3D-printable portable open-source platform for low-cost lens-less holographic cellular imaging

Abstract

Digital holographic microscopy is an emerging, potentially low-cost alternative to conventional light microscopy for micro-object imaging on earth, underwater and in space. Immediate access to micron-scale objects however requires a well-balanced system design and sophisticated reconstruction algorithms, that are commercially available, however not accessible cost-efficiently. Here, we present an open-source implementation of a lens-less digital inline holographic microscope platform, based on off-the-shelf optical, electronic and mechanical components, costing less than $190. It employs a Blu-Ray semiconductor-laser-pickup or a light-emitting-diode, a pinhole, a 3D-printed housing consisting of 3 parts and a single-board portable computer and camera with an open-source implementation of the Fresnel-Kirchhoff routine. We demonstrate 1.55 μm spatial resolution by laser-pickup and 3.91 μm by the light-emitting-diode source. The housing and mechanical components are 3D printed. Both printer and reconstruction software source codes are open. The light-weight microscope allows to image label-free micro-spheres of 6.5 μm diameter, human red-blood-cells of about 8 μm diameter as well as fast-growing plant Nicotiana-tabacum-BY-2 suspension cells with 50 μm sizes. The imaging capability is validated by imaging-contrast quantification involving a standardized test target. The presented 3D-printable portable open-source platform represents a fully-open design, low-cost modular and versatile imaging-solution for use in high- and low-resource areas of the world.

Figure 1

Developed laboratory DIHM and 3D printable DIHM setup. Schematics of the (a) fibre-coupled LD pickup inline illumination. (b) LED pinhole setup. (c) Image of the laboratory fibre-coupled laser-pickup setup and dimensions. (d) Image of the complete 3D-printed LED set-up. (e) Exploded view of the three developed and used 3D printed parts with dimensions (CAD files open accessible, see methods chapter). Schematically depicted light propagation not to scale.

Figure 2

Holograms and according reconstructions of PMSs and human RBCs. Each inset shows a single sphere or RBC enlargd to five times its original size. (a) Hologram of PMSs captured with LD setup. (b) Reconstruction of (a). (c) Hologram of PMSs captured with LED setup. (d) Reconstruction of (c). (e) Hologram of RBCs captured with laser setup. (f) Reconstruction of (e). (g) Hologram of RBCs captured with LED setup. (h) Reconstruction of (g).

Figure 3

Holograms and according reconstructions of TBY2s. The insets are depicted magnified by a factor of three. (a) Hologram captured with LD setup. (b) Reconstruction of (a). (c) Hologram captured with LED setup. (d) Reconstruction of (c).

Figure 4

Imaging of a 1951 USAF target to quantify the accessible spatial resolution. (a) LD setup. Groups 8 and 9 are shown enlarged. (b) LED setup. Groups 6 to 9 are shown enlarged. (c) Contrast of the different elements for LD illumination. The inset shows the intensity profile plot for horizontal and vertical elements 3 of group 8. (d) Contrast for LED illumination. Additionally included are reported contrast values, where either an unspecified laser or an LED emitting at 470 nm (25 μm pinhole) had been employed (not specified further).

Figure 5

(a) The fully portable DIHM system consisting of (1) USB-port power bank, (2) 3D printed housing containing Raspberry Pi and LED control circuit, (3) LED DIHM system as presented in Fig. 1(d). (b) Closeup of the Raspberry Pi single-board computer. (c) Closeup of the LED control circuit. (d) Schematic of the circuit for biasing the LED using the Raspberry Pi’s GPIOs.