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

Abstract

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.