On-chip temperature sensing and control for cell immobilization and culture system

This paper presents a temperature sensing and controlling microfluid chip for cell immobilization using a thermo-sensitive hydrogel (PNIPAAm). The ITO (Indium Tin Oxide) microheaters fabricated by micromachining technology, perform heating of the solution of cell, PNIPAAm and Calcein-AM (fluorescent dye) in microchannels. It is important to note that a thick gel formation cause to block the observation of culturing cells due to the autofluorescence of gel which reduce the S/N ratio. For the present study, we are targeting to fabricate a suspended micro-bridge above a microheater to limit the height of gel to form "thin and transparent gel layer" above the heater. The research was focused on controlling of gel thickness which eliminated unnecessary interferences of autofluorescence of gel in the observation by the inverted microscope, and a better S/N ratio can be obtained than the conventional observation with uncontrolled gel thickness. All the heating and a suspended biocompatible micro-bridge were integrated on a chip, in which yeast cells immobilization can be performed by the gelation of the PNIPAAm solution.