In the case of the flow cytometry experiment, the above IgG molecules were labeled with fluorescein isothiocyanate (FITC) molecules

In the case of the flow cytometry experiment, the above IgG molecules were labeled with fluorescein isothiocyanate (FITC) molecules. but also in the medical and pharmaceutical industries. Introduction Numerous types of proteins such as ion channels, receptors and antigens are embedded in the membranes of biological cells and some regions of those proteins appear outside the cells’ surfaces. Those proteins are interacting with other foreign biomolecules and ions under different physiological conditions [1]. The activities of all the organisms such as electric signal transfer, ATP synthesis and cells’ adhesion are controlled by the biochemical interactions occurring at the surfaces of living cells [2], [3], [4]. Investigating the biochemical events occurring at the surfaces of the cells is Rabbit Polyclonal to COX7S important in the fields of cell biology and biochemistry and as a result, a number of different techniques for the estimation of the interactions between biomolecules and the membranes of cells have been developed [5], [6], [7]. Baksh et al. presented a simple protein-binding assay that utilizes the BMS-819881 structural change in clusters composed of microparticles derivatized with lipid-membranes, which is induced by the attachment of proteins to the membranes on the particles [5]. Detecting antigen-antibody reactions occurring at the surfaces of living cells is essential for investigating the membrane structures of individual living cells and therefore has been carried out in the field of cancer, human immunodeficiency virus (HIV) and malaria diagnosis [8], [9], [10], [11], [12]. For instance, Nagrath et al. demonstrated a capture of circulating tumor cells (CTCs), which would be causing metastasis of cancer to the other parts of a body, onto the surfaces of micropillars modified with the antibody molecules against the CTCs in a microchip, using a cancer patient’s whole blood [8]. In order to detect the antigen-antibody reactions at the surfaces of biological cells, the antibody molecules modified with fluorescent dyes are often attached to the cells and the fluorescence intensity of the dyes is measured using a fluorescent microscope, spectrometer or flow cytometer, through which a number of new findings and ideas have been derived in the field of life science [13], [14], [15]. However, the above facilities and equipment are, in general, large-scale and expensive due to complicated optical components such as light sources, photomultipliers, wavelength filters etc. Advanced synthesizing techniques are also required for the fluorescence labeling onto antibody molecules. In the case of cellular analysis using monoclonal antibodies in particular, there is an urgent demand for label-free detections of BMS-819881 antigen-antibody reactions at the surfaces of living biological cells. When biological cells are dispersed in aqueous solution, electric double layers are established around them since the surfaces of the cells are normally electrically charged. If an electric field is applied to the cells’ suspension, the cells move in the direction of the electric field. Note that the electrophoretic mobility of each cell is proportional to the charge quantity at the cell’s surface. Once antibody molecules are attached to the surfaces of the cells, the surface charges are slightly changed and as a result, the electrophoretic mobilities alter [16], [17]. Utilizing this phenomenon, antigen-antibody reactions at the cells’ surfaces have been detected without any labeling onto the antibody molecules in a microchannel [18], [19]. However, quantitative label-free analysis of the number of antibody molecules attached to the surface of each cell has not yet been carried out using a microdevice. In this article, we present a label-free method for a determination of the number of biomolecules attached to individual cells by measuring the electrophoretic mobility of the cells in a microchannel. Materials and Methods The outline of the electrophoretic mobility measurement system is shown in Fig. 1. We fabricated a microchannel on the surface of a polydimethlsiloxane (PDMS) substrate by the conventional soft lithography method [20]. First, we made a micropattern on SU-8 2035 (MicroChem, MA) attached to the surface of an Si substrate with the UV lithography method, poured PDMS liquid (Momentive, NY) into the micropatterned substrate and left it at rest for 12 BMS-819881 h at room temperature in order to solidify the PDMS liquid. We peeled the solidified PDMS substrate from the micropatterned Si substrate, made two holes at the ends of the microchannel and attached the PDMS substrate to the glass substrate. The length, width and.