Design, Fabrication, and Testing of a Microfluidic Device for Thermotaxis and Chemotaxis Assays of Sperm.

Infertile couples needing assisted reproduction are increasing, so a fundamental understanding of motile sperm migration is required. This paper presents an advanced microfluidic device for sperm motion analysis utilizing chemotaxis and thermotaxis simultaneously for the first time. The proposed device is a transparent polydimethylsiloxane- and glass-based microfluidic chip system providing a low-cost, useful, and disposable platform for sperm analysis. The concentration gradient of the chemoattractant (acetylcholine) and the temperature difference are formed along the microchannel. The temperature gradient is generated and controlled by a microheater and microsensor. Thermotactic and chemotactic responses of mouse sperm were examined using the proposed device. Experimental results show that motile mouse sperm are attracted more sensitively under integrated conditions of chemotaxis and thermotaxis rather than individual conditions of chemotaxis and thermotaxis. This sperm analysis device is expected to be a useful tool for the study of mammalian sperm migration and the improvement of artificial insemination techniques.

Separation of progressive motile sperm from mouse semen using on-chip chemotaxis.

We present a novel method for the separation of progressive motile sperm from non-progressive motile and immotile sperm. This separation was accomplished by inducing chemotaxis along a longitudinal chemical gradient in a microchip composed of a biocompatible polydimethysiloxane layer and a glass substrate. In a preliminary experiment using fluorescent rhodamine B as a marker, we verified that a chemical gradient was generated by diffusion within the microchannel. We used acetylcholine as a chemoattractant to evaluate the chemotactic response of sperm. We tested the response to a 1/2 to 1/64 dilution series of acetylcholine. The results of a mouse sperm chemotaxis assay showed that progressive motile sperm swam predominantly toward the outlet at an optimal chemical gradient of 0.625 (mg/ml)/mm of acetylcholine. This device provides a convenient, disposable, and high-throughput platform that could function as a progressive motile sperm sorter for potential use in intracytoplasmic sperm injection.

Microchip-based multiplex electro-immunosensing system for the detection of cancer biomarkers.

Microfluidic-based microchips have become the focus of research interest for immunoassays and biomarker diagnostics. This is due to their aptitude for high-throughput processing, small sample volume, and short analysis times. In this paper, we describe the development of a microchip-based multiplex electro-immunosensing system for simultaneous detection of cancer biomarkers using gold nanoparticles and silver enhancer. Our microchip is composed of biocompatible poly(PDMS) and glass substrates. To fix the antibody-immobilized microbeads, we used pillar-type microfilters within a reaction chamber. An immunogold silver staining (IGSS) method was used to amplify the electrical signal that corresponded to the immune complex. To demonstrate this approach, we simultaneously assayed three cancer biomarkers, alpha-fetoprotein (AFP), carcinoembryonic antigen (CEA), and prostate-specific antigen (PSA) on the microchip. The electrical signal generated from the result of the immunoreaction was measured and monitored by a PC-based system. The overall assay time was reduced from 3-8 h to about 55 min when compared to conventional immunoassays. The working range of the proposed microchip was from 10(-3) to 10(-1) microg/mL of the target antigen.

A novel microfluidic biosensor based on an electrical detection system for alpha-fetoprotein.

Conventional immunoassays are labor intensive, expensive and time consuming and require large pieces of equipment for detection. Therefore, we have developed and characterized a novel immunoassay methodology comprised of microbeads and microbiochips. In this method, microbeads are used to filter and immobilize antibodies and an immuno-gold silver staining (IGSS) method is then used to amplify electrical signals that correspond to the bound antibodies. The chip used for this system is composed of an inexpensive and biocompatible polydimethylsiloxane (PDMS) layer over a Pyrex glass substrate that contains a platinum (Pt) microelectrode, which is used to detect the electrical signal in this system, the microelectrode is fabricated on the substrate and a microchannel and pillar-type microfilter is formed in the PDMS layer. A sandwich immunoassay approach was applied to detect alpha-fetoprotein (AFP), a cancer biomarker, using this system. The results of this study showed that the time required for a complete assay was reduced by 1h and a detection limit as low as 1 ng/mL was attained when this system used, which indicates that similar bead-based electrical detection systems could be used for the diagnosis of many forms of cancer.