Lens-free imaging for biological applications

Abstract

Lens-free (or lensless) imaging is emerging as a cost-effective, compact, and lightweight detection method that can serve numerous biological applications. Lens-free imaging can generate high-resolution images within a field-portable platform, which is ideal for affordable point-of-care devices aiming at resource-limited settings. In this mini-review, we first describe different modes of operation for lens-free imaging and then highlight several recent biological applications of this emerging platform technology.

Figure 1

Schematics of digital in-line holography (DIH) (A) and incoherent or partially coherent lens-free on-chip imaging (B) methods. z₁ is the distance between the aperture and the object planes, z₂ is the distance between the object and the image sensor planes, and d is the diameter of the aperture. In DIH, a small aperture and a coherent light source (e.g., a laser) are used where the object is placed closer to the light source. In incoherent or partially coherent lens-free on-chip imaging platforms, a relatively larger aperture and an incoherent or partially coherent light source is used, and the object is placed much closer to the image sensor plane.

Figure 2

Images of underwater species obtained using digital in-line holography (DIH). (A) Paramecium (length: 320 μm, width: 46.8 μm). Trajectories of various underwater species. (B) Ciliate (length: 25 μm, width: 13 μm), (C) Didinium (length: 133 μm, width: 77 μm), and (D) Rotifer (length: 200 μm, width: 100 μm). Reproduced with permission of Applied Optics.

Figure 3

Lens-free imaging for cardiotoxicity testing. (A) Schematic of a cardiotoxicity sensor that uses direct projection. Embryonic stem cell–derived cardiomyocytes are placed on a complementary metal oxide semiconductor image sensor extracted from a Web cam. (B) The effects of two drugs (isoprenaline and doxorubicin) on beating rate variations of cardiomyocytes were investigated. Isoprenaline (doxorubicin) is found to increase (decrease) the beating rates of cardiomyocytes. Reproduced with permission of the Lab on a Chip.

Figure 4

Lens-free optical tomography on a chip using partially coherent digital in-line holography. (A) The sample is illuminated from multiple angles using a partially coherent light source to record lens-free in-line holograms of the specimen on the chip. (B) Images of C. elegans obtained using lens-free optical tomography. Tomogram of an entire worm corresponding to a plane that is 3 μm above the center of the worm (top). Tomograms for the anterior of the worm at different layers (bottom) and a microscope comparison image (40×, NA = 0.65, bottom right). Reproduced with permission of the PNAS.