High-resolution label-free cellphone microscopy using contact ball lenses

It is shown that an imaging system of a millimeter-scale ball lens made by LASFN35 glass with index $n=2.05$ at $\lambda = 480$nm contacting objects can be used to improve the resolution of cellphone-base microscopy. The resolution can be improved from ~35 $\mu m$ to ~600nm over a ~20*20 $\mu m^{2}$ field of view by real imaging through the contact ball lens. With optimization of parameters of the contact ball lenses, finer resolution can be achieved, which can lead to a wide range of applications in mobile biomedical imaging.