Abstract:
A connector for establishing electrical connection between a testing device and a test strip with a biological fluid thereon includes a contact pad on the test strip, and one or more contact wires in the testing device. When the strip is inserted into the testing device, part of the strip&#39;s end engages a contact portion of a contact wire and deflects it in a direction normal to the direction of insertion. In certain embodiments the radius of curvature (in the direction of insertion) of the contact portion is controlled to reduce abrasion of the strip by the wire. In other embodiments the radius of curvature (perpendicular to the direction of insertion) is controlled to reduce the abrasion of the strip by the wire. Sometimes the contact portion and/or contact pad is plated with a sacrificial material to reduce the coefficient of friction. In other embodiments various numbers of contacts receive the end of the strip substantially simultaneously, or are staggered in rows to distribute the resistance presented.

Description:
PRIORITY CLAIM  
       [0001]     This patent application is a continuation of U.S. Ser. No. 11/409,383, filed on Apr. 21, 2006, which is incorporated herein by reference in its entirety. 
     
    
     TECHNICAL FIELD OF THE INVENTION  
       [0002]     The present invention relates to testing apparatus for testing the presence or concentration of one or more substances in a biological fluid, and more particularly to such a device that includes one or more electrical connections between a test strip (bearing a sample of the biological fluid) and a test meter.  
       BACKGROUND OF THE INVENTION  
       [0003]     Measuring the concentration of substances, particularly in the presence of other substances, is important in many fields. This is especially true in medical testing and diagnosis. For example, the measurement of glucose in body fluids, such as blood, is crucial to the effective treatment of diabetes.  
         [0004]     Multiple methods are known for measuring the concentration of analytes, for example glucose, in a blood sample. Such methods typically fall into one of two categories: optical methods and electrochemical methods. Optical methods generally involve reflectance or absorbance spectroscopy to observe the spectrum shift in a reagent. Such shifts are caused by a chemical reaction that produces a color change indicative of the concentration of the analyte. Electrochemical methods generally involve, alternatively, amperometric or coulometric responses indicative of the concentration of the analyte. See, for example, U.S. Pat. Nos. 4,233,029 to Columbus, 4,225,410 to Pace, 4,323,536 to Columbus, 4,008,448 to Muggli, 4,654,197 to Lilja et al., 5,108,564 to Szuminsky et al., 5,120,420 to Nankai et al., 5,128,015 to Szuminsky et al., 5,243,516 to White, 5,437,999 to Diebold et al., 5,288,636 to Pollmann et al., 5,628,890 to Carter et al., 5,682,884 to Hill et al., 5,727,548 to Hill et al., 5,997,817 to Crismore et al., 6,004,441 to Fujiwara et al., 4,919,770 to Priedel, et al., and 6,054,039 to Shieh, which are hereby incorporated in their entireties.  
         [0005]     A sample-receiving portion of the testing apparatus typically controls the geometry of the blood sample. In the case of blood glucose meters, for example, the blood sample is typically placed onto or into a disposable test strip that is inserted into a test meter. In the case of electrochemical test meters, electrical signals must be transferred between the meter and the test strip and vice versa.  
         [0006]     Test system designers desire to minimize the size of the sample required for accurate measurement in order to improve the user experience. The resulting test sensor and test strip miniaturization has resulted in the use of thin film test strip patterns comprised of noble metals deposited on plastic substrates, such as by plating and subsequent laser ablation, to form the electrodes and associated connector contact pads of the test strip. These techniques allow for improved edge quality and improved dimensional resolution of the metallized features on the test strip. Such thin film coatings are highly prone to scratching by current commercially available connectors. Therefore, reducing abrasion between the test strip contact pad and meter connector contact wire is especially important in biosensor designs. Repeat insertions of the test strip (two to four times) can render these thin film-coated biosensors useless. Even the first-time insertion of the test strip into the test meter may cause some removal of these thin film coatings by the test meter connector. The result is a less reliable connection between the contact pad on a test strip and the connector contact wire in the test meter.  
         [0007]     Reducing abrasion between the test strip contact pad and meter connector contact wire is also important for longevity of the test meter. A typical test meter may have a life cycle requirement of over 10,000 test strip insertions. During normal use, a single test strip may be inserted and removed from the meter several times before the test is successfully performed. Abrasive contact between the connector contact wire and contact pad can reduce the longevity of the test meter connector, thereby further reducing the reliability of the system. Some biosensor systems are designed for use by consumers, who sometimes put still further stresses on the test system by using the system in environments at the margins of its design specifications, such as in high-humidity environments, or exposing the device to air containing corrosive components.  
         [0008]     Thus, there is a need for further contributions and improvements to biosensor system technology, including connectors that provide improved performance and resistance to abrasion of test strip contact pads and meter connector contact wires.  
       SUMMARY OF THE INVENTION  
       [0009]     Some forms of the present invention improve user experience by increasing the probability of the test meter connector making a reliable contact with the inserted test strip. One form includes a system for measuring an analyte of interest in a biological fluid, where a connector provides an interface between a test strip bearing the biological fluid and a test meter. The analyte of interest is applied to a test strip having at least one contact pad for mating with the connector when the test strip is inserted through an opening in the meter housing. The connector comprises at least one contact wire disposed within the housing, where each contact wire has a distal portion and a proximal portion. The contact wire&#39;s proximal portion engages the connector housing and anchors the distal portion to the connector housing. The contact wire contacts the test strip upon insertion.  
         [0010]     Initially, the contact wire is in a resting position relative to the connector housing. As the test strip is moved into the connector opening it touches the contact wire. Upon further insertion, the test strip creates a normal force acting upon the contact wire&#39;s distal portion. The normal force deflects the contact wire from its resting position and flexes portions of the contact wire in a spring fashion. Further insertion of the test strip causes the contact wire&#39;s distal portion to come into electrical contact with the contact pad. When the test strip is fully inserted, the contact wire squeezes the test trip between the contact portion of the contact wire and the connector housing. The test strip is withdrawn after the system performs the desired test. The contact wire returns to its resting position once the contact wire is no longer in contact with the test strip.  
         [0011]     Another form of the invention is a testing system comprising a meter (including a housing, a connector, and an electronic circuit) and a test strip. The electronic circuit produces an output signal corresponding to the presence or concentration of an analyte in a sample of bodily fluid that is in contact with the test strip inserted into the connector. At least one embodiment of this form includes a connector having one or more contact wires. Each contact wire is configured to allow the contact wire to engage a contact pad on a test strip and communicate with the test system. Further, when a test strip is inserted into the connector, the test strip exerts a force against the contact wire that is substantially normal to the direction of insertion to allow the contact wire to engage the contact pad.  
         [0012]     Yet another embodiment of the present invention is a device for testing an analyte on a test strip, comprising a connector having a plurality of contact wires. The proximal portion of each contact wire is fixed at least at one point within a connector housing. Part of the distal portion of each contact wire has a concave shape. In other embodiments, the contact wire has a convex-shaped portion. The “contact portion” of the contact wire that engages the test strip or contact pad has a desired radius of curvature, which may be at least about 3 mm, 4 mm, or 6 mm. Controlling the contact portion&#39;s radius of curvature reduces the frictional force that develops between the contact wire and test strip during insertion and removal, and minimizes the resulting abrasion.  
         [0013]     Still other embodiments of the present invention include features and techniques for extending, rounding, or smoothing the end of the contact portion of the contact wire in the direction of insertion. Certain embodiments include a distal portion that has a cantilevered form and a contact portion that extends in the direction of test strip extraction. Certain other embodiments include a distal portion that has a cantilevered form and a contact portion that extends in the direction of test strip insertion.  
         [0014]     Some embodiments further include rounding or smoothing the radius of curvature of the contact wire perpendicular to the direction of test strip insertion. Other embodiments of the present invention include a technique of plating the contact portion of the contact wire with soft, electrically conductive materials that are sacrificed during the test strip insertion and extraction process to minimize abrasion of the contact pad and other parts of the test strip. In certain other embodiments, the contact portion is plated with a non-gold material. Some embodiments include contact wires plated with soft metallic materials, and the wires each have a contact portion with a relatively small radius of curvature. In at least one such embodiment, a contact portion plated with a soft sacrificial material has a minimum radius of curvature less than 1 mm. Still other embodiments include techniques and features to minimize the normal force applied to the test strip by the distal portion during test strip insertion and extraction.  
         [0015]     Other embodiments of the present invention include a minimally abrading connector comprising a single-piece connector housing and n contact wires held in a substantially rigid relationship. When the test strip is inserted into the connector, the n contact wires establish electrical contacts with the test strip&#39;s contact pads. Some embodiments have a further feature of staggering the position of the n contact wires in two, three, or more rows to increase the density of contact pad placement on test strips.  
         [0016]     Certain embodiments of the present invention include contact wires having a distal end. In certain of these embodiments, the distal end is approximately loop-shaped. In certain of these embodiments, the distal end distributes energy imparted to the contact wire from friction with a test strip generates force distributed through directions that span at least 90 degrees. In certain of these embodiments, the distal end of the contact wires are formed to avoid positive feedback in frictional forces between the contact wires and the test strip.  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0017]      FIG. 1  is a perspective view of a biological testing system according to one embodiment of the present invention.  
         [0018]      FIG. 2  is a sectional view of a connector according to one embodiment of the invention.  
         [0019]      FIG. 3  is a perspective view of a contact wire according to one embodiment of present invention.  
         [0020]      FIG. 4  is a perspective view of a contact wire according to one embodiment of present invention.  
         [0021]      FIG. 5  is a perspective view of a contact wire according to one embodiment of present invention.  
         [0022]      FIG. 6  is a side sectional view of a system according to one embodiment of the present invention.  
         [0023]      FIG. 7  is a side sectional view of a system according to one embodiment of the present invention.  
         [0024]      FIG. 8  is a side view of a contact portion of a contact wire in electrical contact with a contact pad in one embodiment of the present invention.  
         [0025]      FIG. 9  is a cross-sectional view of a contact portion of a contact wire in electrical contact with a contact pad in one embodiment of the present invention.  
         [0026]      FIG. 10  is a perspective view of a contact wire according to one embodiment of present invention.  
         [0027]      FIG. 11  is sectional view of a system according to one embodiment of the present invention.  
         [0028]      FIG. 12  is a side sectional view of a system according to one embodiment of the present invention.  
         [0029]      FIG. 13  is a side sectional view of a system according to one embodiment of the present invention.  
         [0030]      FIG. 14  is a side view of the contact wire at the point of contact in one embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0031]     For the purpose of promoting an understanding of the principles of the present invention, reference will now be made to the embodiment illustrated in the drawings and specific language will be used to describe the same. It will, nevertheless, be understood that no limitation of the scope of the invention is thereby intended; any alterations and further modifications of the described or illustrated embodiments, and any further applications of the principles of the invention as illustrated therein are contemplated as would normally occur to one skilled in the art to which the invention relates.  
         [0032]     A system for testing blood according to the present invention enables greater contact density with higher reliability on thin film metallized plastic substrates. These higher densities enable one to include additional electrodes that are used in some embodiments to assure the measurement accuracy and reliability for supporting a fast, small volume test. Smaller samples, in turn, make blood testing easier and less uncomfortable. This can mean a significant improvement in the standard of living, especially for people who require regular blood testing, such as diabetics.  
         [0033]     Smaller sample sizes with equivalent reliability are achieved through increased density of measurement electrodes. Recent improvements in laser ablation techniques for the manufacture of medical test strips have significantly increased the resolution and fineness of metallized contact pad and connector trace geometries on test strips. While this innovation has enabled more contacts to be placed in a given area, the resulting detailed and delicate structures are susceptible to abrasive damage. As a result, measurement reliability is threatened. In order to preserve measurement reliability, a less abrasive connection system, and techniques minimizing test strip abrasion during insertion and extraction, are needed. Embodiments of the present invention provide a significant improvement in this aspect of the art.  
         [0034]     The present invention minimizes or eliminates abrasion of test strip contact pads formed of a thin layer of metal when the test strip is inserted into a test meter. Little or no damage to the test strip thin film surface by the connector, nor to the connector contact wire by the test strip, occurs in some embodiments of the present invention due to the contact wire of the connector being formed with a rounded surface in one or more dimensions.  
         [0035]     Generally, exemplary biological testing system  20  shown in  FIG. 1  includes a reusable testing meter  30  having an end  34 . A disposable test strip  40  is inserted in direction I through slot  32  in end  34 . Strip  40  includes at least one contact pad  42  (four such contact pads are shown in  FIG. 1  by way of example only) near its end  44 . These contact pads are connected via conductors  46  to electrodes (not shown) near the end of strip  40  opposite end  44  (i.e., near the end in the direction indicated by directional arrow E). As a non-limiting example, one embodiment has four contact pads connected to four electrodes. Other embodiments of the invention may include more or fewer contact pads or electrodes, different numbers and patterns of conductor traces  46 , and/or different numbers of electrodes on a given test strip  40 . The test strip  40  is inserted into testing device  30  in insertion direction I.  
         [0036]     As illustrated in the cutaway view of assembly  36  shown in  FIG. 2 , in one embodiment of the present invention, system  20  receives a test strip  40  inserted through slot  32  into testing device  30  by movement of the test strip  40  in direction B. Slot  32  in testing device  30  may comprise an end of a connector housing for receiving the test strip  40  or, alternatively, slot  32  may simply be an opening in testing device  30  situated adjacent to the connector housing. The connector housing  50  includes first side  50 A and a second side (opposite first side  50 A and not visible in the sectional view of  FIG. 2 ), top  50 C, base  50 D, front  50 E, and back  50 F. Connector housing  50  additionally defines wire slot  52  and assembly slot  56  therein.  
         [0037]     As described hereinabove, the front side  50 E includes an opening for slot  32 , a corridor for passing test strips  40  through front side  50 E to the region of wire slot  52 . As an additional, optional feature, the opening of slot  32  on front  50 E may include beveling as shown to help guide test strip  40  into slot  32 . Assembly slot  56  has first assembly feature  56 A and second assembly feature  56 B (opposite of first assembly feature  56 A). Assembly features  56 A and  56 B provide a path through which alignment portion  80  of contact wire  60  is passed when the connector assembly  36  is being assembled, as described in greater detail hereinbelow.  
         [0038]     Wire slot  52  extends into housing  50  in the direction of insertion I for test strip  40 , and has a width in direction N 1 . Wire slot  52  is defined by first wire slot wall  52 A, second wire slot wall  52 B (opposite first wire slot wall  52 A), front wire slot wall  52 C, back  50 F, projection  54 , first wire slot floor  58 A, second wire slot floor  58 B, and top  50 A.  
         [0039]     The floor of wire slot  52  comprises first wire slot floor  58 A, projection  54 , and second wire slot floor  58 B. First wire slot floor  58 A extends to a first plane approximately normal to wire slot walls  52 A and  52 B and connects first wire slot wall  52 A and second wire slot wall  52 B. Second wire slot floor  58 B extends to at least one second plane substantially normal to wire slot walls  52 A and  52 B and connects first and second wire slot walls  52 A and  52 B. Protrusion  54  connects the first wire slot floor  58 A to second wire slot floor  58 B and connects first wire slot wall  52 A and second wire slot wall  52 B. Wire slot  52  may further include front wall  52 C of some thickness that lies in a plane substantially normal to first wire slot floor  58 A and connects to first wire slot wall  52 A and second wire slot wall  52 B.  
         [0040]     The opening of slot  32  into wire slot  52  is defined by a gap between front wire slot wall  52 C and wire slot floor  58 A. In some embodiments, the connector housing back  50 F provides an opening for the contact wire  60  to pass through housing back  50 F. In other embodiments, as shown in  FIG. 2 , a portion of the wire slot  52  extends to the back  50 F and creates an opening for the contact wire  60  to pass through back  50 F. Although  FIG. 2  shows a connector assembly comprising a connector housing  50  having a single wire slot  52  for accepting a single contact wire  60 , it is understood that this is for illustrative purposes and that other embodiments having multiple contact wires and wire slots or multiple contact wires per wire slot are contemplated.  
         [0041]     In some embodiments, first wire slot floor  58 A and second wire slot floor  58 B are coplanar. In other embodiments, first wire slot floor  58 A and second wire slot floor  58 B lie in different planes. In still other embodiments, as shown in  FIG. 2 , second wire slot floor  58 B is shaped or angled to provide a multi-planar transition from protrusion  54  to the connector back  50 F.  
         [0042]     In the embodiment illustrated in  FIG. 2 , connector assembly  36  is formed by placing contact wire  60 , having a distal portion  70  and proximal portion  62 , into wire slot  52  of connector housing  50 . The distal portion  70  is placed in proximity with the first wire slot floor  58 A, while the proximal portion  62  is placed in proximity with the second wire slot floor  58 B. As test strip  40  is inserted, it passes through slot  32  and comes into contact with distal portion  70  of contact wire  60 . The distal portion  70  includes portions of contact wire  60  that allow some freedom of movement or flexing in the normal directions N 1  and N 2  to permit test strip  40  to pass between the contact wire  60  and first wire slot floor  58 A of the connector housing  50 . While distal portion  70  flexes, proximal portion  62  remains in a substantially fixed position relative to the connector housing  50 .  
         [0043]     As illustrated in  FIG. 3 , one embodiment of the present invention has at least one contact wire  60  with a proximal portion  62  and a distal portion  70 . Proximal portion  62 , including the combination of alignment portion  80  and engaging portion  90 , aligns and secures contact wire  60  within a connector housing assembly. Alignment portion  80  has features for aligning contact wire  60  in the connector housing. Alignment portion  80  includes a first protrusion  80 A and second protrusion  80 B adapted to interface with assembly slot  56 . In at least one embodiment, alignment portion  80  includes features that are substantially keystone or coffin shaped. The alignment portion  80  can have alternative shapes or protrusions that provide improved engagement with assembly slot  56  and function to align contact wire  60  in the connector housing  50 . The present invention includes those shapes and features that would be recognized by those skilled in the art as adapted for engaging assembly slot  56 .  
         [0044]     Similarly, some embodiments of engaging portion  90  have protrusions  90 A and  90 B to engage walls of wire slot  52 . As a non-limiting example, engagement portion  90  can have a number of regular or irregular shapes. Other embodiments of engagement portion  90  have various shapes or features including tabs, edges, protrusions, and ridges that hold proximal end  62  in a fixed position within wire slot  52 . Thus, the present invention includes those shapes and features that would be recognized by those skilled in the art as adapted for stable contact between engaging portion  90  and the walls or floor of wire slot  52 .  
         [0045]     Proximal portion  62  of wire  60  also includes end portion  68  to provide an electrical connection to the internal circuitry of the testing meter  30 . The proximal portion  62  may further include as features wire segment  64  and curve segment  66 . Wire segment  64  and curve segment  66  work in combination with engaging portion  90  to provide a transition between alignment portion  80  and wire end  68 . As shown in  FIG. 2 , curve segment  66  orients alignment portion  80  relative to engaging portion  90 . Wire segment  64  is bent to position wire end  68  relative to engaging portion  90 .  
         [0046]     Distal portion  70 , also shown in  FIG. 3 , includes contact portion  72 , contact portion end  72 A, transition portion  74 , arm portion  76 , and spring portion  78 . As described below in greater detail, the distal portion  70  is used to create a backward-pointing or reverse-cantilevered structure relative to the proximal portion  62 . The contact portion  72  provides a curved (i.e. radius of curvature in parallel planes) and/or spoon-shaped (i.e. radius of curvature in perpendicular planes), low-abrasive point of contact between the contact wire  60  and a test strip  40 . As described below, spring portion  78  and arm portion  76  hold contact portion  72  in position for receiving the test strip  40 . As a further feature, contact portion  72  and contact portion end  72 A may be shaped or extended to minimize abrasion of the test strip  40  during insertion (and extraction) of the test strip  40  into (and out of) the meter  30 .  
         [0047]     Certain embodiments of the present invention combine the functionality of contact portion  72  and arm  76  into a single body. Other embodiments combine the functionality of several portions of proximal portion  62 . As a non-limiting example, in one embodiment contact wire  60  combines the functionality of alignment portion  80  and engaging portion  90  into a single wire segment. Still other embodiments may combine the functionality of wire segment  64  and curve segment  66 .  
         [0048]     As further illustrated in  FIG. 4 , one embodiment of the present invention comprises contact wire  60 ′ having proximal portion  62  and distal portion  70 ′. The distal portion  70 ′ includes contact portion  72 ′, contact portion end  72 A′, arm portion  76 ′, and spring portion  78 ′. Contact portion  72 ′ provides a curved or spoon-shaped, low-abrasive point of contact between the contact wire  60 ′ and a test strip  40 . As described below, the distal portion  70 ′ is used to create a forward-pointing or cantilevered structure relative to the proximal portion  62 . Contact portion  72 ′ and arm portion  76 ′ combine to make a convex curve such that the contact portion end  72 A′ extends substantially in the direction of extraction E. Spring portion  78 ′ and arm portion  76 ′ hold contact portion  72 ′ in position for receiving the test strip. As a further feature, contact portion  72 ′ and contact portion end  72 A′ may be shaped or extended to minimize abrasion to the test strip during insertion and extraction of the test strip into the testing device.  
         [0049]     As illustrated in  FIG. 5 , another embodiment of the present invention includes contact wire  160  having a proximal portion  62  and distal portion  170 . Distal portion  170  includes contact portion  172 , contact portion end  172 A, arm portion  176 , and spring portion  178 . Contact wire  160  is similar in form and function to wire  60 , except the functionality of arm portion  76  combines the functions of transition portion  174  (having a convex curvature that causes contact portion end  172 A to extend in the direction of insertion I) and arm  176 . Otherwise, elements  172 ,  172 A, and  178  of  FIG. 5  are analogous in form and function to elements  72 ,  72 A, and  78  of  FIG. 3 .  
         [0050]     It will be appreciated that the contact wires tend to act as springs that can store mechanical energy imparted through friction with a test strip  40 . It has been determined by the inventors that friction causes less damage (both to the test strips and the contact wires themselves) when the frictional force is imparted to the contact wires with “dragging” contract, rather than “pushing contact.” Thus, the contact wires are preferably formed with a roughly loop-shaped portion, as, for example, contact wire  60  has in distal portion  70 . These loop-shaped structures cause the stored energy to be stored throughout a relatively large arc, meaning that little of the spring&#39;s force is applied in the direction normal to the test strip  40 . Preferably, energy imparted to the contact wire through friction with the test strip  40  is distributed over directions spanning at least 90 degrees. The loop-like form therefore greatly reduces the positive feedback of frictional forces, giving the contact wires less of a tendency to bite or dig in.  
         [0051]     Another advantage of contact wires with curved forms like those shown in  FIGS. 3-5  is that they are less likely to be deformed by catching on defects in test strips (or even other objects that might be inserted). Because the tip of the contact wire is above the edge of the slot  32 , it does not make contact with the test strip, even if there are significant discontinuities in the surface.  
         [0052]     Contact wires are advantageously flattened, as shown in  FIGS. 3-5 . This biases them to deform in the plane perpendicular to the test strip  40  and the direction of insertion I, rather than to the side, where they might come into contact with an adjacent contact wire.  
         [0053]     Turning to  FIG. 6 , a side cross-sectional view of the assembly  36  is shown. Contact wire  60  forms a reverse cantilever structure anchored by proximal end  62  and has a fulcrum point at spring portion  78 . Arm  76  acts as the beam of the cantilever structure supporting contact portion  72  and transition portion  74 . Contact portion end  72 A serves as the end of the cantilever and points in the direction of the fulcrum point.  
         [0054]     Contact wire  60  is held in a substantially fixed orientation relative to connector housing  50  by alignment portion  80  and engaging portion  90 . The alignment portion  80  is held in place by protrusions  80 A and  80 B (see  FIG. 3 ) engaging with assembly features  56 A and  56 B (see  FIG. 2 ), respectively, of assembly slot  56 . Similarly, protrusions  90 A and  90 B (see  FIG. 3 ) engage wire slot walls  52 A and  52 B (see  FIG. 2 ), respectively, and hold engaging portion  90  in a substantially fixed position relative to the wire slot walls and to second wire slot floor  58 B. As a result, contact portion  72  is thus held in its rest position relative to first wire slot floor  58 A.  
         [0055]     Generally, the contact portion  72  is initially in its resting position with contact portion  72  touching or near first wire slot floor  58 A. As test strip  40  is inserted into the assembly  36 , test strip end  44  engages contact wire  60  and deflects contact portion  72  in the normal direction N 1  away from its resting position. The deflection creates a force on the contact wire  60  at the point of contact between contact portion  72  and test strip  40  that is substantially in direction N 1 , which is normal to direction of insertion I. This normal force is translated through transition segment  74  to arm portion  76 . Arm portion  76  operates in large part as a lever upon spring portion  78 . This allows test strip  40  to pass between the contact wire  60  and first wire slot floor  58 A.  
         [0056]     The stored energy in the spring portion  78 , by this normal force in the direction N 1 , creates a counter-force in normal direction N 2  upon test strip  40 . This counter-force acts to squeeze test strip  40  between the contact portion  72  and first wire slot floor  58 A. Upon full insertion of test strip  40 , as shown in  FIG. 7 , contact portion  72  comes into substantial electrical contact with contact pad  42 , and test strip end  44  rests proximate to or in contact with projection  54 .  
         [0057]     When the test strip  40  is extracted from the test meter  30 , the test strip  40  moves substantially in the direction of extraction, E, which is opposite the direction of insertion, I. Spring portion  78  continues to squeeze test trip  40  between contact portion  72  and first wire slot floor  58 A until the test strip  40  reaches the initial contact position as shown in  FIG. 6 . As the test strip  40  continues to move in the direction of extraction E, contact portion  72  returns to its resting position proximal to first wire slot floor  58 A. The test strip  40  continues to move in the direction of extraction E until it exits the connector housing  50 .  
         [0058]     As will be appreciated by those skilled in the art, reducing the normal counter-force applied to test strip  40  consequentially reduces the frictional or abrading forces applied to test strip  40  and contact pad  42 . Thus, some embodiments of the present invention adjust the length of arm portion  76  to control the magnitude of the normal force in direction N 1  required to overcome the counter-force produced by the spring portion  78 . Other embodiments use a technique of controlling the elasticity of spring portion  78  to limit the normal force required at the contact portion  72  to deflect contact wire  60 . Still other embodiments employ a combination of arm length and spring elasticity as controlling factors. Some embodiments limit the normal counter-force exerted upon the contact pad  42  to less than 0.4 N. Still other embodiments limit the normal counter-force applied at the contact portion  72  to less than 0.3 N. Other embodiments limit the normal counter-force to between 0.1 N and 0.3 N.  
         [0059]     Certain embodiments of the present invention reduce abrasive damage to test strip  40  by controlling the radius of curvature of the contact portion  72 . As shown in  FIG. 8 , the contact wire  60  has a convex shape and includes a contact portion  72  with a radius of curvature R C  measured in a plane parallel to the direction of insertion I and perpendicular to the surface of the contact pad. The effect of increasing the radii of curvature at the points of contact is to lower the abrading force applied per unit area of the test strip  40  (and contact pad  42 , which is of particular interest). Additional embodiments of contact wire  60  include techniques and features for smoothing, rounding, and/or extending wire end  72 A. Certain of these techniques have the benefit of reducing the abrading force applied to the contact pad  42  and diminishing wear on contact portion  72  and/or contact pad  42 .  
         [0060]     Certain embodiments include a contact portion  72  having a radius of curvature, R C , greater than 3 mm. In other embodiments, the contact portion has a radius of curvature greater than 4 mm. In still other embodiments, the radius of curvature is greater than 6 mm. In certain embodiments, the radius of curvature can vary over the region of contact portion  72 . Illustratively, during insertion and extraction, the test strip  40  may have several points of contact with contact portion  72 . Each point of contact may have a different radius of curvature R C , R C ′, and R C ″; however, at each point of contact with test strip  40 , contact portion  72  has a minimum desired radius of curvature.  
         [0061]     As shown in  FIG. 9 , other embodiments of the present invention further reduce the abrading tendency of the sliding contact between contact wire  60  and test strip  40  by providing and controlling a cross-sectional radius of curvature, R P , of the contact wire  60 . As illustrated, the cross-sectional radius of curvature R P  is measured in a plane perpendicular to the direction of insertion I and perpendicular to the plane of the contact pad. In at least one embodiment, R P  is larger than 1 mm. In certain embodiments R P  is greater than 2 mm. Other embodiments have a radius of curvature R P  greater than 4 mm. In still other embodiments, in regions where R C =R P , the surface of contact wire  60  has a spherical surface quality at the point of contact with contact pad  42 . In addition, other embodiments include as a feature end  72 A that is rounded or beveled.  
         [0062]     As shown in  FIG. 10 , at least one embodiment of the present invention comprises a contact wire  260  having a proximal portion  62  and distal portion  270 . The distal portion  270  includes contact portion  272 , of contact portion end  272 A, transition segment  274 , arm portion  276 , and spring portion  278 . Contact wire  260  is similar in form and function to wire  60 ′ (see  FIG. 4 ), except the functionality of arm portion  76 ′ ( FIG. 4 ) is divided into transition segment  274 , having a concave curvature that causes contact portion end  272 A to extend in the direction of extraction E, and arm  276 . Otherwise, elements  272 ,  272 A, and  278  of  FIG. 10  are analogous in form and function to elements  72 ′,  72 A′, and  78 ′ of  FIG. 4 .  
         [0063]     The proximal portion  62  of contact wire  260  is held in a substantially fixed position relative to the connector housing  50  by alignment portion  80  and engaging portion  90 . Similar to distal portion  70 ′ in  FIG. 4 , distal portion  270  includes a convex curve that permits contact portion end  272 A to extend substantially in the direction of extraction E.  
         [0064]     As illustrated in  FIG. 11 , connector assembly  236  includes contact wire  260  (within wire slot  52 ) and connector housing  50 . Similar to assembly  36  of  FIG. 6 , contact wire  260  is held in a substantially fixed orientation relative to connector housing  50  by alignment portion  80  and engaging portion  90 . As a result, distal portion  270  forms a cantilevered structure, with a fulcrum point at spring portion  278 , and is held in a rest position over the first wire slot floor  58 A.  
         [0065]     As shown in  FIG. 12 , contact portion  272  is initially held in its rest position in substantial proximity to wire slot floor  58 A by spring portion  278  until test strip  40  is inserted through slot  32  of the test device  30 . As test strip  40  is inserted and comes into contact with the distal portion  270 , it creates a normal force in direction N 1  acting upon distal portion  270 , which force deflects contact portion  272  away from its rest position over wire slot floor  58 A. This normal force is transmitted through transverse segment  274  to arm  276  which acts upon spring portion  278 .  
         [0066]     As illustrated in  FIG. 13 , the test strip end  44  abuts projection  54  when fully inserted into the test device. Contact portion  272  comes into electrical contact with contact pad  42  while spring portion  278  squeezes the test strip  40  between the contact wire  260  and first wire slot floor  58 A. During extraction, test strip  40  moves substantially in the direction of extraction E. Spring portion  278  continues to squeeze test strip  40  between contact portion  272  and first wire slot floor  58 A. As test strip  40  moves in the direction of extraction, contact portion  272  returns to its resting position. Test strip  40  continues to move in the direction of extraction E until it exits the connector housing  50 .  
         [0067]     Some embodiments of the present invention, as shown in  FIG. 14 , include contact wire  260  having a contact portion  272  with a radius of curvature R C  and a cross-sectional radius of curvature R P  (not shown). Similar to contact wire  60  of  FIG. 8 , increasing the radius of curvature of the contact portion  272  distributes the normal force across a larger area and decreases the abrasions inflicted upon the test strip  40 .  
         [0068]     Additional embodiments of the present invention include a technique of plating the contact portion with an electrically conductive material that is softer than the material used to form the contact pad  42  on test strip  40 . During insertion and extraction of test strip  40 , a portion of the soft plating material is sacrificed to reduce the abrasions on the test pad  42 . In one non-limiting example, the contact wire is made of phosphor bronze and is plated with Ni/NiPd at the contact surface. Likewise, test strips  40  can be designed so that little or no low-resistance contact metal is scraped off contact pad  42  during insertion and extraction of test strip  40 . Additionally, the plating material should be chosen so that the material will not form a cold contact weld with the materials used to form test strip  40  or test pad  42 . Illustratively, in one embodiment, the contact pad  42  is gold and is plated with German Silver. As a result, some embodiments include a contact portion plated with a soft conductive material have a minimum radius of curvature R C &lt;1 mm.  
         [0069]     A non-limiting list of exemplary plating materials for plating the contact portion of the contact wire includes, but is not limited to, Pd, Ni, NiPd, NiCo, Sn, SnPb, Ag, Cu, Au, and German Silver. Certain embodiments plate the contact portion with non-gold materials. In other embodiments, the plating material has a hardness index KHV50 less than 900. In still other embodiments, the plating material has a hardness index KHV50 between 300 and 650. Alternatively, some embodiments use plating material with a harness index KHV50 between 60 and 300. Other embodiments use a plating material with a hardness index KHV50 between 25 and 60. In still other embodiments, the plating material has a hardness index KHV50 less than 25. In yet other embodiments, the plating material has a hardness index KHV50 less than 20. The plating thickness applied to the contact portion depends upon the desired number of test strip insertions and extractions a testing system is expected to survive. Illustratively, German Silver plated contact wires have a plating thickness between 4 mils and 7 mils. In other embodiments, the contact portion&#39;s plating thickness is less than 2 mils, while in still others the contact portion&#39;s plating thickness ranges between 0.25 mil and 1.5 mils. See TABLE 1 for a non-limiting chart of potential plating materials and related harnesses and plating thickness.  
                       TABLE 1                               Typical Thickness Ranges       Metal Plating   Hardness (KHV50)   in Microns                   Au   40 soft   flash-2.5       Au   180-200 hard   flash-2.5       Pd   400-450   0.5-1.25       Pd—Ni   500-550   0.5-1.25       Pd—Co   600-650   0.5-1.25       Sn   15-25   2.5-5         Sn—Pb   13-20   2.5-5         Ag   40-60   flash-2.5       Ni   300    1-2.5                  
 
         [0070]     It has been empirically determined by the inventors that the best compliment to thin film gold is a plating of 20/80 NiPd alloy.  
         [0071]     In certain embodiments, an under-plating of copper is used to further decrease friction between the contact pad  42  and the contact portion  40 . Copper (like other suitable soft metals) tends to fill gaps, so that an underplating tends to make the contact surfaces smoother. Those skilled in the art will readily recognize that many other types of metals can be used for underplating.  
         [0072]     Other embodiments of the present invention include various numbers of contact pads and contact wires. In one non-limiting illustrative example, a connector may include eight contact wires. In some embodiments, the wires are placed in non-staggered row arrangements. In still other embodiments, the wires are placed in staggered row arrangements. As a result, adjacent neighboring wires come into contact with contact pads at various points during insertion process. The staggering approach allows higher pin and contact pad densities as compared to a single-row design.  
         [0073]     All publications, prior applications, and other documents cited herein are hereby incorporated by reference in their entirety as if each had been individually incorporated by reference and fully set forth. This application incorporates by reference, in their entireties, U.S. patent application Ser. No. 10/935,522 (entitled BIOLOGICAL TESTING SYSTEM, filed Sep. 7, 2004 attorney docket number RDID-03009-US/7404-478), SYSTEM AND METHOD FOR ANALYTE MEASUREMENT USING AC EXCITATION (U.S. Provisional Application No. 60/480,298, filed Jun. 20, 2003), METHOD OF MAKING A BIOSENSOR (case number BMID 9958 CIP US, filed Jun. 20, 2003), DEVICES AND METHODS RELATING TO ANALYTE SENSORS (U.S. Provisional Application No. 60/480,397, filed Jun. 20, 2003), and U.S. patent application Ser. No. 10/264,891 (entitled ELECTRODES, METHODS, APPARATUSES COMPRISING MICRO-ELECTRODE ARRAYS, filed Oct. 4, 2002), and U.S. Pat. No. 6,379,513 B1.  
         [0074]     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.