There are many elements that make an assay effective in the laboratory, such as fluid volumes and their manipulations, temperature, timing and lighting. When translating that assay from the lab to a product, intensive discovery research is required to determine 1) what are the most critical elements and 2) understanding how those elements and other factors influence results.
Fluid handling is a critical and often challenging example. This process typically needs to be miniaturized to transfer the assay to a POC device, but fluid dynamics differ between a test tube and a cartridge.
For example, moving 50µL of a fluid (the size of a raindrop) with a pipette on a lab bench is a trivial process. On the other hand, manipulating such a small volume of fluid though a channel in a POC cartridge presents a challenge due to dead volumes of the channel.
Mixing may also be an issue when adapting the original bench-side approach (aspirate and dispense, or vortex) to a microfluidic cartridge. It is important to understand how fluids are mixed—rapidly, slowly, vigorously, gently—and develop the instrument and cartridge accordingly.
Methods such as shuttling of fluids back and forth, stir bars, or bubbling are all methods of mixing that are commonly used in a POC cartridge, but they may not be sufficient for the assay. If the method chosen for the cartridge is different from that used on the bench, the assay needs to be re-evaluated using the new method.
Temperature control is another area that can make or break an assay. Some assays require tight thermal controls to ensure a chemical process, such as denaturing DNA or lysing a cell, or even an optimal incubation environment.
When performing these steps on a work bench, equipment dedicated to these tasks are used. They are designed with the optimal geometry and heating components to ensure the steps are completed properly and efficiently.
When performing these steps in a POC cartridge, you encounter competing requirements, such as the need for increasing thermal contact versus the need to keep the cartridge small. Equipment such as PCR, spectrometer and vortex machines may be used when performing a single assay in the lab; however, trying to combine all three into a benchtop system while maintaining their performance poses challenges. During the assay translation process, it is essential to identify the thermal accuracy and precision requirements for the POC device and to understand how making trade-offs in these areas will affect performance.
Once you understand the discrete workflow steps performed in the lab and their sensitivities, you must test different ways to adapt them to a cartridge—changing the original protocol as little as possible. Using this process to identify potential problems with the workflow fundamentals enables you to begin development on solutions early.
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