The application of on-chip optofluidic microscopy for imaging Giardia lamblia trophozoites and cysts

Abstract

The optofluidic microscope (OFM) is a lensless, low-cost and highly compact on-chip device that can enable high-resolution microscopy imaging. The OFM performs imaging by flowing/scanning the target objects across a slanted hole array; by measuring the time-varying light transmission changes through the holes, we can then render images of the target objects at a resolution that is comparable to the holes' size. This paper reports the adaptation of the OFM for imaging Giardia lamblia trophozoites and cysts, a disease-causing parasite species that is commonly found in poor-quality water sources. We also describe our study of the impact of pressure-based flow and DC electrokinetic-based flow in controlling the flow motion of Giardia cysts--rotation-free translation of the parasite is important for good OFM image acquisition. Finally, we report the successful microscopy imaging of both Giardia trophozoites and cysts with an OFM that has a focal plane resolution of 0.8 microns.

Figure 1

(a) The planar geometry and the aperture array arrangement of the on-chip OFM. (b) A cross-sectional scheme of the OFM device. (c) A photo of the fabricated on-chip OFM device. (A US dime is placed aside for size comparison and the red line represents the microfluidic channel)

Figure 1

(a) The planar geometry and the aperture array arrangement of the on-chip OFM. (b) A cross-sectional scheme of the OFM device. (c) A photo of the fabricated on-chip OFM device. (A US dime is placed aside for size comparison and the red line represents the microfluidic channel)

Figure 2

G. lamblia images. Images taken from the on-chip OFM device of cysts (a–d), trophozoites (h–k). Images taken from a conventional light transmission inverted microscope with a 40 × objective of cysts (e–f) and trophozoites (l–m). Direct projection images on a 2.2 μm CMOS imaging sensor chip of cyst (g) and trophozoite (n). (Scale bars: 10 μm)

Figure 3

The microfluidic motion of a Giardia cyst when (a) driven by pressure and (b) driven by DC electrokinetics at 30V (E = 10 V/mm). (c) A graph showing the distribution of sample rotation under pressure-based and electrokinetic-based drive. The horizontal axis quantifies the magnitude of rotation after 300 μm of travel in the microfluidic channel.

Figure 3

The microfluidic motion of a Giardia cyst when (a) driven by pressure and (b) driven by DC electrokinetics at 30V (E = 10 V/mm). (c) A graph showing the distribution of sample rotation under pressure-based and electrokinetic-based drive. The horizontal axis quantifies the magnitude of rotation after 300 μm of travel in the microfluidic channel.