Abstract:
A test strip for testing a blood sample is provided with a fluid transport feature to facilitate transport of a blood sample obtained from a lancing operation through a capillary channel to a measurement site. A fluid transport path is defined on the major face of the strip terminating at the mouth of the capillary channel. The fluid transport path includes a depending portion at one end opposite the mouth of the channel. The depending portion extends away from the strip on the side facing the fluid sample, such that a droplet of fluid sample contacting the depending portion is directed toward the mouth of the capillary channel. Thereafter the sample moves by capillary action to the measurement site.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention is in the field of fluid sample acquisition and testing. In particular, the invention is directed to a test strip having features that facilitate transport of a blood sample obtained from a person&#39;s body to a measurement site on the strip. 
     2. Description of the Related Art 
     In the medical and diagnostic field, and particularly in the field of diabetes care, it is often desirable to perform testing on a fluid sample, such as a blood sample, collected on a test strip. The trend is to collect and test smaller fluid samples, including sub-microliter samples (i.e., samples having a volume of 1 μL or less). In this context, it is desirable to be able to direct a fluid sample collected on a test strip to a measurement site on the strip, and to ensure that enough of the sample is available to perform the required testing of the sample. 
     It would be desirable in this context to have means to direct the fluid sample to the measurement site, ensuring sufficient sample to perform a measurement, without requiring involvement by the user. 
     In application Ser. No. 12/502,594, filed concurrently herewith, a device has been proposed in which a strip having a bending portion is positioned opposite a fluid sample collected from a user&#39;s body. The bending motion leverages adherence and transport dynamics of the fluid sample on the strip to ensure that sufficient sample reaches the measurement site from a given minimum sample volume. It would be desirable in this context to have a strip that facilitates movement of a fluid droplet to the measurement site after the fluid has been contacted by a rolling bend portion of a strip to a measurement site on the strip. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         FIG. 1  depicts a test strip according to the invention. 
         FIG. 2A ,  FIG. 2B ,  FIG. 2C  and  FIG. 2D  depict layers that may be stacked to form a test strip laminate. 
         FIG. 3  shows a cross section of the stacked layers of  FIG. 2A  through  FIG. 2D . 
         FIG. 4A ,  FIG. 4B , and  FIG. 4C  depict a test strip according to the invention in a bending state proximate a blood sample to be tested, at different stages during the procedure of contacting the sample. 
         FIG. 5A ,  FIG. 5B ,  FIGS. 5C , and  5 D depict the positioning of a fluid sample droplet on the test strip at different stages after a droplet of fluid sample is contacted with a test strip. 
         FIG. 6  depicts an alternative embodiment of a test strip according to the invention. 
         FIG. 7A ,  FIG. 7B ,  FIG. 7C ,  FIG. 7D , and  FIG. 7E  depict embodiments of the test strip according to the invention, where the depending portion has different shapes and configurations. 
     
    
    
     SUMMARY OF THE INVENTION 
     In one aspect, the invention is a diagnostic test strip for testing a fluid sample, including for example, a blood sample obtained from a patient&#39;s body in a lancing operation. The strip has a first major side which is positioned facing a sample. A capillary channel having a mouth at one end and containing a measurement site toward the opposite end is positioned on the major side, such that fluid sample contacting the strip moves from the mouth through the capillary channel to the measurement site. The strip is provided with a fluid transport path which may be defined as having one end at the mouth of the capillary channel. A depending portion extends away from the strip on the side facing the fluid sample, such that a droplet of fluid sample contacting the depending portion is directed from the depending portion, along the fluid transport path, and to the mouth of the capillary channel. 
     In a preferred embodiment, the strip is provided with a lancet hole for passage of a lancet, and the fluid transport path extends from the side of the lancet hole adjacent the depending portion to the mouth of the capillary channel. The lancet passes through the hole to acquire blood from a patient, which is drawn with the lancet back through the lancet hole. The strip is arranged to a have a rolling bend in the portion of the strip that contacts the fluid sample, which causes a depending portion on the side of the lancet hole to extend in the direction of the fluid sample. This may be accomplished using slits extending from the sides of the hole, for example. The reduced width of the depending portion causes the droplet to be guided toward the longitudinal centerline of the strip and toward the mouth of the capillary channel. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1 , test strip  10  is shown with the major side facing up. A top layer is removed to show the features of capillary channel  20 . Fluid transport path  30  extends from the depending portion  50  to the mouth  21  of the capillary channel  20 . In the embodiment shown, trenches  80  on opposite sides of the fluid transport path  30  are recessed. Surface tension and adhesion of the sample fluid to the fluid transport path  30  prevent sample fluid from flowing into the trenches  80 . 
     The strip may be a multilayer laminate made up of layers as shown in  FIG. 2A ,  FIG. 2B ,  FIG. 2C  and  FIG. 2D , stacked to obtain a cross-sectional configuration such as shown in  FIG. 3 . Layers used to form a strip include layer  18  patterned with cutouts  22 ,  24  to form the depending portion  50 ; layer  16  defining reagent wells  26 ,  28  for electrochemical determination of blood glucose; layer  14 , which defines the capillary channel walls, and top layer  12 , which forms the top of the capillary channel including notch  32  at the mouth and vent  34  at the rear of the channel, which assist capillary flow of the sample. The design of the layers may be modified without departing from the scope of the invention. The construction of multilayer laminate test strips is described in U.S. Pat. Nos. 7,192,405 and 7,498,132, for example, incorporated herein by reference, and will not be further elaborated. 
     In the embodiment depicted in these Figures, lancet hole space  40 , is provided for passage of a lancet. A fluid transport path  30  extends from the edge of lancet hole space  40  to the mouth of the capillary channel  20 . In the embodiment shown, the capillary channel  20  comprises wells  26 ,  28 , containing reagents for performance of a diagnostic test, such as a blood glucose measurement using an electrochemical reaction. However, any method of performing a diagnostic test may be used, and the invention is not limited to the use of electrochemical reagents to perform the diagnostic test. 
     The fluid transport path  30  is preferably constructed of a hydrophobic material, so that a fluid sample should form a contact angle with the fluid transport path of greater than at least about 50 degrees, preferably greater than about 60 degrees and most preferably greater than about 70 degrees. Materials such as Mylar® having the appropriate characteristics can be used as laminate materials. Alternatively, treatments can be performed to render a different material for the fluid transport path more hydrophobic, including without limitation, silane or Rainex® coatings. 
     The fluid transport path  30  is provided with a depending portion  50 . When the strip initially contacts the fluid sample to be tested, the depending portion  50  preferentially contacts a droplet of fluid sample so that the droplet is directed to the center of the strip. The edges of the depending portion have reduced width d at the contact point which causes the droplet to be directed toward the center of the strip and toward the mouth of the capillary channel. 
     The length of the fluid transport path  30  may vary from about 2 mm to about 6 mm. The path length should be larger than the blood droplet diameter to allow detection of the drop before filling the capillary. As the length of the path increases, the chance for sample loss also increases requiring a larger initial sample. 
     In preferred embodiments, the fluid transport path  30  is raised with respect to an area or areas adjacent the strip. It is believed that a droplet contacting a narrower raised portion initially will tend to stay on that path as the fluid progresses toward the capillary channel. The edge of the raised area creates a sharp change in direction of the surface that the sample is in contact with, and surface tension and contact angle keep it from falling off. While not limiting of the invention, in the preferred embodiment shown in  FIG. 1 , recesses  80  adjacent the fluid transport path  30  extend on either side of the fluid transport path for substantially its entire length, from near the depending portion  50  to near the mouth of the capillary channel  20 . Being narrower, the fluid transport path prevents loss of the sample along the strip. 
       FIG. 4A ,  FIG. 4B  and  FIG. 4C  depict a preferred embodiment in which a strip according to the invention is positioned proximate a fluid sample in a bending state, and moved so that a fluid sample (such as a blood droplet) is transported from the lancet hole space  40  on the fluid transport path  30  to the mouth of the capillary channel  20 . The strip is moved in a rolling bend motion, in the direction shown by arrow.  FIG. 4C  represents a point in time shortly after  FIG. 4B , which represents a point in time shortly after  FIG. 4A . The bend in the strip causes the depending portion  50  to extend away from the strip toward the fluid sample. Preferably, the depending portion extends at least about 100 μm to contact the fluid sample, measured as a distance on a line perpendicular to a line tangent to the bend of the strip to the most extended point on the depending portion away from the surface of the strip. 
       FIG. 5A ,  FIG. 5B ,  FIGS. 5C , and  5 D which are arranged in a similar time-lapsed format, show how the droplet is centered on the strip and travels to the capillary channel. In  FIG. 5A , a droplet is shown oriented on one side of the strip as the depending portion contacts the strip. In  FIG. 5B , as the leading edge of the depending portion advances in the direction of travel A, the droplet is directed along the curved edge of the depending portion  50  toward the center of the strip.  FIG. 5C  shows the droplet moments later, centered and directed toward the mouth of the capillary channel. 
     In a preferred embodiment, the depending portion  50  is formed at the side of the lancet hole space. Slits  70  are cut into the strip, as shown in  FIGS. 7A ,  7 B,  7 C,  7 D, and  7 E so that depending portion is able to extend away at least about 100 μm from the plane of the strip when the strip bends, and preferably about 250 μm, or more. The curve or angle of the edge of the depending portion  50  guides the droplet toward the centerline of the strip where the mouth of the capillary channel is located. The slits  70  may have a length of about 1 mm to about 2 mm. The shape of slits  70  is not particularly limited, and the depending portion  50  may have a V shape, a U shape or any other convenient shape. Generally, it is preferred to have the shape of the depending portion narrow in the direction of the droplet. Thus, the slits  70  may form a crescent shape in some embodiments and a triangle in other embodiments. The curved slits in this embodiment are believed to assist in directing the droplet toward the center of the strip. 
     In an alternative embodiment, the depending portion may be placed on a strip as shown in  FIG. 6 . In  FIG. 6 , depending portion  52  extends from the side of an individual strip and contacts and guides the droplet to the capillary channel in a similar fashion to the previously described embodiments, in that initial contact of the blood sample is with a narrow part of the depending portion. In this embodiment, the channel  20  is on the side of the strip. 
     Without departing from the scope of the invention, test strips according to the invention may be embodied as several strip “units” on a continuous strip, so that a plurality of test sites can be located on a single strip and multiple test capability may be provided in a single device. Alternatively, single strips may be provided. 
     The foregoing description of the preferred embodiments is not to be deemed limiting of the invention, which is defined in the following claims.