Developing assays and sensors for a capstone project is an excellent way for students to demonstrate hands-on skills working in fields like biomedical engineering, chemistry, or environmental sciences. When considering incorporating assay or sensor development, students should first research needs and opportunities in areas related to their major/coursework. They can look at pressing issues being addressed by academic researchers or industries. Developing an assay or sensor to analyze an important problem could help advance scientific understanding or technology applications.

Once a potential topic is identified, students should perform a thorough literature review on current methods and technologies being used to study that issue. By understanding the state-of-the-art, students are better positioned to design a novel assay or sensor that builds on prior work. Their project goal should be to develop a method that offers improved sensitivity, selectivity, speed, simplicity, cost-effectiveness or other advantageous metrics over what is already available.

With a targeted need in mind, students then enter the planning phase. To develop their assay or sensor, they must first determine the biological/chemical/physical principles that will be exploited for recognition and detection elements. Examples could include immunoassays based on antibody-antigen interactions, DNA/RNA detection using probes and primers, electrochemical sensors measuring redox reactions, or optical techniques like fluorescence or surface plasmon resonance.

After selection of a method, students must design the assay or sensor components based on their identified recognition mechanism. This involves determining things like surface chemistries, probe molecules, reagents, fluidics systems, instrumentation parameters and other factors essential to making their proposed method work. Students should rely on knowledge from completed coursework to inform their design choices at this conceptual stage.

With a design established on paper, students can then prototype their assay or sensor. Prototyping allows for testing design concepts before committing to final fabrication. Initial assays or sensors need not be fully optimized but should adequately demonstrate the underlying recognition principles. This trial phase allows students to identify design flaws and make necessary adjustments before moving to optimization. Prototyping is also important for gaining hands-on experience working in lab environments.

Optimizing assay or sensor performance involves iterative experimentation to refine design parameters like receptor densities, reagent formulations, material choices, signal transduction mechanisms and measurement conditions (e.g. temperatures, voltages). At this stage, students systematically vary different aspects of their prototype to determine formulations and setups offering the best sensitivity, limits of detection, selectivity over interferences and other relevant analytical figures of merit. Method validation experiments are also recommended.

As optimization progresses, students should thoroughly characterize assay or sensor performance by determining analytical metrics like linear range, precision, accuracy, reproducibility and shelf life. Results should be reported quantitatively against pre-set project goals so it is clear whether their developed method fulfills the intended application. Method characterization helps establish the reliability and robustness of any new technique to achieve desired outcomes.

Fabrication of final assay or sensor prototypes may be required depending on the complexity of the design. Things like microfluidic chips, printed electrodes or 3D printed plastic casings could necessitate specialized fabrication resources. Collaboration may be needed if an emphasis is placed on engineering aspects rather than just benchtop method development. Regardless, a pilot study testing the developed method on real samples related to the application should form the capstone demonstration.

Strong communication and documentation throughout the development process is critical for any capstone project. Regular meetings with advisors and periodic progress updates allow for feedback to iteratively improve the work as issues arise. Comprehensive final reports and presentations that clearly convey the motivation, methods, results and conclusions are paramount. Developing complete standard operating procedures and future work recommendations also increases the impact. Assay and sensor projects provide an excellent vehicle for demonstrating independent research skills when incorporated into capstone experiences.