Lab Chip 11, 2535–2540 (2011)

Credit: UTKAN DEMIRCI

The ability to select the healthiest and most motile sperm from a sample could bring tremendous benefits to assisted reproductive technology. The current challenge is to image and track a large number of sperm cells simultaneously. Xiaohui Zhang and co-workers in the USA have now used a lensless CCD integrated inside a microfluidic chip to record the motility of sperm cells in situ as they move inside a microfluidic channel. The device's field of view is almost 20 times that of a conventional microscope, which facilities the sorting and tracking of a population of sperm. The chip consists of a 1.5-mm-thick PMMA layer, a 50-μm-thick directed self-assembly layer and a glass coverslip. The researchers placed a CCD sensor underneath the chip and inserted a protective glass film between the two layers. They then cut a 7-mm-long channel out of the directed self-assembly layer and created inlet and outlet ports of sizes 0.65 mm and 2 mm, respectively, on the PMMA layer. The sperm inside the channel diffracted and transmitted light when the chip was illuminated from above. Shadows generated by diffraction were imaged using the CCD to identify and track the most motile sperm, and those that reached the outlet were then extracted from the channel. This set-up allows for both horizontal and vertical configurations, similar to the swimming-up clinical method. The researchers are confident that this simple and portable device will be useful for fertility clinics and possibly even for use at home.