Label-free cellphone microscopy with submicron resolution through high-index contact ball lens for in vivo melanoma diagnostics and other applications

Developing megapixel large-area CCD and CMOS sensor arrays in the 2000-s stimulated ideas about developing microscope systems operating without heavy and bulky microscope stands and objectives by using microoptics approach in combination with imaging by cellphone cameras. Due to limited magnification, however, the best resolution of such systems is currently limited by the finite size of the pixels at similar to 1.5 mu m level. We propose a novel approach to designing such microscope systems based on using contact ball lenses with index of refraction close to 2, which are capable of imaging biomedical and nanoplasmonic objects with extraordinarily high magnification and resolution. By using ball lenses made from glass with index n = 2.02 at lambda = 600 nm we build a cellphone camera-based microscope system with up to x50 magnification and resolution fundamentally limited at similar to 600 nm level due to diffraction of light. It is demonstrated that the operation of such system is a subject for strong dispersive effects in glass leading to a complicated tradeoff of magnification, resolution, and field-of-view (FOV) in the proximity to critical index of 2. Using this system, we performed imaging of melanoma samples which shows a potential of developing biopsy-free in vivo histology of skin using ball lens-assisted smartphone microscopy.