Imaging & identification of malaria parasites using cellphone microscope with a ball lens

Abstract

We have optimized the design and imaging procedures, to clearly resolve the malaria parasite in Giemsa-stained thin blood smears, using simple low-cost cellphone-based microscopy with oil immersion. The microscope uses a glass ball as the objective and the phone camera as the tube lens. Our optimization includes the optimal choice of the ball lens diameter, the size and the position of the aperture diaphragm, and proper application of immersion, to achieve diagnostic capacity in a wide field of view. The resulting system is potentially applicable to low-cost in-the-field optical diagnostics of malaria as it clearly resolves micron-sized features and allows for analysis of parasite morphology in the field of 50 × 50 μm, and parasite detection in the field of at least 150 × 150 μm.

Fig 1. Cellphone camera coupled to classical microscope (top), and used as a tube lens coupled to external micro-objective (bottom).

Fig 2. Ball lens coupled to the cellphone lens, to form a microscope and the zemax model of the aperture inserted behind the ball lens.

Fig 3. The third element of the last group of the 1951 USAF target, imaged without immersion, resolved with the optimized cellphone microscope, equipped with a properly stopped 0.5 mm ball lens.

The width of the smallest resolved bar in the inset is 0.77 μm, corresponding to F_max = 645 lp/mm.

Fig 4. Images of in vitro cultured P. falciparum parasites in Giemsa-stained thin blood smears taken with 0.5 mm ball lens cell-phone microscope registered without immersion oil, with high contrast masking the cell contents (a) and with immersion revealing parasites inside blood cells (b).

Fig 5. Images of Giemsa-stained thin blood smears with in vitro cultured P. falciparum parasites taken with 1 mm ball lens cell-phone microscope (a), and non infected red blood cells (b).

Fig 6. Images of in vitro cultured P. falciparum parasites in Giemsa-stained thin blood smears taken with 1mm ball lens cell-phone microscope using 4x digitally zoom.

Visualizing an early ring stage trophozoite (red arrow) and a matured trophozoite (green arrow). Raw data from cell-phone microscope (a). HDR mode (b).

Fig 7. Images of in vitro cultured P. falciparum parasites in Giemsa-stained thin blood smears.

Taken with 0.5 mm ball lens cell-phone microscope (left). Taken with 0.5mm ball lens cell-phone microscope, with applied 4× digital zoom and HDR mode (middle). Image of in vivo human P. falciparum infection taken by light microscope, ×60 objective obtained using a high-end Zeiss Light microscope in Leiden University Malaria group laboratory (right).

Fig 8. Motorized prototype with automated x-y movement of blood sample, which enables fast acquisition of large number of images.

Fig 9. Overview of the system design (a) depicts the battery back up and micro-controller used for the digital control of the stepper motor (b) shows the circuitry while (c) depicts the attachment of the ball lens mounted in a piece of aluminum foil and attached to the smart-phone with a scotch tape.