  We proposed a Smartphone-based Optical Sectioning (SOS) microscope based on
the HiLo technique, with a single smartphone replacing a high-cost illumination
source and a camera sensor.We built our SOS with off-the-shelf optical
mechanical cage systems with 3D-printed adapters to integrate the smartphone
with the SOS main body seamlessly.The liquid light guide can be integrated with
the adapter, guiding the smartphone LED light to the digital mirror device with
neglectable loss.We used an electrically tunable lens (ETL) instead of a
mechanical translation stage to realize low-cost axial scanning. The ETL was
conjugated to the objective lens back pupil plane (BPP) to construct a
telecentric design by a 4f configuration. This can exempt images of different
layers from the variation in magnification. SOS has a 571.5 {\mu}m telecentric
scanning range and an 11.7 {\mu}m axial resolution. The broadband smartphone
LED torch can effectively excite fluorescent polystyrene (PS) beads. We
successfully used SOS for high contrast fluorescent PS beads imaging with
different wavelengths and optical sectioning imaging of accumulated fluorescent
PS beads. To our knowledge, the proposed SOS is the first smartphone-based HiLo
optical sectioning microscopy. It is a powerful, low-cost tool for biomedical
research in resource-limited areas.
