application of a uniformly distributed sample onto a reactive surface and control of the sample volume.
The aforementioned advantages permit one to choose a sample volume appropriate to the chemistry and reactivity of the reactive material by varying the thickness 5 of the capillary gap and hence the total volume entrained by the sample reading chamber of the device.
Excess fluid beyond the capacity of the capillary overflow chamber may be absorbed by filter paper or other absorbent medium attached to the device adjacent 10 to or directly over a suitable opening of the overflow chamber.
Other features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the drawings. 15
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of one embodiment of the capillary gap device of the present invention;
FIG. 2 is a top view of the top layer of one embodi- 20 ment of the capillary gap device of the present invention showing the openings or ports formed therein; • FIG. 3 is a top view of the spacer layer of one embodiment of the capillary gap device of the present invention showing the chamber formed therein; 25
FIG. 4 is an end view of the capillary gap device taken along lines 4—4 in FIG. 1;
FIG. 5 is a perspective view of another embodiment of the present invention;
FIG. 6 is a top view of an alternative arrangement of 30 the present invention;
FIG. 7 is a top view of another embodiment of the invention;
FIG. 8 is an end view of the embodiment shown in FIG. 7 taken along lines 8—8; 35
FIG. 9 is a perspective view of another embodiment of the invention;
FIG. 10 is an exploded view of an alternative arrangement of the present invention;
FIG. 11 is a perspective view of the upper layer 40 shown in FIG. 10;
FIG. 12 is a schematic side view of another embodiment of the invention showing a particular configuration for a spacer layer;
FIG. 13 is a perspective .view of another embodiment 45 of the capillary gap device of the present invention;
FIG. 14 is a top view of the top layer of the embodiment of the invention shown in FIG. 13;
FIG. IS is a perspective view of another embodiment of the capillary gap device of the present invention; 50
FIG. 16 is a top view of the top layer of the embodiment of the invention shown in FIG. 15;
FIG. 17 is a graph of the reactivity per second and describes the effect of format design on the dose response film curve for a glucose sensitive film; and 55
FIG. 18 shows a comparison of test precision for an open and a capillary gap format device.
Major problems associated with dry reagent films and papers are solved by the device of the invention. It is difficult utilizing prior art materials to obtain an applica- 60 tion of an uniformly distributed sample over a finite surface area of a test surface. In many instances, the sample will not travel into the sample chamber under proper conditions, too much sample is in contact with the sample chamber or not enough of the liquid is in 65 contact therewith. The present invention permits close and carefully monitored control of the sample volume so that only a previously determined calibrated amount
of liquid to be analyzed will be in contact with the test surface. Therefore, these advantages permit one to choose a sample volume that is appropriate to the particular test that is being carried out taking into consideration the nature of the fluid that is being tested and the nature of the reagent film. The present invention can be fabricated in various different dimensions and therefore the thickness of the capillary gap can be varied as desired. Hence, the capillary gap devices can be made in various sizes depending upon the total volume of the sample that is desired to be entrained of the sample. This will depend upon the particular means chosen for reading the results; i.e., either automatic or visual means. The device of the present invention provides a means for dealing with the problem of excess sample so that any excess liquid does not interfere with obtaining a proper reading. Thus, in accordance with the invention, excess fluid flows into an overflow chamber through an overflow proportioning channel and, if necessary, out an overflow port or opening. If desired, some sort of absorbing material can be either attached to the device or adjacent thereto so as to absorb the excess liquid.
It is important to note that the present invention is not simply a fluid transport or spreading device but instead is a volume metering device which is designed to accommodate a range of sample volumes from a minimum of about 5 to 10 micro liters up to about 100 to 200 micro liters without washing or wiping off the excess liquid.
It is therefore an important feature of the present invention to provide a fluid metering device in a capillary gap structure containing a sample chamber of a defined volume.
It is a further feature of the present invention to provide a capillary gap device which has a capillary lock for air release and prevention of backflow into the sample application port.
A further feature of the present invention is to provide for proportioned flow of the sample fluid into a capillary overflow chamber which accommodates the liquid volume beyond the minimum required to fill the sample chamber. The volume of the sample chamber can be varied to accommodate excess sample as well when this is compatible with the chemistry of the reagent film that is chosen.
A further feature of the present invention is to provide for complete removal of sample fluid from the sample application port by capillary action. Thus, no washing or wiping is required nor does any excess sample fluid remain exposed in the aperture. In operation in accordance with the invention, any residual sample which remains in the sample application port would be drawn into the overflow chamber and the sample application port is thereby evacuated. Any excess overflow beyond the capacity of the capillary overflow chamber can be taken care of by utilizing an absorbent pad as an optional feature of the invention.
A still further feature of the present invention is a capillary gap device wherein no exchange can occur between liquid in the sample chamber and liquid in the overflow chamber due to the creation of an air gap in the overflow proportioning channel. This can enchance the end point chemistries which are carried out in the sample chamber depending upon the particular nature of the reactive material.