Dipstick colorimetric assays are widely used in tests ranging from urine testing, to clinical chemistry, to environmental testing. Colorimetric dipstick assays use a cellulose pad impregnated with detection reagents that give a color reaction when processed. They provide a rapid test that is easy to read.

The dipstick format can also be used for a solid-phase immunoassay. In this application, immunologically active substances such as antigens or antibodies are immobilized on membranes attached to a plastic support to create a dipstick assay.

Selecting dipstick cellulose papers

The base cellulose is a key part of the system, so the correct choice of absorbance capacity, wicking rate and wet strength are critical to the success of your producing a working assay. The Whatman™ range of cellulose materials for colorimetric assays offers a highly consistent and inert substrate for absorption of the active chemicals required for dipstick tests. The purity of the cellulose base material coupled with Whatman™ quality manufacturing practices makes these papers the an excellent choice for large-scale manufacturing.

Our range of papers also includes a wet-strengthened grade, CF2, which contains an FDA approved resin that binds the cellulose fibers together. This significantly increases the strength of the paper, especially when it is wet. The use of the wet-strengthened grade therefore reduces waste during manufacture (due to snapping of the cellulose during coating) and also reduces the risk of the pad decomposing during use.

Design considerations when selecting your absorbent pad

The most important characteristic is absorption capacity, as this will determine whether the pad can handle the sample volume as well as any impregnated reagents. Beyond this, test the material for compatibility with your sample liquid and enzymatic reaction products. Pad thickness is also an indicator of mechanical stability, which may be important depending on the manufacturing method of your final assay.

Technical Specifications

Dipstick colorimetric assays

Grade Thickness (μm @53kPA)
Water absorption (mg/cm2)
CF 1
176 18.7
CF 2
172 16.1
CF 3
322 34.6
CF 4
782 49.9
CF 6
1450 136.3
CF 7
1873 252.3

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