Before beginning development of a lateral flow assay, the critical requirements of the intended test should be defined. These requirements, often referred to as design requirements or design inputs, describe the function, performance, usability, and safety requirements of the assay in relation to its intended use. They provide a framework for subsequent development and optimization. Examples include whether the result is qualitative or quantitative, limit of detection, analytical range, assay run time, and shelf life.
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From Design Requirements to Assay Optimization
General design requirements establish the initial targets for development. Assay optimization then determines whether the proposed design can meet those requirements and provides the data needed to refine the final specifications.
What Are Assay Design Requirements?
Assay design requirements should be comprehensive, unambiguous, non-conflicting, and measurable. Developing useful requirements requires a clear understanding of the assay's intended purpose and how it will ultimately be used.
For development of a commercial test, it can be useful to first prepare a Customer Needs Report that captures functional, handling, and diagnostic needs based on the intended user and market. Commercial diagnostic tests may also be subject to regulatory requirements, including FDA oversight in the United States. As development progresses, verification and validation studies can then measure assay performance against the established requirements.
General Lateral Flow Assay Design Requirements
Before feasibility work begins, define the general requirements for the assay based on its intended use. Each requirement should identify a specific characteristic and a measurable target. For example, an Assay Run Time requirement might specify that the test must produce a reliable result in less than 25 minutes.
| Requirement Area | What It Defines | Examples |
|---|---|---|
| Design Characteristics & Functionality | What the assay is expected to do and how its performance will be measured. | Analysis method, target analyte, test format, assay run time, sensitivity, specificity, analytical range, precision, interference, limit of detection, clinical performance |
| Physical Properties | Physical constraints associated with the test strip, cartridge, reader, or other system components. | Cartridge dimensions, conjugate and sample ports, overfill volume, reader requirements |
| Handling Requirements | Conditions under which the test will be stored, handled, and operated. | Operating temperature and humidity, storage temperature, storage duration, equilibration time |
| Sample Requirements | Requirements associated with sample collection, preparation, transport, and storage. | Sample type, sample volume, storage temperature, sample treatment such as centrifugation |
Additional requirements may address packaging, shipping, labeling, regulatory considerations, and safety. Identifying these constraints early can reduce the risk of redesign or delays later in development.
Assay Optimization & Feasibility
Once the initial design requirements have been defined, they can be translated into a development plan with measurable milestones. Assay optimization then tests whether the design can achieve those targets.
During optimization, requirements may need to be added, adjusted, or removed as new information becomes available. The design requirements should therefore remain a living document throughout early development. The goal is to reach a point where assay performance can demonstrate feasibility against the requirements needed for the intended product.
Optimization also requires evaluating the physical components of the lateral flow strip. Our Material Starter Kit for Lateral Flow provides multiple nitrocellulose membranes, conjugate pads, sample pads, wick pads, and other materials for screening during assay development.
Affinity reagent selection is another important early development decision. Once the assay requirements are established, the next step is to identify antibodies that can provide the necessary sensitivity, specificity, and performance in the intended lateral flow format.
Next: Select and prepare the antibodies