Conjugate reagent may be successfully applied to the pad in a number of ways, depending on the process scale and the degree of dosing control required. The required scale of the process will be directly linked to projected sales of the final product. The degree of dosing control required is related the robustness of the assay system, and tends to be more critical for semi-quantitative assay systems than for qualitative assays, in which conjugate reagent is typically used in excess.
Conjugate reagent can be soaked in sheet or band form in a manual soaking process. This typically involves simply soaking a sheet or a band of conjugate pad material in a defined volume of conjugate reagent under defined conditions. This results in a fully wetted conjugate sheet or band that must then be dried. This method is simple and cost-effective at small scale but may not be as reproducible as the alternatives below.
Conjugate may be soaked using a more automated process that the above, in which conjugate pad is in roll form and a reel-to-reel soaking method is used. This typically involves feeding the pad material from the roll to a collector via a soaking tank where the conjugate pad is immersed in the conjugate reagent. Conjugate reagent is absorbed into the pad material, which is then subject to an in-line drying process. This method does require some sophisticated equipment but is deemed to have the advantage of being more reproducible than a manual system.
Conjugate reagent may be applied using a spraying or dispensing technique. This is performed using a special-purpose dispensing system—for example, with equipment employing a positive-displacement syringe with air-spraying nozzle. Typically, the conjugate reagent is applied to the pad as the pad is moved under the dispense head. This application technique can be used as a semimanual or semi-automated process. This method is considered to be capable of controlling the conjugate dose more effectively than soaking, but the performance of the process is dependent to a large extent on the physical properties of the conjugate pad material in terms of absorption capacity, wicking rate, and consistency both within and between lots of material.
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