Revealed: The impact of PVC adhesive on migration in chromatography detection!
During the research and development process, we often find that after adding the sample, the entire NC film becomes red or near the CT line, so we should pay attention to the influence of our PVC base plate adhesive (there are other reasons that lead to the previous results, which will be introduced later). Appropriate adhesive The adhesive layer helps manufacturers improve processing and extend the shelf life of membrane-based diagnostic products.
I believe everyone knows that materials used for chromatography diagnostic testing have two common characteristics: porous and permeable and associated brittleness. In order to make up for the lack of physical strength of this type of material, this type of material is usually assembled to a specific bracket through the use of adhesives. Previously, product developers have used virtually every type of adhesive to assemble these substances, including thermoset adhesives. Now, with the development of adhesive technology, a series of adhesives suitable for chromatography detection applications have been manufactured. By selecting an adhesive that effectively binds the porous materials used in a chromatographic test strip, product developers can ensure correct results and other performance throughout the product's lifetime.
In most chromatography applications, most product developers specify pressure-sensitive adhesives (PSAS) (full name for pressure-sensitive adhesives), which do not introduce corresponding complications in the design, processing, or use of the product. The use of pressure-sensitive adhesives (PSAS) has proven to be a reliable method of bonding the components of a chromatographic test strip together using an appropriate adhesive pattern.
In a typical chromatography application, the bonding of the components is accomplished by the penetration of the adhesive into the porous material, thereby connecting all the components together. This adhesive migration process under normal conditions is called cold flow. Because no heat is provided during the penetration of the pressure-sensitive adhesive (PSA) into other components of the chromatography test strip, a certain degree of cold flow is the basis for the formation of the connection between the various substances. However, adhesives with insufficient or excessive cold flow can also present challenges for developers of such diagnostic products.
To ensure the correct production and performance of chromatography products, product developers must research what type of adhesive to use and select an adhesive that has the best balance of bond strength and migration properties. The effects caused by adhesive migration have generally been minimized when product developers have studied, tested, and allowed for some degree of the effects of adhesive migration.
Take a look at the scope of the migration's impact:
Excessive adhesive migration can affect many components in a chromatographic assay if the adhesive is not reviewed before use. If the degree of cold flow is too low, the adhesion force will be too low and the components of the product will not be fully bonded. Therefore, to achieve high adhesion, product developers must search for an adhesive that can provide a high degree of cold flow.
On the other hand, too high a degree of cold flow will cause pore clogging, local hydrophobicity and product redissolution problems, which will also interfere with product performance. These phenomena are mainly caused by the migration and penetration of the adhesive into the porous material after the various components of the product are bonded, especially during long-term storage.
In many cases, problems associated with cold flow can be solved by using direct-cast membranes. For example, such films can be backed by a plastic film to prevent adhesive from entering the film pores, thereby eliminating vertical adhesive penetration during product storage. However, there are situations where product developers must use unbacked films due to significant differences in product processing or performance characteristics between backed and unbacked films.
Even when direct-cast membranes are used, excessive adhesive migration can interfere with the functionality of other components of the product, including sample pads, adhesive conjugate pads, and absorbent paper. For example, when sample pads are used to control sample volume during product testing, adhesive migration and penetration into the sample pad can affect the total effective sample volume.
Similarly, when a product is tested and includes a filtration step (for example, the testing of some products requires whole blood separation processing), the migration of the adhesive will block the filtration function of the membrane to a certain extent, so that only a small amount of effective sample is generated during product testing.
Adhesive migration can also occur in certain products where a plastic film is attached to the membrane to act as a protective layer - a product model that is increasingly used. When adhesive vertical penetration migration occurs in products with a backing film, the impact is more significant than in products without a backing film. Excessive adhesive migration will prevent the visual inspection line from strengthening, resulting in a significant reduction in the strength of the inspection line.
Manufacturers developing membrane-based quantitative detection products also encounter the same problems involving cold flow phenomena. Adhesive migration blocks the porous structure of a particular material, causing the material's bed volume to decrease and thereby affecting the scale of the assay. Today's common quantitative testing instruments take readings by optical methods (reflection or transmission).
In either case, a partially blocked membrane can alter the amount of specimen and gel-bound conjugates that pass through the capture zone, thereby altering the sensitivity of the product assay. Adhesive migration and blocking of part of the membrane structure will also change the effective light absorption or light reflection of the material, thereby affecting the detection reading.
A similar effect occurs with magnetic particle-based detection systems, which detect based on the total number of gel-bound conjugates bound to the capture zone. If the active area of the capture zone becomes clogged with adhesive migration, the test result reading will drop accordingly. Additionally, these readings can further deteriorate as the adhesive migrates during product storage, so samples of the same concentration will result in different readings over time.
Regardless of the quantitative detection method, the presence of local hydrophobic sites on the detection membrane can greatly affect the detection of the product. Non-wettable patches on the membrane can cause variations in assay results, especially when these hydrophobic patches are regularly present within the capture area.
Someone has done research on adhesive migration:
Pressure-sensitive adhesives are classified by their associated hardness grades. High-hardness pressure-sensitive adhesives feature low cold flow and low original adhesion. Low hardness pressure-sensitive adhesives have the characteristics of high cold flow and high original adhesion.
Three types of adhesives with different hardnesses were produced to study the effects of different adhesives on chromatography materials. In the investigation, each adhesive was coated with a 23-um layer on a plastic support plate, which is a typical sheet material used in diagnostic products. This type of sheet material also includes nitrocellulose membranes, cellulose membranes, and fiberglass products in a range of pore sizes.
These diagnostic materials were adhesively laminated at a constant pressure of 20 kPa and sealed in aluminum foil bags. The packed aluminum foil bags are stored in a constant temperature room (20°C) or in a constant temperature incubator (37°C). In the investigation and research, corresponding samples are taken at certain intervals for performance testing.
A chromatographic immunoassay was used to assess the effects of different forms of adhesives. The speed of horizontal movement is assessed by measuring the time it takes for deionized water to travel a specific distance (7.5 cm for fiberglass and cellulose membranes; 2 cm for nitrocellulose membranes).
Using a typical chromatographic detection format (monoclonal anti-ßhCG antibody capture and gelation for binding HCG in urine), the performance of the nitrocellulose membrane, the protein used, the strength of the capture line, and the hydrophobicity were examined plaque. All tests were repeated 10 times using two independent materials.
These flake-like materials were also analyzed using scanning electron microscopy (SEM). For these inspections, cross-sections of these sheets of material were cut for measurement of bondline thickness.
The results of this study showed that the horizontal migration speed of all materials laminated to adhesive sheets increased over time, compared with the results of migration tests for membranes without thin sheet material support. The degree of reinforcement depends on the hardness of the adhesive used to bond the materials. The following is a summary of the results of this test: migration time, examination of hydrophobic patches, strength of capture lines, and depth of adhesive migration and penetration.
