Membranes and pads

• Choice of separation times allows for test optimization.
• Separation in 30–120 seconds for rapid assays that save time.
• No appreciable red cell hemolysis for improved reproducibility of results.
• Appropriate for a range of blood volumes to enhance the separation rate according to the volume of blood available.

You should consider the following characteristics:

• Thickness: generally, the thicker the pad the higher the water absorbency
• Water absorption : this determines the total amount of sample that can be applied
• Wicking rate: this 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

Our conjugate release pads do not require treatment prior to conjugate application as they are inherently hydrophilic. This means the material rewets rapidly every time for improved test consistency. The open structure of the material allows rapid penetration by both conjugate and sample. They also provide high conjugate release levels to reduce both waste and reagent costs.

The NC membrane is the heart of the lateral-flow test, where the target molecule is bound and where the results are displayed.

The role of the membrane is to immobilize the capture molecules (typically antibodies) at the test and the control lines in a way that their binding properties for their respective target molecule are preserved, and to guide the flow of the sample and the detection conjugate to the reaction area. To do this, the membrane must have a high and consistent protein binding capacity as well as porosity and wettability to allow a capillary flow of aqueous samples. The protein binding and capillary flow characteristics depend on the physical and chemical properties of the nitrocellulose membrane.

Unbacked and backed membranes are the two main types. Unbacked membranes give more options as they allow for use of the belt side or air side. However, without the backing, they do not have the rigidity of a backed membrane and can be trickier to run through a reel-to-reel format. Backed membranes are sturdier than unbacked membranes and easier to use for manufacturing.

In a lateral-flow assay, the absorbent pad or wick is the component that is located on the end opposite to the sample application zone. Its primary function is to act as a sink for the reagents.

Cytiva offers a variety of cellulose and glass fiber materials as well as cellulose-glass fiber blends to ensure that all sample types and specific needs can be addressed. CF3, CF4, CF5, and GR470 are medium weight grades that can accept medium and larger volumes. CF7 is a very thick grade for high sample volumes.