6 has a refractive index of 1.60388 and a thickness of 2800 nm.
  • the resonance angle has no deviation from the center of the detector. Linearity expectation is 0.9998
  • Figure 13 is a Monte Carlo simulation result of the linearity of the present invention under Gaussian noise with a 40 dB signal to noise ratio superimposed.
  • the output beam wavelength of the laser is 980.
  • the refractive index of the prism 4 and the glass substrate 13 is 1.7053 (Q980nm)
  • the refractive index of gold is 0.185145+6.15041
  • the thickness of the gold layer 5 and the lower gold layer 7 are 30 nm
  • the refractive index of the dielectric layer 6 is 1.60388.
  • thickness is 2800nm.
  • the resonance angle is 0.12 degrees from the center of the detector. Linearity expectation is 0.99959
  • the present embodiment can also increase the linear range of the measurement. Due to the increase of the linear range, it is not necessary to perform strict zero adjustment before the measurement in this embodiment, which greatly saves the measurement time.
  • the measurement method according to the present invention is based on the principle of signal feedback and external field adjustment of the refractive index of the dielectric layer in the SPR structure, and has a large dynamic measurement range and a high degree of measurement automation.
  • the measuring system of the present invention is compact in structure and strong in stability.
  • the non-mechanical scanning method is used by the external field controllable device, and it is not necessary to use a conventional device such as a turntable or a monochromator.
  • the measurement result is not affected by the position of the multi-unit photodetector, and the optical detecting mechanical component is completely eliminated, and the structure is very compact. Due to the shortening of the optical path, the optical detection section greatly enhances the stability of the optical path and reduces the influence of external vibration and other factors.
  • the measurement method of the present invention has the characteristics of rapid response.
  • the intensity scan performed by the external field device can be completed very quickly, and the external field device can respond quickly according to the calculation result of the signal zero point detecting device.
  • the signal zero point detecting device can quickly check Measurement and calculation, these factors greatly accelerate the response speed of the measurement method.
  • the measuring method of the present invention has the characteristics of high detection resolution.
  • the use of external field intensity scanning removes the constraints of the mechanical factors on the detection resolution in the traditional SPR scanning mode. Due to the precise control of the external field strength and the stability of the entire measurement system, the noise caused by the mechanical device can be eliminated.
  • the measurement system The advantage of fast response makes other measurement influencing factors negligible, so the resolution of the measurement method is completely dependent on the noise performance of the photodetector in the signal detection device.
  • the measuring method of the present invention has the characteristics of high linearity.
  • the refractive index of the dielectric layer included in the SPR structure and the external field signal for changing the refractive index of the dielectric layer are completely linearly corresponding, and the change of the refractive index of the dielectric layer and the change of the refractive index of the detection layer are also highly linear, and the linearity is linear. It has nothing to do with the state of the measurement system, so the measurement method of the present invention has a linearity of 4 ⁇ high.

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Description

一种基于共振角度测量的 SPR传感器及其测量方法 技术领域
本发明涉及传感器及传感技术领域， 具体地说， 本发明涉及一种 基于共振角度测量的 SPR传感器及其测量方法。
背景技术
表面等离子共振（Surface Plasmon Resonance , 筒称为 SPR)传 感器通过存在于金属层和电介质界面的表面等离子波 （ Surface Plasmon Wave，筒称为 SPW ) 实现界面附近光学性质 （比如电介质厚 度、 折射率等）细微变化的探测。 通过棱镜入射光束产生衰减全反射 ( At tenuated Tota l Ref lect ion, 筒称为 ATR ) , 可以在界面上激 发倏逝波， 当 Ρ-偏振光束中平行于界面的波矢分量与 SPW的波矢分 量匹配时， 光束能量通过倏逝波耦合进入 SPW, 引起界面所反射的反 射光能量减弱。 而一定波长的光束在满足入射角度条件时， 能量耦合 进入 SPW的比例最大，这种现象称为 SPR现象，此时反射光能量最弱。 反射光能量最弱时所对应的入射角度称为共振角度，反射光强的响应 曲线上强度衰减的尖峰称为共振吸收峰。由于界面附近电介质厚度或 折射率的改变会相应引起 SPW的波矢发生变化， 进而改变光束与 SPW 能量耦合性质， 导致共振角度发生变化， 因此可以利用这种易于探测 的共振角度的变化来检测电介质厚度或折射率的改变。
20世纪 80年代， 基于 SPR原理的 SPR传感器就开始用于检测界 面附近检测物折射率和厚度的变化 ( J. G. Gordon I I， S. Erns t, Surf ace plasmons as a probe of the e lectrochemica l interface, Surface Sc i ence, 101, 499, 1980 ) , 近些年来 SPR传感器在药物筛 选、生化研究等领域都得到了广泛应用，目前已经成为定性和定量（比 如动力学参数与检测物浓度） 分析生物分子反应的重要工具 （J. Homo la, Surf ace Plasmon Resonance Sensor s for Detect ion of Chemica l and Bio logica l Spec ies, Chemica l Revi ews, 108, 462, 2008 )。 而其中， 基于共振角度测量的 SPR传感器又是应用 较为广泛的一类 SPR传感器。 在上述应用中， SPR传感器的检测分辨 率和响应时间是非常重要的性能指标， 其中分辨率用检测物折射率 ( Refract ive Index Uni t, 筒称为 RIU ) 最小可测变化描述。
基于共振角度测量的 SPR传感器是 SPR传感器中重要的一类。现 有技术中基于共振角度测量的 SPR传感器从测量方式看主要可以分 为两类， 其中一类是采用准直光束， 通过机械装置旋转棱镜和单元光 电探测器的位置来实现入射角度的扫描。它的缺点是其测量结果容易 受机械漂移的影响， 导致误差较大， 另外， 用机械装置旋转棱镜进行 扫描需要耗费大量时间。 而另一类是固定棱镜和多单元光电探测器 (比如线性二极管阵列， LDA, 或者电荷耦合装置， CCD )的位置， 采 用聚焦光束覆盖一定范围的入射角度（K. Mat subara, S. Kawata, S. Minami, A Compact Surf ace Plasmon Resonance Sensor for Measurement of Water in Proces s, Appl ied Spec troscopy, 42， 1375, 1988)实现快速的入射角度扫描。这种类型的 SPR传感器能够消除上述第一类 SPR传感器的所述缺点， 但是它的分 辨率受反射光覆盖的探测器单元数影响，棱镜和多单元光电探测器之 间的距离越远， 探测器单元数越多， 分辨率越高， 但由于 SPR传感器 的体积上的限制， 这一类传感器难以达到较高的分辨率。
针对上述第一类 SPR传感器， 为解决机械漂移、耗费时间过多等 问题， 美国专利 US666787提出了在金属层和检测物之间加入可以通 过电压改变调节折射率的介质层的技术方案。当检测物折射率改变引 起共振角度变化时， 改变施加于介质层的电压以调节折射率， 使单元 探测器测得的反射光强度最小，通过测量此时的电压变化即可以得到 共振角度的偏移量， 进而得到检测物折射率的变化信息。 该方案中， 采用单元光电探测器测量固定位置的反射光强度并判断测量结果是 否为强度最小值， 所以避免了机械操作而带来的误差。 但是， 由于探 测噪声的影响， 该方案难以准确且可以重复地得到反射光强度最小 值， 因此也难以准确地得到共振角度的偏移量。
而对于上述第二类 SPR传感器，为了在不增加体积的前提下提高 分辨率， 美国专利 US6784999提出了通过探测器阵列（该探测器阵列 至少具有 2个探测器单元）所获得的光强度的差分来获取所述共振角 度并进而得到检测物折射率变化信息的技术方案。该方案在检测前需 要严格调节光电探测器阵列的位置，使反射光强度最小的位置处于光 电探测器阵列中央以使光电探测器阵列左、右两部分信号的差与和的 比值， 即差分信号接近 0。 在检测物质过程中， 由于光电探测器的差 分信号和共振角度的偏移近似成线性对应关系，因此通过差分信号可 以得到共振角度的偏移， 从而实现检测物折射率变化的测量， 利用该 方案， 在入射光束波长为 635nm时分辨率可以达到 3 x 10— 8RIU ( N. J. Tao, S. Bous saad, W. L. Huang, R. A. Arechaba leta, and J. D'Agnese, H igh resolut ion surf ace plasmon resonance spectroscopy, Review of Sc ient if i c Ins trument s, 70, 12, 4656, 1999 )。 这种方案的缺点是需要严格保证共振角度所对应的反射光位 于探测器阵列的中央。这是因为探测器差分信号越大所述线性对应关 系的线性度就越差， 因此这一方案探测器位置的调节非常困难， 而且 重复性差。 此外这种方案中金属层-检测物结构直接加工在棱镜， 所 产生的共振吸收峰深度和宽度比值小，峰的形状容易因为探测噪声而 改变， 影响测量结果的准确性。 发明内容
本发明的任务是提供一种响应时间短、 测量线性度高、 高分辨 率的基于共振角度测量的 SPR传感器及其测量方法。
为实现上述发明目的， 本发明提供了一种基于共振角度测量的 SPR传感器， 包括：
光束输出装置， 用于输出线性偏振光的聚焦光束；
SPR传感芯片， 包括介质层、 与被检测物接触的金属层以及容纳 被检测物的样品池；
光电探测装置，所述光电探测装置是含有多个光电探测器单元的 差分式光电探测器线性阵列，用于接收被 SPR结构反射装置所反射的 聚焦光束；
可调外场生成装置，用于生成外场并将该外场施加到所述 SPR传 感芯片的介质层以调节所述介质层的折射率；
其中，所述差分式光电探测器线性阵列是以所述光电探测器线性 阵列中心为分界点， 将光电探测器单元分成数目相同的两组， 在测量 时， 分别将两组光电探测器单元的输出信号叠加， 然后对两组光电探 测器单元的叠加信号分别求差与和，得出差与和的比值作为所述差分 式光电探测器线性阵列的输出信号。 或声光材料等折射率可调的材料；所述可调外场生成装置所生成的外 场施加到所述介质层上。
其中， 所述电光材料为折射率对电场变化有线性响应， 即具有电 光效应的材料， 可以选择 L iNb03、 KDP、 ADP、 KD*P、 L i Ta03等无机 电光材料或 DAST ( 4 -曱基氨基 - N -曱基-芪曱苯橫酸盐 )等有机 电光材料及其复合物。
其中， 所述 SPR测量系统还包括数据处理装置， 用于接收所述 光电探测装置的输出并根据所述可调外场生成装置所施加的外场得 出所述被检测物 （通常是溶液） 的折射率。
其中， 所述光电探测装置的光电探测器可以选择位置敏感探测 器、 平衡探测器、 CCD、 多单元光子计数器等双单元或多单元对光 参数敏感的光电检测器， 其中光参数包括光束强度、 相位和光动量 等。
其中， 所述外场包括电场、 磁场、 声场或温度。
其中， 所述样品池可以选择玻璃、 塑料等制成。
本发明还提供了一种基于上述 SPR传感器的检测物折射率测量 方法， 包括下列步骤：
( 1 ) 在样品池中通入折射率已知的标准物， 将聚焦光束入射 到所述 SPR传感芯片， 由光电探测装置接收反射光信号并输出标定 步骤差分信号；
( 2 )在样品池中通入被检测物， 然后通过所述可调外场生成装 置改变所施加的外场，直至所述光电探测装置输出的差分信号与所述 标定步骤差分信号相同， 记录此时可调外场生成装置所施加的外场；
( 3 )根据外场与不同检测物折射率的对应关系， 得出被检测物 的折射率。
其中， 所述步骤（1 ) 中， 还包括调节所述 SPR传感器使得共振 角度偏离所述光电探测装置的探测器阵列中心的角度小于 0. 12度， 然后再记录光电探测装置此时输出的差分信号作为标定步骤差分信 号。
本发明中的 SPR传感器及其测量方法具有下列技术效果：
1. 本发明动态测量范围大， 测量自动化程度高。
2. 本发明的测量系统结构紧凑， 稳定性强。
3. 本发明的测量方法具有快速响应的特点。
4. 本发明所述的测量方法具有高检测分辨率的特点。
5. 本发明所述的测量方法具有高线性度的特点。 附图说明
以下， 结合附图来详细说明本发明的实施例， 其中： 图 1示出了基于差分式光电探测器线性阵列的探测原理，其中 为共振角度， θ 、 分别为探测器覆盖入射角范围的左右边界，
Figure imgf000007_0001
图 2示出了本发明一个实施例的测量系统及其工作原理， 其中 a部分为测量装置结构示意图， b部分为由于被检测层 10物质发生 改变和介质层 6外加电压的变化， 导致 WCSPR共振角度偏移以及 由此带来的差分光电探测器阵列输出信号变化的示意图， c部分为 当被检测层 10物质的改变引起差分光电探测器阵列输出信号变化 后调节介质层 6外加电压直到输出信号返回标定点的示意图， d部 分为根据 b、 c部分得到的介质层 6外加电压和被检测层 10物质的 折射率之间对应关系的示意图；
图 3示出了本发明一个实施例的 WCSPR结构共振角度和强度随 被检测层折射率变化的响应曲线；
图 4示出了本发明一个实施例的 WCSPR结构共振角度和强度随 介质层折射率变化的响应曲线；
图 5示出了本发明一个实施例的 WCSPR结构的共振角度随被检 测层折射率变化；
图 6示出了本发明一个实施例的 WCSPR结构的共振角度随介质 层折射率变化的计算结果；
图 7示出了本发明一个实施例中， 通过计算模拟出的施加在介 质层的外场电压与不同检测物折射率的对应关系；
图 8示出了本发明另一个实施例中， 通过计算模拟出的施加在 介质层的外场电压与不同检测物折射率的对应关系；
图 9示出了专利 US666787的一个线性度仿真统计结果； 图 10示出了专利 US6784999的一个线性度仿真统计结果； 图 11示出了专利 US6784999的另一个线性度仿真统计结果； 图 12示出了本发明的一个线性度仿真统计结果；
图 1 3示出了本发明的另一个线性度仿真统计结果。
图面说明
1-激光器 2-偏振片 3-透镜 4-棱镜
5-上金属层 6-介质层 7-下金属层 8-可调电压输出装置
9-生物标记 10-被检测物 11 -差分式光电探测器阵列
12-数据处理系统 13 -玻璃基底 14-样品池 具体实施方式
本实施例将外场补偿与差分式光电探测器线性阵列相结合，提供 了一种基于外场补偿的差分式 SPR传感器，该 SPR传感器相对于现有 的差分 SPR传感器（即基于差分式光电探测器线性阵列的 SPR传感 器）， 能够提高测量结果的线性度。 同时， 本实施例的基于外场补偿 的差分式 SPR传感器还能够降低差分式 SPR传感器的操作复杂度，避 免繁瑣的调零操作。 下面分别从工作原理、 结构和测量步骤， 以及对 比仿真试验结果三个部分详细描述本实施例。
1. 基于外场补偿的差分式 SPR传感器的工作原理
SPR传感器的核心部件之一是 SPR传感芯片。参考图 2的 a部分， 在本实施例中， SPR传感芯片包括上金属层 5、 介质层 6、 下金属层 7 和样品池 14。 芯片可以制备在玻璃基底 1 3或者棱镜 4上， 下金属层 7的下表面处设置样品池 14 , 所述下金属层 7的下表面与样品池 14 之间留有一定间隙。 所述样品池 14用于乘放被检测物 10 , 并且被检 测物 1 0的液面（被检测物 1 0—般为液态物质）与下金属层 7的下表 面接触。 特别地， 根据被检测物浓度和种类的需要， 本实施例还可以 在下金属层 7、 被检测物 10之间的界面处加入生物标记 9。 所述基于外场补偿的差分式 SPR传感器中存在两个灵敏度参数， 共振角度对所述介质层 6的折射率 和被检测物 10 (根据应用也可 以是生物标记 9 ) 的折射率 n4的灵敏度， 它们的表达式如式 1-1。
Figure imgf000009_0001
其中， Cl、 C2均为常数。
图 1示出了基于差分式光电探测器线性阵列的探测原理， 其中, 探测器信号定义如式 1-2,
J = 層, / 層 ( 1-2 )
Figure imgf000009_0002
其中 R为所述可调谐 SPR传感器中反射光强度对入射角度的响应 关系。
当检测物为参考检测物时对图 1中的共振吸收峰（实线）进行多 项式展开，得到式（1-3)。其中 为共振角度离探测器中心的偏移量。 ^α, + α^θ-θ,+ )2 ( 1_3 ) 当检测物为其他物质时， n4发生改变， 共振角度发生 Δ Θ Μ的变 化， 1-3变成 1-4。
Rx ^a [+ «3 (θ - ^ - Δ^ο! + γ) =άι+α^ θ-θι- C2An4 + γ) ( 1-4 ) 对所述介质层折射率进行调节， 共振角度发生 Δ Θ。2的变化， 得 到 1-5式。
R2 « ά[ + 3 θ-θ - Αθ02 )2 = α[ + α {θ -θχ- CtA«4 - C2An2 )2 ( 1-5 ) 将 1-3、 1-5代入 1-2式分别得到探测器的输出 J。, 如1- 6, 其 中△ Θ。为共振角度的改变量。
Figure imgf000010_0001
将 1-6两者相等之后计算得到 1-7式：
3 2_( 2 + 9 = () ( 1_7 ) 解 1-7得到 1-8。
Αθ = Ο^ΑΘ = β +9χ
3r ( i—8 ) 实际测量中△ Θ值通常小于 1度， 为共振角度离探测器中心的 偏移量， 而 β 是探测器阵列所覆盖入射角度范围的一半， β 远大于
Υ (至少 10倍）， 因此△ Θ第二个解过大（至少为 10度），可以舍去, 由 1-8可以得到 1-9。
C2An4 + Cxl^n2 = 0 ( 1—9 )
1-9式说明可以通过测量 n2的变化可以实现 n4的测量，而且测量 结果和 γ值是否为 0无关。 具体地说， 要测量被检测物 10的折射率 η4, 可以首先选定折射率已知的标准物， 得出 SPR传感芯片使用标准 物时的共振角度。 然后将 SPR传感芯片的标准物换成被检测物 10，此 时， 由 1-9式可知， 只要改变介质层 6的折射率 n2, 使其达到一个适 当的取值，就可以补偿 SPR传感芯片中被检测物替换标准物所造成的 折射率变化，从而使得整个 SPR传感芯片的共振角度不变。众所周知， 来反推出被检测物 10的折射率 n4。而本实施例则可以利用上述原理， 通过对介质层 6施加外场来改变其折射率 n2以补偿被检测物的折射 率 n4的变化， 这样， 可以把对 n4的测量转换为较为筒单的对 n2的测 量。
另一方面， 从 1-9式还可看出， 不论 n4的变化是多少， 利用补偿 原理进行测量的测量结果均不受 γ和 J的影响， 即不存在系统误差， 因此基于外场补偿的差分式 SPR传感器相对于现有的差分式 SPR传感 器， 能够提高测量结果的线性度。 下面以专利 US6784999为例， 给出 对现有的差分式 SPR传感器的系统误差的理论分析。
在专利 US6784999中， 将 1-4代入 1-2得到 1-10。
J =
β2+3,γ2 2 ( 1-10)
μ 一 ^ + 2
3
解 1-10得到 1-11。
2 + 士 2 j)2 +β2- ― 4y2J
ΑΘ = ^ J ^ -—— （1- 由于 β 远大于 γ , 因此当 Δ Θ 取 （ 1_11 ) 中的解
Figure imgf000011_0001
时， Δθ« ( l-J/3) /J0 实际测量中，
2J 差分探测器阵列 A、 B两部分信号大小相近， 所以 J远小于 1, 也造 成 ΔΘ过大（至少为 10度） ， 因此舍去这个解。
对（1-11 ) 中另一个解， 当 γ=0时有 Δ Θ « 因此， 可以 利用这一近似线性关系， 通过对 J的测量来得出 △ Θ。 但是当 γ≠0 时， Δ Θ 与 J的对应关系是复杂的非线性关系，这是利用 Δ θ 来测量将会产生严重的系统误差， 该误差和丫、 J均有关。 因此专利
US6784999所提供的方案必须在每次测量前进行严格地调零， 即使 γ =0。
综上所述， 将外场补偿的测量方式与差分式 SPR传感器相结合， 能够有效地提高测量的线性度， 减小系统误差， 同时， 还能够省略或 筒化普通差分式 SPR传感器的调零步骤， 从而有效提高测量效率。
2. 基于外场补偿的差分式 SPR传感器的结构和测量步驟
根据上述第 1部分所叙述的原理， 本实施例提供了一种可进行高线性 度测量得基于差分式光电探测器线性阵列的可调谐 SPR传感器， 参考 图 2 , 该 SPR传感器包括： 波长为 980nm的激光器 1、 偏振片 2 (如果激 光器 1输出光束为 p偏振，偏振片 2可以不用）、透镜 3、折射率为 1. 7053 ( Q980nm )的棱镜 4、 上金层 5、 介质层 6、 下金层 7、 可调电压输出装 置 8、 被检测物 10 (根据应用也可以是生物标记 9 )、 差分式光电探测 器线性阵列 11、 数据处理系统 12和样品池 14。 金的折射率为
0. 185145+6. 15041 , 上金层 5、 下金层 7厚度均为 30nm。 介质层 6采用 具有电光效应的高分子材料（Kun Wang, et a l. Hybr id d ifferent ia l interrogat ion method for sens i t ive surf ace plasmon resonance measurement enabled by electro-opt ica l ly tunable SPR sensors, Opt ics Expres s, 17, 4468, 2009 ),折射率为 1. 60388 ,厚度为 2800nm。
其中， 上金属层 5、 介质层 6和下金属层 7依次制备于棱镜 4的 底面上， 可调电压输出装置 8由数据处理系统 12控制， 可调电压输 出装置 8的电压输出端和上金属层 5、 下金属层 7连接。 激光器 1生 成的光束通过透镜 3聚焦于棱镜 4与上金属层 5的界面，并在此界面 反射进入差分式光电探测器线性阵列 11。
另外， 本实施例中， 还可以在棱镜 4底部表面设置一个玻璃基底 13 , 所述玻璃基底 13和棱镜 4折射率相同， 并且二者之间的缝隙用 折射率相同的匹配层填充。 这样， 上金属层 5、 介质层 6和下金属层 7依次制备于玻璃基底 13上。 激光器 1生成的光束通过透镜 3聚焦 于玻璃基底 13与金属层 5界面， 并在此界面反射进入差分式光电探 测器线性阵列 11。 样品池 14用于乘放被检测物 10, 材料一般可选用聚二曱基硅氧 坑（ Poly (dimethyls iloxane) , PDMS )。
本实施例中的可调谐 SPR传感器的棱镜 4、上金属层 5、介质层 6、 下金属层 7和被检测物 10 (根据应用也可以是生物标记 9 )采用了波 导耦合表面等离子共振 (waveguide-coupled SPR, WCSPR )结构。
由 Fresnel 理， WCSPR反射光功率表达式如 2-1。
Figure imgf000013_0001
其中 ,ί+1是相邻层界面处的反射率， 是每层的厚度， k。x是棱 镜内平行界面的波矢分量， λ 是入射光波长， Θ 是入射角度， k。z,i 是每层垂直界面的波矢分量， n,是每层的折射率。 下标 i为 0到 4时 依次分别代表棱镜 4、 上金属层 5、 介质层 6、 下金属层 7和被检测 物 10 (或生物标记 9)。
由 （ 2-1 ) 式可以看出， 改变被检测层 10 (或生物标记 9 ) 的折 射率， WCSPR结构的反射光强度和共振角度会发生改变。本实施例中， 取入射光波长为 980 nm, 棱镜为 ZF-3棱镜， 折射率为 1.7053, 上金 属层 5和下金属层 7的材料均为 Au,其折射率为 0.185145+6.15041, 厚度均为 30 nm, 介质层的折射率为 1.60388, 厚度为 2.8 μηι，电光 系数为 10pm/V, 没有生物标记 9，探测器阵列覆盖入射角度范围为 3 度。
图 3示出了本实施例的 WCSPR结构共振角度和强度随被检测层 折射率变化的响应曲线；图 5示出了共振角度随被检测层 9折射率变 化的响应； 改变介质层 6的折射率， WCSPR结构的反射光强度和共振 角度也会发生改变，如图 4示出了 WCSPR结构共振角度和强度随介质 层折射率变化的响应曲线。
本实施例中，基于电光效应， 通过改变可调电压输出装置 8的输 出电压来线性地调节介质层 6的折射率。电光效应 (Electro-Optical
Effect, 又称之为 Pockels效应） 是一种非线性光学效应，具有电光 效应的光学材料可以通过施加电场来使其折射率 n发生 Δ n的变化， 如 2-2,其中 d为材料厚度， V为施加于材料的电压， γ 33为电光系数。
可以看出， Δη随 V线性变化， 只要得到施加于材料的电压 V, 即可获得 Δη。
测量开始前， 多单元光电探测器 11接收从 WCSPR结构反射的覆 盖一定角度范围的光束后，将多单元探测器的单元沿覆盖角度范围方 向分为两半，分别称之为 A、 B两部分， 通过对两部分单元对光束的响 应求和得到两个结果， 分别称之为 A、 B, 并通过图 2 中 b 部分的 (A-B) I (A+B)运算得到标定信号。 由（ 1-9 )可知测量结果和测量开始 前 （A-B)/(A+B)运算得到的结果无关，因此本实施例可省去对探测器 阵列的调 0操作， 大大节省了测量时间， 降低了测量的操作复杂度。
具体地，利用本实施例的 SPR传感器进行折射率检测的方法包括 下列步骤：
1 )标定步骤： 在 SPR传感芯片中的样品池 14中通入折射率已知 的标准物 （一般可选磷酸盐緩沖液（Phosphate Buffer Solution, PBS) )。 将可调电压输出装置 8 的电压输出端和上金层 5、 下金层 7 连接， 输出电压为 0V, 激光器 1输出光束经过透镜 3 (如果激光器 1 输出光束为不是 P偏振， 需要经过偏振片 2)聚焦于棱镜 4 (如果采 用了玻璃基底 13, 则为玻璃基底 13) 与上金层 5的界面， 并在此界 面反射进入差分式光电探测器线性阵列 11, 差分式光电探测器线性 阵列 11 的信号输入数据处理系统 12 , 计算并记录差分信号 (A-B) I (A+B)。
2 )测量步骤： 在 SPR传感芯片中的样品池 14 中通入被检测物 10, SPR传感器的其余部件的位置均保持不变。 由于被检测物 10或 生物标记 9 (根据被检测物的种类和浓度， 可以加入生物标记 9 ) 的 折射率相对于标准物发生了变化， SPR共振角度产生偏移， 差分式光 电探测器线性阵列 11接收棱镜 4 (如果采用了玻璃基底 13, 则为玻 璃基底 13 )与上金层 5的界面的反射光束， 数据处理系统 12根据差 分式光电探测器线性阵列 11的输出得到差分信号（A-B) I (A+B)。此时 的差分信号必然偏离于标定步骤的差分信号。 如图 2中 c部分所示， 由于公式（ 2-2 )介质层 6的折射率 n、 介质层厚度 d、 介质层电光系 数 Y 33和（ 1-1 )中 、 C2为 WCSPR结构参数， 因此可根据公式（ 1-9 )、
( 2-2 )初步计算出使差分信号返回标定点所需要的电压值 S, 然后 在 S-5V到 S+5V的范围内，以步长 10mV来调节介质层 6的外加电压。 在每次改变电压值时，差分式光电探测器线性阵列 11接收棱镜 4(如 果采用了玻璃基底 13, 则为玻璃基底 13 ) 与上金属层 5的界面的反 射光束，数据处理系统 12根据差分式光电探测器线性阵列 11的输出 得到差分信号（A-B) I (A+B)并和标定步骤差分信号比较， 直到本步骤 所测得的差分信号与标定步骤差分信号相等， 记录此时的外加电压， 并根据施加在介质层的外场电压与不同被检测物折射率的对应关系 得到被检测物折射率的测量结果， 测量结果如图 2的 d部分所示。施 加在介质层的外场电压与不同被检测物折射率的对应关系可根据
( 1-9 )和（2-2 )预先计算得出。 图 7示出了本发明一个实施例中， 通过计算模拟出的施加在介质层的外场电压与不同被检测物折射率 的对应关系； 该实施例中， 被检测物 10折射率为 1.333, 并且该实 施例中标定步骤的探测器阵列的差分信号为 0;图 8示出了本发明另 一个实施例中， 通过计算模拟出的施加在介质层的外场电压与不同 检测物折射率的对应关系，该实施例中，被检测物 10折射率为 1.333 , 标定步骤的探测器阵列的差分信号为 -0.01582。
一般地， 本实施例不需要在标定步骤中进行繁瑣的调零操作。但 是， 在实际测量时， 可以根据实际情况， 使共振角度尽量对应于探测 器阵列的中心， 这样有助于进一步提高测量的线性度。 当共振角度偏 离探测器阵列中心的角度小于 0. 12度时， 测量的线性度可以保持在 0. 9999以上。
3. 线性度仿真结果
固定检测物为 PBS ,如图 2所示选取一部分入射角度范围，将（1-2) 算得的反射光强按 A、 B两部分进行积分,计算差分信号（ A-B )/( A+B ), 记录该值 S1 , 然后改变检测物折射率进行如（2-2)的介质层折射率扫 描。
专利 US666787的仿真原理是改变折射率之前记录反射光最低点 对应点对应的角度，然后改变折射率和介质层上的电压使此时反射光 最低点对应点对应的角度和之前的重合。
专利 US6784999 的仿真原理是改变折射率之前将共振角度调至 探测器中心， 改变折射率后记录比值即可。
图 9是叠加 40dB信噪比的高斯噪声条件下，专利 US666787线性 度的蒙特卡洛（Monte Car lo ) 计算统计结果。 其中棱镜折射率为 1. 7053 , 金层厚度为 40nm, 折射率可调介质层厚度为 50腿， 入射光 波长为 980nm。 线性度期望值为 0. 99903。
图 10是叠加 40dB信噪比的高斯噪声条件下，专利 US6784999线 性度的 Monte Car lo计算统计结果。 其中棱镜折射率为 1. 7053 , 金 层厚度为 40腿，入射光波长为 980nm,共振角度对探测器中心无偏差。 线性度期望值为 0. 99961。
图 11是叠加 40dB信噪比的高斯噪声条件下，专利 US6784999线 性度的 Monte Car lo计算统计结果。 其中棱镜折射率为 1. 7053 , 金 层厚度为 40nm, 入射光波长为 980nm, 共振角度对探测器中心偏差 0. 1度。 线性度期望值为 0. 99924。
图 12是叠加 40dB信噪比的高斯噪声条件下， 本发明线性度的 Mont e Car l o仿真统计结果。 激光器输出光束波长为 980腿， 棱镜 4 和玻璃基底 1 3 折射率为 1. 7053 ( Q980nm ) , 金的折射率为 0.185145+6.15041, 上金层 5、 下金层 7厚度均为 30nm, 介质层 6折 射率为 1.60388, 厚度为 2800nm。 共振角度对探测器中心无偏差。 线 性度期望值为 0.9998
图 13是叠加 40dB信噪比的高斯噪声条件下， 本发明线性度的 Monte Carlo仿真统计结果。 激光器输出光束波长为 980 棱镜 4 和玻璃基底 13 折射率为 1.7053 ( Q980nm ), 金的折射率为 0.185145+6.15041, 上金层 5、 下金层 7厚度均为 30nm, 介质层 6折 射率为 1.60388, 厚度为 2800nm。 共振角度对探测器中心偏差 0.12 度。 线性度期望值为 0.99959
由图 9 10 11 12 13可以发现， 三者的线性度分布均呈正态 分布， 但是本发明方法中即使共振角度偏离探测器中心 0.12度， 线 性度期望值仍大于前两者， 意味着在检测物折射率变化相同时， 本方 法可以进行更线性的测量（输出信号的变化更真实地反映折射率的变 化）； 同时标准偏差（频率最高数的 1/2.718对应的两个线性度之间 的距离）小于前两者， 因此在具有相同分布的高斯噪声影响下， 本发 明方法的测量线性度不容易受到干扰，这样对相同样品的测量重复性 更好。 综合上述两个优点， 本发明方法可以实现更精确的测量。
另外， 可以看出， 本实施例还能增加测量的线性范围， 由于线性 范围的增加， 本实施例中不必在测量前进行严格的调零， 这样大大地 节省了测量时间。
本实施例的 SPR传感器及其测量方法具有以下优点：
1. 本发明所述的测量方法基于信号反馈和外场调节所述 SPR 结构中介质层折射率的原理，动态测量范围大，测量自动化程度高。
2. 本发明所述的测量系统结构紧凑， 稳定性强。 通过外场可控 装置使用非机械扫描方法， 不需要使用转台、 单色仪等传统设备， 同 时测量结果不受多单元光电探测器位置的影响，完全消除了光学检测 机械部件， 结构十分紧凑。 光学检测部分由于光路的缩短， 使得光路 的稳定性大大增强， 减少了外界震动等因素的影响。
3. 本发明所述的测量方法具有快速响应的特点。 外场装置进行 的强度扫描可以非常快的完成，同时外场装置可以根据信号零点检测 装置计算的结果迅速进行响应， 此外， 信号零点检测装置可以快速检 测和计算， 这些因素都大大加快了所述测量方法的响应速度。
4. 本发明所述的测量方法具有高检测分辨率的特点。 外场强度 扫描的采用摆脱了传统 SPR 扫描方式中机械因素对检测分辨率的制 约， 由于外场强度的可精确控制性和整个测量系统的稳定性， 机械装 置带来的噪声可以消除， 此外， 测量系统快速响应的优点使得其它测 量影响因素可以忽略，所以测量方法的分辨率完全取决于信号检测装 置中光电探测器的噪声性能。
5. 本发明所述的测量方法具有高线性度的特点。 发明所述 SPR 结构中包括的介质层折射率和改变介质层折射率的外场信号是完全 线性对应的，而介质层折射率的改变和检测层折射率的变化也是高度 线性的， 这种线性度和测量系统的状态没有关系， 所以本发明所述的 测量方法具有 4艮高的线性度。

Claims

权 利 要 求
1、 一种基于共振角度测量的 SPR传感器， 包括：
光束输出装置， 用于输出线性偏振光的聚焦光束；
SPR传感芯片， 包括介质层、 与被检测物接触的金属层以及容纳 被检测物的样品池；
光电探测装置，所述光电探测装置是含有多个光电探测器单元的 差分式光电探测器线性阵列，用于接收被 SPR结构反射装置所反射的 聚焦光束；
可调外场生成装置，用于生成外场并将该外场施加到所述 SPR传 感芯片的介质层以调节所述介质层的折射率。
2、 根据权利要求 1所述的基于共振角度测量的 SPR传感器， 其 特征在于，所述差分式光电探测器线性阵列是以所述光电探测器线性 阵列中心为分界点， 将光电探测器单元分成数目相同的两组。
3、根据权利要求 1或 2所述的基于共振角度测量的 SPR传感器， 其特征在于， 所述 SPR传感芯片的介质层的材料是电光材料、 热光材 料或声光材料。
4、 根据权利要求 3所述的基于共振角度测量的 SPR传感器， 其 特征在于， 所述电光材料为具有电光效应的材料， 包括 L iNb03、 KDP、 ADP、 KD*P、 L iTa03或 DAST材料及其复合物。
5、根据权利要求 1至 4中任一项所述的基于共振角度测量的 SPR 传感器，其特征在于，所述基于共振角度测量的 SPR传感器还包括数 据处理装置， 用于接收所述光电探测装置的输出并根据所述可调外 场生成装置所施加的外场得出所述被检测物的折射率。
6、根据权利要求 1至 5中任一项所述的基于共振角度测量的 SPR 传感器， 其特征在于， 所述光电探测装置的光电探测器采用位置敏 感探测器、 平衡探测器、 CCD获多单元光子计数器。
7、根据权利要求 1至 6中任一项所述的基于共振角度测量的 SPR 传感器， 其特征在于， 所述外场包括电场、 磁场、 声场或温度。
8、根据权利要求 1至 7中任一项所述的基于共振角度测量的 SPR 传感器， 其特征在于， 所述样品池采用玻璃或塑料制成。
9、一种利用权利要求 1所述的 SPR传感器的测量被检测物折射 率的方法， 包括下列步骤：
( 1 ) 在样品池中通入折射率已知的标准物， 将聚焦光束入射 到所述 SPR传感芯片， 由光电探测装置接收反射光信号并输出标定 步骤差分信号；
(2)在样品池中通入被检测物， 然后通过所述可调外场生成装 置改变所施加的外场，直至所述光电探测装置输出的差分信号与所述 标定步骤差分信号相同， 记录此时可调外场生成装置所施加的外场；
( 3)根据外场与不同检测物折射率的对应关系， 得出被检测物 的折射率。
10、 根据权利要求 9所述的测量被检测物折射率的方法， 其特 征在于， 所述步骤（1 ) 中， 还包括调节所述 SPR传感器使得共振角 度偏离所述光电探测装置的探测器阵列中心的角度小于 0.12度， 然 后再记录光电探测装置此时输出的差分信号作为标定步骤差分信 号。
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