Abstract:
A biochip detection system detects and locates samples that are labeled with multiple fluorescent tags and are located on a biochip. This biochip detection system includes a charge coupled device (CCD) sensor, a broad spectrum light source, a lens, a light source filter, and a sensor filter. The CCD sensor comprises two dimensional CCD arrays to simultaneously detect light waves from at least a substantial portion of the biochip. The broad spectrum light source is optically coupled to the CCD sensor and is configured to be utilized with a variety of different fluorescent tags which have differing excitation wavelengths.  
     The lens and the CCD sensor are optimized and matched to each other such that the sensor operates at or below the diffraction rating of the lens. Further, the resolution of the CCD sensor is matched to the samples on the biochip such that the CCD sensor oversamples each of the samples a sufficient number of times. Additionally, the lens is configured to frame at least a substantial portion of the biochip.  
     The biochip detection system is optimized to provide a higher dynamic range, increased sensitivity, and faster throughput compared to system utilizing laser scanners. Further, the biochip detection system is capable of utilizing a same broad spectrum light source to excite samples labeled with a variety of fluorescent tags.

Description:
FIELD OF THE INVENTION  
         [0001]    The invention relates to the field of detectors for analysis of biological samples located on biochips. More particularly, the invention relates to the field of detectors that analyze samples labeled with a tag while utilizing a charge coupled device sensor.  
         BACKGROUND OF THE INVENTION  
         [0002]    Detection devices that detect and locate samples contained on a biochip via laser light sources and laser scanners are well known in the art. These detection devices require that the samples be labeled by a fluorescent tag. Typically, these detection devices rely on laser light sources to excite the samples that are labeled by a fluorescent tag and causes biologically active samples to output emitted light waves. The laser source is scanned to serially excite each sample on the biochip to detect any emitted light waves from the samples that are biologically active.  
           [0003]    Unfortunately, these detection devices utilizing either the laser light source or the laser scanner suffer from various drawbacks. First, laser scanners utilized to detect the emitted light waves from the exited samples on the biochip typically require wait times upwards of five minutes for sufficient resolution. Because laser scanners operate as a serial scanning device by sequentially detecting one sample at a time on the surface of the biochip, laser scanners are inherently inefficient at detecting the emitted light waves from an array of samples.  
           [0004]    Further, laser light sources utilized within the detection devices inherently only emit coherent light waves which span over an extremely narrow range of wavelengths. Fluorescent tags are generally responsive to a single frequency of light or light from a narrow frequency band. Thus, the use of the laser light sources severely limits the flexibility of those detection devices because only one type of fluorescent tag can be used. To use other tags, additional laser sources must be used. Further, to evaluate a biochip that has been treated with multiple tags, the prior art&#39;s long duration scan cycle must be performed for each one of the required laser sources.  
           [0005]    For example, if samples on a biochip were labeled with two different fluorescent tags and the different tags required light waves with substantially different excitation wavelengths, analyzing these samples would require the user to change laser light sources the analysis of all the samples were completed. Additionally, to be able to handle samples labeled with different fluorescent tags with differing excitation wavelengths, the user is required to have access to a variety of laser light sources. Since laser light sources are costly and specialized items, there are substantial costs and inconveniences associated with utilizing these prior detection devices.  
           [0006]    Therefore, it is desirable to have an ability to detect and locate samples labeled with multiple tags contained on a biochip, without the need for a laser light source. It is also desirable have an ability to detect and locate samples labeled with a tag contained on a biochip, without the need for a serial scanning device.  
         SUMMARY OF THE INVENTION  
         [0007]    The invention is a biochip detection system for detecting and locating samples that are labeled with multiple tags and are located on a biochip. This biochip detection system includes a charge coupled device (CCD) sensor, a broad spectrum light source, a lens, a light source filter, and a sensor filter. The CCD sensor comprises two dimensional CCD arrays to simultaneously detect light waves from at least a substantial portion of the biochip. The broad spectrum light source is optically coupled to the CCD sensor and is configured to be utilized with a variety of different fluorescent tags which have differing excitation wavelengths.  
           [0008]    The light source filter is optically coupled between the light source and the biochip and is configured to only substantially allow light waves that have an excitation wavelength corresponding to a particular fluorescent tag to reach the biochip. The light source filter prevents light waves that have similar wavelengths to an emission wavelength of the particular fluorescent tag from reaching the biochip or the CCD sensor. The sensor filter is optically coupled between the biochip and the CCD sensor and is configured to only substantially allow light waves that have the emission wavelength corresponding to the fluorescent tag to reach the CCD sensor. The sensor filter prevents extraneous light waves from giving the CCD sensor false signals.  
           [0009]    The lens and the CCD sensor are optimized and matched to each other such that the sensor operates at or below the diffraction rating of the lens. Further, the resolution of the CCD sensor is matched to the samples on the biochip such that the CCD sensor oversamples each of the samples a sufficient number of times. Additionally, the lens is configured to frame at least a substantial portion of the biochip.  
           [0010]    The biochip detection system is optimized to provide a higher dynamic range, increased sensitivity, and faster throughput compared to system utilizing laser scanners. Further, the biochip detection system is capable of utilizing a same broad spectrum light source to excite samples labeled with a variety of fluorescent tags. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 illustrates a schematic side view of internal elements of the preferred embodiment of the present invention.  
         [0012]    [0012]FIG. 2 illustrates a schematic side view of the preferred embodiment configured to analyze two sets of samples on a single biochip with each set of samples labeled with a different fluorescent tag.  
         [0013]    [0013]FIG. 3 illustrates a schematic side view of the preferred embodiment configured to analyze a plurality of samples on a single biochip with the plurality of samples labeled with multiple fluorescent tags.  
         [0014]    [0014]FIG. 4 is a graph that illustrates a relationship between a light intensity versus a wavelength of an excitation light of a particular fluorescent tag, an emitted light of this particular fluorescent tag, and the source light as utilized in the present invention.  
         [0015]    [0015]FIG. 5 illustrates a top view of an external housing of an alternate embodiment.  
         [0016]    [0016]FIG. 6 illustrates a side view of the external housing of the alternate embodiment.  
         [0017]    [0017]FIG. 7 illustrates a perspective view of the external housing of the alternate embodiment.  
         [0018]    [0018]FIG. 8 illustrates a side view of a camera housing of the preferred embodiment. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    [0019]FIG. 1 illustrates a side view of the preferred embodiment of the present invention. This preferred embodiment is a biochip detection system  100  as shown in FIG. 1. The biochip detection system  100  preferably includes a lens  120 , a sensor filter  130 , a charge coupled device (CCD) sensor  140 , a light source  150 , and a light source filter  160 . Preferably, the biochip detection system  100  is configured to detect and locate samples  110  within a biochip  170 . The samples  110  and the biochip  170  are shown for exemplary purposes only and are not intended to be part of the present invention. For the purposes of this specification, the biochip  170  is configured to have an array of samples  110  arranged in a predetermined number of rows and columns on top of a substrate. Further, the samples  110  contained within the biochip  170  are capable of including DNA or other biological material. For the biochip detection system  100  to properly operate, the samples  110  are labeled with a tag. The biochip  170  in the preferred embodiment is configured to hold samples  110  which are labeled with multiple tags. However, it will be apparent to those skilled in the art to utilize samples  110  only labeled by one tag on the biochip  170 . The samples  110  in the preferred embodiment are labeled with a fluorescent tag. However, it will be apparent to those skilled in the art to substitute this fluorescent tag with a chemiluminescent tag, colormetric tag, or the like. The process of labeling samples with a tag is well known in the art.  
         [0020]    The biochip detection system  100  detects and locates which ones of the plurality of samples  110  are fluorescently labeled within the biochip  170 . The biochip detection system  100  operates by exciting the samples  110  labeled by a fluorescent tag with light waves having an excitation wavelength thereby generating samples  110  that emit light waves having an emitted wavelength. Next, the CCD sensor  140  simultaneously detects the light waves having the emitted wavelength from at least a portion of the biochip  170 . Specific elements and procedures of the biochip detection system  100  are described in detail below.  
         [0021]    The CCD sensor  140  is preferably configured to include a two dimensional array of charge coupled devices. Preferably by having the CCD sensor  140  as a two dimensional sensor, the biochip detection system  100  is capable of simultaneously imaging either an entire area or a portion of the biochip  170  (depending on the size of the biochip  170 ) for light waves emitted by the samples  110 . By simultaneously imaging all the biochip  170 , the CCD sensor  140  allows the biochip detection system  100  to complete the detection process in most cases well under one minute and in some cases in twenty-five seconds. In an alternate embodiment, the CCD sensor  140  comprises cooled charge coupled devices. By having the charge coupled devices within the CCD sensor  140  cooled, background noise is reduced and signal clarity is maximized. In this preferred embodiment, the CCD sensor  140  is manufactured by Sony Corporation having the model number ICX 038DLA. It will be apparent to those skilled in the art to utilize a different CCD sensor  140 .  
         [0022]    The light source  150  is preferably a broad spectrum bulb that is configured to output light waves over a wide range of wavelengths. Preferably, the light source  150  is optically coupled to the biochip  170 . Because the light source  150  generates light waves over a wide range of wavelengths, the light source  150  is capable of forming light waves to excite samples labeled with a wide variety of fluorescent tags. In this preferred embodiment, the light source  150  is manufactured by General Electric Corporation having the model number 150 Watt EKE. It will be apparent to those skilled in the art to select a different light source.  
         [0023]    The lens  120  is preferably a compound lens that includes multiple lens elements. The lens  120  is located in an optical path between the biochip  170  and the CCD sensor  140 . Preferably, the lens  120  transmits light waves emitted from the samples  110  to the CCD sensor  140 . The lens  120  is capable of adjusting and optimizing a magnification parameter such that a desired portion of the biochip  170  is captured by the CCD sensor  140  with an appropriate field of view. Preferably, the lens  120  is configured such that the CCD sensor  140  operates at or below the diffraction limit of the lens  120 . In this preferred embodiment, the lens  120  is manufactured by Fujinon having a focal length of 25 millimeters and f-stop of 1:0.85. It will be apparent to those skilled in the art that the lens  120  can be substituted for a different lens or multiple lenses.  
         [0024]    Preferably, the light source filter  160  is optically coupled between the light source  150  and the biochip  170 . The light source filter  160  is preferably configured to substantially only allow light waves generated by the light source  150  with a predetermined excitation wavelength to reach the biochip  170 . The predetermined excitation wavelength corresponds to a particular wavelength that excites one of the samples  110  that is labeled with a particular fluorescent tag. The predetermined excitation wavelength depends on the sample in conjunction with the fluorescent tag. In other words, the light source filter  160  substantially blocks all light waves from the light source  150  with wavelengths other than the predetermined excitation wavelength from reaching the biochip  170 . By blocking substantially all light waves that have wavelengths other than the predetermined excitation wavelength, the light source filter  160  prevents erroneous light waves generated by the light source  150  from giving the CCD sensor  140  erroneous signals.  
         [0025]    Preferably, the sensor filter  130  is optically coupled between the CCD sensor  140  and the biochip  170 . As shown in FIG. 1, the sensor filter  130  is preferably between the CCD sensor  140  and the lens  120 . By placing the sensor filter  130  between the lens  120  and the CCD sensor  140 , the chances of distorting the light waves for detection by the CCD sensor  140  is minimized. Nevertheless, it will be apparent to those skilled in the art that the sensor filter  130  also can be configured between the lens  120  and the biochip  170 . The sensor filter  130  is preferably configured to substantially only allow light waves that are emitted from a sample labeled with a particular fluorescent tag that has a predetermined emitted wavelength to reach the CCD sensor  140 . The predetermined emitted wavelength occurs during excitation of this sample and depends on the sample in conjunction with the particular fluorescent tag. Preferably, the sensor filter  130  is optimized to parameters of the light source  150  and prevents extraneous light waves from reaching the CCD sensor  140  thereby increasing the accuracy and sensitivity of the biochip detection system  100 . It will be apparent to those of ordinary skill in the art that the filter selection is made to correspond with the fluorescent tags and also the sample type.  
         [0026]    The biochip detection system  100  is capable of efficiently detecting and locating samples  110  on the biochip  170 . The CCD sensor  140  and the lens  120  are preferably optimized relative to each other and also to the samples  110  on the biochip  170 . In particular, the CCD sensor  140  preferably has a transmission resolution to oversample each of the samples  110  by eight to nine times. For example, the CCD sensor  140  is preferably configured to have each of the samples  110  be optically detected by eight to nine pixels. Additionally, the lens  120  is preferably optimized to allow the CCD sensor  140  to operate at or below the diffraction limit of the lens  120 .  
         [0027]    In operation, the biochip detection system  100  is preferably configured to analyze the biochip  170 . The samples  110  are contained within the biochip  170  and are labeled with a multiple fluorescent tags. The biochip detection system  100  initiates operation by activating the light source  150 . The light waves emitted from the light source  150  are represented with a light wave  180  in FIG. 1. Next, the light wave  180  preferably passes through the light source filter  160 . As the light wave  180  passes through the filter, some wavelengths of the light wave  180  are blocked. A resultant light wave after passage through the light source filter  160  is represented as a light wave  190  as shown in FIG. 1. Preferably, the light wave  190  only substantially includes light waves with a predetermined excitation wavelength which correspondingly excites the samples  110  which are labeled with the particular fluorescent tag.  
         [0028]    As the samples  110  are excited by the predetermined excitation wavelength in the light wave  190 , the samples  110  produce light waves which are represented by a light wave  200  as shown in FIG. 1. The light wave  200  preferably includes light waves with a predetermined emission wavelength which are produced by the samples  110 . The light wave  200  then passes through the lens  120 . Some extraneous light waves with the predetermined excitation wavelength also pass through the lens  120  as shown by the light wave  190 . Next, the sensor filter  130  preferably blocks out substantially all light waves with wavelengths other than the predetermined emission wavelength; the sensor filter  130  substantially only allows light waves represented by the light wave  200  to reach the CCD sensor  140 . By substantially allowing only light waves having the predetermined emission wavelength to reach the CCD sensor  140 , the CCD sensor  140  is capable of accurately detecting and locating the samples  110  on the biochip  170 . As a result, the CCD sensor  140  is prevented from erroneously detecting stray light waves.  
         [0029]    The biochip detection system  100  is capable of accommodating a variety of fluorescent tags without switching the light source  150 , the lens  120 , or the CCD sensor  140 . To utilize multiple fluorescent tags with the biochip detection system  100 , only the light source filter  160  and the emission filter  130  are preferably changed. By merely changing the light source filter  160  and the sensor filter  130 , the biochip detection system  100  is capable of detecting and locating the samples labeled by this new fluorescent tag. Preferably, the light source filter  160  is changed such that substantially only light waves with an excitation wavelength corresponding to a new fluorescent tag reach the samples labeled by this new fluorescent tag. Further, the sensor filter  130  is preferably changed such that substantially only light waves with an emission wavelength corresponding to the new fluorescent tag reach the CCD sensor  140 .  
         [0030]    [0030]FIG. 2 illustrates the biochip detection system  100  configured to analyze a biochip  210  having two sets of samples with each set of samples labeled by a different fluorescent tag. The configuration of the biochip detection system  100  which includes the light source  150 , the lens  120 , the sensor filters  130  and  130 ′, the light source filters  160  and  160 ′, and the CCD sensor  140  is similar to the biochip detection system  100  in FIG. 1. The sensor filters  130  and  130 ′ are used interchangeably, one each for detecting the presence of different fluorescent tags. The light source filters  160  and  160 ′ are used interchangeably to illuminate the biochip  210  with different wavelengths of light. It will be apparent to those skilled in the art that additional filters can be utilized. The biochip  210  contains a first set of samples  220  which is labeled by a first fluorescent tag, and a second set of samples  230  which is labeled by a second fluorescent tag. First, the biochip detection system  100  is configured to locate and detect the first set of samples  220 . For proper configuration to detect and locate the first set of samples  220 , the source light filter  160  preferably substantially only allows light waves with an excitation wavelength corresponding to the first fluorescent tag to reach the biochip  210 . Further, the sensor filter  130  preferably substantially only allows light waves with an emission wavelength corresponding to the first fluorescent tag to reach the CCD sensor  140 .  
         [0031]    After the biochip detection system  100  is finished detecting and locating the first set of samples  220 , the system  100  is configured to detect and locate the second set of samples  230 . For proper configuration to detect and locate the second set of samples  230 , the source light filter  160 ′ preferably substantially only allows light waves with an excitation wavelength corresponding to the second fluorescent tag to reach the biochip  210 . Further, the sensor filter  130 ′ preferably substantially only allows light waves with an emission wavelength corresponding to the second fluorescent tag to reach the CCD sensor  140 . The filter can be manually changed. For systems used to routinely tests samples labeled with several known fluorescent tags, the filters can be automatically interchanged, for example, using a so-called “jukebox”. Although the first set of samples  220  and the second set of samples  230  are described as being labeled with a fluorescent tag, it will be apparent to those skilled in the art to substitute a fluorescent tag with a chemiluminescent tag, colormetric tag, and the like.  
         [0032]    [0032]FIG. 3 illustrates the biochip detection system  100  configured to analyze a biochip  700  having a plurality of samples  710  wherein each of the plurality of samples  710  are preferably labeled by multiple fluorescent tags. The configuration of the biochip detection system  100  which includes the light source  150 , the lens  120 , the sensor filters  130  and  130 ′, the light source filters  160  and  160 ′, and the CCD sensor  140  remain identical to the biochip detection system  100  in FIG. 2. The sensor filters  130  and  130 ′ are used interchangeably, one each for detecting the presence of different fluorescent tags. The light source filters  160  and  160 ′ are used interchangeably to illuminate the biochip  700  with different wavelengths of light. It will be apparent to those skilled in the art that additional filters can be utilized. The plurality of samples  710  are represented as being labeled by a first fluorescent tag  720  and a second fluorescent tag  730 . It will be apparent to those with ordinary skill in the art to label the plurality of samples  710  with any number of tags.  
         [0033]    First, the biochip detection system  100  is configured to locate and detect the plurality of samples  710  that are labeled with the first fluorescent tag  720 . For proper configuration to detect and locate the plurality of samples  710  that are labeled with the first fluorescent tag  720 , the source light filter  160  preferably substantially only allows light waves with an excitation wavelength corresponding to the first fluorescent tag to reach the biochip  700 . Further, the sensor filter  130  preferably substantially only allows light waves with an emission wavelength corresponding to the first fluorescent tag  720  to reach the CCD sensor  140 .  
         [0034]    After the biochip detection system  100  is finished detecting and locating the plurality of samples  710  that are labeled with the first fluorescent tag  720 , the system  100  is configured to detect and locate the plurality of samples  710  that are labeled with the second fluorescent tag  730 . For proper configuration to detect and locate the plurality of samples  710  that are labeled with the second fluorescent tag  730 , the source light filter  160 ′ preferably substantially only allows light waves with an excitation wavelength corresponding to the second fluorescent tag  730  to reach the biochip  700 . Further, the sensor filter  130 ′ preferably substantially only allows light waves with an emission wavelength corresponding to the second fluorescent tag  730  to reach the CCD sensor  140 . The filter can be manually changed. For systems used to routinely tests samples labeled with several known fluorescent tags, the filters can be automatically interchanged, for example, using a so-called “jukebox”. Although the plurality of samples  710  are described as being labeled with multiple fluorescent tags, it will be apparent to those skilled in the art to substitute multiple fluorescent tags with multiple chemiluminescent tags, colormetric tags, and the like.  
         [0035]    [0035]FIG. 4 illustrates a graph representing intensity of light along the vertical axis and wavelength along the horizontal axis. A curve  300  is representative of the light output from the light source  150  (FIGS. 1, 2, and  3 ). As observed from the curve  300 , the light source  150  outputs light waves preferably at an uniform intensity over a range of wavelengths. A curve  310  is centered around λ Excited  and represents a desired light intensity and wavelength to strike a sample labeled with a particular fluorescent tag in order to excite this sample. A curve  320  is centered around λ Emitted  and represents an emitted light intensity and wavelength from this sample while this sample is excited by light waves represented by the curve  310 .  
         [0036]    The curves  300 ,  310 , and  320  illustrate the functions of the light source filter  160  and the sensor filter  130  as illustrated in FIGS. 1, 2, and  3  and as described above. For example, while in operation, the light source  150  preferably outputs light waves represented by the curve  300 . Preferably, the light source filter  160  substantially only allows light waves that have wavelengths centered around the λ Excited  to reach the sample labeled by this particular fluorescent tag. Consequently, these light waves that have wavelengths centered around the λ Excited  excite the sample and are represented by the curve  310 . While excited, this sample preferably emits light waves that have wavelengths centered around the λ Emitted . Preferably, the sensor filter  130  substantially only allows light waves that have wavelengths centered around the λ Emitted  (which are represented by the curve  320 ) to reach the CCD sensor  140 .  
         [0037]    By having the source light filter  160  prevent light waves that have wavelengths centered around the λ Emitted  from striking this sample, the source light filter  160  prevents erroneous light waves from passing through the sensor filter  130  and striking the CCD sensor  140 . Further, by having the sensor filter  130  prevent light waves that have wavelengths centered around the λ Excited  from passing through the biochip  170  and then striking the CCD sensor  140 , the sensor filter  130  prevents erroneous readings from the CCD sensor  140 . As a result of the source light filter  160  and the sensor filter  130 , fewer or no stray, erroneous light waves strike the CCD sensor  140 .  
         [0038]    [0038]FIG. 5 illustrates an external top view of an alternate embodiment of the biochip detection system  100 . A main housing  400  is configured to hold the biochip  170  and the light source  150 . The main housing  400  is also configured to be light proof. By being light proof, the main housing  400  prevents extraneous light waves from giving the CCD sensor  140  erroneous signals. At least one articulating mirror  410  is utilized within the main housing  400  for appropriately directing light waves from the light source  150  to the biochip  170 . A camera housing  420  is utilized to hold the CCD sensor  140  and coupled to the main housing  400 .  
         [0039]    [0039]FIG. 6 illustrates an external side view of the alternate embodiment of the biochip detection system  100 . The main housing  400  includes a drawer  440  which allows a user to change the biochip  170 , adjust the light source filter  160 , and/or adjust the light source  150 . The drawer  440  includes appropriate seals to engage the main housing  400  such that the main housing  400  remains light proof. A filter box  480  is coupled to the main housing  400 . The filter box  480  is configured to securely hold the sensor filter  130  and has an opening  450  to accept the sensor filter  130 . The camera housing  420  is mounted to the filter box  480  via a camera mounting bracket  430 . Preferably, a light shield  510  is mounted between the camera housing  420  and the filter box  480  to prevent stray light waves from entering either the camera housing  420 , the main housing  400 , or the filter box  480 .  
         [0040]    [0040]FIG. 7 illustrates an external perspective view of the alternate embodiment of the biochip detection system  100 . For the sake of clarity, the camera housing  420 , the camera mounting bracket  430 , and the light shield  510  are omitted from FIG. 6. A fiber optic port  490  is provided in the main housing  400 . The fiber optic port  490  allows the biochip detection system  100  to interface with an external light source which is capable of transmitting light via a fiber optic cable connected to the external light and the fiber optic port  490 . The filter box  480  has a light channel  530  for allowing light to pass through the filter box  480  from the main housing  400  to the camera housing  420 . Further, the filter box  480  also has an opening  505  to accept a ball plunger  500 . A filter holder  460  is configured to hold at least one sensor filter  130  and has a plurality of notches  520 . The filter holder  460  is configured to slide through the opening  450  in the filter box  480 . The ball plunger  500  is configured to engage one of the plurality of notches  520  to appropriately position the filter holder  460  relative to the filter box  480 .  
         [0041]    A preferred embodiment of the external housing is similar to the alternate embodiment as shown in FIGS. 5, 6, and  7 . A main difference between the alternate embodiment and the preferred embodiment is that the preferred embodiment does not utilize the filter box  480  and the filter holder  460  as shown in FIGS. 5, 6, and  7 . Instead, the preferred embodiment of the external housing preferably couples the camera mount bracket  430  directly to the main housing  400 . Further, the camera housing  420  as shown in FIGS. 5 and 6 is modified and replaced in the preferred embodiment by a camera housing  600 . The camera housing  600  is illustrated in FIG. 8. Unlike the alternate embodiment of the camera housing  420  (FIGS. 5 and 6), the camera housing  600  preferably contains a filter wheel  610  which holds at least one sensor filter  130 . Preferably, the filter wheel  610  optically couples the sensor filter  130  between the lens  120  and the CCD sensor  140 . Further, the filter wheel  610  is preferably configured to change positions thus allowing different sensor filters  130  to be optically coupled between the lens  120  and the CCD sensor  140 .  
         [0042]    The present invention has been described in terms of specific embodiments incorporating details to facilitate the understanding of the principles of construction and operation of the invention. Such reference herein to specific embodiments and details thereof is not intended to limit the scope of the claims appended hereto. It will be apparent to those skilled in the art that modifications can be made in the embodiments chosen for illustration without departing from the spirit and scope of the invention.  
         [0043]    Specifically, it will be apparent to one of ordinary skill in the art that the device of the present invention could be implemented in several different ways and the apparatus disclosed above is only illustrative of the preferred embodiment of the invention and is in no way a limitation. For example, it would be within the scope of the invention to vary the dimensions disclosed herein. In addition, it will be apparent that the various aspects of the above-described invention can be utilized singly or in combination with one or more of the other aspects of the invention described herein. In addition, the various elements of the present invention could be substituted with other elements.