An integrated microfluidic chip enabling control and spatially resolved monitoring of temperature in micro flow reactors.

A strength of microfluidic chip laboratories is the rapid heat transfer that, in principle, enables a very homogeneous temperature distribution in chemical processes. In order to exploit this potential, we present an integrated chip system where the temperature is precisely controlled and monitored at the microfluidic channel level. This is realized by integration of a luminescent temperature sensor layer into the fluidic structure together with inkjet-printed micro heating elements. This allows steering of the temperature at the microchannel level and monitoring of the reaction progress simultaneously. A fabrication procedure is presented that allows for straightforward integration of thin polymer layers with optical sensing functionality in microchannels of glass-polydimethylsiloxane (PDMS) chips of only 150 µm width and 29 µm height. Sensor layers consisting of polyacrylonitrile and a temperature-sensitive ruthenium tris-phenanthroline probe with film thicknesses of about 0.5 to 6 µm were generated by combining blade coating and abrasion techniques. Optimal coating procedures were developed and evaluated. The chip-integrated sensor layers were calibrated and investigated with respect to stability, reproducibility, and response times. These microchips allowed observation of temperature in a wide range with a signal change of around 1.6 % per K and a maximum resolution of around 0.07 K. The device is employed to study temperature-controlled continuous micro flow reactions. This is demonstrated exemplarily for the tryptic cleavage of coumarin-modified peptides via fluorescence detection.