This invention relates to calorimetric test strips.
Colorimetric test strips or reagent strips are well known. Areas of use include tap water quality testing, industrial and environmental testing, pool and spa testing, lake and stream testing, aquarium testing and other types of water testing. Test strips also have medical applications including blood and urine analysis. Simple, quick and accurate testing is advantageous, and a test strip must have the necessary detection capability.
Test strips typically include an absorptive carrier bearing a calorimetric indicator, for instance, absorptive paper impregnated with an indicator, or a support having affixed thereto a porous, absorbent carrier bearing an indicator. Exemplary are the test strips of U.S. Pat. Nos. 3,006,735 and 4,904,605. As described therein, the strip may be used by a quick-dipping technique or, in the case of the strip of the ""605 patent, may be moved back and forth vigorously for thirty seconds.
A modified reagent strip including a porous matrix bearing reagents and having exposed opposite faces, is illustrated by U.S. Pat. No. 5,187,100. A blood sample is placed in an aperture that exposes a face of the matrix, and the blood seeps from capillary effect to the opposite face. Glucose in the blood reacts with the reagents which include enzymes. In a similar strip, the matrix is disposed between support members provided with apertures generally in line with each other.
Also known as exemplified by U.S. Pat. No. 4,092,115 is a test strip including a wick member enclosed in a fluid impervious sheath, and including an aperture exposing a portion of the wick member bearing colorimetric indicator. The strip is dipped into a sample and held therein until the wick member absorbs the desired amount of fluid or becomes saturated. A drawback of this type of device is non-uniform color development. Additionally, use of the reagents described therein, produces non-stable color. Also, as shown by U.S. Pat. No. 3,510,263, the faces of a chromatographic test strip may be coated with a water repellent material, and the edges may be uncoated.
There continues to be a need for a colorimetric test strip and methodology of enhanced sensitivity. Uniform color development would be advantageous. Moreover, a broad range of sensitivity would be beneficial. It would be also advantageous for the test strip to be economical to manufacture.
In accordance with the present invention, an improved colorimetric test strip and method useful for a variety of analytes, are provided. The test strip includes a fluid-permeable carrier bearing a calorimetric indicator. The indicator selected, depends upon the analyte of interest. The carrier is beneficially attached to a support advantageously provided with an aperture exposing a face of the carrier. Beneficially, the opposite face of the fluid-permeable carrier is exposed or uncovered, permitting fluid flow through the aperture and carrier.
During an analysis, the carrier may be contacted with a liquid to be analyzed, and the liquid caused to flow through the fluid-permeable carrier and to contact the calorimetric indicator over a selected period of time. When the carrier is dipped into the liquid, a gentle swirling action is beneficially used to cause the liquid to be in flowing contact with the indicator. After the selected contact time, the carrier is evaluated for detectable color change advantageously by viewing the area of the carrier defined by the aperture.
A benefit of the present invention is uniform color development. The color may be compared to a color chart to determine the analyte concentration. The color intensity that develops, increases as the concentration of the analyte in the sample increases and can be quantitatively determined with reproducible sensitivity and accuracy.
In the drawing and in detailed description of the invention that follows, there is essentially shown and described only a preferred embodiment of this invention, simply by way of illustration of the best mode contemplated of carrying out this invention. As will be realized, this invention is capable of other and different embodiments, and its several details are capable of modification in various respects, all without departing from the invention. Accordingly, the drawing and the detailed description are to be regarded as illustrative in nature, and not as restrictive.