  We report the implementation of a fully on-chip, lensless microscopy
technique termed optofluidic ptychography. This imaging modality complements
the miniaturization provided by microfluidics and allows the integration of
ptychographic microscopy into various lab-on-a-chip devices. In our prototype,
we place a microfluidic channel on the top surface of a coverslip and coat the
bottom surface with a scattering layer. The channel and the coated coverslip
substrate are then placed on top of an image sensor for diffraction data
acquisition. Similar to the operation of flow cytometer, the device utilizes
microfluidic flow to deliver specimens across the channel. The diffracted light
from the flowing objects is modulated by the scattering layer and recorded by
the image sensor for ptychographic reconstruction, where high-resolution
quantitative complex images are recovered from the diffraction measurements. By
using an image sensor with a 1.85-micron pixel size, our device can resolve the
550 nm linewidth on the resolution target. We validate the device by imaging
different types of biospecimens, including C. elegans, yeast cells, paramecium,
and closterium sp. We also demonstrate high-resolution ptychographic
reconstruction at a video framerate of 30 frames per second. The reported
technique can address a wide range of biomedical needs and engenders new
ptychographic imaging innovations in a flow cytometer configuration.
