Integrated cooling system for microfluidic PDMS devices used in biological microscopy studies

In this work, a two-channel, water-based cooling system was integrated into a polydimethylsiloxane (PDMS)-glass microfluidic device for application in single-cell biological studies. This system is designed to cool living cells to single-digit temperatures in situ, without requiring any features of the electron-beam fabricated master mould to be changed, and without interfering either biologically or optically with the cells themselves. The temperature profile inside the device was mapped using multiple thermocouples mounted inside the device, over time. A parametric study including coolant flow rate, distance between the cooling channel and the fluidic channel, and number of active cooling channels was performed to evaluate the performance of the system. By using ice water as the coolant, we have demonstrated stable on-chip cooling reaching an average temperature of 4.9 °C when operated at a coolant flow rate of 23 ml min−1 and using two active cooling channels, positioned only 400 µm away from the cell trapping sites. The maximum observed temperature deviation during an 80 min stability test was ±0.2 °C. We have observed that flowing room temperature culture media through the device with active cooling had no influence on the temperature inside the chip, demonstrating its suitability for use in live cell culture experiments. Finally, we have also demonstrated that the active cooling system successfully decreased the cell metabolism of trapped Escherichia coli resulting in a decreased growth rate of the bacteria.