The sample pad begins the lateral flow assay (LFA) by transporting the sample from the point of application to the test components. Choosing a sample pad with the properties that suit your sample will get your LFA off to a good start.
Some of the key properties to consider when selecting a sample pad for your LFA are:
- Thickness — generally, the thicker the pad the higher the water absorbency.
- Water absorption — absorption, measured in mg/cm2, determines total amount of sample that can be applied.
- Wicking rate — lateral flow rate of liquid, wicking rate is how quickly the sample will move through the sample pad onto the conjugate release pad, which ultimately contributes to speed and sensitivity of the test. Generally, the slower the wicking rate, the higher the sensitivity.
Beyond the basics: sample pad additives
Additives in the sample wick can influence and mitigate some undesired properties in the sample. Some sample types show a broad sample-to-sample variation. For example, urine samples differ considerably in pH, ionic strength, and molecular composition. Impregnation of the sample pad with salts and buffers can make samples more similar to each other when they reach the conjugate release and test zones. In other cases an addition of a substance making the sample more viscous may be helpful to reduce the wicking rate and enhance the sensitivity of detection.
Blocking agents can be generic proteins such as BSA, or detergents such as Tween 20. They help avoid non-specific binding of the analyte or detection reagents to the reaction membrane. Efficient blocking will increase the signal-to-noise ratio, enhancing visibility of the test lines by reducing background stain. The addition of blocking agents to the sample pad is often much easier and more cost efficient than adding them to the reaction membrane. This method is often called “blocking on the fly”.
The Whatman™ advantage
To ensure that your assay begins well, Cytiva offers a complete range of sample pads manufactured in controlled environments from high-quality materials, with your requirements in mind.
- Consistent absorbency and wicking rates help ensure test-to-test reproducibility.
- Low protein binding prevents loss of analyte, so test sensitivity is maintained.
- Naturally hydrophilic materials can be rewetted rapidly, even after prolonged storage.
- Formats are compatible with most styles of housing.
- Minimal leakage along the strip avoids contamination of test results.
Whatman™ sample pads are available in a wide range of thicknesses, absorbencies and wicking rates.
per sq cm
(μm @ 53 kPA)
|< 50 µL
||A thin, smooth-surfaced cotton linter paper with a liner flow rate, suitable for small volumes.
||A medium thick cotton linter paper, originally used for separation of inorganic compounds. Larger sample volume than CF1.
||A medium thick cotton linter paper with acid treatment to improve wet strength and reduce trace impurity content. Similar weight and thickness to CF3 with faster wicking.
|> 150 µL
||Untreated bound cellulose suitable for whole blood or serum. Performs well with one or two drops of whole blood.
|> 50 µL
||Untreated bound glass fiber for faster flow than cotton with lower sample retention. Higher absorption capacity than Standard 17.
|> 50 µL
||Untreated bound glass fiber for faster flow than cotton with lower sample retention. Greater tensile strength than Standard 14.
|> 50 µL
||Untreated bound glass fiber particularly suitable for saliva samples and raw milk samples.
|> 50 µL
||Bound glass fiber used as a single or multiple layers for separation.