From Development to Routine Production: Preparing Lateral Flow Assays for Transfer
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In lateral flow assay development, the foundations for successful transfer are often laid during feasibility, when material selection, assembly choices and manufacturability begin to shape the assay design. Formal transfer planning, however, usually begins once a defined prototype is in place and there is sufficient understanding of assay performance, process behaviour and key materials to begin preparing that assay for routine manufacture.
For lateral flow assays, that transition deserves careful preparation. Development may establish that the assay concept is workable and that the desired performance is achievable, but transfer is the stage at which that prototype is developed into a process that can be executed consistently in manufacture. Making that transition requires more than a prototype that performs well in development. Materials need to be brought under appropriate supply and inspection controls, operators need to be trained to execute the process consistently, and documentation needs to capture not only the sequence of steps but also the conditions and observations that matter most. It may also require confirmation that the assay behaves as expected under the intended manufacturing route, particularly where equipment, scale or assembly conditions differ from earlier development work. Alongside this, process understanding needs to be developed far enough that normal manufacturing variation can be managed without compromising the intended assay performance.
Transfer is therefore not simply a handover, but the stage at which development understanding is translated into manufacturing capability.
What Readiness for Transfer Really Means
An assay is ready for transfer when the design and process have matured enough that the remaining task is no longer to define the assay concept itself, but to establish how it will be controlled, documented and reproduced in manufacture.
By this stage, the design intent should be sufficiently fixed, and the main sources of process variability should be understood well enough to support the next phase of transfer activity. Critical materials, particularly biological reagents, should be defined well enough that sensible specifications and incoming controls can later be established. An initial process map should also be in place to define the intended manufacturing route at a level sufficient to support cross-functional discussion, pFMEA and planning for transfer stage robustness work. Operations, quality and QC should already be involved closely enough to understand both the intended process and the reasoning behind its controls.
In practical terms, readiness for transfer means that the assay is sufficiently defined for transfer work to focus on manufacturing readiness, including targeted robustness studies, process definition, documentation, training and pilot preparation, rather than continuing to establish the assay for the first time. It also means that successful execution should no longer depend mainly on knowledge held by the development team.
Once that level of maturity has been reached, transfer can begin to move from development judgement into a more structured cross-functional phase, with planning, risk review and manufacturing definition starting to take shape around the assay.
Designing with Manufacturing Margin
One of the most important disciplines before transfer is knowing when an assay has reached the right endpoint in development. This is not about accepting lower performance. The assay still needs to meet its design inputs for sensitivity, specificity, reproducibility and usability. The question is whether further optimisation is still improving the product or whether it is narrowing the manufacturing margin needed to hold that performance in routine production.
In lateral flow, it is entirely possible to tune an assay very close to its technical optimum. That may look attractive in development, but it can leave the process with less tolerance to normal manufacturing variation. Small shifts in biological reagents, material behaviour, hold times or process settings can then have a greater effect because the assay is already being operated near its practical limit.
A stronger transfer position is one in which the assay meets its intended requirements with enough operating space to support routine manufacture. From the customer’s perspective, the most valuable outcome is not the strongest isolated development result, but the best performance that can be delivered consistently through manufacture and supply.
Transfer Consideration: Conjugate Stability and Sensitivity Margin | |
Consideration: | During development, sensitivity may be improved through conjugate optimisation, particularly through pH and antibody loading. In some cases, however, those conditions can leave less stability margin across the manufacturing window, with performance shifting between deposition events, making it harder to define a conjugate quantity that remains suitable across the batch. |
How to strengthen transfer readiness: | Once the required performance has been achieved, it is worth assessing whether further signal gain is adding product value or reducing manufacturing margin. Where sensitivity is being improved through conjugate optimisation, those gains are best considered alongside conjugate stability under representative manufacturing conditions, so that the transferred process is not dependent on conditions that are harder to hold consistently in routine manufacture. |
Planning Transfer as a Cross-Functional Activity
Transfer planning works best when the technical team, operations, quality control and quality assurance are involved early enough that pilot and validation batches can be used to confirm and strengthen the process, rather than to work through basic process uncertainties. The assay should be defined clearly enough that its intended manufacturing route, control points and acceptable outcomes can be understood consistently across the teams that will run, support and review it. That shared understanding helps transfer move from development led execution into routine manufacturing control while preserving the understanding established during development.
In practice, that alignment needs to be captured in a transfer plan or transfer protocol that defines how the transfer phase will be carried out. At a minimum, this should describe the intended manufacturing route, the scope of the transfer activities, the key roles and responsibilities across teams and the planned sequence from pilot preparation through pilot batches and into validation planning. It should also make clear what materials are to be used, what documents are to be generated or updated, how training will be approached, how observations and deviations will be captured and what evidence will be needed before the assay is considered ready to progress.
Practical readiness is part of that same plan. Manufacturing equipment access needs to be available at the right time and in the right sequence, particularly where shared assets are involved. Staff availability needs to reflect the shift patterns that may be used in manufacture, especially where early execution benefits from technical support on the floor. Time also needs to be protected between runs so that transfer learning can be reviewed and documented while it is still current.
A well constructed transfer plan therefore acts not just as a schedule, but as the framework that links technical intent, manufacturing execution and quality oversight through the transition into routine production.
Using pFMEA and Robustness Studies to Shape Transfer
Once transfer planning is in place, one of the most useful next steps is to convert development learning into a structured transfer strategy.
Development usually generates a large amount of practical process knowledge. Certain steps may have proved more susceptible to small changes in conditions, some materials may have behaved differently lot to lot, and factors such as hold times, striping, drying, assembly, lamination, cutting, reagent handling or environmental exposure may all have shown themselves to influence the process more than expected. pFMEA provides a structured way to translate those observations into ranked process risks.
Used well, pFMEA helps identify which aspects of the process most need to be challenged before manufacture can be considered routine. It supports decisions about where robustness studies should focus, where process limits need better definition, where documents need more detail and where manufacturing controls will later need to be strongest.
Robustness studies are then most useful when they are designed around those real process questions rather than around arbitrary stress. Their purpose is not simply to show that the assay survives challenge, but to define the range in which the process can still deliver the intended performance. In transfer terms, this is one of the most important shifts in mindset: the process is no longer being judged only by how well it performs at its optimum, but by how well it performs across the operating space it will need in routine production.
By the time this work is complete, the process should be understood not only in terms of what gives the best result, but in terms of what range of operation remains acceptable and how that range will be monitored during manufacture. In many programmes, that stage of targeted robustness work takes place over roughly six to eight weeks once a defined prototype is available, allowing process limits, material risks and control priorities to be challenged before pilot manufacture begins.
Translating Development Knowledge into Manufacturing Practice
A major output of transfer preparation is the conversion of development knowledge into forms that can support routine manufacture. This includes formal production documentation, but also the practical knowledge that underpins successful execution and is often less visible in development records alone. The point is not simply to create documents, but to make the process reproducible by making it understandable, controllable and capable of being executed consistently in manufacture.
For that reason, transfer ready documentation needs to do more than describe the sequence of operations. It needs to reflect what actually matters in practice. Incoming inspection should focus on the material attributes that genuinely influence assay function, while manufacturing instructions and in-process methods should define what acceptable execution looks like where the process is less tolerant.
Alongside formal records, tacit knowledge developed during R&D is often highly valuable during transfer and should be captured deliberately before it remains confined to experience alone. Development teams usually build an intuitive understanding of the assay over time. They recognise visual cues, notice subtle differences in material behaviour and know where the process is more or less tolerant.
A structured application note prepared by the development team can help bridge the gap. Used well, it provides a controlled reference for the key design elements, material choices, critical process features and practical execution considerations that need to remain visible during transfer into manufacture. Its main value is between the end of feasibility and pilot manufacture, when robustness work is still refining the process and manufacturing documentation is being developed in parallel.
Alongside this, the wider transfer package may also include annotated photographs, short videos, examples of acceptable and unacceptable outcomes, troubleshooting notes and practical observations recorded during transfer activity. These materials can support training, document refinement and more consistent execution in practice. Together, they help ensure that the process being transferred includes not only what is written down formally, but also what matters most in use. By the start of pilot batches, that understanding should have been translated into the formal manufacturing documents, so that the application note has served its purpose as a bridge between development and routine transfer documentation.
Transfer Consideration: When Written Instructions Leave Room for Variation | |
Consideration: | During transfer, different operators may follow the same written step but still execute it differently in practice. For example, manual pressure applied to lids before roller closing may vary between operators. Where the lid is not aligned correctly or the engagement pins are not properly seated before entering the roller, reject rates can increase because the lid is damaged or the strip beneath it is disturbed during closing. |
How to strengthen transfer readiness: | Where steps depend on practical judgement, transfer should include direct observation of how different operators execute the process, with enough opportunity to refine the documentation around what actually matters in practice. In some cases, it can also be helpful for manufacturing operators to see or trial key steps during development or late stage development work, so that documentation reflects how the process is really performed rather than how it is assumed to be performed. Clear images, annotated examples and operator feedback can all help define acceptable execution more effectively before routine manufacture begins. |
Training for Manufacture
Once development knowledge has been translated into a more transferable form, training becomes the point at which that knowledge is converted into consistent manufacturing practice.
At this stage, the objective is not simply to show operators the sequence of steps, but to make clear which aspects of execution are protecting assay performance. In routine manufacture, consistency depends not only on following the process, but on recognising when the process is behaving as expected and when it is beginning to move away from its intended state. Training is therefore most useful when it links practical execution to the parts of the assay that are less tolerant to variation.
This does not require turning manufacturing training into a scientific lecture. It means explaining, at the right level, what key materials are doing, which process steps protect assay performance and what signs indicate that the process is behaving as expected. In a lateral flow setting, that may include the significance of reagent handling, deposition consistency, alignment, timing or the reasons certain checks are positioned where they are. The purpose is not to reproduce development knowledge in full, but to ensure that the features of execution which matter most to assay performance are understood at the point of manufacture.
Training should also reflect how the process will actually be run. Where different shift patterns may be used in routine manufacture, support should be available across those shifts during pilot and early validation activity so that execution can be observed consistently and the process can be embedded in the way it will later be used.
Pilot Batches as the Bridge into Routine Manufacture
Pilot batches are often the most informative part of the transfer pathway because they show how the process behaves when it is executed in a realistic manufacturing setting.
This phase often takes around three to four weeks, depending on the number of process steps, the manufacturing format and the batch size. It is often the first point at which the process is exercised in a way that begins to reflect routine manufacturing conditions.
This is the stage at which draft instructions are tested in practice, in-process checks are assessed for usefulness, training is observed in execution and technical assumptions from development are either confirmed or refined. In some programmes, material generated during this phase may also support indicative performance verification and indicative or accelerated stability studies, but the main value of pilot manufacture lies in what it reveals about the process itself.
Strong pilot execution depends on close coordination on the floor. Transfer team members, development staff, operations and QC can each contribute useful observations, provided responsibilities are clear and there is enough time to review them properly. Practical records such as photographs, videos, annotated examples and structured observations can be especially useful at this stage because they preserve process knowledge in a form that can later support training, troubleshooting and document updates.
Transfer Consideration: Running Pilot Batches in Parallel | |
Consideration: | Running pilot or validation batches in parallel can appear to shorten the transfer timeline. In some cases, however, it can also reduce the opportunity to review learning between runs and apply improvements progressively, so that the same issues are carried into multiple batches. |
How to strengthen transfer readiness: | Where batches are intended to support transfer learning, it is usually more effective to plan them in a sequence that leaves time between runs for review, document update and confirmation that the process and its controls are ready for the next batch. This helps ensure that later runs are based on current understanding rather than unresolved issues carried forward unchanged. |
Between batch review is one of the most valuable parts of pilot work. Taking time as a team to assess what was observed, what should be clarified and what should change before the next run helps ensure that the process strengthens as the campaign progresses.
Yield analysis should also be one of the main outputs of pilot work. Looking at losses, rejects or rework by step, operator, team, shift or failure mode can help show where the process is behaving predictably and where additional refinement is still needed. In transfer terms, this is one of the clearest indicators of whether the process is genuinely moving towards routine manufacture or still depends too heavily on development intervention.
When the Assay is Ready for Validation
An assay is ready for validation when the manufacturing process is established well enough that validation is no longer being used to work out how the assay should be made, but to confirm that it can be made reproducibly under representative manufacturing conditions.
In practice, that means the assay design is sufficiently fixed, the key manufacturing and QC documents are mature, operator training has already been exercised in practice and the main sources of process variability are understood well enough that they have either been addressed or deliberately challenged through robustness studies and pilot work. Critical materials, in-process controls and batch execution expectations should also be defined clearly enough that validation can proceed through the normal manufacturing framework rather than depending on development led adjustments during execution.
By this stage, pilot batches should already have shown that the process can be run as intended, with acceptable yield, useful in-process controls and a clear understanding of where variability matters most. Validation should then serve to confirm routine reproducibility, rather than continue refining core aspects of the process.
Process Validation Under Representative Manufacturing Conditions
A common process validation structure includes three validation batches. The key point, however, is not simply the number of batches. It is that the validation exercise demonstrates repeatability and reproducibility under representative manufacturing conditions, using the process, materials, people and controls that will support routine production.
That means validation planning should distinguish carefully between controls that are deliberately imposed for the study and controls that will exist routinely in manufacture. A common example is lot diversity. Where validation is designed to include structured material diversity, particularly for biologicals, the intended lots should be identified in advance and coordinated with supply chain so that they are reserved, picked and issued in a controlled way for each batch. Clear picking lists, batch-specific material allocation and robust traceability help ensure that the planned material combinations are used correctly. Importantly, this should be done through the same kind of material control framework that routine manufacture will rely on later, so that the discipline used during validation can be carried forward into standard production.
Different operators, teams and shifts may also need to be included where they reflect how the process will actually be run. The purpose is not only to show that the product can be made successfully, but that it can be made reproducibly under the same kinds of conditions that routine production will later use.
For many programmes, process validation takes around two to three months to complete, depending on batch size, process complexity and the manufacturing model being used. By that stage, validation should be confirming routine reproducibility rather than continuing to define the process itself.
Analytical Performance Verification Alongside Transfer
Transfer does not only need to show that the assay can be made reproducibly. It also needs to show that the transferred process continues to support the intended analytical behaviour of the product.
This becomes particularly important once manufacturing relevant conditions are introduced. Changes in process definition, material control, scale-up conditions or routine manufacturing variability may all influence assay response in ways that were not fully visible during earlier development work. At that stage, analytical performance verification helps confirm that the transferred assay still supports the expected sensitivity, specificity, reproducibility and overall response profile. This creates an important link between manufacturing readiness and the wider analytical evidence package for the product.
In many programmes, that work begins once the first validation batch is available and then develops further alongside the broader analytical validation plan. Where clinical studies are required, those usually sit on a longer timeline and may continue beyond the manufacturing validation phase.
A fuller discussion of analytical performance verification sits beyond the scope of this article, but it is an important companion to transfer because it helps confirm not only that the assay can be made reproducibly, but that it continues to perform as intended under manufacturing conditions.
Supporting the Transition into Routine Manufacture
Transfer does not end with pilot or even with successful validation batches. There is usually a further period in which the process is being established within routine manufacture and supported through normal production controls, trend review and continued learning.
Once pilot and validation activities are complete, the process begins to generate routine manufacturing data. That creates a useful opportunity to review yields, rejects, deviations, QC outcomes and operator feedback in a more systematic way. Early trend review can help confirm that the process is settling into a stable pattern and can also identify where further clarification or tightening may still be useful.
At this stage, the goal is for routine production to become fully owned by the manufacturing system, supported by clear documentation, capable teams and process understanding that is no longer dependent on informal expert intervention. That is the final test of transfer: not whether the assay can be made under focused technical supervision, but whether it can now be sustained through standard manufacturing practice.
Conclusion
Preparing a lateral flow assay for transfer is the stage at which development decisions are tested against the realities of manufacture.
Although the formal transfer phase usually begins once feasibility has established that the selected format, critical raw materials and prototype can support the intended performance, transfer success is shaped much earlier by development choices that take manufacturability into account. By the time an assay moves into transfer, the objective is no longer to optimise in isolation, but to establish a process that can tolerate the conditions of routine production while continuing to meet its design requirements.
That depends on more than analytical performance alone. It requires sufficient manufacturing margin in the assay design, a clear understanding of where process variability matters, documentation that captures what is important in practice and a transfer pathway that uses robustness studies, pilot manufacture and validation to confirm that the process is ready to be reproduced under representative conditions.
A well executed transfer therefore provides more than a successful handover. It establishes the technical and operational basis for routine production, so that the intended assay performance can be sustained through normal manufacturing controls, realistic material variability and standard production practice.
Learn more about Fleet Bioprocessing’s Lateral Flow Assay Development and Transfer to Manufacture services. Contact us to discuss your project and how we can support your assay through to routine manufacture.
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