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 poorquality 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.

Microfluidic approaches for isolation, detection, and characterization of extracellular vesicles: Current status and future directions

“…Optical detection techniques have been efficiently implemented on-chip, where they are used as a microfluidic biosensor formatted for online fluorescence (Ryu 2011), chemiluminescence (Guan 2015), surface plasmon resonance (SPR) based measurements (Luo 2008, Huang 2009) and surface enhanced Raman spectroscopy (SERS) based optical sensing (Qian 2008). Instead, other parts such as microscopes, spectrophotometers, charge-coupled devices (CCDs) and photomultiplier tubes (PMTs) have yet to be fully integrated to microfluidic devices, for now remaining off-chip because of difficulties in miniaturization (Schwarz 2001, Huang 2005, Myers 2008, Wolter 2008, Lee 2009, Huh 2009). If effectively integrated on chip in the future, optical detection methods, specifically SERS, could have the potential for online detection of all major clinically relevant properties of a single vesicles at high speed, with high sensitivity at micron- and nanometer dimensions (Huh 2009, Stremersch 2016).…”

Optical imaging techniques in microfluidics and their applications

“…With better microfluidic control on the biological samples using DC electrokinetics, spherical/ ellipsoidal biological samples, such as pollen spores, Chlamydomonas, and Giardia lamblia trophozoites and cysts, were able to be imaged at the high resolution of 800 nm. 82,83 Based on the first version of the aperture-based OFM device, a few derivatives of compact OFM devices have been developed over the following years. In 2010, a new version of the OFM device, termed the subpixel resolving OFM (SROFM) was been developed by Zheng et al 84,85 This scheme eliminates the need for the metal mask and sub-micron apertures; instead, it employs the pixel super resolution algorithm to reconstruct a highresolution image from a sequence of low-resolution images, as shown in Fig.…”

Lensfree Optofluidic Microscopy and Tomography

“…One approach for achieving this has been the OFM. 10,19,22,28 In this mentioned approach, a digital sensor is covered with an opaque layer with submicrometer apertures punched through it. If the holes are positioned appropriately and an object is made to controllably flow in close proximity to the aperture plane, then a microscopic image of the object can be obtained with a resolution smaller than the physical pixel size of sensor chip.…”

“…One other major optofluidic platform that has been added to this emerging set of tools is optical microscopy. 10,12,19,22,28,30 Its integration with microfluidic devices would allow the miniaturization and simplification of optical imaging instruments for applications in, e.g., telemedicine and global health.…”

“…One such approach, termed optofluidic microscope (OFM), is based on a slanted array of nano-apertures (e.g., <1 lm in diameter) placed at the bottom of a microfluidic channel. 10,19,22,28 As an object flows over and in close proximity to these nanoapertures, light is collected from each aperture, and by digitally processing each aperture's intensity signal (through time-to-space conversion), a microscopic image of the specimen within the micro-channel can be synthesized. The major contribution of this study is to get around the pixel size limitation of digital sensors (e.g., CCD or CMOS chips) through fabrication of sub-micron apertures, so that a decent lensfree spatial resolution can be achieved within the optofluidic chip.…”