Abstract:
An optical reagent format with a precise capillary channel is made by molding a format on a carrier of a precise predetermined thickness. The carrier includes an insert at least a portion of which is molded in the format. Once the format is made, the insert is detached from the carrier and removed from the format leaving a precisely dimensioned capillary channel with an inlet and vent. A reagent may be applied in the capillary channel and the format used to measure the analyte in a fluid such as blood. 
     An electrochemical sensor with a capillary channel is formed by placing a sacrificial insert and electrodes on a sensor base and applying plastic material. After the plastic material is cured, the sacrificial is removed leaving a capillary channel in the sensor. The inserts may be removed by a tool including a clamp for clamping and holding each insert stationary and a sliding block to which the sensor is secured.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This is a divisional application of U.S. Ser. No. 10/010,233, filed Dec. 7, 2001, which issued as U.S. Pat. No. 6,911,130; Ser. No. 10/010,233 claims priority back to Application Ser. No. 60/254,626, filed Dec. 12, 2000. 

   FIELD OF THE INVENTION 
   The present invention related to precision capillary channels for sensors and the method of making them. 
   BACKGROUND OF THE INVENTION 
   Sensors are used for sampling a fluid, mixing the fluid with a reagent, and making an analysis of the mixed sample. One form of sensor includes a capillary channel between two optical paths and a reagent in the channel. Another sensor is injection molded with a capillary channel between a base and lid. Electrodes and a reagent are located in the channel. A test fluid is drawn into the channel by capillary action and reacts with the reagent. In the first sensor, a light source is applied to one of the optical paths, and light from the light source is transmitted through the fluid in the channel and directed to a detector applied to the other optical path. In the second sensor an electric current accrossed the electrodes is measured. 
   A significant problem in the fabrication of optical reagent sensors is the production of a precision optical path length. This has been achieved by producing an optically clear part having a cavity of a certain depth. The cavity is covered by an optically clear lid. The precise depth of the cavity is difficult to produce repeatedly, but even if the depth can be repeatedly produced, it is very difficult to attach a lid and control the path length due to the tolerances of the method of attachment. In addition, if the attachment uses adhesives, variations in adhesives adds to the tolerances. Other types of attachment such as sonic welding each has their own variability. 
   The difficulty in repeatedly producing a cavity of a precise depth is critical when producing an optical reagent sensor that is to be used in the -transmission mode. In the transmission mode the path length in the capillary gap is directly proportional to an analyte being tested. If an identical analyte is measured in two sensors that have different path lengths, the results reported will be different due to the path lengths. There is a need for a method of making optical reagent sensors with precise capillary channels that can be produced without variances or tolerances. 
   Similarly, the formation of a capillary channel in an injection molded sensor is difficult to produce. The usual way to fabricate sensors of this type is to precision screen print active areas within a capillary area formed by a shaped top lid. It is desirable to reduce the cost and assembly required by this construction. Moreover, it is difficult to provide electrodes in a small molded capillary channel of less that 0.005 inch in height and it is desirable to provide a sensor of this size with molded electrodes so that such a sensor could be used for electrochemical analysis. 
   SUMMARY OF THE INVENTION 
   The present invention is directed to an optical reagent sensor and an electrochemical sensor and to a method for making an optical reagent sensor and an electrochemical sensor. The optical reagent sensor includes a precision capillary channel with an inlet and a vent. To fabricate such a sensor, a carrier made of a material that is chemically etched, punched, die cut or otherwise formed to a predetermined configuration and with precision thickness is provided as an insert. An optical sensor is molded onto the carrier and once the molded material is cured, the insert is detached from the carrier and removed from the sensor leaving a precise capillary channel in the sensor. A reagent can be applied to the channel for a particular analyte to be tested. The sensor is used by drawing a test fluid into the capillary channel. 
   The electrochemical sensor of the present invention includes individual electrodes or contacts molded into the sensor. This process includes placing a first electrode in a base mold and placing a sacrificial insert in the mold above the first electrode. A second electrode is then placed in the base over the insert. A top mold is placed on the base mold and plastic material is injected into the top and base molds. After curing, the sensor is removed from the mold and the sacrificial insert is removed leaving a capillary channel with the two contact/electrodes in the channel. 
   Since the force required to remove the insert from the fabricated sensor could be quite high, it is desirable to use a tool that clamps the insert securely in place while applying a force on the sensor. The tool includes a clamp for clamping the insert in a stationary position and a moveable block to which the sensor is secured. A drive mechanism is coupled to the block to move the block relative to the clamp thereby withdrawing the insert from the sensor. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the drawings in which: 
       FIG. 1  is a perspective view of a sensor format on a carrier; 
       FIG. 2  id a perspective view of a chain of sensor formats on a carrier; 
     FIG,  3  is an enlarged view of a sensor format removed from a carrier with a portion of the carrier between the legs of the format; 
       FIG. 4  is a reduced view of the sensor format illustrated in  FIG. 3  with the portion of the carrier removed from between the legs of the format; 
       FIG. 5  is a perspective view of an alternative embodiment of the sensor format illustrated in  FIGS. 1-4  on a carrier; 
       FIG. 6  is an enlarged view of the format illustrated in  FIG. 5  with the carrier removed; 
       FIG. 7  is a perspective view of a bottom mold of a molding tool for molding an electrochemical biosensor with a first contact positioned in the bottom mold; 
       FIG. 8  is a view similar to  FIG. 7  with a sacrificial protective insert positioned in the bottom mold; 
       FIG. 9  is a view similar to  FIG. 8  with a second contact positioned in the bottom mold; 
       FIG. 10  is a perspective view of the molding tool with a top mold placed on the bottom mold; 
       FIG. 11  is an enlarged perspective view of a molded electrochemical biosensor with a sacrificial insert in the biosensor; 
       FIG. 12  is a perspective view of a tool used to remove the inserts from the biosensors illustrated in  FIGS. 1-11 ; 
       FIG. 13  is a perspective view of an optical sensor with an insert; 
       FIG. 14  is a view similar to  FIG. 13  with the insert withdrawn; and 
       FIG. 15  is a perspective view of the optical sensor of  FIG. 13 . 
   

   While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof have been shown by way of examples in the drawings and will herein be described in detail. It should be understood, however, that it is not intended to limit the invention to the particular forms disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Referring to  FIGS. 1-4 , the sensor format  10  of the present invention is illustrated. The format  10  is an optical pipe formed of light transmission material. A light source is applied to the end  12  of a first leg  14  of the format  10 . Light from the light source travels the length of the first leg  14  until it strikes a first end surface  16  that is at a 45° angle to the longitudinal axis of the first leg  14 . The light is reflected by the end surface  16  through a capillary gap  18 . Light that is not absorbed by material in the gap  18  strikes a second end surface  20  which is at a 45° angle to a longitudinal axis of a second leg  22  of the format  10 . This light is reflected the length of the second leg  22  to a detector positioned at an end  24  of the second leg  22 . 
   The format  10  is used in the transmission mode and the path length in the gap  18  is directly proportional to an analyte being tested. If the same analyte is measured in two different formats that have different path lengths, the results reported will be different due to the different path lengths. The format  10  of the present invention is made in a manner to insure a capillary gap  18  of a precise thickness for each format  10  to minimize or eliminate any differences reported due to different path lengths through the gap  18 . 
   The format  10  is formed by injection molding over a single carrier  26  with an insert  28  or a multiple carrier  30  with multiple inserts  32 . The single carrier  26  and the multiple carrier  30  are of a material, such as metal, that can be chemically etched, laser cut, mechanically punched, die cut or a similar fabrication process, to a known precise thickness and configuration required to form a precise capillary gap  18 . The thickness of the carriers  26  and  30  are dependent on the desired light path length of the gap  18 . The carriers  26  and  30  can be formed of materials whose melt temperatures are above the melt temperature of the format material and the carrier material must have sufficient tensile strength to allow removal of the inserts  28  and  32  from the format  10  after the format  10  has been molded. 
   To mold a format  10 , the single carrier  26  and the multiple carrier  30  are positioned and secured in a molding tool by tractor feed or pin position holes  34 . Plastic material is injected into the molding tool and the formats  10  are formed on the single carrier  26  and the multiple carrier  30 . Once the plastic material is cured and the carriers  26  and  30  removed from the molding tool, the inserts  28  and  32  are separated from the carriers  26  and  30 , respectively, and removed from the formats  10  leaving a precise capillary gap  18 . Each gap  18  is of the same size and thickness due to the precision thickness and dimension of the inserts  28  and  32 . A reagent can be wicked into each gap  18  and dried. If the gap  18  must be sealed on the sides, lids (not shown) can be secured to the sides of the format  10  without being part of the optical path. 
   An extension  36  of each carrier  26  and  30  extends between the first leg  14  and the second leg  22  of each format  10  and provides an opaque light barrier between the legs  14  and  22  or light paths ( FIG. 3 ). The extension  36  also provides structural integrity to the legs  14  and  22  and the format  10 . If a light barrier or structural integrity is not needed, the extension  36  can be removed from between the legs  14  and  22  ( FIG. 4 ). 
   A format  110  that requires sides to be sealed and provides a direct optical read is shown in  FIGS. 5 and 6 . The format  110  is injection molded onto a carrier  112  in a manner similar to the molding of the reagent format  10  in  FIGS. 1-4 . The carrier  112  is of the same material as the carriers  26  and  30  and fabricated in the same manner to a known precise thickness to form a precise capillary gap  114 . The gap  114  is formed by an insert  116  that is part of the carrier  112 . 
   The carrier  112  is positioned in a molding tool by tractor feed or pin position holes  118 , and casting material is injected into the molding tool to form the formats  110 . After the casting material has cured, the carrier  112  is removed from the molding tool and the inserts  116  are extracted from the formats  110  leaving the precise capillary gaps  114  of micron sizes. There is an entrance or inlet  117  to each gap  114  and a vent formed by extensions  119  on carrier  112  on a side opposite the inlet  118 . The gap  114  is enclosed on the sides  114 A and  114 B and sides or a lid is not required to form the gap  114 . 
   The format  110  includes a first cone  120  above the gap  114  and a second cone  122  below the gap. The shape of the cones  120  and  122  can be any shape such as square and need not be the truncated cone shape shown in the drawings. A light source is placed at an end  124  of the first cone  120  and a light or optical detector is placed at an end  126  of the second cone  122 . Light from the light source travels through the first cone  120  to an analyte in the gap  114 , and light passing through the gap  114  and the analyte passes along the second cone  122  to the optical detector for measurement of the analyte or other specimen. The cones  120  and  122  isolate the optical components (light source and detector) from the gap  114  and the specimen in the gap to prevent contamination. If contamination is not an issue, the cones  120  and  122  can be eliminated. 
   Referring to  FIGS. 7-11  an electrochemical sensor  210  is illustrated. The sensor  210  includes a first electrode  212  and a second electrode  214  molded into the sensor  210  ( FIG. 11 ). The sensor  210  also includes a precise small capillary channel formed by a sacrificial insert  216 . 
   The sensor  210  is injection molded in a molding tool  218  having a bottom mold  220  and a top mold  222  ( FIG. 10 ). The bottom mold  220  ( FIGS. 7-9 ) includes a cavity  224  in the shape of the sensor  210 . A plurality of locator pins  226 ,  228 ,  230 ,  232 ,  234 ,  236 ,  238  and  240  are provided on the bottom mold for properly locating the first and second electrodes  212  and  215  and the sacrificial insert  216 . 
   The first and second electrodes  212  and  214  are loaded in the bottom mold  220  by stacking them such that the sacrificial insert  216  extends between them. The first electrode  212  is loaded first by fitting holes in the first electrode  212  over locator pins  226 ,  228 , and  230  ( FIG. 7 ). The sacrificial insert  216  is loaded next by fitting holes  238  and  240  in the insert over locator pins  238  and  240  ( FIG. 8 ). The sacrificial insert  216  extends into the cavity  224  and over and on a forward end of the first electrode  212 . The second electrode  214  is loaded in the bottom mold  220  onto locator pins  232 ,  234  and  236  with its forward end over and on the sacrificial insert  216  and over the forward end of the first electrode  212  ( FIG. 9 ). The top mold  222  is then placed on the bottom mold  220  and compressed to provide compressive loading of both sides of the sacrificial insert  216 . This compressive loading can be provided by raised portions in the bottom mold  220  and the top mold  222  that engage the sacrificial insert  216  between them as the top mold  222  is mounted on the bottom mold  220 . 
   Once the molding tool  218  is assembled ( FIG. 10 ), plastic material is injected into the tool  218 . Due to the compressive loading, the cavity  224  is filled with plastic material but since plastic can not flow into the stack of the forward ends of the first and second electrodes  212  and  214  and the insert  216 , the plastic material does not flow between the forward ends of the electrodes  212  and  214  and the insert  216 . 
   Once the plastic material has cured, the molding tool  218  is opened and the sensor  210  with the first electrode  212  and second electrode  214  and the insert  216  are removed. The insert  216  is then removed from the sensor  210  leaving a precise small capillary channel  242  ( FIG. 11 ) with the first electrode  212  on the bottom of the channel  242  and the second electrode  214  on the top of the channel  242 . 
   An optical version of the electrochemical sensor  210  is illustrated in  FIGS. 13-15 . In these  FIGS. 13-15  there is illustrated an optical sensor  410 . The optical sensor  410  is molded in a manner and tool similar to that for the sensor  210  except instead of electrodes  212 ,  214 , the optical sensor  410  includes an access window  412  for source optics and an access window for detector optics directly below the access window  412 . A capillary cavity or channel  414  is formed in the optical sensor  410  between the access windows so that light from source optics directed into the access window  412  passes through a specimen in the capillary cavity or channel  414  and is read by detector optics positioned at the lower access window. 
   A mold or tool that forms the optical sensor  410  includes inserts that are highly polished and extend into the mold. As plastic material is injected into the mold, the plastic material flows around the inserts to form the access windows. Since the inserts are highly polished, the access windows are clear with little distortion. 
   The capillary cavity or channel  414  is formed by an insert  416  that may be made of stainless steel or similar material. The insert  416  is similar to the insert  216  in  FIGS. 7-11  and includes fitting holes  438  and  440  that fit over locator pins similar to pins  238  and  240  in a mold ( FIG. 8 ). 
   Because the insert  416  is very thin and large pressures occur in the mold during molding of the optical sensor  410 , an access hole  418  is formed in the optical sensor  410  by a portion of the mold that grips the insert  416  and holds it stable as plastic material flows around the insert  416 . The optical sensor  410  also includes a hole  446  similar to the hole  346  in the sensor  210 . 
   In each of the above described embodiments the insert  28  or  216  must be removed from the sensor  14  or  210 , respectively, and the force required to do this could be quite high. Therefore, it is desirable to have a tool that will hold the sensor  14  or  210  securely in place and supply sufficient force inline to the insert  28  or  216  to withdraw the insert  28  or  216  from the sensor  14  or  210 . An insert removal tool or extractor  300  to accomplish these objectives is illustrated in  FIG. 12 . The extractor  300  is secured to a base  312  and includes a clamp  314 . The clamp  314  may be a DeStaca clamp with a handle  316  pivotally mounted on a stand  318 . The stand  318  is secured to the base  312 . The handle  316  is coupled to a clamp head  320  by a linkage  322  such that rotating the handle  316  causes the clamp head  320  to move toward and away from the base  312 . 
   The base  312  includes a cavity  324  in which is positioned a sliding block  326 . A cover plate  328  is secured to the base  312  over a portion of the cavity  324 . The cover plate  328  has a slot  330  through which extends a drive pin and bearing  332  that are attached to the sliding block  326 . An extraction drive lever  334  is pivotally mounted on the base  312  by a pin  336  and abuts the drive pin and bearing  332  such that as the extraction drive lever  334  is pivoted in a clockwise direction about the pin  336  as view in  FIG. 12 , the drive pin and bearing  332  are moved in the slot  330  moving the sliding block  326  out the end of the cavity  324 . 
   To remove an insert  28 ,  216  or  416  the sensor  14 ,  210  or  410  (in  FIG. 12  sensor  210  is illustrated) is placed in the cavity  324  with the holes  238  and  240  ( FIG. 11 ) in the sensor  216  placed over the pins  342  and  344  which are rigidly mounted on the base  312 . A hole  346  ( FIG. 11 ) in the sensor  210  is positioned over a sensor pin  348  on the sliding block  326 . Accordingly, the sensor  210  is secured to the sliding block  326  and the insert  216  is secured to the base  312 . A force distribution block  340  is placed over the pins  342  and  344  and clamped down onto the insert  216  by the clamp  314 . 
   The insert  216  is withdrawn from the sensor  210  by a force inline with the sensor  210  and insert  216  by pivoting the extraction drive lever  334  to move the sliding block  326  in the cavity  324 . This action pulls the sensor  210  away from the insert  216  cleanly withdrawing the insert. 
   While the present invention has been described with reference to one or more particular embodiments, those skilled in the art will recognize that many changes may be made thereto without departing from the spirit and scope of the present invention. Each of these embodiments and obvious variations thereof is contemplated as falling within the spirit and scope of the claimed invention, which is set forth in the following claims.