A microfluidic needle for sampling and delivery of chemical signals by segmented flows

This novel microfluidic needle-like device consist of parallel hydrophobic channels and seven 2 µm hydrophilic capillaries at the tip. The Laplace pressure in these capillaries creates a 19 kPa barrier pressure that prevents oil from exiting the hydrophobic channels. We demonstrated the delivery and sampling of aqueous droplets through these capillaries. There is a linear relationship between the recorded fluorescence intensity of samples and the external sampled dye concentration (10 to 40 µg/mL). We measured a response time of approximately 5 s. It will be a useful tool for in vivo on-line detection of chemical signals that change at sub 10s time scales.