Abstract:
To observe and analyze intermolecular interactions such as diffusion and/or binding behaviors of molecules in a sample in a reacting state against optical stimulation, while applying the optical stimulation to a desired region in the sample by irradiating stimulus light. There is provided a fluorescence microscope apparatus comprising: a fluorescence image-capturing optical system; a stimulus light-irradiation optical system which includes a scanner for; a control unit which acquires temporal observation data by repeatedly capturing images using said image-capturing optical system while applying optical stimulation using the stimulus light-irradiation optical system; an analysis unit; and a display unit.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application No. 60/927,237, filed May 2, 2007. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a fluorescence microscope apparatus. 
     This application is based on Japanese Patent Application No. 2008-0692246, the content of which is incorporated herein by reference. 
     2. Description of Related Art 
     Raster Image Correlation Spectroscopy (RICS, refer to Document 1 below), Image Correlation Spectroscopy (ICS, refer to Document 2 below), and other methods have been studied and developed as algorithms for measuring and analyzing diffusion and binding behaviors, and moving directions of intracellular molecules in a living biological sample such as living cells, and such methods are attracting the attention of researchers. 
     Document 1: Michelle A. Digman, Measuring Fast Dynamics in Solutions and Cells with a Laser Scanning Microscope, Biophysical Journal Vol. 89, 2005. 
     Document 2: Paul W. Wiseman, Spatial mapping of integrin interactions and dynamics during cell migration by Image Correlation Microscopy, Journal of Cell Science 117, 2004. 
     Such analysis methods for determining diffusion coefficients and the like are carried out on the basis of image data of an analyte, which are obtained as scanned images through a laser scanning microscope. The image data to be used consist of scanned images of a sample in a static state. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a microscope apparatus capable of observing and analyzing intermolecular interactions such as diffusion and/or binding behaviors of molecules in a sample in a reacting state against optical stimulation, while applying the optical stimulation to a desired region in the sample by irradiating stimulus light. 
     In order to achieve the above object, the present invention provides the following solutions. 
     The present invention provides a fluorescence microscope apparatus comprising: a fluorescence image-capturing optical system for capturing fluorescence images of a sample; a stimulus light-irradiation optical system which includes a scanner for applying optical stimulation to an optional region in the sample by irradiating stimulus light; a control unit which acquires temporal observation data by repeatedly capturing images using the image-capturing optical system while applying optical stimulation using the stimulus light-irradiation optical system, an analysis unit which analyzes intermolecular interactions through analysis of changes in fluorescence intensity caused by molecular fluctuations within a confocal volume with use of the temporal observation data; and a display unit which displays an analysis result from the analysis unit. 
     In the above invention, said irradiation optical system may include a scanning optical system which irradiates a point in the sample with excitation light while scanning the excitation light being irradiated at the point; and said fluorescence image-capturing optical system may have a confocal aperture for confocal detection of fluorescence light emitting from the sample. 
     Moreover, in the above invention, said irradiation optical system may include a scanning optical system which irradiates a point in the sample with excitation light that generates fluorescence through multiphoton absorption while scanning the excitation light being irradiated at the point. 
     The above invention may also be designed such that: said irradiation optical system irradiates a surface of the sample with excitation light; said fluorescence image-capturing optical system includes an imaging optical system which projects the fluorescence images on a two-dimensional imaging element; and said analysis unit carries out analysis using each pixel of the two-dimensional imaging element as a confocal volume. 
     Moreover, in the above invention, said analysis unit may execute Raster Image Correlation Spectroscopy (RICS). 
     Furthermore, in the above invention, said analysis unit may execute Image Correlation Spectroscopy (ICS). 
     The above invention may also comprise a region specifying unit which specifies a desired region with respect to the temporal observation data, wherein said analysis unit carries out analysis of diffusion and/or binding behaviors of molecules caused by the optical stimulation, with use of the fluorescence intensity data within the specified region. 
     According to the present invention, an effect capable of observing and analyzing intermolecular interactions such as diffusion and/or binding behaviors of molecules in a sample in a reacting state against optical stimulation, while applying the optical stimulation to a desired region in the sample by irradiating stimulus light, is demonstrated. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is an entire schematic diagram showing a fluorescence microscope apparatus according to a first embodiment of the present invention. 
         FIG. 2  is an explanatory diagram showing temporal observation images (XY-T images) captured by the fluorescence microscope apparatus of  FIG. 1 . 
         FIG. 3  is a diagram illustrating a relation between a molecule in a static state and laser beam spots. 
         FIG. 4  is a diagram illustrating a relation between a molecule in a moving state due to diffusion and laser beam spots. 
         FIG. 5  is a diagram showing a measurement region within a temporal observation image captured by the fluorescence microscope apparatus of  FIG. 1 . 
         FIG. 6  is a diagram illustrating a movement of a molecule due to diffusion when a stimulation laser beam for uncaging is irradiated at a position away from the measurement region of  FIG. 5 . 
         FIG. 7  is a flowchart illustrating a procedure for specifying and analyzing the measurement region of  FIG. 5 . 
         FIG. 8  is an explanatory diagram showing temporal observation images (XY-T images) captured by the fluorescence microscope apparatus of  FIG. 1 . 
         FIG. 9  is an entire schematic diagram showing a fluorescence microscope apparatus according to a second embodiment of the present invention. 
         FIG. 10  is a diagram showing a modified example of the fluorescence microscope apparatus of  FIG. 9 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     First Embodiment 
       FIG. 1  shows a schematic configuration of a scanning microscope apparatus (fluorescence microscope apparatus) according to a first embodiment of the present invention. 
     In  FIG. 1 , the reference symbol  1  denotes a scanning microscope main body. The scanning microscope main body  1  is connected with a computer (control unit)  2 . The computer  2  is also connected with an operation panel (region specifying unit)  3 , an excitation laser device  4 , a stimulation laser device (stimulus light-irradiation optical system)  121 , and an image monitor (display unit)  5 . 
     In the scanning microscope main body  1 , an excitation (observation) laser beam emitting from the excitation laser device  4  is reflected by an excitation dichroic mirror (fluorescence image-capturing optical system)  102  and made incident into a scanning unit (scanning optical system)  104 . The scanning unit  104  comprises a scanner  104 A and a composing mirror  104 B. In the drawing, the reference symbol  104 C denotes a pupil projection lens, and the reference symbol  104 D denotes a focusing lens. 
     The scanner  104 A has a galvanometer mirror for scanning in the X axis direction and a galvanometer mirror for scanning in the Y axis direction. The scanner  104 A scans a laser beam from the excitation laser device  4  in the X and Y axis directions according to a scan control signal from the computer  2 . Moreover, the composing mirror  104 B is a dichroic mirror for composing the excitation (observation) laser beam and a stimulation laser beam that will be described later. The composing mirror  104 B allows transmission of excitation (observation) laser beams (such as fluorescence from a sample) and other observation light (such as visible light and IR) but reflects stimulation laser beams (such as UV and purple light). 
     The excitation (observation) laser beam, which has been scanned in the X and Y axis directions, passes through the composing mirror  104 B, and is irradiated as a spotlight on an observation sample (sample)  108  placed on a stage  107 , via an object lens  106  attached to a revolver  105 . 
     Light from the observation sample  108  caused by the irradiation on the spotlight, such as reflected light, or fluorescence light emitting from the observation sample  108 , is collected by the object lens  106  to return to the incident optical path. The collected light passes through the dichroic mirror  102 , and light having wavelengths to be detected is exclusively extracted through a barrier filter (fluorescence image-capturing optical system)  110 . 
     The detection light that has passed through the barrier filter  110  is let incident into a photoelectric converter (fluorescence image-capturing optical system)  101  such as a photomultiplier, and is subjected to photoelectric conversion into electric signals corresponding to the quantity of the detection light. The analog signals output from the photoelectric converter are converted into digital signals corresponding to the quantity of detection light, by an A/D input channel  2   b  installed in the computer  2 . A calculating/processing unit (analysis unit)  2   a  in the computer  2  combines these digital signals and the scanning position information of the scanner  104 A to construct a two dimensional image. The image thus constructed is saved in a memory  2   c  and output as visual information on the image monitor  5 . 
     In the present scanning microscope apparatus, arrangement of a confocal aperture (fluorescence image-capturing optical system)  109  in a conjugate position with respect to the observation sample  108  enables use as a confocal scanning microscope apparatus that exclusively detects light from the focus position to make an image while eliminating light from sources other than the focus position. The reference symbol  103  denotes a mirror (fluorescence image-capturing optical system), and the reference symbol  111  denotes a confocal lens (fluorescence image-capturing optical system). 
     Moreover, in the present scanning microscope apparatus, use of infrared pulse laser which generates two-photon excitation for the excitation laser device  4  and detection of fluorescence generated by the two photon excitation enable use as a multiphoton excitation scanning microscope apparatus that exclusively observes the position of collected excitation laser beams in a three dimensional space of a sample, even without the confocal aperture  9 . 
     The stage  107  is an electrically-operated stage which is movable in the X and Y directions which are orthogonal to the optical axis of the microscope (object lens  106 ). Moreover, the revolver  105 , or the stage  107  with use of a Z motor  107 A provided inside or outside the microscope, enables focus position control in the Z direction. The Z direction is the direction of the optical axis of the microscope (object lens  106 ). The position control in the X, Y, and Z directions is controlled by the computer  2 . 
     On the other hand, the scanning unit  104  is connected with a stimulus light irradiation unit  122 . The stimulus light irradiation unit  122  also has a galvanometer mirror for scanning in the X axis direction and a galvanometer mirror for scanning in the Y axis direction as a scanner  122 A, to scan a stimulation laser beam from the stimulation laser device  121  in the X and Y axis directions according to a scan control signal from the computer  2 . The reference symbol  122 B denotes a pupil projection lens. 
     It is also possible to irradiate stimulus light at one desired point on the sample by holding the X and Y galvanometer mirrors which constitute the scanner  122 A at desired angles. The laser beam, which has been scanned in the X and Y axis directions, is reflected by the composing mirror  104 B in the scanning unit and is composed with the excitation (observation) laser beam. The composite beam travels through the object lens  106  attached to the revolver  105 , and is irradiated as a spotlight on the observation sample  108  placed on the stage  107 . 
     The operation panel  3  has a pointing device such as a track ball, a joystick, or a mouse, as well as a keyboard. The operation panel  3  accepts instructions input by an observer, and outputs an instruction to start scanning a laser beam and a command to capture an image as well as outputs to the computer  2  a command to adjust the sensitivity of the photoelectric converter  101 . Moreover, the operation panel is also used to set the wavelengths and intensities of an excitation (observation) laser beam and a stimulation laser beam, and to specify a region of interest (ROI) when an excitation (observation) laser beam or a stimulation laser beam is to be irradiated exclusively on a desired point or region (ROI) within a field of view of one screen. 
     The computer  2  takes charge of control of the entire apparatus. In particular, when an instruction to scan is input from the operation panel  3 , the computer  2  outputs a scan control signal to the scanning unit  104  and the stimulus light irradiation unit  122 . Also, the computer  2  converts analog signals of the observation sample  108  from the photoelectric converter  101  into digital data through the A/D input channel, transfers the digital data to the memory  2   c , and displays the image and the scanning menu on the image monitor  5 . 
     Furthermore, the computer  2  is designed to make settings such as the sensitivity of the photoelectric converter  101  (e.g., applied voltage in cases of a photomultiplier), the amplifier gain, and the offset, in accordance with a sensitivity adjustment command from the operation panel  3 . Moreover, programs  2   d  in the computer  2  execute respective controls such as control of the scanning unit in the scanning microscope main body  1 , injection of a laser beam from the excitation laser device  4  into the microscope, and output of the image information from the memory to the image monitor  5 . 
     As a technique for analyzing molecular dynamics such as diffusion and binding behaviors, and moving directions, there is a technique called Raster Image Correlation Spectroscopy (RICS). The RICS technique is a technique in which: a scanning microscope capture temporal observation images (XY-T images) are captured under scanning conditions where one pixel size is sufficiently small as compared to the spot size of an excitation laser beam (for example, 60×/NA 1.42 magnification of the object lens and 5× zoom of the scanner (galvanoscanner)); and the autocorrelation function (Equation (1), refer to academic Document 1 for details) is employed to determine a diffusion coefficient of molecules per pixel dwell time and per line repetition time, based on time intervals of the pixel scanning time and the line scanning time for capturing the image data. The temporal observation images (XY-T images) refer to a group of a series of XY images captured in one certain observation position repeatedly for a plurality of times at predetermined time intervals. 
     
       
         
           
             
               
                 
                   
                     
                       
                         
                           
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     When a particle stays still or is slowly moving, a fluorescence signal emitting from the molecule is detected by several spots as shown in  FIG. 3 . In the case of  FIG. 3 , the fluorescence signal from the molecule is detected only by the first spot and the second spot. Application of the RICS technique to the temporal observation data obtained through observation of such a molecule provides a small diffusion coefficient. 
     When a particle is rapidly moving, a fluorescence signal emitting from the molecule is detected by many spots as shown in  FIG. 4 . In the case of  FIG. 4 , the fluorescence signal from the molecule is detected by all of the first spot to the fourth spot. Application of the RICS technique to the temporal observation data obtained through observation of such a molecule provides a large diffusion coefficient. The magnitude correlation between these diffusion coefficients enables analysis of the difference in the diffusion rate of respective molecules. 
     The measurement of the diffusion rate can be achieved not only by calculation processing of the entire field of view of the temporal observation image, but also by specifying a desired measurement region in the temporal observation image as shown in  FIG. 5  and targeting fluorescence signals in the measurement region. By using this processing, diffusion of intracellular molecules and binding behaviors of molecules around the cell membrane can be captured as one temporal observation image, and can be observed and measured at a same time point. 
     Next, the operation of the first embodiment using the system configured as mentioned above is described. 
     As an example, here is a description of a case where a sample injected with a caged indicator and a fluorescence indicator, which is sensitive to calcium ion concentration, is irradiated with an excitation laser beam having a wavelength of 488 nm from the excitation laser device  4  ( FIG. 1 ), to carry out analysis by detecting fluorescence generated from the calcium ion concentration-sensitive fluorescence indicator.  FIG. 6  shows the manner in which the sample reacts against optical stimulation for uncaging when applied to a desired position of the sample.  FIG. 7  shows the procedure (flowchart) for specifying and analyzing the measurement region of the sample in this manner. 
     Step S 1 ) First, in order to specify the position to be uncaged (=optically stimulated), an observation image (reference image (XY image)) of the site to be measured is captured and displayed as a reference image on the image monitor  5 . 
     Step S 2 ) Using the reference image, the position or region (ROI,  FIG. 6 ) to be optically stimulated (uncaged) is specified. 
     Steps S 3  and S 4 ) Condition settings for temporal observation (XY-T image capturing) of the sample are specified or input. Examples of the condition settings include the number of X pixels, the number of Y pixels, information on the object lens (magnification and numerical aperture), the zoom size of scanning (information on the scanning width for laser scanning), the laser wavelength, the scan rate (pixel rate, line rate, and frame interval), and the number of frames to be captured. 
     Scanning of an excitation laser beam is started to capture XY-T images; while, as shown in  FIG. 6 , irradiating the specified position or region with a stimulation laser beam having a wavelength of 355 nm from the stimulation laser device  121  ( FIG. 1 ) to apply stimulation such that the caged group of the caged reagent is cleaved. The manner in which the calcium ion concentration is changed by the substance released from the caged reagent at this time is saved in the memory  2   c  of the computer ( FIG. 1 ) as temporal observation data, and is displayed on the image monitor  5  ( FIG. 1 ) as T (time) series images. 
     Step S 5 ) In the temporal observation data displayed on the image monitor  5 , a measurement region is formed around the cell membrane using the operation panel  3  ( FIG. 1 ). 
     Steps S 6  to S 8 ) Fluorescence signals within the measurement region are processed with the RICS technique. Conditions required for the RICS calculation have been already set as the XY-T image capturing conditions in Steps S 3  and S 4 ). The pixel size can be calculated from the XY-T image capturing conditions (number of X pixels, number of Y pixels, magnification of the object lens, and zoom size of scanning). D (diffusion coefficient) and G(0) are calculated based on these parameters and the Equation (1). 
     Here, “G(0)=1/N (N is the number of molecules)” means the value of the autocorrelation function G(τ)=(ΔF(t)ΔF(t+τ))/F(t) 2  in the case where τ=0 (initial value). The concentration of molecules is discussed in terms of this value. 
     By so doing, diffusion and binding behaviors of molecules around the cell membrane involved in the cleavage of the caged group can be measured. 
     In the present invention, a scanning microscope apparatus comprises a mechanism which controls optical stimulation independently of temporal observation by arranging another scanning optical system that is different from the optical system for capturing images, and an analysis method such as the RICS technique is applied to the temporal observation data acquired by capturing images with use of the scanning microscope apparatus, by which behaviors of intracellular molecules can be continuously analyzed during and after cell stimulation. 
     Second Embodiment 
     As shown in  FIG. 9 , a fluorescence microscope apparatus uses a mercury lamp house  130  and a CCD camera (imaging optical system)  131 , instead of the scanning unit  104  (FIG.  1 ), the excitation laser device  4  ( FIG. 1 ), and the photoelectric converter  101  in the scanning microscope apparatus according to the first embodiment mentioned above. In such a fluorescence microscope apparatus, optical stimulation is applied with use of the stimulus light irradiation unit  122  ( FIG. 1 ) according to the first embodiment during temporal observation to acquire the temporal observation data. 
     As shown in  FIG. 8 , the Image Correlation Spectroscopy (ICS) technique, which is capable of obtaining the diffusion coefficient per frame repetition time of the temporal observation data, is applied. By so doing, similarly to the first embodiment, behaviors of intracellular molecules can be continuously analyzed during and after cell stimulation. 
     The ICS technique is a technique for calculating the diffusion coefficient using information on brightness changes in the T direction for respective pixels in temporal image data. Since the resolution time for the information on the brightness changes is the time for capturing one frame, ICS is inferior to RICS in terms of speed. However, it is possible to calculate the diffusion coefficient even in the configuration of the present embodiment which employs non-confocal detection, by using the calculation technique of substituting one pixel in the CCD camera with a confocal volume. 
     ICS can also be used in the first embodiment. 
     Modified Example 1 
     A total internal reflection fluorescence microscope apparatus as shown in  FIG. 10 , which comprises a laser light source  141  and a total reflection illumination device  142 , instead of the mercury lamp house in the fluorescence microscope apparatus according to the second embodiment mentioned above, can also be used. 
     The two dimensional position of a stimulation laser beam from the laser light source  141  is set by an XY galvano scanner  143 . Then, the stimulation laser beam is irradiated on a sample S through a pupil projection lens  144 , a dichroic mirror (or a half mirror)  145 , a focusing lens  146 , and an object lens  147 , to apply optical stimulation to the observation sample  108 . 
     The total reflection illumination device  142  comprises: laser light sources  148 ,  149 , and  150  which emit laser beams of a plurality of wavelengths; beam expanders  151  which adjust the luminous flux diameter of laser beams from the respective laser light sources  148  to  150 ; a mirror  152 ; dichroic mirrors  153  and  154 ; an acoustooptic device  155  such as AOTF which modulates laser beams from the laser light sources  149  and  150 ; a variable magnification lens  156  for adjusting the illumination region, which is movable along the optical axis direction A; a drive mirror  157  for adjusting the blurring amount, which is moved along the optical axis direction A to thereby adjust the deflection angle so as to adjust the incident angle of laser beams into the specimen; and a pupil projection lens  158 . 
     Moreover, the total internal reflection fluorescence microscope apparatus comprises: an object lens  159  arranged on the opposite side to the object lens  147  relative to the observation sample  108 ; a focusing lens  160 ; a variable magnification lens  161 ; and an electron multiplier CCD  162 . 
     With the dichroic mirror  145 , laser beams from the laser light sources  148  to  150  are converged along the optical path of the stimulation laser beam from the laser light source  141  and made incident at shallow angles that satisfy total reflection conditions with respect to the observation sample  108 . 
     With use of the total internal reflection fluorescence microscope apparatus, behaviors of intracellular molecules in the observation sample  108  such as cells can be continuously analyzed during and after cell stimulation, by using temporal observation data having a high signal/noise ratio, within the depth resolution of about 100 nm from the surface of a cover glass. 
     According to the present invention, a microscope apparatus comprises a mechanism which controls optical stimulation independently of temporal observation by arranging another scanning optical system that is different from the scanning optical system or fluorescence observation optical system for capturing images, and an analysis method such as the RICS technique is applied to the temporal observation data acquired by capturing images with use of the microscope apparatus, by which behaviors of intracellular molecules can be continuously and accurately analyzed during and after cell stimulation.