On-Slide Reagent Concentration Feedback and Control

This project required the team to develop a system to monitor the concentration of an ionic buffer solution dispensed onto a standard 75x25 mm microscope slide. Because some tests done by Ventana are extremely sensitive to the ionic concentration of the on-slide fluid, the company wants a way to measure ionic concentration noninvasively. Evaporation and replenishment of the fluid containing the tissue sample cause variation in ionic concentration, which can adversely affect the quality of histopathology staining. The designed system uses a refractometer to measure in real time the refractive index of the buffer solution, which correlates with ionic concentration. When evaporation raises the ionic concentration, a technician can add a precise volume of buffer solution to compensate. By using an infrared laser to refract light into the solution and onto a complementary metal-oxide semiconductor sensor, the resulting angle of refraction can be used to assess the concentration as a function of temperature. A graphical user interface, which allows the user to measure concentration see it change over time, is implemented using a touch screen and Raspberry Pi microcontroller.