Lateral Flow Immunoassays are used by point-of-care markets for immunological testing. Examples of utilization of immunoassays include cholesterol, cardiac markers, diabetes testing. Recently, and due to some constraining patent issues, many manufacturers of lateral flow assays have invested into R&D to develop multiplexing assays on complex platforms for very specific applications, and to improve the design of current lateral flow substrate to increase reproducibility in the final product.
The lateral flow immunoassay format was developed in the seventies and within 10 years became a standard platform for a variety of Point of Care (PoC) tests. The benefits of this format were:
- Ease of use
- Requires relatively small amount of sample
- Adequate level of sensitivity
- Ease of manufacture in large scale
- Stability of the final product at room temperature (shelf life)
- Ease of implementation with a reader technology
- Ease of approval by regulatory instances (format well know by the market)
- Relatively inexpensive to manufacture
For many tests, this format was very attractive. However, recent market needs have evolved into higher demands, requiring LFIA tests to produce more than the traditional “yes/no” result. The progression of lateral flow tests to true quantitative formats is an active area of current research and development. Traditionally, a lateral flow immunoassay device is assembled with a variety of materials and reagents (Figure 1). Typical components are a backing card, membrane, sample pad, absorbent pad, conjugate pad, and possible a wick. The tests are assembled during a “Batch Process” or an “In Line Process”, the first one being far more common until recent years. The batch process starts with a roll of each material; i.e. membrane, sample pad, conjugate pad, sample pad, wick material, and individual backing cards. Each material goes through its own process independently and then once complete the final test is assembled. The other alternative to the Batch process is the In-Line method. An In Line process starts with all materials in roll format, and is typically achieved with three types of modules. The first is the reagent dispensing and drying module, the second is the slitting module, where processed webs are cut down to narrower widths for lamination, and the third module is the actual lamination of the LFIA. Typically In-Line approaches are designed to meet the specific needs of an application. The In Line approach allows multi-tasking between both dispensing and impregnation applications, and has capacity for in-line drying and quality control monitoring.