Open Source 3D‐printed focussing mechanism for cellphone‐based cellular microscopy.

Summary: The need to improve access to microscopes in low‐resource and educational settings coupled with the global proliferation of camera‐enabled cellphones has recently led to an explosion in new developments in portable, low‐cost microscopy. The availability of accurate ball lenses has resulted in many variants of van Leeuwenhoek‐like microscopes. Combined with cellphones, they have the potential for use as portable microscopes in education and clinics. The need for reproducibility in such applications implies that control over focus is critical. Here, we describe a 3D‐printed focussing mechanism based on a rack and pinion mechanism, coupled to a ball lens‐ based microscope. We quantify the time‐stability of the focussing mechanism through an edge‐based contrast measure used in autofocus cameras and apply it to 'thin smear' blood sample infected with Plasmodium as well as onion skin cells. We show that stability of the z‐focus is in the micrometre range. This development could, we believe, serve to further enhance the utility of a low‐cost and robust microscope and encourage further developments in field microscopes based on the Open Source principle. Lay Description: The wide spread of cellphones with cameras makes them an attractive platform for digital microscopy. Such microscopes could help improve microscope access in clinics and classrooms in the form of 'field microscopes', if they could be adapted for imaging cells. We integrate a 3D printed focussing mechanism made with recyclable plastic with ball‐lens microscope of the Leeuwenhoek type. We demonstrate how the device can help stabilise to a focal plane for acquiring movies of a thin‐smear of blood infected with Plasmodium and onion skin cells using a cellphone. The stability of focus is expectedly less precise as compared to research‐grade microscopes, but is of the range of a few micrometers. We believe, the focussing device demonstrates it is possible to obtain reliable and reproducible images of typical samples used in clinics and classrooms. By making the design files of this device open‐source we believe it could serve as a small step in improved, affordable and accurate 'field microscopes'. [ABSTRACT FROM AUTHOR]