An ultra-low-cost focus-tunable smartphone-based microscope

Smartphone-based biomedical devices are a popular solution for rapid and point-of-care diagnostics. Current smartphone-based microscopes use a fixed focal position, allowing them to be applied only to well-prepared thin samples. By taking advantage of the inherent flexibility of low-cost fused deposition modeling (FDM) 3D printing materials, we address the issues of optical focus tuning when making and using smartphone-based microscopes. We achieved a tuning accuracy of similar to 5 micron with a novel structure design. It shrinks the mechanical displacement by a factor of similar to 11 through a seesaw-like component. For comparison, the processing accuracy of FDM 3D printing is similar to 200 micron. Combing with the built-in flashlight illumination and an off-theshelf smartphone lens, the total manufacturing cost of our smartphone-based microscope is less than 4 USD. We demonstrated the capability of this design in imaging thick biological specimens. We further applied this device in the cell culture monitoring because of its portability and flexibility. We observed the morphological differences of cells on multiple focal planes and recorded the biological processing of cell division in situ. We think this work will help expand the application scenario of smartphone-based biomedical tools and provide a useful reference for the design of such devices.