A guide for Lateral Flow Absorbent Pad

Lateral flow absorbent pads are used for many purposes these days. The highest level of quality and purity is guaranteed with customizable absorbent pads for lateral flow immunoassay applications. The lateral flow absorbent pad collects liquid after processing. They have multiple benefits while retaining purity.

 They are known for the following benefits:

  • It has uniform absorption, thus giving accurate results.
  • It has high material purity.
  • These pads are hydrophilic
  • The lateral flow wicking material has a wide range of thickness and absorbance.  

Purpose of Lateral flow absorbent pads

Lateral flow absorbent pads are used for the following two purposes. 

Purpose # 1

The sample of absorbent pads and conjugate can be controlled to be released from the membrane or conjugate pad according to strip confirmation. A person’s urine or saliva sample composition can vary significantly based on a variety of factors (e.g. how they eat, their age, etc.). In the presence of compositional differences and pH variations, the detection of the target analyte may be compromised. Absorbent pad is made of one layer of lint-free spunbond fabric that is ultrasonically bonded to one layer of meltblown polypropylene sorbent. 

First, there is the sample pad, which is one of the components of the lateral flow test strip. By contacting the sample, it has the advantage of controlling for these differences. The material and pretreatment of the sample pad must be evaluated so that the sample can flow optimally before it is introduced to the other reagents in the system.

Purpose # 2

As a filter, it leaves the target analyte unaffected and removes unwanted components of the sample. A sample matrix needs to be protected from unwanted material when it contains whole blood and solubilized solids. These samples can be filtered using the sample pad. 

As the fluid flows through the test strip, the sample pad will catch any unwanted particulate matter while allowing the fluid to flow through the analyte of interest. As a result of a filter that holds back the red blood cells, the assay will pass through the plasma/serum while the red blood cells are held back.

Important factors to note

There are a few factors which you should keep in mind while choosing the right lateral flow wicking material or absorbent pads. 

Thickness of the membrane

By having a thicker membrane you can add more material to the bed (i.e. a higher volume of air can be displaced), which will increase the space available to hold samples. The thickness of the membrane would also affect the housing size, as compression of the sample pad would dramatically reduce the amount of sample absorbed into it.

Good Tensile Strength

Lamination can be very challenging when you are working with materials that have low tensile strength. Making preparations for manufacturing requires this consideration. You must look for pads with good tensile strength. 

Type of Mesh

Filters or weaved meshes usually make up most sample pads. Meshes made of woven fibre (e.g. glass fibre) typically have a low bed volume and can be handled easily with their good strength and tensile properties. Since woven meshes do not retain volume, they are unsuitable for pre-treatment, because blocking reagents cannot be contained within them. Cellulose fibre filters are excellent for loading buffers and blocking reagents with a variety of buffer strengths and bed volumes.

Treatment of Lateral flow Wicking Material

It is common practice to treat sample pads with blocking reagents, proteins, detergents, and surfactants in lateral flow experiments. A buffer optimized for the samples can aid in normalizing them before they are introduced to the conjugate pad, and in this way prevent any non-specific interactions caused by differences in pH, protein composition, mucins, salt concentrations, and other molecules that may interfere with the antibody system. 

Adding proteins, surfactants, salts, and/or polymers at the appropriate concentrations to treatment buffers can normalize the sample pH and sodium concentration, block nonspecific binding, improve flow, and enhance the reproducibility of the test. 

For saliva samples, the difference in viscosity in the samples may pose a challenge in terms of what to include in the sample pad treatment. Increasing the salt and surfactant concentrations can break down mucins and proteins, resulting in decreased viscosity and better flow. 

When testing whole blood, these components may cause hemolysis of red blood cells and cause undesirable passage through the membrane of these lysed cells.

Immersion Treatment 

An automated dispenser (Isoflow, Kinematic, Biodot) can spray uniformly all over the sample pad directly after immersion, or by immersion separately. As a follow-up treatment, we recommend curing in an air convection oven at 37°C for 30-60 minutes, followed by drying overnight in a desiccated environment at 18-25°C (*20% relative humidity). 

Sample pads are ready for use once they have dried overnight. Sample pads treated with reagents should be stored at room temperature (18-25°C), in a dry environment (*20%). Otherwise, moisture may be absorbed into the pads, which will destabilize the reagents.