Evaporation and focus degradation mitigation in in-incubator live cell imaging for capacitance lab-on-CMOS microsystem calibration

Lab-on-CMOS is an instrumentation technology that combines miniaturized bioanalytical hardware with complementary metal-oxide semiconductor (CMOS) electronics to provide integrated biosensing in a compact format. This paper focuses on a class of lab-on-CMOS systems that utilize capacitance sensing as a means to monitor cell cultures and track cell proliferation, as well as other cell life-cycle events. In this paradigm, changes in interfacial capacitance result from the activity of adherent cells at a bioelectronic interface. These changes are mapped to cell proliferation or life-cycle events using ground-truth measurements such as live cell imaging from real-time microscopy. This paper identifies instrumentation challenges that arise from conducting these ground-truth measurements in a calibrated cell culture environment, i.e., when the lab-on-CMOS system is deployed inside a CO2 cell culture incubator. In particular, we provide a detailed study of evaporation and focus degradation mitigation techniques for application in-incubator live cell imaging during lab-on-CMOS capacitance sensor calibration tasks. We show that autofocusing the microscopy column and provisioning the lab-on-CMOS with an immersion lid are two approaches that significantly improve the quality of live cell imaging ground-truth measurements over long periods.