Optofluidic Microscopy
(Primary student researchers: Xiquan Cui, Xin Heng, Lap-Man Lee)
Incorporation of optics into microfluidics has brought forth a wide spectrum of applications related to imaging, sensing, spectroscopy, and displays. At present, microfluidics-based imaging still relies on bulky optical microscopes, although the microfluidic system itself is usually compact. In Biophotonics lab, we are developing a compact optical imaging device, termed optofluidic microscope (OFM). The major component of OFM is a metal coated CMOS sensor array on which a linear array of subwavelength nanoapertures is patterned (See Fig. 1). Then this device is hermetically sealed on the floor of a microfluidic delivery channel. The nanoaperture array is laid down in a slanted fashion under microfluidic channel [see Fig. 2(a)]. This novel configuration allows sample imaging with a spatial resolution that is defined by nanoaperture’s size and alleviates the constraints by the pixel width and pitch size of the underlying linear array CCD. Light transmission through each nanoaperture changes when occluded by biological samples flowing across the nanoaperture array region. We examined our prototype’s performance by imaging the newly hatched larvae of C. elegans. Several reconstructed images are shown in Fig. 2(b). In addition, high resolution and high throughput of this initial OFM prototype makes it well suited as a phenotyping device that can effectively sort out worms of different genotypes or at different developmental stages. Wild-type larvae and dpy-24 (described as ‘weakly dumpy’) mutants were used in the phenotyping study. The morphological aspect-ratio map [see Fig. 2(c)] illustrates a successful separation of the two genotypes. This is the first time that both nematode imaging and quantitative phenotyping are successfully performed on a compact microfluidic chip. Although the proof-of-concept experiment still uses an inverted microscope for data recording, full integration of OFM with a CCD array is straightforward. The integration of other micro-optical components into OFM will readily add more functionality to the lab-on-a-chip.

Fig. 1: compact OFM prototype, compared with a US quarter.

 

Fig. 2: (a) OFM's layout. Red arrows: illumination; green arrow: flow direction (b) Several OFM images of wild-typeC. elegans; white bar =25 µm (for all images);(c) Aspect ratio map, blue data points: wild -type L1 larvae; red: dpy24 L1 larvae.

REFERENCE:
Xin Heng, David Erickson, Larry R. Baugh, Zahid Yaqoob, Paul W. Sternberg, Demetri Psaltis, and Changhuei Yang. 'Optofluidic Microscopy: A Method for Implementing High Resolution Optical Microscope On A Chip,' Lab on a Chip, DOI:10.1039/b604676b (2006). http://www.rsc.org/Publishing/Journals/LC/article.asp?doi=b604676b

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