Abstract:
Disclosed is a double-sided grating waveguide biosensor. The double-sided grating waveguide biosensor is used to sense the properties of a sample solution. The double-sided grating waveguide biosensor comprises a sequential stack of a plastic grating having a grating part, a waveguide layer having a double-sided grating structure, and a channel chip. Furthermore, the sample solution is guided into the channel chip; the light beam is coupled into the waveguide layer via the double-sided grating structure, propagates in the waveguide layer, and penetrates outward. The double-sided waveguide biosensor detects the properties of the sample solution via a variation of a light beam intensity of the outgoing light beam.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit under 35 U.S.C. §119 of Taiwanese Patent Application No. 101138833, filed Oct. 19, 2012, which is hereby incorporated by reference in its entirety. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to a biosensor, and particularly, a double-sided grating waveguide biosensor with a double-sided grating structure. 
     2. Description of the Related Art 
     In recent years, the biomedical sensing industry pays more and more attention to the accuracy and convenience when conducting a specific detection, while optical biosensors are exactly able to meet these requirements. Due to the fact that the development of optical waveguide devices gradually becomes more mature, people begin to utilize optical waveguide devices in detecting. Conventionally, an optical waveguide biosensor is either equipped with a prism or a grating as the coupling device to couple in a light beam into the waveguide layer. The detecting purpose is achieved by measuring the variations of the angle and the wavelength of the light beam source. However, measuring the variations of the angle and the wavelength of the light beam requires complex measurement instruments. 
     Additionally, manufacturing of grating biosensors are rather difficult, because grating is not easy to produce. Currently, the conventional manufacturing methods of grating biosensors are imprinting, ion erosion, or the holographic technique. However, these methods are too complex to mass-produce. Besides, the grating biosensors manufactured by these three methods are all single-sided. 
     BRIEF SUMMARY 
     Based on the problems of the prior arts, one of the objects of the present invention is to provide a double-sided grating waveguide biosensor to detect properties of a sample solution. The present invention provides a waveguide layer comprising a double-sided grating structure to achieve the goal of effectively coupling a light beam within the preset range into the waveguide layer to perform a detecting. Moreover, a new manufacturing method of the double-sided grating waveguide biosensor is applied to realize the purpose of mass production and cost reduction. 
     Thus, the present invention provides a double-sided grating waveguide biosensor to sense the properties of a sample solution. The double-sided grating waveguide biosensor at least comprises a plastic grating, a waveguide layer, and a channel chip. The material of the plastic grating is, for example, cyclic-olefin copolymers (COCs), polycarbonate, acrylic, polypropene, or other suitable plastic material with high transparency. One surface of the plastic grating is provided with a grating part. The waveguide layer is located on the surface with the grating part of the plastic grating, and part of the waveguide layer is located on the grating part to form a double-sided grating waveguide structure. Furthermore, the double-sided grating structure comprises two waveguide grating parts corresponding to each other. The material of the waveguide layer is, for example, titanium dioxide, zirconium dioxide, silicon dioxide, titanium sesquioxide, tantalum pentoxide, zinc oxide, or suitable material with high refraction index and stable chemical properties, to increase the sensing sensitivity and range of the double-sided grating waveguide biosensor. 
     Additionally, the channel chip is installed on the waveguide layer such that the sample solution can be guided into a storage space of the channel chip. When the light beam is coupled into the waveguide layer via the double-sided grating structure and propagates along the waveguide layer, the double-sided grating waveguide biosensor of the present invention detects the properties of the sample solution via the variations of a light beam intensity of the light beam penetrating out of the waveguide layer. 
     Additionally, the double-sided grating waveguide biosensor of the present invention further comprises a recognition molecule layer fixedly bonded to the surface of the waveguide layer between the waveguide layer and the channel chip. The recognition molecule layer is designed to interact with the sample solution such that the double-sided grating waveguide biosensor of the present invention can have a good limit of detection in sensitivity when it is used to perform a measurement. 
     Additionally, the plastic grating of the double-sided grating waveguide biosensor of the present invention has a plurality of gaps. The plurality of gaps are located between the plastic grating and the waveguide layer. 
     Additionally, the double-sided grating structure is provided with one or both of a coupling position and an angle of coupling ranged from −90 to 90 degrees. A distance between the coupling position and a terminal of the double-sided grating structure is within 0 to 2 centimeters. Besides, the ranges of the coupling position and the angle of coupling and the coupling position and the angle of coupling of the peak light beam intensity do not change with the variations of the refraction index. Furthermore, the detecting sensitivity does not change with the variations of the angle of coupling and the coupling position. 
     Thus, one of the features of the detecting method by using the double-sided grating waveguide biosensor of the present invention is to couple in the light beam into the waveguide layer of the double-sided grating structure and to detect the light beam intensity of the coupling output, such that the light beam can possess the coupling capability within a range. Within this range, the sensitivity of the double-sided grating waveguide biosensor does not change with the different selections of the angle of coupling and the coupling position. Another feature of the sensing method by using the double-sided grating waveguide biosensor of the present invention is to simplify the complexity of the detecting processes by measuring the light beam intensity of the coupling output. 
     As above-mentioned, the double-sided grating waveguide biosensor of the present invention may have one or more characteristics and advantages as described below:
         (1) The detection sensitivity and range of the double-sided grating waveguide biosensor of the present invention is enhanced by means of the high refraction index and the stable chemical characteristics of the material of the waveguide layer.   (2) With the double-sided grating structure of the recognition layer and the waveguide layer, the double-sided grating waveguide biosensor of the present invention can have a good limit of detection in sensitivity when it is used to perform a measurement.   (3) The light beam is provided with the coupling capability within a range through coupling in the light beam into the waveguide layer of the double-sided grating structure and detecting the light beam intensity of the coupling output. Within this range, the detection sensitivity of the double-sided grating waveguide biosensor of the present invention does not change with the different selections of the angle of coupling and the coupling position.   (4) The complexity of the sensing processes is simplified through detecting the light beam intensity of the coupling output.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is the structure diagram showing a double-sided grating waveguide biosensor according to the first preferred embodiment of the present invention; 
         FIG. 2  is a SEM graph of the plastic grating and the waveguide layer which are shown on  FIG. 1 ; 
         FIG. 3  is the structure diagram showing a double-sided grating waveguide biosensor according to the second preferred embodiment of the present invention; 
         FIG. 4  is a SEM graph of the plastic grating and the waveguide layer which are shown on  FIG. 3 ; 
         FIG. 5  is the relationship diagram showing the light beam intensity of the coupling outcome and the refraction index of a double-sided grating waveguide biosensor according to the second preferred embodiment of the present invention; 
         FIG. 6  is a relationship diagram showing the light beam intensity of the coupling outcome and the concentration of the sampling solution showing a double-sided grating waveguide biosensor with a recognition molecule layer according to the first preferred embodiment of the present invention; 
         FIG. 7  is a flow diagram showing the manufacturing method of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention; 
         FIGS. 8   a - 8   c  are processing sectional diagrams showing the imprinting of the grating structure of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention; 
         FIG. 9  is a state diagram showing the manufacturing of the plastic grating of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention; 
         FIG. 10  is a flow diagram showing the detection method of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention; 
         FIG. 11  is a detection system diagram showing a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention; 
         FIG. 12  is a relationship diagram showing the light beam intensities of the sample solutions with different refraction indices and the angle of coupling of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention; 
         FIG. 13  is a relationship diagram showing the light beam intensities of the sample solution with different refraction indices and the coupling position of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention; 
         FIG. 14  is a relationship diagram showing the light beam intensities of different angles of coupling and the refraction index of a double-sided grating waveguide biosensor according to the first preferred embodiment of the present invention; 
         FIG. 15  is a relationship diagram showing the light beam intensities of different coupling positions and the refraction index of a double-sided grating waveguide biosensor according to the first preferred embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Referring to  FIGS. 1-2 ,  FIG. 1  is the structure diagram showing a double-sided grating waveguide biosensor according to the first preferred embodiment of the present invention,  FIG. 2  is a SEM micrograph of the plastic grating and the waveguide layer which shown on  FIG. 1 . As shown in  FIGS. 1-2 , the double-sided grating waveguide biosensor of the present invention at least comprises a plastic grating  110 , a waveguide layer  120 , a channel chip  130 , and further comprises, for example, a recognition molecule layer  140 . Furthermore, the material of the plastic grating is, for example, cyclic-olefin copolymers, polycarbonate, acrylic, polypropene, or other suitable plastic material with high transparency. A surface  112  of the plastic grating  110  is provided with a grating part  111 , and the grating part  111  and the plastic grating  110  are generated together in one step. 
     Additionally, a waveguide layer  120  is located on the surface  112 , and part of the waveguide layer  120  is located on the grating part  111  to form a double-sided grating waveguide structure  121 . Besides, the double-sided grating structure  121  comprises two waveguide grating parts  122  corresponding to each other. The double-sided grating structure  121  is designed to guide the external light beam into the waveguide layer  120 . When the surface effective refraction index of the waveguide layer  120  is changed, the optical properties will change accordingly. These optical properties can be, for example, the angle of coupling, the coupling energy, the wavelength, or the phase, etc. The optical property can also be, for example, the light beam intensity of the light beam penetrated outward the waveguide layer  120 . Besides, the material of the waveguide layer  120  can be, for example, titanium dioxide, zirconium dioxide, silicon dioxide, titanium sesquioxide, tantalum pentoxide, zinc oxide, or other material which has higher refraction index than that of plastic grating  110 . 
     Additionally, the waveguide layer  120  can be, for example, deposited on the surface  112  of the plastic grating  110 . The deposit method can be, for example, sputtering coating, evaporation, dip coating, spin coating, or any method which enables the waveguide layer  120  to be uniformly deposited on the surface  112  of the plastic grating  110 . Thus, the waveguide layer  120  can be, for example, deposited smoothly and uniformly on the plastic grating  110 . Since the grating part  111  is located on the surface  112  of the plastic grating  110 , the waveguide layer  120  on the grating part  111  can be provided with the double-sided grating structure  121  which comprises two waveguide grating parts  122  corresponding to each other. Furthermore, the height of the grating of each the two waveguide grating parts  122  are roughly equal to that of the grating part  111 . 
     Thus, one of the features of the double-sided grating waveguide biosensor  100  of the present invention is that the detection sensitivity and range of the double-sided grating waveguide biosensor  100  of the present invention is enhanced by means of the high refraction index and the stable chemical characteristics of the material of the waveguide layer  120 . 
     Additionally, further referring to  FIGS. 3-4 ,  FIG. 3  is the structure diagram showing a double-sided grating waveguide biosensor according to the second preferred embodiment of the present invention,  FIG. 4  is a SEM micrograph of the plastic grating and the waveguide layer which shown on  FIG. 3 . The second preferred embodiment of the double-sided grating waveguide biosensor of the present invention shown on  FIG. 3  is similar to the first preferred embodiment of the double-sided grating waveguide biosensor shown on  FIG. 1 . The difference between them is the plastic grating  110  of the second preferred embodiment has a plurality of gaps  113 , wherein the gaps  113  are formed on the surface  112  of the plastic grating  110  and located between the plastic grating  110  and the waveguide layer  120  to further enhance the detecting sensitivity of the double-sided grating waveguide biosensor  100 . 
     Additionally, the channel chip  130  is, for example, located on the waveguide layer  120  such that a user can guide in a sample solution  400  and use the double-sided grating waveguide biosensor  100  of the present invention to detect the properties, for example the refraction index, of the sample solution  400 . Besides, the user can make use of the properties of the sample solution  400  to decide the composition, concentration, or other properties of the sample solution  400 . Furthermore, the channel chip  130  can be, for example, provided with an outer shell and a storage space. The storage space is used to store the sample solution  400  for detection. The material of the outer shell is, for example, cyclic-olefin copolymers, polycarbonate, acrylic, polypropene, or other suitable plastic material with high transparency. Besides, the outer shell can be, for example, provided with holes to guide the sample solution  400  into the storage space or guide it out. 
     Based on the properties, for example the refraction index, of different sample solutions  400 , the double-sided grating waveguide biosensor  100  of the present invention detects the different light beam intensities of the coupling outcomes. Thus, the properties of the sample solution  400  can be analyzed based on the corresponding relationship between the refraction index and the light beam intensity. 
     Numerical experimental data are provided to confirm that the double-sided grating waveguide biosensor  100  of the present invention can derive the refraction index of the sample solution  400  by detecting the light beam intensity. Referring to  FIG. 5 ,  FIG. 5  is the relationship diagram showing the light beam intensity of the coupling outcome and the refraction index of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention. As shown in  FIGS. 1 and 5 , the sucrose solutions of refraction indices of 1.343, 1.353, 1.363, and 1.373 and the deionized (DI) water are guided into the channel chip, and then a laser light beam is guided into the waveguide layer  120  to detect the laser light beam intensity after the light beam is coupled with the waveguide layer  120 . The material of the waveguide layer  120  is titanium dioxide. 
     Furthermore, the first step of the sensing processes is, for example, guided in the deionized water into the channel chip  130 , and then the laser light beam is guided into the waveguide layer  120 . Afterward, a syringe pump, for example, is used to push the sucrose solution of the refraction index of 1.343 into the channel chip  130 , and then the sucrose solutions of the refraction indices of 1.353, 1.363, and 1.373 are injected into the channel chip  130  sequentially in a 1 minute interval. Finally, the deionized water is injected into the channel chip  130  again and held for 2 minutes. In  FIG. 5  the horizontal axis is the refraction index of the sample solution  400 , while the vertical axis is the processed signal strength of the light beam intensity of the coupling outcome. It can be observed in  FIG. 5  that the sensor resolution of the double-sided grating waveguide biosensor  100  of the second preferred embodiment of the present invention can reach up to 5.13×10 −6  refractive index unit (RIU). Besides, the detecting sensitivity of the double-sided grating waveguide biosensor of the second preferred embodiment, which has gaps located between the plastic grating and the waveguide layer, is greater than that of the first preferred embodiment. Thus, the processed signal strength can be used to obtain the refraction index of the sample solution  400  and further derive the properties of the sample solution  400 . 
     Additionally, the double-sided grating waveguide biosensor  100  of the present invention further comprises the recognition molecule layer  140  fixedly bonded to the surface of the waveguide layer  120  between the waveguide layer  120  and the channel chip  130 . The recognition molecule layer  140  is designed to interact with the sample solution  400  such that the detection sensitivity of the double-sided grating waveguide biosensor  100  of the present invention can be further increased. Besides, the material of the recognition molecule layer  140  can be, for example, an antibody molecule or other suitable recognition molecules. 
     Numerical experimental data are provided to confirm that the detection sensitivity of the double-sided grating waveguide biosensor  100  of the present invention can be increased. First, the phosphate buffer solution (PBS) is guided into the channel chip  130 , and then the syringe pump is used to pump in the anti-dinitrophenyl antibody (anti-DNP) solution with the density of 1×10 −7  g/cm 3  into the channel chip  130 . Afterward, the concentration of the anti-DNP solution is elevated and injected into the channel chip  130  in every  30  minutes, until the concentration of the anti-DNP solution reaches 1×10 −5  g/cm 3 . Referring to  FIG. 6 ,  FIG. 6  is a relationship diagram showing the light beam intensity of the coupling outcome and the concentration of the sampling solution of a double-sided grating waveguide biosensor with the recognition molecule layer according to the first preferred embodiment of the present invention. In  FIG. 6  the horizontal axis is the concentration of the sample solution, while the vertical axis is the processed signal strength of the light beam intensity of the coupling outcome. As shown in  FIGS. 1 and 6 , the double-sided grating waveguide biosensor  100  of the present invention can reach the limit of detection (LOD) of 7.81×10 −8  g/cm 3 . 
     Thus, one of the features of the double-sided grating waveguide biosensor  100  of the present invention is that the double-sided grating waveguide biosensor  100  of the present invention can have a good limit of detection when performing a detection with the help of the double-sided grating structure  121  of the waveguide layer  20  and the recognition molecule layer  140 . 
     Referring to  FIGS. 7 to 9 ,  FIG. 7  is a flow diagram showing the manufacturing method of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention.  FIGS. 8   a - 8   c  are processing sectional diagrams showing the imprinting of the grating structure of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention.  FIG. 9  is a state diagram showing the manufacturing of the plastic grating of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention. As shown in  FIG. 1  and  FIGS. 7 to 9 , the manufacturing method of the double-sided grating waveguide biosensor  100  of the present invention begin with, for example, generating a grating mold  210  (Step  510 ). Specifically, generate a sol-gel layer  212  on a substrate  211  by, for example, spread-coating the sol-gel over the substrate  211  made of hard material. Afterward, utilize a grating master mold  220  with the grating master structure to imprint the grating structure  213  on the sol-gel layer  212 . Furthermore, vacuum-pumping or high temperature baking, for example, can be used to harden the sol-gel layer  212  and remove the bubbles within the sol-gel layer  212 . Finally, the grating mold  210  is generated after the grating master mold  220  is removed. 
     When imprinting the grating structure  213 , for example, the grating master mold  220  is first located above the sol-gel layer  212 , and then pressed into the sol-gel layer in the x-direction. Thus, the grating structure  213  is generated on the sol-gel layer  212 . Remove the grating master mold  220  away from the sol-gel layer  212  in the opposite of the x-direction and wait until the sol-gel layer is frozen, the grating mold is generated. After the grating master mold  220  is removed, we can proceed to, for example, the modifications of the grating mold  210 . 
     After the grating mold  210  is generated, the next step is to produce the plastic grating  110  (Step  520 ). Specifically, the grating mold  210  is utilized to perform a shaping on a plastic material to produce the plastic grating  110  which comprises the grating part  111  on the surface  112 . Among which, the shaping process of the plastic material can be the injection molding, the injection compression, the hot pressing, the extrusion molding, the vacuum shaping, or other plastic shaping methods. After the plastic material is shaped into the plastic grating  110 , the grating mold  210  is separated from the plastic grating  110  to produce the plastic grating  110  with the grating part  111 . Besides, the plastic material can be, for example, cyclic-olefin copolymers, polycarbonate, acrylic, polypropene, or other suitable plastic material with high transparency. Steps  510  and  520  are the flow steps to produce the plastic grating of the double-sided grating waveguide biosensor  100  of the present invention. 
     Thus, one of the features of the double-sided grating waveguide biosensor  100  of the present invention is that the plastic grating  110  can be mass-produced to reduce the cost by using the grating mold  210  to perform the shaping of the plastic material. 
     After the plastic grating  110  is generated, the next step is to generate the waveguide layer  120  on the plastic grating  110  (Step  530 ). Furthermore, the waveguide layer  120  is generate on the surface  112  with the grating part  111  of the plastic grating  110 , and part of the waveguide layer  120  is located on the grating part  111  to form a double-sided grating waveguide structure  121 . The waveguide layer  120  can be, for example, deposited on the plastic grating  110 . Thus, the double-sided grating structure  121  of the waveguide layer  120  comprises two waveguide grating parts corresponding to each other. Afterward, the channel chip  130  is installed on the waveguide layer  120  (Step  540 ) to complete the double-sided grating waveguide biosensor  100  of the present invention. After Step  540 , the recognition molecule layer  140  can be selectively generated on the waveguide layer  120  (Step  550 ). After the channel chip  130  is installed, for example, the recognition molecule layer  140  is injected and fixedly bonded to the surface of the waveguide layer  120  between the waveguide layer  120  and the channel chip  130  to enhance the detection sensitivity of the double-sided grating waveguide biosensor  100  of the present invention. 
     Thus, one of the features of the double-sided grating waveguide biosensor  100  of the present invention is that the double-sided grating waveguide biosensor  100  of the present invention can be mass-produced with the reduced cost by using the grating mold  210  to produce the optical grating  110  and by using the deposit technologies to generate the waveguide layer  120  on the plastic grating  110 . 
     Referring to  FIGS. 10 and 11 ,  FIG. 10  is a flow diagram showing the detection method of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention.  FIG. 11  is a detection system diagram showing a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention. As shown in  FIGS. 1 ,  10 , and  11 , in the detection method of using the double-sided grating waveguide biosensor  100  of the present invention, the sample solution  400  can be guided into the channel chip  130  of the double-sided grating waveguide biosensor  100  (Step  620 ). Afterward, a light beam  311  can be coupled into the waveguide layer  120  (Step  630 ). Specifically, a light source  310  can be used to emit a light beam  110  such as a laser light beam. The light beam is guided into the plastic grating  110  via an optical device  320 , and then coupled into the waveguide layer  120  via the double-sided grating structure  121 . Furthermore, the optical device  320  can be, for example, a beam splitter, an optical fading lens, a convex lens, or any device which can change the direction or the property of the light beam  311 . 
     Additionally, the double-sided grating waveguide biosensor can be, for example, located on a rotary stage  330 . The rotary stage  330  is used to adjust the angle θ of coupling and the coupling position of the light beam  311  when coupling into the waveguide layer  120 . Furthermore, the angle θ of coupling and the coupling position within their specific preset ranges do not change with the variations of the refraction index of the sample solution  400 . The coupling position and the angle of coupling of the peak light beam intensity do not change with the variations of the refraction index, either. Thus, any of the light beams  311  within the preset range can be effectively coupled into the waveguide layer  120 . The angle θ of coupling is ranged from −90 to 90 degrees. The coupling position is located on the double-sided grating structure  121 , and the distance d between the coupling position and the terminal  123  of the double-sided grating structure is within 0 to 2 centimeters. 
     After Step  630 , the light beam intensity is detected (Step  640 ). For example, the light detector  340  is used to detect the intensity of the light beam  311  emitted from the waveguide layer  120  of the double-sided grating waveguide biosensor  100 . Afterward, the numerical value of the light beam intensity of the light beam  311  is processed (Step  650 ). For example, a data processing system  350  is used to process the light beam intensity detected by the light detector  340 , such that the user can utilize the variation data of the light beam intensity to calculate the detection sensitivity and analyze the properties of the sample solution  400 . 
     Numerical experimental data are provided to confirm that the angle θ of coupling and the coupling position within their specific preset ranges do not change with the variations of the refraction index of the sample solution  400  and the light beam  311  is effectively coupled into the waveguide layer  120  in the detection method of the double-sided grating waveguide biosensor  100  of the present invention. Referring to  FIG. 12 ,  FIG. 12  is a relationship diagram showing the light beam intensities of the sample solutions with different refraction indices and the angle of coupling of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention. As shown in  FIGS. 1 and 12 , the range of the angle θ of coupling remains the same, no matter the refraction index of the sample solution  400  is 1.333, 1.343, or 1.353. In other words, the variations of the refraction index of the sample solution  400  do not change the range of the angle θ of coupling. Besides, the angle of coupling of the peak light beam intensity does not change with the variations of the refraction index of the sample solution  400 . The light beam intensity is apparently greater as the angle of coupling is between 13.3° and 14.1°. 
     Referring to  FIG. 13 ,  FIG. 13  is a relationship diagram showing the light beam intensities of the sample solution with different refraction indices and the coupling position of a double-sided grating waveguide biosensor according to the preferred embodiment of the present invention. As shown in  FIGS. 1 and 13 , the light beam can be effectively coupled into the waveguide layer  120 , no matter the refraction index of the sample solution  400  is 1.333, 1.343, or 1.373 and where the coupling position is. Thus, the light beam intensity is changed apparently as the distance d between the coupling position and a terminal  123  of the double-sided grating structure  121  is within 0 to 2 centimeters. Besides, the variations of the refraction index of the sample solution  400  do not change the range of the coupling position. Within this range, the angle of coupling of the peak light beam intensity does not change with the variations of the refraction index of the sample solution  400 . 
     Referring to  FIG. 14 ,  FIG. 14  is a relationship diagram showing the light beam intensities of different angles of coupling and the refraction index of a double-sided grating waveguide biosensor according to the first preferred embodiment of the present invention. As shown in  FIGS. 1 and 14 , the deionized water and the sucrose solutions of refraction indices of 1.343, 1.353, 1.363, or 1.373 are separately guided in the channel chip  130  to carry out the detection. First, the deionized water is injected into the channel chip  130 , and then the light beam  311  is coupled into the waveguide layer  120  with the angle of coupling of 13.3287°. Afterward, a syringe pump, for example, is used to push the sucrose solution of the refraction index of 1.343 into the channel chip  130 , and follow by sucrose solutions of increasing refraction indices in a 1 minute interval until the sucrose solution of the refraction index of 1.373 is injected. Finally, the deionized water is injected into the channel chip  130  and holds for 2 minutes to complete a detection cycle. Afterward, the angle of coupling is adjusted to 13.4435°, 13.5435°, 13.6435°, 13.7435°, and 13.8435° separately, and then the above detection procedures are repeated. As shown in  FIG. 14 , the detected signal strength maintains a linear relationship with the refraction index of the sample solution  400 . In other words, the detection sensitivity of the double-sided grating waveguide biosensor  100  of the present invention does not change with the variations of the angles of coupling. 
     Referring to  FIG. 15 ,  FIG. 15  is a relationship diagram showing the light beam intensities of different coupling positions and the refraction index of a double-sided grating waveguide biosensor according to the first preferred embodiment of the present invention. As shown in  FIGS. 1 and 15 , the deionized water and the sucrose solutions of refraction indices of 1.343, 1.353, 1.363, or 1.373 are separately guided in the channel chip  130  to carry out the detection. First, the deionized water is injected into the channel chip  130 , and then the light beam  311  is coupled into the waveguide layer  120  at the coupling position of 1.66 mm away from the terminal  123  of the double-sided grating structure  121 . Afterward, a syringe pump, for example, is used to push the sucrose solution of the refraction index of 1.343 into the channel chip  130 , and follow by sucrose solutions of increasing refraction indices in a 1 minute interval until the sucrose solution of the refraction index of 1.373 is injected. Finally, the deionized water is injected into the channel chip  130  and held for 2 minutes to complete a detection cycle. Afterward, the coupling position is adjusted to 3.80 mm and 5.35 mm separately, and then the above detection procedures are repeated. As shown in  FIG. 15 , the detected signal strength maintains a linear relationship with the refraction index of the sample solution  400 . In other words, the detection sensitivity of the double-sided grating waveguide biosensor  100  of the present invention does not change with the variations of the coupling position. 
     Thus, one of the features of the double-sided grating waveguide biosensor  100  of the present invention is that both using the double-sided grating structure  121  to couple in the light beam into the waveguide layer  120  and detecting the intensity of the outgoing light beam allow the light beam to possess the coupling capability within a range. Besides, the detection sensitivity of the double-sided grating waveguide biosensor  100  does not change with the variations of the angle of coupling and the coupling position. 
     Another feature of features of the double-sided grating waveguide biosensor  100  of the present invention is that the complexity of the detection procedures is reduced by detecting the light beam intensity of the coupling outcome. 
     In summation, although the present invention has been described with reference to the foregoing preferred embodiment, it will be understood that the invention is not limited to the details thereof. Various equivalent variations and modifications may still occur to those skilled in this art in view of the teachings of the present invention. Thus, all such variations and equivalent modifications are also embraced within the scope of the invention as defined in the appended claims.