Manufactured nanoparticles (MNPs) are microscopic materials (sub-100 nm) having physical and chemical properties uniquely different from their respective bulk materials. MNPs have found applications in optical, electronic, and biomedical fields and numerous novel products containing MNPs are entering the market each year [1, 2]. However, there are many reports of cyto- or genotoxicity of MNPs . A rapid and reproducible screening tool for analyzing and determining MNP toxicity in vitro in a high throughput manner would be desirable to safeguard against toxic effects to humans.
This paper reports a novel approach of using a simple design of microfluidic device to assess the cyto- and genotoxicity of MNPs in a high throughput manner. The microfluidic toxicological testing platform is based on mammalian cells that are immobilized inside microchannels and subsequently used for toxicological analysis of MNPs. Our group has previously developed a lab-on-a-chip toxicological testing platform that contains different cell types immobilized to the surface using antibody-cell surface antigen recognition . While this lab-on-a-chip platform and other commonly used well-plate culture techniques  used for MNP toxicological testing are performed under static conditions, there are reports showing that flow through systems may be significantly more relevant highlighting the advantages of using a microfluidic platform approach .
A schematic diagram of the crossed flow design of the microfluidic system is shown in Figure 1 where a glass substrate is functionalized with cell adhesion molecules to bind to various types of cells, and parallel streams of the cell suspensions and nanoparticle suspensions are perfused into the chip sequentially. As a proof of concept, a polydimethylsiloxane (PDMS)-based microfluidic chip containing 5 inlets for cell suspension and 5 inlets for nanoparticle solutions is designed, fabricated, and characterized (Fig. 2).
Collagen 1 or antibodies against cell surface antigens were first immobilized on epoxy-silane functionalized glass substrates using a microarrayer system prior to the perfusion of cells (Fig. 3). An array of 25 spots (diameters of 350 µm) of cell clusters were thus generated. Using two cell dyes as model treatments, we have demonstrated to be able to deliver up to 5 conditions per treatment simultaneously to the immobilized cells array (Fig. 4). Furthermore, we have used this platform to assess cell viability when subjected to simultaneous treatments with solutions of different tonicity (hence toxicity). Finally, we have shown to perfuse solutions of microparticles with various surface modifications (decorated with different antibody concentrations) to the cell microarray (Fig. 5). We have chosen microparticles as proof of concept working towards using nanoparticles in the future.
We are now scaling up the number of microchannels for immobilization of larger number of cell populations and for screening of large number of nanoparticles. This cross flow microfluidic configuration platform can provide a faster readout, is cost effective, offers time-resolved monitoring, and retains high magnification imaging capability. It could potentially lead to the reduction of animal model experiments and achieve a new testing standard for nanoparticle toxicity.