(521a) Combining Rapid Formation of Chemical Gradients with Cellular Response for Development of a Portable Water Toxicity Sensor

The ability to build pumpless fluidic devices that generate controllable chemical gradients for rapid and accurate analysis of water samples for broad-range chemical contamination is of significant benefit for field testing of water safety and security. This work describes rapid generation of a centimeter-length chemical concentration gradient combined with a cytotoxicity test as a prototype for a fieldable microfluidic cell-based water toxicity sensor. Generation of the concentration gradient is rapid and the gradient profile in the device can be easily altered and controlled by varying the initial analyte concentration and by manipulating the timing of the forward and backward flow. The further integration of cellular response in the presence of contaminants shifts the paradigm for field sensing where results are obtained on total sample toxicity rather than contaminant identification. Here we describe device fabrication and operation followed by an application of this portable fluidic device for cytotoxicity testing upon rapid concentration gradient generation. The device application employs dichlorofluorescein (DCF), a fluorescent marker of cellular oxidative stress, to generate a visual cytotoxicity scale along the microchannel. PC-12 rat pheochromocytoma cells loaded with the non-fluorescent DCF precursor 2'7'-dichlorodihydrofluorescein diacetate (H2DCFDA) were seeded within the microchannels, and concentration gradients of several industrial chemicals with known toxicities were established. PC-12 cells exposed to gradients of chemicals which produce reactive oxygen species as a mode of toxicity exhibited decreasing and quantifiable fluorescence along the channel, corresponding to the decrease in toxin concentration and indicating decreasing amounts of cellular oxidative stress along the gradient. These fluorescence profiles were then used to generate a general toxicity scale against which toxicity levels of unknown fluid samples can be measured. This simple and rapid approach for gradient generation on a controllable centimeter-length scale together with cell culture is a promising platform for constructing a cell-based toxicity sensor that uses a combination of MEMS with a realistic and relevant bioresponse.