Developing a consumable for your point of care diagnostic solution?

This blog highlights my top recommendations for translating point of care assays that are simple, low cost and easy to use.

1. Understand disease panel requirements through a Target Product Profile (TPP)

The first step in developing your assay is to understand the target product profile (TPP). The TPP outlines the desired profile or characteristics of a target product that is aimed at a particular disease or diseases.  The TPP states the intended use, target populations and other desired attributes of the product to be developed, including safety and efficacy related characteristics. The World Health Organization (WHO) has TPPs which can be downloaded from their website. Inside the TPP document, you can find names of technical experts in the field, terminologies, disease and technology status and concepts, TPP details, framework of evaluations and other relevant resources.

In most cases, medtech companies create their own TPPs and use them internally as planning tools that guide their development efforts. The TPP could also be used as reference for product approval submissions to regulatory bodies like the FDA and Health Canada.

WHO TPPs for specific disease panel targets can also serve as guides for product research and development. Before developing your laboratory workflow, check the published TPPs or similar documents within your organization.

2. Identify assay type and mode of detection

After reviewing the TPP, you can now identify which type of assay to use with the target disease. From the same document, you can identify details including assay processes, workflow and the recommended test and evaluation framework. Crosscheck the document with current research publications and industry partners including potential suppliers or technology service providers. Drafting the workflow and the detection methodology is a must. Assay development experience will play a major role at this stage. However, personal biases must be considered when choosing which assay to use. If you have intellectual property for your assay, the TPP will serve as a guide but you can create a work around to adapt it to your concept microfluidic  cartridge designs. Typical assay types include cell based, immune assay, molecular assays and/or in combination with other assay types.

3. Implement assay workflow on the bench

After a thorough review of TPPs and research publications, you are ready to embark on the actual bench work. At this stage you will develop and implement your assay.  You will generate lots of data and identify the proper mix of reagents, volume, timing and procedural steps. This is an iterative process where you identify the best combination of specificity and sensitivity. For initial work, I recommend you use well established standards for detection.  Data generated will become the baseline of your assay development.

Use good laboratory practice (GLP), particularly in data recording, test procedures and adherence to protocols.  GLP is a set of principles intended to assure the quality and integrity of non-clinical laboratory studies that support research or permits for products regulated by government agencies.

4. Translating assay workflow to a microfluidic cartridge

Once you have good, repeatable data, you are ready to translate your assay workflow to a microfluidic cartridge.  Here you will need to repeat the same workflow with the goal of reducing the working reagent volume as well as the number of steps. For example, if you are using an immunoassay, you need to determine the minimum volume of reagent that could produce the same result as the one initially used.  How many washing steps do you need? Is there a way to reduce the washing steps and the amount of reagent used? Do you need a dry reagent and reconstitution buffers?   How much waste fluid must be discarded? Do you require excitation temperature to hasten the reaction or incubation period?  What is your required detection method? Does it work in a smaller platform? After you make your adjustments, it is advisable to reassess the resulting workflow that will be implemented on the cartridge.

5. Design and Implement the microfluidic cartridge

After tweaking and adjusting the workflow, you are ready to proceed with the cartridge design. Use the data generated and the modified workflow to create cartridge requirement specifications. First, identify the mode of detection (i.e. chemiluminescence, laser excitation and emission, electro chemistry). The design of the cartridge must be adjusted based on the detection mode.   Determine reagent characteristics including volume, viscosity, temperature, and boiling/freezing point of the reagents and the like. All requirements must be documented properly.  Because the cartridge has multiple components, a system diagram must be drafted. This includes all processes beginning with the introduction of sample through to the final detection and reporting. The next step is to identify working volume and assay components including waste. The best method is to adapt a modular approach. Each step in the workflow is designed independently with sub-system testing until the required outputs are satisfied.   With modular testing, both the input and output must be considered. Identify the type of input and exit port required with respect to the next module.  Another important component is the mode of actuation. This addresses how you move the fluid inside the channel.  Does the system require pneumatic, diaphragm or centrifugal force to actuate the fluid inside the channel?

After completing the modular sub-system testing with your assay in the cartridge, it’s time to integrate the components. The integration requires putting the identified components into a final cartridge design and create a working prototype. This can be done initially with machined parts or any rapid prototyping technique that produces a relatively good quality working cartridge. The rapid prototype cartridge will provide a sense of real dimension as integrated to other components.  The reader design is usually done in parallel with the cartridge integration. Depending on the complexity of the detection method, it could also be done just after the review of TPP – particularly if the detection means is novel and includes hardware and software development. During the design and implementation, it is useful to incorporate a usability study on the cartridge and instrument as well as the disposal mechanism for biological materials (e.g. blood, plasma, and molecular reagents).

6. Test performance and quality

Last is performance evaluation and quality testing. This includes mechanical and fluidic characterization, detection means, overall system performance and finally, assay performance. To produce a repeatable and reliable cartridge, consider subjecting it to multiple tests such as leak, temperature, durability, and shelf life and shipping tests.