Abstract
We report a deep learning-enabled field-portable and cost-effective imaging flow cytometer that automatically captures phase-contrast color images of the contents of a continuously flowing water sample at a throughput of 100 mL/h. The device is based on partially coherent lens-free holographic microscopy and acquires the diffraction patterns of flowing micro-objects inside a microfluidic channel. These holographic diffraction patterns are reconstructed in real time using a deep learning-based phase-recovery and image-reconstruction method to produce a color image of each micro-object without the use of external labeling. Motion blur is eliminated by simultaneously illuminating the sample with red, green, and blue light-emitting diodes that are pulsed. Operated by a laptop computer, this portable device measures 15.5 cm × 15 cm × 12.5 cm, weighs 1 kg, and compared to standard imaging flow cytometers, it provides extreme reductions of cost, size and weight while also providing a high volumetric throughput over a large object size range. We demonstrated the capabilities of this device by measuring ocean samples at the Los Angeles coastline and obtaining images of its micro- and nanoplankton composition. Furthermore, we measured the concentration of a potentially toxic alga (Pseudo-nitzschia) in six public beaches in Los Angeles and achieved good agreement with measurements conducted by the California Department of Public Health. The cost-effectiveness, compactness, and simplicity of this computational platform might lead to the creation of a network of imaging flow cytometers for large-scale and continuous monitoring of the ocean microbiome, including its plankton composition.
Highlights
Plankton form the base of the oceanic food chain, and they are important components of the whole marine ecosystem
Flow cytometry is usually coupled with a fluorescence readout to detect the autofluorescence of chlorophyll, phycocyanin, and phycoerythrin found in algae and cyanobacteria
We were able to identify most of the plankton types detected by our device based on the reconstructed images, as detailed in the captions of Fig. 2
Summary
Plankton form the base of the oceanic food chain, and they are important components of the whole marine ecosystem. Some of the widely utilized and commercially available imaging flow cytometers include the Flowcam[21] (Fluid Imaging Technologies), Imaging Flowcytobot[22] (McLane Research Laboratories), and CytoSense[23] (Cytobouy b.v.) These systems are able to perform imaging of the plankton in a flow, they still have some important limitations. The shallow depth-of-field of the microscope objective necessitates hydrodynamic focusing of the liquid sample into a few-μm-thick layer using a stable sheath flow This restricts the size of the objects that can be imaged (e.g., to
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