Students work in groups to create soap bubbles on a smooth surface, recording their observations from which they formulate theories to explain what they see (color swirls on the bubble surfaces caused by refraction). Then they apply this theory to thin films in general, including porous films used in biosensors, listing factors that could change the color(s) that become visible to the naked eye, and learn how those factors can be manipulated to give information on gene detection. Finally (by experimentation or video), students see what happens when water is dropped onto the surface of a Bragg mirror.

Students learn the relevant equations for refraction (index of refraction, Snell's law) and how to use them to predict the behavior of light waves in specified scenarios. After a brief review of the concept of refraction (as learned in the previous lesson), the equations along with their units and variable definitions, are introduced. Student groups work through a few example conceptual and mathematical problems and receive feedback on their work. Then students conduct the associated activity during which they practice using the equations in a problem set, examine data from a porous film like those used in biosensors, and apply the equations they learned to a hypothetical scenario involving biosensors.

Through this concluding lesson and its associated activity, students experience one valuable and often overlooked skill of successful scientists and engineers communicating your work and ideas. They explore the importance of scientific communication, including the basic, essential elements of communicating new information to the public and pitfalls to avoid. In the associated activity, student groups create posters depicting their solutions to the unit's challenge question accurate, efficient methods for detecting cancer-causing genes using optical biosensors which includes providing a specific example with relevant equations. Students are also individually assessed on their understanding of refraction via a short quiz. This lesson and its associated activity conclude the unit and serve as the culminating Go Public phase of the Legacy Cycle, providing unit review and summative assessment.

By this point in the unit, students have learned all the necessary information and conceptualized a design for how an optical biosensor could be used to detect a target strand of DNA associated with a cancer-causing gene as their solution to the unit's challenge question. Now student groups act as engineers again, using a poster format to communicate and prove the validity of the design. Successful posters include a description of refraction, explanations of refraction in a thin film, and the factors that can alter the interference pattern of a thin film. The posters culminate with an explanation of what is expected to be seen in a biosensing device of this type if it were coupled to a target molecule, proven with a specific example and illustrated with drawings and diagrams throughout. All the poster elements combine to prove the accuracy and viability of this method of gene detection. Together with its associated lesson, this activity functions as part of the summative assessment for this unit.

Students are introduced to the unit challenge discovering a new way to assess a person's risk of breast cancer. Solving this challenge requires knowledge of refraction and the properties of light. After being introduced to the challenge question, students generate ideas related to solving the challenge, and then read a short online article on optical biosensors that guides their research towards solving the problem.

Through four lessons and three hands-on activities, students learn the concepts of refraction and interference in order to solve an engineering challenge: "In 2013, actress Angelina Jolie underwent a double mastectomy, not because she had been diagnosed with breast cancer, but merely to lower her cancer risk. But what if she never inherited the gene(s) that are linked to breast cancer and endured surgery unnecessarily? Can we create a new method of assessing people's genetic risks of breast cancer that is both efficient and cost-effective?" While pursuing a solution to this challenge, students learn about some high-tech materials and delve into the properties of light, including the equations of refraction (index of refraction, Snell's law). Students ultimately propose a method to detect cancer-causing genes by applying the refraction of light in a porous film in the form of an optical biosensor. Investigating this challenge question through this unit is designed for an honors or AP level physics class, although it could be modified for conceptual physics.

Students are introduced to the concept of refraction. After making sure they understand the concepts of diffraction and interference, students work collaboratively to explain optical phenomena that cannot be accounted for via these two mechanisms alone. Then, through the associated activity, students see first-hand how refraction can work with interference to produce color patterns, similar to how nanosensors work. Finally, students apply their knowledge of refraction to the original challenge question to generate a possible solution in the form of a biosensor.

In the first half of this two-part activity, students practice solving problems involving refraction using the index of refraction and Snell's law equations; they mathematically solve for precise angles and speeds caused by refraction. In the second half of the activity, a hands-on lab, they apply the analytical skills required by the problem set to reflectance measurements of porous silicon thin films, including how reflectance measurements would change if various aspects of the film were altered. Students predict the data output in the form of reflectance measurements when samples are altered, which connects to the idea of being able to make predictions about the data output of a biosensing thin film that couples with a target molecule.